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surface modification of perovskite film plays an important role on the suppression of surface defects for the fabrication of high‑efficiency perovskite solar cells. here, 1h‑pyrazole‑1‑carboxamidine hydrochloride (pah) as a multifunctional heterocyclic ring‑based organic ionic salt to modify the surface of fapbi3 film at room temperature is demonstrated. xps and ftir results demonstrate that the sufficient active sites contribute to the interaction between pah and surface pb ions of the perovskite, which is helpful to reduce the trap states on the perovskite film so as to increase the device performance. the modification is beneficial to the suppression of charge recombination and the promotion of charge transfer by anchoring to the uncoordinated pb ions on the surface both at the interface of stacking layers and the grain boundary. with prolonged charge carrier lifetime and elevated charge transfer, an improved pce of 20.9% is obtained for the as‑prepared planar devices based on fapbi3, along with simultaneous enhancement of open circuit voltage and fill factor. the findings further pave the way for utilizing novel organic salts for surface modification, which presents a promising route for the fabrication of efficient photovoltaic devices. | interfacial modification by low‑temperature anchoring surface uncoordinated pb for efficient fapbi3 perovskite solar cells |
nakhlite meteorites are igneous rocks from mars that were aqueously altered ~630 million years ago. hydrothermal systems on earth are known to provide microhabitats; knowledge of the extent and duration of these systems is crucial to establish whether they could sustain life elsewhere in the solar system. here, we explore the three-dimensional distribution of hydrous phases within the miller range 03346 nakhlite meteorite using nondestructive neutron and x-ray tomography to determine whether alteration is interconnected and pervasive. the results reveal discrete clusters of hydrous phases within and surrounding olivine grains, with limited interconnectivity between clusters. this implies that the fluid was localized and originated from the melting of local subsurface ice following an impact event. consequently, the duration of the hydrous alteration was likely short, meaning that the martian crust sampled by the nakhlites could not have provided habitable environments that could harbor any life on mars during the amazonian. aqueous alteration in the martian mil 03346 meteorite does not originate from a large-scale hydrothermal system. | the scale of a martian hydrothermal system explored using combined neutron and x-ray tomography |
cometary ices are rich sources of organic molecules relevant to prebiotic chemistry and may have played a key role in the delivery of the building blocks of life to earth. comets endure thermal processing of their surfaces during their orbits around the sun. furthermore, icy grain precursors of cometary materials may have experienced heating in the solar nebula. despite the important role that this thermal processing could play in the chemistry of ices, little effort has been devoted to understanding the purely thermal reactivity involving electronically stable molecules. both methylamine (ch3nh2) and carbonyl sulfide (ocs) have been detected in the cometary coma of comets, particularly in 67p-churyumov-geramenisko (67p) visited by the rosetta spacecraft. we present here the first laboratory study addressing the reactivity induced by thermal processing of methylamine and ocs mixed ice. mimicking a realistic scenario within which the surface of the comet is thermally processed as a result of its path close to the sun, we demonstrate that the methylthiocarbamate anion in salt with methylammonium, [ch3nhocs]- [ch3nh3]+, and thiocarbamic acid dimer are formed by nucleophilic addition of ocs on methylamine. this study shows that a thermally driven reaction chemically analogous to the one proposed as a condensing pathway of amino acids in the early earth may take place in cometary ice. the formed thiocarbamate is a known intermediate in the formation of peptides. furthermore, the consumption of ocs by this reaction with methylamine may account for the missing sulfur in dense clouds and protostars. | thermal reaction in cometary and pre-cometary ices: formation of thiocarbamate in ocs-ch3nh2 mixed ices |
natural graphite forms in a range of metamorphic and hydrothermal environments across timelines spanning from the birth of the solar system, to the evolution of early precambrian life, and the development of contemporary geotectonic cycles. a precise timeline of these and other graphite-forming events, however, has hitherto been obscured by a lack of radiometric ages and as such, chronologies are inferred from host-rock or hydrothermal mineral ages. herein we examine the re-os systematics and chronology of graphite formed in a suite of terrestrial and extraterrestrial environments (n = 17) with the principal aim of establishing the viability of re-os geochronology of natural graphite. graphite re and os contents and isotopic ratios exhibit a wide range of values that extend up to 1520 ppb re, 19,577 ppt os, and 4101 and 42.18 for 187re/188os and 187os/188os ratios, respectively. these values are broadly comparable to those reported for crustal sulfides, organic-rich sedimentary rocks, and hydrocarbons. x-ray diffraction crystallinity data reveals that graphite re abundances show a broadly inverse correlation with graphite formation temperature and crystallinity (d002 and lc(002)) with interplanar spacing (d002) having the strongest anti-correlation with graphite re contents. graphite re-os geochronology is demonstrated with two independent case studies (wollaston-mudjatik transition shear zones, saskatchewan, canada and merelani hills, tanzania) yielding precise (<1%) re-os isochron dates of 1731.52 ± 7.43 ma (2σ; mswd = 1.3) and 586.89 ± 2.39 ma (2σ; mswd = 1.2) that are consistent, within uncertainty, to their mineralization ages constrained by other radiometric methods. these data confirm that graphite mineralization was synchronous with trans-hudsonian exhumation and tsavorite-tanzanite gemstone mineralization, respectively. method accuracy, however, appears contingent on the analytical protocols used to isolate graphite, e.g. handpicking vs. heavy liquids (spt) and water, with the latter perturbing graphite re-os systematics by as much as 20%. we, therefore, recommend handpicking paired with magnetic separation and grain mount examination. our re-os age results are then coupled with new sims carbon isotope data (wollaston-mudjatik transition graphite: δ13c = -21.64 to -15.28‰; merelani hills graphite: δ13c = -25.90 to -24.36‰) and 187os/188osi isotope data (wollaston-mudjatik transition graphite = 0.3119 ± 0.0037; merelani hills graphite = 1.680 ± 0.038) to constrain graphitic carbon to sedimentary carbonate/organic (wollaston-mudjatik transition graphite) and organic (merelani hills graphite) carbon sources. this unique pairing of isotope systems in graphite provides the first detailed chronology of localized carbon mobility in the earth's crust. re-os graphite geochronology likely has wide applications in ore-deposit and metamorphic geology with the potential to reshape our understanding of carbon cycling in the crust-mantle system, and for graphite exploration initiatives that are critical for a global transition to a green economy. | re-os systematics and chronology of graphite |
there is ongoing interest in developing a stable, low-cost, 1.6-1.8 ev top-cell material that can be used for two-junction (tandem) solar cells, particularly in combination with a silicon bottom cell. in this work, polycrystalline gainp is grown and characterized to explore its properties and use for this purpose. the film composition and deposition temperature are varied to determine their effects on grain size, morphology, and photoluminescence (pl) over a range of bandgaps from 1.35 to 1.7 ev. an al-assisted post-deposition treatment for 1.7-ev polycrystalline gainp results in a 90-fold increase in peak photoluminescence (pl) intensity, a 220-fold increase in integrated pl intensity, and increased time-resolved pl lifetime from <2 ns to 44 ns. the increase in pl intensity and lifetime is attributed to a reduction of nonradiative minority-carrier recombination at the top surface, and at grain boundaries near the surface, due to the formation of a higher-bandgap algainp alloy. these materials provide a viable path toward increased minority-carrier concentration under illumination and improved recombination properties needed for high-efficiency tandem solar cells. | investigation of polycrystalline gaxin1 - xp for potential use as a solar cell absorber with tunable bandgap |
the open‑circuit voltage (voc) is the main limitation to higher efficiencies of cu(in,ga)se2 solar cells. one of the most critical parameters directly affecting voc is the charge carrier lifetime. therefore, it is essential to evaluate the extent to which inhomogeneities in material properties limit the carrier lifetime and how postdeposition treatments (pdts) and growth conditions affect material properties. time‑resolved photoluminescence (trpl) microscopy is employed at conditions similar to one sun to study carrier lifetime fluctuations in cu(in,ga)se2 with light (na) and heavy (rb) alkalis, different substrates, and grown at different temperatures. pdt lowers the amplitude of minority carrier lifetime fluctuations, especially for rb‑treated samples. upon pdt, the grains' carrier lifetime increases, and the analysis suggests a reduction in grain boundary recombination. furthermore, lifetime fluctuations have a small impact on device performance, whereas voc calculated from trpl (and continuous‑wave pl) agrees with device values within the limits of investigated pdt samples. finally, up to about half a per cent external radiative efficiencies are experimentally determined from trpl metrics, and internal radiative efficiencies are approximated. the findings demonstrate that the highest absorber material quality investigated is still limited by nonradiative recombination (grain or grain boundary) and is comparable to state‑of‑the‑art absorbers. | charge carrier lifetime fluctuations and performance evaluation of cu(in,ga)se2 absorbers via time‑resolved‑photoluminescence microscopy |
formamidinium lead triiodide (fapbi3) is considered as an alternative to methylammonium lead triiodide (mapbi3) because of its lower band gap and better thermal stability. however, owing to the large size of fa cations, it is difficult to synthesize high‑quality fapbi3 thin films without the formation of an undesirable yellow phase. smaller sized cations, such as ma and cs, have been successfully used to suppress the formation of the yellow phase. whereas fa and ma lead triiodide perovskite solar cells (pvscs) have achieved power conversion efficiencies (pces) higher than 20 %, the pces of formamidinium and cesium lead triiodide (fa1−xcsxpbi3) pvscs have been only approximately 16.5 %. herein, we report our examination of the main factors limiting the pces of (fa1−xcsxpbi3) pvscs. we find that one of the main limiting factors could be the small grain sizes (≈120 nm), which leads to relatively short carrier lifetimes. we further find that adding a small amount of lead thiocyanate [pb(scn)2] to the precursors can enlarge the grain size of (fa1−xcsxpbi3) perovskite thin films and significantly increase carrier lifetimes. as a result, we are able to fabricate (fa1−xcsxpbi3) pvscs with significantly improved open‑circuit voltages and fill factors and, therefore, enhanced pces. with an optimal 0.5 mol % pb(scn)2 additive, the average pce is increased from 16.18±0.50 (13.45±0.78) % to 18.16±0.54 (16.86±0.63) % for planar fa0.8cs0.2pbi3 pvscs if measured under reverse (forward) voltage scans. the champion cell registers a pce of 19.57 (18.12) % if measured under a reverse (forward) voltage scan, which is comparable to that of the best‑performing ma‑containing planar fa‑based lead halide pvscs. | improving the performance of formamidinium and cesium lead triiodide perovskite solar cells using lead thiocyanate additives |
surface modification of cs0.1(ch3nh3)0.9pbi3 is investigated by antisolvent-assisted crystallization (asac). the perovskite solar cells (pscs) of fto/sno2/cs0.1(ch3nh3)0.9pbi3/spiro-ometad/ag are also fabricated. it is found that isopropanol-treated devices exhibit a power conversion efficiency (pce) of 16.3%, which is higher than chlorobenzene- (11.5%) and toluene-treated devices (12.8%). the efficiency enhancement by isopropanol treatment can be attributed to better surface coverage, larger grain size, and less pinholes confirmed by scanning electron microscopy (sem) and x-rays diffraction (xrd) results, indicating an increase in short-circuit current density (jsc). in addition, the increase in open-circuit voltage (voc) can be confirmed by photoluminescence (pl) spectra, which can be suggested to the reduce the nonradiative recombination loss in the isopropanol-treated film. the wettability of perovskite films is studied by contact angle measurement, resulting in a higher hydrophobic surface from isopropanol-treated devices. also, the charge dynamic behavior of psc devices is investigated by open-circuit voltage decay (ocvd) measurement. it is found that the charge carrier lifetime of the isopropanol-treated device is longer than that of chlorobenzene and toluene. therefore, surface modification of perovskite by isopropanol treatment can enhance efficiency and isopropanol can be used as an alternative green antisolvent for the perovskite process. | surface modification of cs 0.1 (ch 3 nh 3 ) 0.9 pbi 3 by isopropanol as green antisolvent for efficiency enhancement of perovskite solar cells |
double perovskite sr2nimoo6 nanoparticles were synthesized via the chemical sol-gel route. the phase formation was investigated through x-ray polycrystalline diffraction (xrd) and rietveld refinements. the perovskite crystallized in worm-like nano-grains with the diameter of 20-50 nm. the optical properties were measured by the optical absorption spectra. the nanoparticles present an indirect allowed transition with a narrow band gap of 2.1 ev. sr2nimoo6 nanoparticles have obvious photocatalytic ability on the degradation of rhodamine b (rhb) solutions under the irradiation of visible light. the transport behaviors of the excitons were investigated from the photoluminescence spectra and the corresponding decay lifetimes. sr2nimoo6 nanoparticles present several advantages for photocatalysis such as the appropriate band energy positions, the quenched luminescence, and the coexistence of multivalent ions in the lattices. | synthesis, surface structure and optical properties of double perovskite sr2nimoo6 nanoparticles |
bismuth‑based ternary halides have recently gained a lot of attention as lead‑free perovskite materials. however, photovoltaic performances of these devices remain poor, mostly due to their low‑dimensional crystal structure and large bandgap. here, a dynamic hot casting technique to fabricate silver bismuth iodide‑based perovskite solar cells under an ambient atmosphere with power conversion efficiencies above 2.5% is demonstrated. silver bismuth iodides are 3d analogs of complex ternary bismuth halides with a suitable bandgap for a single junction solar cell. as far as it is known, these results represent the highest efficiency for solution processed air‑stable lead‑free perovskite solar cells. the enhanced solar cell performance via this dynamic hot casting technique can be attributed to long carrier lifetimes, micrometer‑sized crystalline grains, and pinhole free thin‑film formation with uniform morphology. this work provides a new direction for fabrication of solution‑processed lead‑free perovskite solar cells with a rapid fabrication strategy irrespective of the processing environment. | superior performance of silver bismuth iodide photovoltaics fabricated via dynamic hot‑casting method under ambient conditions |
we have developed a procedure for tracking sunspots observed by the helioseismic and magnetic imager on the solar dynamics observatory and for making curvature-corrected space/time maps of the associated line-of-sight magnetic field and continuum intensity. we apply this procedure to 36 sunspots, each observed continuously for nine days around its central meridian passage time, and find that the proper motions separate into two distinct components depending on their speeds. fast (∼3-5 km s-1) motions, comparable to evershed flows, are produced by weak vertical fluctuations of the horizontal canopy field and recur on a timescale of 12-20 min. slow (∼0.3-0.5 km s-1) motions diverge from a sunspot-centered ring whose location depends on the size of the sunspot, occurring in the mid-penumbra for large sunspots and at the outer edge of the penumbra for small sunspots. the slow ingoing features are contracting spokes of a quasi-vertical field of umbral polarity. these inflows disappear when the sunspot loses its penumbra, and may be related to inward-moving penumbral grain. the slow outgoing features may have either polarity depending on whether they originate from quasi-vertical fields of umbral polarity or from the outer edge of the canopy. when a sunspot decays, the penumbra and canopy disappear, and the moat becomes filled with slow outflows of umbral polarity. we apply our procedure to decaying sunspots, to long-lived sunspots, and to numerical simulations of a long-lived sunspot by rempel. | tracking the magnetic flux in and around sunspots |
comet c/2002 s2, a member of the kreutz family of sungrazing comets, was discovered in white-light images of the large angle and spectromeric coronagraph experiment coronagraph on the solar and heliospheric observatory (soho) on 2002 september 18 and observed in h i lyα emission by the soho ultraviolet coronagraph spectrometer (uvcs) instrument at four different heights as it approached the sun. the h i lyα line profiles detected by uvcs are analyzed to determine the spectral parameters: line intensity, width, and doppler shift with respect to the coronal background. two-dimensional comet images of these parameters are reconstructed at the different heights. a novel aspect of the observations of this sungrazing comet data is that, whereas the emission from most of the tail is blueshifted, that along one edge of the tail is redshifted. we attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. in order to use the comet to probe the density, temperature, and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a monte carlo simulation of the h i lyα emission of a comet moving through a coronal plasma. from the outgassing rate, we estimate a nucleus diameter of about 9 m. this rate steadily increases as the comet approaches the sun, while the optical brightness decreases by more than a factor of 10 and suddenly recovers. this indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms, and molecules produced by the comet. | probing the solar wind acceleration region with the sun-grazing comet c/2002 s2 |
iapetus possesses two spectacular characteristics: (i) a high equatorial ridge which is unique in the solar system and (ii) a large flattening (a - c = 34 km) inconsistent with its current spin rate. these two main characteristics have probably been acquired in iapetus' early past as a consequence of coupled interior-rotation evolution. previous models have suggested that rapid despinning may result either from enhanced internal dissipation due to short-lived radioactive elements or from interactions with a sub-satellite resulting from a giant impact. for the ridge formation, different exogenic and endogenic hypotheses have also been proposed, but most of the proposed scenarios have not been tested numerically. in order to model simultaneously internal heat transfer, tidal despinning and shape evolution, we have developed a two-dimensional axisymmetric thermal convection code with a deformable surface boundary, coupled with a viscoelastic code for tidal dissipation. the model includes centrifugal and buoyancy forces, a composite non-linear viscous rheology as well as an andrade rheology for the dissipative part. by considering realistic rheological properties and by exploring various grain size values, we show that, in the absence of additional external interactions, despinning of a fast rotating iapetus is impossible even for warm initial conditions (t > 250 k). alternatively, the impact of a single body with a radius of 250-350 km at a velocity of 2 km/s may be sufficient to slow down the rotation from a period of 6-10 h to more than 30 h. by combining despinning due to internal dissipation and an abrupt change of rotation due to a giant impact, we determined the parameters leading to a complete despinning and we computed the corresponding shape evolution. we show that stresses arising from shape change affect the viscosity structure by enhancing dislocation creep and can lead to the formation of a large-scale ridge at the equator as a result of rapid rotation change for initial rotation periods of 6 h. | despinning and shape evolution of saturn's moon iapetus triggered by a giant impact |
to clarify the mechanism of efficiency enhancement effect by potassium (k) treatment for cu(in1- x ga x )(se1- y s y )2 (cigsse) solar cells, we investigated the physical properties of deep and shallow defect levels of cigsse solar cells without or with potassium fluoride treatment via using steady state photo-capacitance and admittance spectroscopy. the results show that the defect density of deep levels (such as 0.8 and 0.7 ev above valance band) are similar, suggesting that the k treatment does not drastically change the deep defect properties. for the shallow levels, the activation energy of interface-related shallow defect decreased from 183 to 120 mev upon k treatment, suggesting the modification of interface. the modified interface may be caused by the diffusion of potassium to grain boundaries and the formation of cu-depleted layer in the near surface region of cigsse, resulting in the prolonged minority carrier lifetime. a new level with activation energy of 250 mev was found after k treatment, and it contributed to the increase of carrier density. these features well explained the enhanced device performance of cigsse solar cells by k treatment in terms of defects. | influence of potassium treatment on electronic properties of cu(in1- x ga x )(se1- y s y )2 solar cells studied by steady state photo-capacitance and admittance spectroscopy |
the distribution of minority carrier transport parameters (i.e., minority carrier lifetime, diffusion coefficient, and two surfaces recombination velocities) of multicrystalline silicon (mc-si) solar cell was investigated using laser-induced photocarrier radiometry (pcr). images of the amplitude and phase of the pcr measurements clearly showed the crystal boundaries of the mc-si solar cell. the distribution of minority carrier transport parameters was obtained by best fitting the experimental results to the theoretical two-layer carrier density wave model of solar cells. the best-fitting results demonstrated that there was great difference in the minority carrier transport parameters among various grains. | carrier transport parameter imaging in a multicrystalline silicon solar cell by laser-induced photocarrier radiometry |
solar cells/photovoltaic, a renewable energy source, is appraised to be the most effective alternative to the conventional electrical energy generator. a cost-effective alternative of crystalline wafer-based solar cell is thin-film polycrystalline-based solar cell. this paper reports the numerical analysis of dependency of the solar cell parameters (i.e., efficiency, fill factor, open-circuit voltage and short-circuit current density) on grain size for thin-film-based polycrystalline silicon (si) solar cells. a minority carrier lifetime model is proposed to do a correlation between the grains, grain boundaries and lifetime for thin-film-based polycrystalline si solar cells in matlab environment. as observed, the increment in the grain size diameter results in increase in minority carrier lifetime in polycrystalline si thin film. a non-equivalent series resistance double-diode model is used to find the dark as well as light (am1.5) current-voltage (i-v) characteristics for thin-film-based polycrystalline si solar cells. to optimize the effectiveness of the proposed model, a successive approximation method is used and the corresponding fitting parameters are obtained. the model is validated with the experimentally obtained results reported elsewhere. the experimentally reported solar cell parameters can be found using the proposed model described here. | effect of grain boundaries on the performance of thin-film-based polycrystalline silicon solar cells: a numerical modeling |
plants play an important role in human life because they are the only organisms that can convert light energy from the sun into food. products produced from plants such as fruits, vegetables, cereals, essential oils and many others are rich in carbohydrate, protein, vitamins and fibre that are necessary for health maintenance. they are an integral part of our regular diet because they are all of the food that people eat. plants are arranged in a hierarchical classification that is called taxonomy, and any given organism can be classified throughout the hierarchy. such an arrangement allows related organisms to be classified. there are various taxonomic levels and each level is given a name (e.g., kingdom, division (phylum), class, order, family, genus, species). for example, the taxonomic class of monocotyledonous involves different families, but in this article, only the families of poaceae (formerly called gramineae) and fabaceae (also called leguminosae) are considered. some of the major crops of these families that yield highly nutritious edible seeds or grains are known as cereals and legumes respectively. legumes include common beans, peas, soybean, peanut and lentils while the most important crops of cereals are wheat, rice, corn, barley and rye. their products account for a large part of the energy, carbohydrate and protein of the daily diet of every person in the world. consequently, they play a fundamental role in the food security in the uk, as well as food security globally. | the role of food crops within the poaceae and fabaceae families as nutritional plants |
cu(in,ga)se2 solar cells have markedly increased their efficiency over the last decades currently reaching a record power conversion efficiency of 23.3%. key aspects to this efficiency progress are the engineered bandgap gradient profile across the absorber depth, along with controlled incorporation of alkali atoms via post‑deposition treatments. whereas the impact of these treatments on the carrier lifetime has been extensively studied in ungraded cu(in,ga)se2 films, the role of the ga‑gradient on carrier mobility has been less explored. here, transient absorption spectroscopy (tas) is utilized to investigate the impact of the ga‑gradient profile on charge carrier dynamics. minority carriers excited in large cu(in,ga)se2 grains with a [ga]/([ga]+[in]) ratio between 0.2–0.5 are found to drift‑diffuse across ≈1/3 of the absorber layer to the engineered bandgap minimum within 2 ns, which corresponds to a mobility range of 8.7–58.9 cm2 v−1 s−1. in addition, the recombination times strongly depend on the ga‑content, ranging from 19.1 ns in the energy minimum to 85 ps in the high ga‑content region near the mo‑back contact. an analytical model, as well as drift‑diffusion numerical simulations, fully decouple carrier transport and recombination behaviour in this complex composition‑graded absorber structure, demonstrating the potential of tas. | insights from transient absorption spectroscopy into electron dynamics along the ga‑gradient in cu(in,ga)se2 solar cells |
all‑inorganic perovskite solar cells (pvscs) have drawn widespread attention for its superior thermal stability. carbon‑based devices are promising to demonstrate excellent long‑term operational stability due to the hydrophobicity of carbon materials and the abandon of organic hole‑transporting materials (htms). however, the difficulty to control the crystallinity process and the poor morphology leads to serious non‑radiative recombination, resulting in low voc and power conversion efficiency (pce). in this article, the crystal formation process of all‑inorganic perovskites is controlled with a facile composition engineering strategy. by bromide incorporation, high‑quality perovskite films with large grain and fewer grain boundaries are achieved. as‑prepared perovskite films demonstrate longer carrier lifetime, contributing to lower energy loss and better device performance. fabricated carbon‑based htm‑free pvscs with cspbi2.33br0.67 perovskite realized champion pce of 12.40%, superior to 8.80% of cspbi3‑based devices, which is one of the highest efficiencies reported for the carbon‑based all‑inorganic pvscs to date. the high voc of 1.01 v and ff of 70.98% indicate the significance of this composition engineering method. moreover, fabricated carbon‑based devices exhibit excellent stability, and unencapsulated device retains over 90% of its initial efficiency under continuous one sun illumination for 250 h in n2 atmosphere and keeps ~84% of its original value after stored in ambient environment with rh 15–20% for 200 h. this work provides a facile way to fabricate high‑performance and stable carbon‑based all‑inorganic pvscs. | low‑temperature processed carbon electrode‑based inorganic perovskite solar cells with enhanced photovoltaic performance and stability |
increasing performance demand associated with the short lifetime of consumer electronics has triggered fast growth in electronic waste, leading to serious ecological challenges worldwide. herein, a robust strategy for judiciously constructing flexible perovskite solar cells (pscs) that can be conveniently biodegraded is reported. the key to this strategy is to capitalize on meniscus‑assisted solution printing (masp) as a facile means of yielding cross‑aligned silver nanowires in one‑step, which are subsequently impregnated in a biodegradable elastomeric polyester. intriguingly, the as‑crafted hybrid biodegradable electrode greatly constrains the solvent evaporation of the perovskite precursor solution, thereby generating fewer nuclei and in turn resulting in the deposition of a large‑grained dense perovskite film that exhibits excellent optoelectronic properties with a power conversion efficiency of 17.51% in pscs. more importantly, the hybrid biodegradable electrode‑based devices also manifest impressive robustness against mechanical deformation and can be thoroughly biodegraded after use. these results signify the great potential of masp for controllably assembling aligned conductive nanomaterials for biodegradable electrodes. as such, it represents an important endeavor toward environmentally friendly, multifunctional and flexible electronic, optoelectronic, photonic, and sensory materials and devices. | large‑grained perovskite films enabled by one‑step meniscus‑assisted solution printing of cross‑aligned conductive nanowires for biodegradable flexible solar cells |
post deposition underwater treatment with a nanosecond nd3+:yag laser is proposed and demonstrated for the passivation of electrical defects in 400-1000 nm-thick a-si thin films needed for solar cells. the proposed pulsed laser beam-overlap technique also allows simultaneous annealing and texturing. atomic hydrogen, oxygen, and hydroxyl radicals activated by the breakdown of water by laser heating passivate the dangling bonds in the crystal grains, improving the solar cell performance. the presence of hydrogen observed after water annealing using x-ray photo electron spectroscopy (xps), raman spectroscopy, and attenuated total reflectance-fourier transform infrared spectroscopy (atr-ftir) shows that the passivation improvement is caused by diffusion of atomic hydrogen. after underwater annealing, relative improvement in the life time of minority carriers was measured to be approximately 13% and the efficiency of n-asi/p-csi solar cells is found to be increased ( 2 to 3%) when compared to that in air. | enhanced electrical characteristics of a-si thin films by hydrogen passivation with nd3+:yag laser treatment in underwater for photovoltaic applications |
here, we introduced acetamidine (c2h3n2h3, aa)-based salt as an additive in the fabrication of perovskite (ch3nh3pbi3) layer for perovskite solar cells. it was found that as an amidine-based salt, this additive successfully enhanced the crystallinity of ch3nh3pbi3 and helped to form smooth and uniform films with comparable grain size and full coverage. besides, perovskite film with additive showed a much longer carrier lifetime and an obviously enhanced open-circuit voltage in the corresponding devices, indicating that the acetamidine-based salt can reduce the carrier recombination in both the film and device. we further demonstrate a promising perovskite device based on acetamidine salt by using a configuration of ito/tio2/perovskite/spiro-ometad/au under < 150 °c fabrication condition. a power conversion efficiency (pce) of 16.54% was achieved, which is much higher than the control device without acetamidine salt. these results present a simple method for film quality optimization of perovskite to further improve photovoltaic performances of perovskite solar cells, which may also benefit the exploration of a cation in perovskite materials. project supported by young talent thousand program and enn group. | the investigation of an amidine-based additive in the perovskite films and solar cells |
drying is one way of post-harvest handling to extend the shelf life, especially for agricultural crops. in general, post-harvest drying is only done naturally by using heat from solar energy or commonly called conventional drying. in this study, the grain was dried using a fluidized bed dryer. however, the fluidized bed dryer was modified by adding a pipe heat exchanger. the purpose of this study was to find the effect of grain mass and air intake temperatures on drying time. the indonesian government has carried out sni provisions for milling the maximum water content in the material which is 14%. in this study, the grain used was the newly harvested grain where the water content was about 20% with a tolerance of ± 1%. the mass variations in this study were 0.4 kg, 0.6 kg and 0.8 kg and the temperature variations applied were 55°c, 60°c, and 65° c. the results showed the highest heat loss occurs at the highest mass because the air velocity is not able to circulate properly. | the effect of grain mass variations on drying time by adding a pipe heat exchanger to a fluidized bed dryer |
grain boundaries in multi-crystalline silicon are crucial to the minority carrier lifetime, and thus, solar cell efficiency. therefore, further understanding on the grain boundary development during crystal growth is needed. this in situ observation study is focused on the solidification interface behavior and the grain boundary development between different orientation crystals - considering both stable and unstable growth conditions. silicon seeds with <1 0 0> and <1 0 0> + 20° growth direction orientations were partially melted and then solidified inside an observation furnace, and a digital and an infrared (ir) microscopes were utilized for the visualizations and temperature profile measurements, respectively. the unstable growth was found to exhibit continuous fluctuations with increasing amplitudes in the growth velocity which were related to the buildup of undercooling and the growth of facets. the electron backscatter diffraction (ebsd) analysis showed that twin nucleation occurred from the valley of the faceted groove for the low-undercooling stable growth, whereas random grain nucleation occurred from the tip of the facets for the high-undercooling unstable growth. the measured negative temperature gradient inside the groove was used to explain the growth behavior under the unstable condition. | in situ observation of the solidification interface and grain boundary development of two silicon seeds with simultaneous measurement of temperature profile and undercooling |
unlike pb‑based perovskites, it is still a challenge for realizing the targets of high performance and stability in mixed pb–sn perovskite solar cells owing to grain boundary traps and chemical changes in the perovskites. in this work, proposed is the approach of in‑situ tin(ii) inorganic complex antisolvent process for specifically tuning the perovskite nucleation and crystal growth process. interestingly, uniquely formed is the quasi‑core–shell structure of pb–sn perovskite–tin(ii) complex as well as heterojunction perovskite structure at the same time for achieving the targets. the core–shell structure of pb–sn perovskite crystals covered by a tin(ii) complex at the grain boundaries effectively passivates the trap states and suppresses the nonradiative recombination, leading to longer carrier lifetime. equally important, the perovskite heterostructure is intentionally formed at the perovskite top region for enhancing the carrier extraction. as a result, the mixed pb–sn low‑bandgap perovskite device achieves a high power conversion efficiency up to 19.03% with fill factor over 0.8, which is among the highest fill factor in high‑performance pb–sn perovskite solar cells. remarkably, the device fail time under continuous light illumination is extended by over 18.5‑folds from 30 to 560 h, benefitting from the protection of the quasi‑core–shell structure. | in situ tin(ii) complex antisolvent process featuring simultaneous quasi‑core–shell structure and heterojunction for improving efficiency and stability of low‑bandgap perovskite solar cells |
energy is a major requirement in everyday life. the harvesting energy, as well as the storing energy, are crucial to being developed. many individual types of research of dssc or other solar cells systems, as well as the energy storage systems, have greatly improved. many disadvantages are arising for a separated device e.g. loss of converted energy from solar cell, or need other expensive devices for unused converted energy. to overcome the problem, it is necessary to combine the solar cells and their storage in one integrated system. in this report, we show the charging performance of electrical energy from dssc into a supercapacitor section. in this study, we simply describe the synthesis of various photoanodes of sno2:tio2 composite nanoparticles for a various fraction of wt% tio2 i.e. 0, 9, 18, 27, 36, and 100%. the films have been prepared using the screen-printing method followed by blending with dye β-carotene and combined an additional layer of zno symmetric supercapacitor to build a solar-supercapacitor. it is found that tio2 and sno2 particles were successfully synthesized with the grain size ranged from 8.9 nm to 26 nm. the gap energy produced by sno2/tio2 composite nanoparticles is 3.07 to 3.15 ev. the addition of tio2 nanoparticles increases the efficiency of solar cells. the performance of optimum solar cell sno2:tio2 composite nanoparticle showed by 36 wt% tio2 device with jsc, voc, fill factor, and the efficiency of 0.388 ma, 0.806 v, 0.452, and 0.819% respectively. the charging from dssc into supercapacitor was measured to btain their capacitance. it is shown that the supercapacitor section can store the energy produced by the conversion of light into electricity in the solar cell section. | effect of (sno2:tio2) nanoparticles on charging performance of integrated dye-sensitized solar cell-supercapacitor |
a composite nucleant with si powder as the main component was introduced to prepare high-performance multicrystalline (hpm) silicon ingot in this work. the effect of different sizes of si powder on the ingot performance was investigated and compared with the conventional hpm silicon ingot which seeded from poly-si particles. it is proved that the composite nucleant with si powder of large particle size (d50 = 355 μm) can induce small and uniform grains, showing uniform minority carrier lifetime distribution and low dislocation cluster area ratio. meanwhile, the length of red zone at the ingot bottom is significantly shorter than conventional hpm silicon ingot, which significantly increases the yield of the ingot. the ingot grown with suitable composite nucleant can achieve high cell efficiency and the solar cells have low light-induced degradation (lid) value due to low interstitial oxygen concentration which are comparable to the conventional hpm silicon ingot. | production of high performance multi-crystalline silicon ingot by using composite nucleant |
lead halide perovskites in the form of nanocrystalline quantum dots (qds) have emerged as a new class of semiconductor materials for photovoltaics (pvs) and optoelectronics. thanks to the nanoscale size-induced lattice strain and enhanced contribution from the surface energy [1], perovskite qds have shown superior phase stability at room temperature over their thin film bulk counterparts offering a promising strategy to significantly increase stability and hence lifetime of the perovskite devices. other notable advantages including wider compositional tunability, smaller voltage loss and unprecedented device architectures make perovskite qds a promising candidate for developing qd-based tandems and tandems with other perovskites or silicon [2,3]. in addition, perovskite qds allow easier scale-up and more rapid manufacturing by decoupling grain-crystallization from film-deposition. when incorporated in pv devices, cesium and formamidinium lead triiodide (cspbi3 and fapbi3) qds have yielded promising power conversion efficiencies (pces) with a previous record of 13.4% [2], outperforming traditional chalcogenide qd solar cells (qdscs). nevertheless, the susceptible nature of cspbi3 and fapbi3 qds towards moisture and polar solvents [1,4] makes it difficult to further increase the pces. the mixed-cation cs1-xfaxpbi3 qds with entropically stabilized perovskite structure were then explored, but the reported multinary qds suffer from low optoelectronic quality resulting in even deteriorated efficiency [5] and perovskite qdscs still lag far behind those of the state-of-the-art thin film devices in pce. | a leap towards high performance quantum dot solar cells |
we observed photoexcited carrier responses in solar cells excited by femtosecond laser pulses with spatial and temporal resolution using an optical pump-terahertz emission probe technique. we visualized the ultrafast local variation of the intensity of terahertz emission from a polycrystalline silicon solar cell using this technique and clearly observed the change in signals between a grain boundary and the inside of a grain in the solar cell. further, the time evolution of the pump-probe signals of the polycrystalline and monocrystalline silicon solar cells was observed, and the relaxation times of photoexcited carriers in the emitter layers of crystalline silicon solar cells were estimated using this technique. the estimated relaxation time was consistent with the lifetime of the auger recombination process that was dominant in heavily doped silicon used as an emitter layer for the silicon solar cells, which is difficult to obtain with photoluminescence method commonly used for the evaluation of solar cells. | visualization of photoexcited carrier responses in a solar cell using optical pump—terahertz emission probe technique |
localized surface plasmon resonances (lsprs) are usually achieved by some small grains of noble metal (au, ag et al.) to enhances the light absorption and charge carrier's concentration of photocatalysts, but the wide application of noble metals is limited by their high cost. here, we report the preparation of 0d/2d plasmonic cu2-xs/g-c3n4 nanosheets (cscnns) and the utilization of lsprs generated from cu2-xs nanodots instead of noble metals to improve the photocatalytic activity for degradation of typical antibiotic levofloxacin (lvx). one-step hydrothermal method was employed to grow the highly dispersed cu2-xs nanodots on the g-c3n4 nanosheets. various characterization techniques verify the strong light absorption capacity and longer carriers' lifetime for cscnns. the analysis of band structure reveals the efficient separation and transmission mechanism of photogenerated electrons and holes. more importantly, lsprs has been proved to be effective in increasing the light absorption in near infrared (nir) region and the theoretical finite difference time domain (fdtd) simulations demonstrated that cu2-xs lspr-induced electromagnetic field in g-c3n4 nanosheets was far stronger than that of ag and au in nir region. consequently, efficient photocatalytic degradation of lvx under full solar spectrum (uv-vis-nir) can be achieved for cscnns. this work will lead to a cheap and efficient lspr photocatalysis system for treatment of antibiotic wastewater or other photocatalytic applications. | 0d/2d plasmonic cu2-xs/g-c3n4 nanosheets harnessing uv-vis-nir broad spectrum for photocatalytic degradation of antibiotic pollutant |
bismuth‑based solar cells have been under intensive interest as an efficient non‑toxic absorber in photovoltaics. within this new family of semiconductors, we herein report a new, long‑term stable copper bismuth iodide (cubii4). a solutionprocessed method under air atmosphere is used to prepare the material. the adopted hi‑assisted dimethylacetamide (dma) co‑solvent can completely dissolve cui and bii3 powders with high concentration compared with other organic solvents. moreover, the high vapor pressure of tributyl phosphate, selected for the solvent vapor annealing (sva), enables complete low‑temperature (≤70 °c) film preparation, resulting in a stable, uniform, dense cubii4 film. the average grain size increases with the precursor concentration, greatly improving the photoluminescence lifetime and hall mobility; a carrier lifetime of 3.03 ns as well as an appreciable hall mobility of 110 cm2 v−1s−1 were obtained. xrd illustrates that the crystal structure is cubic (space group fd3m) and favored in the [1 1 1] direction. moreover, the photovoltaic performance of cubii4 was also investigated. a wide bandgap (2.67 ev) solar cell with 0.82 % power conversion efficiency is presented, which exhibits excellent long‑term stability over 1008 h under ambient conditions. this air‑stable material may give an application in future tandem solar cells as a stable short‑wavelength light absorber. | solution‑processed air‑stable copper bismuth iodide for photovoltaics |
directional solidification (ds) is the most popular technique for massive production of multicrystalline silicon (mc-si) in the solar industry. constant improvement of the quality of silicon ingot production remains a research focus. in this work, the temperature distribution, thermal stresses, and melt-crystal (m/c) interface during the ds process with different pulling-down rates were studied by transient numerical simulation and verified by experiment. the results show that the thermal stresses and interface shape during crystal growth play an equally important role in the control of crystal quality, requiring an appropriate pulling-down rate to achieve thermal conditions in the furnace that provide an ideal temperature field in the silicon with lower thermal stresses and a suitable growth interface. based on these results, an mc-si ingot grown at 10 μm/s in a pilot-scale ds process had a larger grain size, vertical columnar structure, fewer defects, and a longer minority-carrier lifetime above 3 μs. this suggests that improvement of the quality of mc-si ingots for solar cells requires comprehensive consideration of the effect of the thermal field conditions on the thermal stresses and grain orientation in the solidification process. | effect of heat transfer during the vacuum directional solidification process on the crystal quality of multicrystalline silicon |
in thin film solid-state heterojunction solar cells (hscs), titanium-dioxide (tio2) electrodes need to be optimized to have large specific surface area, controllable pore sizes, and superior light scattering properties. in this study, we synthesize hierarchical nanoporous tio2 beads with sub-micron diameters by a template-free, fast, and low-temperature synthetic scheme to satisfy the aforementioned requirements for hscs. these nanoporous tio2 beads are composed of numerous tio2 nano crystallites that provide mesopores, and the inter-particle distances of size-controlled tio2 beads can provide additional controllable macropores. we report the first successful application of tio2 bead films (sp250, sp450) with controllable hierarchical nanostructure to be sensitized with sb2s3 for all-solid-state heterojunction solar cells (sb-hscs). the sb-hscs made using the controlled tio2 beads as photoanodes exhibit a superior light-to electricity conversion efficiency of 4.8%, yielding more than 15% enhancement in comparison with that (3.6%) of commercial tio2 nanoparticle (np40) electrodes. the well-tailored photoanode with high surface area, fewer grain boundaries, multi-scale pore structure, and enhanced optical scattering results in much better infiltration of hole-conducting materials, decreased recombination with increased electron lifetime, and enhanced light scattering, which result in the enhanced photovoltaic properties. | facile control of intra- and inter-particle porosity in template-free synthesis of size-controlled nanoporous titanium dioxides beads for efficient organic-inorganic heterojunction solar cells |
in this work, polycrystalline cuznsn(s,se)4 thin films were deposited on soda lime glass by a facile thermal evaporation method using a single source. the temperature dependence of electrical conductivity in the dark σd and under illumination σph has been evaluated over 290 k-425 k. the synthesized thin films exhibit a p-type semiconductor, regardless of the zinc ratio. the electrical conductivities for all compositions increase with increasing temperature indicating semiconducting behaviour of the material, and were explained by the thermionic emission model over grain boundary barriers. the grain boundary barrier energy decreases on exposure to light and was found to vary with zn concentration. the photoconductivity increases with light intensity and the calculations reveal that the recombination process is bimolecular in nature. the persistent photoconductivity was measured and the decay process exhibited non-exponential behaviour, and then the concept of a differential lifetime was used. the temperature dependence of the differential lifetime was studied for all films. understanding of the current results is quite important for polycrystalline solar cell thin films. | an investigation on photoconductivity of non-stoichiometric cuznsn(s, se)4 thin films for photovoltaic applications |
data returned from the cassini-huygens mission have strengthened enceladus, a small icy moon of saturn, as an important target in the search for life in our solar system. information gathered from cassini to support this includes the presence of a subsurface liquid water ocean, vapor plumes and ice grains emanating from its south polar region, and the detection of essential elements and organic material that could potentially support life. however, several outstanding questions remain regarding the connectivity of plume material to the ocean and the composition of the complex organic material. herein we introduce tiger, a mission concept developed during the 2020 planetary science summer school at nasa's jet propulsion laboratory. tiger is a flyby mission that would help further constrain the habitability of enceladus through two science objectives: (1) determine whether enceladus's volatile inventory undergoes synthesis of complex organic species that are evidence for a habitable ocean, and (2) determine whether enceladus's plume material is supplied directly from the ocean or if it interfaces with other reservoirs within the ice shell. to address the science goals in a total of eight flybys, tiger would carry a four-instrument payload, including a mass spectrometer, a single-band ice-penetrating radar, an ultraviolet imaging spectrograph, and an imaging camera. we discuss tiger's instrument and mission architecture, as well as the trades and challenges associated with a habitability-focused new frontiers-class flyby mission to enceladus. | tiger: concept study for a new frontiers enceladus habitability mission |
we report correlated 49ti and 28si excesses in 14 x grains, confirming the absence of the short-lived isotope 49v during grain condensation in sne. | decoding mixing in supernovae: correlated silicon and titanium isotopic signatures in presolar sic grains of type x |
we investigate the evolutionary effects on the brightness of a sunspot as well as on the properties of its fine-structures using two sets of time series of g-band images of a single sunspot in noaa 10944 recorded at two symmetric locations on the solar disc by hinode/sot (solar optical telescope). the second time series (phase w) was recorded 2.5 d after recording the first time series (phase e). both time series of images were corrected for instrumental stray light; then the p-mode oscillations were removed. our analysis demonstrates that the spatially and temporally averaged intensities of the umbra as well as the penumbra in both phases are practically the same. nevertheless, considering only intensities smaller than 1.0iph the penumbra in the phase w is brighter with a contrast of 2 per cent. however, the ratio of the peak intensities of penumbral grains to their background intensities decreases, on average, from 2.9 to 2.6 from phase e to phase w. the penumbra is on average, 6.9 times brighter than the umbra in both phases. the umbra gets smaller in size with a ratio of 0.90 and its magnetic field strength decreases about 200 g after the 2.5 d evolution. although the central umbral dots (uds) with lifetimes longer than 2 min are by the factor of 1.6 more frequent in phase e, the most of the physical and kinematic properties of uds do not show considerable changes after the sunspot evolution at this 2.5 d time interval. the registered uds have intensities smaller than 0.84iph with a mean intensity of about 0.29iph. the equivalent diameters of the individual uds have a symmetric distribution around 180 km with a standard deviation about 35 km. the brightest uds show a constant median diameter. the uds registered in both phases have a mean lifetime of 7.4 min. our results suggest that uds with a certain lifetime have an admissible lower limit for their mean size which grows with lifetime. the proper motions of uds show velocities less than 1.0 kms−1 with a maximum population around 0.2 kms−1. the uds formed in the phase w are faster when the umbral area is smaller and the magnetic field is weaker. | comparative study of a sunspot at two different instances of time |
combined with advanced crystal growth technology and reduced dislocation densities, the higher tolerance to metal contamination of n-type silicon makes n-type cast-grown silicon a potential option for low cost high quality substrates for solar cells. using a combination of photoconductance based lifetime testing and photoluminescence imaging, we have investigated the carrier lifetime in wafers from the bottom, middle, and top parts of a n-type high-performance multicrystalline (hpm) silicon ingot, and wafers from n-type mono-like silicon ingots after each high temperature solar cell processes, including after boron diffusion, phosphorus diffusion, and hydrogenation. although boron diffusion leads to a degradation of the sample lifetime, phosphorus diffusion and hydrogenation is effective at recovering the lifetime in the intra-grain region and at the grain boundaries respectively. quasi-steady-state photoconductance (qsspc) measurements show that the arithmetic average lifetime of hpm silicon wafers and mono-like silicon wafers can reach up to 1.8 and 3.3 ms respectively for a process sequence including a boron diffusion, with corresponding implied open circuit voltage of about 720 mv. if the boron diffusion can be avoided, average lifetimes up to 3.0 and 6.6 ms can be achieved respectively, highlighting the excellent potential of n-type cast-grown materials. | n-type high-performance multicrystalline and mono-like silicon wafers with lifetimes above 2 ms |
it is unmistakably paradoxical that the weakest point of the photoactive organic-inorganic hybrid perovskite is its instability against light. why and how perovskites break down under light irradiation and what happens at the atomistic level during the degradation still remains unanswered. in this paper, we revealed the fundamental origin and mechanism for irreversible degradation of hybrid perovskite materials from our new experimental results and ab initio molecular dynamics (aimd) simulations. we found that the photo-generated charges trapped along the grain boundaries of the perovskite crystal result in oxygen-induced irreversible degradation in air even in the absence of moisture. the present result, together with our previous experimental finding on the same critical role of trapped charges in the perovskite degradation under moisture, suggests that the trapped charges are the main culprit in both the oxygen- and moisture-induced degradation of perovskite materials. more detailed roles of oxygen and water molecules were investigated by tracking the atomic motions of the oxygen- or water-covered ch3nh3pbi3(mapbi3) perovskite crystal surface with trapped charges via aimd simulation. in the first few picoseconds of our simulation, trapped charges start disrupting the crystal structure, leading to a close-range interaction between oxygen or water molecules and the compositional ions of mapbi3. we found that there are different degradation pathways depending on both the polarity of the trapped charge and the kind of gas molecule. especially, the deprotonation of organic cations was theoretically predicted for the first time in the presence of trapped anionic charges and water molecules. we confirmed that a more structurally stable, multi-component perovskite material(ma0.6fa0.4pbi2.9br0.1) exhibited a much longer lifespan than mapbi3 under light irradiation even in 100% oxygen ambience. | atomistic mechanism for trapped-charge driven degradation of perovskite solar cells |
in this paper, the two-step sequential deposition method was used to prepare the ch3nh3pbbrxi3-x films by introducing ch3nh3br in the precursors. the surface morphology of the pbi2 films was controlled by anti-solvent extraction (ase) to improve the microstructure and photo-physical properties of the perovskite films. it was noteworthy that, compared to the compact pbi2 films, the porous pbi2 films facilitated the growth of crystals and bromine incorporation in films, and the prepared perovskite films exhibited enlarged grain size, increased light absorption, enhanced br incorporation and prolonged carrier lifetime, which resulted in excellent photo-electrical properties of the ch3nh3pbbrxi3-x films. with porous pbi2 templates, the inverted planar perovskite solar cells based on films with appropriate br incorporation (ch3nh3br/ch3nh3i mole ratio = 3/7) showed a photovoltaic conversion efficiency (pce) of 14.9%, and the stability of the devices in air was elevated. consequently, the high-quality ch3nh3pbbrxi3-x films can be obtained with porous pbi2 templates for improving the performance of the perovskite solar cells. | enhanced photovoltaic performance of ch3nh3pbbrxi3-x-based perovskite solar cells via anti-solvent extraction |
pure sulfide cu2znsns4 thin films were fabricated on mo‑coated glass substrates by facile spray deposition of aqueous precursor solutions containing cu(no3)2, zn(no3)2, sn(ch3so3)2, and thiourea followed by annealing at 600 °c. when a precursor solution containing a stoichiometric composition of cu, zn, and sn was used, the resulting cu2znsns4 thin film contained a cu2−xs impurity phase owing to the evaporation of sn components during the annealing process. the cu2−xs impurity in the cu2znsns4 thin film was removed by reducing the concentration of cu in the precursor solution. this resulted in an improvement of the structural features (i.e., grain sizes and compactness) as well as the electric properties such as acceptor densities, the nature of the acceptor defects, and carrier lifetimes. a solar cell based on the cu2znsns4 film with an empirically optimal composition showed conversion efficiency of 8.1 %. the value achieved was one of the best efficiencies of cu2znsns4‑based cells derived from a non‑vacuum process. | impact of precursor compositions on the structural and photovoltaic properties of spray‑deposited cu2znsns4 thin films |
thin film heterojunction solar cells based on cusb(s,se)2 absorbers are investigated for two primary reasons. first, antimony is more abundant and less expensive than elements used in current thin film photovoltaics, in, ga, and te, and so, successful integration of sb based materials offers greater diversification and scalability of solar energy. second, the cusb(s,se) 2 ternary is chemically, electronically, and optically similar to the well-known, high efficiency, cuin(s,se)2 based materials. it is therefore postulated that the copper antimony ternaries will have similar defect tolerant electronic transport that may allow for similar highly efficient photoconversion. however, cusb(s,se)2 forms a layered crystal structure, different from the tetrahedral coordination found in conventional solar absorbers, due to the non-bonding lone pair of electrons on the antimony site. thus examination of 2d antimony ternaries will lend insight into the role of structure in photoconversion processes. to address these questions, the semiconductors of interest (cusbs 2 & cusbse2) were first synthesized on glass by combinatorial methods, to more quickly optimize process condi- tions. radio-frequency (rf) magnetron co-sputtering from sb2(s,se)3 and cu 2(s,se) targets were used, without rotation, to produce chemical and flux graded libraries which were then subjected to high throughput characterization of structure (xrd), composition (xrf), conductivity (4pp), and optical absorption (uv/vis/nir). this approach rapidly identified processes that generated phase pure material with tunable carrier concentration by applying excess sb 2(s,se)3 within a temperature window bound by the volatility of sb2(s,se)3 and stability of the ternary phase. the resulting phase pure thin films were then incor- porated into the traditional cuingase2 (cigs) substrate photovoltaic (pv) architecture, and the resulting device performance was correlated to gradients in composition, sputter flux, absorber thickness, and grain orientation. this combinatorial work was complimented by individual measurements of photoluminescence (pl), capacitance-voltage (cv), external quantum efficiency (eqe), terahertz (thz) spectroscopy, and photoelectrochemical (pec) measurements. cusbs2-based libraries produced devices with just 1% power conversion efficiency, mainly limited by high levels of recombination associated with high density of shallow trap states. conversely, the selenide variant showed more promise, with initial cells producing significantly more photocurrent, nearly 60% of the theoretical maximum, and likewise 5% efficient devices, mainly due to fewer trap states. however, the selenide is still limited by short carrier diffusion lengths, therefore demonstrating that structure does seem to play limiting role in photoconversion processes. overall, the cusb(s,se)2 material system is only likely to merit further exploration if it can be incorporated into an alternate device structure less dependent on collection by diffusion. there is a small possibility that oriented selenide films with anisotropic carrier lifetimes could improve performance, though this is unlikely considering initial oriented sulfide films did not demonstrate much improved performance. this work demonstrated the utility of the combinatorial device fabrication applied to the search for new, scalable photovoltaic materials. an innovative chemical system was quickly explored in-depth and optimized for devices; continued efforts of this type are likely to produce better materials, or at the very least, quickly expand the library of well-scrutinized photovoltaic materials. | cusb(s,se)2 thin film heterojunction photovoltaic devices |
cdte is a material well-suited to solar cell applications due to its 1.5 ev direct bandgap and high optical absorption. to meet energy demands, cdte solar cells must be produced at a low-cost and with high throughput which often demands the use of non-ideal polycrystalline cdte. as a result of careful process control, current thin-film poly-cdte cells have been shown to be somewhat defect tolerant with proven industry success. yet despite this success poly-cdte cells are still far from their predicted shockley-queisser theoretical limits. the next generation cells must demonstrate higher open-circuit voltages, fill factors, and longer minority carrier lifetimes. playing a major role in doping, defect migration, carrier recombination, and current transport are 2d extended defects both within grains and between grains as grain boundaries (gbs). a further understanding of these defects is needed which exhibit either high symmetry such as the csl structures or those mixed or random gbs with low symmetry. their corresponding formation and electronic behavior will be needed to develop methods to mitigate their effects and instead promote higher doping with less minority carrier recombination. predictions and guidance on electronic and thermodynamic properties can be obtained from model atomic structures within the framework of ab-initio density-functional theory. bulk point defect formation energies were determined for comparison to calculations of point defects along gb structures. model atomic structures of gbs can also be created rapidly and over a wide parameter space using the grain boundary genie code developed for this project. commonly observed low-angle and special coincident grain boundaries structures were created and a subset relaxed to determine their local strain environment and interfacial energy with for comparison to stem observations. additionally, a series of random angle or 'mixed' grain boundaries were created and investigated corresponding to possible interfaces between grains that cannot be observed in stem. | application of ab-initio methods to grain boundaries and point defects for poly-cdte solar cells |
the objective of this thesis is to describe the correlated study of individual presolar grains via nano-scale secondary ion mass spectrometry (nanosims), transmission electron microscopy (tem), and scanning transmission x-ray microscopy (stxm) utilizing x-ray absorption near edge structure (xanes), with a focus on connecting these correlated laboratory studies to astrophysical phenomena. the correlated isotopic, chemical, and microstructural studies of individual presolar grains provide the most detailed description of their formation environments, and help to inform astrophysical models and observations of stellar objects. as a part of this thesis i have developed and improved upon laboratory techniques for micromanipulating presolar grains and embedding them in resin for ultramicrotomy after nanosims analyses and prior to tem characterization. the new methods have yielded a 100% success rate and allow for the specific correlation of microstructural and isotopic properties of individual grains. knowing these properties allows for inferences to be made regarding the condensation sequences and the origins of the stellar material that condensed to form these grains. nanosims studies of ultramicrotomed sections of presolar graphite grains have revealed complex isotopic heterogeneities that appear to be primary products of the grains' formation environments and not secondary processing during the grains' lifetimes. correlated excesses in 15n and 18o were identified as being carried by tic subgrains within presolar graphite grains from supernovae (sne). these spatially-correlated isotopic anomalies pinpoint the origin of the material that formed these grains: the inner he/c zone. complex microstructures and isotopic heterogeneities also provide evidence for mixing in globular sn ejecta, which is corroborated by models and telescopic observations. in addition to these significant isotopic discoveries, i have also observed the first reported nanocrystalline core surrounded by turbostratic graphite within a low-density sn graphite grain. nanocrystalline cores consisting of randomly-oriented 2-4 nm sheets of graphene and surrounded by concentric shells of graphite have been observed in high-density presolar graphite grains from asymptotic giant branch stars, whose grains are typically microstructurally distinct from sn graphite grains. these vastly different stellar environments briefly formed similar nanocrystalline structures before diverging in the structure of their mantling graphite to be typical of agb and sn grains. while relatively few correlated nanosims and tem studies have been performed previously, which this research thesis aims to expand, my collaborators and i also endeavored to add a third correlated technique, stxm/xanes, which had previously not been applied to presolar grains. xanes allows for the investigation of molecular bonds, which we used to help infer physical and chemical properties of stellar ejecta. i investigated the c k-edge and ti l-edge of molecular bonds in both presolar graphite grains and their tic subgrains. the presolar graphite grains, while overwhelmingly composed of aromatic c molecules, host a wide variety of minor organic molecules. considering the large isotopic anomalies in the grains, these minor components are not likely due to contamination. i also investigated the valence state of ti in ti-rich subgrains and plan to work towards illuminating the effect that v in solid solution has upon the tic bonds. | correlated nanosims, tem, and xanes studies of presolar grains |
msl began investigating a contact between murray formation, (fine grained lake deposits) and the younger stimson formation at marias pass in may 2015, on the lower slopes of mt. sharp. images show that the murray formation, with numerous calcium sulfate veins compared to the stimson, is truncated at an erosional contact. mahli images show a white layer a few mm thick at the contact that might be calcium sulfate. the lowermost beds of the stimson unit in the missoula area comprise horizontally laminated or cross-laminated sandstones. the sandstones are poorly sorted with floating granules and very coarse sand grains set in a fine- medium-grained sand 'matrix'. this material directly above the contact is a resistant, basal ledge-forming layer that also forms numerous blocks of float on top of the eroded murray. this basal layer contains light toned fragments, possibly calcium sulfate, eroded from the murray. the poor sorting and presence of sub-angular grains, together with the absence of preferential sorting into size sorted layers would seem to rule out eolian processes for the lowermost beds of the stimson and suggest fluvial processes were responsible for deposition of these beds. for chemostratigraphy, the distance of each chemcam or apxs observation above or below the contact was determined from images and the navcam stereo mesh. the top of the murray near the missoula area is variable in composition, and additional analyses are planned to determine if weathering occurred at the eroded surface. above the contact, the lowest 2 cm of the resistant slab is higher in sio2, and lower in al2o3, k2o and na2o, relative to other stimson analyses. in a few points with low totals, there is a correlation between ca and missing components (presumed to be mostly s). these points could be connected to calcium sulfate in the form of cements and/or incorporation of eroded clasts of murray vein materials. | chemistry of the materials above and below an unconformity between the murray and stimson formations in gale crater, mars |
saturn's ice-covered moon enceladus exhibits large cryovolcanic plumes sourced from a global subsurface ocean that may contain the requisite conditions for life. salt-rich ice particles encountered in the plumes by cassini are thought to originate as frozen ocean droplets, thus capturing a snapshot of ocean chemistry. however, little is known about how enceladus ocean fluids evolve as they freeze, and thus how key indicators of habitability, such as redox-sensitive metals and organic compounds, might be expressed within these salt-rich particles. we investigated fluid evolution and solid phase formation from simulated enceladus ocean fluids during freezing at endmember cooling rates, using parallel thermodynamic modelling and experimental approaches. cryo-imaging techniques showed that even at flash-freezing conditions (>10 k s-1), enceladus-like fluids undergo segregation, whereby the crystallization of ice templates the formation of brine vein networks. the high solute concentrations and confined nature of these brine veins means that vitrification can occur at slower cooling rates than those typically required for vitrification of a bulk solution. at more gradual cooling rates (~1 k min-1), or if flash-frozen samples are re-warmed, crystalline salts precipitate at ice grain boundaries. resulting crystallization textures differ markedly between cooling regimes, showing that they inherit a signature of their formation conditions, and can result in compositional heterogeneity on a sub-10 μm scale. moreover, the mineralogy of carbonate phases can act as a probe for parent fluid ph. the fate of trace bioessential elements such as iron, which are expected in the ocean but have thus far evaded detection in cassini data, are explored, alongside the implications for how organic material, including biological structures, may be incorporated and delivered to space. our findings describe endmember possibilities for solid phase production from enceladus-relevant fluids that add crucial context to the findings of cassini and provide a strong rationale for non-destructive plume measurements by future missions. | phase fractionation and the fate of bioessential elements during freezing of simulated enceladus ocean fluids |
the chalcopyrite semiconductor cuinxga1-x se2 is considered as the most promising material for high efficiency thin film solar cells due to its exceptional radiation stability, tunable direct bandgap, high light absorption coefficient and low cost preparation methods. in this thesis, we present the systematic investigation of the deposition conditions to optimize the cuinxga1-xse2 device performance using the two-step deposition method. further, we utilized nonlinear optical methods to investigate the deposition parameters to optimize the bulk and interface properties of photovoltaic devices. first, we investigated the deposition parameters to optimize the structural, electrical, optical and adhesion properties of molybdenum, mo, and aluminum doped zinc oxide, zno:al, electrode layers. our results show that electrical and adhesion properties of mo films can be optimized by modifying the intrinsic mechanical compressive and tensile stress. mo films deposited under tensile stress exhibit good adhesional strength and high resistivity, whereas films deposited under compressive stress exhibit poor adhesional stress and low resistivity. in order to obtain mo films with both good adhesion and low sheet resistance, we deposited the films in a bilayer structure. similarly, increased ar flux is found to improve the crystalline quality of the zno:al films due to ar-zno:al collisions and heating effect which lead to increased grains size and shape, reducing intergranular voids in zno:al films. moreover, lower sputter pressure is found to increase transmittance of light due to reduced grain boundary scattering of light. post-annealing treatment in hydrogen atmosphere is found to enhance the conductance of the zno:al film which is attributed to desorption of negatively charged species, mainly oxygen from the grain boundaries. second, we investigated the uniformity, morphology and homogeneity of cuinga precursor and cuinxga1-xse2 films. in order to obtain uniform chemical homogeneity, and smooth surface, we deposited the precursor in the mo/in/cuga/in structure. reducing the deposition time for in resulted in a precursor film with smoother morphology, and depositing a stacked structure enabled uniform chemical homogeneity. next, we designed our chemical vapor deposition system to fabricate uniform cuinxga 1-xse2 films with reproducible results. in our chemical vapor deposition system, we incorporated a flow controller to control the selenium diffusion rate, hence the thickness of the moxsey layer, and a pressure regulator to control the selenium vapor pressure in order to fabricate cuinxga 1-xse2 films with the right selenium content and the stoichiometry. a sophisticated exhaust gas collection system is incorporated to trap the unreacted residual se vapor, and prevent the cvd system from contamination and to obtain reproducible results. a graphite cuinga precursor fixture was utilized and oriented normal to the direction of selenium flux. our selenization results show that the cuinxga1-xse2 device performance can be optimized by tuning the cu/in composition. an increase in se flux facilitates in2se3 and ga2se3 phases, resulting in cuinxga 1-xse2 films with larger grains, and better device performances. we also show selenium cracking helps to reduce the defect density in the bulk and interface of the cuingase film by filling in the copper vacancy defects. third, we utilized raman spectroscopy and time-resolved photoluminescence spectroscopy to investigate the deposition parameters to optimize the crystalline quality and therefore the interval radiative quantum efficiency of mbe-grown gaas/algaas double heterostructures. our results reveal an improvement in lattice disorder in both the gaas and algaas layers at elevated temperatures as the as/ga flux ratio is reduced, which is consistent with the obtained longest minority carrier lifetime. moreover, we reveal that incorporation of a distributed bragg reflector layer significantly reduces the defect density in the subsequent layers. our results show that the combined analysis of raman and trpl spectra provide a powerful tool for understanding defect mechanism and carrier dynamics in gaas/algaas dh structures. | optimization of cuinxga1-xse2 solar cells with post selenization |
while the curiosity rover continues to provide growing evidence of the salty paleolake origins of gale crater, the perseverance rover will land in jezero crater in february of 2021 and begin seeking signs of ancient life within the paleolake deposits. further, in 2022 the exomars rover will begin its journey to explore the potential paleolake basin of oxia planum. all these missions seek to understand the habitable environments within martian paleolakes, and their capability for preserving biosignatures of past life. to accomplish their respective goals, all accessible habitable zones with preservation potential will need to be considered, and this should include transitional subsurface habitable zones within the sedimentary deposits. however, there have only been a few studies of these type of environments on earth and as such these environments are still poorly understood, especially in the context of the sedimentary and geochemical environment. across the globe, numerous large paleolakes from the late pleistocene/early holocene boundary have gradually transitioned to modern-day saline/hypersaline basins. the sediments of these paleolake basins tend to have complex mineralogies that include a combination of sulfates, phyllosilicates, carbonates, chlorides, other salts, and ancillary minerals. these paleolake basins also tend to maintain groundwater systems that support a diversity of microorganisms though the microbial ecology, specifically the biogeochemical factors that drive community structure, has yet to be fully constrained in any of these environments. a prime example of this environment is the pilot valley basin in northwestern utah, usa and over the past 8 years, our team has studied the pilot valley paleolake basin as a mars analog environment. our research shows that the organics, brine constituents (e.g. sulfate, nitrate, and chlorine oxyanions), and minerals within the basin sediments provide the necessary components to fuel a diversity of redox reactions. further, the microbial ecosystem in pilot valley is organized into discrete community groups mostly influenced by grain size and other lithological factors. this lithological influence on community structure could impact how, where, and what type of biosignatures get preserved within these transitional subsurface environments. | the importance of transitional habitable zones in the new mars underground |
thin film solar cells based on hybrid organic-inorganic perovskites (hoips) have become highly attractive over the past several years due to a high solar to electric power conversion efficiencies (pces). perovskite materials based on methylammonium lead iodide (ch3nh3pbi3, mapbi3) possess high optical absorption coefficients, long minority carrier lifetimes and diffusion lengths, and desirable optical band gaps, and carrier collection in these materials can be highly efficient when they are paired with appropriate electron and hole transport materials (etms and htms), respectively. additionally, perovskite solar cells (pscs) can be fabricated via a variety of solution-based routes, which are suitable for low-cost, large area manufacturing. the combination of these attributes gives pscs an advantage over currently available commercial photovoltaic (pv) technologies. understanding the nucleation and growth mechanisms, and controlling the grain size and crystallinity in the solution-processed fabrication of perovskite thin films are important to prepare electronic-quality materials for pv applications. we investigated the nucleation and growth mechanisms of mapbi3 formed in a two-step solution process. to prepare the mapbi3 films, pbi2 films were spin-coated and then were reacted with methylammonium iodide (mai) in the isopropanol (ipa) solution at various concentrations. we showed that the conversion rate, grain size, and morphology of mapbi 3 perovskite films depend on the concentration of the mai solution. three distinct perovskite formation behaviors were observed at various mai concentrations, and a tentative model was proposed to explain the reaction mechanisms. the nucleation and growth process of mapbi3 can be significantly changed by adding divalent metal salts into the mai solution. we showed that the incorporation of cd2+ ions significantly improved the grain size, crystallinity, and photoexcited carrier lifetime of mapbi3. formation of (ch3nh3)2cdi4 (ma 2cdi4) perovskite in the solution by reacting the mai and cd2+ is the key for this nucleation and growth change. devices prepared using this approach showed a significant improvement in the pce relative to control devices prepared without cd2+ addition. the improved optoelectronic properties are attributed to a cd-modified film growth mechanism that invokes low dimensional cd-based perovskites. in addition to the cd2+, zn2+ and fe2+ also have the potential to change the nucleation and growth process of mapbi3 formation, to improve the material quality. formation of cd-based perovskites, once the cd2+ ions contacted with mai, successfully applied in the cadmium telluride (cdte) solar cell technology to form a te layer on the cdte surface, that would reduce the schottky barrier height and band bending at the back contact, reducing the recombination at the back junction, and thus improve the device efficiency. we found that cd can be selectively extracted from the cdte surface by reacting mai thin films with the cdte surface, forming ma2cdi4 perovskite. ma2cdi4 is soluble in ipa, therefore can be rinsed out, leaving a te layer behind on the cdte surface. mai treated cdte devices showed a reduction in the barrier height at the back contact for both au and transparent indium tin oxide (ito) electrodes as calculated from the temperature dependent j-v measurements, resulting higher photovoltaic parameters of open circuit voltage (voc), fill factor (ff), and pce relative to the control devices. in addition, only a 6% reduction in transmittance in the near infrared (nir) region occurred in the devices with an ito back electrode due to the mai treatment, indicating this can be potentially used for the fabrication of high performance transparent cdte solar cells that use in tandem solar cell or window applications. | solution-processed fabrication of hybrid organic-inorganic perovskites & back interface engineering of cadmium telluride solar cells |
enceladus is unique amongst ocean worlds in our solar system: the contents of its internal ocean are continuously emitted to space by its present-day activity, and some of these materials are redeposited on the surface. this tiny moon of saturn thus presents an opportunity to directly measure the composition of the ocean and seek evidence for habitability (including past or extant life), either by collecting and analyzing plume particles as previously proposed by discovery and new frontiers mission concepts, or via more ambitious mission concepts that involve landing, surface sampling and analysis, and potential deployment of subsurface probes to reach the ocean itself (hofgartner et al., this meeting). however, the low surface gravity (1% of earth's) and extreme cryogenic conditions in the south pole regions (~ 50 k, away from the tiger stripes) raises questions: how to best sample the upper ~ 1 cm of the surface around a lander, made of most freshly deposited plume materials? what are the expected properties of these materials, i.e. how fast does sintering proceed and how strong would these materials be as function of their exposure age? we provide answers to these questions via a two-pronged approach. first, we surveyed experimentally the time evolution of mechanical strength of large samples of ice spherules at several temperatures. a custom sample preparation system has been developed to synthesize ice spheres with a grain size distribution of mean ~ 12 microns. the samples are subsequently held at temperatures of -30, -50, and -80 c, over extended periods of time (up to 9 months at time of writing), and their strength is tested at frequent intervals using cone penetration tests. the data obtained to date suggests that the observed temperature dependence of the strength evolution is commensurate with expectations from vapor diffusion. second, we developed a new sampling system that enables rapid sampling and transfer of surface materials into receptacles. those receptacles can then deposit the sampled materials into the inlet of an instrument dedicated to analyzing the chemical composition of these materials and seek tracers of past or extant life. the geometry of the system and principles of operation have been established and validated by experimental tests, as well as dynamical simulations. | a new sampling system tailored to experimentally-derived mechanical properties of icy analogs for evolved enceladus surface plume deposits |
with a mean radius of 252 km, enceladus is the second smallest spherical moon of saturn but is the most active icy-moon of the solar system. during its 13 years of mission, cassini was able to image and sample its south pole plumes with great details and reveal the presence of 4 major faults, the tiger stripes, that continuously eject materials from the inner ocean located a few kilometers beneath the surface [1]. such activity was not reported at the north pole which is heavily cratered. in this study, we report the presence of 2 major stripes at the north pole, 3 times smaller than their counterpart at the south pole. they form a x-shape slightly offset by a few degrees from the planetographic north pole.this network of faults is 100 km long, up to 4 km wide, with an estimated shear of 3 km [2]. no active plume are reported, however, using very-high resolution cassini-vims observations (at 2 km/pixel), we clearly observe a local increase of the 1.04, 1.25, 1.5 and 2.0 μm band depths on the faults [3]. this signature is known to be associated with an increase of the grain size of the ice, analog to the one observed at the south pole [4-7]. the presence of a fresnel peak at 3.1 μm also indicates the presence of crystalline in this region [8]. finally, due to its lower signature, we might have a small signal of co2 at 4.26 μm [9]. these observations are consistent with a global ocean underneath enceladus ice shell [10] and provide additional constrains about its thickness at the north pole. references: [1] porco et al. (2006) [2] bland et al. (2018) [3] robidel et al. (2020) [4] jaumann et al. (2008) [5] newman et al . (2008) [6] taffin et al. (2012) [7] scipioni et al. (2017) [8] hansen and mccord (2004) [9] combe et al. (2019) [10] choblet et al. (2017) | faults network on enceladus north pole |
organic molecules are the building blocks of life and this is why the search for amino acids and their complex organic precursors at different stages of star and planet formation is one of the exciting topics in modern astronomy. understanding how, when and where organics (simple as well as complex including potentially prebiotic molecules) are formed is one of the most important questions for astrochemistry/astrobiology. complex organics have been detected in prestellar cores, protostars, and protoplanetary disks. can a part of the organic content observed in these regions be preserved during the protostellar stages and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? by looking at the cometary compositions, observations of solar-type protostars can help to address this critical question. in this context, here we will present our observations towards the solar-type protostar iras 16293-2422 in the 3mm band of the iram 30m telescope along with existing alma observations. we will also describe how the chemo-dynamical simulations using the state-of-the-art gas-grain-bulk chemical-kinetic model can help us to understand the chemical composition of comet 67p observed by rosetta. for the first time, we will also shed light on to the possibility of protostellar inheritance of glycine (king of the rosetta zoo) on to the comet 67p. | the chemical link between comet 67p/c-g and low mass protostar iras 16293-2422: integrative studies in observational astronomy and chemical-dynamical modeling |
enceladus is one of the most likely places to find evidence of extant or extinct extraterrestrial life. enceladus has a global, subsurface, liquid water ocean with evidence to support hydrothermal activity at the ocean-core interface. the plume of enceladus, likely originating from the subsurface ocean, allows the ocean to be characterized without the need for a landed mission and contains a plethora of organic molecules. the cda instrument utilized cassini's velocity to characterize molecules within plume ice grains via impact-induced ionization. however, impact-induced ionization under these conditions is not well understood, and it is unclear if this process can be "soft" enough to keep large organic molecules intact for subsequent mass spectral analysis. it is critical to understand these processes and how they affect organic molecule survivability for a return mission to enceladus to search for signs of life and to characterize the subsurface ocean composition via the plume. | hypervelocity sampling of the enceladus plume: implications for astrobiology investigations |
in recent years, there has been a growing interest in the robotic exploration of icy bodies that have shown particularly favorable conditions for the emergence of life, like enceladus and europa. one of the main challenges for the design and control of planetary robotic exploration systems is the lack of information about the surface mechanical behavior. to date, only remote sensing data is available, which only loosely constrains the properties of the surface. to better characterize the surface mechanical behavior and enable the simulation of robot-terrain interactions, a numerical model of the terrain is needed. in this work, we present a physics-based numerical mechanical model of icy surfaces that explicitly represents the microstructure and its evolution upon sintering. the model is based on the discrete element method with frictional and cohesive intergranular interactions. the model dimension and grain size is carefully tuned following a pareto-optimality analysis. the effect of grain and bond parameters is also examined in details with a sensitivity analysis. finally, calibration to laboratory analogs of planetary porous ice is performed following a proposed probabilistic method. the cohesion energy density and the friction coefficient were found to be descriptive parameters that established a link between the micro- and macro-mechanical properties of porous ice. the model also revealed good correspondence between the evolution of the bond strength and the overall sample strength, which suggests that the strengthening of ice in the sample resulted from the evolution of a large-scale network due to intergranular bonding. our results demonstrate that this methodology can provide a critical link between theoretical and experimental studies, and show the critical impact of sintering on the mechanical properties of ice plume deposits to design robust robotic systems. | modeling and simulation of planetary porous ice analogs |
defects in high performance multi-crystalline silicon wafers can be detrimental to the lifetime of the solar cell. it is, therefore, important to study and understand the underlying structure and chemical elements present at these defective areas in order to suppress them. the underlying cause of the d-band emission line " v e r y i n t e n s e d 3" (vid3) has not yet been understood, although many theories have been proposed. in this paper, we have investigated the underlying causes of the d-band emission peak vid3 by hyperspectral photoluminescence imaging, scanning electron microscopy, electron backscatter diffraction, scanning transmission electron microscopy, and density functional theory (dft) to understand the defect structure in areas of a vid3 emission peak in more detail. we found a high vid3 peak intensity at sub-grain and σ 3 twin boundaries bordering to grains with a small misorientation, which suggests higher stress in these regions. defects close to the twin boundary indicate a light element dopant in the area, such as oxygen. dft calculations show that oxygen is prone to segregate to this boundary. | investigation of veryintensed3-band emission in multi-crystalline silicon wafers using electron microscopy and hyperspectral photoluminescence imaging |
carbonized bamboo‑derived carbon nanodots (cnds) as efficient additives for application in perovskite solar cells (pscs) are reported. these carboxylic acid‑ and hydroxyl‑rich cnds interact with the perovskite through hydrogen bonds and, thereby, promote the carriers' lifetimes and realize high‑performance p–i–n pscs having the structure indium tin oxide/niox/ch3nh3pbi3 (mapbi3)/pc61bm/bcp/ag. as a result of interactions between the cnds and the perovskite, the presence of the nonvolatile cnd additive increases the power conversion efficiency (pce) of the psc from 14.48% ± 0.39% to 16.47% ± 0.26%. furthermore, adding urea, a lewis base, increases the pce to 20.2%—the result of a significant increase in the crystal size and a lower content of grain boundary defects and, therefore, longer carrier lifetimes. cells containing these two additives (without encapsulation) exhibit excellent shelf‑life and air‑stability, maintaining their high pces after storage in air—at a temperature of 25 °c and a humidity of 40%—for over 500 h. this performance is among of the best ever reported for p–i–n psc devices incorporating carbon‑based additives. | carbon nanodot additives realize high‑performance air‑stable p–i–n perovskite solar cells providing efficiencies of up to 20.2% |
the activity of most comets within 3au of the sun is dominated by the sublimation of frozen water, the most abundant ice in comets. some comets, however, are active well beyond the water-ice sublimation limit. studying distantly active comets provides valuable opportunities to explore primitive bodies when water-ice sublimation is largely dormant, which is the case for most of a comet's lifetime. beyond 4 au, super-volatiles such as co or co2 are thought to play a major role in driving observed activity. carbon monoxide is of special interest because it is a major contributor to comae and has a very low sublimation temperature. three bodies dominate the observational record and modeling efforts for distantly active small bodies: the long-period comet c/1995 o1 hale-bopp and the short-period comets (with centaur orbits) 29p/schwassmann wachmann 1 and 2060 chiron. hale-bopp's long-period orbit means it has experienced very little solar heating in its lifetime and is analogous to dynamically new comets making their first approach to the sun. because chiron and 29p have much smaller orbits closer to the sun, they have experienced much more thermal processing than hale-bopp and this is expected to have changed their chemical composition from their original state. we point out that the observed co production rates and line-widths in these three distantly active objects are consistent with each other when adjusted for heliocentric distance. this is particularly interesting for hale-bopp and 29p, which have approximately the same radius. the consistent co production rates may point to a similar co release mechanism in these objects. we also discuss how observed radio line profiles support that the development and sublimation of icy grains in the coma at about 5-6 au is probably a common feature in distantly active comets, and an important source of other volatiles within 6 au, including h2o, hcn, ch3oh, and h2co. | gaseous activity of distant comets |
with the discovery that many exoplanetary systems harbor several closely-spaced planets, questions relating to their stability have become relevant. we have integrated closely-spaced planetary systems, with the goal of quantifying their stability times over very long time scales (up to ten billion years). each of our systems started out with five identical, earth-mass planets orbiting a solar-mass star, with orbits being spaced as a geometric sequence, and initial eccentricities up to e = 0.05 given to either one, or all, planets. for all planets eccentric, we ran several sets of simulations: one where the initial periapses were aligned, and others with randomized (either over all azimuths or a restricted range) initial periapse angles. in all cases, the trend in system lifetimes follows a log-linear relationship between time to close encounter and initial separation (with differing slopes). on a more granular level, we find substantial differences in life times at resonances for low eccentricity systems, but those differences are reduced in magnitude for higher eccentricities and/or randomized periapses. for systems with just one planet eccentric, the time to close encounter depends on which planet starts out eccentric: an eccentric intermediate planet typically shortens the time to close encounter compared to the same value of eccentricity given to either the inner or outer planet. if all planets start out with the same eccentricity and aligned periapses, stability is restored — such systems are on average only slightly less stable than initially circular ones. angular momentum deficit does not appear to influence stability times, suggesting that mean motion resonances play the dominant role over secular resonances. survival probabilities are calculated for any given initial separation and given time for systems where all five planets start out with eccentricities 0.01 or 0.05, respectively, and randomized periapses. the resulting probabilities of survival at fixed given time, plotted as a function of initial separation, have significantly different behaviors depending on initial system eccentricity. | eccentricity and the lifetimes of closely-spaced five-planet systems |
small molecules such as methanimine (ch_{2}nh), methylamine (ch _{3}nh _{2}), hydroxylamine (nh _{2}oh) and methyl isocyanate (ch _{3}nco) belong to a select group of so-called prebiotic molecules that are thought to be at the basis of amino-acid and peptide-bond formation. on earth, amino-acids are important building blocks of life, which through peptide bonds link with each other to form proteins. recent alma observations have shown for the first time that ch _{2}nh and ch _{3}nco are present around the low-mass, sun-like, protostar iras 16293-2422, showing that prebiotic building blocks could already have been present at the earliest formational stages of our own solar system. [1][2] this work is conducted as part of the protostellar interferometric line survey, a broad band alma survey of the protostellar binary iras 16293-2422. the detections of ch _{2}nh and ch _{3}nco rotational transitions are presented and integrated emission maps show their presence at solar system scales ( 60 au) around the protostar. supporting solid-state laboratory data shows that ch _{3}nco has its origin in the ice mantles of interstellar dust grains. non-detections of nh _{2}oh and ch _{3}nh _{2} are used to constrain chemical pathways to interstellar amino-acid formation. specifically, the abundance comparison of ch3nh2 between this low-mass protostar and the galactic centre source sgr b2 shows that ch _{3}nh _{2} is depleted by at least 1-2 orders of magnitude in iras 16293-2422. this shows that around low-mass protostars ch _{2}nh might be a more relevant precursor to amino-acid formation than ch _{3}nh _{2}. [1] n.f.w. ligterink et al., month. not. roy. astron. soc. 469 (2017) 2219 [2] n.f.w. ligterink et al., astronomy & astrophysics, subm. (2018) | the inventory of prebiotic building blocks around a young, sun-like protostar |
water and complex organic molecules play an important role in the emergence of life. they have been detected in different types of astrophysical environments (protostars, prestellar cores, outflows, protoplanetary disks, comets, etc). in particular, they show high abundances towards the warm inner regions of protostars, where the icy grain mantles thermally desorb. can a part of the molecular content observed in these regions be preserved during the star formation process and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? by comparison with cometary studies, interferometric observations of solar-type protostars can help to address this important question. we present recent results obtained with the plateau de bure interferometer about water deuteration, glycolaldehyde and ethylene glycol towards the low-mass protostar ngc 1333 iras2a. | water and complex organic molecules in the warm inner regions of solar-type protostars |
mission preparation for lunar exploration using landers has been rapidly increasing, and strong demand should arise toward precise understanding of the electrostatic environment. the lunar surface, which has neither a dense atmosphere nor a global magnetic field, gets charged electrically by the collection of surrounding charged particles of the solar wind or the earth's magnetosphere. as a result of the charging processes, the surface regolith particles behave as "charged dust grains". dust particles have been suggested to have adverse effects on exploration instruments and living organisms during the lunar landing missions, and their safety evaluation is an issue to be solved for the realization of sustainable manned lunar explorations. it is necessary to develop comprehensive and organized understanding of lunar charging phenomena and the electrodynamic characteristics of charged dust particles.it is widely accepted that the surface potential of the lunar dayside is, "on average" several to 10 v positive due to photoelectron emission in addition to the solar wind plasma precipitation. recent studies, however, have shown that insulating and rugged surfaces of the moon tend to make positive and negative charges separated and irregularly distributed, and intense and structured electric fields can be formed around them. this strong electric field lies in the innermost part of the photoelectron sheath and may contribute to mobilizations of the charged dust particles. since this strong electric field develops on a spatial scale of less than the debye length and can take various states depending on the lunar surface geometry, it is necessary to update the research approach. in this paper, we will discuss the direction of the near-surface plasma, electrostatic, and dust environment for upcoming lunar landing missions. | lunar plasma and electrostatic environment: numerical approach and its future prospects |
the need for sustainable materials in engineering applications cannot be overemphasized. engineering innovation and material manufacturing and processing are now geared towards longevity and safety. aluminium is one of the few materials that meets the ever-increasing demand for lightweight and high strength materials for various industries, including; aircraft industries, marine, solar panels, automobile, construction companies and many other applications to mention but just a few. aluminium is known to possess excellent mechanical properties which makes them very useful and desirable. however, the final metallurgical and mechanical properties which characterise the final quality and strength of every weld depends on: (i) the technique employed in the welding of the component together and (ii) the selected process parameters for the welding operation. this work focuses on analysing the effect of heat input as a function of welding current, welding voltage and welding speed on the mechanical and microstructural behaviour of 150 × 100 × 3 mm3 aluminium sheets produced by metal inert gas welding. the parameters were set to represent the low, medium and high heat input values. it is imperative to determine the mechanical properties as a function of the structural integrity of welds to ascertain their functionality and durability for typical applications. tensile testing, vickers hardness and microstructural examination were performed. the result revealed finer grain structures at lower heat input and more grain deformation and elongation occurring as heat input increases. the hardness property reduces (from 43.57 hv to 39.48 hv in the fusion zone as heat input increases. the width of the weld bead increases (from 328 μm to 496 μm) as heat input increases. however, the selected welding parameters did not greatly influence the tensile properties of the welded joints. | mechanical and microstructural properties of mig welded aluminium alloy |
ongoing in situ investigation of the phyllosilicate trough "glen torridon" [gt] by the curiosity (msl) rover has allowed the correlation of orbitally defined units with sedimentologically defined members, and with bulk geochemical trends, as identified by the apxs instrument. the jura mbr (herein jura_gt), comprising mudstones (abundant pebbles, rare bedrock) and (less commonly) sandstones, roughly correlates with the smooth clay-bearing unit (scbu), identified from orbit. up elevation, the knockfarril hill mbr (kh), a mixture of sandstones and (less commonly) mudstone, roughly correlates with the fractured clay bearing unit (fcbu). a third unit, the fractured intermediate unit (fiu), (predominantly sandstone) lies between the clay-rich units and the overlying sulfate units, which represent a significant change in environmental conditions from the fluvio-lacustrine murray formation units. changing depositional environments within gt are indicated by the transition from mudstone-dominated (jura_gt) to sandstone-dominated (kh & fiu) lithologies. bulk chemistry is broadly similar for jura_gt and kh, suggesting a common source; the fiu shows a broad range for elements such as na, cl, so. locally, mg, k, zn, mn & br are amongst the highest identified in > 400 m of murray fm to date. k concentrations and associated elemental relationships (k is negatively correlated with mn, mg & zn, but positively with si & ni) are strongly correlated with grainsize (typically: fine grained - high k/low mg; coarse grained - low k/high mg). whilst the jura_gt is stratigraphically equivalent to, and likely syn-depositional with, the jura mbr on the vera rubin ridge (vrr), a change in bulk chemistry is identified from the ridge (vrr) to the trough (gt). gt targets trend (with some variations with respect to members) to lower si, al, na, ni, mn and higher ti, fe, mg, k, p, cr, zn, br. this geochemical change is also reflected mineralogically (in drill samples), from the hematite-rich (up to 15 wt. %), clay-poor vrr to the clay-rich (≥ 30% wt.), hematite-poor gt. the correlation of strong geochemical trends (k-mg-zn-mn) with grainsize in the gt targets are indicative of sorting processes; differences between the vrr and gt are attributed to later post-depositional alteration, related to the ridge and the greenheugh pediment. | alpha particle x-ray spectrometer (apxs) (msl) analysis of the glen torridon clay rich units, below the greenheugh pediment, gale crater, mars |
formation of stellar systems similar to our solar system begins from gravitational collapse of an interstellar cloud comprised of gas and dust. in the densest regions of such clouds the temperature drops to as low as 10 k, while the lifetime of the cloud is long enough to accrete most of the gas-phase material (with exception of he and h _{2}) onto dust grain surfaces [1]. the depletion of gas-phase species on a grain surface results in a rich chemistry triggered by atom- and radical-addition reactions between accreting species. hydrogenation of co molecules under such conditions results in the formation of organic molecules as complex as a three-carbon bearing sugar alcohol glycerol - a backbone glycerides - a necessary component for the formation of micelles and cell membranes in aqueous solutions [2]. however, this "bottom-up" approach meets increasing difficulties in production of long amphiphilic molecules such as fatty alcohols and fatty acids, another missing component in the formation of such glycerides. we present the results of a laboratory based research aiming to investigate formation of coms starting from carbon chains, at the earliest stages of star formation. we show that two simplest representatives of carbon chains, hcch and hccch _{3}, can efficiently participate in hydroxylation reactions resulting in formation of various alcohols and aldehydes upon reaction of oh radicals with unsaturated carbon-carbon bonds [3,4]. the proposed reaction mechanism holds much potential to form larger coms starting from various -(c≡c) _{n}- containing carbon chains observed in star-forming regions. such coms can either themselves participate in the formation of micelles in warm aqueous solutions, or form ether bonds with glycerol. thus, the presence of simplest lipid precursors on young planets may be plausable under the assumption that at least a fraction of the original icy-dust material survives upon transfer to an early planet surface. [1] p. caselli and c. ceccarelli, 2012, a&arv 20, p. 56 [2] g. fedoseev et al., 2017, apj 842, p. 52 [3] d. qasim et al., 2019, acs earth space chem 3, p. 986 [4] k.-j. chuang et al., 2020, a&a, 635, a199 | carbon chains reservoir as a source for solid-state formation of coms under cold dark cloud conditions |
the purpose of this work is to develop organic/inorganic hybrid solar cells based on electroplated cdte. the materials used in this research are cds, cdte and pani. these materials have been characterised by xrd, raman spectroscopy, edx, sem, afm, uv-vis spectroscopy, pec, c-v and dc measurements, ups and pl for their structural, compositional, morphological, optical, electrical and defect properties. cds has electrodeposited from the electrolyte using (nh[4])[2]s[2]o[3] as the sulphur source. the optimum growth voltage (v[g]) and temperature (t[g]) are obtained at 1455 mv and 85°c, respectively. the best annealing condition is found to be at 400°c for 20 minutes in the presence of cdcl[2]+cdf[2]. cdte thin films were electrodeposited from cdcl[2] precursor and a comprehensive study was carried out for the first time. the work has demonstrated a better understanding of material issues and some clues on the effect of cdcl[2] treatment. the optimum v[g] and annealing condition were obtained at 698 mv with respect to the calomel electrode and 420°c for 20 minutes in the presence of cdcl[2]+cdf[2] or cdcl[2]+cdf[2]+gacl[3]. the development of pani thin films has been established using anodic and cathodic deposition. the pernigraniline salt pani grown from anodic has an amorphous structure, large bandgap and cementing growth effect while leucoemeraldine salt pani grown from cathodic deposition shows the best crystallinity at v[g]=1654 mv with respect to carbon anode, smaller grain size, higher resistivity and lower bandgap. the cds, cdte and pani thin films have been studied in device structures, assessing their solar cell device performance. the best of cds/cdte solar cell was observed with efficiency of 5.8% when using cds thin film treated with cdcl[2]+cdf[2] at 400°c. the best solar cell from cdte study shows the efficiency of 6.8% when using cdte thin films treated with cdcl[2]+cdf[2] at 420°c. further study demonstrates that a device with g/fto/n-cds( 200 nm)/n-cdte( 1200 nm)/p-cdte( 300 nm)/au shows high j[sc] and highest efficiency (7.7%) due to the formation of n-n heterojunction, p-n homojuction and ohmic contact within the structure. the efficiency of the solar cell increased from -2.4% to -4.2% when incorporating -81 nm thick pani layer grown from anodic deposition. the devices incorporating zns, znte and cdse layers show the prospect of graded bandgap solar cell, but proper optimisation on each material should be carried out before using in multi-layer device structures. the study on the lifetime of solar cells show slow degradation and it maintained more than 83% of its initial efficiency after 9,000 hours. | organic/inorganic hybrid solar cells based on electroplated cdte |
titan, the largest moon of saturn, is the place in the solar system showing the most earth-like landscapes. titan"s dense atmosphere and cold temperatures enable a complex methane hydrological cycle that have shaped the surface, very similarly to the water cycle on earth. titan has another peculiar feature: a wealth of organic grains is created by photochemistry in its atmosphere and progressively deposited at its surface. such atmospheric production of organics likely occurred on earth before the apparition of life; that is the reason why a better understanding of the formation processes, chemical composition and physical properties of these grains is of great interest.the dragonfly mission has recently been selected by nasa to explore titan"s surface with a rotorcraft circa 2035 (lorenz et al., 2018). dragonfly will explore a region of organic sand dunes with monthly flights of a few kilometres each aiming to an impact crater named selk. in addition to chemical analyses, dragonfly is equipped with several sensors intended to characterize its environment. among them, as part of the dragonfly geophysical and meteorological (dragmet) package, the efield instrument will record the ac electric field at low frequencies (~5-100 hz).efield consists in two spherical electrodes accommodated at different locations on the rotorcraft. the main scientific objective of efield is to measure schumann resonances on titan. such resonances may have been detected by the huygens probe in 2005 (unless it was an artefact of probe motion; lorenz and le gall, 2020) and would be an indication of the existence of an underground global salty ocean (beghin et al., 2012). another scientific objective of efield is the detection and characterization of charged grains. this work is dedicated to this secondary objective.the exploration area of dragonfly is covered by sand grains, most likely organic in nature, maybe mixed with ice. surface winds can sometimes put them in saltation or suspension. in the process, these organic grains are likely to get charged by friction (triboelectric effect; méndez-harper et al., 2017), and would then induce a perturbation on the electric field detectable by the efield antennas. to estimate the significance of this perturbation and test the possibility to measure it, we have built a numerical model that simulates the trajectory of charged particles in the probe environment, subjected to turbulent wind flows, gravity and electrostatic forces. first results show that charged particles will induce a strong measurable signal on the efield spectra. we are thus currently investigating how these spectra can be used to derive information on the grains (number, charge, size or density). on titan, efield will work in synergy with wind sensors and a microscopic imager that will observe grains deposited at the surface.the next steps in our simulations will be to account for the perturbations induced by the nearby body of dragonfly. in parallel, we are building a prototype antenna to test it and check the ability of our model to reproduce its measurements in the laboratory and in the frame of field campaigns. | detection of charged organic grains at the surface of titan with the efield/dragmet sensor on board dragonfly |
what is the habitability of a salty subsurface environment in a hyperarid region, where the salts are mixtures of chlorides, chloride hydrates, and hydrous sulfates? we report a new concept developed on the basis of observations on mars, field investigations at dlt playa in qaidam basin on tibet plateau, and the laboratory studies of chlorides and sulfates. the water activities maintained in a closed environment by either chlorides or by hydrous sulfates have been studied separately in laboratory. it was found that hydrous sulfates can keep high water activities (i.e., high relative humidity rh levels) in a closed environment (e.g., subsurface salty layers), and also require high rh for their deliquescence in order to generate liquid brine to support the essential functions of life form. in contrast, the deliquescence of chlorides and chloride hydrates can happen at mid-low rh levels, but an environment filled with chlorides and chloride hydrates would not provide a suitable rh range to induce their own deliquescence even with a considerable temperature (t) change, because their capability of maintaining a water activity (i.e., a rh level) in an enclosure is not a strong dependent of temperature. the coexistence of chlorides and hydrous sulfates was found by the in situ measurements of all landed missions to mars (rovers and landers). this coexistence was also found in the subsurface of dlt playa on tibet plateau by a detailed mineralogy study (laser raman spectroscopy and xrd). in addition, microbial life at dlt was evidenced by four types of analyses. within dlt subsurface, the highly hydrated sulfates (mgso4.6-7h2o) would provide a suitable rh range (90-97%) for the deliquescence of co-existing chlorides (mgcl2.6h2o, kmgcl3.6h2o, nacl, rh need to be > 33, 65, 75%) to start, which will form thin films of liquid brine at the surface of salt grains. furthermore, we have found that the rates of deliquescence of chlorides are strong dependents of temperature. thus a higher t during day time at dlt would generate a thicker brine film at grain surface. these parameters, sunlight, warmer t, and more aqueous brine, would favor life, i.e., the halophiles found at dlt. this analog study shows that a salty subsurface (mixtures of chlorides, hydrated sulfates, and even perchlorates) in hyperarid region can have high habitability potentials. | high habitability potentials generated by subsurface salt mixtures at dlt playa on tibet plateau |
indoor photovoltaic devices have garnered profound research attention in recent years due to their prospects of powering 'smart' electronics for the internet of things (iot). here it is shown that all-inorganic cs-based halide perovskites are promising for indoor light harvesting due to their wide bandgap matched to the indoor light spectra. highly crystalline and compact cspbibr2 perovskite based photovoltaic devices have demonstrated a power conversion efficiency (pce) of 14.1% under indoor illumination of 1000 lx and 5.9% under 1 sun. this study revealed that a reduction in grain misorientation, as well as suppression of defects in the form of metallic pb in the perovskite film are crucial for maximising the photovoltaic properties of cspbibr2 based devices. it was demonstrated that a pinhole free cspbibr2/spiro-ometad interface preserves the perovskite α phase and enhances the air stability of the cspbibr2 devices. these devices, despite being unencapsulated, retained > 55% of the maximum pce even when stored under 30% relative humidity for a shelf-life duration of 40 days and is one of the best stability data reported so far for cspbibr2 devices. | crystalline grain engineered cspbibr2 films for indoor photovoltaics |
future exploration of ocean world interiors, believed to harbor conditions conducive to life, will require penetrating an ice shell up to 10s of km thick while maintaining robust communication with a surface lander. micro-tethers offer unparalleled data transfer rates (for minimal size, mass & power) and sufficient length (20+ km), but are not rated for survivability under the thermo-mechanical conditions expected at europa. the europa signals through the ice (sti) project aims to characterize the viability of employing various tethers by measuring their strength/performance & deployment mechanism in a laboratory setting that simulates shearing and fault conditions at europa. for this work (fig. 1), double-jointed blocks of polycrystalline ice with controlled grain size, porosity, and impurity content are fabricated in a three-compartment mold. tethers currently employed for polar submersible exploration are embedded in the ice and retained in tension. a custom tether tensile tester (t3) apparatus is used to calibrate optical working strength & ultimate tensile strength. a servo-hydraulic biaxial cryogenic deformation apparatus is used to shear the tethers across two sliding ice "faults", at an applied shear stress, velocity, temperature & ice composition. normal stress of 100 kpa is maintained, with a vertical piston driven at a constant shear rate until optical and/or mechanical failure. we consider end-member scenarios for shear rates on strike-slip faults, between creeping (10-7 m/s) and icequakes (10-3 m/s), and characterize communication performance with an optical backscatter reflectometer for fiber optics (optical power loss & strain), and a milliohm meter for copper tether (resistance for conductors). failure mode is identified by microscopic characterization. preliminary results of t3 calibration & double shearing tests for tethers in europa-like ice and environmental conditions will be discussed. results will be used to map out viable stress regimes for communication using tethers, along with identifying effects of pre-tension on tensile strength & communication performance. europa sti will enable development of tethered communication techniques to operate in harsh conditions, with implications for subsurface exploration of ocean worlds and the search for extraterrestrial life. | how (not) to lose communication with your submersible on europa: an experimental study for characterizing the shear performance of tethers under confinement in ice |
we have developed and implemented a log maximum likelihood approach to retrieve surface thermal inertia (ti) values using a combination of mars global surveyor tes, odyssey themis, and mars reconnaissance orbiter crism long wavelength data. tes (3 km/pixel) and themis (100 m/pixel) data stabilize the retrieval results, and crism data are included to extend retrievals down to 18 m/pixel. this approach inverts the krc numerical thermal model simultaneously for multiple overlapping observations to estimate ti values from observed surface temperatures and lambert albedos. initial application of the approach to gale crater, including the plains to the north of mount sharp, and the northern slopes traversed by the curiosity rover, shows ti values at 18 m/pixel that are similar in magnitude to those retrieved from 100 m/pixel themis data alone. the high spatial resolution retrievals provide fine spatial details not observed before, including delineation of relatively small wind-blown sand deposits within glen torridon that correspond in crism data to a spectral dominance of high-calcium pyroxene and olivine, and in hirise-based elevation data to local low regions. the combination of ti values for grains size, crism single-scattering albedo for mineralogy, and curiosity's observations is used in nonlinear retrievals of compositional and textural information for the various deposits, both for scientific and rover mobility purposes. | high spatial resolution thermal inertia mapping of mount sharp and northern plains, gale crater, mars |
icy grain mantles are the main reservoir for volatile elements in star-forming regions across the universe, as well as the formation site of pre-biotic complex organic molecules (coms) seen in our solar system. through the iceage early release science program, we will trace the evolution of pristine and complex ice chemistry in a representative low-mass star-forming region through observations of a: pre-stellar core, class 0 protostar, class i protostar, and protoplanetary disk. comparing high spectral resolution (r~1500-3000) and sensitivity (s/n~100-300) observations from 3 to 15 micron to template spectra, we will map the spatial distribution of ices down to ~20-50 au in these targets to identify when, and at what visual extinction, the formation of each ice species begins. such high-resolution spectra will allow us to search for new coms, as well as distinguish between different ice morphologies, thermal histories, and mixing environments.the analysis of these data will result in science products beneficial to cycle 2 proposers. a newly updated public laboratory ice database will provide feature identifications for all of the expected ices, while a chemical model fit to the observed ice abundances will be released publically as a grid, with varied metallicity and uv fields to simulate other environments. we will create improved algorithms to extract nircam wfss spectra in crowded fields with extended sources as well as optimize the defringing of miri lrs spectra in order to recover broad spectral features. we anticipate that these resources will be particularly useful for astrochemistry and spectroscopy of fainter, extended targets like star forming regions of the smc/lmc or more distant galaxies. | the iceage ers program: probing building blocks of life during the jwst era |
sand dunes on the floor of gale crater have been investigated by the curiosity rover, but the source of the sand is still unknown. we test the hypothesis that the sand could be sourced from the 5 km tall sedimentary central mound, mt. sharp, by investigating whether dark toned sand is eroding out of mt. sharp. we map out the location of the sand on mt. sharp using visible images (themis-vis, ctx, hirise). in this study, we assume that the dark toned patches that are blue in themis-vis and hirise color contain sand-sized particles. we test whether sand on mt. sharp is constrained to a particular layer or if the sand is distributed across the entire central mound. we also determine the sand's mineralogy using near-infrared spectra (crism). if the sand's mineralogy changes downslope in a predictable way (e.g.grain size sorting), this would support the hypothesis that the sand originated from mt. sharp and is moving downslope to be a source for the dunes on the crater floor. our map of the distribution of sand on mt. sharp reveals that dark toned sand is pervasive throughout the lower mound. in addition, there are many occurrences in hirise images where dark toned sand appears to be eroding from a specific layer within mt. sharp and being transported downslope. we did not observe any dark toned sand patches on the upper mound. the sand dunes on the crater floor vary from olivine-rich to cpx-rich. preliminary results from this study suggest that the sand on mt. sharp is a mixture of olivine and cpx. this is consistent with the sand dunes on the crater floor being sourced from sand that is eroding out of mt. sharp, and future work will determine whether the sand's mineralogy changes downslope. the presence of sand in the lower mound, and its absence in the upper mound, has implications for mt. sharp's formation mechanism(s). coarse grained material eroding out of layers in lower mt. sharp is consistent with curiosity results that show sand-sized materials are present in the section of the lower mound the rover has traversed. the absence of sand on the upper mound supports the hypothesis that it consists primarily of grains finer than sand. | mt. sharp as a source of the sand within gale crater |
using the recently developed ultra compact imaging spectrometer (ucis) (0.4-2.5 μm) to generate outcrop-scale infrared images and compositional maps, a mars-relevant field site near china ranch in the mojave desert has been surveyed and sampled to analyze the synergies between instruments in the mars 2020 rover instrument suite. the site is broadly comprised of large lacustrine gypsum beds with fine-grained gypsiferous mudstones and interbedded volcanic ashes deposited in the pleistocene, with a carbonate unit atop the outcrop. alteration products such as clays and iron oxides are pervasive throughout the sequence. mineralogical mapping of the outcrop was performed using ucis. as the 2020 rover will have an onboard multispectral camera and ir point spectrometer, mastcam-z and supercam, this process of spectral analysis leading to the selection of sites for more detailed investigation is similar to the process by which samples will be selected for increased scrutiny during the 2020 mission. the infrared image is resampled (spatially and spectrally) to the resolutions of mastcam-z and supercam to simulate data from the mars 2020 rover. hand samples were gathered in the field (guided by the prior infrared compositional mapping), capturing samples of spectral and mineralogical variance in the scene. after collection, a limited number of specimens were chosen for more detailed analysis. the hand samples are currently being analyzed using jpl prototypes of the mars 2020 arm-mounted contact instruments, specifically pixl (planetary instrument for x-ray lithochemistry) and sherloc (scanning habitable environments with raman & luminescence). the geologic story as told by the mars 2020 instrument data will be analyzed and compared to the full suite of data collected by hyperspectral imaging and terrestrial techniques (e.g. xrd) applied to the collected hand samples. this work will shed light on the potential uses and synergies of the mars 2020 instrument suite, especially with regards to spectral (i.e. remote) recognition of important and interesting samples on which to do contact science. | outcrop-scale hyperspectral studies of a lacustrine-volcanic mars analog: examination with a mars 2020-like instrument suite |
polar faculae are the unipolar footpoints of field lines near the sun's poles and are visible as bright points on the edges of granules. their number has been shown to correlate with the strength of the polar magnetic field, and therefore better understanding polar faculae enables better understanding of the polar magnetic field and its evolution, as well as conditions and convective motions at the poles. we present two methods of tracking faculae. in one the standard deviation of hmi continuum intensity images is calculated over a day and the facular candidates identified by their trails. the other overlays images of the progressive standard deviation over the course of the day with individual hmi magnetograms to show the close relationship between the facular candidates and the magnetic field. we apply this method to one pole each day for a week every 6 months, beginning september 2010. our results confirm that faculae track regions of unipolar magnetic field that match the polarity of the visible pole. we observe the motion of the faculae and distinguish between motion due to the sun's rotation and "proper motion" due to faculae moving on the sun's surface, confirming that faculae participate in convective motions at the poles. this method provides a larger daily count of faculae than previous studies, allowing for a valid statistical determination of the facular lifetime. we show that the lifetime has a mode of 1-3 hours, with some faculae lasting up to 10 hours. | two new methods for counting and tracking the evolution of polar faculae |
inhomogeneous microscopic carrier transport is difficult to study, but important in many condensed-matter applications. for example, the role of grain boundaries (gbs) in polycrystalline semiconductors has been controversial for 20 years. in cadmium telluride (cdte) solar cells, electron-beam-induced current (ebic) measurements consistently demonstrate enhanced current collection along gbs, which is argued as evidence for interpenetrating cdte p-n current-collection networks critical to high efficiency. conversely, cathodoluminescence (cl) measurements consistently indicate that gbs are deleterious low-lifetime regions. here, we apply transport imaging (ti) in conjunction with spatially correlated ebic, cl, and scanning kelvin probe force microscopy measurements to understand carrier drift, diffusion, and recombination in polycrystalline cdte. we simultaneously observe gb potential wells, reduced carrier lifetime at gbs, and seemingly contradictory enhanced gb current collection, and then describe their coexistence with microscopic ti and physical arguments. the results provide visualization of inhomogeneous transport that is critical to understanding and engineering polycrystalline solar technology. | direct microscopy imaging of nonuniform carrier transport in polycrystalline cadmium telluride |
dye-sensitized solar cell (dssc) using pt-standard cathode possesses a major drawback that its price is high. this work deals with the preparation of palladium (pd) cathode via a simple technique that is liquid phase deposition (lpd) technique for dssc. the influence of pd content in term of the concentration of potassium hexachloropalladate (k2pdcl6) on the properties and the performance of the device has been investigated. the xrd analysis reveals that the dominant phase of pd exists in the sample. the uv-vis transmission signifies that the transmittance of the sample is significantly influenced by the concentration of k2pdcl6. according to the fesem observation, the grain size of pd increases with the concentration of k2pdcl6. the device fabricated using pd cathode prepared at 1.00 mm k2pdcl6 yielded the highest efficiency (η) of 4.12%, while that of the device with pt cathode was 5.04%. this is due to this device owns the lowest series resistance (rs), highest recombination resistance (rcr) and longest carrier lifetime (τ). in conclusions, the efficiency of the device is found to be significantly affected by pd content. pd cathode is able to substitute pt as cathode for the device since the efficiency for both devices is comparable. | palladium films as cathode in dye-sensitized solar cell: influence of the concentration of potassium hexachloropalladate |
saturn's icy moon enceladus is with its roughly 500 km diameter a differentiated geological active body that harbours a liquid ocean between its rocky core and icy mantle. this ocean is among the most promising places to host extraterrestrial life in our solar system.at enceladus' south pole terrain, active geysers form a passage from the ocean to the surface; erupting ice, dust and gas particles. most of those particles escape the moon's gravity, but some portion falls back to the surface. considering the current output, about 10 m of snow gets sedimented at a distance of about 100 m away from the geyseres within 105-106 years. hence, depending on the timescale the geysers are active at the same location, the snow layer would have a thickness of some km already, assuming no densification.a first model of the density profile of the snow layer as a function of the ice/vacuum ratio will be provided at the conference. to investigate the density at the surface, mainly the distribution of the ice grain shapes and the grain sizes have to be considered and put into a state equation. for modelling the density change in respect to the depth, also the pressure from the overlying weight has to be accounted for. as temperatures at enceladus' surface are too low, neither sintering nor processes such as melting and re-freezing can thereby contribute to densification. these processes however are acting in terrestrial glaciers. we propose therefore, because the temperatures on enceladus are far below the melting point of ice, to consider the ice grains on enceladus rather as sand than as snow in respect to these materials on earth, when modelling the density within the snow layer.after obtaining the ratio between ice and vacuum, it is possible to define the dielectric properties of the snow layer. the dielectric profile in turn is the primary diagnostic property for radar based geophysical investigation. it determines the velocity of radio waves in a medium as well as their reflection and refraction at interfaces. because of the above mentioned possibility that primitive extraterrestrial life might exist in enceladus' hidden ocean, there will likely be future space missions with the aim to reach a water reservoir and probe it. a well-defined density profile could then help to radar navigate a melting probe through the ice. | modelling the dielectric properties of the geyser deposited snow layer on enceladus |
cdte solar cells have reached efficiencies comparable to multicrystalline silicon and produce electricity at costs competitive with traditional energy sources. recent efficiency gains have come partly from shifting from the traditional cds window layer to new materials such as cdse and mgzno, yet substantial headroom still exists to improve performance. thin film technologies including cu(in,ga)se2, perovskites, cu2znsn(s,se)4, and cdte inherently have many grain boundaries that can form recombination centers and impede carrier transport; however, grain boundary engineering has been difficult and not practical. in this work, it is demonstrated that wide columnar grains reaching through the entire cdte layer can be achieved by aggressive postdeposition cdte recrystallization. this reduces the grain structure constraints imposed by nucleation on nanocrystalline window layers and enables diverse window layers to be selected for other properties critical for electro‑optical applications. computational simulations indicate that increasing grain size from 1 to 7 µm can be equivalent to decreasing grain‑boundary recombination velocity by three orders of magnitude. here, large high‑quality grains enable cdte lifetimes exceeding 50 ns. | obtaining large columnar cdte grains and long lifetime on nanocrystalline cdse, mgzno, or cds layers |
analyses of the vector magnetic field on solar magnetic structures led to the jurčák criterion, an empirical law that connects a critical value of the vertical component of the magnetic field to the umbral magnetoconvective mode in stable sunspots. we study the evolution of the vertical component of the magnetic field (bver) on evolving pores and the existence of an equivalent critical vertical magnetic value to provide steadiness. indeed, we find that areas with weak bver are unstable and granulation takes over them. however, areas with strong bver show longer lifetimes. | solar pores - a magnetic evolution laboratory |
recent single crystal paleointensity (scp) data from apollo samples reveal null magnetic fields for the moon between 3.9 and 3.2 ga (tarduno et al., 2021). the absence of a long-lived lunar magnetic field resolves the multiple paradoxes associated with prior (cisowski et al., 1983) and continuing (evans and tikoo, 2021) interpretations of a core dynamo. these paradoxes include the lack of pervasive large-scale lunar magnetic anomalies, and the lack of sufficient core energy to sustain a dynamo needed to explain nominal high magnetic field measurements from prior studies of bulk apollo samples, if such data actually recorded a global lunar magnetic field. measurements of young lunar glass indicate that the strong nominal field reported in prior studies might instead record impact-induced magnetizations associated with charge separation (tarduno et al., 2021). here we report new scp and whole rock paleointensity data from ~3.75 billion-year-old high-ti mare basalt samples 70035 and 75035. bulk rock mare basalts are known to contain large non-ideal magnetic minerals (multidomain state, md). in contrast, our new sem analyses show that the single crystals analyzed (feldspars) contain minute magnetic minerals in the size range of ideal magnetic recorders (single domain). moreover, we find that the single crystals record null remanent fields, whereas the bulk rocks nominally record anomalously high (>100 μt) fields. we attribute the latter to mark the preference of md grains to preserve impact-induced magnetizations, whereas the sd-bearing single silicates document the true absence of a long-lived magnetic field of the moon. as the moon was not shielded by a magnetosphere for most of its history, solar winds are expected to have implanted helium, hydrogen, and other volatile resources into the regolith. lunar soils buried and sealed by later lava flows (fagents et al., 2010) should be considered prime scientific targets for future missions. the isotopic signatures of buried soils can preserve records of the composition of ancient solar winds and earth's atmosphere that are essential for understanding the terrestrial environment during the earliest development of life on the planet. | absence of a long-lived lunar dynamo: opportunities to learn about the early earth and solar wind during future exploration |
the exposures of interbeds of mostly fine gravels observed en route to pahrump valley in gale crate appear to provide no direct indication of channel scale or slope, but they for the first time on mars reveal the bedload grain size distribution. this is in contrast to remote sensing analysis of martian channel landforms where width and slope can be estimated and possibly flow depth inferred, but grain size of the channel bed is unknown. strong terrestrial correlations of discharge and channel width (once corrected for reduced velocity due to lower gravity) likely gives the best estimates of channel flows from remote sensing observations. calculations based on roughness arguments or estimated grain size and critical shear stresses have much larger error. what can be done, however, if we only know the grain size- the case for the gravel exposures in gale? we show that crude positive correlations of channel slope with median grain size, can then be used to estimate channel depth and width, each of which vary inversely with channel slope. these empiricisms suggest that the fluvial conglomerates in gale with grain sizes 4.5 to 9.5 mm may have had been deposited by a channel of a slope between 0.01 and 0.0001, about 0.62 to 2.1 m deep, and 10 to 50 m wide. using the median bankfull stream velocity from terrestrial studies of 0.9 m/s (corrected for martian gravity) the predicted discharge is about 5.6 to 94.5 m3/s. the estimated widths alone predict 6 to 85.6 m3/s for the 10 to 50 m channels widths, respectively. this analysis suggests that the gravel bedded rivers that delivered the sand and finer size delta building sediment towards the base of the present mt. sharp were of modest scale and slope, placing constraints on the eventual stratigraphic reconstruction of the deposits here. | what gravel size may tell us about the rivers draining from the north wall of gale crater |
context. the frequencies, lifetimes, and eigenfunctions of solar acoustic waves are affected by turbulent convection, which is random in space and in time. since the correlation time of solar granulation and the periods of acoustic waves (∼5 min) are similar, the medium in which the waves propagate cannot a priori be assumed to be time independent.aims: we compare various effective-medium solutions with numerical solutions in order to identify the approximations that can be used in helioseismology. for the sake of simplicity, the medium is one dimensional.methods: we consider the keller approximation, the second-order born approximation, and spatial homogenization to obtain theoretical values for the effective wave speed and attenuation (averaged over the realizations of the medium). numerically, we computed the first and second statistical moments of the wave field over many thousands of realizations of the medium (finite-amplitude sound-speed perturbations are limited to a 30 mm band and have a zero mean).results: the effective wave speed is reduced for both the theories and the simulations. the attenuation of the coherent wave field and the wave speed are best described by the keller theory. the numerical simulations reveal the presence of coda waves, trailing the ballistic wave packet. these late arrival waves are due to multiple scattering and are easily seen in the second moment of the wave field.conclusions: we find that the effective wave speed can be calculated, numerically and theoretically, using a single snapshot of the random medium (frozen medium); however, the attenuation is underestimated in the frozen medium compared to the time-dependent medium. multiple scattering cannot be ignored when modeling acoustic wave propagation through solar granulation. movies associated to figs. 3 and 9 are available at https://www.aanda.org | acoustic wave propagation through solar granulation: validity of effective-medium theories, coda waves |
with the discovery that many exoplanetary systems harbor several closely-spaced planets, questions relating to their stability have become relevant. we have integrated closely-spaced planetary systems, with the goal of quantifying their stability times over very long time scales (up to ten billion years). each of our systems started out with five identical, earth-mass planets orbiting a solar-mass star, with orbits being spaced as a geometric sequence, and initial eccentricities up to e = 0.05 given to either one, or all, planets. for all planets eccentric, we ran several sets of simulations: one where the initial periapses were aligned, and others with randomized (either over all azimuths or a restricted range) initial periapse angles. in all cases, the trend in system lifetimes follows a log-linear relationship between time to close encounter and initial separation (with differing slopes). we confirmed this relationship up to initial orbit separations of approximately 10 hill radii for small eccentricity (e=0.01), and up approximately 13 hill radii for the largest considered eccentricity (e=0.05). to on a more granular level, we find substantial differences in life times at resonances for low eccentricity systems, but those differences are reduced in magnitude for higher eccentricities and/or randomized periapses. for systems with just one planet eccentric, the time to close encounter depends on which planet starts out eccentric: an eccentric intermediate planet typically shortens the time to close encounter compared to the same value of eccentricity given to either the inner or outer planet. if all planets start out with the same eccentricity and aligned periapses, stability is restored — such systems are on average only slightly less stable than initially circular ones. angular momentum deficit does not appear to influence stability times, suggesting that mean motion resonances play the dominant role over secular resonances. this was checked by comparing systems with identical total angular momentum deficit for the same initial separations. we chose to compare systems with innermost planet eccentric with their corresponding systems with outermost planet eccentric (i.e., identical amd, implying smaller initial eccentricity). survival times were consistent with merely initial separation and eccentricity playing the dominant roles: amd does not appear to influence the behavior of those systems. finally, survival probabilities are calculated for any given initial separation and given time for systems where all five planets start out with eccentricity 0.05 and randomized periapses. here we considered batches with periapses randomly chosen within 45, 90, 135, 180, and 360 degrees, respectively. a broader choice of periapse angles is inversely correlated with the appearance of clear peaks and troughs in survival times. for periapse angles chosen within the full circle, we plot probabilities of survival at some fixed given times, as a function of initial separation. we show that their trends exhibit significantly different behaviors depending on initial system eccentricity. | eccentricity and the lifetimes of closely-spaced five-planet systems |
recent results from the curiosity mars rover have identified enrichments of manganese in rock targets throughout gale crater. some of these are inferred to be mn-oxide minerals. high concentrations of mn on earth are typically found as secondary mineral deposits, requiring abundant liquid water and highly oxidizing conditions to form. the earliest terrestrial manganese deposits are associated with the rise of free oxygen in the atmosphere 2.5 gya. thus the discovery of mn-oxides on mars raises the possibility that the martian atmosphere once contained more oxygen. here we assess mn abundance in all rocks analyzed by chemcam along the rover's traverse over sols 778-1384. during this time 477 rocks were analyzed with a total of 3296 sampling locations. of these, 125 ( 4%) on 61 rocks (12%) were found to contain abundances of mn 2-sigma over the mean, corresponding to 1.3 wt% mno. this is similar to results for rock targets from the first 777 sols of the traverse. relationships between mn and major and minor elements were also assessed for all rock targets. higher mn is associated with lower si and higher fe, na, al, and li. elevated mn was found in a range of rock types, including conglomerates, fine-grained sandstones, and veins. libs data were examined for potential shot-to-shot trends to determine whether mn is associated with surface features such as coatings or layers; no strong trends were identified. remote micro-imager (rmi) images of rock targets were analyzed for texture, grain size, and albedo. no specific rock features were correlated with mn abundance. of sampling locations with mn abundances above 2-sigma, over 50% were in the stimson formation, the youngest geologic unit identified in gale to date. our results suggest that mn in this region may have be concentrated prior to incorporation into sediments, and the observed compositional and spatial variations may be the result of differing source regions. work is ongoing to better understand the nature of mn in the stimson. | chemcam observations of manganese in rock targets (sols 778-1384): an indicator of redox and habitability conditions |
perovskite have recently become a topic of intense interest in the field of material science due to their promising applications as light harvesting materials in solar cell devices. the champion perovskite at this time is ch3nh3pbi3 (mapbi3), however there is a major concern with the toxicity of the lead atom. using first principles density functional theory (dft) calculations, we examine the electronic properties of point defects and grain boundaries (gbs) in two tin-based perovskite alternatives, masni3 and cssni3. we find evidence that defects and gbs in both hybrid and inorganic perovskites are beneficial to electronic performance due to intrinsic p-doping without the generation of deep states. we also show that masni3 is intrinsically less stable than cssni3 according to chemical potential diagram and formation energy comparisons. we also provide evidence to support experimental observations of charge collection and separation at the gb due to band bending at the interface. furthermore, we find wider bandgaps at the gb, pointing to a synergistic effect between charge collection and increased charge carrier lifetime at the interface. | the role of defects and grain boundaries in the electronic structures of hybrid and inorganic tin iodide perovskites: a dft study |
accurate gas-phase abundances of ions in the interstellar medium may be obtained through the analysis of interstellar absorption lines, but only if the oscillator strengths (f-values) of the relevant transitions are well known. for dominant ions, comparison of the gas-phase abundance with the appropriate solar reference abundance yields the degree to which the element is incorporated into interstellar dust grains. singly-ionized lead is the dominant form of this element in the neutral interstellar medium. however, while pb ii has several strong resonance lines in the ultraviolet, the f-values for these transitions are uncertain. here, we present the first experimentally determined oscillator strengths for the pb ii transitions at 1203.6 å and 1433.9 å, obtained from lifetime measurements made using beam-foil techniques. we also present new detections of these lines in the interstellar medium from an analysis of archival spectra acquired by the space telescope imaging spectrograph onboard the hubble space telescope. notably, our observations of the pb ii λ1203 line represent the first detection of this transition in interstellar gas. our experimental f-values for the pb ii λ1203 and λ1433 transitions are consistent with recent theoretical results, including our own relativistic calculations, but are significantly smaller than previous values based on older calculations. for the pb ii λ1433 line, in particular, our new f-value yields an increase in the interstellar abundance of pb of 0.43 dex over estimates based on the f-value listed by morton. with our revised f-values, and with our new detections of pb ii λ1203 and λ1433, we find that the depletion of pb onto interstellar grains is not nearly as severe as previously thought, and is very similar to the depletions seen for elements such as zn and sn, which have similar condensation temperatures. | the interstellar abundance of lead: experimental oscillator strengths for pb ii λ1203 and λ1433 and new detections of pb ii in the interstellar medium |
the discoveries of the apollo era arouse the interest of scientific community to research the lunar environment and the development of future missions to gather scientific data to corroborate recent theories. particularly in lunar horizon glow, forward scattering of the sunlight by the electrically charged dust grains above the terminator region requires to be investigated further. for this reason, the data gathered by a lunar mission is valuable to improve our understanding regarding lunar environment. nowadays, low-cost satellite platforms facilitated the access to space for university institutes and research centers worldwide. in this paper, we propose an attitude determination and control system (adcs) for a 2u cubesat to be inserted into lunar orbit as a piggyback from a main mission. due to the high interest to observe the light scattering by lofted dust particles in the lunar exosphere during lunar sunrise and sunset, a guidance and navigation scheme is also proposed. through numerical simulations, we demonstrate the adcs performance by the use of pulsed plasma thrusters (ppt) during pointing maneuvers towards lunar horizon glow. the proposed position of ppt along the satellite body contributes the orbit maintenance and the desaturation of reaction wheels. because the maneuvers are dependent on the sun position, a feasibility analysis were performed in orbits with different local sidereal time. based on these results, the proposed adcs is found suitable for 2u cubesats to perform its maneuvers towards the accomplishment of its objectives. additionally, we demonstrate that the increase of its mission lifetime by maintaining its orbit from ppt thrust is possible. | pulsed plasma thrusters based attitude control for a 2u cubesat mission towards the observation of the lunar horizon glow |
cathodoluminescence (cl) measurements can be applied to assess grain-boundary (gb) and grain-interior (gi) recombination in thin-film solar cell materials and made quantitative if we can develop cl models that account for material and measurement complexities. recently, we developed a three-dimensional numerical cl model, based in matlab, that simulates the gi cl intensity as a function of four parameters: grain size, gi lifetime, and gb and surface recombination velocities. the model assumes that gb electrostatic potentials are screened by the high excesscarrier densities used in the cl measurement such that transport is governed by ambipolar diffusion. here, we develop models to address directly gb potentials and their effects on these measurements. first, we transfer the matlab-based model to comsol software, and then introduce shallow donors to the gbs to produce potentials. we also develop a two-dimensional model in comsol to simulate cl gb contrast with gb potentials. simulations indicate that gb potentials can increase or decrease cl intensities relative to the zero-potential case. however, the high electron-beam currents typically applied in cl measurements minimize the impact of gb potentials. | numerical simulations of cathodoluminescence measurements in thin-film solar cells |
jupiter's moon europa is embedded deep within the jovian magnetosphere and is thus exposed to bombardment by charged particles, from thermal plasma to more energetic particles at radiation belt energies. in particular, energetic charged particles are capable of affecting the uppermost layer of surface material on europa, in some cases down to depths of several meters (johnson et al., 2004; paranicas et al., 2009, 2002). examples of radiation-induced surface alteration include sputtering, radiolysis and grain sintering; processes that are capable of significantly altering the physical properties of surface material. radiolysis of surface ices containing sulfur-bearing contaminants from io has been invoked as a possible explanation for hydrated sulfuric acid detected on europa's surface (carlson et al., 2002, 1999) and radiolytic production of oxidants represents a potential source of energy for life that could reside within europa's sub-surface ocean (chyba, 2000; hand et al., 2007; johnson et al., 2003; vance et al., 2016). accurate knowledge of europa's surface radiation environment is essential to the interpretation of space and earth-based observations of europa's surface and exosphere. furthermore, future landed missions may seek to sample endogenic material emplaced on europa's surface to investigate its chemical composition and to search for biosignatures contained within. such material would likely be sampled from the shallow sub-surface, and thus, it becomes crucial to know to which degree this material is expected to have been radiation processed.here we will present modeling results of energetic electron and proton bombardment of europa's surface, including interactions between these particles and surface material. in addition, we will present predictions for biosignature destruction at different geographical locations and burial depths and discuss the implications of these results for surface sampling by future missions to europa's surface. | europa's surface radiation environment and considerations for in-situ sampling and biosignature detection |
introduction: the plumes of enceladus offer an opportunity to access a sample of water from its internal ocean. however, to gain valuable insights into the ocean's composition, it is necessary to take into account any possible process that would alter the mixture between the water table and the geysers. the adsorption of refractory compounds on the ice walls in the vents could partition them depending on their properties. evaluating the effect of this fractionation is critical in anticipating which organics could be detected by a future mission. models: we used a model using the temkin isotherm and published experimental desorption energies for our compounds of interest. the model calculates how the coverage of an ice surface exposed to the flow can evolve with time and what is the final composition of the adsorbed mixture is. the model considers the ice walls and the ice grains, as the latter have the potential to gather the most sticky compounds and put them within reach of sampling by a spacecraft. our list of species included formaldehyde, methanol, acetic acid, formic acid, ethanol, butanol, benzene and hexanal.results: we found that simple hydrocarbons have a very short residence time on ice, and are expected to stay in gas phase. oxygen-bearing organic compounds, though, stick to the ice and will be concentrated on the walls and ice grains, with the exception of formaldehyde. with the species listed above originally in equal abundance in gas phase, we found the ice surface to hold mostly formic acid, acetic acid and butanol, with a small amount of ethanol and hexanal. the high number of collisions in the closed space of a 1 meter wide vent allows for a gas/adsorbed equilibration within a second. way forward: the possible impact of ammonia, detected in the plumes, is unknown. ammonia can accumulate on the ice surface and influence adsorption of other species, and potentially create a liquid layer by depressing the freezing point of water. the impact of these scenarios need to be explored (e.g., liquid layer shifting equilibrium towards one described by henry's law) so that an observational test be devised to determine which of these factors is the most influential. | effect of adsorption on ice surfaces on the composition of enceladus' plumes: partitioning of oxygen-bearing organics |
metal halide perovskites (mhps) have been considered as a hot research field for optoelectronic devices such as perovskite light emitting diodes (peleds), photodetectors, and solar cells. peleds with high quality are required to achieve the final aim of commercialization. therefore, to commercialize the peleds, perovskite emissive thin films need to be modified through a time-saving economic process. this report provides a practical, unique postprocessing method to appropriately recrystallize the perovskite emissive layer. this method combines 5 min of atmospheric plasma treatment with different annealing low temperatures at a short time (10 min), consuming a short time (totally 15 min), and does not require vacuum equipment. based on the obtained results, applying these processes reduces the grain size of the mapbbr3. it also increases the plqy and, consequently, the carrier recombination rate. also, based on the time-resolved photoluminescence (trpl) results, the average pl lifetime increases from 60.54 ns to 82.3 ns. therefore, the fabricated devices' luminance and external quantum efficiency (eqe) increase to the maximum value of ∼68,500 cd/m2 and ∼20.5%, respectively. | considering the effectiveness of a unique combined annealing-based postprocessing method on the optoelectronic properties of mapbbr3-based light emitting diodes |
reflectance spectroscopy in the visible and near-infrared (vnir) is a common technique used to study the mineral composition of solar system bodies from remote sensed and in-situ robotic exploration. in the vnir spectral range, both crystal field and vibrational overtone absorptions can be present with spectral characteristics (i.e. albedo, slopes, absorption band with different positions and depths) that vary depending on composition and texture (e.g. grain size, roughness) of the sensed materials. the characterization of the spectral variability related to the rock texture, especially in terms of grain size (i.e., both the size of rock components and the size of particulates), commonly allows to obtain a wide range of information about the different geological processes modifying the planetary surfaces. this work is aimed at characterizing how the grain size reduction associated to fault zone development produces reflectance variations in rock and mineral spectral signatures. to achieve this goal we present vnir reflectance analysis of a set of fifteen rock samples collected at increasing distances from the fault core of the vado di corno fault zone (campo imperatore fault system - italian central apennines). the selected samples had similar content of calcite and dolomite but different grain size (x-ray powder diffraction, optical and scanning electron microscopes analysis). consequently, differences in the spectral signature of the fault rocks should not be ascribed to mineralogical composition. for each sample, bidirectional reflectance spectra were acquired with a field-pro spectrometer mounted on a goniometer, on crushed rock slabs reduced to grain size <800, <200, <63, <10 μm and on intact fault zone rock slabs. the spectra were acquired on dry samples, at room temperature and normal atmospheric pressure. the source used was a tungsten halogen lamp with an illuminated spot area of ca. 0.5 cm2and incidence and emission angles of 30˚ and 0˚ respectively. the spectral analysis of the crushed and intact rock slabs in the vnir spectral range revealed that in both cases, with increasing grain size: (i) the reflectance decreases (ii) vnir spectrum slopes (i.e. calculated between wavelengths of 0.425 - 0.605 μm and 2.205 - 2.33 μm, respectively) and (iii) carbonate main absorption band depth (i.e. vibrational absorption band at wavelength of ∼2.3 μm) increase. in conclusion, grain size variations resulting from the fault zone evolution (e.g., cumulated slip or development of thick damage zones) produce reflectance variations in rocks and mineral spectral signatures. the remote sensing analysis in the vnir spectral range can be applied to identify the spatial distribution and extent of fault core and damage zone domains for industrial and seismic hazard applications. moreover, the spectral characterization of carbonate-built rocks can be of great interest for the surface investigation of inner planets (e.g. earth and mars) and outer bodies (e.g. galilean icy satellites). on these surfaces, carbonate minerals at different grain sizes are common and usually related to water and carbon distribution, with direct implications for potential life outside earth (e.g. mars). | vnir reflectance spectroscopy of natural carbonate rocks: implication for remote sensing identification of fault damage zones |
while traversing the northern flank of aeolis mons, gale crater, mars science laboratory rover curiosity encountered a decametre-thick sandstone unit unconformably overlying the lacustrine murray formation. this sandstone contains cross-bed sets on the order of 1 m thick, composed of uniform mm-thick laminations of uniform thickness, and lacks silt- or mud-grade sediments. cross sets are separated by sub-horizontal bounding surfaces which extend for tens of metres across outcrops. dip-azimuths of cross-laminations are predominantly toward the north-east, which is oblique to the north-west slope of the unconformity on which the sandstone accumulated. this sandstone was designated the stimson formation after mt. stimson, where it was delineated from the murray formation. textural analysis of this sandstone revealed a bi-modal sorting with well-rounded grains, typical of particles transported by aeolian processes. stacked cross-bedded sets, representing the migration of aeolian dune-scale bedforms, combined with the absence of finer-grained facies characteristic of interdune deposits, suggest that the stimson accumulated by aerodynamic processes and that the depositional surface was devoid of moisture which could have attracted dust to form interdune deposits. reconstruction of this "dry" dune-field based on architectural measurements suggest that cross sets were emplaced by the migration of dunes with minimum heights of 10m, that were spaced 160 m apart. the dune field covered an area of 30-45 km2, and was confined to the break-in-slope at the base of aeolis mons. cross-set dips suggest that the palaeowind drove these dunes toward the north east, oblique to the slope of the unconformity on which these sandstones accumulated. construction of a dry dune field in gale crater required an environment of extreme aridity with absence of water at the surface and within the shallow sub-surface. this is in stark contrast to the lacustrine environment in which the underlying murray formation accumulated. the contrast in depositional environments between these units suggest that the prevailing climate in gale crater changed, at least temporarily, from a humid environment with surface water that had potential for sustaining life, to a barren desert with reduced potential for habitability at the surface. | from lakes to sand seas: a record of early mars climate change explored in northern gale crater, mars |
paleomagnetic studies have shown that a dynamo magnetic field of tens of µt likely existed on the surface of the moon from at least 4.5 to 3.6 ga and declined to several µt by 3.3 ga [weiss and tikoo, 2014]. furthermore, a recent analysis of lunar regolith breccia 15498 found that the lunar surface field was still 5 µt at 1-2.5 ga [tikoo et al., 2015]. however, a key unknown is when the dynamo finally ceased. to address this, we studied the melt glass matrix of apollo lunar regolith breccia 15015. 40ar/39ar measurements suggest that the glass formed at 1.0 ± 0.2 ga [eglinton et al., 1974], consistent with its trapped 40ar/36ar model age of 0.5 ± 0.4 ga [fagan et al. 2014]. hysteresis data indicate a predominately pseudo-single domain grain size, making 15015 an exceptional paleomagnetic recorder among lunar rocks. alternating field (af) demagnetization and anhysteretic remanence (arm) paleointensity experiments found that 15015 subsamples with faces exposed to band-saw cutting at johnson space center contain highly stable natural remanence (nrm) (>420 mt) and yield paleointensities up to 60 µt, but have nrm directions that are highly non-unidirectional across the parent sample. subsamples taken away from the saw-cut faces (>5 mm depth) contain no stable nrm and formed in a paleofield <0.1 µt (fig. 1). thermal demagnetization of band-sawed samples found that their af-stable nrm demagnetizes by 150°c, indicating that their stable nrms are in fact partial thermoremanence (trm) overprints from the band-saw cutting process, rather than true lunar total trm. thus, the lunar surface paleomagnetic field recorded by 15015 was apparently extremely weak (<0.1 µt) at 1.0 ga. for typically assumed lunar interior parameters, essentially all published models of the lunar dynamo predict surface fields >0.1 µt for > 90% of the time period while the dynamo is active. such a minimum field is comparable to estimates of the strongest lunar crustal surface fields and below even the weakest known dynamo surface field in the solar system today. therefore, our 0.1 µt upper limit indicates that the lunar dynamo likely turned off sometime between 2.5 ga and 1.0 ga. this timing appears to be consistent with both thermochemical convection due to core crystallization and mantle precession as the major power sources for the late lunar dynamo. | lifetime of the lunar dynamo constrained by the young apollo regolith breccia 15015 |
sunspots are the most prominent manifestations of magnetic fields on the visible surface of the sun (photosphere). while historic records mention sunspot observations by eye more than two thousand years ago, the physical nature of sunspots has been unraveled only in the past century starting with the pioneering work of hale and evershed. sunspots are compact magnetic-field concentrations with a field strength exceeding 3,000 g in their center, a horizontal extent of about 30 mm and typical lifetimes on the order of weeks. research during the past few decades has focused on characterizing their stunning fine structure that became evident in high-resolution observations. the central part of sunspots (umbra) appears, at visible wavelengths, dark due to strongly suppressed convection (about 20% of the brightness of unperturbed solar granulation); the surrounding penumbra with a brightness of more than 75% of solar granulation shows efficient convective energy transport, while at the same time the constraining effects of magnetic field are visible in the filamentary fine structure of this region. the developments of the past 100 years have led to a deep understanding of the physical structure of sunspots. key developments were the parallel advance of instrumentation; the advance in the interpretation of polarized light, leading to reliable inversions of physical parameters in the solar atmosphere; and the advance of modeling capabilities enabling radiation magnetohydrodynamic (mhd) simulations of the solar photosphere on the scale of entire sunspots. these developments turned sunspots into a unique plasma laboratory for studying the interaction of strong magnetic field with convection. the combination of refined observation and data analysis techniques provide detailed physical constraints, while numerical modeling has advanced to a level where a direct comparison with remote sensing observations through forward modeling of synthetic observations is now feasible. while substantial progress has been made in understanding the sunspot fine structure, fundamental questions regarding the formation of sunspots and sunspot penumbrae are still not answered. | sunspots |
evaporation experiments of sic in the low pressure-h2-h2o gas mixture showed that presolar sic grains could survive at temperatures lower than ~800 °c during the disk lifetime. sic could survive more efficiently than presolar silicates in the disk. | survivability of presolar sic grains in the protosolar disk: an experimental study of evaporation kinetics of sic in the low pressure-h2-h2o gas mixture |
convection plays an important role in the transport of material within many stars. in stars like the sun, the size of convection-related surface features is a small percentage of the surface radius. however, in red supergiants (rsgs), granules and convection cells are much larger. understanding surface features on rsgs-particularly their size, contrast, and lifetime-is vital to understanding these stars in a more general sense. we present the results of a long-term study of surface features on rsg using the michigan infrared combiner (mirc/mircx after 2016) at the center for high angular resolution (chara) array on mt. wilson. in the form of some the highest resolution images of any star (apart from the sun) yet produced, we present yearly surface images spanning 2011-2012 and 2014-2016 for the star az cyg and images from 2015-2016 for su per. we analyze the size, contrast, and lifetime of the features, providing a stringent test against 3-dimensional radiative hydrodynamics (3d rhd) models of rsgs. we also highlight future directions for research in rsg surface imaging, including the impact of optical interferometers planned for construction during the 2020-2030 decade. | high resolution imaging of red supergiants: a long-term imaging project with the chara array |
photovoltaics (pv) are an enabling technology in the field of aerospace, allowing satellites to operate far beyond the technological limitations of chemical batteries by providing a constant power source. however, launch costs and payload volume constraints result in a demand for the highest possible mass and volume specific power generation capability, a proxy for which is device power conversion efficiency. enhancing the efficiency of iii-v pv devices beyond the single-junction shockley queisser (sq) limit has been a driving goal in pv development. two competing loss mechanisms are thermalization, where photon energy in excess of the absorbing material's bandgap is lost to heat, and transmission or non-absorption, where a photon has too little energy to generate an electron-hole pair in the semiconductor. a further complication regarding the longevity of pv on satellites is damage due to exposure of high energy particle radiation limiting the operational life of the satellite via gradual degradation in efficiency. in this work, two approaches to achieving higher power conversion efficiency are explored. the first, for devices at beginning of life, is towards the development of a prototype intermediate band solar cell (ibsc) where the spectrum is split into three optical transitions via the formation of an intermediate band between the conduction and valence bands of a wide bandgap host material. towards this goal, an inas/alassb quantum dot solar cell (qdsc) capable of enabling sequential absorption is demonstrated via a two-step photon absorption measurement and photoreflectance is used to demonstrate the presence of intraband optical transitions. the second approach, focusing on power generation at end of life, utilizes multijunction photovoltaics where successively higher bandgap materials are stacked in series to optically split the solar spectrum to reduce both thermalization and transmission loss. the addition of inas/gaas qds to a gaas subcell and ingaas strain balanced quantum well superlattices to inverted metamorphic multijunction (imm) devices are explored in order to improve device current retention as material is damaged due to knock-on events displacing atoms from the crystalline lattice. a third section of this work focuses on reducing costs by demonstrating a model for performance of iii-v devices grown on polycrystalline virtual substrates considering two primary extended defects: the effects of crystal grain boundaries and the effects of antiphase boundaries induced by growing polar iii-v materials on nonpolar ge substrates. | development and characterization of novel iii-v materials for high efficiency photovoltaics |
comets are among the most erosive bodies in the solar system. mass wasting events such as landslides, scarp retreat, and cliff collapses fundamentally reduce topographic expression on comet nuclei and flattening them over time [1-2]. thus, older comet nuclei tend to have flatter surfaces [1-2] that are less likely to experience mass wasting events. the existing paradigm of comet evolution suggests that the activity of such nuclei decreases as they age and evolve. nevertheless, such highly evolved nuclei are not necessarily less active than younger, less evolved nuclei. these mass wasting events can also expose buries volatile ices to the surface, increasing activity and providing a mechanism of comet reactivation [2-3]. comet 103p/hartley 2 exemplifies this paradox. the nucleus of hartley 2 is presently extremely flat [3], and exhibited no detectable outbursts during the epoxi flyby, which are indicative of mass wasting events [2,4,5]. nevertheless, hartley 2 is a hyperactive comet, whose activity is dominated by co2 sublimation in a region on its small lobe [6]. here we discuss how a massive landslide triggered this activity when hartley 2 had a faster rotation period in the past [3]. hartley 2's unique nucleus shape maintains a nearly globally flat surface as its rotation state changes, and only experiences large mass wasting events when its principle axis rotation period reaches ~11 hours, at which its hyperactive region becomes prone to landslides [3]. the nucleus subsequently spun down to its present spin state, and is presently depositing h2o-rich grains across the nucleus, creating secondary activity from this exposed h2o. this deposition further smooths out topography, but the location of these depositional regions is likely sensitive to the rotation state of the nucleus. thus, hartley 2's present landscape is a combination of erosion and deposition, both of which smooth and flatten the nucleus over time. references: [1] vincent, j.-b. et al. 2017. mnras 479, s329 [2] steckloff, j.k. & samarasinha, n.h. 2018. icarus 312, 172 [3] steckloff, j.k. et al. 2016. icarus 272, 60 [4] steckloff, j.k. & melosh, h.j. 2016. aas-dps #48. abstract #206.06 [5] pajola, m. et al. nat. astron. 1, 0092 [6] a'hearn, m.f. et al. 2011. science 332, 1396 | avalanches and snowfields: the evolving landscapes and activity of comet 103p/hartley 2 |
among many molecules in space water is rather special. it is found in large variety of astronomical environments ranging from cold interstellar molecular clouds to stellar photospheres, circumstellar envelopes, atmospheres of icy planets and in cometary comas. in these media water molecules represent the major reservoir of oxygen, control chemistry of many species, both in the gas phase and on the grain surfaces and are potentially connected with the emergence of life. in the warm star-forming regions water emission dominates the process of gas cooling and can undergo population inversion and emit maser-like radiation, creating the brightest line in the radio universe, which carries information about physical conditions in these environments. observation and analysis of ortho-to-para ratio of water helps to understand its evolution through all stages of star formation, from molecular cloud to planetary system. lastly, the detection of water isotopologues in cometary comas, and the comparison of the deuterium abundance of water on earth and in comets, is an exciting new window into the early history of earth. in all these applications a quantitative analysis and conclusions are only possible if the precise excitation/quenching schemes of ortho- and para-h2o, hdo and d2o by collisions with typical background gasses are known in a broad range of temperatures. mixed quantum/classical theory (mqct) is a new method that enables calculations for larger molecules, heavier quenchers, and higher collision energies than it was possible before, leading to a breakthrough in the computational studies of collisional energy transfer. a user-ready computer program mqct is now available for calculations of collisional cross sections using massively parallel high performance computer systems. it is specifically tuned for hard problems that require large memory and many cpu cores. in this project will use mqct to generate unified datasets of collision rate coefficients, suitable for astrochemical modelling, for deposition to relevant databases and incorporation into the existing radiative transfer simulation codes, including: i) production of database for rotational transitions in deuterated water + water collisions, important in cometary comas and atmospheres of icy planets (such as jupiter moons), up to the temperature range of t ~ 800 k which will also cover such environments as warm star-forming regions and chemically reach outflows of solar-like proto-stars. combinations of h2o, hdo and d2o will be considered, including quantum selection rules for transitions between ortho- and parastates and treating identical collision partners as indistinguishable. these data will be unique; no information on these processes exist so far. ii) generation of a database for collisional excitation and quenching of deuterated water molecules by simple quenchers in a broad range of temperatures up to t ~ 2000 k, suitable for the modeling of various astrophysical environments such as hot cores and corinos, outflow shocks, and the innermost regions of protoplanetary discs. all isotopic substitutions will be studied, starting with h2o, hdo and d2o collided with para-h2, ortho-h2, he and co. these datasets will significantly expand the range of temperatures, types of isotopes and quenchers available today. iii) development of theory, code and exploratory calculations for coupled ro-vibrational transitions at higher temperatures, t > 2000 k, relevant to circumstellar environments and outer atmospheres of red-giant stars, where the collisional excitation and quenching of bending mode of h2o starts playing role. if successful, this part of the project will also result in the population of a database for collisional rate coefficients of water isotopologues, but now including excitation and quenching of their bending modes, by such quenchers as h2, he, co and h2o. | one database of collisional energy transfer rates for all water isotopologues |
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