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Orientation before destruction. A multiscale molecular dynamics study: The emergence of ultra-fast X-ray free-electron lasers opens the possibility
of imaging single molecules in the gas phase at atomic resolution. The main
disadvantage of this imaging technique is the unknown orientation of the sample
exposed to the X-ray beam, making the three dimensional reconstruction not
trivial. Induced orientation of molecules prior to X-ray exposure can be highly
beneficial, as it significantly reduces the number of collected diffraction
patterns whilst improving the quality of the reconstructed structure. We
present here the possibility of protein orientation using a time-dependent
external electric field. We used ab initio simulations on Trp-cage protein to
provide a qualitative estimation of the field strength required to break
protein bonds, with 45 V/nm as a breaking point value. Furthermore, we
simulated, in a classical molecular dynamics approach, the orientation of
ubiquitin protein by exposing it to different time-dependent electric fields.
The protein structure was preserved for all samples at the moment orientation
was achieved, which we denote `orientation before destruction'. Moreover, we
find that the minimal field strength required to induce orientation within ten
ns of electric field exposure, was of the order of 0.5 V/nm. Our results help
explain the process of field orientation of proteins and can support the design
of instruments for protein orientation. | cond-mat_mtrl-sci |
Giant electrophononic response in PbTiO$_3$ by strain engineering: We demonstrate theoretically how, by imposing epitaxial strain in a
ferroelectric perovskite, it is possible to achieve a dynamical control of
phonon propagation by means of external electric fields, which yields a giant
electrophononic response, i.e. the dependence of the lattice thermal
conductivity on external electric fields. Specifically, we study the
strain-induced manipulation of the lattice structure and analyze its interplay
with the electrophononic response. We show that tensile biaxial strain can
drive the system to a regime where the electrical polarization can be
effortlessly rotated and thus yield giant electrophononic responses that are at
least one order of magnitude larger than in the unstrained system. These
results derive directly from the almost divergent behavior of the electrical
susceptibility at those critical strains that drive the polarization on the
verge of a spontaneous rotation. | cond-mat_mtrl-sci |
The Benefits of Trace Cu in Wrought Al-Mg Alloys: The softening and strengthening contributions in pre-deformed and aged
Al-Mg-Cu alloys containing 3wt.%Mg and 0.5wt.%Cu are evaluated by a combination
of microscopy, mechanical testing and modelling. A refined phenomenological
model for the work hardening response, accounting for the separate effects of
recovery and precipitation, is shown to be suitable for an unambiguous
determination of the precipitation hardening contribution in these alloys.
Significantly, it is found that the mechanical response of these alloys is not
strongly impacted by Cu content (in the low Cu content regime), pre-deformation
level or aging temperature meaning that the alloys are robust with respect to
variations in composition. This is interesting from the perspective of alloy
design concepts based on `recycling friendly' compositions in applications that
include paint-baking. | cond-mat_mtrl-sci |
Modeling of Nucleation Processes: Nucleation is the onset of a first-order phase transition by which a
metastable phase transforms into a more stable one. Such a phase transition
occurs when an initial system initially in equilibrium is destabilized by the
change of an external parameter like the temperature or the pressure. If the
perturbation is small enough, the system does not become unstable but rather
stays metastable. In diffusive transformations, the system then evolves through
the nucleation, the growth and the coarsening of a second phase. Such a phase
transformation is found in a lot of situations in materials science like
condensation of liquid droplets from a supersaturated vapor, solidification,
precipitation from a supersaturated solid solution, ... The initial stage of
all these different processes can be well described within the same framework.
Since its initial formulation in 1927 by Volmer, Weber and Farkas and its
modification in 1935 by Becker and D\"oring the classical nucleation theory has
been a suitable tool to model the nucleation stage in phase transformations. In
this article, we first describe this theory. A kinetic approach, the cluster
dynamics, can also be used to describe nucleation. This constitutes the second
part of this article. The links as well as the difference between both
descriptions are emphasized. Since its initial formulation, the classical
nucleation theory has been enriched, so as to take into account the fact that
clusters other than monomers can migrate and react. It has been also extended
to multi-component systems. These generalizations of the initial formalism are
also presented. | cond-mat_mtrl-sci |
Brownian Motion of Graphene: We study the Brownian motion (BM) of optically trapped graphene flakes. These
orient orthogonal to the light polarization, due to the optical constants
anisotropy. We explain the flake dynamics, measure force and torque constants
and derive a full electromagnetic theory of optical trapping. The understanding
of two dimensional BM paves the way to light-controlled manipulation and
all-optical sorting of biological membranes and anisotropic macromolecules. | cond-mat_mtrl-sci |
Modification of electron states in CdTe absorber due to a buffer layer
in CdS/CdTe solar cells: By application of the ac admittance spectroscopy method, the defect state
energy distributions were determined in CdTe incorporated in thin film solar
cell structures concluded on ZnO, ZnSe, and ZnS buffer layers. Together with
the Mott-Schottky analysis, the results revealed a strong modification of the
defect density of states and the concentration of the uncompensated acceptors
as influenced by the choice of the buffer layer. In the solar cells formed on
ZnSe and ZnS, the Fermi level and the energy position of the dominant deep trap
levels were observed to shift closer to the midgap of CdTe suggesting the
mid-gap states may act as recombination centers and impact the open-circuit
voltage and the fill factor of the solar cells. For the deeper states, the
broadening parameter was observed to increase indicating fluctuations of the
charge on a microscopic scale. Such changes can be attributed to the
grain-boundary strain and the modification of the charge trapped at the
grain-boundary interface states in polycrystalline CdTe | cond-mat_mtrl-sci |
Hafnia for analog memristor: Influence of stoichiometry and crystalline
structure: The highly non-linear switching behavior of hafnia memristor actually hinders
its wide application in neuromorphic computing. Theoretical understanding into
its switching mechanism has been focused on the processes of conductive
filament generation and rupture, but possible phase transition and
crystallization around the region of conductive filaments (CFs) due to the
variation of O content have been paid less attention to. In this paper,
HfO$\mathrm{_x}$ structural models covering the full stoichiometries from Hf to
HfO$\mathrm{_2}$ were established, and the crystal structure evolution during
the reduction process of hafnia was obtained through first-principles
calculation. The electronic structures and O vacancy migration characteristics
of these structures were analyzed. A criterion was prescribed to predict the
mode of abrupt binary switching or gradual conductance modulation according to
the structure evolution of the CFs. In particular, factors that influence the
merging of tiny conductive channels into strong filaments are intensively
discussed, including the anisotropy of O vacancy migration and the size effect.
The feasibility of Mg doping to achieve robust gradual switching is discussed. | cond-mat_mtrl-sci |
Quantitative characterization of surface topography using spectral
analysis: Roughness determines many functional properties of surfaces, such as
adhesion, friction, and (thermal and electrical) contact conductance. Recent
analytical models and simulations enable quantitative prediction of these
properties from knowledge of the power spectral density (PSD) of the surface
topography. The utility of the PSD is that it contains statistical information
that is unbiased by the particular scan size and pixel resolution chosen by the
researcher. In this article, we first review the mathematical definition of the
PSD, including the one- and two-dimensional cases, and common variations of
each. We then discuss strategies for reconstructing an accurate PSD of a
surface using topography measurements at different size scales. Finally, we
discuss detecting and mitigating artifacts at the smallest scales, and
computing upper/lower bounds on functional properties obtained from models. We
accompany our discussion with virtual measurements on computer-generated
surfaces. This discussion summarizes how to analyze topography measurements to
reconstruct a reliable PSD. Analytical models demonstrate the potential for
tuning functional properties by rationally tailoring surface topography -
however, this potential can only be achieved through the accurate, quantitative
reconstruction of the power spectral density of real-world surfaces. | cond-mat_mtrl-sci |
Domain Dynamics in Piezoresponse Force Microscopy: Quantitative
Deconvolution and Hysteresis Loop Fine Structure: Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is
studied using the combination of local hysteresis loop acquisition with
simultaneous domain imaging. The analytical theory for PFS signal from domain
of arbitrary cross-section is developed and used for the analysis of
experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest
formation of oblate domain at early stage of the domain nucleation and growth,
consistent with efficient screening of depolarization field within the
material. The fine structure of the hysteresis loop is shown to be related to
the observed jumps in the domain geometry during domain wall propagation
(nanoscale Barkhausen jumps), indicative of strong domain-defect interactions. | cond-mat_mtrl-sci |
Effect of nitrogen introduced at the SiC/SiO$_2$ interface and SiC side
on the electronic states by first-principles calculation: In this study, using first-principles calculations, we investigate the
behavior of electrons at the SiC/SiO$_2$ interface when nitrogen is introduced
as a dopant within a few nm of the SiC surface. When a highly doped nitrogen
layer (5$\times$10$^{19}$ cm$^{-3}$) is introduced within a few nm of the
SiC(11$\bar{2}$0) surface, the electronic state is not significantly affected
if the doping region is less than 4 nm. However, if the doping region exceeds 4
nm, the effect of quantum confinement decreases, which increases the electron
density induced in the inversion layer. As for the wave function, even when an
electric field is applied, the peak shifts toward the direction in which the
electrons are pulled away from the interface. This reduces the effect of
electron scattering at the interface and improves electron mobility. | cond-mat_mtrl-sci |
Selection of strain and fitting schemes for calculating higher-order
elastic constants: Criteria of selecting strain and fitting schemes are proposed for the
calculation of higher-order elastic constants more efficiently, robustly and
accurately. As demonstrated by the third-order elastic constants (TOECs) of
diamond, the proposed method is 3-5 times faster than existing methods, and the
range of strain for getting correct TOECs is expanded. In addition, our result
provides an evidence for the inaccuracy of some previous experiments caused by
higher-order effect, and the difference among experiments and several different
theoretical methods is resolved. Finally, we give the recommend TOECs values
for diamond. | cond-mat_mtrl-sci |
Disordered Hyperuniform Solid State Materials: Disordered hyperuniform (DHU) states are recently discovered exotic states of
condensed matter. DHU systems are similar to liquids or glasses in that they
are statistically isotropic and lack conventional long-range translational and
orientational order. On the other hand, they completely suppress normalized
infinite-wavelength density fluctuations like crystals, and in this sense
possess a hidden long-range order. Very recently, there are several exciting
discoveries of disordered hyperuniformity in solid-state materials, including
amorphous carbon nanotubes, amorphous 2D silica, amorphous graphene, defected
transition metal dichalcogenides, defected pentagonal 2D materials, and
medium/high-entropy alloys. It has been found the DHU states of these materials
often possess a significantly lower energy than other disorder models, and can
lead to unique electronic and thermal transport properties, which resulted from
mechanisms distinct from those identified for their crystalline counterparts.
For example, DHU states can enhance electronic transport in 2D amorphous
silica; DHU medium/high-entropy alloys realize the Vegard's law, and possess
enhanced electronic band gaps and thermal transport at low temperatures. These
unique properties open up many promising potential device applications in
optoelectronics and thermoelectrics. Here, we provide a focused review on these
important new developments of hyperuniformity in solid-state materials, taking
an applied and ``materials'' perspective, which complements the existing
reviews on hyperuniformity in physical systems and photonic materials. Future
directions and outlook are also provided, with a focus on the design and
discovery of DHU quantum materials for quantum information science and
engineering. | cond-mat_mtrl-sci |
Properties of $(TiZrNbCu)_{1-x}$$Ni_{x}$ Metallic Glasses: Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure
and properties of $(TiZrNbCu)_{1-x}$$Ni_{x}$ (x$\leq$0.25) amorphous high
entropy alloys (a-HEA) have been extended to x=0.5 in order to compare
behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The
amorphous state of all samples was verified by thermal analysis and X-ray
diffraction (XRD). XRD indicated a probable change in local atomic
arrangements, i.e. short-range-order (SRO) for x$\geq$0.35. Simultaneously,
thermal parameters, such as the first crystallization temperature $T_{x}$ and
the liquidus temperature showed a tendency to saturate for x$\geq$0.35 . The
same tendency also appeared in the magnetic susceptibility $\chi_{exp}$ and the
linear term in the low temperature specific heat {\gamma}. The Debye
temperatures and Youngs moduli also tend to saturate for x$\geq$0.35. These
unusual changes in SRO and all properties within the amorphous phase seem
correlated with the change of valence electron number (VEC) on increasing x. | cond-mat_mtrl-sci |
Equivalent circuit representation of hysteresis in solar cells that
considers interface charge accumulation: Potential cause of hysteresis in
perovskite solar cells: If charge carriers accumulate in the charge transport layer of a solar cell,
then the transient response of the electric field that originates from these
accumulated charges results in hysteresis in the current-voltage ($J$-$V$)
characteristics. While this mechanism was previously known, a theoretical model
to explain these $J$-$V$ characteristics has not been considered to date. We
derived an equivalent circuit from the proposed hysteresis mechanism. By
solving the equivalent circuit model, we were able to reproduce some of the
features of hysteresis in perovskite solar cells. | cond-mat_mtrl-sci |
Ferrous Metal Matrix Composites Status Scope and Challenges: The present paper is an effort to culminate the status, scopes and challenges
in the development of ferrous metal matrix composites (FMMCs). The FMMCs are
old but less in use than the non-ferrous metal matrix composites (NFMMCs), as
far as literature and actual applications are concerned. Therefore, this
stimulates the exploration of the reasons behind the scarcity of literature and
field applications of the FMMCs, which must be investigated scientifically. The
powder metallurgy route is the most used process for fabricating iron and steel
based FMMCs by reinforcing particulates. At the same time, the in-situ method
has been used for the fabrication and cast iron-based FMMCs. The main
characteristics being considered during the designing and fabrication of FMMCs
are wear resistance and improved specific mechanical properties. To fabricate
cheaper and eco-friendly FMMCs, traditionally used costly reinforcements such
as SiC, WC, TiC, SiO2, TiO2, TiB2 are required to be replaced by inexpensive
industrial wastes like red-mud, fly-ashes and grinding swarf. The data
extracted from the web of science exhibited that the FMMCs have been researched
less than the NFMMCs. The increasing number of research papers on FMMCs
indicates a bright future. FMMCs are going to be a favourite topic among
researchers and manufacturers. Higher strengths, wear resistance, dimensional
stability at elevated temperatures, and, most importantly, the lower cost will
put forward the FMMCs as a stiff competitor of NFMMCs. In developing and mass
production of FMMCs for field applications, challenges like oxidation and
higher weight still require special research efforts. | cond-mat_mtrl-sci |
Universal solvent restructuring induced by colloidal nanoparticles: Colloidal nanoparticles, used for applications from catalysis and energy
applications to cosmetics, are typically embedded in matrixes or dispersed in
solutions. The entire particle surface, which is where reactions are expected
to occur, is thus exposed. Here we show with x-ray pair distribution function
analysis that polar and non-polar solvents universally restructure around
nanoparticles. Layers of enhanced order exist with a thickness influenced by
the molecule size and up to 2 nanometers beyond the nanoparticle surface. These
results show that the enhanced reactivity of solvated nanoparticles includes a
contribution from a solvation shell of the size of the particle itself. | cond-mat_mtrl-sci |
Calculation of the specific heat in ultra-thin free-standing silicon
membranes: The specific heat of ultra-thin free-standing membranes is calculated using
the elastic continuum model. We first obtain the dispersion relations of the
discrete set of acoustic modes in the system. The specific heat is then
calculated by summing over the discrete out-of-plane wavevector component and
integrating over the continuous in-plane wavevector of these waves. In the
low-temperature regime (T < 4 K), the flexural polarization is seen to have the
highest contribution to the total specific heat. This leads to a linear
dependence with temperature, resulting in a larger specific heat for the
membrane compared to that of the bulk counterpart | cond-mat_mtrl-sci |
Sensitive electronic correlation effects on electronic properties in
ferrovalley material Janus FeClF monolayer: The electronic correlation may have essential influence on electronic
structures in some materials with special structure and localized orbital
distribution. In this work, taking Janus monolayer FeClF as a concrete example,
the correlation effects on its electronic structures are investigated by using
generalized gradient approximation plus $U$ (GGA+$U$) approach. For
perpendicular magnetic anisotropy (PMA), the increasing electron correlation
effect can induce the ferrovalley (FV) to half-valley-metal (HVM) to quantum
anomalous Hall (QAH) to HVM to FV transitions. For QAH state, there are a unit
Chern number and a chiral edge state connecting the conduction and valence
bands. The HVM state is at the boundary of the QAH phase, whose carriers are
intrinsically 100\% valley polarized. With the in-plane magnetic anisotropy, no
special QAH states and prominent valley polarization are observed. However, for
both out-of-plane and in-plane magnetic anisotropy, sign-reversible Berry
curvature can be observed with increasing $U$. It is found that these
phenomenons are related with the change of $d_{xy}$/$d_{x^2-y^2}$ and $d_{z^2}$
orbital distributions and different magnetocrystalline directions. It is also
found that the magnetic anisotropy energy (MAE) and Curie temperature strongly
depend on the $U$. With PMA, taking typical $U=$2.5 eV, the electron valley
polarization can be observed with valley splitting of 109 meV, which can be
switched by reversing the magnetization direction. The analysis and results can
be readily extended to other nine members of monolayer FeXY (X/Y=F, Cl, Br and
I) due to sharing the same Fe-dominated low-energy states and electronic
correlations with FeClF monolayer. | cond-mat_mtrl-sci |
Structure-dependent exchange in the organic magnets Cu(II)Pc and
Mn(II)Pc: We study exchange couplings in the organic magnets copper(II) phthalocyanine
(Cu(II)Pc) and manganese(II) phthalocyanine (Mn(II)Pc) by a combination of
Green's function perturbation theory and \textsl{ab initio} density-functional
theory (DFT). Based on the indirect exchange model our perturbation-theory
calculation of Cu(II)Pc qualitatively agrees with the experimental
observations. DFT calculations performed on Cu(II)Pc dimer show a very good
quantitative agreement with exchange couplings that we extract by using a
global fitting for the magnetization measurements to a spin-1/2 Bonner-Fisher
model. These two methods give us remarkably consistent trends for the exchange
couplings in Cu(II)Pc when changing the stacking angles. The situation is more
complex for Mn(II)Pc owing to the competition between super-exchange and
indirect exchange. | cond-mat_mtrl-sci |
Can we predict interface dipoles based on molecular properties?: We apply high-throughput DFT calculations and symbolic regression to hybrid
inorganic/organic interfaces with the intent to extract physically meaningful
correlations between the adsorption-induced work function modifications and the
properties of the constituents. We separately investigate two cases:
Hypothetical, free standing self-assembled monolayers with a large intrinsic
dipole moment, and metal-organic interfaces with a large charge-transfer
induced dipole. For the former we find - without notable prior assumptions -
the Topping model, as expected from literature. For the latter, highly accurate
correlations are found, which are, however, clearly unphysical. | cond-mat_mtrl-sci |
Single-Atom Scale Structural Selectivity in Te Nanowires Encapsulated
inside Ultra-Narrow, Single-Walled Carbon Nanotubes: Extreme nanowires (ENs) represent the ultimate class of crystals: They are
the smallest possible periodic materials. With atom-wide motifs repeated in one
dimension (1D), they offer a privileged perspective into the Physics and
Chemistry of low-dimensional systems. Single-walled carbon nanotubes (SWCNTs)
provide ideal environments for the creation of such materials. Here we present
a comprehensive study of Te ENs encapsulated inside ultra- narrow SWCNTs with
diameters between 0.7 nm and 1.1 nm. We combine state-of-the-art imaging
techniques and 1D-adapted ab initio structure prediction to treat both
confinement and periodicity effects. The studied Te ENs adopt a variety of
structures, exhibiting a true 1D realisation of a Peierls structural distortion
and transition from metallic to insulating behaviour as a function of
encapsulating diameter. We analyse the mechanical stability of the encapsulated
ENs and show that nanoconfinement is not only a useful means to produce ENs,
but may actually be necessary, in some cases, to prevent them from
disintegrating. The ability to control functional properties of these ENs with
confinement has numerous applications in future device technologies, and we
anticipate that our study will set the basic paradigm to be adopted in the
characterisation and understanding of such systems. | cond-mat_mtrl-sci |
Two-dimensional modeling of the self-limiting oxidation in silicon and
tungsten nanowires: Self-limiting oxidation of nanowires has been previously described as a
reaction- or diffusion-controlled process. In this letter, the concept of
finite reactive region is introduced into a diffusion-controlled model, based
upon which a two-dimensional cylindrical kinetics model is developed for the
oxidation of silicon nanowires and is extended for tungsten. In the model,
diffusivity is affected by the expansive oxidation reaction induced stress. The
dependency of the oxidation upon curvature and temperature is modeled. Good
agreement between the model predictions and available experimental data is
obtained. The developed model serves to quantify the oxidation in
two-dimensional nanostructures and is expected to facilitate their fabrication
via thermal oxidation techniques. https://doi.org/10.1016/j.taml.2016.08.002 | cond-mat_mtrl-sci |
Raman and Far Infrared Synchrotron Nanospectroscopy of Layered
Crystalline Talc: Vibrational Properties, Interlayer Coupling and Symmetry
Crossover: Talc is an insulating layered material that is stable at ambient conditions
and has high-quality basal cleavage, which is a major advantage for its use in
van der Waals heterostructures. Here, we use near-field synchrotron infrared
nanospectroscopy, Raman spectroscopy, and first-principles calculations to
investigate the structural and vibrational properties of talc crystals, ranging
from monolayer to bulk, in the 300-750 cm-1 and <60 cm-1 spectral windows. We
observe a symmetry crossover from mono to bilayer talc samples, attributed to
the stacking of adjacent layers. The in-plane lattice parameters and
frequencies of intralayer modes of talc display weak dependence with the number
of layers, consistent with a weak interlayer interaction. On the other hand,
the low-frequency (<60 cm-1) rigid-layer (interlayer) modes of talc are
suitable to identify the number of layers in ultrathin talc samples, besides
revealing strong in-plane and out-of-plane anisotropy in the interlayer force
constants and related elastic stiffnesses of single crystals. The shear and
breathing force constants of talc are found to be 66% and 28%, respectively,
lower than those of graphite, making talc an excellent lubricant that can be
easily exfoliated. Our results broaden the understanding of the structural and
vibrational properties of talc at the nanoscale regime and serve as a guide for
future ultrathin heterostructures applications. | cond-mat_mtrl-sci |
Nearly triple nodal point topological phase in half-metallic GdN: Recent developments in topological semimetals open a way to realize
relativistic dispersions in condensed matter systems. One recently studied type
of topological feature is the "triple nodal point" where three bands become
degenerate. In contrast to Weyl and Dirac nodes, triple nodal points, which are
protected by a rotational symmetry, have nodal lines attached, so that a
characterization in terms of a chirality is not possible. Previous studies of
triple nodal points considered nonmagnetic systems, although an artificial
Zeeman splitting was used to probe the topological nature. Here instead we
treat a ferromagnetic material, half-metallic GdN, where the splitting of the
triple nodal points comes from the spin-orbit coupling. The size of the
splitting ranges from 15 to 150 meV depending on the magnetization orientation,
enabling a transition between a Weyl-point phase and a "nearly triple nodal
point" phase that exhibits very similar surface spectra and transport
properties compared to a true triple-node system. The rich topological surface
states, manipulable via the orientation of the magnetization, make
half-metallic GdN a promising platform for future investigations and
applications. | cond-mat_mtrl-sci |
Will Zigzag Graphene Nanoribbon Turn to Half Metal under Electric Field?: At B3LYP level of theory, we predict that the half-metallicity in zigzag edge
graphene nanoribbon (ZGNR) can be realized when an external electric field is
applied across the ribbon. The critical electric field to induce the
half-metallicity decreases with the increase of the ribbon width. Both the spin
polarization and half-metallicity are removed when the edge state electrons
fully transferred from one side to the other under very strong electric field.
The electric field range under which ZGNR remain half-metallic increases with
the ribbon width. Our study demonstrates a rich field-induced spin polarization
behavior, which may leads to some important applications in spinstronics. | cond-mat_mtrl-sci |
Promising photovoltaic efficiency of a layered silicon oxide crystal
Si$_{3}$O: Computational searching and screening of new functional materials exploiting
earth abundant elements can accelerate developments of their energy
applications. Based on a state-of-the-art materials search algorithm and ab
initio calculations, we demonstrate a recently suggested stable silicon oxide
with a layered structure (Si$_{3}$O) as an ideal photovoltaic material. With
many-body first-principles approaches, the monolayer and layered bulk of
Si$_{3}$O show direct quasiparticle gaps of 1.85 eV and 1.25 eV, respectively,
while an optical gap of about 1.2 eV is nearly independent of the number of
layers. Spectroscopic limited maximum efficiency (SLME) is estimated to be 27%
for a thickness of 0.5 {\mu}m, making it a promising candidate for solar energy
applications. | cond-mat_mtrl-sci |
Viscoelastic Constitutive Artificial Neural Networks (vCANNs) $-$ a
framework for data-driven anisotropic nonlinear finite viscoelasticity: The constitutive behavior of polymeric materials is often modeled by finite
linear viscoelastic (FLV) or quasi-linear viscoelastic (QLV) models. These
popular models are simplifications that typically cannot accurately capture the
nonlinear viscoelastic behavior of materials. For example, the success of
attempts to capture strain rate-dependent behavior has been limited so far. To
overcome this problem, we introduce viscoelastic Constitutive Artificial Neural
Networks (vCANNs), a novel physics-informed machine learning framework for
anisotropic nonlinear viscoelasticity at finite strains. vCANNs rely on the
concept of generalized Maxwell models enhanced with nonlinear strain
(rate)-dependent properties represented by neural networks. The flexibility of
vCANNs enables them to automatically identify accurate and sparse constitutive
models of a broad range of materials. To test vCANNs, we trained them on
stress-strain data from Polyvinyl Butyral, the electro-active polymers VHB 4910
and 4905, and a biological tissue, the rectus abdominis muscle. Different
loading conditions were considered, including relaxation tests, cyclic
tension-compression tests, and blast loads. We demonstrate that vCANNs can
learn to capture the behavior of all these materials accurately and
computationally efficiently without human guidance. | cond-mat_mtrl-sci |
Na9Bi5Os3O24: A Unique Diamagnetic Oxide Featuring a Pronouncedly
Jahn-Teller Compressed Octahedral Coordination of Osmium(VI): The Jahn-Teller theorem constitutes one of the most popular and stringent
concepts, applicable to all fields of chemistry. In open shell transition
elements chemistry and physics, 3d4, 3d9, and 3d7(low-spin) configurations in
octahedral complexes serve as particular illustrative and firm examples, where
a striking change (distortion) in local geometry is associated to a substantial
reduction of electronic energy. However, there has been a lasting debate, about
the fact that the octahedra are found to exclusively elongate, (at least for eg
electrons). Against this background, the title compound displays two marked
features, (1) the octahedron of oxygen atoms around Os6+ (d2) is drastically
compressed, in contrast to the standard JT expectations, and (2) the splitting
of the t2g set induced by this compression is extreme, such that a diamagnetic
ground state results. What we see is obviously a Jahn-Teller distortion
resulting in a compression of the respective octahedron and acting on the t2g
set of orbitals. Both these issues are unprecedented. Noteworthy, the splitting
into a lower dxy (hosting two d electrons with opposite spin) and two higher
dxz and dyz orbitals is so large that for the first time ever the Hund's
coupling for t2g electrons is overcome. We show that these effects are not
forced by structural frustration, the structure offers sufficient space for Os
to shift the apical oxygen atoms to a standard distance. Local electronic
effects appear to be responsible, instead. The relevance of these findings is
far reaching, since they provide insights in the hierarchy of perturbations
defining ground states of open shell electronic systems. The system studied
here, offers substantially more structural and compositional degrees of
freedom, such that a configuration could form that enables Os6+ to adopt its
apparently genuine diamagnetic ground state. | cond-mat_mtrl-sci |
Bulk and surface properties of the Ruddlesden-Popper oxynitride
Sr$_2$TaO$_3$N: Oxynitrides with the perovskite structure are promising candidates for
photocatalysis under visible light due to their appropriate optical and
electronic properties. Recently, layered perovskites have attracted attention
for their improved performance with respect to the bulk perovskites in
photocatalytic water splitting. In this paper, we investigate the structural
and electronic properties of the layered Ruddlesden-Popper oxynitride
Sr$_2$TaO$_3$N and its (001) surfaces using density functional theory (DFT)
calculations. We find that the energetically favoured configuration of the bulk
has an in-plane \textit{cis} anion order and exhibits rotations of the TaO$_6$
octahedra. Furthermore, we show that the TaON-terminated (001) surface
suppresses exciton recombination due to higher-energy surface states, giving a
potential explanation for the good photocatalytic performance. | cond-mat_mtrl-sci |
Understanding atom probe's analytical performance for iron oxides using
correlation histograms and ab initio calculations: Field evaporation from ionic or covalently bonded materials often leads to
the emission of molecular ions. The metastability of these molecular ions,
particularly under the influence of the intense electrostatic field (1010
Vm-1), makes them prone to dissociation with or without an exchange of energy
amongst them. These processes can affect the analytical performance of atom
probe tomography (APT). For instance, neutral species formed through
dissociation may not be detected at all or with a time of flight no longer
related to their mass, causing their loss from the analysis. Here, we evaluated
the changes in the measured composition of FeO, Fe2O3 and Fe3O4 across a wide
range of analysis conditions. Possible dissociation reactions are predicted by
density-functional theory (DFT) calculations considering the spin states of the
molecules. The energetically favoured reactions are traced on to the multi-hit
ion correlation histograms, to confirm their existence within experiments,
using an automated Python-based routine. The detected reactions are carefully
analysed to reflect upon the influence of these neutrals from dissociation
reactions on the performance of APT for analysing iron oxides. | cond-mat_mtrl-sci |
Sensitivity of the MnTe valence band to orientation of magnetic moments: An effective model of the hexagonal (NiAs-structure) manganese telluride
valence band in the vicinity of the A-point of the Brillouin zone is derived.
It is shown that while for the usual antiferromagnetic order (magnetic moments
in the basal plane) band splitting at A is small, their out-of-plane rotation
enhances the splitting dramatically (to about 0.5 eV). We propose extensions of
recent experiments (Moseley et al., Phys. Rev. Materials 6, 014404) where such
inversion of magnetocrystalline anisotropy has been observed in Li-doped MnTe,
to confirm this unusual sensitivity of a semiconductor band structure to
magnetic order. | cond-mat_mtrl-sci |
Parent grain reconstruction from partially or fully transformed
microstructures in MTEX: A versatile generic framework for parent grain reconstruction from fully or
partially transformed child microstructures was integrated into the open-source
crystallographic toolbox MTEX. The framework extends traditional parent grain
reconstruction, phase transformation and variant analysis to all parent-child
crystal symmetry combinations. The inherent versatility of the universally
applicable parent grain reconstruction methods, and the ability to conduct
in-depth variant analysis are showcased via example workflows that can be
programmatically modified by users to suit their specific applications. This is
highlighted by three applications namely, $\alpha$-to-$\gamma$ reconstruction
in a lath martensitic steel, $\alpha$-to-$\beta$ reconstruction in a Ti alloy,
and a two-step reconstruction from $\alpha$-to-$\varepsilon$-to-$\gamma$ in a
twinning and transformation -induced plasticity steel. Advanced orientation
relationship discovery and analysis options, including variant analysis, is
demonstrated via the add-on function library, ORTools. | cond-mat_mtrl-sci |
Novel superhard structures of high-pressure C-N compounds: Through machine learning force field accelerated structure search combined
with first-principles calculations, we have studied the structures of new C-N
compounds with different stoichiometric ratios, and found twelve new superhard
C-N compounds, the energies of these structures are similar to c-C3N4 , which
is possibly synthesized by high pressure experiment, the XRD of Pa-3(C4N)
P3(C4N) and C2/m(C2N) are consistent with previous experimental data and can be
used as the structural candidate. According to the macro hardness model, they
are all superhard structures, with Vickers hardness over 40GPa, even, the
hardness of Pa-3 (C4N) as high as 82.2GPa, and Pa-3 (C4N) combines high tensile
and shear resistance. Compared with the hardness calculated by macro hardness
model and bond resistance model, we obtained the relationship between the
hardness and chemical concentration of C-N compounds under the two models,
besides that, we also calculated the fracture toughness of these structures.
According to Niu's model, P2_1/c(C4N) has the best fracture toughness, which is
higher than WC in calculation, This also indicated the superior mechanical
properties of the novel C-N compounds. Moreover, for nitrogen-rich structures,
they have the potential to be used as high energy density, the energy density
of Pa-3(CN3), P-3c1 (CN4), and I-42d (CN4) are 7.076kJ/g, 7.742kJ/g and
8.045kJ/g, which is close or higher than CL-20, therefore, the C-N compounds
synthesized under high pressure have great potential as ideally superhard
materials and high energy density materials(HEDMs). | cond-mat_mtrl-sci |
Fabrication of ice-templated tubes by rotational freezing:
microstructure, strength, and permeability: We demonstrate a facile and scalable technique, rotational freezing, to
produce porous tubular ceramic supports with radially aligned porosity. The
method is based on a conventional ice-templating process in a rotatory mold and
demonstrated here with yttria-stabilized zirconia (YSZ). We investigated the
effects of solid loading, freezing temperature, and volume of the slurry on the
microstructure, strength (o-ring test and four-point bending), and air
permeability. The results show that pore volume and pore size can be controlled
by the solid loading and freezing temperature respectively, and overall tube
thickness can be adjusted by the volume of slurry initially poured into the
mold. Decreasing pore size and pore volume increases the mechanical properties
but decreases the air permeability. These tubes could be particularly
interesting as tubular membrane supports such as oxygen transport membranes. | cond-mat_mtrl-sci |
Giant anomalous Hall effect from spin-chirality scattering in a chiral
magnet: The electrical Hall effect can be significantly enhanced through the
interplay of the conduction electrons with magnetism, which is known as the
anomalous Hall effect (AHE). Whereas the mechanism related to band topology has
been intensively studied towards energy efficient electronics, those related to
electron scattering have received limited attention. Here we report the
observation of giant AHE of electron-scattering origin in a chiral magnet MnGe
thin film. The Hall conductivity and Hall angle respectively reach 40,000
{\Omega}-1cm-1 and 18 % in the ferromagnetic region, exceeding the conventional
limits of AHE of intrinsic and extrinsic origins, respectively. A possible
origin of the large AHE is attributed to a new type of skew-scattering via
thermally-excited spin-clusters with scalar spin chirality, which is
corroborated by the temperature-magnetic-field profile of the AHE being
sensitive to the film-thickness or magneto-crystalline anisotropy. Our results
may open up a new platform to explore giant AHE responses in various systems,
including frustrated magnets and thin-film heterostructures. | cond-mat_mtrl-sci |
Transport between metals and magnetic insulators: We derive the Onsager response matrix of fluctuation-mediated spin-collinear
transport through a ferromagnetic insulator and normal metal interface driven
by a temperature difference, spin accumulation, or magnetic field. We predict
magnon-squeezing spin currents, magnetic field-induced cooling (magnon Peltier
effect), temperature induced magnetization (thermal magnetic field) as well as
universal spin Seebeck/Peltier coefficients. | cond-mat_mtrl-sci |
Cesium Enhances Long-Term Stability of Lead Bromide Perovskite-Based
Solar Cells: Direct comparison between perovskite-structured hybrid organic-inorganic -
methyl ammonium lead bromide (MAPbBr3) and all-inorganic cesium lead bromide
(CsPbBr3), allows identifying possible fundamental differences in their
structural, thermal and electronic characteristics. Both materials possess a
similar direct optical band-gap, but CsPbBr3 demonstrates a higher thermal
stability than MAPbBr3. In order to compare device properties we fabricated
solar cells, with similarly synthesized MAPbBr3 or CsPbBr3, over mesoporous
titania scaffolds. Both cell types demonstrated comparable photovoltaic
performances under AM1.5 illumination, reaching power conversion efficiencies
of ~6 % with a poly-aryl amine-based derivative as hole transport material.
Further analysis shows that Cs-based devices are as efficient as, and more
stable than methyl ammonium-based ones, after aging (storing the cells for 2
weeks in a dry (relative humidity 15-20%) air atmosphere in the dark) for 2
weeks, under constant illumination (at maximum power), and under electron beam
irradiation. | cond-mat_mtrl-sci |
Quantum Composites with the Functionality Defined by the
Charge-Density-Wave Phase Transitions: We demonstrate a unique class of advanced materials - quantum composites
based on polymers with fillers comprised of a van der Waals quantum material
that reveals multiple charge-density-wave quantum condensate phases. Materials
that exhibit quantum phenomena are typically crystalline, pure, and have few
defects because disorder destroys the coherence of the electrons and phonons,
leading to collapses of the quantum states. We succeeded in preserving the
macroscopic charge-density-wave phases of filler particles after multiple
composite processing steps. The prepared composites manifest strong
charge-density-wave phenomena even above room temperature. The dielectric
constant experiences more than two orders of magnitude enhancement while the
material maintains its electrically insulating properties, opening a venue for
advanced applications in energy storage and electronics. The results present a
conceptually different approach for engineering the properties of materials,
extending the application domain for van der Waals materials. | cond-mat_mtrl-sci |
Thermal conductivity of perovskite KTaO3 and PbTiO3 from first
principles: The low thermal conductivity of piezoelectric perovskites is a challenge for
high power transducer applications. We report first principles calculations of
the thermal conductivity of ferroelectric PbTiO$_3$ and the cubic nearly
ferroelectric perovskite KTaO$_3$. The calculated thermal conductivity of
PbTiO$_3$ is much lower than that of KTaO$_3$ in accord with experiment.
Analysis of the results shows that the reason for the low thermal conductivity
of PbTiO$_3$ is the presence of low frequency optical phonons associated with
the polar modes. These are less dispersive in PbTiO$_3$, leading to a large
three phonon scattering phase space. These differences between the two
materials are associated with the $A$-site driven ferroelectricity of PbTiO$_3$
in contrast to the $B$-site driven near ferroelectricity of KTaO$_3$. The
results are discussed in the context of modification of the thermal
conductivity of electroactive materials. | cond-mat_mtrl-sci |
Enhanced Born Charge and Proximity to Ferroelectricity in Thallium
Halides: Electronic structure and lattice dynamics calculations on thallium halides
show that the Born effective charges in these compounds are more than twice
larger than the nominal ionic charges. This is a result of cross-band-gap
hybridization between Tl-p and halogen-p states. The large Born charges cause
giant splitting between longitudinal and transverse optic phonon modes,
bringing the lattice close to ferroelectric instability. Our calculations
indeed show spontaneous lattice polarization upon lattice expansion starting at
2%. It is remarkable that the apparently ionic thallium halides with a simple
cubic CsCl structure and large differences in electronegativity between cations
and anions can be very close to ferroelectricity. This can lead to effective
screening of defects and impurities that would otherwise be strong carrier
traps and may therefore contribute to the relatively good carrier transport
properties in TlBr radiation detectors. | cond-mat_mtrl-sci |
Acousto-electric Characteristics of Periodically Poled Ferroelectric
Plate: A multidomain two-dimensional periodically poled ferroelectric plate vibrator
is reported for the first time. The theoretical calculations, computer
simulations by the Finite Element Method and experimental data from the lithium
tantalite samples reveal a domain acousto-electric resonance. A polarization
inversion in a y-rotated cut of a ferroelectric chip is firstly done. The
acousto-electric characteristics of the vibrator are calculated and measured. | cond-mat_mtrl-sci |
Chemical gradients across phase boundaries between martensite and
austenite in steel studied by atom probe tomography and simulation: Partitioning at phase boundaries of complex steels is important for their
properties. We present atom probe tomography results across martensite /
austenite interfaces in a precipitation-hardened maraging TRIP steel (12.2 Mn,
1.9 Ni, 0.6 Mo, 1.2 Ti, 0.3 Al; at.%). The system reveals compositional changes
at the phase boundaries: Mn and Ni are enriched while Ti, Al, Mo, and Fe are
depleted. More specific, we observe up to 27 at.% Mn in a 20 nm layer at the
phase boundary. This is explained by the large difference in diffusivity
between martensite and austenite. The high diffusivity in martensite leads to a
Mn-flux towards the retained austenite. The low diffusivity in the austenite
does not allow accommodation of this flux. Consequently, the austenite grows
with a Mn-composition given by local equilibrium. The interpretation is based
on DICTRA and mixed-mode diffusion calculations (using a finite interface
mobility). | cond-mat_mtrl-sci |
Ferroelectricity induced by acentric spin-density waves in YMn$_2$O$_5$: The commensurate and incommensurate magnetic structures of the
magnetoelectric system YMn$_{2}$O$_{5}$, as determined from neutron
diffraction, were found to be spin-density waves lacking a global center of
symmetry. We propose a model, based on a simple magneto-elastic coupling to the
lattice, which enables us to predict the polarization based entirely on the
observed magnetic structure. Our data accurately reproduce the
temperature-dependence of the spontaneous polarization, in particular its sign
reversal at the commensurate-incommensurate transition. | cond-mat_mtrl-sci |
Effects of CdCl$_2$ treatment on the local electronic properties of
polycrystalline CdTe measured with photoemission electron microscopy: To investigate the effects of CdCl$_2$ treatment on the local electronic
properties of polycrystalline CdTe films, we conducted a photoemission electron
microscopy (PEEM) study of polished surfaces of CdTe films in superstrate
configuration, with and without CdCl$_2$ treatment. From photoemission
intensity images, we observed the tendency for individual exposed grain
interiors to vary in photoemission intensity, regardless of whether or not
films received CdCl$_2$ treatment. Additionally, grain boundaries develop
contrast in photoemission intensity images different from grain interiors after
an air exposure step, similar to observations of activated grain boundaries
using scanning Kelvin probe force microscopy studies. These results suggest
that work function varies locally, from one grain interior to another, as well
as between grain boundaries and grain interiors. | cond-mat_mtrl-sci |
Verification of Wiedemann-Franz law in silver with moderate residual
resistivity ratio: Electrical and thermal transport were studied in a vacuum-annealed
polycrystalline silver wire with residual resistivity ratio 200-400, in the
temperature range 0.1-1.2K and in magnetic fields up to 5T. Both at zero field
and at 5T the wire exhibits the Wiedemann-Franz law with the fundamental Lorenz
number, contrary to an earlier report [Gloos, K. et al, Cryogenics 30, 14
(1990)]. Our result demonstrates that silver is an excellent material for
thermal links in ultra-low-temperature experiments operating at high magnetic
fields. | cond-mat_mtrl-sci |
A numerical strategy for coarse-graining two-dimensional atomistic
models at finite temperature: the membrane case: We present a numerical strategy to compute ensemble averages of
coarse-grained two-dimensional membrane-like models. The approach consists in
generalizing to these two-dimensional models a one-dimensional strategy exposed
in [Blanc, Le Bris, Legoll, Patz, JNLS 2010], which is based on applying the
ergodic theorem to Markov chains. This may be considered as a first step
towards computing the constitutive law associated to such models, in the
thermodynamic limit. | cond-mat_mtrl-sci |
A detailed analysis of impact collision ion scattering spectroscopy of
bismuth selenide: Impact collision ion scattering spectroscopy (ICISS), which is a variation of
low energy ion scattering (LEIS) that employs large scattering angles, is
performed on Bi2Se3 surfaces prepared by ion bombardment and annealing (IBA).
ICISS angular scans are collected experimentally and simulated numerically
along the [120] and [-1 -2 0] azimuths, and the match of the positions of the
flux peaks shows that the top three atomic layers are bulk-terminated. A newly
observed feature is identified as a minimum in the multiple scattering
background when the ion beam incidence is along a low index direction.
Calculated scans as a function of scattering angle are employed to identify the
behavior of flux peaks to show whether they originate from shadowing, blocking
or both. This new method for analysis of large-angle LEIS data is shown to be
useful for accurately investigating complex surface structures. | cond-mat_mtrl-sci |
Valley Degree of Freedom in Two-Dimensional van der Waals Materials: Layered materials can possess valleys that are indistinguishable from one
another except for the momentum. These valleys are individually addressable in
momentum space at the K and K' points in the first Brillouin zone. Such valley
addressability opens up the possibility of utilizing the momentum state of
quasi-particles as a completely new paradigm in quantum and classical
information processing. This review focuses on the physics behind valley
polarization and talks about carriers of valley degree of freedom (VDF) in
layered materials. Then we provide a detailed survey of simple spectroscopic
techniques commonly utilized to identify and manipulate valley polarization in
van der Waals layered materials. Finally, we conclude with the recent
developments towards the manipulation of VDF for device application and
associated challenges. | cond-mat_mtrl-sci |
Multiferroicity and hydrogen-bond ordering in (C2H5NH3)2CuCl4 featuring
dominant ferromagnetic interactions: We demonstrate that ethylammonium copper chloride, (C2H5NH3)2CuCl4, a member
of the hybrid perovskite family is an electrically polar and magnetic compound
with dielectric anomaly around the Curie point (247 K). We have found large
spontaneous electric polarization below this point accompanied with a color
change in the sample. The system is also ferroelectric, with large remnant
polarization (37{\mu}C/cm2) that is comparable to classical ferroelectric
compounds. The results are ascribed to hydrogen-bond ordering of the organic
chains. The coexistence of ferroelectricity and dominant ferromagnetic
interactions allows to relate the sample to a rare group of magnetic
multiferroic compounds. In such hybrid perovskites the underlying hydrogen
bonding of easily tunable organic building blocks in combination with the 3d
transition-metal layers offers an emerging pathway to engineer multifuctional
multiferroics. | cond-mat_mtrl-sci |
Theory of domain structure in ferromagnetic phase of diluted magnetic
semiconductors near the phase transition temperature: We discuss the influence of disorder on domain structure formation in
ferromagnetic phase of diluted magnetic semiconductors (DMS) of p-type. Using
analytical arguments we show the existence of critical ratio $\nu_{\rm {cr}}$
of concentration of charge carriers and magnetic ions such that sample critical
thickness $L_{\rm{cr}}$ (such that at $L<L_{\rm{cr}}$ a sample is monodomain)
diverges as $\nu \to \nu_{\rm {cr}}$. At $\nu > \nu_{\rm {cr}}$ the sample is
monodomain. This feature makes DMS different from conventional ordered magnets
as it gives a possibility to control the sample critical thickness and emerging
domain structure period by variation of $\nu $. As concentration of magnetic
impurities grows, $\nu_{\rm {cr}}\to \infty$ restoring conventional behavior of
ordered magnets. Above facts have been revealed by examination of the
temperature of transition to inhomogeneous magnetic state (stripe domain
structure) in a slab of finite thickness $L$ of p-type DMS. Our analysis is
carried out on the base of homogeneous exchange part of magnetic free energy of
DMS calculated by us earlier [\prb, {\bf 67}, 195203 (2003)]. | cond-mat_mtrl-sci |
Cathodoluminescence spectroscopy of monolayer hexagonal boron nitride: Cathodoluminescence (CL) spectroscopy is a powerful technique for studying
emission properties of optoelectronic materials because CL is free from
excitable bandgap limits and from ambiguous signals due to simple light
scattering and resonant Raman scattering potentially involved in the
photoluminescence (PL) spectra. However, direct CL measurements of atomically
thin two-dimensional materials, such as transition metal dichalcogenides and
hexagonal boron nitride (hBN), have been difficult due to the small excitation
volume that interacts with high-energy electron beams (e-beams). Herein,
distinct CL signals from a monolayer hBN, namely mBN, epitaxial film grown on a
highly oriented pyrolytic graphite substrate are shown by using a home-made CL
system capable of large-area and surface-sensitive excitation by an e-beam. The
spatially resolved CL spectra at 13 K exhibited a predominant 5.5-eV emission
band, which has been ascribed to originate from multilayered aggregates of hBN,
markedly at thicker areas formed on the step edges of the substrate.
Conversely, a faint peak at 6.04 eV was routinely observed from atomically flat
areas. Since the energy agreed with the PL peak of 6.05 eV at 10 K that has
been assigned as being due to the recombination of phonon-assisted direct
excitons of mBN by Elias et al. [Nat. Commun. 10, 2639 (2019)], the CL peak at
6.04 eV is attributed to originate from the mBN epilayer. The CL results
support the transition from indirect bandgap in bulk hBN to direct bandgap in
mBN, in analogy with molybdenum disulfide. The results also encourage to
elucidate emission properties of other low-dimensional materials with reduced
excitation volumes by using the present CL configuration. | cond-mat_mtrl-sci |
Crystallization Mechanism Tuned Phase-Change Materials: Quantum Effect
on Te-Terminated Boundary: While phase-change materials (PCMs) composed of chalcogenide have different
crystallization mechanisms (CM), such as nucleation-dominated Ge2Sb2Te5 (GST)
and growth-dominated GeTe (GT), revealing the essential reason of CM as well as
the tuned properties is still a long-standing issue. Here, we remarkably find
the distinct stability of Te-terminated (111) boundaries (TTB) in different
systems, which provides a path to understand the difference in CM. It stems
from the quantum effect of molecular orbital theory: the optimal local chemical
composition results in the formation of TTB without dangling bonds (DB) in GST
but with DB in GT, where DB destabilizes boundary due to its distorted local
environment mismatching Oh symmetry of p orbitals. Moreover, the inner vacancy
concentration in GST is alterable and controlled by TTB, manifested by the
absence of cubic-to-hexagonal transition in carbon-doped GST of small grains
and minimized inner vacancy. Finally, the charge transport property (CTP) is
controlled by boundary via changing the density of charge or hole nearby as
well as vacancy. These findings open the door to tune CTP by CM, which is
necessary for achieving low-power and ultrafast devices. | cond-mat_mtrl-sci |
Role of polyhedron unit in distinct photodynamics of zero-dimensional
organic-inorganic hybrid tin halide compounds: The zero-dimensional (0D) metal halides comprise periodically distributed and
isolated metal-halide polyhedra, which act as the smallest inorganic quantum
systems and can accommodate quasi-localized Frenkel excitons. These excitons
exhibit unique photophysics including broadband photon emission, huge Stokes
shift, and long decay lifetime. The polyhedra can have different symmetries due
to the coordination degree of the metal ions. Little is known about how the
polyhedron type affects the characteristics of the 0D metal halide crystals. We
synthesize and comparatively study three novel kinds of 0D organic-inorganic
hybrid tin halide compounds. They are efficient light emitters with a highest
quantum yield of 92.3%. Although they have the same compositional organic
group, the most stable phases are composed of octahedra for the bromide and
iodide but disphenoids (see-saw structures) for the chloride. They separately
exhibit biexponential and monoexponential luminescence decays due to different
symmetries (Ci group for octahedra and C2 group for disphenoids) and
corresponding different electronic structures. The chloride has the largest
absorption photon energy among the three halides, but it has the smallest
emission photon energy. A model regarding the unoccupied energy band degeneracy
is proposed based on the experiments and density functional theory
calculations, which explains well the experimental phenomena and reveals the
crucial role of polyhedron type in determining the optical properties of the 0D
tin halide compounds. | cond-mat_mtrl-sci |
Quantum transport evidence of the boundary states and Lifshitz
transition in Bi$_4$Br$_4$: The quasi-one-dimensional van der Waals compound Bi$_4$Br$_4$ was recently
found to be a promising high-order topological insulator with exotic electronic
states. In this paper, we study the electrical transport properties of
Bi$_4$Br$_4$ bulk crystals. Two electron-type samples with different electron
concentrations are investigated. Both samples have saturation resistivity
behavior in low temperature. In the low-concentration sample, two-dimensional
quantum oscillations are clearly observed in the magnetoresistance
measurements, which are attributed to the band-bending-induced surface state on
the (001) facet. In the high-concentration sample, the angular
magnetoresistance exhibits two pairs of symmetrical sharp valleys with an
angular difference close to the angle between the crystal planes (001) and
(100). The additional valley can be explained by the contribution of the
boundary states on the (100) facet. Besides, Hall measurements at low
temperatures reveal an anomalous decrease of electron concentration with
increasing temperature, which can be explained by the temperature-induced
Lifshitz transition. These results shed light on the abundant surface and
boundary state transport signals and the temperature-induced Lifshitz
transition in Bi$_4$Br$_4$. | cond-mat_mtrl-sci |
Formation of cBN nanocrystals by He+ implantations of hBN: The structural modifications of polycrystalline hexagonal boron nitride
implanted with He+ ion beams at energies between 200 keV and 1.2 MeV to
fluences of 1.0 \times 1017 ions \cdot cm-2 were investigated using micro-Raman
spectroscopy. The measured Raman spectra show evidence of implantation-induced
structural transformations from the hexagonal phase to nanocrystalline cubic
boron nitride, rhombohedral boron nitride and amorphous boron nitride phases.
The first-order Longitudinal-Optical cBN phonon was observed to be downshifted
and asymmetrically broadened and this was explained using the spatial
correlation model coupled with the high ion implantation-induced defect
density. | cond-mat_mtrl-sci |
Interlayer Configurations in Twisted Bilayers of Folded Graphene: The folding of monolayer graphene leads to new layered systems, termed
twisted bilayer graphene (TBG), generally displaying a certain interlayer
rotation away from crystallographic alignment. We here present an atomic force
microscopy study on folded graphene, revealing unexpectedly large twist angle
dependent modulations of ~3 angstrom in interlayer distance. At the TBG
surface, we find enhanced friction attributable to superlubricity in between
incommensurate layers. At the bended edge, the radius of curvature scales with
the folded length, congruent to earlier studies on carbon nanotubes. | cond-mat_mtrl-sci |
ATiO$_{3}$/TiO (A=Pb, Sn) superlattice: bridging ferroelectricity and
conductivity: We propose to insert TiO layers to perovskite ATiO$_{3}$ to form a
superlattice and use first-principles calculations to investigate its basic
properties. Our computational analysis shows that the structure, which consists
of repeated ATiO_{3} and TiO layers, has strong anisotropic conductivity. The
structure immediately suggests a possible control of its conductivity by ion
displacements related to its intrinsic ferroelectricity. In addition, we have
obtained the structural information of its low-energy phases with the aid of
phonon calculation and examined their evolution with epitaxial strain. Since
the number of possible combinations is huge, we have therefore suggested an
approach to mix perovskites and simpler metal-oxides to build materials with
novel properties. | cond-mat_mtrl-sci |
Chemical functionalization on planar polysilane and graphane: Two dimensional materials are important for electronics applications. A
natural way for electronic structure engineering on two dimensional systems is
on-plane chemical functionalization. Based on density functional theory, we
study the electronic structures of fluorine substituted planar polysilane and
graphane. We find that carbon and silicon present very different surface
chemistry. The indirect energy gap of planar polysilane turns to be direct upon
fluorine decoration, and the gap width is mainly determined by fluorine
coverage regardless of its distribution on the surface. However, electronic
structure of fluorine doped graphane is very sensitive to the doping
configuration, due to the competition between antibonding states and
nearly-free-electron (NFE) states. With specific fluorine distribution pattern,
zero-dimensional and one-dimensional NFE states can be obtained. We have also
studied the chemical modification with -OH or -NH$_2$ group. Carbon seems to be
too small to accommodate big functional groups on its graphane skeleton with a
high concentration. | cond-mat_mtrl-sci |
Single crystal growth of TIMETAL LCB titanium alloy by a floating zone
method: The methodology of single crystal growth of metastable $\beta$-Ti alloy
TIMETAL LCB in an optical floating zone furnace is presented in this paper.
Chemical compositions of both precursor material and single crystals were
checked. It was found that the concentration of base alloying elements did not
change significantly during the growth process, while the concentrations of
interstitial elements O and N increased. DSC measurement determined that this
concentration shift has a slight impact on ongoing phase transformations, as in
the single-crystalline material peak associated with $\alpha$ phase
precipitation moves by a few degrees to a lower temperature and peak attributed
to diffusion controlled growth of $\omega$ particles shifts to a higher
temperature. X-ray reciprocal space maps were measured and their simulation
showed that the single crystal has a mosaic structure with mean size of mosaic
blocks of approximately 60 nm. | cond-mat_mtrl-sci |
Machine learning driven simulated deposition of carbon films: from
low-density to diamondlike amorphous carbon: Amorphous carbon (a-C) materials have diverse interesting and useful
properties, but the understanding of their atomic-scale structures is still
incomplete. Here, we report on extensive atomistic simulations of the
deposition and growth of a-C films, describing interatomic interactions using a
machine learning (ML) based Gaussian Approximation Potential (GAP) model. We
expand widely on our initial work [Phys. Rev. Lett. 120, 166101 (2018)] by now
considering a broad range of incident ion energies, thus modeling samples that
span the entire range from low-density ($sp^{2}$-rich) to high-density
($sp^{3}$-rich, "diamond-like") amorphous forms of carbon. Two different
mechanisms are observed in these simulations, depending on the impact energy:
low-energy impacts induce $sp$- and $sp^{2}$-dominated growth directly around
the impact site, whereas high-energy impacts induce peening. Furthermore, we
propose and apply a scheme for computing the anisotropic elastic properties of
the a-C films. Our work provides fundamental insight into this intriguing class
of disordered solids, as well as a conceptual and methodological blueprint for
simulating the atomic-scale deposition of other materials with ML-driven
molecular dynamics. | cond-mat_mtrl-sci |
Many-body Green's function GW and Bethe-Salpeter study of the optical
excitations in a paradigmatic model dipeptide: We study within the many-body Green's function GW and Bethe-Salpeter
formalisms the excitation energies of a paradigmatic model dipeptide, focusing
on the four lowest-lying local and charge-transfer excitations. Our GW
calculations are performed at the self-consistent level, updating first the
quasiparticle energies, and further the single-particle wavefunctions within
the static Coulomb-hole plus screened-exchange approximation to the GW
self-energy operator. Important level crossings, as compared to the starting
Kohn-Sham LDA spectrum, are identified. Our final Bethe-Salpeter singlet
excitation energies are found to agree, within 0.07 eV, with CASPT2 reference
data, except for one charge-transfer state where the discrepancy can be as
large as 0.5 eV. Our results agree best with LC-BLYP and CAM-B3LYP calculations
with enhanced long-range exchange, with a 0.1 eV mean absolute error. This has
been achieved employing a parameter-free formalism applicable to metallic or
insulating extended or finite systems. | cond-mat_mtrl-sci |
The electronic structure of liquid water within density functional
theory: In the last decade, computational studies of liquid water have mostly
concentrated on ground state properties. However recent spectroscopic
measurements have been used to infer the structure of water, and the
interpretation of optical and x-ray spectra requires accurate theoretical
models of excited electronic states, not only of the ground state. To this end,
we investigate the electronic properties of water at ambient conditions using
ab initio density functional theory within the generalized gradient
approximation (DFT/GGA), focussing on the unoccupied subspace of Kohn-Sham
eigenstates. We generate long (250 ps) classical trajectories for large
supercells, up to 256 molecules, from which uncorrelated configurations of
water molecules are extracted for use in DFT/GGA calculations of the electronic
structure. We find that the density of occupied states of this molecular liquid
is well described with 32 molecule supercells using a single k-point (k = 0) to
approximate integration over the first Brillouin zone. However, the description
of the density of unoccupied states (u-EDOS) is sensitive to finite size
effects. Small, 32 molecule supercell calculations, using Gamma-the point
approximation, yield a spuriously isolated state above the Fermi level.
Nevertheless, the more accurate u-EDOS of large, 256 molecule supercells may be
reproduced using smaller supercells and increased k-point sampling. This
indicates that the electronic structure of molecular liquids like water is
relatively insensitive to the long-range disorder in the molecular structure.
These results have important implications for efficiently increasing the
accuracy of spectral calculations for water and other molecular liquids. | cond-mat_mtrl-sci |
Classical potential describes martensitic phase transformations between
the $α$, $β$ and $ω$ titanium phases: A description of the martensitic transformations between the $\alpha$,
$\beta$ and $\omega$ phases of titanium that includes nucleation and growth
requires an accurate classical potential. Optimization of the parameters of a
modified embedded atom potential to a database of density-functional
calculations yields an accurate and transferable potential as verified by
comparison to experimental and density functional data for phonons, surface and
stacking fault energies and energy barriers for homogeneous martensitic
transformations. Molecular dynamics simulations map out the
pressure-temperature phase diagram of titanium. For this potential the
martensitic phase transformation between $\alpha$ and $\beta$ appears at
ambient pressure and 1200 K, between $\alpha$ and $\omega$ at ambient
conditions, between $\beta$ and $\omega$ at 1200 K and pressures above 8 GPa,
and the triple point occurs at 8GPa and 1200 K. Molecular dynamics explorations
of the dynamics of the martensitic $\alpha-\omega$ transformation show a
fast-moving interface with a low interfacial energy of 30 meV/\AA$^2$. The
potential is applicable to the study of defects and phase transformations of
Ti. | cond-mat_mtrl-sci |
Sub-ps thermionic electron injection effects on exciton-formation
dynamics at a van der Waals semiconductor/metal interface: Inorganic van der Waals bonded semiconductors like transition metal
dichalcogenides are subject of intense research due to their electronic and
optical properties which are promising for next-generation optoelectronic
devices. In this context, understanding the ultrafast carrier dynamics, as well
as charge and energy transfer at the interface between metals and
semiconductors is crucial and yet quite unexplored. Here, we present an
experimental study on how thermally induced ultrafast charge carrier injection
affects the exciton formation dynamics in bulk WS2 by employing a
pump-push-probe scheme, where a pump pulse induces thermionic injection of
electrons from the gold substrate into the conduction band of the
semiconductor, and another delayed push pulse excites direct transitions in the
WS2. The transient response shows different dynamics on the sub-ps timescale by
varying the delay between pump and push pulses or by changing the pump fluence,
thus disclosing the important role of ultrafast hot electron injection on the
exciton formation dynamics. Our findings might have potential impact on
research fields that target the integration of ultrafast optics at the boundary
of photonics and electronics, as well as in optically-driven CMOS and quantum
technologies. | cond-mat_mtrl-sci |
Transformation kinetics of alloys under non-isothermal conditions: The overall solid-to-solid phase transformation kinetics under non-isothermal
conditions has been modeled by means of a differential equation method. The
method requires provisions for expressions of the fraction of the transformed
phase in equilibrium condition and the relaxation time for transition as
functions of temperature. The thermal history is an input to the model. We have
used the method to calculate the time/temperature variation of the volume
fraction of the favored phase in the alpha-to-beta transition in a zirconium
alloy under heating and cooling, in agreement with experimental results. We
also present a formulation that accounts for both additive and non-additive
phase transformation processes. Moreover, a method based on the concept of path
integral, which considers all the possible paths in thermal histories to reach
the final state, is suggested. | cond-mat_mtrl-sci |
Combined SANS and SAXS study of the action of ultrasound on the
structure of amorphous zirconia gels: In the present work, we have studied for the first time the combined effect
of both sonication and precipitation pH on the structure of amorphous zirconia
gels synthesized from zirconium(IV) propoxide. The techniques of small-angle
neutron and X-ray scattering (SANS and SAXS) and low temperature nitrogen
adsorption provided the integral data on the changes in the microstructure and
mesostructure of these materials caused by ultrasonic (US) treatment. Amorphous
ZrO2.xH2O synthesized under ultrasonic treatment was found to possess a very
structured surface, characterized by the surface fractal dimension 2.9-3.0,
compared to 2.3-2.5 for the non US-assisted synthesis, and it was also found to
possess a higher specific surface area, while the sizes of the primary
particles remain unchanged. | cond-mat_mtrl-sci |
Thermoelectric properties of marcasite and pyrite FeX$_2$(X=Se,Te): A
first principle study: Electronic structure and thermoelectric properties of marcasite (m) and
synthetic pyrite (p) phases of FeX$_2$ (X=Se,Te) have been investigated using
first principles density functional theory and Boltzmann transport equation.
The plane wave pseudopotential approximation was used to study the structural
properties and full-potential linear augmented plane wave method was used to
obtain the electronic structure and thermoelectric properties (thermopower and
power factor scaled by relaxation time). From total energy calculations we find
that m-FeSe$_2$ and m-FeTe$_2$ are stable at ambient conditions and no
structural transition from marcasite to pyrite is seen under the application of
hydrostatic pressure. The calculated ground state structural properties agree
quite well with available experiments. From the calculated thermoelectric
properties, we find that both m and p forms are good candidates for
thermoelectric applications. However, hole doped m-FeSe$_2$ appears to be the
best among all the four systems. | cond-mat_mtrl-sci |
Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation: We present experimental results on the photoluminescence (PL) of
gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO
targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL
spectra in the UV spectral region correspond to the exciton recombination in
the nanoclusters which are crystallized and cooled down to the temperature of
the ambient gas in the ablation chamber. The time evolution of the spectra as
well as their dependence on the ambient gas pressure are discussed. | cond-mat_mtrl-sci |
First Principles Study of the Giant Magnetic Anisotropy Energy in Bulk
Na4IrO4: In 5d transition metal oxides, novel properties arise from the interplay of
electron correlations and spin--orbit interactions. Na4IrO4, where 5d
transition-metal Ir atom occupies the center of the square-planar coordination
environment, is synthesized. Based on density functional theory, we calculate
its electronic and magnetic properties. Our numerical results show that the
Ir-5d bands are quite narrow, and the bands around the Fermi level are mainly
contributed by d_{xy},d_{yz} and d_{zx} orbitals. The magnetic easy-axis is
perpendicular to the IrO4 plane, and the magnetic anisotropy energy (MAE) of
Na4IrO4 is found to be very giant. We estimate the magnetic parameters by
mapping the calculated total energy for different spin configurations onto a
spin model. The next nearest neighbor exchange interaction J2 is much larger
than other intersite exchange interactions and results in the magnetic ground
state configuration. Our study clearly demonstrates that the huge MAE comes
from the single-ion anisotropy rather than the anisotropic interatomic spin
exchange. This compound has a large spin gap but very narrow spin-wave
dispersion, due to the large single-ion anisotropy and relatively small
exchange couplings. Noticing this remarkable magnetic feature originated from
its highly isolated IrO4 moiety, we also explore the possiblity to further
enhance the MAE. | cond-mat_mtrl-sci |
Electronic, transport and optical properties of monolayer $α$ and
$β-$GeSe: A first-principles study: The extraordinary properties and the novel applications of black phosphorene
induce the research interest on the monolayer group-IV monochalcogenides. Here
using the first-principles calculations, we systematically investigate the
electronic, transport and optical properties of monolayer $\alpha-$ and
$\beta-$GeSe, the latter of which was recently experimentally realized. We
found that, monolayer $\alpha-$GeSe is a semiconductor with direct band gap of
1.6 eV, and $\beta-$GeSe displays indirect semiconductor with the gap of 2.47
eV, respectively. For monolayer $\beta-$GeSe, the electronic/hole transport is
anisotropic with an extremely high electron mobility of 7.84
$\times10^4$$cm^2/V\cdot {s}$ along the zigzag direction, comparable to that of
black phosphorene. Furthermore, for $\beta-$GeSe, robust band gaps nearly
disregarding the applied tensile strain along the zigzag direction is observed.
Both monolayer $\alpha-$ and $\beta-$GeSe exhibit anisotropic optical
absorption in the visible spectrum. | cond-mat_mtrl-sci |
The commensurate phase of multiferroic HoMn2O5 studied by X-ray magnetic
scattering: The commensurate phase of multiferroic HoMn2O5 was studied by X-ray magnetic
scattering, both off resonance and in resonant conditions at the Ho-L3 edge.
Below 40 K, magnetic ordering at the Ho sites is induced by the main Mn
magnetic order parameter, and its temperature dependence is well accounted for
by a simple Curie-Weiss susceptibility model. A lattice distortion of
periodicity twice that of the magnetic order is also evidenced. Azimuthal scans
confirm the model of the magnetic structure recently refined from neutron
diffraction data for both Mn and Ho sites, indicating that the two sublattices
interact via magnetic superexchange. | cond-mat_mtrl-sci |
Electron emission from plasmonically induced Floquet bands at metal
surfaces: We explore the possibility of existence of plasmonically generated electronic
Floquet bands at metal surfaces by studying the gauge transformed
electron-surface plasmon interaction in the prepumped plasmonic coherent state
environment. These bands may promote non-Einsteinian electron emission from
metal surfaces exposed to primary interactions with strong electromagnetic
fields. Resonant behaviour and scaling of emission yield with the parent
electronic structure and plasmonic state parameters are estimated for Ag(111)
surface. Relative yield intensities from non-Einsteinian emission channels in
photoelectron spectra offer the means to calibrate the mediating plasmonic
fields and therefrom ensuing surface Floquet bands. | cond-mat_mtrl-sci |
A critical study of the elastic properties and stability of Heusler
compounds: Phase change and tetragonal $X_{2}YZ$ compounds: In the present work, the elastic constants and derived properties of
tetragonal and cubic Heusler compounds were calculated using the high accuracy
of the full-potential linearized augmented plane wave (FPLAPW). To find the
criteria required for an accurate calculation, the consequences of increasing
the numbers of $k$-points and plane waves on the convergence of the calculated
elastic constants were explored. Once accurate elastic constants were
calculated, elastic anisotropies, sound velocities, Debye temperatures,
malleability, and other measurable physical properties were determined for the
studied systems. The elastic properties suggested metallic bonding with
intermediate malleability, between brittle and ductile, for the studied Heusler
compounds. To address the effect of off-stoichiometry on the mechanical
properties, the virtual crystal approximation (VCA) was used to calculate the
elastic constants. The results indicated that an extreme correlation exists
between the anisotropy ratio and the stoichiometry of the Heusler compounds,
especially in the case of Ni$_{2}$MnGa. | cond-mat_mtrl-sci |
Cubic-scaling iterative solution of the Bethe-Salpeter equation for
finite systems: The Bethe-Salpeter equation (BSE) is currently the state of the art in the
description of neutral electron excitations in both solids and large finite
systems. It is capable of accurately treating charge-transfer excitations that
present difficulties for simpler approaches. We present a local basis set
formulation of the BSE for molecules where the optical spectrum is computed
with the iterative Haydock recursion scheme, leading to a low computational
complexity and memory footprint. Using a variant of the algorithm we can go
beyond the Tamm-Dancoff approximation (TDA). We rederive the recursion
relations for general matrix elements of a resolvent, show how they translate
into continued fractions, and study the convergence of the method with the
number of recursion coefficients and the role of different terminators. Due to
the locality of the basis functions the computational cost of each iteration
scales asymptotically as $O(N^3)$ with the number of atoms, while the number of
iterations is typically much lower than the size of the underlying
electron-hole basis. In practice we see that , even for systems with thousands
of orbitals, the runtime will be dominated by the $O(N^2)$ operation of
applying the Coulomb kernel in the atomic orbital representation | cond-mat_mtrl-sci |
THz emission from Co/Pt bilayers with varied roughness, crystal
structure, and interface intermixing: Femtosecond laser excitation of a Co/Pt bilayer results in the efficient
emission of picosecond THz pulses. Two known mechanisms for generating THz
emission are spin-polarized currents through a Co/Pt interface, resulting in
helicity-independent electric currents in the Pt layer due to the inverse
spin-Hall effect and helicity-dependent electric currents at the Co/Pt
interface due to the inverse spin-orbit torque effect. Here we explore how
roughness, crystal structure and intermixing at the Co/Pt interface affect the
efficiency of the THz emission. In particular, we varied the roughness of the
interface, in the range of 0.1-0.4 nm, by tuning the deposition pressure
conditions during the fabrication of the Co/Pt bilayers. To control the
intermixing at the Co/Pt interface a 1-2 nm thick CoxPt1-x alloy spacer layer
was introduced with various compositions of Co and Pt. Finally, the crystal
structure of Co was varied from face centered cubic to hexagonal close packed.
Our study shows that the roughness of the interface is of crucial importance
for the efficiency of helicity-dependent THz emission induced by femtosecond
laser pulses. However, it is puzzling that intermixing while strongly enhancing
the helicity-independent THz emission had no effect on the helicity-dependent
THz emission which is suppressed and similar to the smooth interfaces. | cond-mat_mtrl-sci |
Investigation of thickness dependent composition of boron carbide thin
films by resonant soft x-ray reflectivity: Boron carbide thin films of different thicknesses deposited by ion beam
sputtering were studied. The deposited films were characterized by grazing
incidence hard x-ray reflectivity (GIXR), resonant soft x-ray reflectivity
(RSXR), x-ray photo electron spectroscopy (XPS), resonant Rutherford
backscattering spectrometry (RRBS), and time of flight secondary ion mass
spectrometry (TOF-SIMS). An in-depth profile of the chemical elements
constitute the films is reconstructed based on analysis of reflectivity curves
measured in the vicinity of B K-edge. The composition of films is closely
dependent on film thickness. Boron to Carbon (B/C) ratio reaches to ~4 as the
thickness of deposited films increases. The B/C ratio estimated from RSXR
measurements are in agreement with the RRBS measurements. TOF-SIMS data also
suggested that decrease in boron content with decrease in film thickness. XPS
measurements confirm the presence of little amount of B atoms on the surface of
low thickness film. | cond-mat_mtrl-sci |
Magnetic ordering and fluctuation in kagome lattice antiferromagnets, Fe
and Cr jarosites: Jarosite family compounds, KFe_3(OH)_6(SO_4)_2, (abbreviate Fe jarosite), and
KCr_3(OH)_6(SO_4)_2, (Cr jarosite), are typical examples of the Heisenberg
antiferromagnet on the kagome lattice and have been investigated by means of
magnetization and NMR experiments. The susceptibility of Cr jarosite deviates
from Curie-Weiss law due to the short-range spin correlation below about 150 K
and shows the magnetic transition at 4.2 K, while Fe jarosite has the
transition at 65 K. The susceptibility data fit well with the calculated one on
the high temperature expansion for the Heisenberg antiferromagnet on the kagome
lattice. The values of exchange interaction of Cr jarosite and Fe jarosite are
derived to be J_Cr = 4.9 K and J_Fe = 23 K, respectively. The 1H-NMR spectra of
Fe jarosite suggest that the ordered spin structure is the q = 0 type with
positive chirality of the 120 degrees configuration. The transition is caused
by a weak single-ion type anisotropy. The spin-lattice relaxation rate, 1/T_1,
of Fe jarosite in the ordered phase decreases sharply with lowering the
temperature and can be well explained by the two-magnon process of spin wave
with the anisotropy. | cond-mat_mtrl-sci |
A Temporal Filter to Extract Doped Conducting Polymer Information
Features from an Electronic Nose: Identifying relevant machine-learning features for multi-sensing platforms is
both an applicative limitation to recognize environments and a necessity to
interpret the physical relevance of transducers' complementarity in their
information processing. Particularly for long acquisitions, feature extraction
must be fully automatized without human intervention and resilient to
perturbations without increasing significantly the computational cost of a
classifier. In this study, we investigate on the relative resistance and
current modulation of a 24-dimensional conductimetric electronic nose, which
uses the exponential moving average as a floating reference in a low-cost
information descriptor for environment recognition. In particular, we
identified that depending on the structure of a linear classifier, the 'modema'
descriptor is optimized for different material sensing elements' contributions
to classify information patterns. The low-pass filtering optimization leads to
opposite behaviors between unsupervised and supervised learning: the latter one
favors longer integration of the reference, allowing to recognize five
different classes over 90%, while the first one prefers using the latest events
as its reference to clusterize patterns by environment nature. Its electronic
implementation shall greatly diminish the computational requirements of
conductimetric electronic noses for on-board environment recognition without
human supervision. | cond-mat_mtrl-sci |
Electronic structure and properties of pure and doped $ε$-FeSi
from ab-initio local density theory: Local density calculations of the electronic structure of FeSi,
FeSi_{1-x}Al_x and Fe_{1-x}Ir_xSi systems in the B20 structure are presented.
Pure FeSi has a semi-conducting gap of 6 mRy at 0 K.
Effects of temperature (T) in terms of electronic and vibrational excitations
are included. Various measurable properties, such as magnetic susceptibility
chi(T), electronic specific heat C(T), thermoelectric power S(T), relative
variations in resistivity rho(T), and peak positions in the density-of-states
(DOS) are calculated. The feedback from vibrational disorder onto the
electronic structure is found to be essential for a good description of most
properties, although the results for S(T) in undoped FeSi can be described up
to about 150 K without considerations of disorder. Above this T, only the
filling of the gap due to disorder accompanied by exchange enhancement, can
explain the large susceptiblity. The overall good agreement with experimental
data for most properties in doped and pure FeSi suggests that this system is
well described by LDA even at large T. Doped FeSi can be described quite well
from rigid-band shifts of the Fermi energy on the DOS of pure FeSi.
Spin-polarization in Ir doped FeSi leads to a semi-metallic magnetic state at
low T. (Submitted to Phys. Rev. B) | cond-mat_mtrl-sci |
Factors influencing graphene growth on metal surfaces: Graphene forms from a relatively dense, tightly-bound C-adatom gas, when
elemental C is deposited on or segregates to the Ru(0001) surface. Nonlinearity
of the graphene growth rate with C adatom density suggests that growth proceeds
by addition of C atom clusters to the graphene edge. The generality of this
picture has now been studied by use of low-energy electron microscopy (LEEM) to
observe graphene formation when Ru(0001) and Ir(111) surfaces are exposed to
ethylene. The finding that graphene growth velocities and nucleation rates on
Ru have precisely the same dependence on adatom concentration as for elemental
C deposition implies that hydrocarbon decomposition only affects graphene
growth through the rate of adatom formation; for ethylene, that rate decreases
with increasing adatom concentration and graphene coverage. Initially, graphene
growth on Ir(111) is like that on Ru: the growth velocity is the same nonlinear
function of adatom concentration (albeit with much smaller equilibrium adatom
concentrations, as we explain with DFT calculations of adatom formation
energies). In the later stages of growth, graphene crystals that are rotated
relative to the initial nuclei nucleate and grow. The rotated nuclei grow much
faster. This difference suggests first, that the edge-orientation of the
graphene sheets relative to the substrate plays an important role in the growth
mechanism, and second, that attachment of the clusters to the graphene is the
slowest step in cluster addition, rather than formation of clusters on the
terraces. | cond-mat_mtrl-sci |
Determining the Fundamental Failure Modes in Ni-rich Lithium Ion Battery
Cathodes: Challenges associated with in-service mechanical degradation of Li-ion
battery cathodes has prompted a transition from polycrystalline to single
crystal cathode materials. Whilst for single crystal materials,
dislocation-assisted crack formation is assumed to be the dominating failure
mechanism throughout battery life, there is little direct information about
their mechanical behaviour, and mechanistic understanding remains elusive.
Here, we demonstrated, using in situ micromechanical testing, direct
measurement of local mechanical properties within LiNi0.8Mn0.1Co0.1O2 single
crystalline domains. We elucidated the dislocation slip systems, their critical
stresses, and how slip facilitate cracking. We then compared single crystal and
polycrystal deformation behaviour. Our findings answer two fundamental
questions critical to understanding cathode degradation: What dislocation slip
systems operate in Ni-rich cathode materials? And how does slip cause fracture?
This knowledge unlocks our ability to develop tools for lifetime prediction and
failure risk assessment, as well as in designing novel cathode materials with
increased toughness in-service. | cond-mat_mtrl-sci |
Experimental exploration of ErB$_2$ and SHAP analysis on a
machine-learned model of magnetocaloric materials for materials design: Stimulated by a recent report of a giant magnetocaloric effect in HoB$_2$
found via machine-learning predictions, we have explored the magnetocaloric
properties of a related compound ErB$_2$, that has remained the last
ferromagnetic material among the rare-earth diboride (REB$_2$) family with
unreported magnetic entropy change |{\Delta}SM|. The evaluated $|\Delta S_M|$
at field change of 5 T in ErB$_2$ turned out to be as high as 26.1 (J kg$^{-1}$
K$^{-1}$) around the ferromagnetic transition (${T_C}$) of 14 K. In this
series, HoB$_2$ is found to be the material with the largest $|\Delta S_M|$ as
the model predicted, while the predicted values showed a deviation with a
systematic error compared to the experimental values. Through a coalition
analysis using SHAP, we explore how this rare-earth dependence and the
deviation in the prediction are deduced in the model. We further discuss how
SHAP analysis can be useful in clarifying favorable combinations of constituent
atoms through the machine-learned model with compositional descriptors. This
analysis helps us to perform materials design with aid of machine learning of
materials data. | cond-mat_mtrl-sci |
Origin of training effect of exchange bias in Co/CoO due to irreversible
thermoremanent magnetization of the magnetically diluted antiferromagnet: The irreversible thermoremanent magnetization of a sole, magnetically diluted
epitaxial antiferromagnetic Co$_{1-y}$O(100) layer is determined by the mean of
its thermoremanent magnetizations at positive and negative remanence. During
hysteresis-loop field cycling, thermoremanent magnetization exhibits successive
reductions, consistent with the training effect (TE) of the exchange bias
measured for the corresponding Co$_{1-y}$O(100)/Co bilayer. The TE of exchange
bias is shown to have its microscopic origin in the TE of the irreversible
thermoremanent magnetization of the magnetically diluted AFM. | cond-mat_mtrl-sci |
Intermittency in aging: The fluctuation-dissipation relation (FDR) is measured on the dielectric
properties of a gel (Laponite) and of a polymer glass (polycarbonate). For the
gel it is found that during the transition from a fluid-like to a solid-like
state the fluctuation dissipation theorem is strongly violated. The amplitude
and the persistence time of this violation are decreasing functions of
frequency. Around $1Hz$ it may persist for several hours. A very similar
behavior is observed in polycarbonate after a quench below the glass transition
temperature. In both cases the origin of this violation is a highly
intermittent dynamics characterized by large fluctuations. The relevance of
these results for recent models of aging are discussed. | cond-mat_mtrl-sci |
Electronic structure and stability of hydrogen defects in diamond and
boron doped diamond: A density functional theory study: Isolated hydrogen and hydrogen pairs in bulk diamond matrix have been studied
using density functional theory calculations. The electronic structure and
stability of isolated and paired hydrogen defects are investigated at different
possible lattice sites in pure diamond and boron doped diamond. Calculations
revealed that isolated hydrogen defect is stable at bond center sites for pure
diamond and bond center puckered site for boron doped diamond. In case of
hydrogen pairs, H2 defect (one hydrogen at bond center and second at
anti-bonding site) is stable for pure diamond, while for boron doped diamond
B-H2BC complex (one H atom at the B-C bond centered puckered position and the
other one at the puckered position of one of the C-C bond first neighbor of the
B atom) is most stable. Multiple hydrogen trapping sites in boron doped diamond
has also been studied. Calculated results are discussed and compared with
previously reported theoretical results in detailed. | cond-mat_mtrl-sci |
First-principles based simulations of electronic transmission in
ReS$_{2}$/WSe$_{2}$ and ReS$_{2}$/MoSe$_{2}$ type-II vdW heterointerfaces: Electronic transmission in monolayer ReS$_{2}$ and ReS$_{2}$ based van der
Waals (vdW) heterointerfaces are studied here. Since ReS$_{2}$/WSe$_{2}$ and
ReS$_{2}$/MoSe$_{2}$ type-II vdW heterostructures are suitable for near
infrared (NIR)/short-wave infrared (SWIR) photodetection, the role of
interlayer coupling at the heterointerfaces is examined in this work. Besides,
a detailed theoretical study is presented employing density functional theory
(DFT) and nonequilibrium Green's function (NEGF) combination to analyse the
transmission spectra of the two-port devices with ReS$_{2}$/WSe$_{2}$ and
ReS$_{2}$/MoSe$_{2}$ channels and compare the near-equilibrium conductance
values.Single layer distorted1T ReS$_{2}$ exhibits formation of parallel chains
of 'Re' - 'Re' bonds, leading to in-plane anisotropy. Owing to this structural
anisotropy, the charge carrier transport is very much orientation dependent in
ReS$_{2}$. Therefore, this work is further extended to investigate the role of
clusterized 'Re' atoms in electronic transmission. | cond-mat_mtrl-sci |
Atomic-Scale Tailoring of Chemisorbed Atomic Oxygen on Epitaxial
Graphene for Graphene-Based Electronic Devices: Graphene, with its unique band structure, mechanical stability, and high
charge mobility, holds great promise for next-generation electronics.
Nevertheless, its zero band gap challenges the control of current flow through
electrical gating, consequently limiting its practical applications. Recent
research indicates that atomic oxygen can oxidize epitaxial graphene in a
vacuum without causing unwanted damage. In this study, we have investigated the
effects of chemisorbed atomic oxygen on the electronic properties of epitaxial
graphene, using scanning tunneling microscopy (STM). Our findings reveal that
oxygen atoms effectively modify the electronic states of graphene, resulting in
a band gap at its Dirac point. Furthermore, we demonstrate that it is possible
to selectively induce desorption or hopping of oxygen atoms with atomic
precision by applying appropriate bias sweeps with an STM tip. These results
suggest the potential for atomic-scale tailoring of graphene oxide, enabling
the development of graphene-based atomic-scale electronic devices. | cond-mat_mtrl-sci |
Function follows form: From semiconducting to metallic towards
superconducting PbS nanowires by faceting the crystal: In the realm of colloidal nanostructures, with its immense capacity for shape
and dimensionality control, the form is undoubtedly a driving factor for the
tunability of optical and electrical properties in semiconducting or metallic
materials. However, influencing the fundamental properties is still challenging
and requires sophisticated surface or dimensionality manipulation. In this
work, we present such a modification for the example of colloidal lead sulphide
nanowires. We show that the electrical properties of lead sulphide
nanostructures can be altered from semiconducting to metallic with indications
of superconductivity, by exploiting the flexibility of the colloidal synthesis
to sculpt the crystal and to form different surface facets. A particular
morphology of lead sulphide nanowires has been synthesized through the
formation of {111} surface facets, which shows metallic and superconducting
properties in contrast to other forms of this semiconducting crystal, which
contain other surface facets ({100} and {110}). This effect, which has been
investigated with several experimental and theoretical approaches, is
attributed to the presence of lead rich {111} facets. The insights promote new
strategies for tuning the properties of crystals as well as new applications
for lead sulphide nanostructures. | cond-mat_mtrl-sci |
Quantum effects in graphene monolayers: Path-integral simulations: Path-integral molecular dynamics (PIMD) simulations have been carried out to
study the influence of quantum dynamics of carbon atoms on the properties of a
single graphene layer. Finite-temperature properties were analyzed in the range
from 12 to 2000~K, by using the LCBOPII effective potential. To assess the
magnitude of quantum effects in structural and thermodynamic properties of
graphene, classical molecular dynamics simulations have been also performed.
Particular emphasis has been laid on the atomic vibrations along the
out-of-plane direction. Even though quantum effects are present in these
vibrational modes, we show that at any finite temperature classical-like motion
dominates over quantum delocalization, provided that the system size is large
enough. Vibrational modes display an appreciable anharmonicity, as derived from
a comparison between kinetic and potential energy of the carbon atoms. Nuclear
quantum effects are found to be appreciable in the interatomic distance and
layer area at finite temperatures. The thermal expansion coefficient resulting
from PIMD simulations vanishes in the zero-temperature limit, in agreement with
the third law of thermodynamics. | cond-mat_mtrl-sci |
Elastic and thermodynamic properties of the shape-memory alloy AuZn: The current work reports on the elastic shear moduli, internal friction, and
the specific heat of the B2 cubic ordered alloy AuZn as a function of
temperature. Measurements were made on single-crystal and polycrystalline
samples using Resonant Ultrasound Spectroscopy (RUS), semi-adiabatic
calorimetry and stress-strain measurements. Our results confirm that this alloy
exhibits the shape-memory effect and a phase transition at 64.75 K that appears
to be continuous (second-order) from the specific heat data. It is argued that
the combination of equiatomic composition and a low transformation temperature
constrain the chemical potential and its derivatives to exhibit behavior that
lies at the borderline between that of a first-order (discontinuous) and a
continuous phase transition. The acoustic dissipation does not peak at the
transtion temperature as expected, but shows a maximum well into the
low-temperature phase. The Debye temeprature value of 219 K, obtained from the
low-temperature specific heat data is in favorable agreement with that
determined from the acoustic data (207 K) above the transition. | cond-mat_mtrl-sci |
Photo-Hall, photorefractive and photomagnetoelectric effects in tungsten
bronzes and related tetragonal ferroelectrics: We present an extensive study of the electric, magnetic and elastic responses
of tetragonal ferroelectrics under illumination, using a new theory
intertwining material and wave symmetries. Optical rectification,
photomagnetic, photovoltaic and phototoroidal vector responses are worked out
as functions of the wave vector and wave polarization directions. Second-order
response tensors associated with photoelastic, photomagnetoelectric,
photorefractive effects and photoconductivity are described. We discuss in
detail the photo-Hall and a new non-linear optical effect in tungsten bronzes.
Finally, we compare the properties of tetragonal materials with those of
hexagonal, orthorhombic and trigonal ferroelectrics previously reported in the
literature. | cond-mat_mtrl-sci |
TC++: First-principles calculation code for solids using the
transcorrelated method: TC++ is a free/libre open-source software of the transcorrelated (TC) method
for first-principles calculation of solids. Here, the TC method is one of the
promising wave-function theories that can be applied to periodic systems with
reasonable computational cost and satisfactory accuracy. We present our
implementation of TC++ including a detailed description of the divergence
correction technique applied to the TC effective interactions. We also present
the way to use TC++ and some results of application to simple periodic systems:
bulk silicon and homogeneous electron gas. | cond-mat_mtrl-sci |
Strain engineering of epitaxial oxide heterostructures beyond substrate
limitations: The limitation of commercially available single-crystal substrates and the
lack of continuous strain tunability preclude the ability to take full
advantage of strain engineering for further exploring novel properties and
exhaustively studying fundamental physics in complex oxides. Here we report an
approach for imposing continuously tunable, large epitaxial strain in oxide
heterostructures beyond substrate limitations by inserting an interface layer
through tailoring its gradual strain relaxation. Taking BiFeO3 as a model
system, we demonstrate that the introduction of an ultrathin interface layer
allows the creation of a desired strain that can induce phase transition and
stabilize a new metastable super-tetragonal phase as well as morphotropic phase
boundaries overcoming substrate limitations. Furthermore, continuously tunable
strain from tension to compression can be generated by precisely adjusting the
thickness of the interface layer, leading to the first achievement of
continuous O-R-T phase transition in BiFeO3 on a single substrate. This
proposed route could be extended to other oxide heterostructures, providing a
platform for creating exotic phases and emergent phenomena. | cond-mat_mtrl-sci |
Nanowire growth and sublimation: CdTe quantum dots in ZnTe nanowires: The role of the sublimation of the compound and of the evaporation of the
constituents from the gold nanoparticle during the growth of semiconductor
nanowires is exemplified with CdTe-ZnTe heterostructures. Operating close to
the upper temperature limit strongly reduces the amount of Cd present in the
gold nanoparticle and the density of adatoms on the nanowire sidewalls. As a
result, the growth rate is small and strongly temperature dependent, but a good
control of the growth conditions allows the incorporation of quantum dots in
nanowires with sharp interfaces and adjustable shape, and it minimizes the
radial growth and the subsequent formation of additional CdTe clusters on the
nanowire sidewalls, as confirmed by photoluminescence. Uncapped CdTe segments
dissolve into the gold nanoparticle when interrupting the flux, giving rise to
a bulb-like (pendant-droplet) shape attributed to the Kirkendall effect. | cond-mat_mtrl-sci |
Cyclic Ferroelectric Switching and Quantized Charge Transport in
CuInP$_2$S$_6$: The van der Waals layered ferroelectric CuInP$_2$S$_6$ has been found to
exhibit a variety of intriguing properties arising from the fact that the Cu
ions are unusually mobile in this system. While the polarization switching
mechanism is usually understood to arise from Cu ion motion within the
monolayers, a second switching path involving Cu motion across the van der
Waals gaps has been suggested. In this work, we perform zero-temperature
first-principles calculations on such switching paths, focusing on two types
that preserve the periodicity of the primitive unit cell: ``cooperative" paths
preserving the system's glide mirror symmetry, and ``sequential" paths in which
the two Cu ions in the unit cell move independently of each other. We find that
CuInP$_2$S$_6$ features a rich and varied energy landscape, and that sequential
paths are clearly favored energetically both for cross-gap and through-layer
paths. Importantly, these segments can be assembled to comprise a globally
insulating cycle with the out-of-plane polarization evolving by a quantum as
the Cu ions shift to neighboring layers. In this sense, we argue that
CuInP$_2$S$_6$ embodies the physics of a quantized adiabatic charge pump. | cond-mat_mtrl-sci |
Dzyaloshinskii-Moriya interaction from unquenched orbital angular
momentum: Orbitronics is an emerging and fascinating field that explores the
utilization of the orbital degree of freedom of electrons for information
processing. An increasing number of orbital phenomena are being currently
discovered, with spin-orbit coupling mediating the interplay between orbital
and spin effects, thus providing a wealth of control mechanisms and device
applications. In this context, the orbital analog of spin Dzyaloshinskii-Moriya
interaction (DMI), i.e. orbital DMI, deserves to be explored in depth, since it
is believed to be capable of inducing chiral orbital structures. Here, we
unveil the main features and microscopic mechanisms of the orbital DMI in a
two-dimensional square lattice using a tight-binding model of t2g orbitals in
combination with the Berry phase theory. This approach allows us to investigate
and transparently disentangle the role of inversion symmetry breaking, strength
of orbital exchange interaction and spin-orbit coupling in shaping the
properties of the orbital DMI. By scrutinizing the band-resolved contributions
we are able to understand the microscopic mechanisms and guiding principles
behind the orbital DMI and its anisotropy in two dimensional magnetic
materials, and uncover a fundamental relation between the orbital DMI and its
spin counterpart, which is currently explored very intensively. The insights
gained from our work contribute to advancing our knowledge of orbitalrelated
effects and their potential applications in spintronics, providing a path for
future research in the field of chiral orbitronics. | cond-mat_mtrl-sci |
Experimental realization of chiral Landau levels in two-dimensional
Dirac cone systems with inhomogeneous effective mass: Chiral zeroth Landau levels are topologically protected bulk states that give
rise to chiral anomaly. Previous discussions on such chiral Landau levels are
based on three-dimensional Weyl degeneracies. Their realizations using
two-dimensional Dirac point systems, being more promising for future
applications, were never reported before. Here we propose a theoretical and
experimental scheme for realizing chiral Landau levels in a photonic system. By
introducing an inhomogeneous effective mass through breaking local parity
inversion symmetries, the zeroth-order chiral Landau levels with one-way
propagation characteristics are experimentally observed. In addition, the
robust transport of the chiral zeroth mode against defects in the system is
experimentally tested. Our system provides a new pathway for the realization of
chiral Landau levels in two-dimensional Dirac systems, and may potentially be
applied in device designs utilizing the transport robustness. | cond-mat_mtrl-sci |
Designing magnetic properties in CrSBr through hydrostatic pressure and
ligand substitution: The ability to control magnetic properties of materials is crucial for
fundamental research and underpins many information technologies. In this
context, two-dimensional materials are a particularly exciting platform due to
their high degree of tunability and ease of implementation into nanoscale
devices. Here we report two approaches for manipulating the A-type
antiferromagnetic properties of the layered semiconductor CrSBr through
hydrostatic pressure and ligand substitution. Hydrostatic pressure compresses
the unit cell, increasing the interlayer exchange energy while lowering the
N\'eel temperature. Ligand substitution, realized synthetically through Cl
alloying, anisotropically compresses the unit cell and suppresses the
Cr-halogen covalency, reducing the magnetocrystalline anisotropy energy and
decreasing the N\'eel temperature. A detailed structural analysis combined with
first-principles calculations reveal that alterations in the magnetic
properties are intricately related to changes in direct Cr-Cr exchange
interactions and the Cr-anion superexchange pathways. Further, we demonstrate
that Cl alloying enables chemical tuning of the interlayer coupling from
antiferromagnetic to ferromagnetic, which is unique amongst known
two-dimensional magnets. The magnetic tunability, combined with a high ordering
temperature, chemical stability, and functional semiconducting properties, make
CrSBr an ideal candidate for pre- and post-synthetic design of magnetism in
two-dimensional materials. | cond-mat_mtrl-sci |
Discovering Equations that Govern Experimental Materials Stability under
Environmental Stress using Scientific Machine Learning: While machine learning (ML) in experimental research has demonstrated
impressive predictive capabilities, inductive reasoning and knowledge
extraction remain elusive tasks, in part because of the difficulty extracting
fungible knowledge representations from experimental data. In this manuscript,
we use ML to infer the underlying dynamical differential equation (DE) from
experimental data of degrading organic-inorganic methylammonium lead iodide
(MAPI) perovskite thin films under environmental stressors (elevated
temperature, humidity, and light). We apply a sparse regression algorithm that
automatically identifies the differential equation describing the dynamics from
time-series data. We find that the underlying DE governing MAPI degradation
across a broad temperature range of 35 to 85{\deg}C is described minimally with
three terms (specifically, a second-order polynomial), and not a simple
single-order reaction (i.e. 0th, 1st, or 2nd-order reaction). We demonstrate
how computer-derived results can aid the researcher to develop profound
mechanistic insights. This DE corresponds to the Verhulst logistic function,
which describes reaction kinetics analogous in functional form to autocatalytic
or self-propagating reactions, suggesting future strategies to suppress MAPI
degradation. We examine the robustness of our conclusions to experimental
luck-of-the-draw variance and Gaussian noise using a combination of experiment
and simulation, and describe the experimental limits within which this
methodology can be applied. Our study demonstrates the application of
scientific ML in experimental chemical and materials systems, highlighting the
promise and challenges associated with ML-aided scientific discovery. | cond-mat_mtrl-sci |
A Bayesian Committee Machine Potential for Organic Nitrogen Compounds: Large-scale computer simulations of chemical atoms are used in a wide range
of applications, including batteries, drugs, and more. However, there is a
problem with efficiency as it takes a long time due to the large amount of
calculation. To solve these problems, machine learning interatomic potential
(ML-IAP) technology is attracting attention as an alternative. ML-IAP not only
has high accuracy by faithfully expressing the density functional theory (DFT),
but also has the advantage of low computational cost. However, there is a
problem that the potential energy changes significantly depending on the
environment of each atom, and expansion to a wide range of compounds within a
single model is still difficult to build in the case of a kernel-based model.
To solve this problem, we would like to develop a universal ML-IAP using this
active Bayesian Committee Machine (BCM) potential methodology for
carbon-nitrogen-hydrogen (CNH) with various compositions. ML models are trained
and generated through first-principles calculations and molecular dynamics
simulations for molecules with only CNH. Using long amine structures to test an
ML model trained only with short chains, the results show excellent consistency
with DFT calculations. Consequently, machine learning-based models for organic
molecules not only demonstrate the ability to accurately describe various
physical properties but also hold promise for investigating a broad spectrum of
diverse materials systems. | cond-mat_mtrl-sci |
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