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characterizing the amplitude and wavelength dependence of variations in the intrinsic polarization of classical be stars can help inform how these circumstellar disks change over time. since the observed polarization is a superposition of a component arising from the interstellar medium (isp) and a component intrinsic to the be star itself, robustly determining the isp component is critical to isolating the intrinsic component. we present our analysis of multi-epoch, multi-wavelength photometric and polarimetric imaging of ngc 663. ngc 663 is an open cluster that is known to host a large population of be stars. we use gaia data release 2 to refine the distance and membership of ngc 663, and use these results to construct a refined field star polarization map towards the cluster, thereby enabling us to better quantify the isp along the line of sight. this program is supported by nsf-ast 1411563, 1412110, and 1412135, along with the nsf reu program at the university of oklahoma. | characterizing changes in the be star population of ngc 663 |
interstellar polarization was first discovered over 70 years ago, yet the underlying physical mechanisms that cause the observed polarization were not well understood for decades. recent developments in a quantitative description of radiative alignment torque (rat) theory affirms it as the most promising mechanism to explain interstellar polarization through dust grain alignment. this research seeks to understand and explore the physical significance and limitations of rat theory and its theoretical polarization models by probing a diverse parameter space. we first explored the general use of the "serkowski law" with well-documented polarization data to confirm the suitability of serkowski modeling. we then obtained quantitative insight into the source of dust grain alignment by applying sekowski models to theoretical polarization as outlined in rat theory. polarization observations towards the taurus molecular cloud show a sharp increase in peak polarization wavelength in some regions of large extinction. the implied grain growth is found to be caused by accelerated grain coagulation in regions of higher density and ice formation on the grain surface in regions of higher extinction. we conclude that the polarization trends of the taurus molecular cloud may be explained by grain growth among aligned dust grains. future work will entail verifying modeling accuracy of the taurus molecular cloud, identifying unique solutions, and probing the limitations of the parameter space. | radiative alignment torque modeling |
monitoring of the lens system jvas b0218+357 with the fermi gamma-ray space telescope measured a different time delay to that derived from radio observations. we have re-analysed three months of archival very large array data to produce variability curves with an average sampling of one epoch per day in total flux, polarized flux and polarization position angle (ppa) at 15, 8.4 and 5 ghz. the variability is particularly strong in polarized flux. dense sampling and improved subtraction of the einstein ring has allowed us to produce superior variability curves and a preliminary analysis has resulted in a time delay (11.5 days) which agrees well with the γ -ray value. both images of 0218+357 are subject to strong faraday rotation and depolarization as a result of the radio waves passing through the interstellar medium of the spiral lens galaxy. our data reveal frequency-dependent variations in the ppa that are different in each image and which must therefore result from variable faraday rotation in the lens galaxy on timescales of a few days. our analysis has revealed systematic errors in the polarization position angle measurements that strongly correlate with hour angle. although we have been able to correct for these, we caution that all vla polarization observations are potentially affected. | polarization monitoring of the lens system jvas b0218+357 |
pilot is a balloon-borne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our galaxy at wavelengths 240 and 550 µm with an angular resolution of about two arc-min. pilot optics is composed of an off-axis gregorian telescope and a refractive re-imager system. all these optical elements, except the primary mirror, are in a cryostat cooled to 3k. we used optical and 3d measurements combined with thermo-elastic modeling to perform the optical alignment. this paper describes the system analysis, the alignment procedure, and finally the performances obtained during the first flight in september 2015 | the pilot optical alignment for its first flight |
the polarized instrument for long-wavelength observation of the tenuous interstellar medium (pilot) is a balloon-borne experiment that aims to measure the polarized emission of thermal dust at a wavelength of 240µm (1.2 thz). the pilot experiment flew from timmins, ontario, canada in 2015 and 2019 and from alice springs, australia in april 2017. the in-flight performance of the instrument during the second flight was described in [1]. in this paper, we present data processing steps that were not presented in [1] and that we have recently implemented to correct for several remaining instrumental effects. the additional data processing concerns corrections related to detector cross-talk and readout circuit memory effects, and leakage from total intensity to polarization. we illustrate the above effects and the performance of our corrections using data obtained during the third flight of pilot, but the methods used to assess the impact of these effects on the final science-ready data, and our strategies for correcting them will be applied to all pilot data. we show that the above corrections, and in particular that for the intensity to polarization leakage, which is most critical for accurate polarization measurements with pilot, are accurate to better than 0.4% as measured on jupiter during flight#3. | performance of the polarization leakage correction in the pilot data |
pulsars, especially millisecond pulsars are good tools to research the properties of the interstellar medium. in this talk i will show how millisecond pulsars, as accurate clocks, to study the dispersion measure variations, and as high linear polarization radio sources, to study the rotation measure variations. these studies can be used to understand the turbulence of electron density and magnetic field of interstellar medium in the galaxy. | researching interstellar medium using millisecond pulsars |
we constructed a statistically representative survey sample that probes a wide range of interstellar environment parameters including reddening e(b-v), visual extinction av, total-to-selective extinction ratio rv, and molecular hydrogen fraction fh2. edibles provides the community with optical (~305-1042nm) spectra at high spectral resolution (r~70000 in the blue arm and 100000 in the red arm) and high signal-to-noise (s/n; median value ~500-1000), for a statistically significant sample of interstellar sightlines. many of the >100 sightlines included in the survey already have auxiliary available ultraviolet, infrared and/or polarisation data on the dust and gas components. (2 data files). | vizier online data catalog: the eso dibs large exploration survey (cox+, 2017) |
pulsars are rotating neutron stars which emit lighthouse-like beams. owing to their unique properties, pulsars are a unique astrophysical tool to test general relativity, inform on matter at extreme densities, and probe galactic magnetic fields. understanding pulsars physics and emission mechanisms is critical to these applications. here we uncover that mechanical-optical rotation in the pulsars' magnetosphere affects polarisation in a way which is indiscernible from faraday rotation in the interstellar medium for typical ghz observations frequency, but which can be distinguished in the sub-ghz band. besides being essential to correct for possible systematic errors in interstellar magnetic field estimates, our novel interpretation of pulsar polarimetry data offers a unique means to determine whether pulsars rotate clockwise or counterclockwise, providing new constraints on magnetospheric physics and possible emission mechanisms. combined with the ongoing development of sub-ghz observation capabilities, our finding promises new discoveries, such as the spatial distributions of clockwise rotating or counterclockwise rotating pulsars, which could exhibit potentially interesting, but presently invisible, correlations or features. | do pulsars rotate clockwise or counterclockwise? |
the fir distribution at high galactic latitudes, observed with planck, is filamentary with coherent structures in polarization. these structures are also closely related to hi filaments with coherent velocity structures. there is a long-standing debate about the physical nature of these structures. they are considered either as velocity caustics, fluctuations engraved by the turbulent velocity field or as cold three-dimensional density structures in the interstellar medium (ism). we discuss different approaches to data analysis and interpretation in order to work out the differences. we considered mathematical preliminaries for the derivation of caustics that characterize filamentary structures in the ism. using the hessian operator, we traced individual fir filamentary structures in hi from channel maps as observed and alternatively from data that are provided by the velocity decomposition algorithm (vda). vda is claimed to separate velocity caustics from density effects. based on the strict mathematical definition, the so-called velocity caustics are not actually caustics. these vda data products may contain caustics in the same way as the original hi observations. caustics derived by a hessian analysis of both databases are nearly identical with a correlation coefficient of 98%. however, the vda algorithm leads to a 30% increase in the alignment uncertainties when fitting fir/hi orientation angles. we used hi absorption data to constrain the physical nature of fir/hi filaments and determine spin temperatures and volume densities of fir/hi filaments. hi filaments exist as cnm structures; outside the filaments no cnm absorption is detectable. the cnm in the diffuse ism is exclusively located in filaments with fir counterparts. these filaments at high galactic latitudes exist as cold density structures; velocity crowding effects are negligible. | caustics and velocity caustics in the diffuse interstellar medium at high galactic latitudes |
classical be stars are the only main sequence stars that possess keplerian decretion circumstellar disks ruled by viscous processes. the physical properties of the disk can be studied by modeling its physical structure and solving the radiative transfer problem. at this point, the calculation of synthetic observables arises as a tool to investigate the physical quantities of these systems. among the proposed models to explain be star disks, the viscous decretion disk model is the only one correctly explaining a large set of evidence that implies that viscous shear is the mechanism driving the disk outflow. modeling of observations requires elaborate procedures to achieve reliable results. in the case of be stars, the system under study is very complex. the central star is affected by fast rotation and stellar pulsation. the disk structure varies in time, and depends in a complex way on several factors, e.g., disk feeding rate, viscosity, the presence of a binary companion, etc. another source of complication is the complex interplay between stellar and disk parameters. we present a new tool for modeling be star observations that takes into consideration most of the relevant physical processes. named beatlas, it consists of two parts. the first part is a grid of be star models that cover all the relevant physical parameters of the star (mass, age, rotation rate, etc.) and the disk (size, density structure, density scale, etc.). beatlas was computed with the radiative transfer code hdust. the stellar parameters were obtained from the geneva stellar evolution models. the second part is a set of computer tools to the fit of the observations with beatlas using bayesian statistics to infer the posterior probabilities of each stellar and disk parameter. beatlas allows for using prior information, such as distance, v sin i and inclination, when available. our main goal with beatlas is to provide means for studying b and be stars observations into account all the relevant parameters and their cross correlations. beatlas was first applied to study of 111 oba stars. using iue data and prior information (v sin i) and hipparcos parallax) about these stars, we were able to derive their stellar and geometrical parameters, as well as the corresponding interstellar extinction. a comparison of our results of those from the literature yielded in general good results. deviant cases must still be analyzed in more detail, but one possibility under investigation is that they due to fundamental differences between our approach and some of the ones used in the literature (e.g., rotating vs. non-rotating models) which limits the viability of a direct comparison. a second application was on the be star beta cmi, which was modelled by klement et al. 2015 also using the viscous decretion disk model. the results show the ability of beatlas to quickly recover the disk and stellar parameters. furthermore, a detailed analysis of the results show that our procedure does indeed provide for more robust and realistic error estimates by properly considering the coupling between the parameters. finally, a third application was on the be star alpha arae. we present new observations (polarization, spectroscopy and sub-mm photometry) that, together with data obtained from the literature, show that alpha arae had a stable disk for the last 50 years. we found a disk density slope (n = 2.44^{+0.27}_{-0.16}) that is inconsistent with the standard theory that predicts that isothermal steady-state disks should have n=3.5. two effects may be responsible for this: non-isothermal effects in the disk, or the effects of a binary companion. our results provide evidence that alpha arae is a binary system. in our case, evidence came for the change of the sed slope in the sub-mm domain, here interpreted as being caused by an unseen binary companion that truncates the disk of the primary. | beatlas: a grid of synthetic spectra for be stars |
polarization from dust thermal emission at far-infrared wavelengths is a useful probe of magnetic fields in dense star-forming environments, as interstellar dust grains are expected to align with these fields through radiative alignment torques (rats). such polarimetric observations have found that magnetic fields contribute to regulating star formation processes in low-mass molecular clouds, but few studies have quantified their influence in massive starburst regions. this presentation will therefore focus on multi-wavelength observations of polarization toward the 30 doradus star-forming region in the large magellanic cloud (also known as the tarentula nebula). we present publicly available data at 53, 89, 154, and 214 µm obtained with the hawc+ polarimetric camera aboard the stratospheric observatory for infrared astronomy (sofia). we use an angular dispersion analysis to fit the turbulent-to-ordered magnetic energy and the turbulent correlation length in multiple regions of the cloud, and compare the results between wavelengths. combined with spectroscopic data (i.e., sofia, apex), we measure the plane-of-sky amplitude of the magnetic field through the davis-chandrasekhar-fermi method. these multi-wavelength observations also offer a unique opportunity to probe the alignment efficiency of different dust populations in a variety of extreme environments. specifically, we characterize the measured polarization as a function of column density and temperature for each available wavelength in the regions of interest. these results may help to understand observed discrepancies in the angular dispersion analysis between data sets, as the polarization efficiency of dust populations is expected to change depending on the physical properties of their environment. | dust alignment and magnetic fields in the 30 doradus star-forming region |
stellar-mass black holes in low-mass x-ray binaries are natural laboratories for studying the interaction of matter and radiation under extreme physical conditions. these systems spend most of their lifecycle residing in the inactive (quiescent) state, sometimes suddenly bursting out, increasing their brightness by several orders of magnitude over the entire spectrum. their optical and infrared emission is a product of a complex interplay between the jet, wind, accretion disc, and hot accretion flow components. the study of the contributions of various components and their properties to the observed spectrum is crucial for the understanding of the mechanisms leading to outbursts. one of the effective, and often overlooked, ways of such study is optical polarimetry since the polarization carries information about the geometrical properties of the emitting/scattering media, which may otherwise be inaccessible to an observer. we present the results of multiwavelength (bvr) polarimetric studies of a sample of eight black hole x-ray binaries during outbursts and those residing in the quiescent (or near-quiescent) state. we surveyed both long- and short-period systems located at different galactic latitudes. careful analysis of the interstellar polarization in the direction of the sources allowed us to estimate the intrinsic polarization of all binaries. intrinsic polarization is found to be small (<0.2%) for sources in bright soft states. it was found to be significant in the rising hard state of maxi j1820+070 at the level of 0.5% and negligible in the decaying hard state. four out of five sources observed during quiescence show no evidence of significant intrinsic polarization. the only exception is maxi j1820+070, which showed substantial (>5%) intrinsic quiescent-state polarization with a blue spectrum. the absence of intrinsic polarization at the optical wavelengths puts constraints on the potential contribution of non-stellar (jet, hot flow, accretion disc) components to the total spectra of quiescent black hole x-ray binaries. | high precision optical polarimetry of black hole x-ray binaries |
dust induced polarization, from the uv to mm-waves, is an efficient way to probe the magnetic fields in the interstellar medium (ism), but relies on a quantitative understanding of the underlying grain alignment, along the line of sight. with the development of the paradigm of radiative alignment torque (rat) theory, major advances have been made in understanding how and where the polarization is generated. however, several details of the alignment physics still need to be fully understand, as well as the effect of the environment on different scales. we will discuss some of the open questions in grain alignment as well as highlight how different physical scales and the polarization spectrum (with an emphasis on the fir/sub-mm wave) can be used to further improve our understanding of the ism magnetic fields, as well as the roles of grain characteristics and environmental parameters affect their measurements. | understanding interstellar polarimetry - grain alignment and physical scales |
interstellar communication transmitters, intended to be discovered and decoded to information bits, are expected to transmit signals that contain message symbols quantized in at least one of the degrees of freedom of the transmitted signal. a hypothesis is proposed that signal quantization, in the form of multiplicative values of one or more signal measurements, may be observable during the reception of hypothetical discoverable interstellar communication signals. in previous work, using single and multiple synchronized radio telescopes, candidate hypothetical interstellar communication signals comprising delta-t delta-f opposite circular polarized pulse pairs have been reported and analyzed (ref. arxiv:2105.03727, arxiv:2106.10168, arxiv:2202.12791). in the latter report, an apparent quantization of delta-f at multiples of 58.575 hz was observed. in the current work, a machine process has been implemented to further examine anomalous delta-f and delta-t quantization, with results reported in this paper. as in some past work, a 26 foot diameter radio telescope with fixed azimuth and elevation pointing is used to enable a right ascension filter to measure signals associated with a celestial direction of interest, relative to other directions, over a 6.3 hour range of right ascension. the 5.25 plus or minus 0.15 hour right ascension, -7.6 degrees plus or minus 1 degree declination celestial direction presents repetition and quantization anomalies, during an experiment lasting 157 days, with the first 143 days overlapping the previous experiment. | symbol quantization in interstellar communications: methods and observations |
we present an analysis of potential follow-up polarimetric microlensing observations to study the stellar atmospheres of distant stars. first, we produce synthetic microlensing events using the galactic model, stellar population and interstellar dust toward the galactic bulge. we simulate the polarization microlensing light curves and pass them through the instrument specifications of the focal reducer and low dispersion spectrograph (fors2) polarimeter at the very large telescope (vlt), and then analyse them. we find that the accuracy of the vlt allows us to constrain the atmospheres of cool red giant branch (rgb) stars. assuming that about 3000 microlensing events are detected per year by the optical gravitational lensing experiment (ogle) telescope, we expect to detect almost 20, 10, 8 and 5 polarization microlensing events for the following four criteria: being three consecutive polarimetric data points above the baseline with 1σ, 2σ, 3σ and 4σ, respectively, in the polarimetric light curves. we generalize the covariance matrix formulation and present the combination of polarimetric and icinformation that leads us to measure the scattering optical depth of the atmosphere and the inner radius of the stellar envelope of rgb stars. these two parameters could determine the dust opacity of the atmosphere of cool rgb source stars and the radius where dust can be formed. | measuring stellar atmosphere parameters using follow-up polarimetric microlensing observations |
the nature of the dust in the dispersed interstellar medium is determined by various observational limitations, which we summarize with special attention paid to published reddening curves. we highlight the potential of future mid-infrared spectra as well as of polarization observations to determine the stoichiometry of silicate grains. we show that our previous two-component dust model is consistent with the flatness of the polarization curve in the submillimetre wavelength range, between 0.2 and 3 mm, as observed by the planck satellite. contemporary data can be modelled including a population of micro-meter sized grains that we call dark dust. | dust in the diffuse ism |
the linear polarization of thermal dust emission provides a powerful tool to probe interstellar and circumstellar magnetic fields, because aspherical grains tend to align themselves with magnetic fields lines. however, while the radiative alignment torque (rat) theory provides a quantitative framework for the understanding of this phenomenon, some aspects of this grain alignment mechanism still need to be quantitatively tested. one such aspect is the possibility that the reference direction for the alignment may change from the magnetic field ("brat") to the radiation field k-vector ("krat") in areas of strong radiation fields, such as the regions affected by massive star formations feedback mechanisms. currently, the poor understanding of the b- to k-rat transition precludes the opportunity of making reliable measurements of the magnetic fields, and thus magnetic field support, toward hii regions or pdrs, for example. in order to provide a well-characterized prototypical system to compare to ab initio rat theory, our work focuses on investigating this grain alignment transition toward the orion bar that undergoes intense irradiation from the trapezium cluster, the most massive o-type star in the cluster, with multi-wavelength sofia hawc+ chop-nod and scan-pol dust polarization observations. the aim is to quantify to what extent the k-rat mechanism could contribute to the polarization, and to extrapolate our conclusions to other regions of similar conditions. from our estimation of the radiation field and volume density, we can predict the grain size above which this alignment transition can occur. however, we also discuss the rotational grain disruption of grains, that potentially takes place on the irradiated edge of the bar. we conclude that most grains should be rotationally disrupted before they could reach the typical size after which the alignment shifts from "brat" to "krat". | the origin of dust polarization in the orion bar |
the semi-regular variable star v canum venaticorum (v cvn) is well known for its unusual linear polarization position angle (pa). decades of observing v cvn reveal a nearly constant pa spanning hundreds of pulsation cycles. this phenomenon has persisted through variability that has varied by two magnitudes in optical brightness and through variability in the polarization amplitude over 0.3 and 6.9%. additionally, the polarization fraction of v cvn varies inversely with brightness. this paper presents polarization measurements obtained over three pulsation cycles. we find that the polarization maximum does not always occur precisely at the same time as the brightness minimum. instead, we observe a small lead or lag in relation to the brightness minimum, spanning a period of a few days up to three weeks. furthermore, the pa sometimes exhibits a non-negligible rotation, especially at lower polarization levels. to elucidate the unusual optical behavior of v cvn, we present a list of literature sources that also exhibit polarization variability with a roughly fixed pa. we find this correlation occurs in stars with high tangential space velocities, for instance, "runaway" stars, suggesting that the long-term constant pa is related to how the circumstellar gas is shaped by the star's high-speed motion through the interstellar medium. tables a.2-a.6 are available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/677/a96. all raw fits files are available on https://zenodo.org/record/7997101 | a multiyear photopolarimetric study of the semi-regular variable v cvn and identification of analog sources |
context. over its 13 yr of operation (1990-2002), the faint object camera (foc) on board the hubble space telescope (hst) observed 26 individual active galactic nuclei (agns) in ultraviolet (uv) imaging polarimetry. however, not all of the observations have been reduced and analyzed or set within a standardized framework.aims: we plan to reduce and analyze the agn observations that have been neglected in the foc archives using a consistent, novel, and open-access reduction pipeline of our own. we then extend the method to the full agn sample, thus leading to potential discoveries in the near future.methods: we developed a new pipeline in python that will be able to reduce all the foc observations in imaging polarimetry in a homogeneous way. most of the previously published reduced observations are dispersed throughout the literature, with the range of different analyses and approaches making it difficult to fully interpret the foc agn sample. by standardizing the method, we have enabled a coherent comparison among the different observational sets.results: in this first paper of a series exploring the full hst/foc agn sample, we present an exhaustively detailed account of how to properly reduce the observational data. current progress in cross-correlation functions, convolution kernels, and a sophisticated merging and smoothing of the various polarization filter images, together with precise propagation of errors, has provided state-of-the-art uv polarimetric maps. we compare our new maps to the benchmark agn case of ngc 1068 and successfully reproduce the main results previously published, while pushing the polarimetric exploration of this agn futher, thanks to a finer resolution and a higher signal-to-noise ratio (s/n) than previously reported. we also present, for the first time, an optical polarimetric map of the radio-loud agn ic 5063 and we examine the complex interactions between the agn outflows and the surrounding interstellar medium (ism).conclusions: thanks to our newly and standardized reduction pipeline, we were able to explore the full hst/foc agn sample, starting with observations that had not been previously published (e.g., ic 5063 here). this pipeline will allow us to make a complete atlas of uv polarimetric images of the 26 unique agns observed by the foc, highlighting the importance and necessity of (imaging) polarimeters for the upcoming new generation of 30-m class telescopes. | forgotten treasures in the hst/foc uv imaging polarimetric archives of active galactic nuclei. i. pipeline and benchmarking against ngc 1068 and exploring ic 5063 |
we observed selected regions of the l1495/b213 cloud with the iram 30m telescope during one session in february-march 2013 and another one the following june. in both sessions we used the emir heterodyne receiver in frequency-switching mode together with the vespa autocorrelator. the observations consisted of simultaneous on-the-fly maps in the lines of n2h+(1-0) (93.17ghz) and c18o(2-1) (219.56ghz) in dual polarization mode. all fits files are data cubes with the same spatial limits as the maps shown in the paper (fig. 2) and have 400 velocity channels. the files were generated using the original data files, which were in class format, which is the native format of the iram 30m telescope. (2 data files). | vizier online data catalog: dense cores in l1495/b213 complex (tafalla+, 2015) |
spectropolarimetry is a powerful tool for diagnostic of interstellar matter and gives information about the geometry of the ejected material after the novae outbursts. in this paper are presented spectropolarimetric observations of the recurrent nova t crb at quiescence obtained with forero2 attached to the cassegrain focus of the 2.0 m rcc telescope of the bulgarian rozhen national astronomical observatory. the interstellar polarization toward t crb was estimated using the field stars method. the spectropolarimetric observations were obtained from february 2018 to august 2021. in the wavelength range from 4800 å to 8200 å the maximum of the degree of linear polarization is pmax(obs) (%) = 0 . 46 ± 0 . 01 at λ ≈ 5200 å. the position angle is p . a.obs = 100 ° . 8 ± 0 ° . 9 . during the observations, there is no intrinsic polarization in t crb, and the derived values represent interstellar polarization. the polarization toward t crb is due to the foreground interstellar dust located at the distance up to ≈ 400 pc. based on the degree of polarization the interstellar extinction toward t crb is eb-v ≈ 0 . 07 . | interstellar polarization and extinction toward the recurrent nova t crb |
magnetic fields appear to be ubiquitous in the astrophysical environments of our universe, but are still poorly understood despite playing an important role in understanding different-scale celestial objects (e.g., earth, planets, stars, normal galaxies, active galactic nuclei, clusters etc.). we briefly review the results and progress in magnetic field estimation based on rotation measures from the large-scale interstellar medium, megaparsec-scale radio jets to the plasma near the black-hole horizon. we find that there is no evident correlation between electron density and magnetic field in warm ionized plasma, which suggests that the estimation of the magnetic field from the ratio of the rotation measure and dispersion measure correctly reflects the intrinsic field. the estimation of the magnetic field from the rotation measure is also discussed near the black hole horizon in m 87. the square kilometre array will greatly improve the understanding of the magnetic field in our universe, which will provide high-quality polarization imaging and extragalactic rotation measures in the near future. | magnetic field and faraday rotation from large-scale interstellar medium to plasma near the black-hole horizon |
we present faraday rotation measure (rm) values derived at l and p bands as well as some 60 stokes-parameter profiles, both determined from our long-standing arecibo dual-frequency pulsar polarimetry programmes. many of the rm measurements were carried out towards the inner galaxy and the anticentre on pulsars with no previous determination, while others are remeasurements intended to confirm or improve the accuracy of existing values. stokes-parameter profiles are displayed for the 58 pulsars for which no meaningful stokes profile at lower frequency is available and 4 without a high-frequency pair. this is a population that includes many distant pulsars in the inner galaxy. a number of these polarized pulse profiles exhibit clear interstellar-scattering tails; none the less, we have attempted to interpret the associated emission-beam structures and to provide morphological classifications and geometrical models where possible. | polarization measurements of arecibo-sky pulsars: faraday rotations and emission-beam analyses |
aims: dh cephei is a well-known massive o+o-type binary system on the northern sky, situated at the center of young open cluster ngc 7380. our high-precision multi-band polarimetry clearly reveals that variations of linear polarization in this system are synchronous with the phase of the orbital period. we used the observed variations of stokes parameters q and u to derive the orbital inclination i, orientation ω, and the direction of rotation. moreover, in order to obtain a rough estimation of the interstellar polarization in the vicinity of dh cep, we observed polarization arising from the neighboring stars in the cluster.methods: we used the dipo1-2 polarimeter in combination with the remotely controlled 60 cm tohoku t60 telescope to obtain linear polarization measurements of dh cep in the b, v, and r passbands at the accuracy level of ~0.003%. to obtain an estimation of interstellar polarization of dh cep, we observed more than a dozen field stars identified as members of ngc 7380 and in the close proximity to dh cep. a lomb-scargle period search was applied to the acquired polarization data to reveal the dominating frequency in polarization variations. we used a standard analytical method based on a two-harmonics fourier fit to derive the inclination, orientation, and the direction of rotation of the binary orbit.results: the variations of stokes parameters in all three b, v, and r passbands clearly suggest an unambiguous periodic signal at 1.055 d with an amplitude of variations of ~0.2%, which corresponds to half of the known orbital period of 2.11 d. this type of polarization variability is expected for a binary system with light-scattering material distributed symmetrically with respect to the orbital plane. in addition to the regular polarization variability, there is a nonperiodic component, which is strongest in the b passband. in the v passband, we obtained our most reliable values for the orbital inclination i = 46° + 11°/ − 46° and an orientation of the orbit on the sky of ω = 105° ± 55°, with 1σ confidence intervals. using our best estimate of i and the polametric amplitude in the v passband, we estimated that the mass loss from the system is ~3.4 × 10−7 m⊙ yr−1. the direction of the binary system rotation on the plane of the sky is clockwise. our polarimetric observations of neighboring stars of dh cep in ngc 7380 reveal that the polarization of the cluster stars is most likley due to aligned interstellar dust in the foreground. the polarization data for dh cep are only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/677/a75 | high-precision broadband linear polarimetry of early-type binaries. iv. the dh cephei binary system in the open cluster of ngc 7380 |
we present 0.″4 resolution imaging polarimetry at 8.7, 10.3, and 12.5 μm, obtained with canaricam at the gran telescopio canarias, of the central 0.11 pc × 0.28 pc (4.″2 × 10.″8) region of w51 irs2. the polarization, as high as ~14%, arises from silicate particles aligned by the interstellar magnetic field (b-field). we separate, or unfold, the polarization of each sightline into emission and absorption components, from which we infer the morphologies of the corresponding projected b-fields that thread the emitting- and foreground-absorbing regions. we conclude that the projected b-field in the foreground material is part of the larger-scale ambient field. the morphology of the projected b-field in the mid-infrared (mid-ir) emitting region spanning the cometary h ii region w51 irs2w is similar to that in the absorbing region. elsewhere, the two b-fields differ significantly with no clear relationship between them. the b-field across the w51 irs2w cometary core appears to be an integral part of a champagne outflow of gas originating in the core and dominating the energetics there. the bipolar outflow, w51north jet, that appears to originate at or near sma1/n1 coincides almost exactly with a clearly demarcated north-south swath of lower polarization. while speculative, comparison of mid-ir and submillimeter polarimetry on two different scales may support a picture in which sma1/n1 plays a major role in the b-field structure across w51 irs2. | gtc/canaricam mid-infrared polarimetry of magnetic fields in star-forming region w51 irs2 |
we present a 3d map of magnetic field orientation on the surface of the local bubble, a low-density cavity in the nearby interstellar medium created by supernovae. this map is the first of its kind to fully chart magnetic fields over an observed superbubble. recent work mapping the 3d shape and dynamics of the local bubble has revealed that the formation of all young stars within 200 pc of the sun was triggered by the bubble's rapid expansion (zucker et al. 2022). the exact mechanics of this expansion, and the role that magnetic fields in the surrounding interstellar medium have played in regulating its evolution, is not yet clear. by combining detailed models of the bubble's geometry (derived from 3d dust mapping, pelgrims et al. 2020) with the assumption that magnetic field vectors are tangent to the bubble's surface, we are able to infer the 3d magnetic field orientation from planck plane-of-the-sky dust polarization orientations. we analyze the relationship between the bubble's inferred magnetic field and background starlight polarimetry observations, and discuss how magnetic fields may have affected the dynamics of the local bubble and other nearby structures in the ism. the sao reu program is funded in part by the national science foundation reu and department of defense assure programs under nsf grant no. ast-2050813, and by the smithsonian institution. | a 3d map of the local bubble's magnetic field |
molecules and particles make up ~40%-70% of carbon in the interstellar medium, yet the exact chemical structure of these constituents remains unknown. we present carbon k-shell absorption spectroscopy of the galactic interstellar medium obtained with the low energy transmission grating spectrometer on board the chandra observatory that directly addresses this question. we probe several lines of sight, using bright active galactic nuclei as backlighters. we make our measurements differentially with respect to the bright source mrk 421, in order to take the significant carbon k absorption in the instrument into account. in the spectrum of the blazar 1es 1553+113 we find evidence for a novel feature: strong extinction on the low-energy side of the neutral c 1s-2p resonance, which is indicative of scattering by graphite particles. we find evidence for characteristic particle radii of order 0.1-0.15 μm. if this explanation for the feature is correct, limits on the mass of the available carbon along the line of sight may imply that the grains are partially aligned, and the x-rays from the source may have intrinsic polarization. | x-ray spectroscopy of interstellar carbon: evidence for scattering by carbon-bearing material in the spectrum of 1es 1553+113 |
we present a study of synthetic observations of polarized dust emission at 353 ghz as seen by an observer within a cavity in the interstellar medium (ism). the cavity is selected from a magnetohydrodynamic simulation of the local ism with time-dependent chemistry, star formation, and stellar feedback in form of supernova explosions with physical properties comparable to the local bubble ones. we find that the local density enhancement together with the coherent magnetic field in the cavity walls makes the selected candidate a translucent polarization filter to the emission coming from beyond its domains. this underlines the importance of studying the local bubble in further detail. the magnetic field lines inferred from synthetic dust polarization data are qualitatively in agreement with the all-sky maps of polarized emission at 353 ghz from the planck satellite in the latitudes interval 15° ≲ |b| ≲ 65°. as our numerical simulation allows us to track the galactic mid-plane only out to distances of $250\,$ pc, we exclude the region |b| ≲ 15° from our analysis. at large galactic latitudes, our model exhibits a high degree of small-scale structures. on the contrary, the observed polarization pattern around the galactic poles is relatively coherent and regular, and we argue that the global toroidal magnetic field of the milky way is important for explaining the data at |b| ≳ 65°. we show that from our synthetic polarization maps, it is difficult to distinguish between an open and a closed galactic cap using the inferred magnetic field morphology alone. | modelling local bubble analogs: synthetic dust polarization maps |
we present the first deep polarimetric study of galactic synchrotron emission at low radio frequencies. our study is based on 21 observations of the european large area infrared space observatory survey-north 1 (elais-n1) field using the low-frequency array (lofar) at frequencies from 114.9 to 177.4 mhz. these data are a part of the lofar two-metre sky survey deep fields data release 1. we used very low-resolution (4.3') stokes qu data cubes of this release. we applied rotation measure (rm) synthesis to decompose the distribution of polarised structures in faraday depth, and cross-correlation rm synthesis to align different observations in faraday depth. we stacked images of about 150 h of the elais-n1 observations to produce the deepest faraday cube at low radio frequencies to date, tailored to studies of galactic synchrotron emission and the intervening magneto-ionic interstellar medium. this faraday cube covers ~36 deg2 of the sky and has a noise of 27 µjy psf-1 rmsf-1 in polarised intensity. this is an improvement in noise by a factor of approximately the square root of the number of stacked data cubes (~√20), as expected, compared to the one in a single data cube based on five-to-eight-hour observations. we detect a faint component of diffuse polarised emission in the stacked cube, which was not detected previously. additionally, we verify the reliability of the ionospheric faraday rotation corrections estimated from the satellite-based total electron content measurements to be of ~0.05 gad m-2. we also demonstrate that diffuse polarised emission itself can be used to account for the relative ionospheric faraday rotation corrections with respect to a reference observation. the faraday cube is only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/674/a119 | lofar deep fields: probing faint galactic polarised emission in elais-n1 |
the linear polarization of thermal dust emission provides a powerful tool to probe interstellar and circumstellar magnetic fields, because aspherical grains tend to align themselves with magnetic field lines. while the radiative alignment torque (rat) mechanism provides a theoretical framework for this phenomenon, some aspects of this alignment mechanism still need to be quantitatively tested. one such aspect is the possibility that the reference alignment direction changes from the magnetic field ("b-rat") to the radiation field k-vector ("k-rat") in areas of strong radiation fields. we investigate this transition toward the orion bar pdr, using multiwavelength sofia hawc+ dust polarization observations. the polarization angle maps show that the radiation field direction is on average not the preferred grain alignment axis. we constrain the grain sizes for which the transition from b-rat to k-rat occurs in the orion bar (grains ≥ 0.1 μm toward the most irradiated locations), and explore the radiatively driven rotational disruption that may take place in the high-radiation environment of the bar for large grains. while the grains susceptible to rotational disruption should be in suprathermal rotation and aligned with the magnetic field, k-rat aligned grains would rotate at thermal velocities. we find that the grain size at which the alignment shifts from b-rat to k-rat corresponds to grains too large to survive the rotational disruption. therefore, we expect a large fraction of grains to be aligned at suprathermal rotation with the magnetic field, and to potentially be subject to rotational disruption, depending on their tensile strength. | the origin of dust polarization in the orion bar |
the dominion radio astrophysical observatory's john a. galt 26 m radio telescope serves multiple roles for the canadian radio astronomy community. it is currently earmarked to serve as an interferometric reference for the canadian hydrogen intensity mapping experiment (chime), canadian hydrogen observatory and radio transient detectors (chord), and deep dish development array 6m (d3a6) experiments. the attributes of this telescope make it ideal for spectropolarimetric studies of the interstellar medium, however instrumental conversion of unpolarized radiation into a polarized signal can corrupt the astronomical signal as the telescope undergoes various loading conditions. to characterize these effects, a finite element (fe) model of the telescope was constructed, based on available blue prints and supplemented by manual measurements. gravity and wind load cases were analyzed for several elevation angles. the fe model will be validated by measuring the first several vibration modes of the actual telescope using the step-release method. this paper will describe the model development and analytical predictions, as well as the experimental approach used to validate these predictions, and will summarize initial results from these tests (if available). | reverse finite element modelling and verification testing of the john a. galt 26 m radio telescope |
magnetic fields are believed to play a crucial role in the dynamics and evolution of protoplanetary disks. polarized (sub)millimeter dust emission has been established as a reliable tool to probe the magnetic field on the relatively large scales of molecular clouds, dense star-forming cores and protostellar envelopes, based on the well-known mechanism of magnetically aligned grains. however, this canonical mechanism fails to explain the first spatially resolved disk polarization detected in a t tauri star, hl tau, through the combined array for research in millimeter-wave astronomy (carma). we are thus motivated to search for alternative explanations. the goal of this thesis is to explore the origins of the disk polarization, with an emphasis on dust scattering. we start by developing a semi-analytic theory for the dust scattering-induced polarization in a disk inclined to the line of sight under the simplification that the disk is both optically and geometrically thin. we show that dust scattering can naturally explain the two main features of the hl tau disk polarization observed by carma: (1) the polarized intensity distribution is elongated along the major axis, and (2) the polarization orientation is along the minor axis. both are unavoidable consequences of a simple geometric effect. the broad agreement between the simplified theory and the carma data played an important role in establishing dust scattering as a viable alternative to magnetic grain alignment for producing disk polarization. furthermore, in order to produce polarization at the observed level of about 1%, the scattering grains must have sizes of order several tens of um, which are much larger than those in the general interstellar medium (of order 0.1 um or less). the dust polarization is thus a powerful tool for probing the grain growth in the disk, the crucial first step towards the formation of planetesimals and ultimately planets. we then study the interplay between the polarization produced by dust scattering and that by magnetically aligned (ellipsoidal) grains under the same simplification. the scattering of (sub)millimeter light by aligned ellipsoidal grains is computed through the so-called "electrostatic approximation." we show that the interplay can produce polarization patterns that are very different from those produced by the two mechanisms individually, including a "butterfly-shaped" pattern with two "null" (zero polarization) points. we find tentative evidence for this composite pattern in the very large array (vla) 8 mm polarization data of the deeply embedded protostar ngc 1333 iras4a1. if confirmed, it would imply not only that magnetic fields exist on the disk scale but also that they are strong enough to align the large grains responsible for the 8 mm emission. we quantify the effects of the optical depth on the scattering-induced polarization through a combination of analytic illustration, approximate semi-analytic modeling using formal solutions to the radiative transfer equation, and monte carlo simulations. we find that for an inclined, optically thick disk with a finite geometric thickness, the near side will be brighter than the far side in polarized intensity. it is a robust signature that can be used to distinguish the scattering-induced polarization from that by other mechanisms, such as aligned grains. this asymmetry is weaker in a well-settled (dust) disk with a smaller thickness. as such, it can be used to probe the dust settling, a process important for the grain growth and dust dynamics. the last part of the thesis presents ongoing work on another mechanism for disk polarization, the radiative alignment. it was recently proposed as an explanation of the elliptical polarization pattern observed by the atacama large millimeter/submillimeter array (alma) in the hl tau disk at 3 mm. we show that the radiative alignment produces a circular (or concentric), rather than elliptical, polarization pattern. an elliptical pattern can be produced if the dust grains are aligned aerodynamically.however, both mechanisms predict a strong azimuthal variation in the polarized intensity, which is not observed. we conclude that neither of these two mechanisms alone can explain the data and the origin of the alma 3 mm polarization in hl tau remains a mystery. the flood of alma data and relatively early stage of theoretical development should make the field of disk polarization an exciting area of research that is poised for rapid growth. | origins of (sub)millimeter disk polarization |
we propose polarization of scattered optical light from intermediate galactic latitude infrared cirrus as a new diagnostic to constrain models of interstellar dust and the anisotropic interstellar radiation field (aisrf). for single scattering by a sphere, with mie scattering phase functions for intensity and polarized intensity for a dust model at a given wavelength (sloan r and g bands), and with models of anisotropic illumination from the entire sky (represented in healpix), we develop the formalism for calculating useful summary parameters for an integrated flux nebula (ifn): the average of the phase function weighted by the illumination, polarization angle (ψ), and polarization fraction (p). to demonstrate the diagnostic discrimination of polarization from scattered light, we report on the effects of different anisotropic illumination models and different dust models on the summary parameters for the spider ifn. the summary parameters are also sensitive to the ifn location, as we illustrate using frankie illumination models. for assessing the viability of dust and aisrf models, we find that observations of ψ and p of scattered light are indeed powerful new diagnostics to complement joint modeling of the intensity of scattered light (related to the average phase function) and the intensity of thermal dust emission. however, optically thin ifns that can be modeled using single scattering are faint and p is not large, as it could be with rayleigh scattering, and so these observations need to be carried out with care and precision. results for the draco nebula compared to the spider illustrate the challenge. | diagnostics from polarization of scattered optical light from galactic infrared cirrus |
the unique biosignature of life on earth is the homochirality of organic compounds such as amino acids, proteins, and sugars. the origin of this homochirality has remained a mystery for over a century. while high-energy spin-polarized (spin-up or spin-down) electrons (spes) from the $\beta$ decay of radioactive nuclei discovered by lee and yang (1956) and wu et al. (1957) have been proposed as a potential source of symmetry breaking, their exact role on homochirality is much debated. here we suggest magnetically aligned dust grains as a new source of spes due to photoemission of electrons having aligned spins by the barnett effect. for the interstellar uv radiation field of strength $g_{\rm uv}$, we found that the spe emission rate is $\gamma_{\rm pe}^{\rm spe}\sim 10^{-14}g_{\rm uv}$ electrons per second per h, the fraction of spin-polarized to total photoelectrons is $\sim 10\%$, and the spe yield (photoelectron number per uv photon) can reach $\sim 1\%$, using the modern theory of grain alignment. low-energy spes from aligned grains would cause chiral symmetry breaking of interstellar chiral molecules due to spin-selective (dipole-dipole) interactions. finally, we suggest magnetically aligned grains as chiral agents that facilitate and enrich the chiral asymmetry of chiral molecules. our proposed mechanism might explain the detection of chiral asymmetry in the ism, comets, and meteorites due to the ubiquitous uv radiation and magnetically aligned grains, paving the way for understanding the origin and distribution of life in the universe. this mechanism based on magnetic grain alignment implies the role of magnetic fields on chirality symmetry breaking. | photoemission of spin-polarized electrons from aligned grains and chiral symmetry breaking |
the linear polarization of thermal dust emission provides a powerful tool to probe interstellar and circumstellar magnetic fields, because aspherical grains tend to align themselves with magnetic field lines. while the radiative alignment torque (rat) mechanism provides a quantitative framework for the understanding of this phenomenon, some aspects of this grain alignment mechanism still need to be observationally tested. one such aspect is the possibility that the reference direction for the alignment may change from the magnetic field ("b-rat") to the radiation field k-vector ("k-rat") in areas of strong radiation fields, such as the regions affected by massive star formations radiative feedback mechanisms. currently, the poor constrain of the b- to k-rat transition complicates the reliable measurements of the magnetic fields, and thus magnetic field support, toward hii regions or pdrs, for example. we thus need a prototypical system to compare to rat theories. our work focuses on investigating this grain alignment transition toward the orion bar, a well-characterized pdr, that undergoes intense irradiation from the trapezium cluster. multi wavelength sofia hawc+ polarimetric dust polarization observations is the ideal method to investigate that. the goal is to quantify to what extent the k-rat mechanism could contribute to the polarization. the rat theory predicts that the transition from b-rat to k-rat will happen faster for larger grains. our results constrain the grain sizes for which this transition can occur in the orion bar. we also explore the radiatively driven rotational disruption of the grains, that allegedly takes place in the high-radiation environment of the bar. we conclude that k-rat is not the dominant cause of dust polarization in the orion bar, because grain size at which the alignment shifts from b-rat to k-rat occurs, corresponds to grains too large to survive the rotational disruption. | the origin of dust polarization in the orion bar |
among all the available observational techniques for studying magnetic fields in the dense cold phase of the interstellar medium, linear polarization of spectral lines, referred to in the literature as the goldreich-kylafis effect (goldreich & kylafis 1981; hereafter "gk effect"), remains one of the most underutilized methods. in this study, we implement the gk effect into the multilevel, non-local thermodynamic equilibrium radiative transfer code pyrate. different modes of polarized radiation are treated individually with separate optical depths computed for each polarization direction. we benchmark our implementation against analytical results and provide tests for various limiting cases. in agreement with previous theoretical results, we find that in the multilevel case the amount of fractional polarization decreases when compared to the two-level approximation, but this result is subject to the relative importance between radiative and collisional processes. finally, we post-process an axially symmetric, non-ideal magnetohydrodynamic chemo-dynamical simulation of a collapsing prestellar core and provide theoretical predictions regarding the shape (as a function of velocity) of the polarization fraction of co during the early stages in the evolution of molecular clouds. the code is freely available to download. | a multilevel implementation of the goldreich-kylafis effect into the radiative transfer code pyrate |
carbon‑based electrodes represent a promising approach to improve stability and up‑scalability of perovskite photovoltaics. the temperature at which these contacts are processed defines the absorber grain size of the perovskite solar cell: in cells with low‑temperature carbon‑based electrodes (l‑cpscs), layer‑by‑layer deposition is possible, allowing perovskite crystals to be large (>100 nm), while in cells with high‑temperature carbon‑based contacts (h‑cpscs), crystals are constrained to 10–20 nm in size. to enhance the power conversion efficiency of these devices, the main loss mechanisms are identified for both systems. measurements of charge carrier lifetime, quasi‑fermi level splitting (qfls) and light‑intensity‑dependent behavior, supported by numerical simulations, clearly demonstrate that h‑cpscs strongly suffer from non‑radiative losses in the perovskite absorber, primarily due to numerous grain boundaries. in contrast, large crystals of l‑cpscs provide a long carrier lifetime (1.8 µs) and exceptionally high qfls of 1.21 ev for an absorber bandgap of 1.6 ev. these favorable characteristics explain the remarkable open‑circuit voltage of over 1.1 v in hole‑selective layer‑free l‑cpscs. however, the low photon absorption and poor charge transport in these cells limit their potential. finally, effective strategies are provided to reduce non‑radiative losses in h‑cpscs, transport losses in l‑cpscs, and to improve photon management in both cell types. | perovskite solar cells with carbon‑based electrodes – quantification of losses and strategies to overcome them |
the carrier lifetime is one of the key parameters for perovskite solar cells (pscs). however, it is still a great challenge to achieve long carrier lifetimes in perovskite films that are comparable with perovskite crystals owning to the large trap density resulting from the unavoidable defects in grain boundaries and surfaces. here, by regulating the electronic structure with the developed 2-thiopheneformamidinium bromide (thfabr) combined with the unique film structure of 2d perovskite layer caped 2d/3d polycrystalline perovskite film, an ultralong carrier lifetime exceeding 20 µs and carrier diffusion lengths longer than 6.5 µm are achieved. these excellent properties enable the thfa-based devices to yield a champion efficiency of 24.69% with a minimum voc loss of 0.33 v. the unencapsulated device retains ≈95% of its initial efficiency after 1180 h by max power point (mpp) tracking under continuous light illumination. this work provides important implications for structured 2d/(2d/3d) perovskite films combined with unique fa-based spacers to achieve ultralong carrier lifetime for high-performance pscs and other optoelectronic applications. | ultralong carrier lifetime exceeding 20 µs in lead halide perovskite film enable efficient solar cells |
the rates of excited-state decay through recombination processes determine the usefulness of a semiconductor for ambipolar devices. we find that recombination rates in chalcogenide perovskites are promising for continued progress towards solar cells. chalcogenides in the perovskite and related crystal structures ("chalcogenide perovskites" for brevity) may be useful for future optoelectronic and energy-conversion technologies inasmuch as they have good excited-state, ambipolar transport properties. in recent years, several studies have suggested that semiconductors in the ba–zr–s system have slow non-radiative recombination rates. here, we present a time-resolved photoluminescence (trpl) study of excited-state carrier mobility and recombination rates in the perovskite-structured material bazrs3, and the related ruddlesden–popper phase ba3zr2s7. we measure state-of-the-art single crystal samples, to identify properties free from the influence of secondary phases and random grain boundaries. we model and fit the data using a semiconductor physics simulation, to enable more direct determination of key material parameters than is possible with empirical data modeling. we find that both materials have shockley–read–hall recombination lifetimes on the order of 50 ns and excited-state diffusion lengths on the order of 5 μm at room temperature, which bodes well for ambipolar device performance in optoelectronic technologies including thin-film solar cells. | time-resolved photoluminescence studies of perovskite chalcogenides |
to overcome obstacle of unbalanced hole and electron diffusion behavior in perovskites, a novel type of rationally designed bulk-heterojunction with c60-fullerene electron extraction material coupled with perovskite is for the first time reported. a facile strategy is developed for pyrrole to modify c60 to realize co-soluble of c60 and perovskites, achieving co-deposition of perovskite/pyrrole-fullerene bulk-heterojunction film via a one-step-spin-coating process. the unique perovskite/pyrrole-fullerene bulk-heterojunction exhibits increased mobility, quenched fluorescence intensity, decreased electron lifetime, large recombination resistance and reduced trap density of states, greatly enhancing charge extraction and transfer ability, thus boosting photoelectric conversion efficiency of solar cells. introducing pyrrole-fullerene can effectively reduce grain boundaries and electron trap density to suppress electron-hole recombination. the enlarged interfacial area between pyrrole-fullerene and perovskite is essential for facilitating extraction of more free electrons from perovskite to fullerene electron acceptor, resulting in a balance of charge extraction and transport. a maximum power conversion efficiency of 18.9% with virtually no hysteresis for the bulk-heterojunction based perovskite solar cells with an optimized concentration of bulk-heterojunction can be obtained. the present strategy for high-performance bulk-heterojunction perovskite solar cells can be potential for industrial photovoltaic applications for its facile and low-cost process route. | one-step-spin-coating route for homogeneous perovskite/pyrrole-c60 fullerene bulk heterojunction for high performance solar cells |
hybrid chemical vapor deposition (hcvd) is a promising method for the up‑scalable fabrication of perovskite solar cells/modules (pscs/psms). however, the efficiency of the hcvd‑based perovskite solar cells still lags behind the solution‑processed pscs/psms. in this work, the oxygen loss of the electron transport layer of sno2 in the hcvd process and its negative impact on solar cell device performance are revealed. as the counter‑measure, potassium sulfamate (h2kno3s) is introduced as the passivation layer to both mitigate the oxygen loss issue of sno2 and passivate the uncoordinated pb2+ in the perovskite film. in parallel, n‑methylpyrrolidone (nmp) is used as the solvent to dissolve pbi2 by forming the intermediate phase of pbi2•nmp, which can greatly lower the energy barrier for perovskite nucleation in the hcvd process. the perovskite seed is employed to further modulate the kinetics of perovskite crystal growth and improve the grain size. the resultant solar cells yield a champion power conversion efficiency (pce) of 21.98% (0.09 cm2) with a stable output performance of 21.15%, and the pces of the mini‑modules are 16.16% (22.4 cm2, stable output performance of 14.72%) and 12.12% (91.8 cm2). furthermore, the unencapsulated small area device shows an outstanding operational stability with a t80 lifetime exceeding 4000 h. | holistic strategies lead to enhanced efficiency and stability of hybrid chemical vapor deposition based perovskite solar cells and modules |
we present a new theoretical estimate for the birthrate of r coronae borealis (rcb) stars that is in agreement with recent observational data. we find the current galactic birthrate of rcb stars to be ≈25% of the galactic rate of type ia supernovae, assuming that rcb stars are formed through the merger of carbon-oxygen and helium-rich white dwarfs. our new rcb birthrate (1.8 × 10-3 yr-1) is a factor of 10 lower than previous theoretical estimates. this results in roughly 180-540 rcb stars in the galaxy, depending on the rcb lifetime. from the theoretical and observational estimates, we calculate the total dust production from rcb stars and compare this rate to dust production from novae and born-again asymptotic giant branch (agb) stars. we find that the amount of dust produced by rcb stars is comparable to the amounts produced by novae or born-again post-agb stars, indicating that these merger objects are a viable source of carbonaceous pre-solar grains in the galaxy. there are graphite grains with carbon and oxygen isotopic ratios consistent with the observed composition of rcb stars, adding weight to the suggestion that these rare objects are a source of stardust grains. | r coronae borealis stars are viable factories of pre-solar grains |
mapbbr3 films were deposited on fto-glass substrates by the spin coating technique. these films were irradiated by cu ions with a flounce rate of 2 ×1014 ions/cm2, 4 ×1014 ions/cm2, and 6 ×1014 ions/cm2 respectively. mapbbr3 films exhibited a crystalline nature and a cubic structure, as verified by xrd. the mapbbr3 film irradiated by 4 ×1014 ions/cm2 cu ions has a large grain size (33 nm) and a small eg (2.11 ev). as a result, the trap-state densities within the perovskite bulk were suppressed at interfaces as well as in the bulk material for smooth and improved carrier transportation. the calculated valence and conduction band edges of mapbbr3 are '-5.60' and '-3.2', respectively. the film exposed to cu ions has the cb edge pushed towards the lower value, making it a preferable solar cell material. the non-irradiated and irradiated films by cu ions have higher carrier life times of 63 ns and 74 ns, respectively. the cell fabricated with ions/cm2 cu ions-mapbbr3 film displayed a champion device with ff (0.84), jsc (9.34 ma-cm-2), voc (1.098), and pce (8.59%). | understanding the influence of cu ions implantation towards highly efficient mapbbr3 perovskite solar cells |
the growth of solar silicon ingots by directional solidification using small random (chips) and large oriented (mono-chucks) seeds was carried out, and the defect formations using the ingots grown from the different seeds were compared. to have a similar growth environment, the seeds were placed side by side in the same crucible for the growth. it was observed that the silicon grown from small chips was more vulnerable to carbide precipitation, but the propagation of dislocation clusters was mitigated due to the existence of grain boundaries. on the other hand, the dislocation clusters could easily propagate in the mono-crystalline regime. as a result, as the ingot grew higher, more and larger dislocation clusters were found in the ingot from the large oriented seeds. images from etched pits, photoluminescence, and minority lifetime were used for the comparison. similar experiments were also carried in a commercial growth system, and the dislocation clusters in the growth from the small chip seeds were much less than that from the chuck seeds. | comparison of defect formations in solar silicon growth from small random and large oriented seeds |
a recent suggestion that acetamide, \ce{ch3c(o)nh2}, could be readily formed on water-ice grains by the acid induced addition of water across the \ce{cn} bond is now shown to be valid. computational modelling of the reaction between \ce{r-cn} (r = h, \ce{ch3}) and a cluster of 32 molecules of water and one \ce{h3o+} proceeds auto-catalytically to form firstly a hydroxy imine \ce{r-c(oh)=nh} and secondly an amide \ce{r-c(o)nh2}. quantum mechanical tunnelling, computed from small-curvature estimates, plays a key role in the rates of these reactions. this work represents the first credible effort to show how amides can be formed from abundant substrates, namely nitriles and water, reacting on a water-ice cluster containing catalytic amounts of hydrons in the interstellar medium with consequential implications towards the origins of life. | peptide bonds in the interstellar medium: facile catalytic formation from nitriles on water–ice grains |
two-photon excitation (2pe) microscopy allows contactless and non-destructive cross-sectional analysis of grain-boundary (gb) and grain-interior (gi) properties in polycrystalline solar cells, with measurements of doping uniformity, space-charge field distribution, and carrier dynamics in different regions of the device. using 2pe time-resolved microscopy, we analyzed charge-carrier lifetimes near the gbs and in the gi of polycrystalline thin-film cdte solar cells doped with as. when the grain radius is larger than the minority-carrier diffusion length, gi lifetimes are interpreted as the bulk lifetimes τb, and gb recombination velocity sgb is extracted by comparing recombination rates in the gi and near gbs. in as-doped cdte solar cells, we find τb = 1.0-2.4 ns and sgb = (1-4) × 105 cm/s. the results imply the potential to improve solar cell voltage via gb passivation and reduced recombination center concentration in the gi. | separating grain-boundary and bulk recombination with time-resolved photoluminescence microscopy |
a smelting multiple recrystallization strategy and its effects on the morphology, composition, and defects of cspbbri2 film were investigated. an optimal number (n = 2) of recrystallization cycles improved the crystallinity and phase purity, minimized the grain boundaries, and optimized the crystal structure, yielding a high-quality perovskite film with significantly reduced defects density. the corresponding photovoltaic devices exhibited a champion efficiency of 16.02% under am 1.5 g illumination and presented an even higher indoor efficiency of 33.50% under an led (2956 k, pin: 334.41 μw/cm2). this recrystallization method offers a promising strategy for developing high-performance indoor and outdoor photovoltaics. direct recrystallization in the cells was also explored to achieve enhanced stability and longer lifetime in humid conditions. | smelting recrystallization of cspbbri2 perovskites for indoor and outdoor photovoltaics |
grain boundaries (gbs) are defects originating in multi-crystalline silicon during crystal growth for device si solar cell fabrication. the presence of gbs changes the coordination of si, making it advantageous for charge carriers to recombine, which brings a significant reduction of carrier lifetimes. therefore, gbs can be highly detrimental for device performances. furthermore, gbs easily form vacancies with deep defect electronic states and are also preferential segregation sites for various impurity species, such as c, n, and o. we studied from first principles the correlation between structural, energetics, and electronic properties of the σ3{111} si gb with and without vacancies, and the segregation of c, n, and o atoms. c and o atoms strongly increase their ability to segregate when vacancies are present. however, the electronic properties of the σ3{111} si gb are not affected by the presence of o, while they can strongly change in the case of c. for n atoms, it is not possible to find a clear trend in the energetics and electronic properties both with and without vacancies in the gb. in fact, as n is not isovalent with si, as c and o, it is more flexible in finding new chemical arrangements in the gb structure. this implies a stronger difficulty in controlling the properties of the material in the presence of n impurity atoms compared to c and o impurities. | the role of si vacancies in the segregation of o, c, and n at silicon grain boundaries: an ab initio study |
context. contrary to what is expected from models of galactic chemical evolution, the isotopic fractionation of silicon (si) in the galaxy has recently been found to be constant. this finding calls for new observations, also at core scales, to re-evaluate the fractionation of si.aims: l1157-b1 is one of the outflow-shocked regions along the blue-shifted outflow that is driven by the class 0 protostar l1157-mm. it is an ideal laboratory for studying the material ejected from the grains on very short timescales because its chemical composition is representative of the composition of the grains.methods: we imaged 28sio, 29sio, and 30sio j = 2-1 emission towards l1157-b1 and b0 with the northern extended millimeter array (noema) interferometer as part of the seeds of life in space (solis) large project. we present here a study of the isotopic fractionation of sio towards l1157-b1. furthermore, we used the high spectral resolution observations on the main isotopologue, 28sio, to study the jet impact on the dense gas. we here also present single-dish observations obtained with the iram 30 m telescope and herschel-hifi. we carried out a non-local thermal equilibrium analysis using a large velocity gradient code to model the single-dish observations.results: from our observations we can show that (i) the 2-1 transition of the main isotopologue is optically thick in l1157-b1 even at high velocities, and (ii) the [29sio/30sio] ratio is constant across the source, and consistent with the solar value of 1.5.conclusions: we report the first isotopic fractionation maps of sio in a shocked region and show the absence of a mass-dependent fractionation in 29si and 30si across l1157-b1. a high-velocity bullet in 28sio has been identified, showing the signature of a jet impacting on the dense gas. with the dataset presented in this paper, both interferometric and single-dish, we were able to study the gas that is shocked at the b1a position and its surrounding gas in great detail. the reduced datacubes and spectra are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/640/a74 based on observations carried out with the iram noema interferometer. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain). | seeds of life in space (solis). viii. sio isotopic fractionation, and a new insight into the shocks of l1157-b1 |
agricultural sensors are powerful tools to optimize crop productivity while conserving natural resources. here we report a crop water-stress detector based on a plasmonically-enhanced micromechanical photoswitch capable of detecting water content in leaves that is lower than a predetermined threshold without consuming electrical power when the leaf is healthy. the detection mechanism exploits the energy in a specific narrow-spectral band of solar radiation reflected off leaves that is strongly correlated to the water content in plants. this biosensor relies on a spectrally selective infrared plasmonic absorber and a thermally sensitive micro-cantilever to harvest the reflected solar energy and further produce a digitized wakeup-bit only when the monitored leaf is water-stressed. in particular, we demonstrate that the detector activates a commercial water pump when a soybean plant is water-stressed. the 10-year battery lifetime of the proposed detector pave the way for the development of high-granularity, maintenance-free sensor networks for large-scale smart-farms. | zero standby power crop water-stress detector leading to the optimization of water usage and yield |
all‑inorganic cesium lead bromide (cspbbr3) perovskite solar cells have attracted enormous attention owing to their outstanding stability in comparison with organic–inorganic hybrid devices. the greatest weakness for inorganic cspbbr3 solar cells is their lower power conversion efficiencies, mainly arising from inferior light‑absorbance range and serious charge recombination at interfaces or within perovskite films. to address this issue, the lattice doping of lanthanide ions (ln3+ = la3+, ce3+, nd3+, sm3+, eu3+, gd3+, tb3+, ho3+, er3+, yb3+, and lu3+) into cspbbr3 films for all‑inorganic solar cells free of hole‑transporting materials and precious metal electrodes is presented. arising from the enlarged grain size and prolonged carrier lifetimes upon incorporating ln3+ ions into perovskite lattice, the performances of these inorganic cspbbr3 solar cell devices are significantly enhanced, achieving a champion efficiency as high as 10.14% and an ultrahigh open‑circuit voltage of 1.594 v under one sun illumination. meanwhile, the nearly unchanged efficiency upon persistent attack by 80% rh in air atmosphere over 110 d and enhanced thermal stability at 80 °c over 60 d provide new opportunities of promoting commercialization of all‑inorganic cspbbr3 perovskite solar cells. | lanthanide ions doped cspbbr3 halides for htm‑free 10.14%‑efficiency inorganic perovskite solar cell with an ultrahigh open‑circuit voltage of 1.594 v |
from time- and spatially resolved optical measurements, we show that extended defects can have a large effect on the charge-carrier recombination in ii-vi semiconductors. in cdte double heterostructures grown by molecular beam epitaxy on the insb (100)-orientation substrates, we characterized the extended defects and found that near stacking faults the space-charge field extends by 2-5 μm. charge carriers drift (with the space-charge field strength of 730-1,360 v cm-1) and diffuse (with the mobility of 260 ± 30 cm2 v-1 s-1) toward the extended defects, where the minority-carrier lifetime is reduced from 560 ns to 0.25 ns. therefore, the extended defects are nonradiative recombination sinks that affect areas significantly larger than the typical crystalline grains in ii-vi solar cells. from the correlative time-resolved photoluminescence and second-harmonic generation microscopy data, we developed a band-diagram model that can be used to analyze the impact of extended defects on solar cells and other electronic devices. | time-resolved correlative optical microscopy of charge-carrier transport, recombination, and space-charge fields in cdte heterostructures |
halide perovskites excel in the pursuit of highly efficient thin film photovoltaics, with power conversion efficiencies reaching 25.5% in single junction and 29.5% in tandem halide perovskite/silicon solar cell configurations. operational stability of perovskite solar cells remains a barrier to their commercialisation, yet a fundamental understanding of degradation processes, including the specific sites at which failure mechanisms occur, is lacking. recently, we reported that performance-limiting deep sub-bandgap states appear in nanoscale clusters at particular grain boundaries in state-of-the-art $cs_{0.05}fa_{0.78}ma_{0.17}pb(i_{0.83}br_{0.17})_{3}$ (ma=methylammonium, fa=formamidinium) perovskite films. here, we combine multimodal microscopy to show that these very nanoscale defect clusters, which go otherwise undetected with bulk measurements, are sites at which degradation seeds. we use photoemission electron microscopy to visualise trap clusters and observe that these specific sites grow in defect density over time under illumination, leading to local reductions in performance parameters. scanning electron diffraction measurements reveal concomitant structural changes at phase impurities associated with trap clusters, with rapid conversion to metallic lead through iodine depletion, eventually resulting in pinhole formation. by contrast, illumination in the presence of oxygen reduces defect densities and reverses performance degradation at these local clusters, where phase impurities instead convert to amorphous and electronically benign lead oxide. our work shows that the trapping of charge carriers at sites associated with phase impurities, itself reducing performance, catalyses redox reactions that compromise device longevity. importantly, we reveal that both performance losses and intrinsic degradation can be mitigated by eliminating these defective clusters. | local nanoscale defective phase impurities are the sites of degradation in halide perovskite devices |
designing next generation concentrated solar power plant solar receivers with current metallic alloys is extremely challenging due to high creep damage accumulation under high temperature operating conditions. new structural materials with high creep resistance must be sought to achieve a desired design life of 30 years to recover the plant capital cost. max phase materials are known to exhibit high creep resistance as well as high fracture toughness and therefore could be a viable option for high temperature receiver designs. this work assesses ti3sic2 max phase as a potential candidate for high temperature receivers through evaluating the creep-rupture life of a reference molten salt receiver. assessments are made for two different grain sizes - a fine-grained (3-5 µm) and a coarse-grained (~ 30 µm) ti3sic2 max phase. results indicate a design life of several tens of years can be achieved for the reference receiver using ti3sic2 max phase compared to less than a year design life using a high temperature nickel based alloy a740h. | assessment of ti3sic2 max phase as a structural material for high temperature receivers |
organic‑inorganic hybrid perovskite solar cells (pscs) have been extensively researched as a promising photovoltaic technology, wherein the orientation of the perovskite film plays a crucial role in the power conversion efficiency (pce) and stability. here, a seed‑mediated method is developed to in situ grow a layer of 2d perovskite seed for epitaxial growth of 3d perovskite atop it to construct a high‑quality 2d/3d heterojunction. it is found that the epitaxial 3d perovskite film exhibits a preferred [112] direction, which is different from traditional perovskites with a preferred [001] orientation. the oriented perovskite film consists of large‑sized grains with low defect density, long charge‑carrier lifetime, and good stability, resulting in efficient pscs with a champion efficiency of 24.83%. in addition, the devices exhibit high stability under ambient, thermal, and continuous light‑soaking conditions. this work provides an effective strategy for achieving high‑quality perovskite films with tunable orientation to simultaneously boost the efficiency and stability of pscs. | orientation engineering via 2d seeding for stable 24.83% efficiency perovskite solar cells |
organic‑inorganic hybrid two‑dimensional (2d) perovskites (n≤5) have recently attracted significant attention because of their promising stability and optoelectronic properties. normally, 2d perovskites contain a monocation [e.g., methylammonium (ma+) or formamidinium (fa+)]. reported here for the first time is the fabrication of 2d perovskites (n=5) with mixed cations of ma+, fa+, and cesium (cs+). the use of these triple cations leads to the formation of a smooth, compact surface morphology with larger grain size and fewer grain boundaries compared to the conventional ma‑based counterpart. the resulting perovskite also exhibits longer carrier lifetime and higher conductivity in triple cation 2d perovskite solar cells (pscs). the power conversion efficiency (pce) of 2d pscs with triple cations was enhanced by more than 80 % (from 7.80 to 14.23 %) compared to pscs fabricated with a monocation. the pce is also higher than that of pscs based on binary cation (ma+‑fa+ or ma+‑cs+) 2d structures. | enhanced charge transport by incorporating formamidinium and cesium cations into two‑dimensional perovskite solar cells |
the degradation/recovery phenomena in ultrathin film solar cells based on cds/cdte are theoretically analysed using sah-noyce-shockley theory for generation and recombination in the depletion region. this theory can explain the overlap of the depletion regions at both front and back contacts where the carrier generation and collection are as important as recombination mechanism. the value of physical parameters such as uncompensated defect density, carrier recombination lifetime and band bending at interface are critically important when reducing the thickness of cdte layer down to sub-micron. the rollover, materials inter-/out-diffusion, complex defect formation and the role of mobile ions are taken into consideration to obtain an insight into the physics of degradation/recovery phenomena in ultrathin cdte film solar cells. both mechanisms are precisely analysed drawing the schematics of the energy band diagrams and mobile ions transport paths which in this case is the grain interior. this means that we neglect the metal diffusion through the grain boundaries which are assumed to be completely passivated. this assumption enabled us to study the role of the defects on the carrier transport in the interiors rather than through the boundaries. | modelling of degradation/recovery phenomena in cds/cdte ultrathin film solar cells |
this study develops two model predictive control approaches to optimize microgrid dispatch, one with participation in real-time ancillary service markets and the other without participation. results are compared to a baseline logic-based control with case study data taken from a grid-tied 326 kw solar photovoltaic, 634 kw/634 kwh battery, and 350 kw diesel generator microgrid portfolio designed to serve an office building. annual performance evaluations show that model predictive control algorithms can reduce operating expenses by up to 13.73% when compared to logic-based controls, and through participation in ancillary service markets, model predictive control can reduce net operating expenses by up to 23.47%. revenue from ancillary service equated to 12.03% of operating costs, with approximately two-thirds of revenue from spinning reserve and one-third from non-spinning reserve. model predictive control with ancillary services maintained battery state of charge an average of 38.78% higher than batteries dispatched by model predictive control without market participation. this reduced battery cycling losses, minimized battery operation and maintenance expenses, and improved battery lifetime. sensitivity analyses indicate that model predictive control with more granular time steps and longer prediction horizons changes the dispatch schedule to further reduce operating costs. intraday simulations indicate that both model predictive control algorithms can adapt to differences in environmental conditions and pricing signals to minimize operational costs. this generalizable finding suggests the inherent modularity, scalability, and robustness of the proposed algorithms can benefit a variety of microgrid configurations and use cases. | model predictive control of microgrids for real-time ancillary service market participation |
although perovskite solar cells (pscs) have made great achievements during the past few years, the efficiency of pscs is only up to 25.5%, which is comparable to silicon-based solar cells. however, long-term stability is still an important problem for future commercialization. enormous efforts have been made to prolong the lifetime of pscs. the novel passivation strategy and advanced encapsulation are investigated, and great achievements are acquired. however, research on the basic understanding of the perovskite structure and the fabrication process of pscs is rare, which stints the initial research for the abecedarian. at the same time, the defects among the perovskite film caused by the uncontrollable crystallization process and the fragile ionic nature also deteriorate the efficiency and stability of the perovskite devices. herein, we summarized the investigations of the mechanism for perovskite materials and the manufacturing process of pscs. the composition of perovskite materials, the orientation of perovskite grain, and various fabrication processes are explained. simultaneously, the novel passivation strategy and technology are also discussed. we believe that a deeper understanding of the perovskite mechanism is beneficial to render more facilities for further development of perovskite application. | basic understanding of perovskite solar cells and passivation mechanism |
composition and film quality of perovskite are crucial for the further improvement of perovskite solar cells (pscs), including efficiency, reproducibility, and stability. here, it is demonstrated that by simply mixing 50% of formamidinium (fa+) into methylammonium lead iodide (mapbi3), a highly crystalline, stable phase, and compact, polycrystalline grain morphology perovskite is formed by using a solvent‑mediated phase transformation process via the synergism of dimethyl sulfoxide and diethyl ether, which shows long carrier lifetime, low trap state density, and a record certified 21.8% power conversion efficiency (pce) in pure‑iodide, alkaline‑metal‑free ma0.5fa0.5pbi3 perovskite‑based pscs. these pscs show very high operational stability, with 85% pce retention upon 1000 h 1 sun intensity illumination. a 17.33% pce module (6.5 × 7 cm2) is also demonstrated, attesting to the scalability of such devices. | the synergism of dmso and diethyl ether for highly reproducible and efficient ma0.5fa0.5pbi3 perovskite solar cells |
seeking strategies of promoting the charge separation and transport of the photo-active layer has been always of significance for the development of high-performance optoelectronic devices. we herein demonstrate an effective way of decorating wo3 nanocrystals in perovskite films for boosted photogenerated carriers transport. the wo3 nanocrystals are generated by a simple technique of pulsed laser irradiation in liquid, then introduced into the perovskite film based on the anti-solvent approach. such decoration is found helpful for the increase of the short-circuit current density (jsc) of the device, which leads to the increase of the photoconversion efficiency (pce) from 17.72% to 19.29%. the improved pce is mainly due to the decoration of the wo3 at the grain boundaries of perovskite films that facilitates the charge transport between the adjacent grains, which is evidenced by the quenching of the film photoluminescence, shortened carrier lifetime, and increased carrier mobility. we thus believe our study provides an effective way of embedding ordinary metal oxides in perovskite films for enhanced optoelectronic performance. | embedding of wo3 nanocrystals with rich oxygen-vacancies in solution processed perovskite film for improved photovoltaic performance |
sediment core er11-16 from køge bugt in southeast greenland is used to assess early holocene palaeoceanographic changes and sediment rafting from icebergs calved from the large outlet glaciers in the area. diatom analysis reconstructs variability in surface water temperature, salinity and sea-ice concentrations, and benthic foraminiferal assemblages is used to reconstruct subsurface ocean conditions. we report holocene thermal maximum in southeast greenland during the early holocene (at least since onset of the record 9100 cal yr bp) until around 4500 cal yr bp, which contrasts with a delay until the mid-holocene of the holocene thermal maximum in south and southwest greenland. the early holocene warming in southeast greenland was caused by a combination of high solar insolation and a weakened subpolar gyre, both of which served to warm the irminger current waters subducting onto the shelf. at the same time, the surface temperature was relatively high and sea-ice cover in the polar surface waters of the east greenland current was relatively low. high levels of iceberg rafting occurred in køge bugt during the early holocene, synchronously with these warm oceanic temperatures. this is attributed to an increase in iceberg production from the extensive, but retreating, greenland ice sheet. the warm surface conditions were interrupted by a marked and short-lived increase in sea ice around 8200 years ago, providing the first evidence of this global cold episode in southeast greenland. after 4500 cal. yr bp, sea-ice cover increased with an expansion of the east greenland current, suppressing the inflow of warmer subsurface irminger current water to the southeast greenland shelf. we relate this oceanic shift to the decreased northern hemisphere summer solar insolation. multi-centennial variability is observed in the grain size spectrum of iceberg rafted debris; a finding we interpret in the context of palaeoceanographic changes. | early holocene palaeoceanographic and glaciological changes in southeast greenland |
ii-vi semiconductors are used in numerous electro-optical applications. for example, cdte-based solar technology is cost competitive with other electricity generation sources, yet there is still significant room to improve. carrier lifetime has historically been well below the radiative recombination limit. lifetimes reaching beyond 100 ns can significantly enhance performance and enable novel device structures. here, double heterostructures (dhs) with passivated interfaces demonstrate lifetimes exceeding 1 μs, yet this appears only for cdsete and not for cdte dhs. we compare the passivation mechanisms in cdte and cdsete dhs. cdsete lifetimes on the order of 1 μs correspond to a combination of superior intragrain lifetime, extremely low grain boundary recombination and greater te4+ interfacial presence compared to cdte. | mechanisms for long carrier lifetime in cd(se)te double heterostructures |
the presence of surface and grain boundary defects in organic–inorganic halide perovskite films can be detrimental to both the performance and operational stability of perovskite solar cells (pscs). here, the effect of chloride additives is studied on the bulk and surface defects of the mixed cation and halide pscs. it is found that using an antisolvent technique, the perovskite film is divided into two layers, i.e., a bottom layer with large grains and a thin capping layer with small grains. the addition of formamidinium chloride (facl) into the precursor solution removes the small‑grained perovskite capping layer and suppresses the formation of bulk and surface defects, providing a perovskite film with enhanced crystallinity and large grain size of over 1 µm. time‑resolved photoluminescence measurements show longer lifetimes for perovskite films modified by facl and subsequently passivated by 1‑adamantylamine hydrochloride as compared to the reference sample. impedance spectroscopy measurements show that these treatments reduce the recombination in the pscs, leading to a champion device with power conversion efficiency (pce) of 21.2%, an open circuit voltage of 1152 mv and negligible hysteresis. the cl treated psc also shows improved operational stability with only 12% pce loss after 700 h under continuous illumination. | controllable perovskite crystallization via antisolvent technique using chloride additives for highly efficient planar perovskite solar cells |
anodically formed tio2 nanotube arrays (tntas) constitute an optoelectronic platform that is being studied for use as a photoanode in photoelectrocatalytic cells, as an electron transport layer (etl) in solar cells and photodetectors, and as an active layer for chemiresistive and microwave sensors. for optimal transport of charge carriers in these one-dimensional polycrystalline ordered structures, it is desirable to introduce a preferential texture with the grains constituting the nanotube walls aligned along the transport direction. through x-ray diffraction analysis, we demonstrate that choosing the right water content in the anodization electrolyte and the use of a post-anodization zinc ion treatment can introduce a preferential texture in sub-micron length transparent tntas formed on non-native substrates. the incorporation of 1.5 atom% of zn in tio2 nanotubes prior to annealing, was found to consistently result in the strongest preferential orientation along the [001] direction. [001] oriented tntas exhibited a responsivity of 523 a w-1 at a bias of 2 v for 365 nm photons, which is among the highest reported performance values for ultraviolet photodetection using titania nanotubes. furthermore, the textured nanotubes without a zn2+ treatment showed a significantly enhanced performance in halide perovskite solar cells that used tntas as the etl. | preferentially oriented tio2 nanotube arrays on non-native substrates and their improved performance as electron transporting layer in halide perovskite solar cells |
dust grains of organic matter were the main reservoir of c and n in the forming solar system and are thus considered to be an essential ingredient for the emergence of life. however, the physical environment and the chemical mechanisms at the origin of these organic grains are still highly debated. in this study, we report high-precision triple oxygen isotope composition for insoluble organic matter isolated from three emblematic carbonaceous chondrites, orgueil, murchison, and cold bokkeveld. these results suggest that the o isotope composition of carbonaceous chondrite insoluble organic matter falls on a slope 1 correlation line in the triple oxygen isotope diagram. the lack of detectable mass-dependent o isotopic fractionation, indicated by the slope 1 line, suggests that the bulk of carbonaceous chondrite organics did not form on asteroidal parent bodies during low-temperature hydrothermal events. on the other hand, these o isotope data, together with the h and n isotope characteristics of insoluble organic matter, may indicate that parent bodies of different carbonaceous chondrite types largely accreted organics formed locally in the protosolar nebula, possibly by photochemical dissociation of c-rich precursors. | insights into the origin of carbonaceous chondrite organics from their triple oxygen isotope composition |
oxygen isotope exchange experiments between tens of nanometer-sized amorphous enstatite grains and water vapor were carried out under a condition of protoplanetary disk-like low water vapor pressure in order to investigate the survivability of distinct oxygen isotope signatures of presolar silicate grains in the protosolar disk. oxygen isotope exchange between amorphous enstatite and water vapor proceeded at 923-1003 k and 0.3 pa of water vapor through diffusive isotope exchange in the amorphous structure. the rate of diffusive isotope exchange is given by d (m2 s-1) = (5.0 ± 0.2) × 10-21 exp[-161.3 ± 1.7 (kj mol-1) r-1 (1/t-1/1200)]. the activation energy for the diffusive isotope exchange for amorphous enstatite is the same as that for amorphous forsterite within the analytical uncertainties, but the isotope exchange rate is ~30 times slower in amorphous enstatite because of the difference in frequency factor of the reaction. the reaction kinetics indicates that 0.1-1 μm-sized presolar amorphous silicate dust with enstatite and forsterite compositions would avoid oxygen isotope exchange with protosolar disk water vapor only if they were kept at temperatures below ~500-650 k within the lifetime of the disk gas. | survivability of presolar oxygen isotopic signature of amorphous silicate dust in the protosolar disk |
transferring the high power conversion efficiencies (pces) of spin‑coated perovskite solar cells (pscs) on the laboratory scale to large‑area photovoltaic modules requires a significant advance in scalable fabrication methods. digital inkjet printing promises scalable, material, and cost‑efficient deposition of perovskite thin films on a wide range of substrates and in arbitrary shapes. in this work, high‑quality inkjet‑printed triple‑cation (methylammonium, formamidinium, and cesium) perovskite layers with exceptional thicknesses of >1 µm are demonstrated, enabling unprecedentedly high pces > 21% and stabilized power output efficiencies > 18% for inkjet‑printed pscs. in‑depth characterization shows that the thick inkjet‑printed perovskite thin films deposited using the process developed herein exhibit a columnar crystal structure, free of horizontal grain boundaries, which extend over the entire thickness. a thin film thickness of around 1.5 µm is determined as optimal for psc for this process. up to this layer thickness x‑ray photoemission spectroscopy analysis confirms the expected stoichiometric perovskite composition at the surface and shows strong deviations and inhomogeneities for thicker thin films. the micrometer‑thick perovskite thin films exhibit remarkably long charge carrier lifetimes, highlighting their excellent optoelectronic characteristics. they are particularly promising for next‑generation inkjet‑printed perovskite solar cells, photodetectors, and x‑ray detectors. | inkjet‑printed micrometer‑thick perovskite solar cells with large columnar grains |
in addition to high efficiencies, upscaling and long‑term operational stability are key pre‑requisites for moving perovskite solar cells toward commercial applications. in this work, a strategy to fabricate large‑area uniform and dense perovskite films with a thickness over one‑micrometer via a two‑step coating process by introducing nh4cl as an additive in the pbi2 precursor solution is developed. incorporation of nh4cl induces the formation of the intermediate phases of x[nh4+]·[pbi2clx]x− and hpbi3−xclx, which can effectively retard the crystallization rate of perovskite leading to uniform and compact full‑coverage perovskite layers across large areas with high crystallinity, large grain sizes, and small surface roughness. the 5 × 5 and 10 × 10 cm2 perovskite solar modules (psms) based on this method achieve a power conversion efficiency (pce) of 14.55% and 10.25%, respectively. these psms also exhibit good operational stability with a t80 lifetime (the time during which the solar module pce drops to 80% of its initial value) under continuous light illumination exceeding 1600 h (5 × 5 cm2) and 1100 h (10 × 10 cm2), respectively. | scalable fabrication of >90 cm2 perovskite solar modules with >1000 h operational stability based on the intermediate phase strategy |
understanding the relationship of photoexcited carrier lifetimes, mobilities, and recombination mechanisms to structural properties and processing of photovoltaic (pv) absorber materials is critical to the design of efficient solar cells. carrier dynamics in pv absorbers have conventionally been characterized by time-resolved photoluminescence (trpl), but trpl may not be suitable or straightforward for all absorbers. alternative noncontact methods can enable measurement of ultrafast carrier dynamics for a wider range of materials. here, we demonstrate the complementary use of time-resolved terahertz spectroscopy (trts) and near-infrared transient reflectance (nirtr) spectroscopy along with trpl to elucidate photoexcited carrier dynamics in a high-quality copper-poor, zinc-rich kesterite cu2zn sn se4 (cztse) single crystal. the single-crystalline nature of the sample eliminates complications arising from grain boundaries, secondary phases, and interfaces associated with thin-film growth. a single-crystal-based pv device exhibited an efficiency of 5.7% and an open circuit voltage (voc) of 400 mv, consistent with the quasi-fermi-level splitting determined using absolute photoluminescence. nirtr showed picosecond-scale cooling and relaxation of carriers into a distribution of band-tail states while trts revealed a characteristic time scale of 200-260 ps for recombination. hall effect and trts measurements revealed electron and hole mobilities in the range of 50 -100 cm2/v s . these dynamics result in a characteristic minority carrier diffusion length of less than 200 nm, leading to incomplete carrier collection, as confirmed by a strongly decreasing external quantum efficiency at long wavelengths. our approach combining ultrafast spectroscopy and device measurements can lead to more detailed understanding of performance-limiting photophysical processes and can accelerate the development of more efficient pvs. | relating carrier dynamics and photovoltaic device performance of single-crystalline cu2zn sn se4 |
recently, cdte-based solar cells have achieved high power conversion efficiency by alloying with cdse. besides the increased photocurrent due to the reduced bandgap, it is also reported that the electron lifetime in the alloyed system is higher than that in the cdte-based system. however, the origin of the improved lifetime is not clear. in this work, using first-principles calculations and the low energy σ3 (112) grain boundary (gb) in polycrystalline cdte as an example, we show that in the alloyed system, se has the tendency to move toward the σ3 (112) gb. consequently, se at the gbs in cdte can effectively passivate the deep gb defect levels, thus reducing carrier recombination and improve solar cell performance. more specifically, we find that the σ3 (112) gb with te-core has the lowest formation energy among the electronically detrimental gb configurations in polycrystalline cdte. the σ3 (112) gb with te-core introduces a deep defect state in the bandgap of cdte, which can act as nonradiative recombination center and reduces the carrier lifetime of cdte. when se segregates to gb and substitutes the te atom at the te dimer site, due to the lower energy of se 4p orbital and the weak coupling between the dimer elements in the gb core, the deep gb states will shift to shallower states toward the valance band maximum of cdte. this can increase the carrier lifetime of the cdsete layer and thus provide a viable explanation to the improved lifetime and performance of se-alloyed cdte solar cells. | enhanced performance of se-alloyed cdte solar cells: the role of se-segregation on the grain boundaries |
in this work, we studied the influence of tio2 morphology on photovoltaic performances, electron transport and charge recombination properties of nanotubes/nanoparticle-based dye-sensitized solar cells. nanotubes and nanoparticles nanostructures have been synthetized by hydrothermal and sol-gel methods, and then characterized using x-ray diffraction, scanning and transmission electron microscopies. electrochemical impedance spectroscopy results have shown that the recombination process becomes less significant when nanotubes amount decreases in the cells induced by the low recombination site concentration due to the small surface area of nanotubes regarding to nanoparticles. however, despite the low recombination rate, a drastic decrease of lifetime has been observed indicating a very low charge transport due to the poor interconnectivity of randomly dispersed tio2 nanotubes in the high nanotubes content cells. proper content of 10-20% nanotubes pile up effectively with nanoparticles favoring a good connection between the grains, and thus facilitating the charge transport in tio2 network. | impedance investigation of tio2 nanotubes/nanoparticles-based dye-sensitized solar cells |
the recent discovery of hot dust grains in the vicinity of main-sequence stars has become a hot issue among the scientific community of debris disks. hot grains must have been enormously accumulated near their sublimation zones, but it is a mystery how such a high concentration of hot grains is sustained. the most difficult conundrum is that the size of hot dust grains is estimated to lie in the submicrometer range, while submicrometer-sized grains are instantly swept away from near-stellar environments by stellar radiation pressure. one and only mechanism proposed for prolonging the residence time of hot grains in the near-stellar environments is trapping of charged nanoparticles by stellar magnetic fields. we revisit the model of magnetic grain trapping around main-sequence stars of various spectral classes by taking into account sublimation and electric charging of the grains. the model of magnetic grain trapping predicts that hot dust grains are present in the vicinity of main-sequence stars with high rotation velocities and intermediate magnetic-field strengths. on the contrary, we find that the detection of hot dust grains has no correlation with the rotation velocities of central stars nor the magnetic field strengths of the stars. our numerical evaluation of electric grain charging indicates that the surface potential of submicrometer-sized grains in the vicinity of main-sequence stars is typically 4- 5v , which is one order of magnitude smaller than the value assumed by the model of magnetic grain trapping. on the basis of our numerical simulation on sublimation of dust grains in the vicinity of a star, it turns out that their lives end due to sublimation in a timescale much shorter than the period of one revolution at the gyroradius. it is, therefore, infeasible to dynamically extend the dwell time of hot grains inside the sublimation zone by magnetic trapping, while we cannot completely rule out the possibility of magnetic grain trapping outside the sublimation zone where the strength of stellar magnetic field has been underestimated in the previous model. nevertheless, the independence of hot dust detection on the stellar rotational velocity and magnetic field strength favors a scenario that some other (yet unnoticed/overlooked) ubiquitous mechanism of grain trapping is at work. | hot grain dynamics by electric charging and magnetic trapping in debris disks |
metal‑halide perovskite solar cells (pscs) have had a transformative impact on the renewable energy landscape since they were first demonstrated just over a decade ago. outstanding improvements in performance have been demonstrated through structural, compositional, and morphological control of devices, with commercialization now being a reality. here the authors present an aerosol assisted solvent treatment as a universal method to obtain performance and stability enhancements in pscs, demonstrating their methodology as a convenient, scalable, and reproducible post‑deposition treatment for pscs. their results identify improvements in crystallinity and grain size, accompanied by a narrowing in grain size distribution as the underlying physical changes that drive reductions of electronic and ionic defects. these changes lead to prolonged charge‑carrier lifetimes and ultimately increased device efficiencies. the versatility of the process is demonstrated for pscs with thick (>1 µm) active layers, large‑areas (>1 cm2) and a variety of device architectures and active layer compositions. this simple post‑deposition process is widely transferable across the field of perovskites, thereby improving the future design principles of these materials to develop large‑area, stable, and efficient pscs. | aerosol assisted solvent treatment: a universal method for performance and stability enhancements in perovskite solar cells |
when studying chemistry of photodissociation regions (pdrs), time dependence becomes important as visual extinction increases, since certain chemical time-scales are comparable to the cloud lifetime. dust temperature is also a key factor, since it significantly influences gas temperature and mobility on dust grains, determining the chemistry occurring on grain surfaces. we present a study of the dust temperature impact and time effects on the chemistry of different pdrs, using an updated version of the meijerink pdr code and combining it with the time-dependent code nahoon. we find the largest temperature effects in the inner regions of high g0 pdrs, where high dust temperatures favour the formation of simple oxygen-bearing molecules (especially that of o2), while the formation of complex organic molecules is much more efficient at low dust temperatures. we also find that time-dependent effects strongly depend on the pdr type, since long time-scales promote the destruction of oxygen-bearing molecules in the inner parts of low g0 pdrs, while favouring their formation and that of carbon-bearing molecules in high g0 pdrs. from the chemical evolution, we also conclude that, in dense pdrs, co2 is a late-forming ice compared to water ice, and confirm a layered ice structure on dust grains, with h2o in lower layers than co2. regarding steady state, the pdr edge reaches chemical equilibrium at early times (≲105 yr). this time is even shorter (<104 yr) for high g0 pdrs. by contrast, inner regions reach equilibrium much later, especially low g0 pdrs, where steady state is reached at ∼106-107 yr. | dust temperature and time-dependent effects in the chemistry of photodissociation regions |
context. previous studies have discovered a population of small granules with diameters less than 800 km located in the intergranular lanes showing differing physical properties. high resolution simulations and observations of the solar granulation, in combination with automated segmentation and temporal tracking algorithms, allow us to study the evolution of the structural and physical properties of these granules and surrounding vortex motions with high temporal and spatial accuracy.aims: we focus on the dynamics of granules, that is, the lifetime of granular cells, the fragmentation behavior, the variation of size, position, emergent intensity and vertical velocity over time and the influence of strong vortex motions. of special interest are the dynamics of small granules compared to regular-sized granules.methods: we developed a temporal tracking algorithm based on our previously developed segmentation algorithm for solar granulation. this was applied to radiation hydrodynamics simulations and high resolution observations of the quiet sun by sunrise/imax.results: the dynamics of small granules differ in regard to their diameter, intensity and depth evolution compared to the population of regular granules. the tracked granules in the simulation and observations reveal similar dynamics regarding their lifetime, evolution of size, vertical velocity and intensity. the fragmentation analysis shows that the majority of granules in the simulations do not fragment, while the opposite was found in the observations. strong horizontal and vertical vortex motions were detected at the location of small granules. compared to granules, regions of strong vertical vorticity show higher intensities and higher downflow velocities, and live up to several minutes.conclusions: the analysis of granules separated according to their diameter in different groups reveals strongly differing behaviors. the largest discrepancies can be found within the groups of small, medium-sized and large granules. therefore, these groups have to be analyzed independently. the predominant location of vortex motions on and close to small granules indicates a strong influence on the dynamics of granules. | dynamics of small-scale convective motions |
commercially available jeffamines (polyetheramine) with average molecular weights of 2000 and 3000 g mol-1; one (m2005), two (d2000), and three (t3000) primary amino groups end-capping on the polyether backbone; and propylene oxide (po) and ethylene oxide (eo) functionality were explored as additives for application in mapbi3 perovskite solar cells (pscs). the results indicated that the embedding of jeffamine additives effectively passivates the defects in the grain boundaries of perovskite through the coordination bonding between the nitrogen atom and the uncoordinated lead ion of perovskite. we fabricated p-i-n psc devices with the structure of glass/indium tin oxide (ito)/niox/ch3nh3pbi3 (with and without jeffamine)/pc61bm/bcp/ag. we observed the interaction between the jeffamine and perovskites. this interaction led to increased lifetimes of the carriers of perovskite, which enabled the construction of high-performance p-i-n pscs. for the jeffamine-d2000-derived device, we observed an increase in the power conversion efficiency from 14.5% to 16.8% relative to the control device. furthermore, the mechanical properties of the perovskite films were studied. the interaction between the additive and perovskite reinforced the flexibility of the thin film, which may pave the way for stretchable optoelectronics. | commercially available jeffamine additives for p-i-n perovskite solar cells |
solution-processed organic/inorganic hybrid halide perovskites are a class of very promising photovoltaic materials because of their extraordinary optoelectronic properties. however, numerous intrinsic defects within perovskite films limit the performance enhancement of perovskite solar cells (pscs). herein, we introduce three different alkali metal fluoride additives into the perovskite precursor to modulate the defect behaviors. the addition of alkali metal fluorides, especially potassium fluoride (kf), significantly passivates grain boundaries and point defects within bulk perovskite films, contributing to increased carrier lifetime and reduced defect state density. by optimizing the concentration of additives, the psc device with 1% kf added has realized a significantly enhanced power conversion efficiency of 20.11%, and ignorable hysteresis. | defect passivation in ch3nh3pbi3 films using alkali metal fluoride additives for highly efficient perovskite solar cells |
interfacial engineering, grain boundary, and surface passivation in organic–inorganic hybrid perovskite solar cells (hypscs) are effective in achieving high performance and enhanced durability. organic additives and inorganic doping are generally used to chemically modify the surface contacting charge transport layers, and/or grain boundaries so as to reduce the defect density. here, a simple but tricky one‑step method to dope organic–inorganic hybrid perovskite with ge for the first time is reported. unlike ge doping to all‑inorganic perovskites, application of gei2 in organic–inorganic perovskite precursors is challenging due to the extremely poor solubility of gei2 in hybrid perovskite ink, leading to failure in the formation of uniform films. however, it is found that addition of methylammonium chloride (macl) into the precursor remarkably increases the solubility of gei2. this macl‑assisted ge doping of hybrid perovskites produces high‑quality crystalline film with its surface passivated with nonvolatile gei2 (geo2) and the volatile macl additive also improves the uniformity of geo2 distribution in the perovskite films. the resulting ge‑doped mixed cation and mixed halide perovskite films with composition fa0.83ma0.17ge0.03pb0.97(i0.9br0.1)3 show superior photoluminescence lifetime, power conversion efficiency above 22%, and greater stability toward illumination and humidity, outperforming photovoltaic properties of hypscs prepared without the ge doping. | macl‑assisted ge doping of pb‑hybrid perovskite: a universal route to stabilize high performance perovskite solar cells |
we report the first microstructural confirmation of circumstellar magnetite, identified in a petrographic thin section of the lapaz icefield 031117 co3.0 chondrite. the o-isotopic composition of the grain indicates an origin in a low-mass (∼2.2 m⊙), approximately solar metallicity red/asymptotic giant branch (rgb/agb) star undergoing first dredge-up. the magnetite is a single crystal measuring 750 × 670 nm, is free of defects, and is stoichiometric fe3o4. we hypothesize that the magnetite formed via oxidation of previously condensed fe dust within the circumstellar envelope of its progenitor star. using an empirically derived rate constant for this reaction, we calculate that such oxidation could have occurred over timescales ranging from approximately ∼9000-500,000 years. this timescale is within the lifetime of estimates for dust condensation within rgb/agb stars. | circumstellar magnetite from the lap 031117 co3.0 chondrite |
positron annihilation lifetime spectroscopy (pals) and doppler broadening positron annihilation spectroscopy (db-pas) depth profiling demonstrate pronounced growth of vacancy clusters at the grain boundaries of as-deposited al-doped zno films deposited as transparent conductive oxide (tco) on cu (in ,ga ) s e2 (cigs) solar cells upon accelerated degradation at 85°c/85 % relative humidity. quantitative fractions of positrons trapped either in the vacancy clusters at the grain boundaries or in zn monovacancies inside the grains of zno:al were obtained by detailed analysis of the pals data using a positron trapping model. the time and depth dependence of the positron doppler depth profiles can be accurately described using a planar diffusion model, with an extracted diffusion coefficient of 35 n m2/hour characteristic for in-diffusion of molecules such as h2o and c o2 into zno:al tco films via the grain boundaries, where they react with the zno:al. this leads to increased open volume at the grain boundaries that imposes additional transport barriers and may lead to charge carrier trapping and nonradiative recombination. simultaneously, a pronounced increase in series resistance and a strong reduction in efficiency of the zno:al capped cigs solar cells is observed on a remarkably similar timescale. this strongly indicates that these atomic-scale processes of molecular in-diffusion and creation of open volume at the grain boundaries play a key role in the degradation of the solar cells. physh: solar cells, positron annihilation spectroscopy, grain boundaries, vacancies, thin films, diffusion, electrical properties, solid state chemistry, optoelectronics | evolution and role of vacancy clusters at grain boundaries of zno:al during accelerated degradation of cu (in ,ga ) s e2 solar cells revealed by positron annihilation |
although the field of solar cells is the most popular application of perovskite materials, their use in radiation detection applications is emerging. the success of perovskites as radiation detectors rests partly on the same material properties that have led to successful optoelectronics applications, meaning that other specific properties, like large stopping power, high mobility lifetime product, fast response, and large bulk resistance, play a role. in this respect, inorganic perovskites are attracting a lot of attention as scintillator materials with performances sensitive to material shape (single crystals, nanocrystals, and thin films) and growth methods. in this study, we report on the morphological, structural, and optical response of thin cspbbr3-based perovskite films, deposited by pulsed laser deposition (pld) and post-growth annealed at 350°c in air, following excitation by different particle sources. the annealing treatment resulted in a prompt structural refinement, grain growth, and oxygen bonding to the pb phase together with an enrichment of the surface in chemo-adsorbed oxygen probably due to cs-o interactions, as evidenced by x-ray photoelectron spectroscopy. the film behavior under 2 mev h+ ion beam irradiation at different fluences was analyzed together with its scintillation properties following an interaction with α particles from an am-241 radioactive source demonstrating a very fast response for an inorganic material (∼5ns) and a photoelectron yield of about ∼47% with respect to a commercial csi:tl scintillator. | high scintillation yield and fast response to alpha particles from thin perovskite films deposited by pulsed laser deposition |
perovskite solar cells (pscs) with state‑of‑the‑art efficiencies contain thermally unstable methylammonium (ma). here, interfacial passivation with pentafluorophenylhydrazine (5f‑phz) to fabricate efficient and stable ma/br‑free pscs is introduced. the 5f‑phz surface treatment quenches the pbi2 and δ‑perovskite phase formed in the pristine film. the surface passivation ameliorates the film chemistries at the surface with modulation of interface band alignment as a consequence of halogen bonding with fluoroarene moieties or nh–nh2 terminals. this results in a much longer carrier lifetime with the passivation at the surface and grain boundaries trap centers. as a result, it boosts the power conversion efficiency (pce) (area ≈ 1 cm2) from 18.10% to 22.29% (voc ≈ 1.096–1.178 v) with superior operational thermal stability. a certified pce of 21.01% with a large area of ≈1.026 cm2 is also achieved. it is found that the surface passivation forms an interfacial embedded layer subsequent to attenuation of defect densities and suppression of ion migration, which is supported by density‑function‑theory calculation. importantly, this approach is effective in enhancing the pce of narrow and wide bandgap perovskite systems. thus, this work opens up a new technique for interface modulation with fluoroarene functional derivatives to achieve superior device performance and stability. | interfacial embedding for high‑efficiency and stable methylammonium‑free perovskite solar cells with fluoroarene hydrazine |
metal halide perovskite solar cells (pscs) have developed rapidly in recent years, due to their high performance and low-cost solution-based fabrication process. these excellent properties are mainly attributed to the high defect tolerance of polycrystalline perovskite films. meanwhile, these defects can also facilitate ion migration and carrier recombination, which cause the device performance and the long-term stability of pscs to deteriorate heavily. therefore, it is critical to passivate the defects, especially at the surfaces of perovskite grains where the defects are most concentrated due to the dangling bonds. here we propose a surface-capping engineering (sce) method to construct 'dangling-bond-free' surfaces for perovskite grains. diamine iodide (methylenediammonium diiodide, mdai2) was used to construct an electroneutral pbx6-mda-pbx6 (x = cl, br or i) layer at the perovskite surfaces. compared to the monovalent fa+ which can only coordinate one [pbx6]4- slab, the bivalent mda2+ can coordinate two [pbx6]4- slabs on both sides, thus realizing a dangling-bond-free surface. solar cells based on sce-perovskite films exhibited a higher power conversion efficiency (pce) of 21.6%, compared with 19.9% of the control group; and maintained over 96% of its initial pce after 13 h during the maximum power point tracking test under continuous am1.5g illumination, whereas the control group only lasted 1.5 h. constructing a dangling-bond-free capping layer on the grain boundary opens new avenues for the fabrication of ultralow-defect polycrystalline semiconductors, paving the way to further improve the pce and lifetime of pscs. | surface-capping engineering for electrically neutral surface of perovskite films and stable solar cells |
we present alma band 6 observations of the luminous blue variable η car obtained within the almagal program. we report sio j = 5 → 4, sis j = 12 → 11, and sin n = 5 → 4 emission in the equatorial region of the homunculus nebula, constituting the first detection of silicon- and sulfur-bearing molecules in the outskirts of a highly evolved, early-type massive star. the sio, sis, and sin trace a clumpy equatorial ring that surrounds the central binary at a projected distance of ~2″, delineating the inner rims of the butterfly-shaped dusty region. the formation of silicon-bearing compounds is presumably related to the continuous recycling of dust due to the variable wind regime of η car, which destroys grains and releases silicon back to the gas phase. we discuss possible formation routes for the observed species, contextualizing them within the current molecular inventory of η car. we find that the sio and sis fractional abundances in localized clumps of the ring, 6.7 × 10-9 and 1.2 × 10-8, respectively, are exceptionally lower than those measured in c- and o-rich agb stars and cool supergiants, while the higher sin abundance, 3.6 × 10-8, evidences the nitrogen-rich chemistry of the ejecta. these abundances must be regarded as strict upper limits, since the distribution of h2 in the homunculus is unknown. in any case, these findings shed new light on the peculiar molecular ecosystem of η car and establish its surroundings as a new laboratory to investigate the life cycle of silicate dust in extreme astrophysical conditions. | first detection of silicon-bearing molecules in η car |
with power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the shockley‑queisser limit. one approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of mascn (ma = methylammonium) and excess pbi2 have been shown to modify film grain structure and improve performance. however, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. in this study, a newly developed carrier‑resolved photo‑hall (crph) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. crph measurements on n‑type mapbi3 films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess pbi2 added to the precursor solution, with little change noted in electron and hole mobility values. grain size variation (120–2100 nm) and mascn addition induce no significant change in carrier‑related parameters considered, highlighting the benign nature of the grain boundaries and that excess pbi2 must predominantly passivate bulk defects rather than defects situated at grain boundaries. this study offers a unique picture of additive impact on mapbi3 optoelectronic properties as elucidated by the new crph approach. | impact of pbi2 passivation and grain size engineering in ch3nh3pbi3 solar absorbers as revealed by carrier‑resolved photo‑hall technique |
intrigued by the extended red giant clump (rc) stretching across the color-magnitude diagram of the stars in a 50 × 50 pc2 region of the large magellanic cloud (lmc) containing the clusters ngc 1938 and ngc 1939, we have studied the stellar populations to learn about the properties of the interstellar medium (ism) in this area. the extended rc is caused by a large and uneven amount of extinction across the field. its slope reveals anomalous extinction properties, with av/e(b - v) ≃ 4.3, indicating the presence of an additional gray component in the optical contributing about 30% of the total extinction in the field and requiring big grains to be about twice as abundant as in the diffuse ism. this appears to be consistent with the number of big grains injected into the surrounding ism by the about 70 sn ii explosions estimated to have occurred during the lifetime of the ∼120 myr old ngc 1938. although this cluster appears relatively small today and would be hard to detect beyond the distance of m31, with an estimated initial mass of ∼4800 m⊙, ngc 1938 appears to have seriously altered the extinction properties in a wide area. this has important implications for the interpretation of luminosities and masses of star-forming galaxies both nearby and in the early universe. | anomalous extinction toward ngc 1938 |
photoactive perovskite semiconductors are highly tunable, with numerous inorganic and organic cations readily incorporated to modify optoelectronic properties. however, despite the importance of device reliability and long service lifetimes, the effects of various cations on the mechanical properties of perovskites are largely overlooked. in this study, the cohesion energy of perovskites containing various cation combinations of methylammonium, formamidinium, cesium, butylammonium, and 5‑aminovaleric acid is reported. a trade‑off is observed between the mechanical integrity and the efficiency of perovskite devices. high efficiency devices exhibit decreased cohesion, which is attributed to reduced grain sizes with the inclusion of additional cations and pbi2 additives. microindentation hardness testing is performed to estimate the fracture toughness of single‑crystal perovskite, and the results indicated perovskites are inherently fragile, even in the absence of grain boundaries and defects. the devices found to have the highest fracture energies are perovskites infiltrated into a porous tio2/zro2/c triple layer, which provide extrinsic reinforcement and shielding for enhanced mechanical and chemical stability. | effect of cation composition on the mechanical stability of perovskite solar cells |
although the power conversion efficiency of perovskite solar cells has improved rapidly, a rational path for further improvement remains unclear. the effect of large morphological heterogeneity of polycrystalline perovskite films on their device performance by photoluminescence (pl) microscopy has now been studied. contrary to the common belief on the deleterious effect of morphological heterogeneity on carrier lifetimes and diffusivities, in neat ch3nh3pbi3(cl) polycrystalline perovskite films, the local (intra‑grain) carrier diffusivities in different grains are all surprisingly high (1.5 to 3.3 cm2 s−1; comparable to bulk single‑crystals), and the local carrier lifetimes are long (ca. 200 ns) and surprisingly homogenous among grains, and uniform across grain boundary and interior. however, there is a large heterogeneity of carrier extraction efficiency at the perovskite grain–electrode interface. improving homogeneity at perovskite grain–electrode contacts is thus a promising direction for improving the performance of perovskite thin‑film solar cells. | limiting perovskite solar cell performance by heterogeneous carrier extraction |
all‑inorganic perovskite solar cells (pscs) have recently received growing attention as a promising template to solve the thermal instability of organic–inorganic pscs. however, the thermodynamic phase instability and relatively low device efficiency pose challenges. herein, highly efficient and stable cspbi1.5br1.5 compositional perovskite‑based inorganic pscs are fabricated using an organic dye, fluorescein isothiocyanate (fitc), as a passivator. the carboxyl and thiocyanate groups of fitc not only minimize the trap states by forming interactions with the under‑coordinated pb2+ ions but also significantly increase the grain size and improve the crystallinity of the perovskite films during annealing. consequently, perovskite films with superior optoelectronic properties, prolonged carrier lifetime, reduced trap density, and improved stability are obtained. the resulting device yields a champion efficiency of 14.05% with negligible hysteresis, which presents the highest reported efficiency for inorganic cspbi1.5br1.5 solar cells reported thus far. in addition, fitc can be generally adopted as attractive passivator to improve the performance of cspbi2br‑ and cspbibr2‑based pscs. furthermore, with a comprehensive comparison of mixed‑halide inorganic perovskites, it is demonstrated that cspbi1.5br1.5 compositional perovskite is a promising candidate with the optimal halide composition for high‑performance inorganic pscs. | organic dye passivation for high‑performance all‑inorganic cspbi1.5br1.5 perovskite solar cells with efficiency over 14% |
hydrogen is a crucial element for crystalline silicon solar cells due to its ability to passivate bulk defects in silicon. the introduction and distribution of hydrogen has gained a lot of interest due to its proposed involvement in the phenomenon termed "light and elevated temperature induced degradation" (letid) in multicrystalline silicon (mc-si) solar cells. letid, which can cause an efficiency loss of about 6-14% (relative) for mc-si perc (passivated emitter and rear cell) devices upon exposure to elevated temperature and illumination, is a serious cause of concern for the silicon photovoltaic industry. interaction of hydrogen with mc-si is complex as mc-si contains grain boundaries, dislocations, large concentrations of impurities and traps which may affect the diffusivity of hydrogen in silicon. understanding the diffusion of hydrogen in mc-si, and how it affects letid, is therefore of great interest. in this contribution, the concentration of hydrogen diffused into p-type mc-si lifetime samples from hydrogen-rich passivation layers (sinx:h and alox:h) fired at different peak firing temperatures is measured by elastic recoil detection analysis (erda) along with rutherford backscattering (rbs). also, experiments are done to study the impact of annealing in the presence of hydrogen on the extent of letid. a correlation is established between the hydrogen concentration diffused into silicon bulk and the extent of letid in lifetime samples fired at different peak firing profiles. | hydrogen diffusion from pecvd silicon nitride into multicrystalline silicon wafers: elastic recoil detection analysis (erda) measurements and impact on light and elevated temperature induced degradation (letid) |
corundum-bearing ca-al-rich inclusions (cais) are a rare class of high-temperature condensates from the inner regions of the protoplanetary disk. their mineralogy is intermediate between isolated corundum grains and cais where corundum has been replaced by lower-temperature phases. these inclusions sample a critical transitional period of the inner nebula where both the sun and protoplanetary disk were rapidly evolving. we conducted o isotopic, al-mg chronological, petrographic, and crystallographic studies of four corundum-bearing inclusions in the murchison cm2 and alha 77307 co3.0 carbonaceous chondrites. within each inclusion, corundum, hibonite, and spinel have indistinguishable 16o-rich compositions. the o isotopic compositions from all inclusions fall within a narrow range of δ17o = -22.8 ± 3.6‰ that matches values of most previously studied micrometer-sized corundum grains and mineralogically pristine cais. these data indicate that, with few exceptions, the most refractory inclusions in carbonaceous chondrites formed from the same o isotopic reservoir. one cai from alha 77307, alh-61, exhibits a continuous corundum mantle overlying a hibonite core, opposite the equilibrium condensation sequence at typical nebular pressures and dust/gas ratios. transmission electron microscopy examination of the hibonite-corundum interface suggests that the corundum condensed on the hibonite and was itself then partially overlain with spinel. additionally, high dust/gas ratios are interpreted from the w- and mo-depleted composition of a refractory metal nugget within a second corundum-bearing cai, alh-160. together, these observations show that the primary formation conditions of some corundum-bearing cais involved non-equilibrium condensation in environments with elevated dust-gas ratios. the corundum-bearing cais studied here have inferred initial 26al/27al ratios that fall within the roughly bimodal distribution of values observed in most cais. alh-160 retains no resolvable excess 26mg while alh-61 has a well-resolved initial 26al/27al ratio of 4.2 ± 0.4 × 10-5. the presence or absence of live 26al at the time of cai formation may record distinct chronology if 26al was initially homogeneously distributed in the early solar system. alternatively, variations in 26al/27al ratios may reflect late injection and/or heterogeneous distribution of 26al. regardless of which model for 26al distribution is correct, the data presented here indicate that formation of corundum-bearing cais was repeated during multiple heating and non-equilibrium condensation events throughout early solar system history and within a single oxygen isotopic reservoir. | corundum-hibonite inclusions and the environments of high temperature processing in the early solar system |
in this work, interface modification of sno2 layer using p-n junction double layer is investigated for the efficiency enhancement of perovskite solar cell (psc). for the double layer, a sn additive layer was applied on a sno2 layer by using the dc magnetron sputtering technique at various deposition times. the highest power conversion efficiency of 15.11% is obtained for psc with a snox additive layer at 5 s sputtering time, compared to 12.89% for the best psc without the additive layer. the effect of the snox additive layer on pscs at optimum sputtering time is further explored via the photoconversion properties of both optical and electrical properties. from the results, it is found that the snox additive layer is essential for efficiency enhancement by forming the p-n junction with a sno2 electron transporting layer (etl) and modifying the interface between the etl and the perovskite layer. the p-n junction of the etl is observed via the diode-like behavior of i-v characteristics. the interface modification can enhance the psc efficiency by improving the quality of the perovskite layer due to the larger grain size and higher absorbance, and by improving the charge transfer. the faster photogenerated charge transfer is confirmed by lower pl intensity and the shorter charge transfer lifetime is confirmed by the fitted open-circuit voltage decay. in addition, the snox additive layer can also eliminate the hysteresis effect of pscs. this interface modification technique for psc efficiency enhancement could be further explored for other etls. | interface modification of sno2 layer using p-n junction double layer for efficiency enhancement of perovskite solar cell |
a solvent soaking and rinsing method, in which the solvent was allowed to soak all over the surface followed by a spinning for solvent draining, was found to produce perovskite layers with high uniformity on a centimeter scale and with much improved reliability. besides the enhanced crystallinity and surface morphology due to the rinsing induced surface precipitation that constrains the grain growth underneath in the precursor films, large-area uniformity with film thickness determined exclusively by the rotational speed of rinsing spinning for solvent draining was observed. with chloroform as rinsing solvent, highly uniform and mirror-like perovskite layers of area as large as 8 cm × 8 cm were produced and highly uniform planar perovskite solar cells with power conversion efficiency of 10.6 ± 0.2% as well as much prolonged lifetime were obtained. the high uniformity and reliability observed with this solvent soaking and rinsing method were ascribed to the low viscosity of chloroform as well as its feasibility of mixing with the solvent used in the precursor solution. moreover, since the surface precipitation forms before the solvent draining, this solvent soaking and rinsing method may be adapted to spinless process and be compatible with large-area and continuous production. with the large-area uniformity and reliability for the resultant perovskite layers, this chloroform soaking and rinsing approach may thus be promising for the mass production and commercialization of large-area perovskite solar cells. | reliable solution processed planar perovskite hybrid solar cells with large-area uniformity by chloroform soaking and spin rinsing induced surface precipitation |
the power conversion efficiency (pce) of tin-based perovskite solar cells (tpscs) was significantly improved when polyvinyl pyrrolidone (pvp) was doped into the formamidinium tin iodide (fasni3) layer with an optimized doping mass. after doping, the fasni3 grain size, film smoothness and average carrier lifetime were largely enhanced, which demonstrate the crystallization quality improvement to fasni3. the champion pce of the enhanced tpsc was improved to 7.83%, which is relatively 27% larger than that of the control, 6.15%. after continuous storage for 15 days, the pce of the enhanced tpsc remained 74.4% of its original value. using the finite difference time domain (fdtd) simulation method, we demonstrated that the light absorption ratio of the fasni3:pvp layer was larger than that of the fasni3 , and the photo-generated carrier density of the enhanced tpsc was approximately 2% ∼ 3% larger than that of the control. the ultimate efficiency of the enhanced tpsc was calculated to be 26.23%. it is potential to dope pvp into fasni3 to further enhance the device performance of tpscs. | enhancing performance of tin-based perovskite solar cells by polyvinyl pyrrolidone doping strategy |
we have analysed the petrography, major element abundances and bulk al-mg isotope systematics of 19 ferromagnesian chondrules from the cv3 chondrites allende, mokoia, and vigarano, together with an al-rich chondrule and refractory olivine from mokoia. co-variations of al/mg with na/mg and ti/mg in our bulk chondrules suggest their compositions are dominantly controlled by reworking of different proportions of chondrule components (e.g. mafic minerals and mesostatis); their precursors are thus fragments from prior generations of chondrules. our samples show a range in fractionation corrected 26mg/24mg (δ‧26mg) ∼ 60 ppm, relative to precisions <±5 ppm (2se) and these values broadly covary with 27al/24mg. the data can be used to calculate model initial 26al/27al, or (26al/27al)0, of the chondrule precursors. our resolvably radiogenic chondrules yield model (26al/27al)0 ∼ 1-2 × 10-5, equivalent to model "ages" of precursor formation ≦1 ma post cai. however, many of our chondrules show near solar δ‧26mg and no variability despite a range in 27al/24mg. this suggests their derivation either from younger precursor chondrules or open system behaviour once 26al was effectively extinct ((26al/27al)0 < 0.8 × 10-5, given the resolution here). evidence for the latter explanation is provided by marked rims of orthopyroxene replacing olivine, indicating reaction of chondrules with a surrounding silicate vapour. concurrent isotopic exchange of mg with a near chondritic vapour during late reworking could explain their isotopic systematics. one ferromagnesian object is dominated by a high mg# olivine with elevated ti and ca abundances. this refractory olivine has a markedly negative δ‧26mg = -16 ± 3 ppm (2se), reflecting its early removal (model age of <0.5 ma post cai), from a reservoir with evolving δ‧26mg. if representative of the chondrule forming region, this grain defines a minimum interval of radiogenic ingrowth for cv chondrites commensurate with (26al/27al)0 > 3.4 ± 0.6 × 10-5. overall, our samples record a sequence of events from the formation of ferromagnesian objects within 0.5 ma of cai to re-equilibration of chondrules and silicate vapour >2 ma post cai, assuming an initially homogeneous 26al/27al. metamorphism on the asteroid parent body may have played a subsequent role in affecting mg isotope composition, but we argue this had a minor influence on the observations here. | chronology of formation of early solar system solids from bulk mg isotope analyses of cv3 chondrules |
observations of the solar photosphere show spatially compact large-amplitude doppler velocity events with short lifetimes. in data from the imaging magnetograph experiment (imax) on the first flight of the sunrise balloon in 2009, events with velocities in excess of 4σ from the mean can be identified in both intergranular downflow lanes and granular upflows. we show that the statistics of such events are consistent with the random superposition of strong convective flows and p-mode coherence patches. such coincident superposition complicates the identification of acoustic wave sources in the solar photosphere, and may be important in the interpretation of spectral line profiles formed in solar photosphere. | doppler events in the solar photosphere: the coincident superposition of fast granular flows and p-mode coherence patches |
this work proposes to utilize si particles embedded in si3n4 layer as low-cost seeds to produce high-quality multi-crystalline silicon (mc-si) ingot by full-melting process. the nucleation mechanism and its effects on minority carrier lifetime distribution, pl defects and oxygen concentration were studied. the results show that the incompletely melted silicon particles embedded in the si3n4 layer can effectively nucleate fine grains with uniform size and few defects. the yield of experiment ingot can be significantly increased due to the quite short length of bottom red zone. finally, the prepared solar cells can also achieve high conversion efficiency and show low light-induced degradation (lid) value. | growth of high-quality multi-crystalline silicon ingot by using si particles embedded in the si3n4 layer |
we investigate the orbital evolution of dust grains in the sublimation region near the white dwarf wd 1145+017. the selection of basalt as the main constituent of transient material around wd1145+017 is dictated by observations of the boundary of the dust-free zone near the sun for zodiacal dust cloud and by the orbital evolution of dust grains of different composition. the rate of sublimation is set by the temperature of dust grains, depending on their size, distance to the host star, and characteristics of the composition material. we consider the influence of radiation pressure and the poynting-robertson drag on the dynamics of the dust grains. the boundaries of sublimation zone near wd1145+017 for grains with the size range of 0.01 to 100 μ m are in the range from 56 to 1000 stellar radius (r*). when calculating the orbital evolution, we assumed that the grain leaves the parent body at a distance much greater than the radius of sublimation. we also estimate the lifetime of dust grains of different sizes and composition starting their orbital motion from a distance of 90 r*, corresponding to the main orbital period of the transit material. the lifetime of grains, considering their orbital evolution is about an order of magnitude less than that obtained from the heat balance alone. sub-micron grains at a distance of 90 r* evaporate almost instantly. basalt grains with a radius larger than 20 μ m can survive for more than a year. the estimated dust accretion rate is 3.2 × 109 g s-1. | on the orbital evolution of dust grains in the sublimation region around wd1145+017 |
high performance multicrystalline silicon wafers used in solar cell processing have been investigated with focus on quantification of the grain boundary effect on lifetime. the lifetime of a set of 16 wafers from different positions along the ingot and after different process steps - phosphorus gettering, sinx:h layer deposition and firing - is measured by µpcd and compared with microstructural information from ebsd. this allows for analysis of the behaviour of grain boundaries and their influence on lifetime during solar cell processing. the minority carrier lifetime of hpmc-si wafers is not increased after the gettering step, but even reduced for some samples. it is shown that the lifetime in areas close to grain boundaries is reduced during the gettering step and this has a stronger effect on the average value than the improvement within the grains. only wafers after both gettering and hydrogenation show an overall improvement in carrier lifetimes. however, in the regions close to the bottom of the ingot, wafers show lifetime degradation after the hydrogenation process. the results are used to obtain quantitative information on recombination velocity of grain boundaries. ( | grain boundary effect on lifetime in high performance multicrystalline silicon during solar cell processing |
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