publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2011-01-30 | Spin transport in magnetically ordered systems: effect of the lattice relaxation time | Spin resistivity $R$ has been shown to result mainly from the scattering of
itinerant spins with magnetic impurities and lattice spins. $R$ is proportional
to the spin-spin correlation so that its behavior is very complicated near and
at the magnetic phase transition of the lattice spins. For the time being there
are many new experimental data on the spin resistivity going from
semiconductors to superconductors. Depending on materials, various behaviors
have been observed. There is however no theory so far which gives a unified
mechanism for spin resistivity in magnetic materials. Recently, we have showed
Monte Carlo results for different systems. We found that the spin resistivity
is very different from one material to another. In this paper, we show for the
first time how the dynamic relaxation time of the lattice spins affects the
resistivity of itinerant spins observed in Monte Carlo simulation. | 1101.5789v1 |
2020-09-16 | Resistive switching in reverse: voltage driven formation of a transverse insulating barrier | Application of an electric stimulus to a material with a metal-insulator
transition can trigger a large resistance change. Resistive switching from an
insulating into a metallic phase, which typically occurs by the formation of
conducting filaments parallel to the current flow, has been an active research
topic. Here we present the discovery of an opposite, metal-to-insulator
switching that proceeds via nucleation and growth of an insulating barrier
perpendicular to the driving current. The barrier formation leads to an unusual
N-type negative differential resistance in the current-voltage characteristics.
Electrically inducing a transverse barrier enables a novel approach to
voltage-controlled magnetism. By triggering a metal-to-insulator resistive
switching in a magnetic material, local on/off control of ferromagnetism can be
achieved by a global voltage bias applied to the whole device. | 2009.07412v1 |
2021-08-14 | Voltage-controlled magnetism enabled by resistive switching | The discovery of new mechanisms of controlling magnetic properties by
electric fields or currents furthers the fundamental understanding of magnetism
and has important implications for practical use. Here, we present a novel
approach of utilizing resistive switching to control magnetic anisotropy. We
study a ferromagnetic oxide that exhibits an electrically triggered
metal-to-insulator phase transition producing a volatile resistive switching.
This switching occurs in a characteristic spatial pattern: the formation of a
transverse insulating barrier inside a metallic matrix resulting in an unusual
ferromagnetic/paramagnetic/ferromagnetic configuration. We found that the
formation of this voltage-driven paramagnetic insulating barrier is accompanied
by the emergence of a strong uniaxial magnetic anisotropy that overpowers the
intrinsic material anisotropy. Our results demonstrate that resistive switching
is an effective tool for manipulating magnetic properties. Because resistive
switching can be induced in a very broad range of materials, our findings could
enable a new class of voltage-controlled magnetism systems. | 2108.06445v1 |
2022-08-02 | Investigating thermal transport in knotted graphene nanoribbons using non-equilibrium molecular dynamics | In this work, we investigated the effect of knots in the thermal transport of
graphene nanoribbons through non-equilibrium molecular dynamics simulations. We
considered the cases of one, two, and three knots are present. Temperature
jumps appear in the temperature profile where the knots are located, which
indicates that they introduce thermal resistances in the system, similar to
interfacial Kapitza resistance present between two different materials and/or
single materials with defects and/or lattice distortions. We found that the
thermal resistance introduced by each individual knot is essentially the same
as the overall resistance increase linearly with the number of knots, as they
behave as thermal resistances associated in series. Also, the relative position
between each knot in the arrangement does not strongly affect the thermal
current produced by the temperature gradient, showing a weak thermal
rectification effect. | 2208.01751v1 |
2010-05-21 | Effect of Heterogeneous Mixing and Vaccination on the Dynamics of Anthelmintic Resistance: A Nested Model | Anthelmintic resistance is a major threat to current measures for helminth
control in humans and animals. The introduction of anthelmintic vaccines, as a
complement to or replacement for drug treatments, has been advocated as a
preventive measure. Here, a computer-based simulation, tracking the dynamics of
hosts, parasites and parasite-genes, shows that, depending on the degree of
host-population mixing, the frequency of totally recessive autosomes associated
with anthelmintic resistance can follow either a fast dynamical regime with a
low equilibrium point or a slow dynamical regime with a high equilibrium point.
For fully dominant autosomes, only one regime is predicted. The effectiveness
of anthelminthic vaccines against resistance is shown to be strongly influenced
by the underlying dynamics of resistant autosomes. Vaccines targeting adult
parasites, by decreasing helminth fecundity or lifespan, are predicted to be
more effective than vaccines targeting parasite larvae, by decreasing host
susceptibility to infection, in reducing the spread of resistance. These
results may inform new strategies to prevent, monitor and control the spread of
anthelmintic resistance, including the development of viable anthelmintic
vaccines. | 1005.3891v1 |
2018-06-20 | Modeling continuous levels of resistance to multidrug therapy in cancer | Multidrug resistance consists of a series of genetic and epigenetic
alternations that involve multifactorial and complex processes, which are a
challenge to successful cancer treatments. Accompanied by advances in
biotechnology and high-dimensional data analysis techniques that are bringing
in new opportunities in modeling biological systems with continuous phenotypic
structured models, we study a cancer cell population model that considers a
multi-dimensional continuous resistance trait to multiple drugs to investigate
multidrug resistance. We compare our continuous resistance trait model with
classical models that assume a discrete resistance state and classify the cases
when the continuum and discrete models yield different dynamical patterns in
the emerging heterogeneity in response to drugs. We also compute the maximal
fitness resistance trait for various continuum models and study the effect of
epimutations. Finally, we demonstrate how our approach can be used to study
tumor growth regarding the turnover rate and the proliferating fraction, and
show that a continuous resistance level may result in a different dynamics when
compared with the predictions of other discrete models. | 1806.07557v1 |
2021-01-18 | Hubs-biased resistance distances on graphs and networks | We define and study two new kinds of "effective resistances" based on
hubs-biased -- hubs-repelling and hubs-attracting -- models of navigating a
graph/network. We prove that these effective resistances are squared Euclidean
distances between the vertices of a graph. They can be expressed in terms of
the Moore-Penrose pseudoinverse of the hubs-biased Laplacian matrices of the
graph. We define the analogous of the Kirchhoff indices of the graph based of
these resistance distances. We prove several results for the new resistance
distances and the Kirchhoff indices based on spectral properties of the
corresponding Laplacians. After an intensive computational search we conjecture
that the Kirchhoff index based on the hubs-repelling resistance distance is not
smaller than that based on the standard resistance distance, and that the last
is not smaller than the one based on the hubs-attracting resistance distance.
We also observe that in real-world brain and neural systems the efficiency of
standard random walk processes is as high as that of hubs-attracting schemes.
On the contrary, infrastructures and modular software networks seem to be
designed to be navigated by using their hubs. | 2101.07103v2 |
2021-10-18 | Low-Frequency 1/f Noise Characteristics of Ultra-Thin AlO$_{x}$-Based Resistive Switching Memory Devices with Magneto-Resistive Responses | Low-frequency 1/f voltage noise has been employed to probe stochastic charge
dynamics in AlO$_{x}$-based non-volatile resistive memory devices exhibiting
both resistive switching (RS) and magneto-resistive (MR) effects. A
1/f$^{\gamma}$ noise power spectral density is observed in a wide range of
applied voltage biases. By analyzing the experimental data within the framework
of Hooge's empirical relation, we found that the Hooge's parameter $\alpha$ and
the exponent $\gamma$ exhibit a distinct variation upon the resistance
transition from the low resistance state (LRS) to the high resistance state
(HRS), providing strong evidence that the electron trapping/de-trapping
process, along with the electric field-driven oxygen vacancy migration in the
AlO$_x$ barrier, plays an essential role in the charge transport dynamics of
AlO$_x$-based RS memory devices. | 2110.09331v1 |
2023-07-24 | Clustering MIC data through Bayesian mixture models: an application to detect M. Tuberculosis resistance mutations | Antimicrobial resistance is becoming a major threat to public health
throughout the world. Researchers are attempting to contrast it by developing
both new antibiotics and patient-specific treatments. In the second case,
whole-genome sequencing has had a huge impact in two ways: first, it is
becoming cheaper and faster to perform whole-genome sequencing, and this makes
it competitive with respect to standard phenotypic tests; second, it is
possible to statistically associate the phenotypic patterns of resistance to
specific mutations in the genome. Therefore, it is now possible to develop
catalogues of genomic variants associated with resistance to specific
antibiotics, in order to improve prediction of resistance and suggest
treatments. It is essential to have robust methods for identifying mutations
associated to resistance and continuously updating the available catalogues.
This work proposes a general method to study minimal inhibitory concentration
(MIC) distributions and to identify clusters of strains showing different
levels of resistance to antimicrobials. Once the clusters are identified and
strains allocated to each of them, it is possible to perform regression method
to identify with high statistical power the mutations associated with
resistance. The method is applied to a new 96-well microtiter plate used for
testing M. Tuberculosis. | 2307.12603v1 |
2023-06-19 | On the Active Components in Crystalline Li-Nb-O and Li-Ta-O Coatings from First Principles | Layered-oxide $\mathrm{LiNi_xMn_yCo_{1-x-y}O_2}$ (NMC) positive electrodes
with high Nickel content, deliver high voltages and energy densities. However,
a high nickel content, e.g., $x$ = 0.8 (NMC 811), can lead to high surface
reactivity, which can trigger thermal runaway and gas generation. While claimed
safer, all-solid-state batteries still suffer from high interfacial resistance.
Here, we investigate niobate and tantalate coating materials, which can
mitigate the interfacial reactivities in Li-ion and all-solid-state batteries.
First-principles calculations reveal the multiphasic nature of Li-Nb-O and
Li-Ta-O coatings, containing mixtures of $\mathrm{LiNbO_3}$ and
$\mathrm{Li_3NbO_4}$, or of $\mathrm{LiTaO_3}$ and $\mathrm{Li_3TaO_4}$. The
concurrence of several phases in Li-Nb-O or Li-Ta-O modulates the type of
stable native defects in these coatings. Li-Nb-O and Li-Ta-O coating materials
can form favorably lithium vacancies $\mathrm{Vac^{'}_{Li}}$ and antisite
defects $\mathrm{Nb^{\bullet \bullet \bullet \bullet}_{Li}}$
($\mathrm{Ta^{\bullet \bullet \bullet \bullet}_{Li}}$) combined into
charge-neutral defect complexes. Even in defective crystalline
$\mathrm{LiNbO_3}$ (or $\mathrm{LiTaO_3}$), we reveal poor Li-ion conduction
properties. In contrast, $\mathrm{Li_3NbO_4}$ and $\mathrm{Li_3TaO_4}$ that are
introduced by high-temperature calcinations can provide adequate Li-ion
transport in these coatings. Our in-depth investigation of the
structure-property relationships in the important Li-Nb-O and Li-Ta-O coating
materials helps to develop more suitable calcination protocols to maximize the
functional properties of these niobates and tantalates. | 2306.10716v1 |
2020-01-23 | Large Enhancement of Thermoelectric Efficiency Due to a Pressure-Induced Lifshitz Transition in SnSe | Lifshitz transition, a change in Fermi surface topology, is likely to greatly
influence exotic correlated phenomena in solids, such as high-temperature
superconductivity and complex magnetism. However, since the observation of
Fermi surfaces is generally difficult in the strongly correlated systems, a
direct link between the Lifshitz transition and quantum phenomena has been
elusive so far. Here, we report a marked impact of the pressure-induced
Lifshitz transition on thermoelectric performance for SnSe, a promising
thermoelectric material without strong electron correlation. By applying
pressure up to 1.6 GPa, we have observed a large enhancement of thermoelectric
power factor by more than 100% over a wide temperature range (10-300 K).
Furthermore, the high carrier mobility enables the detection of quantum
oscillations of resistivity, revealing the emergence of new Fermi pockets at
~0.86 GPa. The observed thermoelectric properties linked to the multi-valley
band structure are quantitatively reproduced by first-principles calculations,
providing novel insight into designing the SnSe-related materials for potential
valleytronic as well as thermoelectric applications. | 2001.08674v1 |
2009-07-10 | Cellulose-Bound Magnesium Diboride Superconductivity | Two-phase superconductor tapes were produced by blending high purity
magnesium diboride powder with a liquid ethylcellulose-based polymeric binder.
This procedure produced a material which is easily formable with a high
superconducting transition temperature (38K). We show that the bulk
superconducting properties are not affected by the presence of the binder, nor
is there any evidence of a chemical reaction between the superconducting
particles and the binder. However, the transport properties of the material are
strongly affected by the presence of the binder, which leads to a seven order
of magnitude increase of the normal state resistance along with a seven order
of magnitude decrease of the transport critical current density. This new
material is shown to be equivalent to a system of coupled Josephson junctions. | 0907.1744v1 |
2010-06-27 | Soft capacitor fibers using conductive polymers for electronic textiles | A novel, highly flexible, conductive polymer-based fiber with high electric
capacitance is reported. In its crossection the fiber features a periodic
sequence of hundreds of conductive and isolating plastic layers positioned
around metallic electrodes. The fiber is fabricated using fiber drawing method,
where a multi-material macroscopic preform is drawn into a sub-millimeter
capacitor fiber in a single fabrication step. Several kilometres of fibers can
be obtained from a single preform with fiber diameters ranging between 500um
-1000um. A typical measured capacitance of our fibers is 60-100 nF/m and it is
independent of the fiber diameter. For comparison, a coaxial cable of the
comparable dimensions would have only ~0.06nF/m capacitance. Analysis of the
fiber frequency response shows that in its simplest interrogation mode the
capacitor fiber has a transverse resistance of 5 kOhm/L, which is inversely
proportional to the fiber length L and is independent of the fiber diameter.
Softness of the fiber materials, absence of liquid electrolyte in the fiber
structure, ease of scalability to large production volumes, and high
capacitance of our fibers make them interesting for various smart textile
applications ranging from distributed sensing to energy storage. | 1006.5221v1 |
2015-03-06 | Conductivity of a Weyl semimetal with donor and acceptor impurities | We study transport in a Weyl semimetal with donor and acceptor impurities.
At sufficiently high temperatures transport is dominated by electron-electron
interactions, while the low-temperature resistivity comes from the scattering
of quasiparticles on screened impurities.
Using the diagrammatic technique, we calculate the conductivity
$\sigma(T,\omega,n_A,n_D)$ in the impurities-dominated regime as a function of
temperature $T$, frequency $\omega$, and the concentrations $n_A$ and $n_D$ of
donors and acceptors and discuss the crossover behaviour between the regimes of
low and high temperatures and impurity concentrations.
In a sufficiently compensated material [$|n_A-n_D|\ll(n_A+n_D)$] with a small
effective fine structure constant $\alpha$, $\sigma(\omega,T)\propto
T^2/(T^{-2}-i\omega\cdot\text{const})$ in a wide interval of temperatures.
For very low temperatures or in the case of an uncompensated material the
transport is effectively metallic. We discuss experimental conditions necessary
for realising each regime. | 1503.02078v2 |
2015-10-31 | High-performance Thermal Interface Material Based on Few-layer Graphene Composite | We developed high-performance thermal interface materials (TIMs) based on
few-layer graphene (FLG) composite, where FLG was prepared by the interlayer
catalytic exfoliation (ICE) method. We experimentally demonstrated feasibility
of FLG composites as TIMs by investigating their thermal and mechanical
properties, and reliability. We measured the thermal interface resistance
($R_{int}$) between FLG composite TIMs (FLGTs) and copper and to be 3.2$\pm$1.7
and 4.3$\pm$1.4 $mm^2$K/W for 5 vol.% and 10 vol.% FLGTs at 330 K,
respectively, comparable to or even lower than that of many commercial TIMs. In
addition, the thermal conductivity ($\kappa_{TIM}$) of FLGTs is increased by an
enhancement factor ($\beta$) of ~17 as the FLG concentration increases from 0
to 10 vol.%. We also characterized Vickers hardness and glass transition
temperature ($T_g$) of our FLGTs. We find that our FLGTs are thermally and
mechanically reliable within practical operating temperature and pressure
ranges. | 1511.00076v2 |
2016-02-16 | Perfect charge compensation in extremely large magnetoresistance materials LaSb and LaBi revealed by the first-principles calculations | By the first-principles electronic structure calculations, we have
systematically studied the electronic structures of recently discovered
extremely large magnetoresistance (XMR) materials LaSb and LaBi. We find that
both LaSb and LaBi are semimetals with the electron and hole carriers in
perfect balance. The calculated carrier densities in the order of $10^{20}$
cm$^{-3}$ are in good agreement with the experimental values, implying long
mean free time of carriers and thus high carrier mobilities. With a
semiclassical two-band model, the perfect charge compensation and high carrier
mobilities naturally explain (i) the XMR observed in LaSb and LaBi; (ii) the
non-saturating quadratic dependence of XMR on external magnetic field; and
(iii) the resistivity plateau in the turn-on temperature behavior at very low
temperatures. The explanation of these features without resorting to the
topological effect indicates that they should be the common characteristics of
all perfectly electron-hole compensated semimetals. | 1602.05061v1 |
2016-06-17 | Homogeneously bright, flexible and foldable lighting devices with functionalised graphene electrodes | Alternating current electroluminescent technology allows the fabrication of
large area, flat and flexible lights. Presently the maximum size of a
continuous panel is limited by the high resistivity of available transparent
electrode materials causing a visible gradient of brightness. Here, we
demonstrate that the use of the best known transparent conductor
FeCl$_{3}$-intercalated few-layer graphene boosts the brightness of
electroluminescent devices by 49$\%$ compared to pristine graphene. Intensity
gradients observed for high aspect ratio devices are undetectable when using
these highly conductive electrodes. Flat lights on polymer substrates are found
to be resilient to repeated and flexural strains. | 1606.05482v1 |
2017-10-27 | The Quantum Hall Effect with Wilczek's charged magnetic flux tubes instead of electrons | Composites formed from charged particles and magnetic flux tubes, proposed by
Wilczek, are one model for anyons - particles obeying fractional statistics.
Here we propose a scheme for realizing charged flux tubes, in which a charged
object with an intrinsic magnetic dipole moment is placed between two
semi-infinite blocks of a high permeability ($\mu_r$) material, and the images
of the magnetic moment create an effective flux tube. We show that the scheme
can lead to a realization of Wilczek's anyons, when a two-dimensional electron
system, which exhibits the integer quantum Hall effect (IQHE), is sandwiched
between two blocks of the high-$\mu_r$ material with a temporally fast response
(in the cyclotron and Larmor frequency range). The signature of Wilczek's
anyons is a slight shift of the resistivity at the plateau of the IQHE. Thus,
the quest for high-$\mu_r$ materials at high frequencies, which is underway in
the field of metamaterials, and the quest for anyons, are here found to be on
the same avenue. | 1710.10108v2 |
2020-03-03 | Chemical sensing with atomically-thin metals templated by a two-dimensional insulator | Boosting the sensitivity of solid-state gas sensors by incorporating
nanostructured materials as the active sensing element can be complicated by
interfacial effects. Interfaces at nanoparticles, grains, or contacts may
result in non-linear current-voltage response, high electrical resistance, and
ultimately, electric noise that limits the sensor read-out. Here we report the
possibility to prepare nominally one atom thin, electrically continuous metals,
by straightforward physical vapor deposition on the carbon zero-layer grown
epitaxially on silicon carbide. With platinum as the metal, its electrical
conductivity is strongly modulated when interacting with chemical analytes, due
to charges being transferred to/from Pt. This, together with the scalability of
the material, allows us to microfabricate chemiresistor devices for electrical
read-out of chemical species with sub part-per-billion detection limits. The
two-dimensional system formed by atomically-thin metals open up a route for
resilient and high sensitivity chemical detection, and could be the path for
designing new heterogeneous catalysts with superior activity and selectivity. | 2003.01594v1 |
2020-04-27 | Runaway dynamics in the DT phase of ITER operations in the presence of massive material injection | A runaway avalanche can result in a conversion of the initial plasma current
into a relativistic electron beam in high current tokamak disruptions. We
investigate the effect of massive material injection of deuterium-noble gas
mixtures on the coupled dynamics of runaway generation, resistive diffusion of
the electric field, and temperature evolution during disruptions in the DT
phase of ITER operations. We explore the dynamics over a wide range of injected
concentrations and find substantial runaway currents, unless the current quench
time is intolerably long. The reason is that the cooling associated with the
injected material leads to high induced electric fields that, in combination
with a significant recombination of hydrogen isotopes, leads to a large
avalanche generation. Balancing Ohmic heating and radiation losses provides
qualitative insights into the dynamics, however, an accurate modeling of the
temperature evolution based on energy balance appears crucial for quantitative
predictions. | 2004.12861v3 |
2020-09-04 | Magnon-induced Giant Anomalous Nernst Effect in Single Crystal MnBi | Thermoelectric modules are a promising approach to energy harvesting and
efficient cooling. In addition to the longitudinal Seebeck effect, recently
transverse devices utilizing the anomalous Nernst effect (ANE) have attracted
interest. For high conversion efficiency, it is required that the material
should have a large ANE thermoelectric power and low electrical resistance, the
product of which is the ANE conductivity. ANE is usually explained in terms of
intrinsic contributions from Berry curvature. Our observations suggest that
extrinsic contributions also matter. Studying single-crystal MnBi, we find a
very high ANE thermopower (~10 $\mu$V/K) under 0.6 T at 80 K, and a transverse
thermoelectric conductivity of over 40 A/Km. With insight from theoretical
calculations, we attribute this large ANE predominantly to a new advective
magnon contribution arising from magnon-electron spin-angular momentum
transfer. We propose that introducing large spin-orbit coupling into
ferromagnetic materials may enhance the ANE through the extrinsic contribution
of magnons. | 2009.02211v3 |
2022-02-10 | Nanostructured transition metal dichalcogenide multilayers for advanced nanophotonics | Transition metal dichalcogenides (TMDs) attract significant attention due to
their exceptional optical, excitonic, mechanical, and electronic properties.
Nanostructured multilayer TMDs were recently shown to be highly promising for
nanophotonic applications, as motivated by their exceptionally high refractive
indexes and optical anisotropy. Here, we extend this vision to more
sophisticated structures, such as periodic arrays of nanodisks and nanoholes,
as well as proof-of-concept waveguides and resonators. We specifically focus on
various advanced nanofabrication strategies, including careful selection of
resists for electron beam lithography and etching methods. The specific
materials studied here include semiconducting WS$_2$, in-plane anisotropic
ReS$_2$, and metallic TaSe$_2$, TaS$_2$ and NbSe$_2$. The resulting
nanostructures can potentially impact several nanophotonic and optoelectronic
areas, including high-index nanophotonics, plasmonics and on-chip optical
circuits. The knowledge of TMD material-dependent nanofabrication parameters
developed here will help broaden the scope of future applications of these
materials in all-TMD nanophotonics. | 2202.04898v1 |
2021-01-20 | Electrically-Insulating Flexible Films with Quasi-One-Dimensional van-der-Waals Fillers as Efficient Electromagnetic Shields | We report polymer composite films containing fillers comprised of
quasi-one-dimensional (1D) van der Waals materials, specifically transition
metal trichalcogenides containing 1D structural motifs that enable their
exfoliation into bundles of atomic threads. These nanostructures are
characterized by extremely large aspect ratios of up to 10^6. The polymer
composites with low loadings of quasi-1D TaSe3 fillers (below 3 vol. %)
revealed excellent electromagnetic interference shielding in the X-band GHz and
EHF sub-THz frequency ranges, while remaining DC electrically insulating. The
unique electromagnetic shielding characteristics of these films are attributed
to effective coupling of the electromagnetic waves to the high-aspect-ratio
electrically-conductive TaSe3 atomic-thread bundles even when the filler
concentration is below the electrical percolation threshold. These novel films
are promising for high-frequency communication technologies, which require
electromagnetic shielding films that are flexible, lightweight, corrosion
resistant, electrically insulating and inexpensive. | 2101.08239v1 |
2020-05-07 | Understanding cooperative loading in carbon nanotube fibres through in-situ structural studies during stretching | Carbon nanotube (CNT) fibres are firmly established as a new high-performance
fibre, but their tensile mechanical properties remain a relatively small
fraction of those of the constituent CNTs. Clear structure-property relations
and accurate mechanical models are pressing requirements to bridge this gap. In
this work we analyse the structural evolution and molecular stress transfer in
CNT fibres by performing in-situ synchrotron wide- and small-angle X-ray
scattering and Raman spectroscopy during tensile deformation. The results show
that CNT fibres can be accurately described as network of bundles that slide
progressively according to the initial orientation distribution function of the
material following a Weibull distribution. This model decouples the effects of
CNT alignment and degree of cooperative loading, as demonstrated for fibres
produced at different draw ratios. It also helps explain the unusually high
toughness (fracture energy) of CNT fibres produced by the direct spinning
method, a key property for impact resistance in structural materials, for
example. | 2005.03305v2 |
2020-12-02 | Crystallographic Reconstruction Driven Modified Mechanical Properties in Anisotropic Rhenium Disulfides | Atomic-scale investigation on mechanical behaviors is highly necessary to
fully understand the fracture mechanics especially of brittle materials, which
are determined by atomic-scale phenomena (e.g., lattice trapping). Here,
exfoliated anisotropic rhenium disulfide (ReS2) flakes are used to investigate
atomic-scale crack propagation depending on the propagation directions. While
the conventional strain-stress curves exhibit a strong anisotropy depending on
the cleavage direction of ReS2, but our experimental results show a reduced
cleavage anisotropy due to the lattice reconstruction in [100] cracking with
high resistance to fracture. In other words, [010] and [110] cracks with low
barriers to cleavage exhibit the ultimate sharpness of the crack tip without
plastic deformation, whereas [100] cracks drive lattice rotation on one side of
the crack, leading to a non-flat grain boundary formation. Finally,
crystallographic reconstruction associated with the high lattice randomness of
two-dimensional materials drives to a modified cleavage tendency, further
indicating the importance of atomic-scale studies for a complete understanding
of the mechanics. | 2012.01045v1 |
2021-03-04 | Observation of an Unusual Colossal Anisotropic Magnetoresistance Effect in an Antiferromagnetic Semiconductor | Searching for novel antiferromagnetic materials with large magnetotransport
response is highly demanded for constructing future spintronic devices with
high stability, fast switching speed, and high density. Here we report a
colossal anisotropic magnetoresistance effect in an antiferromagnetic binary
compound with layered structure rare-earth dichalcogenide EuTe2. The AMR
reaches 40000%, which is 4 orders of magnitude larger than that in conventional
antiferromagnetic alloys. Combined magnetization, resistivity, and theoretical
analysis reveal that the colossal AMR effect is attributed to a novel mechanism
of vector-field tunable band structure, rather than the conventional spin-orbit
coupling mechanism. Moreover, it is revealed that the strong hybridization
between orbitals of Eu-layer with localized spin and Te-layer with itinerant
carriers is extremely important for the large AMR effect. Our results suggest a
new direction towards exploring AFM materials with prominent magnetotransport
properties, which creates an unprecedented opportunity for AFM spintronics
applications. | 2103.02818v1 |
2023-01-17 | Comparing Methods of Characterizing Energetic Disorder in Organic Solar Cells | Energetic disorder has been known for decades to limit the performance of
structurally disordered semiconductors such as amorphous silicon and organic
semiconductors. However, in the past years, high performance organic solar
cells have emerged showing a continuously reduced amount of energetic disorder.
While searching for future high efficiency material systems, it is therefore
important to correctly characterize this energetic disorder. While there are
several techniques in literature, the most common approaches to probe the
density of defect states are using optical excitation as in external quantum
efficiency measurements or sequential filling of the tail states by applying an
external voltage as in admittance spectroscopy. A metanalysis of available
literature as well as our experiments using four characterization techniques on
two material systems reveal that electrical, voltage-dependent measurements
frequently yield higher values of energetic disorder than optical measurements.
With drift-diffusion simulations, we demonstrate that the approaches probe
different energy ranges of the subband-gap density of states. We further
explore the limitations of the techniques and find that extraction of
information from a capacitance-voltage curve can be inhibited by an internal
series resistance. Thereby, we explain the discrepancies between measurements
techniques with sensitivity to different energy ranges and electronic
parameters. | 2301.06792v1 |
2023-06-12 | Significant improvement of the lower critical field in Y doped Nb: potential replacement of basic material for the radio-frequency superconducting cavity | The research of high energy and nuclear physics requires high power
accelerators, and the superconducting radio-frequency (SRF) cavity is regarded
as their engine. Up to now, the widely used practical and effective material
for making the SRF cavity is pure Nb. The key parameter that governs the
efficiency and the accelerating field (E_acc) of a SRF cavity is the lower
critical field Hc1. Here, we report a significant improvement of Hc1 for a new
type of alloy, Nb_{1-x}Y_x fabricated by the arc melting technique.
Experimental investigations with multiple tools including x-ray diffraction,
scanning electron microscopy, resistivity and magnetization are carried out,
showing that the samples have good quality and a 30%-60% enhancement of Hc1.
First principle calculations indicate that this improvement is induced by the
delicate tuning of a Lifshitz transition of a Nb derivative band near the Fermi
energy, which increases the Ginzburg-Landau parameter and Hc1. Our results may
trigger a replacement of the basic material and thus a potential revolution for
manufacturing the SRF cavity. | 2306.06915v1 |
2023-07-18 | Observation of giant two-level systems in a granular superconductor | Disordered thin films are a common choice of material for superconducting,
high impedance circuits used in quantum information or particle detector
physics. A wide selection of materials with different levels of granularity are
available, but, despite low microwave losses being reported for some, the high
degree of disorder always implies the presence of intrinsic defects.
Prominently, quantum circuits are prone to interact with two-level systems
(TLS), typically originating from solid state defects in the dielectric parts
of the circuit, like surface oxides or tunneling barriers. We present an
experimental investigation of TLS in granular aluminum thin films under applied
mechanical strain and electric fields. The analysis reveals a class of strongly
coupled TLS having electric dipole moments up to 30 eA, an order of magnitude
larger than dipole moments commonly reported for solid state defects. Notably,
these large dipole moments appear more often in films with a higher
resistivity. Our observations shed new light on granular superconductors and
may have implications for their usage as a quantum circuit material. | 2307.09078v2 |
2024-03-01 | First-principles Investigation of Thermodynamic Properties of CrNbO4 and CrTaO4 | In the present study, the DFT+U method was employed to predict the
thermodynamic properties of Cr2O3, Nb2O5, and Ta2O5. Results were benchmarked
with experimental data showing high accuracy, except for the negative thermal
expansion (NTE) of Nb2O5, which is attributed to its polymorphic complexity.
Additionally, we extended our analysis to rutile-type oxides CrNbO4 and CrTaO4,
examining their entropy and heat capacity at finite temperatures. CrNbO4
displayed slightly higher entropy and heat capacity at high temperatures. The
mean linear thermal expansion coefficients for CrNbO4 and CrTaO4 from 500 K to
2000 K were predicted to be 6.00*10-6/K and 13.49*10-6/K, respectively,
corroborating with DFT predictions and experimental evidence. Our research
highlights the precision of the DFT+U and phonon methods in predicting the
thermodynamic properties of oxide materials, offering insights into the design
of corrosion-resistant materials. | 2403.00705v1 |
2017-03-05 | Response to Comment on 'Spin-Orbit Logic with Magnetoelectric Nodes: A Scalable Charge Mediated Nonvolatile Spintronic Logic' (arXiv:1607.06690) | In this technical note, we address the comments on the energy estimates for
Magnetoelectric Spin-orbit (MESO) Logic, a new logic device proposed by the
authors. We provide an analytical derivation of the switching energy, and
support it with time-domain circuit simulations using a self-consistent
ferroelectric (FE) compact model. While the energy to charge a capacitor is
dissipated in the interconnect and transistor resistance, we note that the
energy to switch a capacitor and a FE is independent of the interconnect
resistance value to the first order. Also device design can mitigate the
parasitic energy losses. We further show the circuit simulations for a sub 10
aJ switching operation of a MESO logic device comprehending: a) Energy stored
in multiferroic; b) Energy dissipation in the resistance of the interconnect,
Ric ; c) Energy dissipation in the inverse spin-orbit coupling (ISOC) spin to
charge converter Risoc; d) Supply, ground resistance, and transistor losses. We
also identify the requirements for the resistivity of the spin-orbit coupling
materials and address the effect of internal resistance of the spin to charge
conversion layer. We provide the material parameter space where MESO (with a
fan-out of 1 and interconnect) achieves sub 10 aJ switching energy with path
for scaling via ferroelectric/magnetoelectric/spin-orbit materials development. | 1703.01559v1 |
2014-11-05 | Modeling of High Composition AlGaN Channel HEMTs with Large Threshold Voltage | We report on the potential of high electron mobility transistors (HEMTs)
consisting of high composition AlGaN channel and barrier layers for power
switching applications. Detailed 2D simulations show that threshold voltages in
excess of 3 V can be achieved through the use of AlGaN channel layers. We also
calculate the two-dimensional electron gas (2DEG) mobility in AlGaN channel
HEMTs and evaluate their power figures of merit as a function of device
operating temperature and Al mole fraction in the channel. Our models show that
power switching transistors with AlGaN channels would have comparable
on-resistance to GaN-channel based transistors for the same operation voltage.
The modeling in this paper shows the potential of high composition AlGaN as a
channel material for future high threshold enhancement mode transistors. | 1411.1447v1 |
2016-11-10 | Ultra-high vacuum compatible preparation chain for intermetallic compounds | We report the development of a versatile material preparation chain for
intermetallic compounds that focuses on the realization of a high-purity growth
environment. The preparation chain comprises of an argon glovebox, an
inductively heated horizontal cold boat furnace, an arc melting furnace, an
inductively heated rod casting furnace, an optically heated floating-zone
furnace, a resistively heated annealing furnace, and an inductively heated
annealing furnace. The cold boat furnace and the arc melting furnace may be
loaded from the glovebox by means of a load-lock permitting to synthesize
compounds starting with air-sensitive elements while handling the constituents
exclusively in an inert gas atmosphere. All furnaces are all-metal sealed,
bakeable, and may be pumped to ultra-high vacuum. We find that the latter
represents an important prerequisite for handling compounds with high vapor
pressure under high-purity argon atmosphere. We illustrate operational aspects
of the preparation chain in terms of the single-crystal growth of the
heavy-fermion compound CeNi2Ge2. | 1611.03392v1 |
2020-08-06 | Granular superconductors for high kinetic inductance and low loss quantum devices | Granular aluminum is a promising material for high kinetic inductance devices
such as qubit circuits. It has the advantage over atomically disordered
materials such as NbN_x, to maintain a high kinetic inductance concomitantly
with a high quality factor. We show that high quality nano-scale granular
aluminum films having a sharp superconducting transition with normal state
resistivity values of the order of 1x10^5 \mu\Omega cm and kinetic inductance
values of the order of 10 nH/sq can be obtained, surpassing state of the art
values. We argue that this is a result of the different nature of the
metal-to-insulator transition, being electronic correlations driven (Mott type)
in the former and disorder driven (Anderson type) in the latter. | 2008.02860v1 |
2023-11-14 | A calculation method to estimate thermal conductivity of high entropy ceramic for thermal barrier coatings | High entropy ceramics are highly promising as next generation thermal barrier
coatings due to their unique disorder structure, which imparts ultra-low
thermal conductivity and good high temperature stability. Unlike traditional
ceramic materials, the thermal resistance in high entropy ceramics
predominantly arises from phonon-disorder scattering rather than phonon-phonon
interactions. In this study, we propose a calculation method based on the
supercell phonon unfolding (SPU) technique to predict the thermal conductivity
of high entropy ceramics, specially focusing on rocksalt oxides structures. Our
prediction method relies on using the reciprocal value of SPU phonon spectra
linewidth as an indicator of phonon lifetime. The obtained results demonstrate
a strong agreement between the predicted thermal conductivities and the
experimental measurements, validating the feasibility of our calculation
method. Furthermore, we extensively investigate and discuss the atomic
relaxation and lattice distortion effects in 5-dopants and 6-dopants rocksalt
structures during the process. | 2311.08246v1 |
2022-04-14 | Non-equilibrium Phonon Thermal Resistance at MoS2/Oxide and Graphene/Oxide Interfaces | Accurate measurements and physical understanding of thermal boundary
resistance (R) of two-dimensional (2D) materials are imperative for effective
thermal management of 2D electronics and photonics. In previous studies, heat
dissipation from 2D material devices was presumed to be dominated by phonon
transport across the interfaces. In this study, we find that in addition to
phonon transport, thermal resistance between non-equilibrium phonons in the 2D
materials could play a critical role too when the 2D material devices are
internally self-heated, either optically or electrically. We accurately measure
R of oxide/MoS2/oxide and oxide/graphene/oxide interfaces for three oxides
(SiO2, HfO2, Al2O3) by differential time-domain thermoreflectance (TDTR). Our
measurements of R across these interfaces with external heating are 2-to-4
times lower than previously reported R of the similar interfaces measured by
Raman thermometry with internal self-heating. Using a simple model, we show
that the observed discrepancy can be explained by an additional internal
thermal resistance (Rint) between non-equilibrium phonons present during Raman
measurements. We subsequently estimate that for MoS2 and graphene, Rint is
about 31 and 22 m2 K/GW, respectively. The values are comparable to the thermal
resistance due to finite phonon transmission across interfaces of 2D materials
and thus cannot be ignored in the design of 2D material devices. Moreover, the
non-equilibrium phonons also lead to a different temperature dependence than
that by phonon transport. As such, our work provides important insights into
physical understanding of heat dissipation in 2D material devices. | 2204.06975v1 |
1996-08-24 | Band Structure and Transport Properties of CrO_2 | Local Spin Density Approximation (LSDA) is used to calculate the energy bands
of both the ferromagnetic and paramagnetic phases of metallic CrO_2. The Fermi
level lies in a peak in the paramagnetic density of states, and the
ferromagnetic phase is more stable. As first predicted by Schwarz, the magnetic
moment is 2 \mu_B per Cr atom, with the Fermi level for minority spins lying in
an insulating gap between oxygen p and chromium d states ("half-metallic"
behavior.) The A_1g Raman frequency is predicted to be 587 cm^{-1}. Drude
plasma frequencies are of order 2eV, as seen experimentally by Chase. The
measured resistivity is used to find the electron mean-free path l, which is
only a few angstroms at 600K, but nevertheless, resistivity continues to rise
as temperature increases. This puts CrO_2 into the category of "bad metals" in
common with the high T_c superconductors, the high T metallic phase of VO_2,
and the ferromagnet SrRuO_3. In common with both SrRuO_3 and Sr_2RuO_4, the
measured specific heat \gamma is higher than band theory by a renormalization
factor close to 4. | 9608006v1 |
2013-01-13 | A new lower limit for the bond breaking strains of defect-free carbon nanotubes: Tight binding MD simulation study | The Order (N) Tight Binding Molecular Dynamics (TBMD) algorithms applied to
simulate the tensile elongations of short (2-2.5 nm) armchair and zigzag Single
Walled Carbon Nanotubes (SWCNTs) without bond breakings or defect formation.
Simulations are repeated at high temperatures. We fix the lower limit of
breaking strains to short SWCNTs without bond breaking or 5-7 defects
formation. At room temperature, the simulated (4,4) SWCNT is able to carry the
strain up to 130% of the relaxed tube length without bond breaking or 5-7
defects formation. This value is 127% for (11,0) SWCNT, 125% for (17,0) SWCNT,
123% for (10,10) SWCNT. In defect free, short nanotubes as the nanotube's
radius increase the bond-breakings occur at lower strain values regardless of
their chirality. This is true when we heat the tubes to higher temperatures.
Bond breaking strain values, tensile strength, Young's modulus of the SWCNTs
are obtained as functions of temperature. Defect free zigzag nanotubes exhibit
higher tensile strength than armchaired ones. Young's modulus of defect free
individual singlewall nanotubes is found to be in the range of 0.400 TPa within
the elastic limit. At room temperature and experimentally realizable strain
values, thinner tubes are more resistant to bond breaking and zigzag tubes over
armchair ones. At high temperatures although the resistance to strain drops the
same trend still holds. We observe a slight decrease of the tensile strength
with increasing temperatures. The same trend is also observed in the Young's
modulus. Results are important in determining a true breaking strains of
SWCNTs. | 1301.2786v1 |
2013-01-28 | Structural disorder, magnetism, and electrical and thermoelectric properties of pyrochlore Nd2Ru2O7 | Polycrystalline Nd2Ru2O7 samples have been prepared and examined using a
combination of structural, magnetic, and electrical and thermal transport
studies. Analysis of synchrotron X-ray and neutron diffraction patterns
suggests some site disorder on the A-site in the pyrochlore sublattice: Ru
substitutes on the Nd-site up to 7.0(3)%, regardless of the different
preparative conditions explored. Intrinsic magnetic and electrical transport
properties have been measured. Ru 4d spins order antiferromagnetically at 143 K
as seen both in susceptibility and specific heat, and there is a corresponding
change in the electrical resistivity behaviour. A second antiferromagnetic
ordering transition seen below 10 K is attributed to ordering of Nd 4f spins.
Nd2Ru2O7 is an electrical insulator, and this behaviour is believed to be
independent of the Ru-antisite disorder on the Nd site. The electrical
properties of Nd2Ru2O7 are presented in the light of data published on all
A2Ru2O7 pyrochlores, and we emphasize the special structural role that Bi3+
ions on the A-site play in driving metallic behaviour. High-temperature
thermoelectric properties have also been measured. When considered in the
context of known thermoelectric materials with useful figures-of-merit, it is
clear that Nd2Ru2O7 has excessively high electrical resistivity which prevents
it from being an effective thermoelectric. A method for screening candidate
thermoelectrics is suggested. | 1301.6661v1 |
2015-01-06 | Coexistence of Electron-Glass Phase and Persistent Photoconductivity in GeSbTe Compounds | It is demonstrated that persistent-photoconductivity (PPC), well-studied in
lightly-doped semiconductors, is observable in GeSbTe compounds using infrared
excitation at cryogenic temperatures. The low level of energy-flux necessary to
induce an appreciable effect seems surprising given the high
carrier-concentration n of these ternary alloys. On the other hand, their high
density of carriers makes GeSbTe films favorable candidates for exhibiting
intrinsic electron-glass effects with long relaxation times. These are indeed
observed in GeSbTe thin-films that are Anderson-localized. In particular, a
memory-dip is observed in samples with sheet resistances larger than app. 100
kOhms at T=4K with similar characteristics as in other systems that exhibit
intrinsic electron-glass effects. Persistent-photoconductivity however is
observable in GeSbTe films even for sheet resistances of the order of 1 kOhm,
well below the range of disorder required for observing electron-glass effects.
These two non-equilibrium phenomena, PPC and electron-glass, are shown to be of
different nature in terms of other aspects as well. In particular, their
relaxation dynamics is qualitatively different; the excess conductance dG/G
associated with PPC decays with time as a stretched exponential whereas a
logarithmic relaxation law characterizes dG(t) of all electron-glasses studied
to date. Surprisingly, the magnitude of the memory-dip is enhanced when the
system is in the PPC state. This counter-intuitive result may be related to the
compositional disorder in these materials extending over mesoscopic scales.
Evidence in support of this scenario is presented and discussed. | 1501.01163v2 |
2018-11-05 | Outstanding Radiation Resistance of Tungsten-based High Entropy Alloys | A novel W-based refractory high entropy alloy with outstanding radiation
resistance has been developed. The alloy was grown as thin films showing a
bimodal grain size distribution in the nanocrystalline and ultrafine regimes
and a unique 4 nm lamella-like structure revealed by atom probe tomography
(APT). Transmission electron microscopy (TEM) and X-ray diffraction show an
underlying body-centered cubic crystalline structure with certain black spots
appearing after thermal annealing at elevated temperatures. Thorough analysis
based on TEM and APT correlated the black spots with second phase particles
rich in Cr and V. After both in situ and ex situ irradiation, these
precipitates evolve to quasi-spherical particles with no sign of
irradiation-created dislocation loops even after 8 dpa at either room
temperature or 1073 K. Furthermore, nanomechanical testing shows a large
hardness of 14 GPa in the as-deposited samples, with a slight increase after
thermal annealing and almost negligible irradiation hardening. Theoretical
modeling based on ab initio methodologies combined with Monte Carlo techniques
predicts the formation of Cr and V rich second phase particles and points at
equal mobilities of point defects as the origin of the exceptional radiation
tolerance. The fact that these alloys are suitable for bulk production coupled
with the exceptional radiation and mechanical properties makes them ideal
structural materials for applications requiring extreme conditions. | 1811.01915v1 |
2017-04-05 | Cubic lead perovskite PbMoO3 with anomalous metallic behavior | A previously unreported Pb-based perovskite PbMoO$_3$ is obtained by
high-pressure and high-temperature synthesis. This material crystallizes in the
$Pm\bar{3}m$ cubic structure at room temperature, making it distinct from
typical Pb-based perovskite oxides with a structural distortion. PbMoO$_3$
exhibits a metallic behavior down to 0.1 K with an unusual $T$-sub linear
dependence of the electrical resistivity. Moreover, a large specific heat is
observed at low temperatures accompanied by a peak in $C_P/T^3$ around 10 K, in
marked contrast to the isostructural metallic system SrMoO$_3$. These transport
and thermal properties for PbMoO$_3$, taking into account anomalously large Pb
atomic displacements detected through diffraction experiments, are attributed
to a low-energy vibrational mode, associated with incoherent off-centering of
lone pair Pb$^{2+}$ cations. We discuss the unusual behavior of the electrical
resistivity in terms of a polaron-like conduction, mediated by the strong
coupling between conduction electrons and optical phonons of the local
low-energy vibrational mode. | 1704.01270v1 |
2018-12-18 | Hidden kagome-lattice picture and origin of high conductivity in delafossite PtCoO$_2$ | We study the electronic structure of delafossite PtCoO$_2$ to elucidate its
extremely small resistivity and high mobility. The band exhibits steep
dispersion near the Fermi level despite the fact that it is formed mainly by Pt
$d$ orbitals that are typically localized. We propose a picture based on two
hidden kagome-lattice-like electronic structure: one originating from Pt
$s+p_x/p_y$ orbitals, and the other from Pt $d_{3z^2-r^2}+d_{xy}/d_{x^2-y^2}$
orbitals, each placed on the bonds of the triangular lattice. In particular, we
find that the underlying Pt $s+p_x/p_y$ bands actually determine the steepness
of the original dispersion, so that the large Fermi velocity can be attributed
to the large width of the Pt $s+p_x/p_y$ band. More importantly, the
kagome-like electronic structure gives rise to "orbital-momentum locking" on
the Fermi surface, which reduces the electron scattering by impurities. We
conclude that the combination of the large Fermi velocity and the
orbital-momentum locking is likely to be the origin of the extremely small
resistivity in PtCoO$_2$. | 1812.07213v2 |
2019-10-29 | Multi-frequency Shubnikov-de Haas oscillations in topological semimetal Pt$_2$HgSe$_3$ | Monolayer jacutingaite (Pt$_2$HgSe$_3$) has been recently identified as a
candidate quantum spin Hall system with a 0.5 eV band gap, but no transport
measurements have been performed so far on this material, neither in monolayer
nor in the bulk. By using a dedicated high-pressure technique, we grow crystals
enabling the exfoliation of 50-100 nm thick layers and the realization of
devices for controlled transport experiments. Magnetoresistance measurements
indicate that jacutingaite is a semimetal, exhibiting Shubnikov-de Haas (SdH)
resistance oscillations with a multi-frequency spectrum. We adapt the
Lifshitz-Kosevich formula to analyze quantitatively the SdH resistance
oscillations in the presence of multiple frequencies, and find that the
experimental observations are overall reproduced well by band structure
ab-initio calculations for bulk jacutingaite. Together with the relatively high
electron mobility extracted from the experiments ($\approx 2000$ cm$^2$/Vs,
comparable to what is observed in WTe$_2$ crystals of the same thickness), our
results indicate that monolayer jacutingaite should provide an excellent
platform to investigate transport in 2D quantum spin Hall systems. | 1910.13228v2 |
2020-10-11 | Observation of Josephson-like tunneling junction characteristics and positive magnetoresistance in Oxygen deficient Nickelate films of $Nd_{0.8}Sr_{0.2}NiO_{3-δ}$ | Nickelate films have recently attracted broad attention due to the
observation of superconductivity in the infinite layer phase of
$Nd_{0.8}Sr_{0.2}NiO_2$ (obtained by reducing Sr doped $NdNiO_3$ films) and
their similarity to the cuprates high temperature superconductors. Here we
report on the observation of a new type of transport in oxygen poor
$Nd_{0.8}Sr_{0.2}NiO_{3-\delta}$ films. At high temperatures, variable range
hopping is observed while at low temperatures a novel tunneling behavior is
found where Josephson-like tunneling junction characteristic with serial
resistance is revealed. We attribute this phenomenon to coupling between
superconductive (S) surfaces of the grains in our Oxygen poor films via the
insulating (I) grain boundaries, which yields SIS junctions in series with the
normal (N) resistance of the grains themselves. The similarity of the observed
conductance spectra to tunneling junction characteristic with Josephson-like
current is striking, and seems to support the existence of superconductivity in
our samples. | 2010.05277v2 |
2021-04-04 | Mesoporous silica nanoparticles containing silver as novel antimycobacterial agents against Mycobacterium tuberculosis | Tuberculosis remains today a major public health issue with a total of 9
million new cases and 2 million deaths annually. The lack of an effective
vaccine and the increasing emergence of new strains of Mycobacterium
tuberculosis (Mtb) highly resistant to antibiotics, anticipate a complicated
scenario in the near future. The use of nanoparticles features as an
alternative to antibiotics in tackling this problem due to their potential
effectiveness in resistant bacterial strains. In this context, silver
nanoparticles have demonstrated high bactericidal efficacy, although their use
is limited by their relatively high toxicity, which calls for the design of
nanocarriers that allow silver based nanoparticles to be safely delivered to
the target cells or tissues. In this work mesoporous silica nanoparticles are
used as carriers of silver based nanoparticles as antimycobacterial agent
against Mtb. Two different synthetic approaches have been used to afford, on
the one hand, a 2D hexagonal mesoporous silica nanosystem which contains silver
bromide nanoparticles distributed all through the silica network and, on the
other hand, a core@shell nanosystem with metallic silver nanoparticles as core
and mesoporous silica shell in a radial mesoporous rearrangement. Both
materials have demonstrated good antimycobacterial capacity in in vitro test
using Mtb, being lower the minimum inhibitory concentration for the nanosystem
which contains silver bromide. Therefore, the interaction of this material with
the mycobacterial cell has been studied by cryo-electron microscopy,
establishing a direct connection between the antimycobactericidal effect
observed and the damage induced in the cell envelope. | 2104.01649v1 |
2021-04-29 | The dominance of non-electron-phonon charge carrier interaction in highly-compressed superhydrides | The primary mechanism governing the emergence of near-room-temperature
superconductivity in superhydrides is widely accepted to be the electron-phonon
interaction. If so, the temperature dependent resistance, R(T), in these
materials should obey the Bloch-Gr\"uneisen equation, where the power-law
exponent, p, should be equal to the exact integer value of p=5. On the other
hand, there is a well-established theoretical result that pure electron-magnon
interaction should be manifested by p=3, and p=2 is the value for pure
electron-electron interaction. Here we aimed to reveal the type of charge
carrier interaction in the layered transition metal dichalcogenides PdTe2,
high-entropy alloy (ScZrNb)0.65[RhPd]0.35, and highly-compressed elemental
boron and superhydrides H3S, LaHx, PrH9 and BaH12 by fitting the temperature
dependent resistance of these materials to the Bloch-Gr\"uneisen equation where
the power-law exponent, p, is a free-fitting parameter. In the result, we
showed that the high-entropy alloy (ScZrNb)0.65[RhPd]0.35 exhibited pure
electron-phonon mediated superconductivity with p = 4.9. Unexpectedly we
revealed that all studied superhydrides exhibit 1.8 < p < 3.2. This implies
that it is unlikely that the electron-phonon interaction is the primary
mechanism for the Cooper pairs formation in highly-compressed superhydrides and
alternative pairing mechanisms, for instance, the electron-magnon, the
electron-polaron, the electron-electron or other, should be considered as the
origin for the emergence of near-room-temperature superconductivity in these
compounds. | 2104.14145v3 |
2021-09-30 | Physical and Mechanical Properties of Cu-Fe System Functionally Graded and Multimaterial Structures after the DED | This paper is devoted to experimental characterisation of linear thermal
expansion coefficient (LTEC) and mechanical characteristics of the laser
deposited Cu-Fe system multilayer functionally graded (FG) structures and
binary Cu-Fe alloys, fabricated from the tin, aluminium, and chromium bronze
with 89-99 wt.% of copper and stainless steel (SS) AISI 316L with 1:1 and 3:1
bronze-to-steel ratio. The best tensile mechanical strength of as-built parts
is demonstrated by the aluminium bronze-stainless steel 1:1 alloy and reaches
876.4 MPa along with low elasticity modulus (11.2 GPa) and 1.684 1/K LTEC.
Contrarily, the worst values of the mechanical characteristics are exhibited by
parts created from the chromium bronze and SS, which failed at 294.0-463.3 MPa
ultimate stress, showed the highest elasticity modulus (up to 42.4 GPa) and
comparatively high average LTEC (up to 1.878 1/K). The aluminium
bronze-stainless steel binary and FG alloys are discussed in the light of
prospective application as the part of gradient materials, created by additive
manufacturing (AM) technologies via the gradient path method and the
alternating layers technique, with expected possibility of application in
aerospace, nuclear, and electronic industry due to advantageous combination of
the antifrictionality, heat conductivity, and oxidation resistance of the
bronze, and the high mechanical strength, corrosion and creep resistance of the
stainless steel. | 2110.00103v1 |
2021-10-26 | Temperature induced first order electronic topological transition in $β$-Ag$_2$Se | $\beta$-Ag$_2$Se is a promising material for room temperature thermoelectric
applications and magneto-resistive sensors. However, no attention was paid
earlier to the hysteresis in the temperature dependence of resistivity
($\rho$($T$)). Here, we show that a broad hysteresis above 35 K is observed not
only in $\rho$($T$), but also in other electronic properties such as Hall
coefficient ($R_H$($T$)), Seebeck coefficient, thermal conductivity and
ultraviolet photoelectron spectra (UPS). We also show that the hysteresis is
not associated with a structural transition. The $\rho$($T$) and $R_H$($T$)
show that $\beta$-Ag$_2$Se is semiconducting above 300 K, but metallicity is
retained below 300 K. While electronic states are absent in the energy range
from the Fermi level ($E_F$) to 0.4 eV below the $E_F$ at 300 K, a distinct
Fermi edge is observed in the UPS at 15 K suggesting that the $\beta$-Ag$_2$Se
undergoes an electronic topological transition from a high temperature
semiconducting state to a low temperature metallic state. Our study reveals
that a constant and moderately high thermoelectric figure of merit ($ZT$) in
the range 300-395 K is observed due to the broad semiconductor to metal
transition in $\beta$-Ag$_2$Se. | 2110.13554v1 |
2021-11-11 | Current-induced superconducting anisotropy of Sr$\mathsf{_2}$RuO$\mathsf{_4}$ | In the unconventional superconductor Sr$\mathsf{_2}$RuO$\mathsf{_4}$, unusual
first-order superconducting transition has been observed in the low-temperature
and high-field region, accompanied by a four-fold anisotropy of the in-plane
upper critical magnetic field $H_{c2}$. The origin of such unusual $H_{c2}$
behavior should be closely linked to the debated superconducting symmetry of
this oxide. Here, toward clarification of the unusual $H_{c2}$ behavior, we
performed the resistivity measurements capable of switching in-plane current
directions as well as precisely controlling the field directions. Our results
reveal that resistive $H_{c2}$ under the in-plane current exhibits an
additional two-fold anisotropy. By systematically analyzing $H_{c2}$ data taken
under various current directions, we succeeded in separating the two-fold
$H_{c2}$ component into the one originating from applied current and the other
originating from certain imperfection in the sample. The former component,
attributable to vortex flow effect, is weakened at low temperatures where
$H_{c2}$ is substantially suppressed. The latter component is enhanced in the
first order transition region, possibly reflecting a change in the nature of
the superconducting state under high magnetic field. | 2111.06097v1 |
2022-03-08 | Electronic effects on the radiation damage in high-entropy alloys | High-entropy alloys (HEAs) are exceptional candidates for radiation-resistant
materials due to their complex local chemical environment and slow defect
migration. Despite commonly overlooked, electronic effects on defects evolution
in radiation environments also play a crucial role by dissipating excess energy
through electron-phonon coupling and electronic heat conduction during cascade
events. We present a systematic study on electronic properties in random-solid
solutions (RSS) in four and five principal elements HEAs and their effect on
defect formation, clustering, and recombination. Electronic properties,
including electron-phonon coupling factor, the electronic specific heat, and
the electronic thermal conductivity, are computed within first-principles
calculations. Using the two-temperature molecular dynamics simulations, we show
that the electron-phonon coupling factor and electronic specific heat play a
critical role in Frenkel pairs formation. Specifically, the electron-phonon
coupling factor quickly dissipates the kinetic energy during primary knock-on
atom events via plasmon excitations and is subsequently dissipated via the
free-electrons conduction. We show that these effects are more critical than
the elastic distortion effects produced by the atomic mismatch. Of tremendous
interest, we show that including lighter elements helps to increase the
electron-phonon coupling factor, suggesting the possibility to improve
radiation resistance in HEA through optimal composition. | 2203.03779v2 |
2019-07-29 | Linear-$T$ resistivity from low to high temperature: axion-dilaton theories | The linear-$T$ resistivity is one of the hallmarks of various strange metals
regardless of their microscopic details. Towards understanding this universal
property, the holographic method or gauge/gravity duality has made much
progress. Most holographic models have focused on the low temperature limit,
where the linear-$T$ resistivity has been explained by the infrared geometry.
We extend this analysis to high temperature and identify the conditions for a
robust linear-$T$ resistivity up to high temperature. This extension is
important because, in experiment, the linear-$T$ resistivity is observed in a
large range of temperatures, up to room temperature. In the axion-dilaton
theories we find that, to have a robust linear-$T$ resistivity, the strong
momentum relaxation is a necessary condition, which agrees with the previous
result for the Guber-Rocha model. However, it is not sufficient in the sense
that, among large range of parameters giving a linear-$T$ resistivity in low
temperature limit, only very limited parameters can support the linear-$T$
resistivity up to high temperature even in strong momentum relaxation. We also
show that the incoherent term in the general holographic conductivity formula
or the coupling between the dilaton and Maxwell term is responsible for a
robust linear-$T$ resistivity up to high temperature. | 1907.12168v3 |
2015-01-16 | Phonon transmission across Mg2Si/Mg2Si1-xSnx interfaces: A first-principles-based atomistic Green's function study | Phonon transmission across interfaces of dissimilar materials has been
studied intensively in the recent years by using atomistic simulation tools
owing to its importance in determining the effective thermal conductivity of
nanostructured materials. Atomistic Green's function (AGF) method with
interatomic force constants from the first-principles (FP) calculations has
evolved to be a promising approach to study phonon transmission in many not
well-studied material systems. However, the direct FP calculation for
interatomic force constants becomes infeasible when the system involves atomic
disorder. Mass approximation is usually used, but its validity has not been
tested. In this paper, we employ the higher-order force constant model to
extract harmonic force constants from the FP calculations, which originates
from the virtual crystal approximation but considers the local force-field
difference. As a feasibility demonstration of the proposed method that
integrates higher-order force constant model from the FP calculations with the
AGF, we study the phonon transmission in the Mg2Si/Mg2Si1-xSnx systems. When
integrated with the AGF, the widely-used mass approximation is found to
overpredict phonon transmission across Mg2Si/Mg2Sn interface. The difference
can be attributed to the absence of local strain field-induced scattering in
the mass approximation, which makes the high-frequency phonons less scattered.
The frequency-dependent phonon transmission across an interface between a
crystal and an alloy, which often appears in high efficiency "nanoparticle in
alloy" thermoelectric materials, is studied. The interfacial thermal resistance
across Mg2Si/Mg2Si1-xSnx interface is found to be weakly dependent on the
composition of Sn when the composition x is less than 40%, but increases
rapidly when it is larger than 40% due to the transition of high-frequency
phonon DOS in Mg2Si1-xSnx alloys. | 1501.04084v1 |
2020-06-19 | Dionysian Hard Sphere Packings are Mechanically Stable at Vanishingly Low Densities | High strength-to-weight ratio materials can be constructed by either
maximizing strength or minimizing weight. Tensegrity structures and aerogels
take very different paths to achieving high strength-to-weight ratios but both
rely on internal tensile forces. In the absence of tensile forces, removing
material eventually destabilizes a structure. Attempts to maximize the
strength-to-weight ratio with purely repulsive spheres have proceeded by
removing spheres from already stable crystalline structures. This results in a
modestly low density and a strength-to-weight ratio much worse than can be
achieved with tensile materials. Here, we demonstrate the existence of a
packing of hard spheres that has asymptotically zero density and yet maintains
finite strength, thus achieving an unbounded strength-to-weight ratio. This
construction, which we term Dionysian, is the diametric opposite to the
Apollonian sphere packing which completely and stably fills space. We create
tools to evaluate the stability and strength of compressive sphere packings.
Using these we find that our structures have asymptotically finite bulk and
shear moduli and are linearly resistant to every applied deformation, both
internal and external. By demonstrating that there is no lower bound on the
density of stable structures, this work allows for the construction of
arbitrarily lightweight high-strength materials. | 2006.11415v3 |
2020-06-30 | Electrothermal Transport Induced Material Re Configuration and Performance Degradation of CVD Grown Monolayer MoS2 Transistors | We report, for CVD-grown monolayer MoS2, the very first results on temporal
degradation of material and device performance under electrical stress. Both
low and high field regimes of operation are explored at different temperatures,
gate bias and stress cycles. During low field operation, current is found to
saturate after hundreds of seconds of operation with the current decay time
constant being a function of temperature and stress cycle. Current saturation
after several seconds during low field operation occurs when a thermal
equilibrium is established. However, high field operation, especially at low
temperature, leads to impact ionization assisted material and device
degradation. It is found that high field operation at low temperature results
in amorphization of the channel and is verified by device and Kelvin Probe
Force Microscopy (KPFM) analyses. In general, a prolonged room temperature
operation of CVD-grown MoS2 transistors lead to degraded gate control, higher
OFF state current and negative shift in threshold voltage (VT). This is further
verified, through micro-Raman and Photoluminescence spectroscopy, which suggest
that a steady state DC electrical stress leads to the formation of localized
low resistance regions in the channel and a subsequent loss of transistor
characteristics. Our findings unveil unique mechanism by which CVD MoS2
undergoes material degradation under electrical stress and subsequent breakdown
of transistor behavior. Such an understanding of material and device
reliability helps in determining the safe operating regime from device as well
as circuit perspective. | 2006.16952v1 |
2020-08-12 | High Rate Hybrid MnO2@CNT Fabric Anode for Li-Ion Batteries: Properties and Lithium Storage Mechanism by In-Situ Synchrotron X-Ray Scattering | High-performance anodes for rechargeable Li-ion battery are produced by
nanostructuring of the transition metal oxides on a conductive support. Here,
we demonstrate a hybrid material of MnO2 directly grown onto fabrics of carbon
nanotube fibres, which exhibits notable specific capacity over 1100 and 500
mAh/g at a discharge current density of 25 mA/g and 5 A/g, respectively, with
coulombic efficiency of 97.5 %. Combined with 97 % capacity retention after
1500 cycles at a current density of 5 A/g, both capacity and stability are
significantly above literature data. Detailed investigations involving
electrochemical and in situ synchrotron X-ray scattering study reveal that
during galvanostatic cycling, MnO2 undergoes an irreversible phase transition
to LiMnO2, which stores lithium through an intercalation process, followed by
conversion mechanism and pseudocapacitive processes. This mechanism is further
confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. The
fraction of pseudocapacitive charge storage ranges from 27% to 83%, for current
densities from 25 mA/g to 5 A/g. Firm attachment of the active material to the
built-in current collector makes the electrodes flexible and mechanically
robust, and ensures that the low charge transfer resistance and the high
electrode surface area remain after irreversible phase transition of the active
material and extensive cycling. | 2008.05169v1 |
2021-12-01 | Unraveling diffusion kinetics of honeycomb structured Na$_2$Ni$_2$TeO$_6$ as a high-potential and stable electrode for sodium-ion batteries | In search of the potential cathode materials for sodium-ion batteries and to
understand the diffusion kinetics, we report the detailed analysis of
electrochemical investigation of honeycomb structured Na$_{2}$Ni$_{2}$TeO$_{6}$
material using cyclic voltammetry (CV), electrochemical impedance spectroscopy
(EIS), galvanostatic charge-discharge (GCD) and galvanostatic intermittent
titration technique (GITT). We found the discharge capacities of 82 and 77
mAhg$^{-1}$ at 0.05~C and 0.1~C current rates, respectively, and the
mid-working potential of $\approx$3.9~V at 1~C and high capacity retention of
80\% after 500 cycles at 0.5~C as well as excellent rate capability. The
analysis of CV data at different scan rates reveals the pseudo-capacitive
mechanism of sodium-ion storage. Interestingly, the {\it in-situ} EIS
measurements show a systematic change in the charge-transfer resistance at
different charge/discharge stages as well as after different number of cycles.
The diffusion coefficient extracted using CV, EIS and GITT lies mainly in the
range of 10$^{-10}$ to 10$^{-12}$ cm$^{2}$s$^{-1}$ and the
de-insertion/insertion of Na$^+$-ion concentration during electrochemical
cycling is consistent with the ratio of Ni$^{3+}$/Ni$^{2+}$ valence state
determined by photoemission study. Moreover, the post-cyclic results of
retrieved active material show very stable structure and morphology even after
various charge-discharge cycles. Our detailed electrochemical investigation and
diffusion kinetics studies establish the material as a high working potential
and long life electrode for sodium-ion batteries. | 2112.00536v1 |
2000-04-19 | Role of in-plane dissipation in dynamics of Josephson lattice in high-temperature superconductors | We calculate the flux-flow resistivity of the Josephson vortex lattice in a
layered superconductor taking into account both the inter-plane and in-plane
dissipation channels. We consider the limiting cases of small fields (isolated
vortices) and high fields (overlapping vortices). In the case of the dominating
in-plane dissipation, typical for high-temperature superconductors, the field
dependence of flux-flow resistivity is characterized by {\it three} distinct
regions. As usual, at low fields the flux-flow resistivity grows linearly with
field. When the Josephson vortices start to overlap the flux-flow resistivity
crosses over to the regime of {\it quadratic} field dependence. Finally, at
very high fields the flux-flow resistivity saturates at the c-axis
quasiparticle resistivity. The intermediate quadratic regime indicates dominant
role of the in-plane dissipation mechanism. Shape of the field dependence of
the flux-flow resistivity can be used to extract both components of the
quasiparticle | 0004337v2 |
2014-11-24 | Spatial heterogeneity in drug concentrations can facilitate the emergence of resistance to cancer therapy | Acquired resistance is one of the major barriers to successful cancer
therapy. The development of resistance is commonly attributed to genetic
heterogeneity. However, heterogeneity of drug penetration of the tumor
microenvironment both on the microscopic level within solid tumors as well as
on the macroscopic level across metastases may also contribute to acquired drug
resistance. Here we use mathematical models to investigate the effect of drug
heterogeneity on the probability of escape from treatment and time to
resistance. Specifically we address scenarios with sufficiently efficient
therapies that suppress growth of all preexisting genetic variants in the
compartment with highest drug concentration. To study the joint effect of drug
heterogeneity, growth rate, and evolution of resistance we analyze a multitype
stochastic branching process describing growth of cancer cells in two
compartments with different drug concentration and limited migration between
compartments. We show that resistance is more likely to arise first in the low
drug compartment and from there populate the high drug compartment. Moreover,
we show that only below a threshold rate of cell migration does spatial
heterogeneity accelerate resistance evolution, otherwise deterring drug
resistance with excessively high migration rates. Our results provide new
insights into understanding why cancers tend to quickly become resistant, and
that cell migration and the presence of sanctuary sites with little drug
exposure are essential to this end. | 1411.6684v1 |
2018-10-23 | Relativistic resistive magnetohydrodynamic reconnection and plasmoid formation in merging flux tubes | We apply the general relativistic resistive magnetohydrodynamics code {\tt
BHAC} to perform a 2D study of the formation and evolution of a reconnection
layer in between two merging magnetic flux tubes in Minkowski spacetime.
Small-scale effects in the regime of low resistivity most relevant for dilute
astrophysical plasmas are resolved with very high accuracy due to the extreme
resolutions obtained with adaptive mesh refinement. Numerical convergence in
the highly nonlinear plasmoid-dominated regime is confirmed for a sweep of
resolutions. We employ both uniform resistivity and non-uniform resistivity
based on the local, instantaneous current density. For uniform resistivity we
find Sweet-Parker reconnection, from $\eta = 10^{-2}$ down to $\eta = 10^{-4}$,
for a reference case of magnetisation $\sigma = 3.33$ and plasma-$\beta = 0.1$.
{For uniform resistivity $\eta=5\times10^{-5}$ the tearing mode is recovered,
resulting in the formation of secondary plasmoids. The plasmoid instability
enhances the reconnection rate to $v_{\rm rec} \sim 0.03c$ compared to $v_{\rm
rec} \sim 0.01c$ for $\eta=10^{-4}$.} For non-uniform resistivity with a base
level $\eta_0 = 10^{-4}$ and an enhanced current-dependent resistivity in the
current sheet, we find an increased reconnection rate of $v_{\rm rec} \sim
0.1c$. The influence of the magnetisation $\sigma$ and the plasma-$\beta$ is
analysed for cases with uniform resistivity $\eta=5\times10^{-5}$ and
$\eta=10^{-4}$ in a range $0.5 \leq \sigma \leq 10$ and $0.01 \leq \beta \leq
1$ in regimes that are applicable for black hole accretion disks and jets. The
plasmoid instability is triggered for Lundquist numbers larger than a critical
value of $S_{\rm c} \approx 8000$. | 1810.10116v2 |
2023-11-06 | Quantification of spin-charge interconversion in highly resistive sputtered Bi$_x$Se$_{1-x}$ with non-local spin valves | The development of spin-orbitronic devices, such as magneto-electric
spin-orbit logic devices, calls for materials with a high resistivity and a
high spin-charge interconversion efficiency. One of the most promising
candidates in this regard is sputtered Bi$_x$Se$_{1-x}$. Although there are
several techniques to quantify spin-charge interconversion, to date reported
values for sputtered Bi$_x$Se$_{1-x}$ have often been overestimated due to
spurious effects related to local currents combined with a lack of
understanding of the effect of the interfaces and the use of approximations for
unknown parameters, such as the spin diffusion length. In the present study,
non-local spin valves are used to inject pure spin currents into
Bi$_x$Se$_{1-x}$, allowing us to directly obtain its spin diffusion length as
well as its spin Hall angle, from 10 K up to 300 K. These values, which are
more accurate than those previously reported in sputtered Bi$_x$Se$_{1-x}$,
evidence that the efficiency of this material is not exceptional. Indeed, the
figure of merit for spin-charge interconversion, given by the product of these
two parameters, is slightly under 1 nm. Our work demonstrates the importance of
considering all material parameters and interfaces when quantifying the spin
transport properties of materials with strong spin-orbit coupling. | 2311.03598v1 |
2015-02-10 | Dichotomy between the hole and electrons behavior in the multiband FeSe probed by ultra high magnetic fields | Magnetoresistivity \r{ho}xx and Hall resistivity \r{ho}xy in ultra high
magnetic fields up to 88T are measured down to 0.15K to clarify the multiband
electronic structure in high-quality single crystals of superconducting FeSe.
At low temperatures and high fields we observe quantum oscillations in both
resistivity and Hall effect, confirming the multiband Fermi surface with small
volumes. We propose a novel and independent approach to identify the sign of
corresponding cyclotron orbit in a compensated metal from magnetotransport
measurements. The observed significant differences in the relative amplitudes
of the quantum oscillations between the \r{ho}xx and \r{ho}xy components,
together with the positive sign of the high-field \r{ho}xy , reveal that the
largest pocket should correspond to the hole band. The low-field
magnetotransport data in the normal state suggest that, in addition to one hole
and one almost compensated electron bands, the orthorhombic phase of FeSe
exhibits an additional tiny electron pocket with a high mobility. | 1502.02922v1 |
2023-10-31 | Unlocking ultrastrong high-temperature ceramics: Beyond Equimolar Compositions in High Entropy Nitrides | Traditionally, increasing compositional complexity and chemical diversity of
high entropy alloy ceramics whilst maintaining a stable single-phase solid
solution has been a primary design strategy for the development of new
ceramics. However, only a handful have shown properties that justify the
increased alloying content. Here, we unveil a groundbreaking strategy based on
deviation from conventional equimolar composition towards non-equimolar
composition space, enabling tuning the metastability level of the
supersaturated single-phase solid solution. By employing high-temperature
micromechanical testing of refractory metal-based high entropy nitrides, we
found that the activation of an additional strengthening mechanism upon
metastable phase decomposition propels the yield strength of a non-equimolar
nitride at 1000 C to a staggering 6.9 GPa, that is 40 % higher than the most
robust equimolar nitride. We show that the inherent instability triggers the
decomposition of the solid solution with non-equimolar composition at high
temperatures, inducing strengthening due to the coherency stress of a
spinodally modulated structure, combined with the lattice resistance of the
product solid solution phase. In stark contrast, the strength of equimolar
systems, boasting diverse chemical compositions, declines as a function of
temperature due to the weakening of the lattice resistance and the absence of
other strengthening mechanisms. | 2310.20441v2 |
2010-09-21 | Large yield production of high mobility freely suspended graphene electronic devices on a PMGI based organic polymer | The recent observation of fractional quantum Hall effect in high mobility
suspended graphene devices introduced a new direction in graphene physics, the
field of electron-electron interaction dynamics. However, the technique used
currently for the fabrication of such high mobility devices has several
drawbacks. The most important is that the contact materials available for
electronic devices are limited to only a few metals (Au, Pd, Pt, Cr and Nb)
since only those are not attacked by the reactive acid (BHF) etching
fabrication step. Here we show a new technique which leads to mechanically
stable suspended high mobility graphene devices which is compatible with almost
any type of contact material. The graphene devices prepared on a
polydimethylglutarimide based organic resist show mobilities as high as 600.000
cm^2/Vs at an electron carrier density n = 5.0 10^9 cm^-2 at 77K. This
technique paves the way towards complex suspended graphene based spintronic,
superconducting and other types of devices. | 1009.4213v2 |
2024-02-04 | High temperature internal friction in a Ti-46Al-1Mo-0.2Si intermetallic, comparison with creep behaviour | Advanced g-TiAl based intermetallics Mo-bearing have been developed to obtain
the fine-grained microstructure required for superplastic deformation to be
used during further processing. In the present work we have studied an alloy of
Ti-46Al-1Mo-0.2Si (at%) with two different microstructures, as-cast material
with a coarse grain size above 300 mm, and the hot extruded material exhibiting
a grain size smaller than 20 mm. We have used a mechanical spectrometer
especially developed for high temperature internal friction measurements to
study the defect mobility processes taking place at high temperature. The
internal friction spectra at different frequencies has been studied and
analyzed up to 1360 K in order to characterize the relaxation processes
appearing in this temperature range. A relaxation peak, with a maximum in
between 900 K and 1080 K, depending on the oscillating frequency, has been
attributed to Ti-atoms diffusion by the stress-induced reorientation of
Al-VTi-Al elastic dipoles. The high temperature background in both
microstructural states, as-cast and extruded, has been analyzed, measuring the
apparent activation parameters, in particular the apparent energies of
Ecast(IF) 4.4 +- 0.05 eV and Eext(IF) 4.75 +- 0.05 eV respectively. These
results have been compared to those obtained on the same materials by creep
deformation. We may conclude that the activation parameters obtained by
internal friction analysis, are consistent with the ones measured by creep.
Furthermore, the analysis of the high temperature background allows establish
the difference on creep resistance for both microstructural states | 2402.03389v1 |
1997-03-03 | Evidence for Kondo Effect in Au80Co20 Ribbons | A minimum in resistivity as a function of temperature for an as-quenched
Au80Co20 ribbon prepared by melt-spinning using a wheel surface speed of 20 m
s^{-1} is found at 25 K. No resistivity minimum is found for an as-quenched
ribbon using a wheel surface speed of 60 m s^{-1}, however, upon heat treatment
of this ribbon a resistivity minimum is recovered. The temperature of the
minimum decreases with increasing total time of heat treatment. These
observations are interpretted as evidence for the microstructural control of
the Kondo effect typically found in dilute magnetic alloys in a giant
magnetoresistance granular material. | 9703030v1 |
2006-05-18 | Intrinsic inhomogeneities and effects of resistive switching in doped manganites | The effect of resistive switching in doped manganites being in the
ferromagnetic state has been studied using resistive and magneto-optic methods.
The visualization of magnetic structure of La0.75Sr0.25MnO3-x single crystals,
and its transformation under electric current proposed local superheating of
the material above the Curie temperature, which was supported by numerical
calculation. The obtained results suggest a significant role of
micrometer-scale inhomogeneity of manganites in phase separation, magnetic and
transport properties of the material. | 0605457v1 |
2008-04-29 | Resistivity reduction of boron-doped multi-walled carbon nanotubes synthesized from a methanol solution containing a boric acid | Boron-doped multi-walled carbon nanotubes (MWNTs) were synthesized using a
methanol solution of boric acid as a source material. Accurate measurements of
the electrical resistivity of an individual boron-doped MWNT was performed with
a four-point contact, which was fabricated using an electron beam lithography
technique. The doped boron provides conduction carriers, which reduces the
resistivity of the MWNT. | 0804.4514v1 |
2018-12-20 | Layer-by-layer resistive switching: multi-state functionality due to electric-field-induced healing of "dead" layers | Materials exhibiting reversible resistive switching in electrical fields are
highly demanded for functional elements in oxide electronics. In particular,
multilevel switching effects allow for advanced applications like neuromorphic
circuits. Here we report on a structurally driven switching mechanism involving
the so-called `dead layers' of perovskite manganite surfaces. Forming a tunnel
barrier whose thickness can be changed in monolayer steps by electrical fields,
the switching effect exhibits well-defined and robust resistive states. | 1812.08563v1 |
2019-10-29 | Improvement in corrosion resistance and biocompatibility of AZ31 magnesium alloy by NH+2 ions | Magnesium alloys have been considered to be favorable biodegradable metallic
materials used in orthopedic and cardiovascular applications. We introduce NH+2
to the AZ31 Mg alloy surface by ion implantation at the energy of 50 KeV with
doses ranging from 1e16 ions/cm2 to 1e17 ions/cm2 to improve its corrosion
resistance and biocompatibility. Surface morphology, mechanical properties,
corrosion behavior and biocompatibility are studied in the experiments. The
analysis confirms that the modified surface with smoothness and hydrophobicity
significantly improves the corrosion resistance and biocompatibility while
maintaining the mechanical property of the alloy. | 1910.13265v1 |
2020-01-08 | UV-laser modification and selective ion-beam etching of amorphous vanadium pentoxide thin films | We present the results on excimer laser modification and patterning of
amorphous vanadium pentoxide films. Wet positive resist-type and Ar ion-beam
negative resist-type etching techniques were employed to develop UV-modified
films. V2O5 films were found to possess sufficient resistivity compared to
standard electronic materials thus to be promising masks for sub-micron
lithog-raphy | 2001.03054v1 |
2006-06-20 | Phase study of oscillatory resistances in high mobility GaAs/AlGaAs devices: Indications of a new class of integral quantum Hall effect | An experimental study of the high mobility GaAs/AlGaAs system at large-$\nu$
indicates several distinct phase relations between the oscillatory diagonal-
and Hall- resistances, and suggests a new class of integral quantum Hall
effect, which is characterized by "anti-phase" Hall- and diagonal- resistance
oscillations. | 0606517v1 |
2017-09-15 | Spontaneous surface reserve formation in wicked membranes bestow extreme stretchability | Soft stretchable materials are key for arising technologies such as
stretchable electronics or batteries, smart textiles, biomedical devices,
tissue engineering and soft robotics. Recent attempts to design such materials,
via e.g. micro-patterning of wavy fibres on soft substrates, polymer
engineering at the molecular level or even kirigami techniques, provide
appealing prospects but suffer drawbacks impacting the material viability:
complexity of manufacturing, fatigue or failure upon cycling, restricted range
of materials or biological incompatibility. Here, we report a universal
strategy to design highly stretchable, self-assembling and fatigue-resistant
synthetic fabrics. Our approach finds its inspiration in the mechanics of
living animal cells that routinely encounter and cope with extreme
deformations, e.g. with the engulfment of large intruders by macrophages,
squeezing and stretching of immune cells in tiny capillaries or
shrinking/swelling of neurons upon osmotic stimuli. All these large instant
deformations are actually mediated and buffered by membrane reserves available
in the form of microvilli, membrane folds or endomembrane that can be recruited
on demand. We synthetically mimicked this behavior by creating nanofibrous
liquid-infused tissues spontaneously forming surface reserves whose unfolding
fuels any imposed shape change. Our process, relying only on geometry,
elasticity and capillarity, allows to endow virtually any material with high
stretchability and reversibility, making it straightforward to implement
additional mechanical, electrical or chemical functions. We illustrate this
with proof-of-concept activable capillary muscles, adaptable slippery liquid
infused porous surfaces and stretchable basic printed electronic circuits. | 1709.05228v1 |
2018-02-26 | Trilayer TMDC Heterostructures for MOSFETs and Nanobiosensors | Two dimensional materials such as Transition Metal Dichalcogenides (TMDC) and
their bi-layer/tri-layer heterostructures have become the focus of intense
research and investigation in recent years due to their promising applications
in electronics and optoelectronics. In this work, we have explored device level
performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M=Mo or, W and X=S
or, Se) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) in the
quantum ballistic regime. Our simulation shows that device 'on' current can be
improved by inserting a WS2 monolayer between two MoS2 monolayers. Application
of biaxial tensile strain reveals a reduction in drain current which can be
attributed to the lowering of carrier effective mass with increased tensile
strain. In addition, it is found that gate underlap geometry improves
electrostatic device performance by improving sub-threshold swing. However,
increase in channel resistance reduces drain current. Besides exploring the
prospect of these materials in device performance, novel trilayer TMDC
heterostructure double gate Field Effect Transistors (FETs) are proposed for
sensing Nano biomolecules as well as for pH sensing. Bottom gate operation
ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation
results found in this work reveal that scaling of bottom gate oxide results in
better sensitivity while top oxide scaling exhibits an opposite trend. It is
also found that, for identical operating conditions, proposed TMDC FET pH
sensors show super-Nernst sensitivity indicating these materials as potential
candidates in implementing such sensor. Besides pH sensing, all these materials
show high sensitivity in the sub-threshold region as a channel material in
nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them. | 1802.09141v1 |
2018-06-07 | Plasmonics in Argentene | Two-dimensional materials exhibit a fascinating range of electronic and
photonic properties vital for nanophotonics, quantum optics and emerging
quantum information technologies. Merging concepts from the fields of ab initio
materials science and nanophotonics, there is now an opportunity to engineer
new photonic materials whose optical, transport, and scattering properties are
tailored to attain thermodynamic and quantum limits. Here, we present
first-principles calculations predicting that Argentene, a single-crystalline
hexagonal close-packed monolayer of Ag, can dramatically surpass the optical
properties and electrical conductivity of conventional plasmonic materials. In
the low-frequency limit, we show that the scattering rate and resistivity
reduce by a factor of three compared to the bulk three-dimensional metal. Most
importantly, the low scattering rate extends to optical frequencies in sharp
contrast to e.g. graphene, whose scattering rate increase drastically in the
near-infrared range due to optical-phonon scattering. Combined with an
intrinsically high carrier density, this facilitates highly-confined surface
plasmons extending to visible frequencies. We evaluate Argentene across three
distinct figures of merit, spanning the spectrum of typical plasmonic
applications; in each, Argentene outperforms the state-of-the-art. This unique
combination of properties will make Argentene a valuable addition to the
two-dimensional heterostructure toolkit for quantum electronic and photonic
technologies. | 1806.02672v1 |
2023-03-22 | Enhanced functional reversibility in lead-free ferroelectric material over long cycle pyroelectric energy conversion | The ferroelectric material usually exhibits temperature dependent spontaneous
polarization, known as pyroelectricity, which can be used to directly convert
thermal energy to electricity from ambient low-grade waste heat. When utilizing
the structural phase transformations of the material, the conversion capability
can be magnified, consequently the device performance can be strongly boosted
by orders of magnitude. However, common ferroelectric oxides suffer the
mechanical fatigue and functional degradation over cyclic phase
transformations, hindering widespread applications of the energy conversion
device. In this paper, we investigate the mechanical and functional
reversibility of the material by lattice tuning and grain coarsening. We
discover the lead-free compound
Ba(Ce$_{0.005}$Zr$_{0.005}$)Ti$_{0.99}$O3-0.10(Ba$_{0.7}$Ca$_{0.3}$)TiO$_3$
(BCZT-0.10BCT) satisfying the compatibility condition among all present phases
by its lattice parameters, making the phase transformations highly reversible.
We demonstrated that the energy conversion device with the equiaxial coarse
grains exhibits exceptional fatigue-resistance, with stable pyroelectric
current output at 4$\mu$A/cm$^2$ over 3,000 energy conversion cycles. Our work
opens a new way to fabricate high-performance material that advances the
pyroelectric energy conversion for practical application in engineering. | 2303.12583v1 |
2023-04-28 | Computational study of III-V direct-gap semiconductors for thermoradiative cell applications | We investigate the performance of thermoradiative (TR) cells using the III-V
group of semiconductors, which include GaAs, GaSb, InAs, and InP, with the aim
of determining their efficiency and finding the best TR cell materials among
the III-V group. The TR cells generate electricity from thermal radiation, and
their efficiency is influenced by several factors such as the bandgap,
temperature difference, and absorption spectrum. To create a realistic model,
we incorporate sub-bandgap and heat losses in our calculations and utilize
density-functional theory to determine the energy gap and optical properties of
each material. Our findings suggest that the effect of absorptivity on the
material, especially when the sub-bandgap and heat losses are considered, can
decrease the efficiency of TR cells. However, careful treatment of the
absorptivity indicates that not all materials have the same trend of decrease
in the TR cell efficiency when taking the loss mechanisms into account. We
observe that GaSb exhibits the highest power density, while InP demonstrates
the lowest one. Moreover, GaAs and InP exhibit relatively high efficiency
without the sub-bandgap and heat losses, whereas InAs display lower efficiency
without considering the losses, yet exhibit higher resistance to sub-bandgap
and heat losses compared to the other materials, thus effectively becoming the
best TR cell material in the III-V group of semiconductors. | 2304.14917v1 |
2005-12-21 | Poly-MTO, {(CH_3)_{0.92} Re O_3}_\infty, a Conducting Two-Dimensional Organometallic Oxide | Polymeric methyltrioxorhenium, {(CH_{3})_{0.92}ReO_{3}}_{\infty} (poly-MTO),
is the first member of a new class of organometallic hybrids which adopts the
structural pattern and physical properties of classical perovskites in two
dimensions (2D). We demonstrate how the electronic structure of poly-MTO can be
tailored by intercalation of organic donor molecules, such as
tetrathiafulvalene (TTF) or bis-(ethylendithio)-tetrathiafulvalene (BEDT-TTF),
and by the inorganic acceptor SbF$_3$. Integration of donor molecules leads to
a more insulating behavior of poly-MTO, whereas SbF$_3$ insertion does not
cause any significant change in the resistivity. The resistivity data of pure
poly-MTO is remarkably well described by a two-dimensional electron system.
Below 38 K an unusual resistivity behavior, similar to that found in doped
cuprates, is observed: The resistivity initially increases approximately as
$\rho \sim$ ln$(1/T$) before it changes into a $\sqrt{T}$ dependence below 2 K.
As an explanation we suggest a crossover from purely two-dimensional
charge-carrier diffusion within the \{ReO$_2$\}$_{\infty}$ planes at high
temperatures to three-dimensional diffusion at low temperatures in a
disorder-enhanced electron-electron interaction scenario (Altshuler-Aronov
correction). Furthermore, a linear positive magnetoresistance was found in the
insulating regime, which is caused by spatial localization of itinerant
electrons at some of the Re atoms, which formally adopt a $5d^1$ electronic
configuration. X-ray diffraction, IR- and ESR-studies, temperature dependent
magnetization and specific heat measurements in various magnetic fields suggest
that the electronic structure of poly-MTO can safely be approximated by a
purely 2D conductor. | 0512544v1 |
2017-10-10 | Clustered vacancies in ZnO: Chemical aspects and consequences on physical properties | Chemical nature of point defects, their segregation, cluster or complex
formation in ZnO is an important area of investigation. In this report, 1.2 MeV
Ar ion beam is used to incorporate defects in granular ZnO. Evolution of
defective state with irradiation fluence 1 x 10^14 and 1 x 10^16 ions/cm2 has
been monitored using XPS, PL and Raman spectroscopic study. XPS study shows
presence of oxygen vacancies (VO) in the Ar ion irradiated ZnO. Zn(LMM) Auger
spectra clearly identifies transition involving metallic zinc in the irradiated
samples. Intense PL emission from IZn related shallow donor bound excitons
(DBX) is visible in the 10 K spectra for all samples. Although overall PL is
largely reduced with irradiation disorder, DBX intensity is increased for the
highest fluence irradiated sample. Raman study indicates damage in both zinc
and oxygen sub-lattice by energetic ion beam. Representative Raman modes from
defect complexes involving VO, IZn and IO are visible after irradiation with
intermediate fluence. Further increase of fluence shows, to some extent, a
homogenization of disorder. Huge reduction of resistance is also noted for this
sample. Certainly, high irradiation fluence induces a qualitative modification
of the conventional (and highly resistive) grain boundary (GB) structure of
granular ZnO. Low resistive path, involving IZn related shallow donors, across
the GB can be presumed to explain resistance reduction. Open volumes (VZn and
VO) agglomerate more and more with increasing irradiation fluence and finally
get transformed to voids. Results as a whole have been elucidated with a model
which emphasizes possible evolution of new defect microstructure that is
distinctively different from the GB related disorder. Based on the model,
qualitative explanations of commonly observed radiation hardness, colouration
and ferromagnetism in disordered ZnO have been put forward. | 1710.03696v1 |
2021-09-23 | Zero Magnetic Field Plateau Phase Transition in Higher Chern Number Quantum Anomalous Hall Insulators | The plateau-to-plateau transition in quantum Hall effect under high magnetic
fields is a celebrated quantum phase transition between two topological states
through either sweeping the magnetic field or tuning the carrier density. The
recent realization of the quantum anomalous Hall (QAH) insulators with tunable
Chern numbers introduces the channel degree of freedom to the dissipation-free
chiral edge transport and makes the study of the quantum phase transition
between two topological states under zero magnetic field possible. Here, we
synthesized the magnetic topological insulator (TI)/TI penta-layer
heterostructures with different Cr doping concentrations in the middle magnetic
TI layers using molecular beam epitaxy (MBE). By performing transport
measurements, we found a zero magnetic field quantum phase transition between
the C = 1 and C = 2 QAH states. In tuning the transition, the Hall resistance
monotonically decreases from h/e2 to h/2e2, concurrently, the longitudinal
resistance exhibits a maximum at the critical point. Our results show that the
ratio between the Hall resistance and the longitudinal resistance is greater
than 1 at the critical point, which indicates that the original chiral edge
channel from the C = 1 QAH state coexists with the dissipative bulk conduction
channels. Subsequently, these bulk conduction channels appear to self-organize
and form the second chiral edge channel in completing the plateau phase
transition. Our study will motivate further investigations of this novel Chern
number change-induced quantum phase transition and advance the development of
the QAH chiral edge current-based electronic and spintronic devices. | 2109.11382v1 |
2023-07-15 | Planar Hall effect and Anisotropic Magnetoresistance in Thin Films of Chiral Antiferromagnet Mn3Sn | Antiferromagnetic Weyl semimetals with spin chirality offer excellent
platforms to address the Berry phase physics, which manifests prominently in
several of their electro-optical and electro-magnetic responses including as a
large anomalous Hall effect (AHE) and spin Hall conductivity. Here, we report
measurements of magneto-transport in c-axis textured Mn3Sn thin films grown on
the [111] plane of single crystal MgO. At room temperature, these films display
a weak uncompensated magnetic moment of \approx 0.12 \micro_{B}/f.u. in the
basal plane and a longitudinal resistivity (\rho_{xx}) close to \approx 3.8
\micro\Omega.m. A residual resistivity ration (\rho_{xx} (300 K)/\rho_{xx} (2
K)) of \approx 3.92 further indicates the high quality of the films. While at
300 K a weak AHE together with field-linear Hall resistivity (\rho_{xy}) is
observed in magnetic fields (H) applied perpendicular to the Kagome planes, the
temperature (T) dependence of \rho_{xy} shows prominent signatures of three
magnetic phases in the temperature regime of 2 to 300 K. The \rho_{xy} also
derives a non-trivial topological contribution (\r{ho}THE \approx 1n\Omega.m)
in the spin glass phase which appears at T \geq 100 K. Our measurements of
anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) over a wide
H-T phase space reveal the hitherto unseen effects in the three magnetic phases
of Mn3Sn. While the AMR and PHE are negative in the inverse triangular spin
phase (250 K \geq T \geq TN), the helical phase (100 \geq T \geq 250 K) is
devoid of anisotropic in-plane resistivity, and the spin glass phase shows a
sign reversal of AMR with the increasing magnetic field. The origin of this
sign change in AMR/PHE is attributed to the emergence of topologically
protected spin textures like skyrmions where the fictitious effective magnetic
field is estimated to be \approx 4.4 tesla. | 2307.07795v1 |
2024-02-27 | Field, frequency and temperature dependence of the surface resistance of nitrogen diffused niobium superconducting radio frequency cavities | We report the RF performance of several single-cell superconducting
radio-frequency cavities subjected to low temperature heat treatment in
nitrogen environment. The cavities were treated at temperature 120 - 165
$^{\circ}$C for an extended period of time (24 - 48 hours) either in high
vacuum or in a low partial pressure of ultra-pure nitrogen. The improvement in
$Q_0$ with a Q-rise was observed when nitrogen gas was injected at $\sim$300
$^{\circ} $C during the cavity cooldown from 800 $^{\circ}$C and held at 165
$^{\circ}$C, without any degradation in accelerating gradient over the baseline
performance. The treatment was applied to several elliptical cavities with
frequency ranging from 0.75 GHz to 3.0 GHz, showing an improved quality factor
as a result of low temperature nitrogen treatments. The Q-rise feature is
similar to that achieved by nitrogen alloying Nb cavities at higher
temperature, followed by material removal by electropolishing. The surface
modification was confirmed by the change in electronic mean free path and tuned
with the temperature and duration of heat treatment. The decrease of the
temperature-dependent surface resistance with increasing RF field, resulting in
a Q-rise, becomes stronger with increasing frequency and decreasing
temperature. The data suggest a crossover frequency of $\sim 0.95$~GHz above
which the Q-rise phenomenon occurs at 2~K. Some of these results can be
explained qualitatively with an existing model of intrinsic field-dependence of
the surface resistance with both equilibrium and nonequilibrium quasiparticle
distribution functions. The change in the Q-slope below 0.95 GHz may result
from masking contribution of trapped magnetic flux to the residual surface
resistance. | 2402.17458v3 |
2010-05-10 | Advances in the Development of Micropattern Gaseous Detectors with Resistive Electrodes | We describe the most recent efforts made by various groups in implementing
resistive electrodes in micropattern gaseous detectors with the aim to combine
in the same design the best features of RPCs (for the example, their robustness
and spark protection property) with the high granularity and thus the good
position resolution offered by microelectronic technology. In the stream of
this activity, we have recently developed two novel detectors with resistive
electrodes: one was based on resistive micromeshes and the second one is a MSGC
with resistive electrodes. We have demonstrated that the resistive meshes are a
convenient construction element for various designs of spark protective
detectors: RPCs type, GEM type and MICROMEGAS type. These new detectors enable
to considerably enhance the RPC and micropattern detectors applications since
they feature not only a high position resolution but also a relatively good
energy resolution (25-30 persent FWHM at 6 keV) and, if necessary, they can
operate in cascaded mode allowing the achievement of a high overall gas gain.
The main conclusion from these studies is that the implementation of resistive
electrodes in micropattern detectors makes them fully spark protected; on this
basis we consider this direction very promising. | 1005.1477v1 |
2020-03-03 | Filled Carbon Nanotubes as Anode Materials for Lithium-Ion Batteries | Downsizing well-established materials to the nanoscale is a key route to
novel functionalities, in particular if different functionalities are merged in
hybrid nanomaterials. Hybrid carbon-based hierarchical nanostructures are
particularly promising for electrochemical energy storage since they combine
benefits of nanosize effects, enhanced electrical conductivity and integrity of
bulk materials. We show that endohedral multiwalled carbon nanotubes (CNT)
encapsulating high-capacity (here: conversion and alloying) electrode materials
have a high potential for use in anode materials for lithium-ion batteries
(LIB). There are two essential characteristics of filled CNT relevant for
application in electrochemical energy storage: (1) rigid hollow cavities of the
CNT provide upper limits for nanoparticles in their inner cavities which are
both separated from the fillings of other CNT and protected against
degradation. In particular, the CNT shells resist strong volume changes of
encapsulates in response to electrochemical cycling, which in conventional
conversion and alloying materials hinders application in energy storage
devices. (2) Carbon mantles ensure electrical contact to the active material as
they are unaffected by potential cracks of the encapsulate and form a stable
conductive network in the electrode compound. Our studies confirm that
encapsulates are electrochemically active and can achieve full theoretical
reversible capacity. The results imply that encapsulating nanostructures inside
CNT can provide a route to new high-performance nanocomposite anode materials
for LIB. | 2003.01379v1 |
2014-10-16 | Electron beam induced current in the high injection regime | Electron beam induced current (EBIC) is a powerful technique which measures
the charge collection efficiency of photovoltaics with sub-micron spatial
resolution. The exciting electron beam results in a high generation rate
density of electron-hole pairs, which may drive the system into nonlinear
regimes. An analytic model is presented which describes the EBIC response when
the {\it total} electron-hole pair generation rate exceeds the rate at which
carriers are extracted by the photovoltaic cell, and charge accumulation and
screening occur. The model provides a simple estimate of the onset of the high
injection regime in terms of the material resistivity and thickness, and
provides a straightforward way to predict the EBIC lineshape in the high
injection regime. The model is verified by comparing its predictions to
numerical simulations in 1 and 2 dimensions. Features of the experimental data,
such as the magnitude and position of maximum collection efficiency versus
electron beam current, are consistent with the 3 dimensional model. | 1410.4435v1 |
2018-04-09 | Self-Modulation Doping Effect in the High-Mobility Layered Semiconductor Bi2O2Se | Recently an air-stable layered semiconductor Bi2O2Se was discovered to
exhibit an ultrahigh mobility in transistors fabricated with its thin layers.
In this work, we explored the mechanism that induces the high mobility and
distinguishes Bi2O2Se from other semiconductors. We found that the electron
donor states lie above the lowest conduction band. Thus, electrons get
spontaneously ionized from donor sites (e.g., Se vacancies) without involving
the thermal activation, different from the donor ionization in conventional
semiconductors. Consequently, the resistance decreases as reducing the
temperature as observed in our measurement, which is similar to a metal but
contrasts to a usual semiconductor. Furthermore, the electron conduction
channels locate spatially away from ionized donor defects (Se vacancies) in
different van der Waals layers. Such a spatial separation can strongly suppress
the scattering caused by donor sites and subsequently increase the electron
mobility, especially at the low temperature. We call this high-mobility
mechanism self-modulation doping, i.e. the modulation doping spontaneously
happening in a single-phase material without requiring a heterojunction. Our
work paves a way to design novel high-mobility semiconductors with layered
materials. | 1804.03186v1 |
2019-05-21 | Persistent antiferromagnetic order in heavily overdoped Ca$_{1-x}$La$_x$FeAs$_2$ | In the Ca$_{1-x}$La$_x$FeAs$_2$ (112) family of pnictide superconductors, we
have investigated a highly overdoped composition (x = 0.56), prepared by
high-pressure, high-temperature synthesis. Magnetic measurements show an
antiferromagnetic transition at TN = 120K, well above the one at lower doping
(0.15 < x < 0.27). Below the onset of long-range magnetic order at TN, the
electrical resistivity is strongly reduced and is dominated by
electron-electron interactions, as evident from its temperature dependence. The
Seebeck coefficient shows a clear metallic behavior as in narrow band
conductors. The temperature dependence of the Hall coefficient and the
violation of Kohler's rule agree with the multiband character of the material.
No superconductivity was observed down to 1.8 K. The success of the
high-pressure synthesis encourages further investigations of the so far only
partially explored phase diagram in this family of Iron-based high temperature
superconductors. | 1905.08640v1 |
2019-09-10 | Low temperature deformation of MoSi$_2$ and the effect of Ta, Nb and Al as alloying elements | Molybdenum disilicide (MoSi$_2$) is a very promising material for high
temperature structural applications due to its high melting point (2030
{\deg}C), low density, high thermal conductivity and good oxidation resistance.
However, MoSi$_2$ has limited ductility below 900 {\deg}C due to its
anisotropic plastic deformation behaviour and high critical resolved shear
stresses on particular slip systems. Nanoindentation of MoSi$_2$ microalloyed
with aluminium, niobium or tantalum showed that all alloying elements cause a
decrease in hardness. Analysis of surface slip lines indicated the activation
of the additional {1 1 0}<1 1 1> slip system in microalloyed MoSi$_2$, which is
not active below 300 {\deg}C in pure MoSi$_2$. This was confirmed by TEM
dislocation analysis of the indentation plastic zone. Further micropillar
compression experiments comparing pure MoSi$_2$ and the Ta-alloyed sample
enabled the determination of the critical resolved shear stresses of individual
slip systems even in the most brittle [0 0 1] crystal direction. | 1909.04707v1 |
2017-07-06 | A General Perspective of Fe-Mn-Al-C Steels | During the last years, the scientific and industrial community has focused on
the astonishing properties of Fe-Mn-Al-C steels. These high advanced steels
allow high-density reductions about ~15% lighter than conventional steels, high
corrosion resistance, high strength (ultimate tensile strength (UTS) ~1 Gpa)
and at the same time ductilities above 60%. The increase of the tensile or
yield strength and the ductility at the same time is almost a special feature
of this kind of new steels, which makes them so interesting for many
applications such as in the automotive, armor and mining industry. The control
of these properties depends on a complex relationship between the chemical
composition of the steel, the test temperature, the external loads and the
processing parameters of the steel. This review has been conceived to tried to
elucidate these complex relations and gather the most important aspects of
Fe-Mn-Al-C steels developed so far. | 1707.01920v2 |
2022-01-11 | Fishtail effect and the vortex phase diagram of high-entropy alloy superconductor | High-entropy alloy (HEA) is an attracting topic raising in materials science
and condensed matter physics. Although several types of superconductors have
been discovered in HEAs, the critical currents (Jc) of HEA superconductors
remain uncharacterized up to now. Here, we systematically study the
current-carrying ability of (TaNb)0.7(HfZrTi)0.5 HEA at various heat treatment
conditions. We obtained the high upper critical field and large current
carrying ability, which point to optimistic applications. Interestingly, the
fishtail or second peak effect was found for the first time in HEA
superconductors, and the position of the vortex pinning force shows a maximum
at 0.72 of the reduced field, which is quite different from the cuprates and
iron-based high-Tc superconductors. Together with the resistive measurements,
the vortex phase diagram is obtained for HEA superconductor. | 2201.03994v1 |
2023-01-12 | Non-centrosymmetric Sr$_{2}$IrO$_{4}$ obtained under High Pressure | Sr$_{2}$IrO$_{4}$ with strong spin-orbit coupling (SOC) and Hubbard repulsion
(U) hosts Mott insulating states. The similar crystal structure, magnetic and
electronic properties, particularly the $d$-wave gap observed in
Sr$_{2}$IrO$_{4}$ enhanced the analogies to cuprate high-$T_{c}$
superconductor, La$_{2}$CuO$_{4}$. The incomplete analogy was due to the lack
of broken inversion symmetry phases observed in Sr$_{2}$IrO$_{4}$. Here, under
high pressure and high temperature conditions, we report a non-centrosymmetric
Sr$_{2}$IrO$_{4}$. The crystal structure and its noncentrosymmetric character
were determined by single crystal X-ray diffraction and high-resolution
scanning transmission electron microscopy (HR-STEM). The magnetic
characterization confirms the Ir$^{4+}$ with $S$ = 1/2 at low temperature in
Sr$_{2}$IrO$_{4}$ with magnetic ordering occurred at around 86 K, where a
larger moment is observed than the ambient pressure Sr$_{2}$IrO$_{4}$.
Moreover, the resistivity measurement shows three-dimensional Mott
variable-range hopping existed in the system. This non-centrosymmetric
Sr$_{2}$IrO$_{4}$ phase appears to be a unique material to offer further
understanding of high-$T_{c}$ superconductivity. | 2301.05282v1 |
2010-12-31 | Processing and study of the composite CdS/Bi-Pb-Sr-Ca-Cu-O | We have fabricated and characterized samples of the superconducting-
semiconducting Bi-Pb-Sb-Sr-Ca-Cu-O/CdS composite. Nano-size particles of CdS
were deposited and introduced into the porosities of the Bi-Pb-Sb-Sr-Ca-Cu-O
material by the spray pyrolysis technique. The morphology and hollow size in
the porous superconducting material as well as the grain size in CdS and the
morphology of the surface of the composite were obtained by Scanning Electron
Microscopy. We obtained the critical superconducting temperature of both the
Bi-Pb-Sb-Sr-Ca-Cu-O and the Bi-Pb-Sb-Sr-Ca-Cu-O/CdS composite measuring the
resistivity. Both show a metallic behaviour just above the superconducting
transition. For the superconductor alone, resistivity starts falling at Tc,on
sup = 99,9 K and reaches zero at Tc,sup=76,3 K. The behaviour of the composite
is different. The transition starts at Tc,on comp = 65,3 K and reaches zero
resistance at Tc,comp = 56,5 K. This seems to indicate that the semiconductor
penetrates the whole superconducting Bi-Pb-Sb-Sr-Ca-Cu-O sample so that there
is no region of pure superconducting material left. Since the materials do not
actually mix (see text) the behaviour might be attributable to the interface.
Also the resistivity curves present a very interesting feature, i.e., below the
temperature at which the composite attains zero-resistivity, a re-entrant
behaviour manifests itself and a finite resistivity peak appears. It increases
to a certain value to drop back to zero at some temperature below. We comment
further on this feature in the text. | 1101.0277v1 |
2009-02-02 | Single crystals of LnFeAsO1-xFx (Ln=La, Pr, Nd, Sm, Gd) and Ba1-xRbxFe2As2: growth, structure and superconducting properties | A review of our investigations on single crystals of LnFeAsO1-xFx (Ln=La, Pr,
Nd, Sm, Gd) and Ba1-xRbxFe2As2 is presented. A high pressure technique has been
applied for the growth of LnFeAsO1-xFx crystals, while Ba1-xRbxFe2As2 crystals
were grown using quartz ampoule method. Single crystals were used for
electrical transport, structure, magnetic torque and spectroscopic studies.
Investigations of the crystal structure confirmed high structural perfection
and show less than full occupation of the (O, F) position in superconducting
LnFeAsO1-xFx crystals. Resistivity measurements on LnFeAsO1-xFx crystals show a
significant broadening of the transition in high magnetic fields, whereas the
resistive transition in Ba1 xRbxFe2As2 simply shifts to lower temperature.
Critical current density for both compounds is relatively high and exceeds
2x109 A/m2 at 15 K in 7 T. The anisotropy of magnetic penetration depth,
measured on LnFeAsO1-xFx crystals by torque magnetometry is temperature
dependent and apparently larger than the anisotropy of the upper critical
field. Ba1-xRbxFe2As2 crystals are electronically significantly less
anisotropic. Point-Contact Andreev-Reflection spectroscopy indicates the
existence of two energy gaps in LnFeAsO1-xFx. Scanning Tunneling Spectroscopy
reveals in addition to a superconducting gap, also some feature at high energy
(~20 meV). | 0902.0224v2 |
2020-03-20 | Anisotropy of the transport properties of NdFeAs(O,F) thin films grown on vicinal substrates | NdFeAs(O,F) thin films having different fluorine contents were grown on 5
deg. or 10 deg. vicinal cut MgO and CaF2 single crystalline substrates by
molecular beam epitaxy. Structural characterisations by reflection high-energy
electron diffraction and x-ray diffraction confirmed the epitaxial growth of
NdFeAs(O,F). The resistivities of the ab-plane and along the c-axis were
derived from the resistivity measurements in the longitudinal and transversal
directions. The c-axis resistivity was always higher than the ab-plane
resistivity, resulting from the anisotropic electronic structure. The
resistivity anisotropy at 300 K was almost constant in the range of 50-90
irrespective of the F content. On the other hand, the resistivity anisotropy at
56 K showed a strong fluorine dependence: the resistivity anisotropy was over
200 for the films with optimum F contents (superconducting transition
temperature Tc around 50 K), whereas the resistivity anisotropy was around 70
for the films in the under-doped regime (Tc between 35 and 45 K). The mass
anisotropy are the effective masses along the c-axis and on the ab-plane) close
to Tc derived from the anisotropic Ginzburg-Landau approach using the
angular-dependency of the ab-plane resistivity was in the range from 2 to 5. On
the assumption that the square of the mass anisotropy is equal to the
resistivity anisotropy, those values are small compared to the normal state
anisotropy. | 2003.09105v1 |
2017-03-23 | Development and characterization of Brassica juncea fruticulosa introgression lines exhibiting resistance to mustard aphid | Background: Mustard aphid is a major pest of Brassica oilseeds. No source for
aphid resistance is presently available in Brassica juncea . A wild crucifer,
Brassica fruticulosa is known to be resistant to mustard aphid. An artificially
synthesized amphiploid, AD-4 (B. fruticulosa x B. rapa var. brown sarson) was
developed for use as a bridge species to transfer fruticulosa resistance to B.
juncea. Using the selfed backcross we could select a large number of lines with
resistance to mustard aphid. This paper reports cytogenetic stability of
introgression lines, molecular evidence for alien introgression and their
reaction to mustard aphid infestation. Results: Majority of introgression lines
had expected euploid chromosome number(2n= 36), showed normal meiosis and high
pollen grain fertility. Well-distributed and transferable simple-sequence
repeats (SSR) markers for all the 18 B. juncea chromosomes helped to
characterize introgression events. Average proportions of recipient and donor
genome in the substitution lines were 49.72 and 35.06%, respectively. Minimum
alien parent genome presence (27.29%) was observed in the introgression line,
Ad3K-280 . Introgressed genotypes also varied for their resistance responses to
mustard aphid infestations under artificial release conditions for two
continuous seasons. Some of the test genotypes showed consistent resistant
reaction. Conclusions: B.juncea-fruticulosa introgression set may prove to be a
very powerful breeding tool for aphid resistance related QTL/gene discovery and
fine mapping of the desired genes/QTLs to facilitate marker assisted transfer
of identified gene(s) for mustard aphid resistance in the background of
commercial mustard genotypes. | 1703.07987v1 |
2020-09-21 | Chaos-induced resistivity in different magnetic configurations | It is widely believed that magnetic reconnection plays an important role in
various eruptive phenomena of space and astrophysical plasmas. The mechanism of
anomalous resistivity, however, has been an open and unsolved problem. The
chaos-induced resistivity proposed by Yoshida (1998) is one of possible
mechanisms for anomalous resistivity. By use of the test particle simulation,
the present work studies the chaos-induced resistivity for different
configurations of reconnection magnetic fields and its distribution in
different chaos regions of reconnection current sheets. The results show that
the chaos-induced resistivity can be 6-7 orders of magnitude higher than the
classical Spitzer resistivity in the X-type chaos regions and 5 orders of
magnitude in the O-type chaos regions. Moreover, in the X-type chaos regions
the chaos-induced resistivity of the magnetized case is higher by a factor of 2
to 3 times than that of the unmagnetized case, but in the O-type chaos regions
the chaos-induced resistivity of the magnetized case is close to or lower than
that of the unmagnetized case. The present work is helpful to the understanding
of the dynamics of reconnection current sheets, especially of the generation
mechanism of the anomalous resistivity of collisionless reconnection regions. | 2009.09745v1 |
2019-12-10 | Temperature and gate effects on contact resistance and mobility in graphene transistors by TLM and Y-function methods | The metal-graphene contact resistance is one of the major limiting factors
toward the technological exploitation of graphene in electronic devices and
sensors. A high contact resistance can be detrimental to device performance and
spoil the intrinsic great properties of graphene. In this paper, we fabricate
graphene field-effect transistors with different geometries to study the
contact and channel resistance as well as the carrier mobility as a function of
gate voltage and temperature. We apply the transfer length method and the
y-function method showing that the two approaches can complement each other to
evaluate the contact resistance and prevent artifacts in the estimation of the
gate-voltage dependence of the carrier mobility. We find that the gate voltage
modulates the contact and the channel resistance in a similar way but does not
change the carrier mobility. We also show that the raising temperature lowers
the carrier mobility, has negligible effect on the contact resistance, and can
induce a transition from a semiconducting to a metallic behavior of the
graphene sheet resistance, depending on the applied gate voltage. Finally we
show that eliminating the detrimental effects of the contact resistance on the
transistor channel current almost doubles the carrier field-effect mobility and
that a competitive contact resistance an be achieved by the zig-zag shaping of
the Ni contact. | 1912.04623v1 |
2019-12-17 | Mitigate Parasitic Resistance in Resistive Crossbar-based Convolutional Neural Networks | Traditional computing hardware often encounters on-chip memory bottleneck on
large scale Convolution Neural Networks (CNN) applications. With its unique
in-memory computing feature, resistive crossbar-based computing attracts
researchers' attention as a promising solution to the memory bottleneck issue
in von Neumann architectures. However, the parasitic resistances in the
crossbar deviate its behavior from the ideal weighted summation operation. In
large-scale implementations, the impact of parasitic resistances must be
carefully considered and mitigated to ensure circuits' functionality. In this
work, we implemented and simulated CNNs on resistive crossbar circuits with
consideration of parasitic resistances. Moreover, we carried out a new mapping
scheme for high utilization of crossbar arrays on convolution, and a mitigation
algorithm to mitigate parasitic resistances in CNN applications. The mitigation
algorithm considers parasitic resistances as well as data/kernel patterns of
each layer to minimize the computing error in crossbar-based convolutions of
CNNs. We demonstrated the proposed methods with implementations of a 4-layer
CNN on MNIST and ResNet(20, 32, and 56) on CIFAR-10. Simulation results show
the proposed methods well mitigate the parasitic resistances in crossbars. With
our methods, modern CNNs on crossbars can preserve ideal(software) level
classification accuracy with 6-bit ADCs and DACs implementation. | 1912.08716v1 |
2017-03-23 | Influence of material parameters on the performance of niobium based superconducting RF cavities | A detailed thermal analysis of a Niobium (Nb) based superconducting radio
frequency (SRF) cavity in a liquid helium bath is presented, taking into
account the temperature and magnetic field dependence of the surface resistance
and thermal conductivity in the superconducting state of the starting Nb
material (for SRF cavity fabrication) with different impurity levels. The drop
in SRF cavity quality factor (Q_0) in the high acceleration gradient regime
(before ultimate breakdown of the SRF cavity) is studied in details. It is
argued that the high field Q_0-drop in SRF cavity is considerably influenced by
the intrinsic material parameters such as electrical conductivity, and thermal
diffusivity. The detail analysis also shows that the current specification on
the purity of niobium material for SRF cavity fabrication is somewhat over
specified. Niobium material with a relatively low purity can very well serve
the purpose for the accelerators dedicated for spallation neutron source (SNS)
or accelerator driven sub-critical system (ADSS) applications, where the
required accelerating gradient is typically up to 20 MV/m,. This information
will have important implication towards the cost reduction of superconducting
technology based particle accelerators for various applications. | 1703.07985v3 |
2015-01-09 | Superconductivity in quasi-one-dimensional Cs2Cr3As3 with large interchain distance | Since the discovery of high-temperature superconductivity (SC) in
quasi-two-dimensional copper oxides, a few layered compounds, which bear
similarities to the cuprates, have also been found to host unconventional SC.
Our recent observation of SC at 6.1 K in correlated electron material K2Cr3As3
(J. K. Bao et al., arXiv: 1412.0067) represents an obviously different
paradigm, primarily because of its quasi-one-dimensional (Q1D) nature. The new
material is structurally featured by the (Cr3As3)2- double-walled subnano-tubes
composed of face-sharing Cr6/2 (As6/2) octahedron linear chains, which are well
separated by columns of K+ counterions. Later, an isostructural superconducting
Rb2Cr3As3 was synthesized, thus forming a new superconducting family. Here we
report the third member, Cs2Cr3As3, which possesses the largest interchain
distance. SC appears below 2.2 K. Similar to the former two sister compounds,
Cs2Cr3As3 exhibits a non-Fermi liquid behavior with a linear temperature
dependence of resistivity in the normal state, and a high upper critical field
beyond the Pauli limit as well, suggesting common unconventional SC in the Q1D
Cr-based material. | 1501.02065v1 |
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