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2021-03-30 | Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films | Magnetic insulators are important materials for a range of next generation
memory and spintronic applications. Structural constraints in this class of
devices generally require a clean heterointerface that allows effective
magnetic coupling between the insulating layer and the conducting layer.
However, there are relatively few examples of magnetic insulators which can be
synthesized with surface qualities that would allow these smooth interfaces and
precisely tuned interfacial magnetic exchange coupling which might be
applicable at room temperature. In this work, we demonstrate an example of how
the configurational complexity in the magnetic insulator layer can be used to
realize these properties. The entropy-assisted synthesis is used to create
single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a
range of strain states. These films show smooth surfaces, high resistivity, and
strong magnetic responses at room temperature. Local and global magnetic
measurements further demonstrate how strain can be used to manipulate magnetic
texture and anisotropy. These findings provide insight into how precise
magnetic responses can be designed using compositionally complex materials that
may find application in next generation magnetic devices. | 2103.16722v1 |
2022-08-03 | Reactive Laser Synthesis of Ultra-high-temperature Ceramics HfC, ZrC, TiC, HfN, ZrN, and TiN for Additive Manufacturing | Ultra-high-temperature ceramics (UHTCs) are optimal structural materials for
applications that require extreme temperature resilience, resistance to
chemically aggressive environments, wear, and mechanical stress. Processing
UHTCs with laser-based additive manufacturing (AM) has not been fully realized
due to a variety of obstacles. In this work, selective laser reaction sintering
(SLRS) techniques were investigated for the production of near net-shape UHTC
ceramics such as HfC, ZrC, TiC, HfN, ZrN, and TiN. Group IV transition metal
and metal oxide precursor materials were chemically converted and
reaction-bonded into layers of UHTCs using single-step selective laser
processing in CH4 or NH3 gas that might be compatible with prevailing powder
bed fusion techniques. Conversion of either metals (Hf, Zr and Ti) or metal
oxides (HfO2, ZrO2, and TiO2) particles was first investigated to examine
reaction mechanisms and volume changes associated with SLRS of single-component
precursor systems. SLRS processing of metal or metal oxide alone produced near
stoichiometric UHTC phases with yields up to 100 wt% total for carbides and
nitrides. However, for single component precursors, gas-solid reactivity
induced volumetric changes resulted in residual stresses and cracking in the
product layer. To mitigate conversion-induced stresses, composite metal/metal
oxide precursors were employed to compensate for the volume changes of either
the metal (which expands during conversion) or the metal oxide precursor (which
contracts). | 2208.02041v2 |
2023-04-24 | Absolute radiation tolerance of amorphous alumina coatings at room temperature | In this study structural and mechanical properties of a 1 um thick Al2O3
coating, deposited on 316L stainless steel by Pulsed Laser Deposition (PLD),
subjected to high energy ion irradiation were assessed. Mechanical properties
of pristine and ion-modified specimens were investigated using the
nanoindentation technique. A comprehensive characterization combining
Transmission Electron Microscopy and Grazing-Incidence X-ray Diffraction
provided deep insight into the structure of the tested material at the nano-
and micro- scale. Variation in the local atomic ordering of the irradiated zone
at different doses was investigated using a reduced distribution function
analysis obtained from electron diffraction data. Findings from nanoindentation
measurements revealed a slight reduction in hardness of all irradiated layers.
At the same time TEM examination indicated that the irradiated layer remained
amorphous over the whole dpa range. No evidence of crystallization, void
formation or element segregation was observed up to the highest implanted dose.
Reported mechanical and structural findings were critically compared with each
other pointing to the conclusion that under given irradiation conditions, over
the whole range of doses used, alumina coatings exhibit excellent radiation
resistance. Obtained data strongly suggest that investigated material may be
considered as a promising candidate for next-generation nuclear reactors,
especially LFR-type, where high corrosion protection is one of the highest
prerogatives to be met. | 2304.11973v1 |
2023-06-01 | Nonlinear characteristics of Ti, Nb, and NbN superconducting resonators for parametric amplifiers | Superconducting resonators and parametric amplifiers are important components
in scientific systems such as kinetic inductance detector arrays,
frequency-domain multiplexers for other superconducting bolometers,
spin-ensemble based memories, and circuit quantum electrodynamics
demonstrators. In this paper, we report microwave measurements of
superconducting Ti, Nb, and NbN resonators and their use as parametric
amplifiers. These half-wave resonators were fabricated under near identical
sputtering and lithographic conditions to ensure a like-for-like comparison of
material properties. We report a wide range of properties and behaviours in
terms of transition temperatures, resistivities, rate-limiting nonlinear
response times, nonlinear dissipation, signs of the nonlinear inductances and
their dependences on temperature and resonance harmonic. We have successfully
operated Nb and NbN resonators as high gain parametric amplifiers, achieving
greater than $20\,\mathrm{dB}$ of power amplification. We have shown that for a
half-wave resonator, amplification can be realised not only in the fundamental
resonance but also in the higher harmonic resonances. Further, for materials
with high transition temperatures, e.g. Nb and NbN, amplification can be
achieved at $\sim4\,\mathrm{K}$, i.e. a temperature maintained by a pulse tube
cooler. Finally, in materials systems that have very fast response times, e.g.
NbN, we have found that a cross-harmonic type of amplification can be achieved
by placing pump tone in a different resonant mode as the signal and the idler.
This wide range of observations will have important implications on the design
and application of superconducting parametric amplifiers. | 2306.00685v2 |
2023-07-17 | MBE growth of axion insulator candidate EuIn2As2 | The synthesis of thin films of magnetic topological materials is necessary to
achieve novel quantized Hall effects and electrodynamic responses. EuIn2As2 is
a recently predicted topological axion insulator that has an antiferromagnetic
ground state and an inverted band structure, but that has only been synthesized
and studied as a single crystal. We report on the synthesis of c-axis oriented
EuIn2As2 films on sapphire substrates by molecular beam epitaxy. By carefully
tuning the substrate temperature during growth, we stabilize the Zintl phase of
EuIn2As2 expected to be topologically non-trivial. The magnetic properties of
these films reproduce those seen in single crystals, but their resistivity is
enhanced when grown at lower temperatures. We additionally find that the
magnetoresistance of EuIn2As2 is negative even up to fields as high as 31T.
while it is highly anisotropic at low fields, it becomes nearly isotropic at
high magnetic fields above 5T. Overall, the transport characteristics of
EuIn2As2 appear similar to those of chalcogenide topological insulators,
motivating the development of devices to gate tune the Fermi energy and reveal
topological features in quantum transport. | 2307.08831v2 |
2023-12-20 | Singular Hall response from a correlated ferromagnetic flat nodal-line semimetal | Topological quantum phases have been largely understood in weakly correlated
systems, which have identified various quantum phenomena such as spin Hall
effect, protected transport of helical fermions, and topological
superconductivity. Robust ferromagnetic order in correlated topological
materials particularly attracts attention, as it can provide a versatile
platform for novel quantum devices. Here, we report singular Hall response
arising from a unique band structure of flat topological nodal lines in
combination with electron correlation in an itinerant, van der Waals
ferromagnetic semimetal, Fe3GaTe2, with a high Curie temperature of Tc=360 K.
High anomalous Hall conductivity violating the conventional scaling,
resistivity upturn at low temperature, and a large Sommerfeld coefficient are
observed in Fe3GaTe2, which implies heavy fermion features in this
ferromagnetic topological material. Our circular dichroism in angle-resolved
photoemission spectroscopy and theoretical calculations support the original
electronic features in the material. Thus, low-dimensional Fe3GaTe2 with
electronic correlation, topology, and room-temperature ferromagnetic order
appears to be a promising candidate for robust quantum devices. | 2312.12889v1 |
2024-02-28 | Multifunctional composite magnet for practical transverse thermoelectrics | Permanent magnets are used in various products and essential for human
society. If omnipresent permanent magnets could directly convert heat into
electricity, they would lead to innovative energy harvesting and thermal
management technologies. However, achieving such "multifunctionality" has been
difficult because of the poor thermoelectric performance of conventional
magnets. Here, we develop a multifunctional composite magnet that enables giant
transverse thermoelectric conversion. The proposed composite material,
comprising alternately and obliquely stacked
SmCo$_5$/Bi$_{0.2}$Sb$_{1.8}$Te$_3$ multilayers, exhibits large remanent
magnetization and coercivity as well as an excellent figure of merit of 0.32
for transverse thermoelectric conversion around room temperature. While having
versatile transverse geometry and high mechanical durability, the thermopile
module based on these composite magnets generates 204 mW at a temperature
difference of 152 K owing to extremely low interfacial electrical and thermal
resistances. The corresponding power density per heat transfer area of 56.7
mW/cm$^2$ is not only record-high among all the transverse thermoelectric
modules but also comparable to those of commercial longitudinal thermoelectric
modules based on the Seebeck effect. The novel functional material enables the
integration of thermoelectric conversion capabilities wherever permanent
magnets are currently used. | 2402.18019v1 |
1996-06-05 | Hall Resistivity in Ferromagnetic Manganese-Oxide Compounds | Temperature-dependence and magnetic field-dependence of the Hall effect and
the magnetic property in manganese-oxide thin films are studied. The
spontaneous magnetization and the Hall resistivity are obtained for a various
of magnetic fields over all the temperature. It is shown that the Hall
resistivity in small magnetic field is to exhibit maximum near the Curie point,
and strong magnetic field moves the position of the Hall resistivity peak to
much high temperature and suppresses the peak value. The change of the Hall
resistance in strong magnetic field may be larger than that of the diagonal
ones. The abnormal Hall resistivity in the ferromagnetic manganese-oxide
thin-films is attributed to the spin-correlation fluctuation scattering. | 9606030v1 |
2002-06-04 | Free flux flow resistivity in strongly overdoped high-T_c cuprate; purely viscous motion of the vortices in semiclassical d-wave superconductor | We report the free flux flow (FFF) resistivity associated with a purely
viscous motion of the vortices in moderately clean d-wave superconductor
Bi:2201 in the strongly overdoped regime (T_c=16K) for a wide range of the
magnetic field in the vortex state. The FFF resistivity is obtained by
measuring the microwave surface impedance at different microwave frequencies.
It is found that the FFF resistivity is remarkably different from that of
conventional s-wave superconductors. At low fields (H<0.2H_c2) the FFF
resistivity increases linearly with H with a coefficient which is far larger
than that found in conventional s-wave superconductors. At higher fields, the
FFF resistivity increases in proportion to \sqrt H up to H_c2. Based on these
results, the energy dissipation mechanism associated with the viscous vortex
motion in "semiclassical" d-wave superconductors with gap nodes is discussed.
Two possible scenarios are put forth for these field dependence; the
enhancement of the quasiparticle relaxation rate and the reduction of the
number of the quasiparticles participating the energy dissipation in d-wave
vortex state. | 0206031v1 |
2003-06-14 | Radiation induced zero-resistance states in GaAs/AlGaAs heterostructures: Voltage-current characteristics and intensity dependence at the resistance minima | High mobility two-dimensional electron systems exhibit vanishing resistance
over broad magnetic field intervals upon excitation with microwaves, with a
characteristic reduction of the resistance with increasing radiation intensity
at the resistance minima. Here, we report experimental results examining the
voltage - current characteristics, and the resistance at the minima vs. the
microwave power. The findings indicate that a non-linear V-I curve in the
absence of microwave excitation becomes linearized under irradiation, unlike
expectations, and they suggest a similarity between the roles of the radiation
intensity and the inverse temperature. | 0306388v2 |
2007-05-12 | Effects of electromagnetic waves on the electrical properties of contacts between grains | A DC electrical current is injected through a chain of metallic beads. The
electrical resistances of each bead-bead contacts are measured. At low current,
the distribution of these resistances is large and log-normal. At high enough
current, the resistance distribution becomes sharp and Gaussian due to the
creation of microweldings between some beads. The action of nearby
electromagnetic waves (sparks) on the electrical conductivity of the chain is
also studied. The spark effect is to lower the resistance values of the more
resistive contacts, the best conductive ones remaining unaffected by the spark
production. The spark is able to induce through the chain a current enough to
create microweldings between some beads. This explains why the electrical
resistance of a granular medium is so sensitive to the electromagnetic waves
produced in its vicinity. | 0705.1775v2 |
2009-12-10 | Dichotomy in the $T$-linear resistivity in hole-doped cuprates | From analysis of the in-plane resistivity $\rho_{ab}(T)$ of
La$_{2-x}$Sr$_x$CuO$_4$, we show that normal state transport in overdoped
cuprates can be delineated into two regimes in which the electrical resistivity
varies approximately linearly with temperature. In the low temperature limit,
the $T$-linear resistivity extends over a very wide doping range, in marked
contrast to expectations from conventional quantum critical scenarios. The
coefficient of this $T$-linear resistivity scales with the superconducting
transition temperature $T_c$, implying that the interaction causing this
anomalous scattering is also associated with the superconducting pairing
mechanism. At high temperatures, the coefficient of the $T$-linear resistivity
is essentially doping independent beyond a critical doping $p_{\rm crit}$ =
0.19 at which the ratio of the two coefficients is maximal. Taking our cue from
earlier thermodynamic and photoemission measurements, we conclude that the
opening of the normal state pseudogap at $p_{\rm crit}$ is driven by the loss
of coherence of anti-nodal quasiparticles at low temperatures. | 0912.2001v1 |
2010-05-25 | Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection | Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to
investigate the system evolution of relativistic magnetic reconnection. A
time-split Harten--Lan--van Leer method is employed. Under a localized
resistivity, the system exhibits a fast reconnection jet with an Alfv\'{e}nic
Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures
are resolved in and around the plasmoid such as the post-plasmoid vertical
shocks and the "diamond-chain" structure due to multiple shock reflections.
Under a uniform resistivity, Sweet--Parker-type reconnection slowly evolves.
Under a current-dependent resistivity, plasmoids are repeatedly formed in an
elongated current sheet. It is concluded that the resistivity model is of
critical importance for RRMHD modeling of relativistic magnetic reconnection. | 1005.4485v2 |
2013-12-18 | Magneto-transport characteristics of a 2D electron system driven to negative magneto-conductivity by microwave photoexcitation | Negative diagonal magneto-conductivity/resistivity is a spectacular- and
thought provoking- property of driven, far-from-equilibrium, low dimensional
electronic systems. The physical response of this exotic electronic state is
not yet fully understood since it is rarely encountered in experiment. The
microwave-radiation-induced zero-resistance state in the high mobility
GaAs/AlGaAs 2D electron system is believed to be an example where negative
magneto-conductivity/resistivity is responsible for the observed phenomena.
Here, we examine the magneto-transport characteristics of this negative
conductivity/resistivity state in the microwave photo-excited two-dimensional
electron system (2DES) through a numerical solution of the associated boundary
value problem. The results suggest, surprisingly, that a bare negative diagonal
conductivity/resistivity state in the 2DES under photo-excitation should yield
a positive diagonal resistance with a concomitant sign reversal in the Hall
voltage. | 1312.5026v1 |
2014-12-19 | Nano-artifact metrics based on random collapse of resist | Artifact metrics is an information security technology that uses the
intrinsic characteristics of a physical object for authentication and clone
resistance. Here, we demonstrate nano-artifact metrics based on silicon
nanostructures formed via an array of resist pillars that randomly collapse
when exposed to electron-beam lithography. The proposed technique uses
conventional and scalable lithography processes, and because of the random
collapse of resist, the resultant structure has extremely fine-scale morphology
with a minimum dimension below 10 nm, which is less than the resolution of
current lithography capabilities. By evaluating false match, false non-match
and clone-resistance rates, we clarify that the nanostructured patterns based
on resist collapse satisfy the requirements for high-performance security
applications. | 1412.6271v1 |
2015-07-15 | ERK/p38 MAPK inhibition reduces radio-resistance to pulsed proton beam in breast cancer stem cells cells | Recent studies have identified highly tumorigenic cells with stem cell-like
characteristics in human cancers, termed cancer stem cells (CSCs). CSCs are
resistant to conventional radiotherapy and chemotherapy owing to their high DNA
repair ability and oncogene overexpression. However, the mechanisms regulating
CSC radio-resistance, particularly proton beam resistance, remain unclear. We
isolated CSCs from the breast cancer cell lines MCF-7 and MDA-MB-231, which
expressed the characteristic breast CSC membrane protein markers
CD44+/CD24-/low, and irradiated the CSCs with pulsed proton beams. We confirmed
that CSCs are resistant to pulsed proton beams and showed that treatment with
p38 and ERK inhibitors reduced CSC radioresistance. Based on these results,
BCSC radio-resistance can be reduced during proton beam therapy by co-treatment
with ERK1/2 or p38 inhibitors, representing a novel approach for breast cancer
therapy. | 1509.02377v1 |
2017-06-23 | Investigating prescriptions for artificial resistivity in smoothed particle magnetohydrodynamics | In numerical simulations, artificial terms are applied to the evolution
equations for stability. To prove their validity, these terms are thoroughly
tested in test problems where the results are well known. However, they are
seldom tested in production-quality simulations at high resolution where they
interact with a plethora of physical and numerical algorithms. We test three
artificial resistivities in both the Orszag-Tang vortex and in a star formation
simulation. From the Orszag-Tang vortex, the Price et. al. (2017) artificial
resistivity is the least dissipative thus captures the density and magnetic
features; in the star formation algorithm, each artificial resistivity
algorithm interacts differently with the sink particle to produce various
results, including gas bubbles, dense discs, and migrating sink particles. The
star formation simulations suggest that it is important to rely upon physical
resistivity rather than artificial resistivity for convergence. | 1706.07721v1 |
2019-07-05 | Impurity scattering induced carrier transport in twisted bilayer graphene | We theoretically calculate the impurity-scattering induced resistivity of
twisted bilayer graphene at low twist angles where the graphene Fermi velocity
is strongly suppressed. We consider, as a function of carrier density, twist
angle, and temperature, both long-ranged Coulomb scattering and short-ranged
defect scattering within a Boltzmann theory relaxation time approach. For
experimentally relevant disorder, impurity scattering contributes a resistivity
comparable to (much larger than) the phonon scattering contribution at high
(low) temperatures. Decreasing twist angle leads to larger resistivity, and in
general, the resistivity increases (decreases) with increasing temperature
(carrier density). Inclusion of the van Hove singularity in the theory leads to
a strong increase in the resistivity at higher densities, where the chemical
potential is close to a van Hove singularity, leading to an apparent
density-dependent plateau type structure in the resistivity, which has been
observed in recent transport experiments. We also show that the Matthissen's
rule is strongly violated in twisted bilayer graphene at low twist angles. | 1907.02856v3 |
2021-01-28 | Contagion-Preserving Network Sparsifiers: Exploring Epidemic Edge Importance Utilizing Effective Resistance | Network epidemiology has become a vital tool in understanding the effects of
high-degree vertices, geographic and demographic communities, and other
inhomogeneities in social structure on the spread of disease. However, many
networks derived from modern datasets are quite dense, such as mobility
networks where each location has links to a large number of potential
destinations. One way to reduce the computational effort of simulating
epidemics on these networks is sparsification, where we select a representative
subset of edges based on some measure of their importance. Recently an approach
was proposed using an algorithm based on the effective resistance of the edges.
We explore how effective resistance is correlated with the probability that an
edge transmits disease in the SI model. We find that in some cases these two
notions of edge importance are well correlated, making effective resistance a
computationally efficient proxy for the importance of an edge to epidemic
spread. In other cases, the correlation is weaker, and we discuss situations in
which effective resistance is not a good proxy for epidemic importance. | 2101.11818v1 |
2023-02-22 | Drugs Resistance Analysis from Scarce Health Records via Multi-task Graph Representation | Clinicians prescribe antibiotics by looking at the patient's health record
with an experienced eye. However, the therapy might be rendered futile if the
patient has drug resistance. Determining drug resistance requires
time-consuming laboratory-level testing while applying clinicians' heuristics
in an automated way is difficult due to the categorical or binary medical
events that constitute health records. In this paper, we propose a novel
framework for rapid clinical intervention by viewing health records as graphs
whose nodes are mapped from medical events and edges as correspondence between
events in given a time window. A novel graph-based model is then proposed to
extract informative features and yield automated drug resistance analysis from
those high-dimensional and scarce graphs. The proposed method integrates
multi-task learning into a common feature extracting graph encoder for
simultaneous analyses of multiple drugs as well as stabilizing learning. On a
massive dataset comprising over 110,000 patients with urinary tract infections,
we verify the proposed method is capable of attaining superior performance on
the drug resistance prediction problem. Furthermore, automated drug
recommendations resemblant to laboratory-level testing can also be made based
on the model resistance analysis. | 2302.11231v2 |
2023-11-03 | Resistive Diffusion in Magnetized ICF Implosions: Reduced Magnetic Stabilization of the Richtmyer Meshkov Instability | Resistive diffusion is typically regarded to be negligible in magnetized ICF
experiments, with magnetic flux effectively compressed during the implosion. In
this work the Richtmyer Meshkov instability at the ice-ablator interface is
taken as an example for investigating resistive effects. For a high temperature
(approximately 100eV) interface with magnetic field applied perpendicular to
shock propagation, perturbation growth is suppressed by magnetic tension.
However, for lower temperature interfaces the resistive diffusion prevents
substantial magnetic field twisting at small scales. ICF implosion simulations
are then used to assess magnetic diffusivity at different interfaces; the
ice-ablator interface is found to be too resistive for the magnetic fields to
enhance stability. For Rayleigh-Taylor growth at the hot-spot edge, on the
other hand, resistivity is estimated to only be a secondary effect, as seen in
previous simulation studies. | 2311.01645v2 |
2024-03-14 | Role of many phonon modes on the high-temperature linear-in-$T$ electronic resistivity | We theoretically consider the possibility that phonons may be playing a role
in the observed linear-in-$T$ resistivity in cuprates by focusing on the
obvious question: How can phonon scattering be consistent with a linear-in-$T$
resistivity with a constant slope given that cuprates have many phonon modes
with different energies and electron-phonon couplings (e.g. 21 phonon modes for
LSCO)? We show using an arbitrarily large number of independent phonon modes
that, within a model Boltzmann transport theory, the emergent high-$T$
linear-in-$T$ resistivity manifests an approximately constant slope independent
of the number of phonon modes except in some fine-tuned narrow temperature
regimes. We also comment on the quantitative magnitude of the linear-in-$T$
resistivity in cuprates pointing out the constraints on the effective
electron-phonon coupling necessary to produce the observed resistivity. | 2403.09890v1 |
2017-02-16 | Anomalous Nonlocal Resistance and Spin-charge Conversion Mechanisms in Two-Dimensional Metals | We uncover two anomalous features in the nonlocal transport behavior of
two-dimensional metallic materials with spin-orbit coupling. Firstly, the
nonlocal resistance can have negative values and oscillate with distance, even
in the absence of a magnetic field. Secondly, the oscillations of the nonlocal
resistance under an applied in-plane magnetic field (Hanle effect) can be
asymmetric under field reversal. Both features are produced by direct
magnetoelectric coupling, which is possible in materials with broken inversion
symmetry but was not included in previous spin diffusion theories of nonlocal
transport. These effects can be used to identify the relative contributions of
different spin-charge conversion mechanisms. They should be observable in
adatom-functionalized graphene, and may provide the reason for discrepancies in
recent nonlocal transport experiments on graphene. | 1702.04955v3 |
2018-06-23 | Crack growth resistance in metallic alloys: the role of isotropic versus kinematic hardening | The sensitivity of crack growth resistance to the choice of isotropic or
kinematic hardening is investigated. Monotonic mode I crack advance under small
scale yielding conditions is modelled via a cohesive zone formulation endowed
with a traction-separation law. R-curves are computed for materials that
exhibit linear or power law hardening. Kinematic hardening leads to an enhanced
crack growth resistance relative to isotropic hardening. Moreover, kinematic
hardening requires greater crack extension to achieve the steady state. These
differences are traced to the non-proportional loading of material elements
near the crack tip as the crack advances. The sensitivity of the R-curve to the
cohesive zone properties and to the level of material strain hardening is
explored for both isotropic and kinematic hardening. | 1806.08986v1 |
2020-01-08 | Novel hypostasis of old materials in oxide electronics: metal oxides for resistive random access memory applications | Transition-metal oxide films, demonstrating the effects of both threshold and
nonvolatile memory resistive switching, have been recently proposed as
candidate materials for storage-class memory. In this work we describe some
experimental results on threshold switching in a number of various transition
metal (V, Ti, Fe, Nb, Mo, W, Hf, Zr, Mn, Y, and Ta) oxide films obtained by
anodic oxidation. Then, the results concerning the effects of bistable
resistive switching in MOM and MOS structures on the basis of such oxides as
V2O5, Nb2O5, and NiO are presented. It is shown that sandwich structures on the
basis of the Au/V2O5/SiO2/Si, Nb/Nb2O5/Au, and Pt/NiO/Pt can be used as memory
elements for ReRAM applications. Finally, model approximations are developed in
order to describe theoretically the effect of nonvolatile unipolar switching in
Pt NiO-Pt structures. | 2001.03026v1 |
2022-04-28 | Ultralow Electron-Surface Scattering in Nanoscale Metals Leveraging Fermi Surface Anisotropy | Increasing resistivity of metal wires with reducing nanoscale dimensions is a
major performance bottleneck of semiconductor computing technologies. We show
that metals with suitably anisotropic Fermi velocity distributions can strongly
suppress electron scattering by surfaces and outperform isotropic conductors
such as copper in nanoscale wires. We derive a corresponding descriptor for the
resistivity scaling of anisotropic conductors, screen thousands of metals using
first-principles calculations of this descriptor and identify the most
promising materials for nanoscale interconnects. Previously-proposed layered
conductors such as MAX phases and delafossites show promise in thin films, but
not in narrow wires due to increased scattering from side walls. We find that
certain intermetallics (notably CoSn) and borides (such as YCo$_3$B$_2$) with
one-dimensionally anisotropic Fermi velocities are most promising for narrow
wires. Combined with first-principles electron-phonon scattering predictions,
we show that the proposed materials exhibit 2-3x lower resistivity than copper
at 5 nm wire dimensions. | 2204.13458v1 |
2022-07-20 | Optimal Structures for Failure Resistance Under Impact | The complex physics and numerous failure modes of structural impact creates
challenges when designing for impact resistance. While simple geometries of
layered material are conventional, advances in 3D printing and additive
manufacturing techniques have now made tailored geometries or integrated
multi-material structures achievable. Here, we apply gradient-based topology
optimization to the design of such structures. We start by constructing a
variational model of an elastic-plastic material enriched with gradient
phase-field damage, and present a novel method to efficiently compute its
transient dynamic time evolution. We consider a finite element discretization
with explicit updates for the displacements. The damage field is solved through
an augmented Lagrangian formulation, splitting the operator coupling between
the nonlinearity and non-locality. Sensitivities over this trajectory are
computed through the adjoint method, resulting in an adjoint problem which we
solve in a similar manner to the forward dynamics. We demonstrate this
formulation by studying the optimal design of 2D solid-void structures
undergoing blast loading. Then, we explore the trade-offs between strength and
toughness in the design of a spall-resistant structure composed of two
materials of differing properties undergoing dynamic impact. | 2207.09678v1 |
1998-05-11 | Two-dimensional arrays of low capacitance tunnel junctions: general properties, phase transitions and Hall effect | We describe transport properties of two-dimensional arrays of low capacitance
tunnel junctions, such as the current voltage characteristic and its dependence
on external magnetic field and temperature. We discuss several experiments in
which the small capacitance of the junctions plays an important role. In arrays
where the junctions have a relatively large charging energy, (i.e. when they
have a low capacitance) and a high normal state resistance, the low bias
resistance increases with decreasing temperature and eventually at very low
temperature the array becomes insulating even though the electrodes in the
array are superconducting. This transition to the insulating state can be
described by thermal activation. In an intermediate region where the junction
resistance is of the order of the quantum resistance and the charging energy is
of the order of the Josephson coupling energy, the arrays can be tuned between
a superconducting and an insulating state with a magnetic field. We describe
measurements of this magnetic-field-tuned superconductor insulator transition,
and we show that the resistance data can be scaled over several orders of
magnitude. Four arrays follow the same universal function. At the transition
the transverse (Hall) resistance is found to be very small in comparison with
the longitudinal resistance. However, for magnetic field values larger than the
critical value.we observe a substantial Hall resistance. The Hall resistance of
these arrays oscillates with the applied magnetic field. features in the
magnetic field dependence of the Hall resistance can qualitatively be
correlated to features in the derivative of the longitudinal resistance,
similar to what is found in the quantum Hall effect. | 9805121v1 |
2020-07-03 | First-principles study of electronic transport and structural properties of Cu$_{12}$Sb$_4$S$_{13}$ in its high-temperature phase | We present an ab initio study of the structural and electronic transport
properties of tetrahedrite, Cu$_{12}$Sb$_4$S$_{13}$, in its high-temperature
phase. We show how this complex compound can be seen as the outcome of an
ordered arrangement of S-vacancies in a semiconducting fematinite-like
structure (Cu3SbS4). Our calculations confirm that the S-vacancies are the
natural doping mechanism in this thermoelectric compound and reveal a similar
local chemical environment around crystallographically inequivalent Cu atoms,
shedding light on the debate on XPS measurements in this compound. To access
the electrical transport properties as a function of temperature we use the
Kubo-Greenwood formula applied to snapshots of first-principles molecular
dynamics simulations. This approach is essential to effectively account for the
interaction between electrons and lattice vibrations in such a complex crystal
structure where a strong anharmonicity plays a key role in stabilising the
high-temperature phase. Our results show that the Seebeck coeffcient is in good
agreement with experiments and the phonon-limited electrical resistivity
displays a temperature trend that compares well with a wide range of
experimental data. The predicted lower bound for the resistivity turns out to
be remarkably low for a pristine mineral in the Cu-Sb-S system but not too far
from the lowest experimental data reported in literature. The Lorenz number
turns out to be substantially lower than what expected from the free-electron
value in the Wiedemann-Franz law, thus providing an accurate way to estimate
the electronic and lattice contributions to the thermal conductivity in
experiments, of great significance in this very low thermal conductivity
crystalline material. | 2007.01809v2 |
2015-03-25 | Anisotropy of Thermal Conductivity of Free-Standing Reduced Graphene Oxide Films Annealed at High Temperature | We investigated thermal conductivity of free-standing reduced graphene oxide
films subjected to a high-temperature treatment of up to 1000 C. It was found
that the high-temperature annealing dramatically increased the in-plane thermal
conductivity, K, of the films from 3 W/mK to 61 W/mK at room temperature. The
cross-plane thermal conductivity, Kc, revealed an interesting opposite trend of
decreasing to a very small value of 0.09 W/mK in the reduced graphene oxide
films annealed at 1000 C. The obtained films demonstrated an exceptionally
strong anisotropy of the thermal conductivity, K/Kc ~ 675, which is
substantially larger even than in the high-quality graphite. The electrical
resistivity of the annealed films reduced to 1 - 19 Ohms/sq. The observed
modifications of the in-plane and cross-plane thermal conductivity components
resulting in an unusual K/Kc anisotropy were explained theoretically. The
theoretical analysis suggests that K can reach as high as ~500 W/mK with the
increase in the sp2 domain size and further reduction of the oxygen content.
The strongly anisotropic heat conduction properties of these films can be
useful for applications in thermal management. | 1503.07239v1 |
2017-03-07 | Thermodynamic Stabilization of Precipitates through Interface Segregation: Chemical Effects | Precipitation hardening, which relies on a high density of intermetallic
precipitates, is a commonly utilized technique for strengthening structural
alloys. Structural alloys are commonly strengthened through a high density of
small size intermetallic precipitates. At high temperatures, however, the
precipitates coarsen to reduce the excess energy of the interface, resulting in
a significant reduction in the strengthening provided by the precipitates. In
certain ternary alloys, the secondary solute segregates to the interface and
results in the formation of a high density of nanosize precipitates that
provide enhanced strength and are resistant to coarsening. To understand the
chemical effects involved, and to identify such systems, we develop a
thermodynamic model using the framework of the regular nanocrystalline solution
model. For various global compositions, temperatures and thermodynamic
parameters, equilibrium configuration of Mg-Sn-Zn alloy is evaluated by
minimizing the Gibbs free energy function with respect to the region-specific
(bulk solid-solution, interface and precipitate) concentrations and sizes. The
results show that Mg$_2$Sn precipitates can be stabilized to nanoscale sizes
through Zn segregation to Mg/Mg$_2$Sn interface, and the precipitates can be
stabilized against coarsening at high-temperatures by providing a larger Zn
concentration in the system. Together with the inclusion of elastic strain
energy effects and the input of computationally informed interface
thermodynamic parameters in the future, the model is expected to provide a more
realistic prediction of segregation and precipitate stabilization in ternary
alloys of structural importance. | 1703.02621v2 |
2020-09-29 | High open-circuit voltage in transition metal dichalcogenide solar cells | The conversion efficiency of ultra-thin solar cells based on layered
materials has been limited by their open-circuit voltage, which is typically
pinned to a value under 0.6 V. Here we report an open-circuit voltage of 1.02 V
in a 120 nm-thick vertically stacked homojunction fabricated with
substitutionally doped MoS2. This high open-circuit voltage is consistent with
the band alignment in the MoS2 homojunction, which is more favourable than in
widely-used TMDC heterostructures. It is also attributed to the high
performance of the substitutionally doped MoS2, in particular the p-type
material doped with Nb, which is demonstrated by the observation of
electroluminescence from tunnelling graphene/BN/MoS2 structures in spite of the
indirect nature of bulk MoS2. We find that illuminating the TMDC/metal contacts
decreases the measured open-circuit voltage in MoS2 van der Waals homojunctions
because they are photoactive, which points to the need of developing
low-resistance, ohmic contacts to doped MoS2 in order to achieve high
efficiency in practical devices. The high open-circuit voltage demonstrated
here confirms the potential of layered transition-metal dichalcogenides for the
development of highly efficient, ultra-thin solar cells. | 2009.13911v1 |
2019-11-25 | Natural-mixing guided design of refractory high-entropy alloys with as-cast tensile ductility | Multi-principal-element metallic alloys have created a growing interest that
is unprecedented in metallurgical history, in exploring the property limits of
metals and the governing physical mechanisms. Refractory high-entropy alloys
(RHEAs) have drawn particular attention due to their (i) high melting points
and excellent softening-resistance, which are the two key requirements for
high-temperature applications; and (ii) compositional space, which is immense
even after considering cost and recyclability restrictions. However, RHEAs also
exhibit intrinsic brittleness and oxidation-susceptibility, which remain as
significant challenges for their processing and application. Here, utilizing
natural-mixing characteristics amongst refractory elements, we designed a
Ti38V15Nb23Hf24 RHEA that exhibits >20% tensile ductility already at the
as-cast state, and physicochemical stability at high-temperatures. Exploring
the underlying deformation mechanisms across multiple length-scales, we observe
that a rare beta prime precipitation strengthening mechanism governs its
intriguing mechanical response. These results also reveal the effectiveness of
natural-mixing tendencies in expediting HEA discovery. | 1911.10975v1 |
2021-12-23 | Record High Tc Element Superconductivity Achieved In Titanium | It is challenging to search for high Tc superconductivity (SC) in transition
metal elements wherein d electrons are usually not favored by conventional BCS
theory. Here we report discovery of surprising SC up to 310 GPa with Tc above
20 K in wide pressure range from 108 GPa to 240 GPa in titanium. The maximum
Tc^onset above 26 K and zero resistance Tc^zero of 21 K are record high values
hitherto achieved among element superconductors. The Hc2(0) is estimated to be
about 32 Tesla with coherence length 32 angstrom. The results show strong s-d
transfer and d-band dominance, indicating correlation driven contributions to
high Tc SC in dense titanium. This finding is in sharp contrast to the
theoretical predications based on pristine electron-phonon coupling scenario.
The study opens a fresh promising avenue for rational design and discovery of
high Tc superconductors among simple materials via pressure tuned
unconventional mechanism. | 2112.12396v3 |
2022-01-12 | Emergence of superconducting dome in insulating ZrNx films via nitrogen manipulation | Reproducing the electronic phase diagram of strongly correlated
high-transition-temperature (high-Tc) superconductors in materials other than
Cu-, Fe-, and Ni-based compounds has been a challenging task. Only very
recently, a few material systems have partially achieved this goal by band
engineering. In this work, we combine film growth, charge transport,
magnetometry, Terahertz Spectroscopy, Raman scattering, and Scanning
Transmission Electron Microscopy to investigate superconductivity and the
normal state of ZrNx, which reveals a phase diagram that bears extraordinary
similarities to those of high-Tc superconductors. Remarkably, even though
superconductivity of ZrNx can be characterized within the
Bardeen-Cooper-Schrieffer paradigm and its normal state can be understood
within the Fermi liquid framework, by tunning the N chemical concentration, we
observe the evolution of a superconducting dome in the close vicinity of a
strongly insulating state and a normal state resistivity mimics its counterpart
of the high-Tc superconductors. | 2201.04340v2 |
2023-06-22 | Scalable Electrodeposition of Eutectic Indium Gallium from an Acetonitrile-Based Electrolyte for Integrated Stretchable Electronics | For the advancement of highly-integrated stretchable electronics, the
development of scalable sub-micrometer conductor patterning is required.
Eutectic gallium indium EGaIn is an attractive conductor for stretchable
electronics, as its liquid metallic character grants it high electrical
conductivity upon deformation. However, its high surface energy precludes
patterning it with (sub)-micron resolution. Herein, we overcome this limitation
by reporting for the first time the electrodeposition of EGaIn. We use a
non-aqueous acetonitrile-based electrolyte that exhibits high electrochemical
stability and chemical orthogonality. The electrodeposited material led to
low-resistance lines that remained stable upon (repeated) stretching to a 100
percent strain. Because electrodeposition benefits from the resolution of
mature nanofabrication methods used to pattern the base metal, the proposed
bottom-up approach achieved a record-high density integration of EGaIn regular
lines of 300 nm half-pitch on an elastomer substrate by plating on a gold seed
layer pre-patterned by nanoimprinting. Moreover, vertical integration was
enabled by filling high aspect ratio vias. This capability was conceptualized
by the fabrication of an omnidirectionally stretchable 3D electronic circuit,
and demonstrates a soft-electronic analogue of the stablished damascene process
used to fabricate microchip interconnects. Overall, this work proposes a simple
route to address the challenge of metallization in highly integrated (3D)
stretchable electronics. | 2306.12781v2 |
2020-05-28 | High-temperature and Abrasion Resistant Selective Solar Absorber under Ambient Environment | Selective solar absorbers (SSAs) with high performance are the key to
concentrated solar power systems. Optical metamaterials are emerging as a
promising strategy to enhance selective photon absorption, however, the
high-temperature resistance (>500C) remains as one of the main challenges for
their practical applications. Here, a multilayered metamaterial system
(Al2O3/W/SiO2/W) based on metal-insulator-metal (MIM) resonance effect has been
demonstrated with high solar absorptance over 92%, low thermal emittance loss
below 6%, and significant high-temperature resistance: it has been proved that
the optical performance remains 93.6% after 1-hour thermal annealing under
ambient environment up to 500C, and 94.1% after 96-hour thermal cycle test at
400C, which is also confirmed by the microscopic morphology characterization.
The spectral selectivity of fabricated SSAs is angular independent and
polarization insensitive. Outdoor tests demonstrate that a peak temperature
rise (193.5C) can be achieved with unconcentrated solar irradiance and surface
abrasion resistance test yields that SSAs have a robust resistance to abrasion
attack for engineering applications. | 2005.14305v1 |
2015-11-22 | On materials destruction criteria | In terms of nonlinear material fracture mechanics, the real
(discrete)-structure material fracture model has been developed. The model
rests on the demonstration of the fact that crack resistance $K_{1c}=2\sigma
\sqrt l$ and fracture toughness are $G_{1c}=J_{1c}=2\sigma l$ obtained on the
basis of energy conservation law and derived without linear material fracture
mechanics assumptions can be respectively taken as force and energy criteria
for non-linear fracture mechanics. It is shown that $G_{1c}=K_{1c}^2/E$ is the
energy criterion of linear fracture mechanics of material and it is
sufficiently less than $G_{1c} = J_{1c}=2\sigma l$. | 1511.07037v1 |
2021-01-31 | Origin of high hardness and optoelectronic and thermo-physical properties of boron-rich compounds B6X (X = S, Se): a comprehensive study via DFT approach | In the present study, the structural and hitherto uninvestigated mechanical
(elastic stiffness constants, machinability index, Cauchy pressure, anisotropy
indices, brittleness/ductility, Poissons ratio), electronic, optical, and
thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have
been explored using density functional theory. The estimated structural lattice
parameters were consistent with the prior report. The mechanical and dynamical
stability of these compounds have been established theoretically. The materials
are brittle in nature and elastically anisotropic. The value of fracture
toughness, KIC for the B6S and B6Se are ~ 2.07 MPam0.5, evaluating the
resistance to limit the crack propagation inside the materials. Both B6S and
B6Se compounds possess high hardness values in the range 31-35 GPa, and have
the potential to be prominent members of the class of hard compounds. Strong
covalent bonding and sharp peak at low energy below the Fermi level confirmed
by partial density of states (PDOS) resulted in the high hardness. The profile
of band structure, as well as DOS, assesses the indirect semiconducting nature
of the titled compounds. The comparatively high value of Debye temperature
({\Theta}D), minimum thermal conductivity (Kmin), lattice thermal conductivity
(kph), low thermal expansion coefficient, and low density suggest that both
boron-rich chalcogenides might be used as thermal management materials. Large
absorption capacities in the mid ultraviolet region (3.2-15 eV) of the studied
materials and low reflectivity (~16 %) are significantly noted. Such favorable
features give promise to the compounds under investigation to be used in UV
surface-disinfection devices as well as medical sterilizer equipment
applications. Excellent correlations are found among all the studied physical
properties of these compounds. | 2102.00446v1 |
2022-10-09 | High-performance non-Fermi-liquid metallic thermoelectric materials | Searching for high-performance thermoelectric (TE) materials in the paradigm
of narrow-bandgap semiconductors has lasted for nearly 70 years and is
obviously hampered by a bottleneck of research now. Here we report on the
discovery of a few metallic compounds, TiFexCu2x-1Sb and TiFe1.33Sb, showing
the thermopower exceeding many TE semiconductors and the dimensionless figure
of merits comparable with the state-of-the-art TE materials. A quasi-linear
temperature (T) dependence of electrical resistivity in 2 K - 700 K and the
logarithmic T-dependent electronic specific heat at low temperature are also
observed to coexist with the high thermopower, highlighting the strong
intercoupling of the non-Fermi-liquid (NFL) quantum critical behavior of
electrons with TE transports. Electronic structure analysis reveals the
existence of fluctuating Fe-eg-related local magnetic moments, Fe-Fe
antiferromagnetic (AFM) interaction at the nearest 4c-4d sites, and two-fold
degenerate eg orbitals antiferromagnetically coupled with the dual-type
itinerant electrons close to the Fermi level, all of which infer to a
competition between the AFM ordering and Kondo-like spin compensation as well
as a parallel two-channel Kondo effect. These effects are both strongly
meditated by the structural disorder due to the random filling of Fe/Cu at the
equivalent 4c/4d sites of the Heusler crystal lattice. The magnetic
susceptibility deviates from ideal antiferromagnetism but can be fitted well by
x(T) = 1/({\theta} + BT{\alpha}), seemingly being consistent with the quantum
critical scenario of strong local correlation as discussed before. Our work not
only breaks the dilemma that the promising TE materials should be heavily-doped
semiconductors, but also demonstrates the correlation among high TE
performance, NFL quantum criticality, and magnetic fluctuation, which opens up
new directions for future research. | 2210.04201v1 |
1997-01-06 | The role of intermediate layers in the c-axis conductivity of layered superconductors | A simplified model of c axis transport in the high T_c superconductors is
presented. Expressions are found for the c axis optical conductivity, the d.c.
resistivity, and the c axis penetration depth. Within the framework of this
model, the pseudogap in the optical conductivity arises naturally as a result
of the layered band structure of the high T_c materials. We discuss the
occurence of the pseudogap in terms of three parameters: a band gap Delta_{ps},
a temperature dependent scattering rate Gamma(T), and the strength of the
interlayer coupling t_{perp}. We are also able to find analytic expressions for
the d.c. conductivity and the low temperature penetration depth in terms of
these three parameters. This work is an attempt to present a simple, unified
picture of c axis properties in the high T_c cuprates. | 9701029v2 |
1999-06-01 | Current dependence of grain boundary magnetoresistance in La_0.67Ca_0.33MnO_3 films | We prepared epitaxial ferromagnetic manganite films on bicrystal substrates
by pulsed laser ablation. Their low- and high-field magnetoresistance (MR) was
measured as a function of magnetic field, temperature and current. At low
temperatures hysteretic changes in resistivity up to 70% due to switching of
magnetic domains at the coercitive field are observed. The strongly non-ohmic
behavior of the current-voltage leads to a complete suppression of the MR
effect at high bias currents with the identical current dependence at low and
high magnetic fields. We discuss the data in view of tunneling and mesoscale
magnetic transport models and propose an explicit dependence of the spin
polarization on the applied current in the grain boundary region. | 9906007v1 |
2001-04-02 | Antiferromagnetic vortex state in a high-temperature superconductor | There is strong evidence that magnetic interactions play a crucial role in
the mechanism driving high-temperature superconductivity in cuprate
superconductors. To investigate this further we have done neutron scattering
experiments on the simplest high-temperature superconductor La(2-x)Sr(x)CuO(4)
(LSCO) in an applied magnetic field. Below the superconducting transition
temperature (Tc), the field penetrates the material via an array of normal
state inclusions or vortices while phase coherent superconductivity
characterized by zero resistance is suppressed to the lower field-dependent
irreversibility temperature. The measurements described here were performed on
underdoped LSCO (x=0.10), which develops static incommensurate order below Tc
in zero field. Our results show that application of a magnetic field enhances
this response without changing the onset temperature. For H=5T the
field-induced signal saturates to three times the zero-field signal and phase
coherent superconductivity is established within the antiferromagnetic phase. | 0104026v1 |
2004-02-13 | High performance n-doped carbon nanotube field-effect transistors | We describe a robust technique for the fabrication of high performance
vertically scaled n-doped field-effect transistors from large band gap carbon
nanotubes. These devices have a tunable threshold voltage in the
technologically relevant range (-1.3V < V_th < 0.5V) and can carry up to 5-6
muA of current in the on-state. We achieve such performance by exposure to
potassium (K) vapor and device annealing in high vacuum. The treatment has a
two-fold effect to: (i) controllably shift V_th toward negative gate biases via
bulk doping of the nanotube (up to about 0.6e/nm), and (ii) increase the
on-current by 1-2 orders of magnitude. This current enhancement is achieved by
lowering external device resistance due to more intimate contact between K
metal and doped nanotube channel in addition to potential reduction of the
Schottky barrier height at the contact. | 0402350v1 |
2005-04-03 | Dependence of Giant Tunnel Magnetoresistance of Sputtered CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on MgO Barrier Thickness and Annealing Temperatur | We investigated the dependence of giant tunnel magnetoresistance (TMR) on the
thickness of an MgO barrier and on the annealing temperature of sputtered
CoFeB/MgO/CoFeB magnetic tunnel junctions deposited on SiO2/Si wafers. The
resistance-area product exponentially increases with MgO thickness, indicating
that the quality of MgO barriers is high in the investigated thickness range of
1.15-2.4 nm. High-resolution transmission electron microscope images show that
annealing at 375 C results in the formation of crystalline CoFeB/MgO/CoFeB
structures, even though CoFeB electrodes are amorphous in the as-sputtered
state. The TMR ratio increases with annealing temperature and is as high as
260% at room temperature and 403% at 5 K. | 0504051v1 |
2006-05-09 | Subgap conductivity in SIN-junctions of high barrier transparency | We investigate the current-voltage characteristics of high-transparency
superconductor-insulator-normal metal (SIN) junctions with the specific tunnel
resistance below 30 kOhm per square micron. The junctions were fabricated from
different superconducting and normal conducting materials, including Nb, Al,
AuPd and Cu. The subgap leakage currents were found to be appreciably larger
than those given by the standard tunnelling model. We explain our results using
the model of two-electron tunnelling in the coherent diffusive transport
regime. We demonstrate that even in the high-transparency SIN-junctions, a
noticeable reduction of the subgap current can be achieved by splitting a
junction into several submicron sub-junctions. These structures can be used as
nonlinear low-noise shunts in Rapid-Single-Flux-Quantum (RSFQ) circuitry for
controlling Josephson qubits. | 0605237v2 |
2002-09-09 | Long-term damage induced by hadrons in silicon detectors for uses at the LHC-accelerator and in space missions | In the present paper, the phenomenological model developed by the authors in
previous papers has been used to evaluate the degradation induced by hadron
irradiation at the future accelerator facilities or by cosmic protons in high
resistivity silicon detectors. The damage has been analysed at the microscopic
(defects production and their evolution toward equilibrium) and at the
macroscopic level (changes in the leakage current of the p-n junction). The
rates of production of primary defects, as well as their evolution toward
equilibrium have been evaluated considering explicitly the type of the
projectile particle and its energy. Vacancy-interstitial annihilation,
interstitial migration to sink, complex (VP, VO, CiOi, CiCs) and divacancy
formation are taken into account for different initial silicon material. The
influence of these defects on the leakage detector current has been calculated
in the frame of the Schokley-Read-Hall model. | 0209086v2 |
2006-11-20 | Correlation between radiation processes in silicon and long-time degradation of detectors for high energy physics experiments | In this contribution, the correlation between fundamental interaction
processes induced by radiation in silicon and observable effects which limit
the use of silicon detectors in high energy physics experiments is investigated
in the frame of a phenomenological model which includes: generation of primary
defects at irradiation starting from elementary interactions in silicon;
kinetics of defects, effects at the p-n junction detector level. The effects
due to irradiating particles (pions, protons, neutrons), to their flux, to the
anisotropy of the threshold energy in silicon, to the impurity concentrations
and resistivity of the starting material are investigated as time, fluence and
temperature dependences of detector characteristics. The expected degradation
of the electrical parameters of detectors in the complex hadron background
fields at LHC & SLHC are predicted. | 0611185v1 |
2008-07-11 | Electronic liquid crystal state in the high-temperature superconductor YBCO(6.45) | Electronic phases with symmetry properties matching those of conventional
liquid crystals have recently been discovered in transport experiments on
semiconductor heterostructures and metal oxides at milli-Kelvin temperatures.
We report the spontaneous onset of a onedimensional, incommensurate modulation
of the spin system in the high-temperature superconductor YBa2Cu3O6.45 upon
cooling below ~150 K, while static magnetic order is absent above 2 K. The
evolution of this modulation with temperature and doping parallels that of the
in-plane anisotropy of the resistivity, indicating an electronic nematic phase
that is stable over a wide temperature range. The results suggest that soft
spin fluctuations are a microscopic route towards electronic liquid crystals,
and nematic order can coexist with high-temperature superconductivity in
underdoped cuprates. | 0807.1861v1 |
2009-08-20 | Scaling relation of the anomalous Hall effect in (Ga,Mn)As | We present magnetotransport studies performed on an extended set of (Ga,Mn)As
samples at 4.2 K with longitudinal conductivities sigma_{xx} ranging from the
low- to the high-conductivity regime. The anomalous Hall conductivity
sigma_{xy}^(AH) is extracted from the measured longitudinal and Hall
resistivities. A transition from sigma_{xy}^(AH)=20 Omega^{-1}cm^{-1} due to
the Berry phase effect in the high-conductivity regime to a scaling relation
sigma_{xy}^(AH) proportional to sigma_{xx}^{1.6} for low-conductivity samples
is observed. This scaling relation is consistent with a recently developed
unified theory of the anomalous Hall effect in the framework of the Keldysh
formalism. It turns out to be independent of crystallographic orientation,
growth conditions, Mn concentration, and strain, and can therefore be
considered universal for low-conductivity (Ga,Mn)As. The relation plays a
crucial role when deriving values of the hole concentration from
magnetotransport measurements in low-conductivity (Ga,Mn)As. In addition, the
hole diffusion constants for the high-conductivity samples are determined from
the measured longitudinal conductivities. | 0908.2935v1 |
2009-11-11 | Temperature dependent nucleation and annihilation of individual magnetic vortices | We studied the temperature dependence of the magnetization reversal in
individual submicron permalloy disks with micro-Hall and bend-resistance
magnetometry. The nucleation field exhibits a nonmonotonic dependence with
positive and negative slopes at low and high temperatures, respectively, while
the annihilation field monotonically decreases with increasing temperature, but
with distinctly different slopes at low and high temperatures. Our analysis
suggests that at low temperatures vortex nucleation and annihilation proceeds
via thermal activation over an energy barrier, while at high temperatures they
are governed by a temperature dependence of the saturation magnetization. | 0911.2267v1 |
2009-12-08 | Correlating the nanostructure and electronic properties of InAs nanowires | The electronic properties and nanostructure of InAs nanowires are correlated
by creating multiple field effect transistors (FETs) on nanowires grown to have
low and high defect density segments. 4.2 K carrier mobilities are ~4X larger
in the nominally defect-free segments of the wire. We also find that dark field
optical intensity is correlated with the mobility, suggesting a simple route
for selecting wires with a low defect density. At low temperatures, FETs
fabricated on high defect density segments of InAs nanowires showed transport
properties consistent with single electron charging, even on devices with low
resistance ohmic contacts. The charging energies obtained suggest quantum dot
formation at defects in the wires. These results reinforce the importance of
controlling the defect density in order to produce high quality electrical and
optical devices using InAs nanowires. | 0912.1511v2 |
2012-05-30 | A Path to Higher Q0 with Large Grain Niobium Cavities | The improvement of the quality factor Q0 of superconducting radio-frequency
(SRF) cavities at medium accelerating gradients (20-25 MV/m) is important in
order to reduce the cryogenic losses in continuous wave (CW) accelerators used
for a variety of applications. In recent years, SRF cavities fabricated from
ingot niobium have become a viable alternative to standard high-purity
fine-grain Nb for the fabrication of high-performing SRF cavities with the
possibility of significant cost reduction. Recent studies demonstrated the
improvement of Q0 at medium field in cavities heat treated at 800-1200 {\deg}C
without subsequent chemical etching [ ]. To further explore this treatment
procedure, a new induction furnace with an all-niobium hot-zone was
commissioned [ ]. A single-cell 1.5 GHz cavity fabricated from ingot material
from CBMM, Brazil, with RRR 200, was heat treated in the new furnace in the
temperature range 800-1400 {\deg}C for several hours. Residual resistance value
of 1 - 5 n\Omega have been consistently achieved on this cavity Q0-values as
high as 4.6\times1010 at 90 mT peak surface magnetic field at 2 K. Q0 values of
about ~2\times1011 have been measured at 1.5 K. | 1205.6736v1 |
2013-01-23 | Superconductivity of interface layer at contact between normal metal and high temperature superconductor | In this research, it is shown that there are the necessary physical
conditions to originate the returning superconductivity in the thin interface
layer at the contact between the normal metal and the high temperature
superconductor (N-S contact). The influences by the temperature T, magnetic
field H and direct current I on the electrical resistance RG of the thin
interface layer G in the multilayered system N-G-S, where N can be one the
normal metal layers of Argentum (Ag), Indium (In), Gallium-Indium (Ga-50%In), G
is the thin interface layer, S is the high temperature superconductor (HTS)
layer of YBa2Cu3O7-x, are researched experimentally. | 1301.5542v2 |
2015-03-23 | Gate-tunable high mobility remote-doped InSb/In_{1-x}Al_{x}Sb quantum well heterostructures | Gate-tunable high-mobility InSb/In_{1-x}Al_{x}Sb quantum wells (QWs) grown on
GaAs substrates are reported. The QW two-dimensional electron gas (2DEG)
channel mobility in excess of 200,000 cm^{2}/Vs is measured at T=1.8K. In
asymmetrically remote-doped samples with an HfO_{2} gate dielectric formed by
atomic layer deposition, parallel conduction is eliminated and complete 2DEG
channel depletion is reached with minimal hysteresis in gate bias response of
the 2DEG electron density. The integer quantum Hall effect with Landau level
filling factor down to 1 is observed. A high-transparency non-alloyed Ohmic
contact to the 2DEG with contact resistance below 1{\Omega} \cdot mm is
achieved at 1.8K. | 1503.06710v1 |
2015-09-10 | Crystal Structure of 200 K-Superconducting Phase of Sulfur Hydride System | This article reports the experimentally clarified crystal structure of a
recently discovered sulfur hydride in high temperature superconducting phase
which has the highest critical temperature Tc over 200 K which has been ever
reported. For understanding the mechanism of the high superconductivity, the
information of its crystal structure is very essential. Herein we have carried
out the simultaneous measurements electrical resistance and synchrotron x-ray
diffraction under high pressure, and clearly revealed that the hydrogen
sulfide, H2S, decomposes to H3S and its crystal structure has body-centered
cubic symmetry in the superconducting phase. | 1509.03156v1 |
2015-09-13 | High-Mobility Holes in Dual-Gated WSe$_2$ Field-Effect Transistors | We demonstrate dual-gated $p$-type field-effect transistors (FETs) based on
few-layer tungsten diselenide (WSe$_2$) using high work-function platinum
source/drain contacts, and a hexagonal boron nitride top-gate dielectric. A
device topology with contacts underneath the WSe$_2$ results in $p$-FETs with
$I_{ON}$/$I_{OFF}$ ratios exceeding 10$^7$, and contacts that remain Ohmic down
to cryogenic temperatures. The output characteristics show current saturation
and gate tunable negative differential resistance. The devices show intrinsic
hole mobilities around 140 cm$^2$/Vs at room temperature, and approaching 4,000
cm$^2$/Vs at 2 K. Temperature-dependent transport measurements show a
metal-insulator transition, with an insulating phase at low densities, and a
metallic phase at high densities. The mobility shows a strong temperature
dependence consistent with phonon scattering, and saturates at low
temperatures, possibly limited by Coulomb scattering, or defects. | 1509.03896v1 |
2016-08-02 | High Current Density and Low Thermal Conductivity of Atomically Thin Semimetallic WTe2 | Two-dimensional (2D) semimetals beyond graphene have been relatively
unexplored in the atomically-thin limit. Here we introduce a facile growth
mechanism for semimetallic WTe2 crystals, then fabricate few-layer test
structures while carefully avoiding degradation from exposure to air. Low-field
electrical measurements of 80 nm to 2 um long devices allow us to separate
intrinsic and contact resistance, revealing metallic response in the thinnest
encapsulated and stable WTe2 devices studied to date (3 to 20 layers thick).
High-field electrical measurements and electro-thermal modeling demonstrate
that ultra-thin WTe2 can carry remarkably high current density (approaching 50
MA/cm2, higher than most common interconnect metals) despite a very low thermal
conductivity (of the order ~3 W/m/K). These results suggest several pathways
for air-stable technological viability of this layered semimetal. | 1608.00988v1 |
2016-10-25 | Pressure-induced superconductivity in the giant Rashba system BiTeI | At ambient pressure, BiTeI is the first material found to exhibit a giant
Rashba splitting of the bulk electronic bands. At low pressures, BiTeI
undergoes a transition from trivial insulator to topological insulator. At
still higher pressures, two structural transitions are known to occur. We have
carried out a series of electrical resistivity and AC magnetic susceptibility
measurements on BiTeI at pressure up to ~40 GPa in an effort to characterize
the properties of the high-pressure phases. A previous calculation found that
the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that
this structure is superconducting with Tc values as high as 6 K. AC magnetic
susceptibility measurements support the bulk nature of the superconductivity.
Using electronic structure and phonon calculations, we compute Tc and find that
our data is consistent with phonon-mediated superconductivity. | 1610.08038v1 |
2016-11-27 | Strained GaN Quantum-Well FETs on Single Crystal Bulk AlN Substrates | We report the first realization of molecular beam epitaxy grown strained GaN
quantum well field-effect transistors on single-crystal bulk AlN substrates.
The fabricated double heterostructure FETs exhibit a two- dimensional electron
gas (2DEG) density in excess of 2x10^13/cm2. Ohmic contacts to the 2DEG channel
were formed by n+ GaN MBE regrowth process, with a contact resistance of 0.13
Ohm-mm. Raman spectroscopy using the quantum well as an optical marker reveals
the strain in the quantum well, and strain relaxation in the regrown GaN
contacts. A 65-nm-long rectangular-gate device showed a record high DC drain
current drive of 2.0 A/mm and peak extrinsic transconductance of 250 mS/mm.
Small-signal RF performance of the device achieved current gain cutoff
frequency fT~120 GHz. The DC and RF performance demonstrate that bulk AlN
substrates offer an attractive alternative platform for strained quantum well
nitride transistors for future high-voltage and high-power microwave
applications. | 1611.08914v1 |
2017-09-19 | Design parameter space for a High Pressure Optimized Dense Plasma Focus operating with Deuterium | The potential of the Dense Plasma Focus (DPF) for industrial applications in
many fields is well recognized, although yet to be realized in practice.
Particularly attractive is the possibility of its use as inexpensive industrial
source of nuclear reactions for diverse high value applications such as fast
pulsed neutron radiography of hydrogenous materials, non-intrusive neutron
interrogation of concealed organic contraband and rapid production of short
lived radioisotopes for medical diagnostics and therapy. Recently, it has been
suggested that it may be possible to operate the DPF efficiently in a
High-Pressure-Optimized (HPO) mode. This paper explores the design parameter
space for such HPO-DPF based on the revised Resistive Gratton-Vargas (RGV)
model with a view to identify a practicable set of system parameters and their
scaling. The current waveform predicted by the revised RGV model for the chosen
set of parameters is fitted to the Lee model to estimate the likely neutron
yield. | 1709.06243v1 |
2017-12-09 | Extremely large magnetoresistance and high-density Dirac-like fermions in ZrB2 | We report the detailed study on transport properties of ZrB2 single crystal,
a predicted topological nodal-line semimetal. ZrB2 exhibits extremely large
magnetoresistance as well as field-induced resistivity upturn and plateau.
These behaviors can be well understood by the two-band model with the perfect
electron - hole compensation and high carrier mobilities. More importantly, the
electrons with small effective masses and nontrivial Berry phase have
significantly high density when compared to those in known topological
semimetals. It strongly suggests that ZrB2 hosts Dirac-like nodal-line
fermions. | 1712.03362v1 |
2018-11-01 | Ultra-thin low frequency perfect sound absorber with high ratio of active area | A concept of ultra-thin low frequency perfect sound absorber is proposed and
demonstrated experimentally. To minimize non-linear effects, an high ratio of
active area to total area is used to avoid large localized amplitudes. The
absorber consists of three elements: a mass supported by a very flexible
membrane, a cavity and a resistive layer. The resonance frequency of the sound
absorber can be easily adjusted just by changing the mass or thickness of the
cavity. A very large ratio between wavelength and material thickness is
measured for a manufactured perfect absorber (ratio = 201) . It is shown that
this high sub-wavelength ratio is associated with narrowband effects and that
the increase in the sub-wavelength ratio is limited by the damping in the
system. | 1811.00897v1 |
2019-06-28 | High pO2 Floating Zone Crystal Growth of the Perovskite Nickelate PrNiO3 | Single crystals of PrNiO3 were grown under an oxygen pressure of 295 bar
using a unique high-pressure optical-image floating zone furnace. The crystals,
with volume in excess of 1 mm3, were characterized structurally using single
crystal and powder X-ray diffraction. Resistivity, specific heat, and magnetic
susceptibility were measured, all of which evidenced an abrupt, first order
metal-insulator transition (MIT) at ~130 K, in agreement with previous
literature reports on polycrystalline specimens. Temperature-dependent single
crystal diffraction was performed to investigate changes through the MIT. Our
study demonstrates the opportunity space for high fugacity, reactive
environments for single crystal growth specifically of perovskite nickelates
but more generally to correlated electron oxides. | 1907.00078v1 |
2020-02-17 | Characterization of High-Purity Germanium (Ge) Crystals for Developing Novel Ge Detectors | High-purity germanium (HPGe) crystals are required to be well-characterized
before being fabricated into Ge detectors. The characterization of HPGe
crystals is often performed with the Hall Effect system, which measures the
carrier concentration, the Hall mobility, and the electrical resistivity. The
reported values have a strong dependence on the size of the ohmic contacts and
the geometry of the samples used in conducting the Hall Effect measurements. We
conduct a systematic study using four samples cut from the same location in a
HPGe crystal made into different sized ohmic contacts or different geometries
to study the variation of the measured parameters from the Hall Effect system.
The results are compared to the C-V measurements provided by the Ge detector
made from the same crystal. We report the systematic errors involved with the
Hall Effect system and find a reliable technique that minimizes the systematic
error to be only a few percent from the Hall Effect measurements. | 2002.07706v2 |
2016-03-13 | A sub-1-volt analog metal oxide memristive-based synaptic device for energy-efficient spike-based computing systems | Nanoscale metal oxide memristors have potential in the development of
brain-inspired computing systems that are scalable and efficient1-3. In such
systems, memristors represent the native electronic analogues of the biological
synapses. However, the characteristics of the existing memristors do not fully
support the key requirements of synaptic connections: high density, adjustable
weight, and low energy operation. Here we show a bilayer memristor that is
forming-free, low-voltage (~|0.8V|), energy-efficient (full On/Off switching at
~2pJ), and reliable. Furthermore, pulse measurements reveal the analog nature
of the memristive device, that is it can be directly programmed to intermediate
resistance states. Leveraging this finding, we demonstrate
spike-timing-dependent plasticity (STDP), a spike-based Hebbian learning rule4.
In those experiments, the memristor exhibits a marked change in the normalized
synaptic strength (>30 times) when the pre- and post-synaptic neural spikes
overlap. This demonstration is an important step towards the physical
construction of high density and high connectivity neural networks. | 1603.03979v1 |
2017-07-24 | Probing local lattice distortion in medium- and high-entropy alloys | The atomic-level tunability that results from alloying multiple transition
metals with d electrons in concentrated solid solution alloys (CSAs), including
high-entropy alloys (HEAs), has produced remarkable properties for advanced
energy applications, in particular, damage resistance in high-radiation
environments. The key to understanding CSAs radiation performance is
quantitatively characterizing their complex local physical and chemical
environments. In this study, the local structure of a FeCoNiCrPd HEA is
quantitatively analyzed with X-ray total scattering and extended X-ray
absorption fine structure methods. Compared to FeCoNiCr and FeCoNiCrMn,
FeCoNiCrPd with a quasi-random alloy structure has a strong local lattice
distortion, which effectively pins radiation-induced defects. Distinct from a
relaxation behavior in FeCoNiCr and FeCoNiCrMn, ion irradiation further
enhanced the local lattice distortion in FeCoNiCrPd due to a preference for
forming Pd-Pd atomic pairs. | 1707.07745v1 |
2019-12-02 | Probing intraband excitations in ZrTe$_5$: a high-pressure infrared and transport study | Zirconium pentatetelluride, ZrTe5, shows remarkable sensitivity to
hydrostatic pressure. In this work we address the high-pressure transport and
optical properties of this compound, on samples grown by flux and charge vapor
transport. The high-pressure resistivity is measured up to 2 GPa, and the
infrared transmission up to 9 GPa. The dc conductivity anisotropy is determined
using a microstructured sample. Together, the transport and optical
measurements allow us to discern band parameters with and without the
hydrostatic pressure, in particular the Fermi level, and the effective mass in
the less conducting, out-of-plane direction. The results are interpreted within
a simple two-band model characterized by a Dirac-like, linear in-plane band
dispersion, and a parabolic out-of-plane dispersion. | 1912.00942v2 |
2019-12-23 | Change of electronic properties on transition from high-entropy to Ni-rich (TiZrNbCu)(1-x)Ni(x) alloys | We present results of comprehensive study of electronic properties of
(TiZrNbCu)(1-x)Ni(x) metallic glasses performed in broad composition range x
encompassing both, high entropy (HE) range, and conventional Ni-base alloy
concentration range, x >= 0.35. The electronic structure studied by
photoemission spectroscopy and low temperature specific heat (LTSH) reveal a
split-band structure of density of states inside valence band with d-electrons
of Ti, Zr, Nb and also Ni present at Fermi level N(E_F), whereas LTSH and
magnetoresistivity results show that variation of N(E_F) with x changes in
Ni-base regime. The variation of superconducting transition temperatures with x
closely follows that of N(E_F). The electrical resistivities of all alloys are
high and decrease with increasing temperature over most of explored temperature
range, and their temperature dependence seems dominated by weak localization
effects over a broad temperature range (10-300 K). The preliminary study of
Hall effect shows positive Hall coefficient that decreases rapidly in Ni-base
alloys. | 1912.11133v1 |
2012-03-27 | Graphene-Graphite Quilts for Thermal Management of High-Power GaN Transistors | Self-heating is a severe problem for high-power GaN electronic and
optoelectronic devices. Various thermal management solutions, e.g. flip-chip
bonding or composite substrates have been attempted. However, temperature rise
still limits applications of the nitride-based technology. Here we demonstrate
that thermal management of GaN transistors can be substantially improved via
introduction of the alternative heat-escaping channels implemented with
few-layer graphene - an excellent heat conductor. We have transferred few-layer
graphene to AlGaN/GaN heterostructure field-effect transistors on SiC
substrates to form the "graphene-graphite quilts" - lateral heat spreaders,
which remove heat from the channel regions. Using the micro-Raman spectroscopy
for in-situ monitoring we have shown that temperature can be lowered by as much
as ~ 20oC in such devices operating at ~13-W/mm power density. The simulations
suggest that the efficiency of the "graphene quilts" can be made even higher in
GaN devices on thermally resistive sapphire substrates and in the designs with
the closely located heat sinks. Our results open a novel application niche for
few-layer graphene in high-power electronics. | 1203.6099v1 |
2018-12-06 | Technologies for Future Vertex and Tracking Detectors at CLIC | CLIC is a proposed linear $e^{+}e^{-}$ collider with center-of-mass energies
of up to $3\,\textrm{TeV}$. Its main objectives are precise top quark and Higgs
boson measurements, as well as searches for Beyond Standard Model physics. To
meet the physics goals, the vertex and tracking detectors require not only a
spatial resolution of a few micrometers and a very low material budget, but
also timing capabilities with a precision of a few nanoseconds to allow
suppression of beam-induced backgrounds.
Different technologies using hybrid silicon detectors are explored for the
vertex detectors, such as dedicated readout ASICs, small-pitch active edge
sensors as well as capacitively coupled High-Voltage CMOS sensors. Monolithic
sensors are considered as an option for the tracking detector, and a prototype
using a CMOS process with a high-resistivity epitaxial layer is being designed.
Different designs using a silicon-on-insulator process are under investigation
for both vertex and tracking detector.
All prototypes are evaluated in laboratory and beam tests, and newly
developed simulation tools combining Geant4 and TCAD are used to assess and
optimize their performance. This contribution gives an overview of the R&D
program for the CLIC vertex and tracking detectors, highlighting new results
from the prototypes. | 1812.02625v1 |
2019-06-22 | Dynamic enlargement of a hole in a sheet: crater formation and propagation of cylindrical shock waves | Predicting the shape of a crater formed by high velocity impact is of
interest in several fields. It can aid in design of more efficient protective
structures, in forensic analysis of bullet holes, and in understanding the
effects of meteorite impact in both space systems and in extreme geological
events. In this paper we present, for the first time, a complete theoretical
solution of the dynamic plane-stress problem. We consider the steady-state
expansion of a cylindrical hole in a strain hardening elastoplastic sheet and
find that a self-similar field emerges if the `specific cavitation energy' is
constant. It is shown that at the quasistatic limit this solution reduces to
available classical solutions, while at high expansion velocities shock waves
can appear. Investigation of the constitutive sensitivities of the expansion
field is conducted and compared with available results for the spherical field
which is commonly applied to predict resistance to high velocity penetration.
It is shown that shock waves appear at significantly lower expansion
velocities, in the plane-stress deformation pattern, for which material
compressibility is found to have a negligible effect. This insensitivity can be
taken advantage of in the future for design of light weight protective layers
by incorporating porosity. | 1906.09514v1 |
2019-10-08 | Visualizing dissipative charge carrier dynamics at the nanoscale with superconducting charge qubit microscopy | The investigation of novel electronic phases in low-dimensional quantum
materials demands for the concurrent development of new measurement techniques
that combine surface sensitivity with high spatial resolution and high
measurement accuracy. We propose a new quantum sensing imaging modality based
on superconducting charge qubits to study dissipative charge carrier dynamics
with nanometer spatial and high temporal resolution. Using analytical and
numerical calculations we show that superconducting charge qubit microscopy
(SCQM) has the potential to resolve temperature and resistivity changes in a
sample as small as $\Delta T\leq0.1\;$mK and $\Delta\rho\leq1\cdot10^{4}
\,\Omega\cdot$cm, respectively. Among other applications, SCQM will be
especially suited to study the microscopic mechanisms underlying interaction
driven quantum phase transitions, to investigate the boundary modes found in
novel topological insulators and, in a broader context, to visualize the
dissiaptive charge carrier dynamics occurring in mesoscopic and nanoscale
devices. | 1910.03583v2 |
2020-06-05 | Anomalous dependence of thermoelectric parameters on carrier concentration and electronic structure in Mn-substituted Fe2CrAl Heusler alloy | We investigate the high temperature thermoelectric properties of Heusler
alloys Fe2-xMnxCrAl (0<x<1). Substitution of 12.5% Mn at Fe-site (x = 0.25)
causes a significant increase in high temperature resistivity (\r{ho}) and an
enhancement in the Seebeck coefficient (S), as compared to the parent alloy.
However, as the concentration of Mn is increased above 0.25, a systematic
decrement in the magnitude of both parameters is noted. These observations have
been ascribed (from theoretical analysis) to a change in band gap and
electronic structure of Fe2CrAl with Mn-substitution. Due to absence of mass
fluctuations and lattice strain, no significant change in thermal conductivity
is seen across this series of Heusler alloys. Additionally, S drastically
changes its magnitude along with a crossover from negative to positive above
900 K, which has been ascribed to the dominance of holes over electrons in high
temperature regime. In this series of alloys, S and \r{ho} shows a strong
dependence on the carrier concentration and strength of d-d hybridization
between Fe/Mn and Cr atoms. | 2006.03234v2 |
2020-06-24 | Tip-induced oxidation of silicene nano-ribbons | We report on the oxidation of self-assembled silicene nanoribbons grown on
the Ag(110) surface using Scanning Tunneling Microscopy and High-Resolution
Photoemission Spectroscopy. The results show that silicene nanoribbons present
a strong resistance towards oxidation using molecular oxygen. This can be
overcome by increasing the electric field in the STM tunnel junction above a
threshold of +2.6 V to induce oxygen dissociation and reaction. The higher
reactivity of the silicene nanoribbons towards atomic oxygen is observed as
expected. The HR-PES confirm these observations: Even at high exposures of
molecular oxygen, the Si 2p core-level peaks corresponding to pristine silicene
remain dominant, reflecting a very low reactivity to molecular oxygen. Complete
oxidation is obtained following exposure to high doses of atomic oxygen; the Si
2p core level peak corresponding to pristine silicene disappears. | 2006.13780v1 |
2020-08-06 | Melting and decomposition of orthorhombic B6Si under high pressure | Melting of orthorhombic boron silicide B6Si has been studied at pressures up
to 8 GPa using in situ electrical resistivity measurements and quenching. It
has been found that in the 2.6-7.7 GPa range B6Si melts congruently, and the
melting curve exhibits negative slope of -31(2) K/GPa that points to a higher
density of the melt as compared to the solid phase. At very high temperatures
B6Si melt appears to be unstable and undergoes disproportionation into silicon
and boron-rich silicides. The onset temperature of disproportionation strongly
depends on pressure, and the corresponding low-temperature boundary exhibits
negative slope of -92(3) K/GPa which is indicative of significant volume
decrease in the course of B6Si melt decomposition. | 2008.02739v1 |
2020-11-02 | GaN/AlGaN 2DEGs in the quantum regime: Magneto-transport and photoluminescence to 60 tesla | Using high magnetic fields up to 60 T, we report magneto-transport and
photoluminescence (PL) studies of a two-dimensional electron gas (2DEG) in a
GaN/AlGaN heterojunction grown by molecular-beam epitaxy. Transport
measurements demonstrate that the quantum limit can be exceeded (Landau level
filling factor $\nu < 1$), and show evidence for the $\nu =2/3$ fractional
quantum Hall state. Simultaneous optical and transport measurements reveal
synchronous quantum oscillations of both the PL intensity and longitudinal
resistivity in the integer quantum Hall regime. PL spectra directly reveal the
dispersion of occupied Landau levels in the 2DEG and therefore the electron
mass. These results demonstrate the utility of high (pulsed) magnetic fields
for detailed measurements of quantum phenomena in high-density 2DEGs. | 2011.01365v1 |
2021-05-31 | Effect of Zr and Al Addition on Nanocluster Formation in Oxide Dispersion Strenghthened Steel-an ab initio Study | Conventional Oxide dispersion strengthened steels are characterized by
thermally stable, high density of Y-Ti-O nanoclusters, which are responsible
for their high creep strength. Ti plays a major role in obtaining a high
density of ultrafine particles of optimum size range of 2-10 nm. In
Al-containing ODS steels developed for corrosion resistance, Y-Al-O clusters
formed are of size range 20 -100 nm, and Ti fails in making dispersions finer
in the presence of Al. Usage of similar alloying elements like Zr in place of
Ti is widely considered. In this study, binding energies of different stages of
Y-Zr-O-Vacancy and Y-Al-O-Vacancy complexes in the bcc Iron matrix are studied
by first-principle calculations. It is shown that in all the stages of
formation, Y-Zr-O-Vacancy clusters have higher binding energy than
Y-Al-O-Vacancy clusters and hence in ferritic steel containing both Zr and Al,
Y-Zr-O-Vacancy clusters are more stable and more favored to nucleate than
Y-Al-O-Vacancy clusters. The bonding nature in each stage is analyzed using
charge density difference plots for the plausible reason for higher stability
of Y-Zr-O-Vacancy clusters. | 2105.15063v1 |
2021-06-07 | Accelerated Corrosion of High Entropy Alloys under Tensile Stress | High entropy alloys are finding significant scientific interest due to their
exotic microstructures and exceptional properties resulting thereof. These
alloys have excellent corrosion resistance and may find broad range of
applications from bio-implants, aerospace components and nuclear industry. A
critical performance metric that determines the application worthiness of the
alloys is the resilience of stressed structural members in a corrosive
environment. This study reports the results from a novel experimental setup to
quantify the corrosion rate under uniaxial tensile stress in a single phase fcc
Al0.1CoCrFeNi high entropy alloy rods. Under a uniform uniaxial applied stress
of 600 MPa, the corrosion current density was observed to increase by three
orders of magnitude and ~150 mV drop in corrosion potential. The mechanism of
accelerated corrosion is identified as surface passivation layer breakdown, pit
initiation on un-passivated surface and rapid pit-propagation along the loading
direction. | 2106.03690v1 |
2021-07-09 | Excavation Learning for Rigid Objects in Clutter | Autonomous excavation for hard or compact materials, especially irregular
rigid objects, is challenging due to high variance of geometric and physical
properties of objects, and large resistive force during excavation. In this
paper, we propose a novel learning-based excavation planning method for rigid
objects in clutter. Our method consists of a convolutional neural network to
predict the excavation success and a sampling-based optimization method for
planning high-quality excavation trajectories leveraging the learned prediction
model. To reduce the sim2real gap for excavation learning, we propose a
voxel-based representation of the excavation scene. We perform excavation
experiments in both simulation and real world to evaluate the learning-based
excavation planners. We further compare with two heuristic baseline excavation
planners and one data-driven scene-independent planner. The experimental
results show that our method can plan high-quality excavations for rigid
objects in clutter and outperforms the baseline methods by large margins. As
far as we know, our work presents the first learning-based excavation planner
for cluttered and irregular rigid objects. | 2107.04171v1 |
2021-07-17 | Vacancy tuned thermoelectric properties and high spin filtering performance in graphene/silicene heterostructures | The main contribution of this paper is to study the spin caloritronic effects
in defected graphene/silicene nanoribbon (GSNR) junctions. Each step-like GSNR
is subjected to the ferromagnetic exchange and local external electric fields,
and their responses are determined using the nonequilibrium Greens function
(NEGF) approach. To further study the thermoelectric (TE) properties of the
GSNRs, three defect arrangements of divacancies (DVs) are also considered for a
larger system, and their responses are re-evaluated. The results demonstrate
that the defected GSNRs with the DVs can provide an almost perfect thermal spin
filtering effect (SFE), and spin switching. A negative differential
thermoelectric resistance (NDTR) effect and high spin polarization efficiency
(SPE) larger than 99.99 percent are obtained. The system with the DV defects
can show a large spin-dependent Seebeck coefficient, equal to 1.2 mV/K, which
is relatively large and acceptable. Appropriate thermal and electronic
properties of the GSNRs can also be obtained by tuning up the DV orientation in
the device region. Accordingly, the step-like GSNRs can be employed to produce
high efficiency spin caloritronic devices with various features in practical
applications. | 2107.08240v1 |
2021-12-24 | Anisotropic thermal expansion and electronic transitions in the Co$_3$BO$_5$ ludwigite | The investigations of the crystal structure, magnetic and electronic
properties of the Co$_3$BO$_5$ at high temperatures were carried out using
powder x-ray diffraction, magnetic susceptibility, electrical resistivity, and
thermopower measurements. The orthorhombic symmetry (Sp.gr. Pbam) was
established at 300 K and no evidence of structural phase transitions was found
up to 1000 K. The thermal expansion of the crystal lattice is strongly
anisotropic. At $T<T_c=550$ K, a large thermal expansion along the c-axis is
observed with simultaneous contraction along a-axis. The activation energy of
the conductivity decreases significantly at high temperatures and follows the
thermal expansion variation, that exhibits two electronic transitions at ~500
and ~700 K, in coincidence with the anomalies of the heat capacity. Electronic
transport was found to be a dominant conduction mechanism in the entire
temperature range. The temperature dependence of the effective magnetic moment
reflects the evolution of the spin state of Co$^{3+}$ ions towards the spin
crossover to a high spin state. The interrelation between the crystal structure
and electronic properties is discussed. | 2112.12941v1 |
2022-01-03 | Deep-potential enabled multiscale simulation of gallium nitride devices on boron arsenide cooling substrates | High-efficient heat dissipation plays critical role for high-power-density
electronics. Experimental synthesis of ultrahigh thermal conductivity boron
arsenide (BAs, 1300 W m-1K-1) cooling substrates into the wide-bandgap
semiconductor of gallium nitride (GaN) devices has been realized. However, the
lack of systematic analysis on the heat transfer across the BAs-GaN interface
hampers the practical applications. In this study, by constructing the accurate
and high-efficient machine learning interatomic potentials, we performed
multiscale simulations of the BAs-GaN heterostructures. Ultrahigh interfacial
thermal conductance (ITC) of 265 MW m-2K-1 is achieved, which lies in the
well-matched lattice vibrations of BAs and GaN. Moreover, the competition
between grain size and boundary resistance was revealed with size increasing
from 1 nm to 100 {\mu}m. Such deep-potential equipped multiscale simulations
not only promote the practical applications of BAs cooling substrates in
electronics, but also offer new approach for designing advanced thermal
management systems. | 2201.00516v3 |
2022-04-01 | Tuning of Carrier Concentration and Superconductivity in High-Entropy-Alloy-Type Metal Telluride (AgSnPbBi)(1-x)/4InxTe | High-entropy-alloy-type (HEA-type) compound superconductors have been drawing
much attention as a new class of exotic superconductors with local structural
inhomogeneity. NaCl-type (Ag,In,Sn,Pb,Bi)Te is a typical HEA-type
superconductor, but the carrier doping mechanism had been unclear. In this
study, we synthesized (Ag,In,Sn,Pb,Bi)Te with various In concentration using
high-pressure synthesis: the studied system is (AgSnPbBi)(1-x)/4InxTe (x =
0-0.4). Single-phase samples were obtained for x = 0-0.3. A semiconductor-like
temperature dependence of resistivity was observed for x = 0, while
superconductivity appeared for the In-doped samples. The highest transition
temperature (Tc) was 3.0 K for x = 0.3. The Seebeck coefficient decreases with
increase of x, which suggests that In3+ generates electron carriers in
(AgSnPbBi)(1-x)/4InxTe. Tuning of carrier concentration and superconducting
properties of (Ag,In,Sn,Pb,Bi)Te would be useful for further investigation of
exotic superconductivity in the HEA-type compound. | 2204.00407v1 |
2022-04-30 | Fluorinated graphene films with graphene quantum dots for electronic applications | This work analyzes carrier transport, the relaxation of non-equilibrium
charge, and the electronic structure of fluorinated graphene (FG) films with
graphene quantum dots (GQDs). The FG films with GQDs were fabricated by means
of chemical functionalization in an aqueous solution of hydrofluoric acid. High
fluctuations of potential relief inside the FG barriers have been detected in
the range of up to 200 mV. A phenomenological expression that describes the
dependence of the time of non-equilibrium charge emission from GQDs on quantum
confinement levels and film thickness (potential barrier parameters between
GQDs) is suggested. An increase in the degree of functionalization leads to a
decrease in GQD size, the removal of the GQD effect on carrier transport, and
the relaxation of non-equilibrium charge. The study of the electronic
properties of FG films with GQDs has revealed a unipolar resistive switching
effect in the films with a relatively high degree of fluorination and a high
current modulation in transistorlike structures with a lower degree of
fluorination. 2D films with GQDs are believed to have considerable potential
for various electronic applications (nonvolatile memory, 2D connections with
optical control and logic elements). | 2205.00205v1 |
2022-06-09 | Field-tunable Weyl points and large anomalous Hall effects in degenerate magnetic semiconductor EuMg$_2$Bi$_2$ | Magnets, with topologically-nontrivial Dirac/Weyl points, have recently
attracted significant attention owing to the unconventional physical
properties, such as large anomalous Hall effects. However, they typically have
a high carrier density and complicated band structure near the Fermi energy. In
this study, we report degenerate magnetic semiconductor EuMg$_2$Bi$_2$, which
exhibits a single valley at the $\Gamma$ point, where the field-tunable Weyl
points form via the magnetic exchange interaction with the local Eu spins. By
the high-field measurements on high-quality single crystals, we observed the
quantum oscillations in resistivity, elastic constant, and surface impedance,
which enabled us to determine the position of the Fermi energy. In combination
with the first-principles calculation, we revealed that the Weyl points are
located in the vicinity of the Fermi energy when the Eu spins are fully
polarized. Furthermore, we observed large anomalous Hall effect (Hall angle
$\Theta_{\mathrm{AH}}\sim0.07$) in the forced ferromagnetic phase, which is
consistent with this field variation of band structure. | 2206.04577v1 |
2023-09-12 | High-pressure hydrothermal growth and characterization of Sr3Os4O14 single crystals | Single crystals of the novel strontium osmate Sr3Os4O14 have been grown by
the hydrothermal method using opposed anvil high-pressure and high-temperature
technique. The reaction took place in sealed gold capsules at 3 GPa and a
temperature of 1100 C, with water acting as a solvent. The employed method
yields up to 1 mm crystals with quite uncommon double-terminated morphologies.
The crystal structure was identified as tetragonal by single-crystal X-ray
diffraction, with lattice parameters a = 12.2909(8) A and c = 7.2478(5) A. The
structural analysis suggests P42nm or P42/mnm as a possible space group. In
general, the structure belongs to the pyrochlore type and is composed of a
network of symmetrically arranged OsO6 octahedra. Resistivity measurements
evidence a metallic behavior, accompanied by a temperature-independent
paramagnetism. Heat capacity measurements reveal a slightly enhanced value of
the Sommerfeld coefficient 34 mJ/mol K2. Superconductivity has not been
observed down to 2 K. | 2309.06138v1 |
2024-02-04 | Comparative study on high temperature mechanical behavior in 3YTZP containing SWCNTs or MWCNTs | Effects on mechanical properties of the presence of either single-walled
carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) in a 3YTZP
matrix have been investigated in this work. Thus, monolithic 3YTZP and 3YTZP
containing 2.5 vol% either SWCNTs or MWCNTs were fabricated by Spark Plasma
Sintering (SPS) at 1250 C. Samples were crept at temperatures between 1100 and
1200 C and stresses between 5 and 230 MPa. Raman spectroscopy measurements
indicate the absence of severe damages in the CNTs structure after sintering
and testing. Scanning electron microscopy studies show that microstructures do
not evolve during creep tests. Mechanical results point out that monolithic
3YTZP exhibits a higher creep resistance than composites since CNTs facilitate
grain boundary sliding during high-temperature deformation. SWCNTs and MWCNTs
have a similar effect on the high temperature mechanical behavior in 3YTZP
where the bundle length and the level of dispersion of CNTs play a crucial
role. | 2402.08130v1 |
2024-03-29 | Synthesis of CaKFe$_4$As$_4$ bulk samples with high critical current density using a spark plasma sintering technique | A high density CaKFe$_4$As$_4$ bulk sample was successfully synthesized using
a spark plasma sintering (SPS) technique. The density of the synthesized sample
was 5.02 g cm$^{-3}$, corresponding to 96.2% of the theoretical density of
CaKFe$_4$As$_4$. Moreover, a reasonably high Vickers hardness of 1 GPa was
measured. The electrical resistivity of the SPS bulk sample was as low as
approximately 600 $\mu\Omega$ cm at 300 K, which is smaller than that of the
ordinary sintered polycrystalline sample by nearly one order of magnitude, and
exhibited a sharp superconducting transition, with the transition width
$\Delta\textit{T}_c$ less than 2 K, indicating an improved grain connectivity.
The critical current density of the SPS bulk sample, as calculated from the
magnetization hysteresis loops (magnetic $\textit{J}_c$), reached 18 kA
cm$^{-2}$ at 4.2 K under 5 T, which is the highest among the iron-based
superconductor polycrystalline samples reported thus far. | 2403.19981v1 |
2016-07-11 | Role of carbon nanotube diameter on thermal interfacial resistance through the analysis of vibrational mismatch: A Molecular Dynamics approach | Carbon nanotube (CNT) have been known to increase the heat transfer at the
solid-liquid interfaces, but have a limitation due to the interfacial thermal
resistance. Vibrational mismatch at the interface leads to this interfacial
thermal resistance, which plays an important role in energy transfer at the
boundary. Negligible work has been reported on the influence of CNT diameter on
the resistance through the vibrational mismatch study. Molecular dynamics
simulations have been performed to investigate the effect of CNT diameter on
interfacial resistance between carbon nanotube (CNT) and water molecules. This
work is an effort to understand the heat transfer phenomenon at the interface
by quantifying the vibrational mismatch. Analysis of the vibrational spectra of
CNT and water molecules is done to study the effect of CNT diameter on
interfacial resistance. Starting with the initial configuration, and
equilibrating the system of CNT and water molecules at 300 K and 1 atm, the CNT
temperature is raised to 700 K by velocity rescaling. This system is now
allowed to relax as a micro-canonical ensemble. Based on the lumped capacitance
analysis, the time constant of the CNT temperature response is determined,
which is then used to compute the interfacial thermal resistance. The
interfacial thermal resistance is observed to be relatively higher for the
larger diameter nanotube. This is attributed to the higher vibrational mismatch
existing for larger diameter CNT as a result of low overlapping region between
vibrational density states of CNT and water molecules. For smaller diameter
CNT, the interfacial thermal resistance is low which results in the efficient
heat transfer at the interface thus, emphasizing the indispensable role of
larger diameter CNTs in the cooling applications. | 1607.03379v2 |
2016-07-22 | Using machine learning to identify factors that govern amorphization of irradiated pyrochlores | Structure-property relationships is a key materials science concept that
enables the design of new materials. In the case of materials for application
in radiation environments, correlating radiation tolerance with fundamental
structural features of a material enables materials discovery. Here, we use a
machine learning model to examine the factors that govern amorphization
resistance in the complex oxide pyrochlore ($A_2B_2$O$_7$). We examine the
fidelity of predictions based on cation radii and electronegativities, the
oxygen positional parameter, and the energetics of disordering and amorphizing
the material. No one factor alone adequately predicts amorphization resistance.
We find that, when multiple families of pyrochlores (with different B cations)
are considered, radii and electronegativities provide the best prediction but
when the machine learning model is restricted to only the $B$=Ti pyrochlores,
the energetics of disordering and amorphization are optimal. This work provides
new insight into the factors that govern the amorphization susceptibility and
highlights the ability of machine learning approaches to generate that insight. | 1607.06789v1 |
2018-11-25 | Electrical and Thermal Properties of SnTe/Sb2Te3 Superlattice Phase Change Materials | The fundamental electrical and thermal properties of the devices consisting
of SnxTe1-x/Sb2Te3 superlattice (SnTeSL) materials have been investigated and
compared with those of the conventional Ge2Sb2Te5 (GST225) and GeTe/Sb2Te3
superlattice (GeTeSL) in terms of their resistance switching characteristics. A
significant reduction in the switching power of SnTeSL is demonstrated by
conducting a proper initialization procedure, varying x in SnxTe1-x/Sb2Te3, and
applying short electric pulses. It is found that the observed drastic power
reduction occurs due to the exponential decrease in the electric current under
the pulse incidence. On the other hand, the thermal properties of the studied
SL materials are very similar to those of the conventional phase change
materials. The obtained transmission electron micrographs and results of
multilevel-cell recording in GeTeSL and SnTeSL via multi-pulse incidence are
totally different from the properties of the phase change materials along the
GeTe-Sb2Te3 pseudo-binary tie line. Two different models (the partial switching
and electric field-induced one) are proposed to elucidate the mechanism of the
resistance switching in the SL materials. | 1811.09969v2 |
2018-12-11 | Thermal resistance by transition between collective and non-collective phonon flows in graphitic materials | Phonons in graphitic materials exhibit strong normal scattering
(N-scattering) compared to umklapp scattering (U-scattering). The strong
N-scattering cause collective phonon flow, unlike the relatively common cases
where U-scattering is dominant. If graphitic materials have finite size and
contact with hot and cold reservoirs emitting phonons with non-collective
distribution, N-scattering change the non-collective phonon flow to the
collective phonon flow near the interface between graphitic material and a heat
reservoir. We study the thermal resistance by N-scattering during the
transition between non-collective and collective phonon flows. Our Monte Carlo
solution of Peierls-Boltzmann transport equation shows that the N-scattering in
graphitic materials reduce heat flux from the ballistic case by around 15%,
30%, and 40% at 100, 200, and 300 K, respectively. This is significantly larger
than ~ 5% reduction of Debye crystal with similar Debye temperature (~ 2300 K).
We associate the large reduction of heat flux by N-scattering with the
non-linear dispersion and multiple phonon branches with different group
velocities of graphitic materials. | 1812.04703v1 |
2021-04-15 | Gas Sensing Properties of single-material SnP3 logical junction via Negative Differential Resistance: Theoretical Study | The field of 2D materials has gained a lot of attention for vast range of
applications. Amongst others, the sensing ability towards harmful gases is the
application, which we explored in the present work using quantum-mechanical
simulations for the SnP3 material. Its electronic properties, namely 1 and 2
layers being semiconducting, while multilayers being metallic, offer a
possibility to build a single-material logical junction. In addition, the
harmful gases studied here show physical adsorption with charge transfer from
the substrate to the gas molecules. Calculated recovery times show promise of a
good sensing material. The I-V characteristics calculated for all cases
indicates that SnP3 could be a viable sensing material towards NO gas via
negative differential resistance. | 2104.07702v1 |
2022-05-23 | Absorption bias: An ideal descriptor for radiation tolerance of nanocrystalline BCC metals | To evaluate the radiation tolerance of nanocrystalline (NC) materials, the
damage effects of Fe and W as typical body-centered cubic (BCC) metals under
uniform irradiation are studied by a sequential multi-scale modelling
framework. An ideal descriptor, the absorption bias (the ratio of the
absorption abilities of grain boundaries (GBs) to interstitials (I) and
vacancies (V)), is proposed to characterize the radiation tolerance of
materials with different grain sizes. Low absorption bias promotes defects
annihilation through enhancing I-V recombination and optimally tuning its
competition with GB absorption. Thus, the lower absorption bias, the higher
anti-irradiation performance of NC BCC metals is. Furthermore, by
comprehensively considering the mechanical property, thermal stability and
radiation resistance, nano-crystals are recommended for Fe-based structural
materials but coarse crystals for W-based plasma-facing materials. This work
reevaluates the radiation resistance of NC materials, resulting in new
strategies for designing structural materials of nuclear devices through
manipulating grain sizes. | 2205.11050v1 |
2009-04-20 | Successive phase transitions under high pressure in FeTe0.92 | We performed magnetization and electrical resistivity measurements under high
pressures of up to 19 GPa for FeTe0.92. The compound shows an anomaly in
magnetization and resistivity at atmospheric pressure due to a structural
distortion accompanied by a magnetic transition. We also observed magnetic and
resistive anomalies under high pressure, suggesting that two pressure-induced
phases exist at a low temperature. Unlike in FeAs-based compounds, no
superconductivity was detected under high pressures of up to 19 GPa, although
the anomaly at atmospheric pressure was suppressed by applying pressure. | 0904.2945v2 |
2012-11-24 | High Rate Resistive Plate Chamber for LHC detector upgrades | The limitation of the detection rate of standard bakelite resistive plate
chambers (RPC) used as muon detectors in the LHC experiments has prevented the
use of such detectors in the high rate regions in both CMS and ATLAS detectors.
One alternative to these detectors are RPCs made with low resistivity glass
plates ($10^{10} {\rm \Omega .cm}$), a beam test at DESY has shown that such
detectors can operate at few thousand Hz/cm$^2$ with high efficiency(> 90%) | 1211.5698v1 |
2018-06-21 | Mutation rate variability as a driving force in adaptive evolution | Mutation rate is a key determinant of the pace as well as outcome of
evolution, and variability in this rate has been shown in different scenarios
to play a key role in evolutionary adaptation and resistance evolution under
stress caused by selective pressure. Here we investigate the dynamics of
resistance fixation in a bacterial population with variable mutation rates and
show that evolutionary outcomes are most sensitive to mutation rate variations
when the population is subject to environmental and demographic conditions that
suppress the evolutionary advantage of high-fitness subpopulations. By directly
mapping a biophysical fitness function to the system-level dynamics of the
population we show that both low and very high, but not intermediate, levels of
stress in the form of an antibiotic result in a disproportionate effect of
hypermutation on resistance fixation. We demonstrate how this behavior is
directly tied to the extent of genetic hitchhiking in the system, the
propagation of high-mutation rate cells through association with high-fitness
mutations. Our results indicate a substantial role for mutation rate
flexibility in the evolution of antibiotic resistance under conditions that
present a weak advantage over wildtype to resistant cells. | 1806.08454v2 |
2015-03-13 | Paper-based spintronics: magneto-resistivity of permalloy deposited onto paper substrates | Driven by low-cost, resource abundance and distinct material properties, the
use of paper in electronics, optics and fluidics is under investigation.
Considering sensor systems based on magneto-resistance principles (anisotropic,
giant, tunnel) that are conventionally manufactured onto inorganic
semiconductor materials, we propose the use of paper substrates for cost
reduction purposes primarily. In particular, we studied the magneto-resistance
sensitivity of permalloy (Py:Ni81Fe19) onto paper substrates. In this work, we
report on our findings with clean room paper (80 g/m2, Rrms = 2.877 {\mu}m, 23%
surface porosity, latex impregnation, no embossed macro-structure). Here, the
Py:Ni81Fe19 coating was manufactured by means of a dry process, sputter
deposition, and spans an area of 10x10 mm2 and a thickness of 70 nm. Employing
a four-point-probe DC resistivity measurement setup, we investigated the change
of electrical resistance of Py:Ni81Fe19 under the presence of an oriented
external magnetic field. In particular, we investigate the magneto-resistive
change at two configurations: (1) the direction of the magnetic field is
parallel to the nominal induced electric current and (2) the direction of the
magnetic field is perpendicular to the electric current. Due to the stochastic
orientation of the fibers interplaying with the Py:Ni81Fe19 coating, the change
in magneto-resistance of the overall system at both measurement configurations
closely corresponds to the classical response of Py:Ni81Fe19 at a +/-45{\deg}
angle between the direction of electrical current and magnetic field. Using the
magneto-optic kerr effect, we observed the formation of domain walls at the
fiber bending locations. Future work will focus on the impact of layer
thickness, fiber dimensions and structure of magnetic coating on the
performance of the paper-based Py:Ni81Fe19 magneto-resistors. | 1503.04853v2 |
2002-12-16 | Effects of Boron Purity, Mg Stoichiometry and Carbon Substitution on Properties of Polycrystalline MgB$_{2}$ | By synthesizing MgB$_{2}$ using boron of different nominal purity we found
values of the residual resistivity ratio ($RRR = R(300 K) / R(42 K)$) from 4 to
20, which covers almost all values found in literature. To obtain high values
of $RRR$, high purity reagents are necessary. With the isotopically pure boron
we obtained the highest $RRR \sim$ 20 for the stoichiometric compound. We also
investigated Mg$_{x}$$^{11}$B$_{2}$ samples with 0.8 $< x <$ 1.2. For the range
Mg$_{0.8}$$^{11}$B$_{2}$ up to Mg$_{1.2}$$^{11}$B$_{2}$ we found average values
of $RRR$ between 14 and 24. For smaller variations in stoichiometry ($x=1\pm
0.1$) $RRR = 18 \pm 3$. All of our data point to the conclusion that high $RRR$
($\sim 20$) and low $\rho_{0}$ ($\leq 0.4 \mu \Omega cm$) are intrinsic
material properties associated with high purity MgB$_{2}$. In addition we have
performed initial work on optimizing the formation of carbon doped MgB$_{2}$
via the use of B$_{4}$C. Nearly single phase material can be formed by reaction
of nominal Mg(B$_{0.8}$C$_{0.2}$)$_{2}$ for 24 hours at $1200^{\circ}C$. The
$T_{c}$ for this composition is between $21.9 K$ and $22.7 K$ (depending on
criterion). | 0212385v1 |
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