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2020-06-28
|
Design of a $β$-Ga$_2$O$_3$ Schottky Barrier Diode With p-type III-Nitride Guard Ring for Enhanced Breakdown
|
This work presents the electrostatic analysis of a novel Ga$_2$O$_3$ vertical
Schottky diode with three different guard ring configurations to reduce the
peak electric field at the metal edges. Highly doped p-type GaN, p-type
nonpolar AlGaN and polarization doped graded p-AlGaN are simulated and analyzed
as the guard ring material, which forms a heterojunction with the Ga$_2$O$_3$
drift layer. Guard ring with non-polar graded p-AlGaN with a bandgap larger
than Ga$_2$O$_3$ is found to show the best performance in terms of screening
the electric field at the metal edges. The proposed guard ring configuration is
also compared with a reported Ga$_2$O$_3$ Schottky diode with no guard ring and
a structure with a high resistive Nitrogen-doped guard ring. The optimized
design is predicted to have breakdown voltage as high as 5.3 kV and a specific
on-resistance of 3.55 m$\Omega$-cm$^2$ which leads to an excellent power figure
of merit of 7.91 GW/cm$^2$.
|
2006.15645v1
|
2020-10-01
|
Impurity Band Conduction in Si-doped \b{eta}-Ga2O3 Films
|
By combining temperature-dependent resistivity and Hall effect measurements,
we investigate donor state energy in Si-doped \b{eta}-Ga2O3 films grown using
metal-organic vapor phase epitaxy (MOVPE). High magnetic field Hall effect
measurements (H = +/-90 kOe) showed non-linear Hall resistance for T < 150 K
revealing two-band conduction. Further analyses revealed carrier freeze-out
characteristics in both bands yielding donor state energies of ~ 33.7 and ~
45.6 meV. The former is consistent with the donor energy of Si in \b{eta}-Ga2O3
whereas the latter suggests a residual donor state, likely associated with a DX
center. This study provides a critical insight into the impurity band
conduction and the defect energy states in \b{eta}-Ga2O3 using high-field
magnetotransport measurements.
|
2010.00193v1
|
2021-03-31
|
Slip band interactions and GND latent hardening in a galling resistant stainless steel
|
Slip activation, slip band interactions, and GND densities in iron-base,
galling resistant alloy Nitronic 60 have been characterised at the grain length
scale using small-scale mechanical testing with high resolution digital image
correlation and high-angular resolution electron backscatter diffraction. By
correlating the two measurement techniques, new insight into slip band
interactions, the generation of lattice curvature and the corresponding
accumulation of geometrically necessary dislocations (GNDs) is provided.
Multiple discrete slip bands are typically active within single grains,
resulting in significant slip band interactions. Crossing slip bands were found
to generate accumulations of GNDs. Regions where slip bands block other slip
bands were associated with the highest GND densities, in excess of three time
the densities of crossing slip bands. Representative crystal plasticity
modelling investigations have demonstrated that discrete slip blocking events
are responsible for locally elevated GND density. This behaviour is
rationalised in terms of lattice curvature associated with the differing levels
of constraint provided by the crossing or blocking-type behaviours. Ferrite
grains are also found to contribute to the generation of GNDs. Together, these
two effects provide significant work hardening mechanisms, likely to be key to
the development of future iron-base hard facing alloys.
|
2103.16864v1
|
2021-06-10
|
Anomalous charge transport of superconducting Cu$_{x}$PdTe$_2$ under high pressure
|
By means of high-pressure resistivity measurements on single crystals, we
investigate the charge transport properties of Cu$_x$PdTe$_2$, notable for the
combination of topological type-II Dirac semimetallic properties with
superconductivity up to $T_c = 2.5$ K. In both cases of pristine ($x = 0$) and
intercalated ($x=0.05$) samples, we find an unconventional $T^4$ power law
behavior of the low-temperature resistivity visible up to $\sim$40 K and
remarkably stable under pressure up to 8.2 GPa. This observation is explained
by the low carrier density $n$, which strongly reduces the $k$-region available
for electron-phonon scattering, as previously reported in other low-$n$
two-dimensional systems, such as multilayer graphene and semiconductor
heterostructures. Our data analysis complemented by specific heat measurements
and supported by previous quantum oscillation studies and \textit{ab initio}
calculations suggests a scenario of one-band charge transport. Within this
scenario, our analysis yields a large value of transport electron-phonon
coupling constant $\lambda_{tr} = 1.2$ at ambient pressure that appears to be
strongly enhanced by pressure assuming a constant effective mass.
|
2106.05613v1
|
2021-06-18
|
Coulomb Drag between a Carbon Nanotube and Monolayer Graphene
|
We have measured Coulomb drag between an individual single-walled carbon
nanotube (SWNT) as a one-dimensional (1D) conductor and the two-dimensional
(2D) conductor monolayer graphene, separated by a few-atom-thick boron nitride
layer. The graphene carrier density is tuned across the charge neutrality point
(CNP) by a gate, while the SWNT remains degenerate. At high temperatures, the
drag resistance changes sign across the CNP, as expected for momentum transfer
from drive to drag layer, and exhibits layer exchange Onsager reciprocity. We
find that layer reciprocity is broken near the graphene CNP at low temperatures
due to nonlinear drag response associated with temperature dependent drag and
thermoelectric effects. The drag resistance shows power-law dependences on
temperature and carrier density characteristic of 1D Fermi liquid-2D Dirac
fluid drag. The 2D drag signal at high temperatures decays with distance from
the 1D source slower than expected for a diffusive current distribution,
suggesting additional interaction effects in the graphene in the hydrodynamic
transport regime.
|
2106.10246v2
|
2021-06-25
|
Direct microscopic evidence of shear induced graphitization of ultrananocrystalline diamond films
|
The origin of ultralow friction and high wear resistance in
ultrananocrystalline diamond (UNCD) films is still under active debate because
of the perplexed tribochemistry at the sliding interface. Herein, we report a
comparative study on surface topography and nanoscale friction of tribofilms,
in wear tracks of two sets of UNCD films having different structural
characteristics. Despite both the films display ultralow coefficient of
friction, the UNCD films grown under Ar atmosphere (UNCDAr) exhibit a high wear
resistance while the wear rate is higher for the films grown in N2 (UNCDN).
Frictional force microscopic (FFM) investigations clearly reveal the
manifestation of shear induced graphitization on both the films. However, the
wear track of UNCDAr films have a large network of a few layer graphene (FLG)
structures over the amorphous carbon tribofilms while only isolated clusters of
FLG structures are present in the wear track of UNCDN films. Here, we
demonstrate the direct micro-/nanoscopic evidence for the formation of large
network of ~ 0.8 - 6 nm thick FLG structures, as a consequence of shear induced
graphitization and discuss their decisive role in ultralow friction and wear.
|
2106.13778v1
|
2023-02-15
|
Metal-bonded Atomic Layers of Transition Metal Carbides (MXenes)
|
Although two-dimensional transition metal carbides and nitrides (MXenes) have
fantastic physical and chemical properties as well as wide applications, it
remains challenging to produce stable MXenes due to their rapid structural
degradation. Here, unique metal-bonded atomic layers of transition metal
carbides with high stabilities are produced via a simple topological reaction
between chlorine-terminated MXenes and selected metals, where the metals enable
to not only remove Cl terminations, but also efficiently bond with adjacent
atomic MXene slabs, driven by the symmetry of MAX phases. The films constructed
from Al-bonded Ti$_3$C$_2$Cl$_x$ atomic layers show high oxidation resistance
up to 400 degrees centigrade and low sheet resistance of 9.3 ohm per square.
Coupled to the multi-layer structure, the Al-bonded Ti$_3$C$_2$Cl$_x$ film
displays a significantly improved EMI shielding capability with a total
shielding effectiveness value of 39 dB at a low thickness of 3.1 micron,
outperforming pure Ti$_3$C$_2$Cl$_x$ film.
|
2302.07720v1
|
2023-03-22
|
A mixed-dimensional model for direct current simulations in presence of a thin high-resistivity liner
|
In this work we present a mixed-dimensional mathematical model to obtain the
electric potential and current density in direct current simulations when a
thin liner is included in the modelled domain. The liner is used in landfill
management to prevent leakage of leachate from the waste body into the
underground and is made of a highly-impermeable high-resistivity plastic
material. The electrodes and the liner have diameters and thickness
respectively that are much smaller than their other dimensions, thus their
numerical simulation might be too costly in an equi-dimensional setting. Our
approach is to approximate them as objects of lower dimension and derive the
corresponding equations. The obtained mixed-dimensional model is validated
against laboratory experiments of increasing complexity showing the reliability
of the proposed mathematical model.
|
2303.12469v1
|
2006-02-03
|
Frequency quenching of microwave induced resistance oscillations in a high mobility two-dimensional electron gas
|
The frequency dependence of microwave-induced resistance oscillations (MIROs)
has been studied experimentally in high-mobility electron GaAs/AlGaAs
structures to explore the limits at which these oscillations can be observed.
It is found that in dc transport experiments at frequencies above 120 GHz,
MIROs start to quench, while above 230 GHz, they completely disappear. The
results will need to be understood theoretically but are qualitatively
discussed within a model in which forced electronic charge oscillations
(plasmons) play an intermediate role in the interaction process between the
radiation and the single-particle electron excitations between Landau levels.
|
0602079v2
|
2010-09-15
|
Controlling electron-phonon interactions in graphene at ultra high carrier densities
|
We report on the temperature dependent electron transport in graphene at
different carrier densities $n$. Employing an electrolytic gate, we demonstrate
that $n$ can be adjusted up to 4$\times10^{14}$cm$^{-2}$ for both electrons and
holes. The measured sample resistivity $\rho$ increases linearly with
temperature $T$ in the high temperature limit, indicating that a
quasi-classical phonon distribution is responsible for the electron scattering.
As $T$ decreases, the resistivity decreases more rapidly following $\rho (T)
\sim T^{4}$. This low temperature behavior can be described by a
Bloch-Gr\"{u}neisen model taking into account the quantum distribution of the
2-dimensional acoustic phonons in graphene. We map out the density dependence
of the characteristic temperature $\Theta_{BG}$ defining the cross-over between
the two distinct regimes, and show, that for all $n$, $\rho(T)$ scales as a
universal function of the normalized temperature $T/\Theta_{BG}$.
|
1009.2988v1
|
2010-11-02
|
Chirality-dependent phonon-limited resistivity in multiple layers of graphene
|
We develop a theory for the temperature and density dependence of
phonon-limited resistivity $\rho(T)$ in bilayer and multilayer graphene, and
compare with the corresponding monolayer result. For the unscreened case, we
find $\rho \approx C T$ with $C \propto v_{\rm F}^{-2}$ in the high-temperature
limit, and $\rho \approx A T^4$ with $A \propto v_{\rm F}^{-2} k_{\rm F}^{-3}$
in the low-temperature Bloch-Gr\"uneisen limit, where $v_{\rm F}$ and $k_{\rm
F}$ are Fermi velocity and Fermi wavevector, respectively. If screening effects
are taken into account, $\rho \approx C T$ in the high-temperature limit with a
renormalized $C$ which is a function of the screening length, and $\rho \approx
A T^6$ in the low-temperature limit with $A \propto k_{\rm F}^{-5}$ but
independent of $v_{\rm F}$. These relations hold in general with $v_{\rm F}$
and a chiral factor in $C$ determined by the specific chiral band structure for
a given density.
|
1011.0741v2
|
2011-07-21
|
Observations of two-dimensional quantum oscillations and ambipolar transport in the topological insulator Bi2Se3 achieved by Cd doping
|
We present a defect-engineering strategy to optimize the transport properties
of the topological insulator Bi2Se3 to show a high bulk resistivity and clear
quantum oscillations. Starting with a p-type Bi2Se3 obtained by combining Cd
doping and a Se-rich crystal-growth condition, we were able to observe a
p-to-n-type conversion upon gradually increasing the Se vacancies by post
annealing. With the optimal annealing condition where a high level of
compensation is achieved, the resistivity exceeds 0.5 Ohmcm at 1.8 K and we
observed two-dimensional Shubnikov-de Haas oscillations composed of multiple
frequencies in magnetic fields below 14 T.
|
1107.4178v2
|
2016-04-13
|
Long Term Performance Studies of Large Oil-Free Bakelite Resistive Plate Chamber
|
Several high energy physics and neutrino physics experiments worldwide
require large-size RPCs to cover wide acceptances. The muon tracking systems in
the Iron calorimeter (ICAL) in the INO experiment, India and the near detector
in DUNE at Fermilab are two such examples. A (240 cm $\times$ 120 cm $\times$
0.2 cm) bakelite RPC has been built and tested at Variable Energy Cyclotron
Centre, Kolkata, using indigenous materials procured from the local market. No
additional lubricant, like oil has been used on the electrode surfaces for
smoothening. The chamber is in operation for $>$ 365 days. We have tested the
chamber for its long term operation. The leakage current, bulk resistivity,
efficiency, noise rate and time resolution of the chamber have been found to be
quite stable during the testing peroid. It showed an efficiency $>$ 95$\%$ with
an average time resolution of $\sim$0.83 ns at the point of measurement at 9000
V throughout the testing period. Details of the long term performance of the
chamber have been discussed.
|
1604.03668v2
|
2016-07-25
|
Influencia del potencial de polarización en la deposición de películas delgadas de NiO
|
Nickel oxide (NiO) is a binary compound with a lot of applications in the
present technology. NiO thin films were deposited by reactive sputtering
magnetron under several voltage biases applied in the glass substrates (0, 50,
100, 200, 300, 400 and 500 V). Films were characterized by profilometry, X-ray
diffraction, elemental composition and electrical resistivity at room
temperature and at low temperatures. The present work showed that despite the
insulating behavior of substrate the residual stress was reduced at high biases
and the (111) texture was promoted. Electrical resistivity was reduced at high
bias and at low temperatures thermal activation of p-type conduction was
detected.
|
1607.07391v1
|
2017-01-29
|
Built-in Homojunction Dominated Intrinsically Rectifying-Resistive Switching in NiO Nanodots for Selection Device-Free Memory Application
|
The intrinsically rectifying-resistive switching (IR-RS) has been regarded as
an effective way to address the crosstalk issue, due to the Schottky diodes
formed at the metal/oxide interfaces in the ON states to suppress the sneak
current at reverse biases. In this letter, we report for the first time another
type of IR-RS that is related to the built-in homojunction. The IR-RS study was
usually limited to macroscopic samples with micron-order pad-type electrodes,
while this work is on NiO nanodots fabricated with ultrathin
anodic-aluminum-oxide templates and acting as nanoscaled analogs of real
devices. The NiO nanodots show high storage density and high uniformity, and
the IR-RS behaviors are of good device performances in terms of retention,
endurance, switching ratio and rectification ratio. The feasibility of the
IR-RS for selection device-free memory application has been demonstrated, by
calculating the maximum crossbar array size under the worst-case scenario to be
3 Mbit.
|
1702.05665v1
|
2018-02-20
|
Perturbation theories behind thermal mode spectroscopy for high-accuracy measurement of thermal diffusivity of solids
|
Thermal mode spectroscopy (TMS) has been recently proposed for accurately
measuring thermal diffusivity of solids from a temperature decay rate of a
specific thermal mode selected by three- dimensional (anti)nodal information
[Phys. Rev. Lett., 117, 195901 (2016)]. In this paper, we find out the
following advantages of TMS by use of perturbation analyses. First, TMS is
applicable to the measurement of high thermal diffusivity with a small size
specimen. Second, it is less affected by thermally resistive films on a
specimen in the sense that the resistance at the interface does not affect the
first-order correction of thermal diffusivity. Third, it can perform doubly
accurate measurement of the thermal diffusivity specified at a thermal
equilibrium state even if the diffusivity depends on temperature in the sense
that the measurement can be performed within tiny temperature difference from
the given state and that the decay rate of the slowest decaying mode is not
affected by the dependence.
|
1802.07378v2
|
2020-02-28
|
Hydrodynamic and ballistic transport over large length scales in GaAs/AlGaAs
|
We study hydrodynamic and ballistic transport regimes through nonlocal
resistance measurements and high-resolution kinetic simulations in a mesoscopic
structure on a high-mobility two-dimensional electron system in a GaAs/AlGaAs
heterostructure. We evince the existence of collective transport phenomena in
both regimes and demonstrate that negative nonlocal resistances and current
vortices are not exclusive to only the hydrodynamic regime. The combined
experiments and simulations highlight the importance of device design,
measurement schemes and one-to-one modeling of experimental devices to
demarcate various transport regimes.
|
2002.12806v3
|
2019-03-07
|
Fe-Sn nanocrystalline films for flexible magnetic sensors with high thermal stability
|
The interplay of magnetism and spin-orbit coupling on an Fe kagome lattice in
Fe3Sn2 crystal produces a unique band structure leading to an order of
magnitude larger anomalous Hall effect than in conventional ferromagnetic
metals. In this work, we demonstrate that Fe-Sn nanocrystalline films also
exhibit a large anomalous Hall effect, being applicable to magnetic sensors
that satisfy both high sensitivity and thermal stability. In the films prepared
by a co-sputtering technique at room temperature, the partial development of
crystalline lattice order appears as nanocrystals of Fe-Sn kagome layer. The
tangent Hall angle, the ratio of Hall resistivity to longitudinal resistivity,
is largely enhanced in the optimal alloy composition of close to Fe3Sn2,
exemplifying the kagome origin even though the films are composed of
nanocrystal and amorphous-like domains. These ferromagnetic Fe-Sn films possess
great advantages as a Hall sensor over semiconductors in thermal stability
owing to the weak temperature dependence of the anomalous Hall responses.
Moreover, the room-temperature fabrication enables us to develop a mechanically
flexible Hall sensor on an organic substrate. These demonstrations manifest the
potential of kagome metal as an untapped reservoir for designing new functional
devices.
|
1903.02689v1
|
2021-01-25
|
Statics and Dynamics of Space-Charge-Layers in Polarized Inorganic Solid Electrolytes
|
The quest for safe high-energy batteries with "5V-class" cathodes and lithium
metal anodes drives research into solid electrolytes. However, reasons for the
large charge transfer resistances -- the major bottleneck of all-solid-state
batteries -- are still debated. In this article, we explore the processes in
incompressible solid electrolytes between blocking electrodes by theory-based
continuum modeling and numerical simulations. We investigate the experimentally
observed wide space-charge-zones in solid electrolytes, which are a possible
cause for the high interfacial resistances. On time scales relevant for battery
applications, we reduce our model equations. Analytic and numeric calculations
predict and study the actual structure of space-charge-layers in solid
electrolytes. To illustrate these dynamics and validate our model,
computational results are presented and compared with experimental
observations. Analog to semiconductors, we determine the material dependent,
asymmetric space-charge-layer width in the low temperature limit approximately.
This allows us to make an explicit statement about the influence of defect
concentrations and dielectric properties on the width of the
space-charge-layers in homogeneous solid electrolytes.
|
2101.10294v1
|
2015-06-01
|
High-pressure study of the Weyl semimetal NbAs
|
We performed a series of high-pressure synchrotron X-ray diffraction (XRD)
and resistance measurements on the Weyl semimetal NbAs. The crystal structure
remains stable up to 26 GPa according to the powder XRD data. The resistance of
NbAs single crystal increases monotonically with pressure at low temperature.
Up to 20 GPa, no superconducting transition is observed down to 0.3 K. These
results show that the Weyl semimetal phase is robust in NbAs, and applying
pressure is not a good way to get a topological superconductor from a Weyl
semimetal.
|
1506.00374v2
|
2020-08-14
|
High-Mobility Carriers Induced by Chemical Doping in the Candidate Nodal-Line Semimetal CaAgP
|
We report the electronic properties of single crystals of candidate
nodal-line semimetal CaAgP. The transport properties of CaAgP are understood
within the framework of a hole-doped nodal-line semimetal. In contrast,
Pd-doped CaAgP shows a drastic increase of magnetoresistance at low magnetic
fields and a strong decrease of electrical resistivity at low temperatures
probably due to weak antilocalization. Hall conductivity data indicated that
the Pd-doped CaAgP has not only hole carriers induced by the Pd doping, but
also high-mobility electron carriers in proximity of the Dirac point.
Electrical resistivity of Pd-doped CaAgP also showed a superconducting
transition with onset temperature of 1.7-1.8 K.
|
2008.06188v1
|
2020-12-19
|
Anomalous behavior in high-pressure carbonaceous sulfur hydride
|
A new experimental study by Snider et al. [Nature 586, 373-377 (2020)]
reported behavior in a high-pressure carbon-sulfur-hydrogen system that has
been interpreted by the authors as superconductivity at room temperature. The
sudden drop of electrical resistance at a critical temperature and the change
of the R vs. T behavior with an applied magnetic field point to
superconductivity. This is a very exciting study in one of the most important
areas of science, hence, it is crucial for the community to investigate these
findings and hopefully reproduce these results. In this comment, we present
calculations that expand upon the arguments put forth by Hirsch and Marsiglio
[arXiv:2010.10307], and offer some speculations about physical mechanisms that
might explain the observed data. In agreement with Hirsch and Marsiglio, we
show that there are errors in the analysis presented in the experimental paper,
and with the correct analysis, the reported R vs. T data significantly deviate
from the expected behavior. In particular, the extremely sharp change in
resistance at the superconducting transition is not consistent with a strongly
type II superconductor.
|
2012.10771v3
|
2021-02-23
|
High magnetic field induced crossover from the Kondo to Fermi liquid behavior in 1$T$-VTe$_{2}$ single crystals
|
The magnetic and magnetotransport properties of metallic 1$T$-VTe$_{2}$
single crystals were investigated at temperatures from 1.3 to 300 K and in
magnetic fields up to 35 T. Upon applying a high magnetic field, it is found
that the electrical resistivity displays a crossover from the logarithmic
divergence of the single-impurity Kondo effect to the Fermi liquid behavior at
low temperatures. The Brillouin scale of the negative magnetoresistivity above
the Kondo temperature $T_{\rm{K}}$ = 12 K indicates that the Kondo features
originate from intercalated V ions, with $S$ = 1/2. Both magnetic
susceptibility and Hall effect show an anomaly around $T_{\rm{K}}$. By using
the modified Hamann expression we successfully describe the
temperature-dependent resistivity under various magnetic fields, which shows
the characteristic peak below $T_{\rm{K}}$ due to the splitting of the Kondo
resonance.
|
2102.11444v1
|
2021-02-26
|
Crossover from itinerant to localized states in the thermoelectric oxide [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]
|
The layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], often expressed as
the approximate formula Ca$_3$Co$_4$O$_9$, is a promising candidate for
efficient oxide thermoelectrics but an origin of its unusual thermoelectric
transport is still in debate. Here we investigate \textit{in-plane} anisotropy
of the transport properties in a broad temperature range to examine the
detailed conduction mechanism. The in-plane anisotropy between $a$ and $b$ axes
is clearly observed both in the resistivity and the thermopower, which is
qualitatively understood with a simple band structure of the triangular lattice
of Co ions derived from the angle-resolved photoemission spectroscopy
experiments. On the other hand, at high temperatures, the anisotropy becomes
smaller and the resistivity shows a temperature-independent behavior, both of
which indicate a hopping conduction of localized carriers. Thus the present
observations reveal a crossover from low-temperature itinerant to
high-temperature localized states, signifying both characters for the enhanced
thermopower.
|
2102.13250v1
|
2021-11-03
|
Devices for Thermal Conductivity Measurements of Electroplated Bi for X-ray TES Absorbers
|
Electroplated Bismuth (Bi) is commonly used in Transition-Edge Sensors (TESs)
for X-rays because of its high stopping power and low heat capacity.
Electroplated Bi is usually grown on top of another metal that acts as seed
layer, typically gold (Au), making it challenging to extrapolate its
thermoelectric properties. In this work, we present four-wire resistance
measurement structures that allow us to measure resistance as a function of
temperature of electroplated Bi independently of Au. The results show that the
thermal conductivity of the Bi at 3 K is high enough to guarantee the correct
thermalization of X-ray photons when used as an absorber for TESs.
|
2111.02503v1
|
2021-11-09
|
Absence of decoherence in the electron-wall system
|
Decoherence is associated with a dissipative environment as described by the
Caldeira-Leggett equation. Anglin and Zurek predicted that a resistive surface
could act as such a dissipative environment for a free electron wave passing
close to it. We scrutinize Zurek's and other promising decoherence theoretical
models by observing electrons passing by an optically excited GaAs surface and
through a gold channel. The high resistivity of the GaAs surface and close
proximity to the gold surface leads to strong decoherence within these
decoherence models. In contradistinction, the observed contrast is high in our
electron diffraction patterns. This implies lower decoherence rates than
suggested by these models, making electron-matter-wave-guides and other
technologies, where quantum coherence of electrons close to materials is
important, a possibility
|
2111.05246v1
|
2022-06-10
|
Fabrication of uniformly doped graphene quantum Hall arrays with multiple quantized resistance outputs
|
In this work, limiting factors for developing metrologically useful arrays
from epitaxial graphene on SiC are lifted with a combination of
centimeter-scale, high-quality material growth and the implementation of
superconducting contacts. Standard devices for metrology have been restricted
to having a single quantized value output based on the $\nu$ = 2 Landau level.
With the demonstrations herein of devices having multiple outputs of quantized
values available simultaneously, these versatile devices can be used to
disseminate the ohm globally. Such devices are designed to give access to
quantized resistance values over the range of three orders of magnitude,
starting as low as the standard value of approximately 12.9 k$\Omega$ and
reaching as high as 1.29 M$\Omega$. Several experimental methods are used to
assess the quality and versatility of the devices, including standard lock-in
techniques and Raman spectroscopy.
|
2206.05098v1
|
2022-06-29
|
On the depletion behaviour of low-temperature covalently bonded silicon sensor diodes
|
Low temperature covalent direct wafer-wafer bonding allows for the fusion of
multiple semiconductor wafers without any additional material at the bonding
interface. In the context of particle pixel detectors this might provide an
alternative to bump-bonding for joining sensors to readout chips. Previous
investigations have shown that the amorphous layer formed at the interface
during bonding is detrimental to charge propagation. To investigate the
influence of the bonding interface on signal collection we have fabricated
custom test structures by bonding high-resistivity N to high-resistivity P-type
silicon wafers thus forming P-N junctions. Scanning transmission electron
microscopy shows indeed the formation of ca. 3nm wide amorphous layer at the
interface. Using a scanning transient current technique (TCT) setup we were
able to record generated signals. Illuminating our sample with light of
different wavelengths and from different sides, indicates that the P side of
the bonded structures can be fully depleted, but not the N side. This indicates
a strongly asymmetric depletion behaviour which we attribute to the presence of
the bonding interface.
|
2206.14717v2
|
2022-07-26
|
Engineering Surface Oxygen Vacancies in $\mathrm{SrTiO_3}$ to Form a High Mobility and Transparent Quasi Two dimensional Electron System
|
Quasi-two-dimensional electron systems (q-2DES) are formed in various
hetero-structures, including oxide interfaces. Oxygen vacancies (OVs) in oxides
like $\mathrm{SrTiO_3}$ are known to produce electronic carriers. A novel way
to produce $\mathrm{SrTiO_{3-\delta}}$ on the surface using a low-energy
$\mathrm{H_2}$ plasma is shown here. It results in a q-2DES with mobility as
high as $\mu \sim 20,000 \; cm^2V^{-1}s^{-1}$, displaying quantum oscillations
in magneto-resistance. We can achieve a sharper or weaker confinement potential
by adjusting the process pressure. The system with sharper confinement displays
clearer quantum oscillations and Kondo-like temperature dependence of
resistance. OVs close to the surface behaving like a correlated Anderson
impurity is responsible for the Kondo behaviour. Quantum oscillations are less
prominent in the weakly confined system. A cross-over from weak-localization to
anti-localization with temperature is seen, but no Kondo behavior. The process
also results in a transparent conductor amenable to lithographic patterning.
This conductor's standard figure of merit is comparable to poly-crystalline ITO
films in the visible regime and extends with similar performance into the
$\lambda$ $\sim 1.5$ $\mu m$ telecommunication wavelength.
|
2207.12933v1
|
2022-09-05
|
Growth of rare-earth monopnictide DySb single crystal by novel Self-flux method
|
This report presents a new synthesis protocol for the single crystal growth
of rare earth monopnictide DySb by self-flux technique. A detailed structural,
transport and magnetic characterization have been done using X-Ray diffraction
(XRD), High resolution X-Ray diffraction (HRXRD), resistivity and magnetization
measurements respectively. The Rietveld refinement of powder XRD pattern
confirms that the grown crystal is in single phase and crystallizes in space
group Fm3m(225) of rock-salt type crystal structure. HRXRD on cleaved crystal
confirms the single crystalline nature while rocking curve analysis reveals the
high quality of the grown crystal. Temperature dependent resistivity and
magnetization measurements show a transition at 9.7K from paramagnetic (PM) to
antiferromagnetic (AFM) state.
|
2209.01930v1
|
2022-10-27
|
Single photon detection performance of highly disordered NbTiN thin films
|
We experimentally investigated the detection performance of highly disordered
NbxTi1-xN based superconducting nanowire single photon detectors (SNSPDs). The
dependence on the composition of the transition temperature Tc for NbxTi1-xN
films show a dome-like behavior on the Nb content, with a maximal Tc at
xNb~0.65 , and the Nb0.65Ti0.35N films also combine relatively large sheet
resistance and intermediate residual resistivity ratio. Moreover, 60-nm-wide
and 7-nm-thick Nb0.65Ti0.35N nanowires show a switching current as high as 14.5
uA, and saturated intrinsic detection efficiency with a plateau of more than 2
uA at 2.4 K. Finally, the corresponding SNSPDs on an alternative SiO2/Ta2O5
dielectric mirror showed a system detection efficiency of approximately 92% for
1550 nm photons, and the timing jitter is around 26 ps. Our results demonstrate
that the highly disordered NbxTi1-xN films are promising for fabricating SNSPDs
for near- and middle-infrared single photons with high detection efficiency and
low timing jitter.
|
2210.15215v1
|
2022-11-24
|
Development of Hybrid Resistive Plate Chambers
|
Resistive Plate Chambers (RPCs) are essential active media of large-scale
experiments as part of the muon systems and (semi-)digital hadron calorimeters.
Among the several outstanding issues associated with the RPCs, the loss of
efficiency for the detection of particles when subjected to high particle
fluxes, and the limitations associated with the common RPC gases can be listed.
In order to address the latter issue, we developed novel RPC designs with
special anode plates coated with high secondary electron emission yield
materials such as Al$_2$O$_3$ and TiO$_2$. The proof of principle was obtained
for various designs and is in progress for the rest. The idea was initiated
following the achievements on the development of the novel 1-glass RPCs.
Here we report on the construction of various different RPC designs, and
their performance measurements in laboratory tests and with particle beams; and
discuss the future test plans.
|
2211.13796v2
|
2023-09-11
|
Experimental realization of a high Curie temperature CoFeRuSn quaternary Heusler alloy for spintronic applications
|
We synthesize CoFeRuSn equiatomic quaternary Heusler alloy using arc-melt
technique and investigate its structural, magnetic and transport properties.
The room temperature powder X-ray diffraction analysis reveals that CoFeRuSn
crystallizes in cubic crystal structure with small amount of DO3 - disorder.
The field dependence of magnetization shows non-zero but small hysteresis and
saturation behavior up to room temperature, indicating soft ferromagnetic
nature of CoFeRuSn. The magnetic moment estimated from the magnetization data
is found to be 4.15 {\mu}B / f.u., which is slightly less than the expected
Slater-Pauling rule. The deviation in the value of experimentally observed
moment from the theoretical value might be due to small disorder in the
crystal. The low temperature fit to electrical resistivity data show absence of
quadratic temperature dependence of resistivity, suggesting half-metallic
behavior of CoFeRuSn. The high Curie temperature and possible half-metallic
behavior of CoFeRuSn make it a highly promising candidate for room temperature
spintronic applications.
|
2309.05493v1
|
2018-04-11
|
Extremely large magnetoresistance in topologically trivial semimetal $α$-WP$_2$
|
Extremely large magnetoresistance (XMR) was recently discovered in many
non-magnetic materials, while its underlying mechanism remains poorly
understood due to the complex electronic structure of these materials. Here, we
report an investigation of the $\alpha$-phase WP$_2$, a topologically trivial
semimetal with monoclinic crystal structure (C2/m), which contrasts to the
recently discovered robust type-II Weyl semimetal phase in $\beta$-WP$_2$. We
found that $\alpha$-WP$_2$ exhibits almost all the characteristics of XMR
materials: the near-quadratic field dependence of MR, a field-induced up-turn
in resistivity following by a plateau at low temperature, which can be
understood by the compensation effect, and high mobility of carriers confirmed
by our Hall effect measurements. It was also found that the normalized MRs
under different magnetic fields has the same temperature dependence in
$\alpha$-WP$_2$, the Kohler scaling law can describe the MR data in a wide
temperature range, and there is no obvious change in the anisotropic parameter
$\gamma$ value with temperature. The resistance polar diagram has a peanut
shape when field is rotated in $\textit{ac}$ plane, which can be understood by
the anisotropy of Fermi surface. These results indicate that both
field-induced-gap and temperature-induced Lifshitz transition are not the
origin of up-turn in resistivity in the $\alpha$-WP$_2$ semimetal. Our findings
establish $\alpha$-WP$_2$ as a new reference material for exploring the XMR
phenomena.
|
1804.03879v1
|
2019-05-02
|
Robust axion insulator and Chern insulator phases in a two-dimensional antiferromagnetic topological insulator
|
The intricate interplay between nontrivial topology and magnetism in
two-dimensional (2D) materials has led to the emergence of many novel phenomena
and functionalities. An outstanding example is the quantum anomalous Hall (QAH)
effect, which was realized in magnetically doped topological insulators (TIs)
in the absence of magnetic field. Recently, the layered van der Waals compound
MnBi2Te4 has been theoretically predicted and experimentally verified to be a
TI with interlayer antiferromagnetic (AFM) order. It is a rare stoichiometric
material with coexisting topology and magnetism, thus represents a perfect
building block for complex topological-magnetic structures. Here we investigate
the quantum transport behaviors of both bulk crystal and exfoliated MnBi2Te4
flakes in a field effect transistor geometry. In the 6 septuple layers (SLs)
device tuned into the insulating regime, we observe a large longitudinal
resistance and zero Hall plateau, which are characteristic of the axion
insulator state. The robust axion insulator state occurs in zero magnetic
field, over a wide magnetic field range, and at relatively high temperatures.
Moreover, a moderate magnetic field drives a quantum phase transition from the
axion insulator phase to a Chern insulator phase with zero longitudinal
resistance and quantized Hall resistance h/e2 (h is the Plank constant and e is
the elemental charge). These results pave the road for using even-number-SL
MnBi2Te4 to realize the quantized topological magnetoelectric effect and axion
electrodynamics in condensed matter systems.
|
1905.00715v2
|
2019-04-24
|
Antisymmetric magnetoresistance in van der Waals Fe3GeTe2/graphite/Fe3GeTe2 tri-layer heterostructures
|
Van der Waals (vdW) ferromagnetic materials are rapidly establishing
themselves as effective building blocks for next generation spintronic devices.
When layered with non-magnetic vdW materials, such as graphene and/or
topological insulators, vdW heterostructures can be assembled (with no
requirement for lattice matching) to provide otherwise unattainable device
structures and functionalities. We report a hitherto rarely seen antisymmetric
magnetoresistance (MR) effect in van der Waals heterostructured
Fe3GeTe2/graphite/Fe3GeTe2 devices. Unlike conventional giant magnetoresistance
(GMR) which is characterized by two resistance states, the MR in these vdW
heterostructures features distinct high, intermediate and low resistance
states. This unique characteristic is suggestive of underlying physical
mechanisms that differ from those observed before. After theoretical
calculations, the three resistance behavior was attributed to a spin momentum
locking induced spin polarized current at the graphite/FGT interface. Our work
reveals that ferromagnetic heterostructures assembled from vdW materials can
exhibit substantially different properties to those exhibited by similar
heterostructures grown in vacuum. Hence, it highlights the potential for new
physics and new spintronic applications to be discovered using vdW
heterostructures.
|
1904.10588v2
|
2007-03-09
|
Nanometer-Scale Materials Contrast Imaging with a Near-Field Microwave Microscope
|
We report topography-free materials contrast imaging on a nano-fabricated
Boron-doped Silicon sample measured with a Near-field Scanning Microwave
Microscope over a broad frequency range. The Boron doping was performed using
the Focus Ion Beam technique on a Silicon wafer with nominal resistivity of 61
Ohm.cm. A topography-free doped region varies in sheet resistance from
1000Ohm/Square to about 400kOhm/Square within a lateral distance of 4
micrometer. The qualitative spatial-resolution in sheet resistance imaging
contrast is no worse than 100 nm as estimated from the frequency shift signal.
|
0703241v1
|
2010-03-15
|
A Memadmittance Systems Model for Thin Film Memory Materials
|
In 1971 the memristor was originally postulated as a new non-linear circuit
element relating the time integrals of current and voltage. More recently
researchers at HPLabs have linked the theoretical memristor concept to
resistance switching behavior of TiO(2-x) thin films. However, a variety of
other thin film materials exhibiting memory resistance effects have also been
found to exhibit a memory capacitance effect. This paper proposes a
memadmittance (memory admittance) systems model which attempts to consolidate
the memory capacitance effects with the memristor model. The model produces
equations relating the cross-sectional area of conductive bridges in resistive
switching films to shifts in capacitance.
|
1003.2842v1
|
2018-09-06
|
Estimation of the electrical and thermal contact resistances and thermoemf of thermoelectric material-metal transient contact layer due to semiconductor surface rougness
|
The impact of semiconductor surface roughness on the electrical and thermal
contact resistances and thermoEMF of thermoelectric material (TEM)-metal
transient contact layer is studied theoretically. The distribution of hollows
and humps on the rough surface is simulated by the truncated Gaussian
distribution. The impact of distribution parameters on the electrical contact
resistance and thermoEMF of thermoelectric material-metal contact is studied.
|
1809.02504v1
|
2022-03-30
|
STeP-CiM: Strain-enabled Ternary Precision Computation-in-Memory based on Non-Volatile 2D Piezoelectric Transistors
|
We propose 2D Piezoelectric FET (PeFET) based compute-enabled non-volatile
memory for ternary deep neural networks (DNNs). PeFETs consist of a material
with ferroelectric and piezoelectric properties coupled with Transition Metal
Dichalcogenide channel. We utilize (a) ferroelectricity to store binary bits
(0/1) in the form of polarization (-P/+P) and (b) polarization dependent
piezoelectricity to read the stored state by means of strain-induced bandgap
change in Transition Metal Dichalcogenide channel. The unique read mechanism of
PeFETs enables us to expand the traditional association of +P (-P) with low
(high) resistance states to their dual high (low) resistance depending on read
voltage. Specifically, we demonstrate that +P (-P) stored in PeFETs can be
dynamically configured in (a) a low (high) resistance state for positive read
voltages and (b) their dual high (low) resistance states for negative read
voltages, without afflicting a read disturb. Such a feature, which we name as
Polarization Preserved Piezoelectric Effect Reversal with Dual Voltage Polarity
(PiER), is unique to PeFETs and has not been shown in hitherto explored
memories. We leverage PiER to propose a Strain-enabled Ternary Precision
Computation-in-Memory (STeP-CiM) cell with capabilities of computing the scalar
product of the stored weight and input, both of which are represented with
signed ternary precision. Further, using multi word-line assertion of STeP-CiM
cells, we achieve massively parallel computation of dot products of signed
ternary inputs and weights. Our array level analysis shows 91% lower delay and
improvements of 15% and 91% in energy for in-memory multiply-and-accumulate
operations compared to near-memory design approaches based on SRAM and PeFET
respectively. STeP-CiM exhibits upto 8.91x improvement in performance and 6.07x
average improvement in energy over SRAM/PeFET based near-memory design.
|
2203.16416v1
|
2013-01-28
|
Can high risk fungicides be used in mixtures without selecting for fungicide resistance?
|
Fungicide mixtures produced by the agrochemical industry often contain
low-risk fungicides, to which fungal pathogens are fully sensitive, together
with high-risk fungicides known to be prone to fungicide resistance. Can these
mixtures provide adequate disease control while minimizing the risk for the
development of resistance? We present a population dynamics model to address
this question. We found that the fitness cost of resistance is a crucial
parameter to determine the outcome of competition between the sensitive and
resistant pathogen strains and to assess the usefulness of a mixture. If
fitness costs are absent, then the use of the high-risk fungicide in a mixture
selects for resistance and the fungicide eventually becomes nonfunctional. If
there is a cost of resistance, then an optimal ratio of fungicides in the
mixture can be found, at which selection for resistance is expected to vanish
and the level of disease control can be optimized.
|
1301.6561v2
|
2005-12-15
|
Introduction to tensorial resistivity probability tomography
|
The probability tomography approach developed for the scalar resistivity
method is here extended to the 2D tensorial apparent resistivity acquisition
mode. The rotational invariant derived from the trace of the apparent
resistivity tensor is considered, since it gives on the datum plane anomalies
confined above the buried objects. Firstly, a departure function is introduced
as the difference between the tensorial invariant measured over the real
structure and that computed for a reference uniform structure. Secondly, a
resistivity anomaly occurrence probability (RAOP) function is defined as a
normalised crosscorrelation involving the experimental departure function and a
scanning function derived analytically using the Frechet derivative of the
electric potential for the reference uniform structure. The RAOP function can
be calculated in each cell of a 3D grid filling the investigated volume, and
the resulting values can then be contoured in order to obtain the 3D
tomographic image. Each non-vanishing value of the RAOP function is interpreted
as the probability which a resistivity departure from the reference resistivity
obtain in a cell as responsible of the observed tensorial apparent resistivity
dataset on the datum plane. A synthetic case shows that the highest RAOP values
correctly indicate the position of the buried objects and a very high spacial
resolution can be obtained even for adjacent objects with opposite resistivity
contrasts with respect to the resistivity of the hosting matrix. Finally, an
experimental field case dedicated to an archaeological application of the
resistivity tensor method is presented as a proof of the high resolution power
of the probability tomography imaging, even when the data are collected in
noisy open field conditions.
|
0512147v1
|
2014-07-24
|
Macro- and microscopic properties of strontium doped indium oxide
|
Solid state synthesis and physical mechanisms of electrical conductivity
variation in polycrystalline, strontium doped indium oxide In2O3:(SrO)x were
investigated for materials with different doping levels at different
temperatures (T=20-300 C) and ambient atmosphere content including humidity and
low pressure. Gas sensing ability of these compounds as well as the sample
resistance appeared to increase by 4 and 8 orders of the magnitude,
respectively, with the doping level increase from zero up to x=10%. The
conductance variation due to doping is explained by two mechanisms:
acceptor-like electrical activity of Sr as a point defect and appearance of an
additional phase of SrIn2O4. An unusual property of high level (x=10%) doped
samples is a possibility of extraordinarily large and fast oxygen exchange with
ambient atmosphere at not very high temperatures (100-200 C). This peculiarity
is explained by friable structure of crystallite surface. Friable structure
provides relatively fast transition of samples from high to low resistive state
at the expense of high conductance of the near surface layer of the grains.
Microscopic study of the electro-diffusion process at the surface of oxygen
deficient samples allowed estimation of the diffusion coefficient of oxygen
vacancies in the friable surface layer at room temperature as 3x10^(-13)
cm^2/s, which is by one order of the magnitude smaller than that known for
amorphous indium oxide films.
|
1407.6471v1
|
2015-03-29
|
Universal low-temperature Ohmic contacts for quantum transport in transition metal dichalcogenides
|
Low carrier mobility and high electrical contact resistance are two major
obstacles prohibiting explorations of quantum transport in TMDCs. Here, we
demonstrate an effective method to establish low-temperature Ohmic contacts in
boron nitride encapsulated TMDC devices based on selective etching and
conventional electron-beam evaporation of metal electrodes. This method works
for most extensively studied TMDCs in recent years, including MoS2, MoSe2,
WSe2, WS2, and 2H-MoTe2. Low electrical contact resistance is achieved at 2 K.
All of the few-layer TMDC devices studied show excellent performance with
remarkably improved field-effect mobilities ranging from 2300 cm2/V s to 16000
cm2/V s, as verified by the high carrier mobilities extracted from Hall effect
measurements. Moreover, both high-mobility n-type and p-type TMDC channels can
be realized by simply using appropriate contact metals. Prominent Shubnikov-de
Haas oscillations have been observed and investigated in these high-quality
TMDC devices.
|
1503.08427v2
|
2017-04-13
|
High-pressure phase diagram, structural transitions, and persistent non-metallicity of BaBiO$_3$: theory and experiment
|
BaBiO$_3$ is a mixed-valence perovskite which escapes the metallic state
through a Bi valence (and Bi-O bond) disproportionation or CDW distortion,
resulting in a semiconductor with a gap of 0.8 eV at zero pressure. The
evolution of structural and electronic properties at high pressure is, however,
largely unknown. Pressure, one might have hoped, could reduce the
disproportionation, making the two Bi ions equivalent and bringing the system
closer to metallicity or even to superconductivity, such as is attained at
ambient pressure upon metal doping. We address the high-pressure phase diagram
of pristine BaBiO$_3$ by ab initio DFT calculations based on GGA and hybrid
functionals in combination with crystal structure prediction methods based on
evolutionary algorithms, molecular dynamics and metadynamics. The calculated
phase diagram from 0 to 50 GPa indicates that pristine BaBiO$_3$ resists
metallization under pressure, undergoing instead at room temperature structural
phase transitions from monoclinic \textit{I2/m} to nearly tetragonal
\textit{P-1} at 7 GPa, possibly to monoclinic \textit{C2/m} at 27 GPa, and to
triclinic \textit{P1} at 43 GPa. Remarkably, all these phases sustain and in
fact increase the inequivalence of two Bi neighboring sites and of their Bi-O
bonds and, in all cases except semimetallic \textit{C2/m}, the associated
insulating character. We then present high-pressure resistivity data which
generally corroborate these results, and show that the insulating character
persists at least up to 80 GPa, suggesting that the \textit{C2/m} phase is
probably an artifact of the small computational cell.
|
1704.04098v1
|
2019-11-18
|
Effect of particle contact on the electrical performance of NTC-epoxy composite thermistors
|
As demand rises for flexible electronics, traditionally prepared sintered
ceramic sensors must be transformed into fully new sensor materials that can
bend and flex in use and integration. Negative temperature coefficient of
resistance (NTC) ceramic thermistors are preferred temperature sensors for
their high accuracy and excellent stability, yet their high stiffness and high
temperature fabrication process limits their use in flexible electronics. Here,
a low stiffness thermistor based on NTC ceramic particles of micron size
embedded in an epoxy polymer matrix is reported. The effect of
particle-to-particle contact on electrical performance is studied by arranging
the NTC particles in the composite films in one of three ways: 1) Low particle
contact, 2) Improved particle contact perpendicular to the electrodes and 3)
dispersing high particle contact agglomerated clumps throughout the polymer. At
50 vol.\% of agglomerated NTC particles, the composite films exhibit a
$\beta$-value of 2069 K and a resistivity, $\rho$, of 3.3$\cdot 10^5$
$\Omega$m, 4 orders of magnitude lower than a randomly dispersed composite at
identical volume. A quantitative analysis shows that attaining a predominantly
parallel connectivity of the NTC particles and polymer is a key parameter in
determining the electrical performance of the composite film.
|
1911.07468v2
|
2021-03-11
|
Review on quasi-2D square planar nickelates
|
In strongly correlated materials, lattice, charge, spin and orbital degrees
of freedom interact with each other, leading to emergent physical properties
such as superconductivity, colossal magnetic resistance and metal-insulator
transition. Quasi-2D square planar nickelates, Rn+1NinO2n+2 (R=rare earth, n=2,
3...), are of significant interest and long sought for cuprate analogue due to
the 3d9 electronic configuration of Ni+, the same as the active ion Cu2+ in the
high-Tc superconducting cuprates. The field has attracted intense attention
since 2019 due to the discovery of superconductivity in thin films of
Nd0.8Sr0.2NiO2, although no superconductivity has been reported in bulk
polycrystalline powders. Herein, we review the synthesis of polycrystalline
powders of quasi-2D square planar nickelates through topotactic reduction of
parent compounds that are synthesized via solid state reaction, precursor
method, high pressure floating zone method and high-pressure flux method. We
emphasize single crystal preparation using the high-pressure floating zone
techniques. We discuss their crystal structure and physical properties
including resistivity, magnetic susceptibility and heat capacity. We highlight
the cuprate-like physics, including charge/spin stripes and large orbital
polarization, identified in single crystals of R4Ni3O8 (R=La and Pr) combining
synchrotron X-ray/neutron single crystal diffraction and density functional
theory calculations. Furthermore, the challenges and possible research
directions of this fast-moving field in the future are briefly discussed.
|
2103.06674v1
|
2022-05-25
|
Stranger than Metals
|
Although the resistivity in traditional metals increases with temperature,
its $T$ dependence vanishes at low or high temperature, albeit for different
reasons. Here, we review a class of materials, known as \lq strange' metals,
that can violate both principles. In materials exhibiting such behavior, the
change in slope of the resistivity as the mean free path drops below the
lattice constant, or as $T \rightarrow 0$, can be imperceptible, suggesting
complete continuity between the charge carriers at low and high $T$. Since
particles cannot scatter at length scales shorter than the interatomic spacing,
strange metallicity calls into question the relevance of locality and a
particle picture of the underlying current. This review focuses on transport
and spectroscopic data on candidate strange metals with an eye to isolate and
identify a unifying physical principle. Special attention is paid to quantum
criticality, Planckian dissipation, Mottness, and whether a new gauge
principle, which has a clear experimental signature, is needed to account for
the non-local transport seen in strange metals. For the cuprates, strange
metallicity is shown to track the superfluid density, thereby making a theory
of this state the primary hurdle in solving the riddle of high-temperature
superconductivity.
|
2205.12979v1
|
2024-03-08
|
Experimental set-up for thermal measurements at the nanoscale using an SThM probe with niobium nitride thermometer
|
Scanning Thermal Microscopy (SThM) has become an important measurement tool
for characterizing the thermal properties of materials at the nanometer scale.
This technique requires a SThM probe that combines an Atomic Force Microscopy
(AFM) probe and a very sensitive resistive thermometry; the thermometer being
located at the apex of the probe tip allows the mapping of temperature or
thermal properties of nanostructured materials with very high spatial
resolution. The high interest of the SThM technique in the field of thermal
nanoscience currently suffers from a low temperature sensitivity despite its
high spatial resolution. To address this challenge, we developed a high
vacuum-based AFM system hosting a highly sensitive niobium nitride (NbN) SThM
probe to demonstrate its unique performance. As a proof of concept, we utilized
this custom-built system to carry out thermal measurements using the 3$\omega$
method. By measuring the $V_{3\omega}$ voltage on the NbN resistive thermometer
in vacuum conditions we were able to determine the SThM probe's thermal
conductance and thermal time constant. The performance of the probe is
demonstrated by doing thermal measurements in-contact with a sapphire sample.
|
2403.05405v2
|
2015-12-17
|
A Novel Material for In Situ Construction on Mars: Experiments and Numerical Simulations
|
A significant step in space exploration during the 21st century will be human
settlement on Mars. Instead of transporting all the construction materials from
Earth to the red planet with incredibly high cost, using Martian soil to
construct a site on Mars is a superior choice. Knowing that Mars has long been
considered a "sulfur-rich planet", a new construction material composed of
simulated Martian soil and molten sulfur is developed. In addition to the raw
material availability for producing sulfur concrete and a strength reaching
similar or higher levels of conventional cementitious concrete, fast curing,
low temperature sustainability, acid and salt environment resistance, 100%
recyclability are appealing superior characteristics of the developed Martian
Concrete. In this study, different percentages of sulfur are investigated to
obtain the optimal mixing proportions. Three point bending, unconfined
compression and splitting tests were conducted to determine strength
development, strength variability, and failure mechanisms. The test results
show that the strength of Martian Concrete doubles that of sulfur concrete
utilizing regular sand. It is also shown that the particle size distribution
plays an important role in the mixture's final strength. Furthermore, since
Martian soil is metal rich, sulfates and, potentially, polysulfates are also
formed during high temperature mixing, which might contribute to the high
strength. The optimal mix developed as Martian Concrete has an unconfined
compressive strength of above 50 MPa. The formulated Martian Concrete is
simulated by the Lattice Discrete Particle Model (LDPM), which exhibits
excellent ability in modeling the material response under various loading
conditions.
|
1512.05461v3
|
1998-09-07
|
Metallic temperature dependence of resistivity in perchlorate doped polyacetylene
|
We have measured the electrical resistivity ($\rho$) and the thermoelectric
power (TEP) of the perchlorate (ClO4^-) doped stretch oriented polyacetylene
(PA) film. For the highly conducting samples ($\sigma_{RT} > 41000 S/cm$), the
temperature dependence of the 4-probe resistivity shows positive temperature
coefficient of resistivity (TCR) from T=1.5K to 300K. For the less conducting
samples, the 4-probe resistivity data show the crossover of TCR with a broad
minimum peak at T=T* > 200K. For samples of $\sigma_{RT}$$>$20000 S/cm, the
$\rho (1.5K)/\rho (300K) <1$, i.e., the resistivity at 1.5K is lower than the
room temperature resistivity value. The temperature dependence of the TEP shows
diffusive linear metallic TEP becoming temperature independent below 40K.
Unlike the others who used Cu(ClO_4)_2 for the ClO_4^- doping, the initial
doping material we used is anhydrous Fe(ClO_4)_3 which is crucial to obtain the
positive TCR from T=1.5K to 300K.
|
9809106v1
|
2006-11-20
|
Using Cluster Dynamics to Model Electrical Resistivity Measurements in Precipitating Al-Sc Alloys
|
Electrical resistivity evolution during precipitation in Al-Sc alloys is
modeled using cluster dynamics. This mesoscopic modeling has already been shown
to correctly predict the time evolution of the precipitate size distribution.
In this work, we show that it leads too to resistivity predictions in
quantitative agreement with experimental data. We only assume that all clusters
contribute to the resistivity and that each cluster contribution is
proportional to its area. One interesting result is that the resistivity excess
observed during coarsening mainly arises from large clusters and not really
from the solid solution. As a consequence, one cannot assume that resistivity
asymptotic behavior obeys a simple power law as predicted by LSW theory for the
solid solution supersaturation. This forbids any derivation of the precipitate
interface free energy or of the solute diffusion coefficient from resistivity
experimental data in a phase-separating system like Al-Sc supersaturated
alloys.
|
0611524v1
|
2008-10-06
|
Strong resistance nonlinearity and third harmonic generation in the unipolar resistance switching of NiO thin films
|
We investigated third harmonic generation in NiO thin films, which exhibit
unipolar resistance switching behavior. We found that the low resistance states
of the films were strongly nonlinear, with variations in the resistance R as
large as 60%. This strong nonlinear behavior was most likely caused by Joule
heating of conducting filaments inside the films. By carefully controlling the
applied dc bias, we obtained several low resistance states, whose values of the
third harmonic coefficient B3f were proportional to R2+w (with w = 2.07). This
suggested that the resistance changes of the NiO films were accompanied by
connectivity changes of the conducting filaments, as observed in classical
percolating systems.
|
0810.0886v1
|
2009-07-19
|
Current Driven tri-stable Resistance States in Magnetic Point Contacts
|
Point contacts between normal and ferromagnetic metals are investigated using
magneto-resistance and transport spectroscopy measurements combined with
micromagnetic simulations. Pronounced hysteresis in the point-contact
resistance versus both bias current and external magnetic field are observed.
It is found that such hysteretic resistance can exhibit, in addition to
bi-stable resistance states found in ordinary spin valves, tri-stable
resistance states with a middle resistance level. We interpret these
observation in terms of surface spin-valve and spin-vortex states, originating
from a substantially modified spin structure at the ferromagnetic interface in
contact core. We argue that these surface spin states, subject to a weakened
exchange interaction, dominate the effects of spin transfer torques on the
nanometer scale.
|
0907.3286v1
|
2014-03-25
|
Electric-Field-Modulated Nonvolatile Resistance Switching in VO2/PMN-PT(111) Heterostructures
|
The electric-field-modulated resistance switching in VO2 thin films grown on
piezoelectric (111)-0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) substrates has
been investigated. Large relative change in resistance (10.7%) was observed in
VO2/PMN-PT(111) hererostructures at room temperature. For a substrate with a
given polarization direction, stable resistive states of VO2 films can be
realized even when the applied electric fields are removed from the
heterostructures. By sweeping electric fields across the heterostructure
appropriately, multiple resistive states can be achieved. These stable
resistive states result from the different stable remnant strain states of
substrate, which is related to the rearrangements of ferroelectric domain
structures in PMN-PT(111) substrate. The resistance switching tuned by electric
field in our work may have potential applications for novel electronic devices.
|
1403.6388v2
|
2015-02-23
|
Phonon residual resistance of pure crystals
|
Using the Boltzmann transport equation, we study phonon residual resistance
of perfect metallic crystals of a finite thickness $d$ along which a weak
constant electric field $E$ is applied. This resistance which is $\propto
d^{-5}E^{-3}$, is due to scattering of electric field-heated electrons with
emission of long-wave acoustic phonons. This electron-phonon interaction is
caused by zero-point vibrations of the atoms in the perfect crystal lattice
sites. Consideration is carried out for Cu, Ag and Au single crystals with the
thickness of about 1 cm, in the fields of the order of 1 mV/cm. Following the
Matthiessen rule, the resistance of the pure crystals the thicknesses of which
are much larger than the electron mean free path, is represented as the sum of
the impurity and phonon residual resistances. The condition on the thickness
$d$ and the field $E$ is found at which the phonon scattering of the
field-heated electrons dominates. Under this condition, the low-temperature
resistances of pure crystals do not depend on the their purity and determine
the phonon residual resistivity of the ideal crystals. The calculations are
performed for Cu with a purity of at least 99.9999%.
|
1502.06486v2
|
2016-02-25
|
Electric fields, weighting fields, signals and charge diffusion in detectors including resistive materials
|
In this report we discuss static and time dependent electric fields in
detector geometries with an arbitrary number of parallel layers of a given
permittivity and weak conductivity. We derive the Green's functions i.e. the
field of a point charge, as well as the weighting fields for readout pads and
readout strips in these geometries. The effect of 'bulk' resistivity on
electric fields and signals is investigated. The spreading of charge on thin
resistive layers is also discussed in detail, and the conditions for allowing
the effect to be described by the diffusion equation is discussed. We apply the
results to derive fields and induced signals in Resistive Plate Chambers,
Micromega detectors including resistive layers for charge spreading and
discharge protection as well as detectors using resistive charge division
readout like the MicroCAT detector. We also discuss in detail how resistive
layers affect signal shapes and increase crosstalk between readout electrodes.
|
1602.07949v1
|
2016-02-26
|
Investigating the Temperature Effects on Resistive Random Access Memory (RRAM) Devices
|
In this paper, we report the effect of filament radius and filament
resistivity on the saturated temperature of ZnO, TiO2, WO3 and HfO2 Resistive
Random Access Memory (RRAM) devices. We resort to the thermal reaction model of
RRAM for the present analysis. The results substantiate decrease in saturated
temperature with increase in the radius and resistivity of filament for the
investigated RRAM devices. Moreover, a sudden change in the saturated
temperature at a lower value of filament radius and resistivity is observed as
against the steady change at the medium and higher value of the filament radius
and resistivity. Results confirm the dependence of saturated temperature on the
filament size and resistivity in RRAM.
|
1602.08262v1
|
2017-11-02
|
Resistivity scaling model for metals with conduction band anisotropy
|
It is generally understood that the resistivity of metal thin films scales
with film thickness mainly due to grain boundary and boundary surface
scattering. Recently, several experiments and ab initio simulations have
demonstrated the impact of crystal orientation on resistivity scaling. The
crystal orientation cannot be captured by the commonly used resistivity scaling
models and a qualitative understanding of its impact is currently lacking. In
this work, we derive a resistivity scaling model that captures grain boundary
and boundary surface scattering as well as the anisotropy of the band
structure. The model is applied to Cu and Ru thin films, whose conduction bands
are (quasi-)isotropic and anisotropic respectively. After calibrating the
anisotropy with ab initio simulations, the resistivity scaling models are
compared to experimental resistivity data and a renormalization of the fitted
grain boundary reflection coefficient can be identified for textured Ru.
|
1711.00796v3
|
2021-02-05
|
Does Non-Genetic Heterogeneity Facilitate the Development of Genetic Drug Resistance?
|
Non-genetic forms of antimicrobial drug resistance can result from
cell-to-cell variability that is not encoded in the genetic material. Data from
recent studies also suggest that non-genetic mechanisms can facilitate the
development of genetic drug resistance. In this Perspective article, we
speculate on how the interplay between non-genetic and genetic mechanisms may
affect microbial adaptation and evolution during drug treatment. We argue that
cellular heterogeneity arising from fluctuations in gene expression, epigenetic
modifications, as well as genetic changes contributes to drug resistance at
different timescales, and that the interplay between these mechanisms may
influence the evolutionary dynamics of pathogen resistance. Accordingly,
developing a better understanding of non-genetic mechanisms in drug resistance
and how they interact with genetic mechanisms will enhance our ability to
combat antimicrobial resistance.
|
2102.03276v1
|
2023-04-10
|
T-square dependence of the electronic thermal resistivity in metallic strontium titanate
|
The temperature dependence of the phase space for electron-electron (e-e)
collisions leads to a T-square contribution to electrical resistivity of
metals. Umklapp scattering are identified as the origin of momentum loss due to
e-e scattering in dense metals. However, in dilute metals like lightly doped
strontium titanate, the origin of T-square electrical resistivity in absence of
Umklapp events is yet to be pinned down. Here, by separating electron and
phonon contributions to heat transport, we extract the electronic thermal
resistivity in niobium-doped strontium titanate and show that it also displays
a T-square temperature dependence. Its amplitude correlates with the T-square
electrical resistivity. The Wiedemann-Franz law strictly holds in the
zero-temperature limit, but not at finite-temperature, because the two T-square
prefactors are different by a factor of $\approx 3$, like in other Fermi
liquids. Recalling the case of $^3$He, we argue that T-square thermal
resistivity does not require Umklapp events. The approximate recovery of the
Wiedemann-Franz law in presence of disorder would account for a T-square
electrical resistivity without Umklapp.
|
2304.04841v2
|
2001-07-03
|
Low temperature resistance minimum in non-superconducting 3R-Nb_{1+x}S_2 and 3R-Ga_xNbS_2
|
We report the structural and electron transport properties of 3R-Nb_{1+x}S_2
(x >= .07) and 3R-Ga_xNbS_2 (.1 <= x <= .33) prepared as polycrystalline
pellets as well as single crystals grown by vapour transport. We observe a
resistance minimum in these compounds between 20-60 K, with the T_min
proportional to x. The resistance scales as rho/rho_min(T/T_min) between .2 <
T/T_min < 2 for different phases with x <= .25 whose resistivity differs by an
order of magnitude. Powder X-ray diffraction (XRD) also shows progressively
increasing intensity of superlattice lines with cation concentration. The
thermopower changes sign around the resistance minimum. The explanation of the
resistance minimum and the simultaneous rapid suppression of superconductivity
is sought in e-e scattering effects in the presence of cation disorder in these
narrow band anisotropic materials.
|
0107067v1
|
2006-08-11
|
Fracture resistance via topology optimisation
|
The fracture resistance of structures is optimised using the level-set
method. Fracture resistance is assumed to be related to the elastic energy
released by a crack propagating in a normal direction from parts of the
boundary which are in tension, and is calculated using the virtual crack
extension technique. The shape derivative of the fracture-resistance objective
function is derived. Two illustrative two-dimensional case studies are
presented: a hole in a plate subjected to biaxial strain; and a bridge fixed at
both ends subjected to a single load in which the compliance and fracture
resistance are jointly optimised. The structures obtained have rounded corners
and more material at places where they are in tension. Based on the results, we
propose that fracture resistance may be modelled more easily but less directly
by including a term proportional to surface area in the objective function, in
conjunction with non-linear elasticity where the Young's modulus in tension is
lower than in compression.
|
0608260v1
|
2016-05-19
|
Resistive Switching Phenomena of HfO2 Films Grown by MOCVD for Resistive Switching Memory Devices
|
The resistive switching phenomena of HfO2 films grown by metalorganic
chemical vapor deposition was studied for the application of ReRAM devices. In
the fabricated Pt/HfO2/TiN memory cells, the bipolar resistive switching
characteristics were observed, and the set and reset states were measured to be
as low as 7 uA and 4 uA, respectively, at VREAD = 1 V. Regarding the resistive
switching performance, the stable RS performance was observed under 40
repetitive dc cycling test with the small variations of set/reset voltages and
currents, and good retention characteristics over 105 s in both LRS and HRS.
These results show the possibility of MOCVD grown HfO2 films as a promising
resistive switching materials for ReRAM applications.
|
1605.06014v1
|
2020-02-10
|
Resistivity minimum in diluted metallic magnets
|
Resistivity minima are commonly seen in itinerant magnets and they are often
attributed to the Kondo effect. However, recent experiments are revealing an
increasing number of materials showing resistivity minima in the absence of
indications of Kondo singlet formation. In a previous work [Z. Wang, K. Barros,
G.-W. Chern, D. L. Maslov, and C. D. Batista, Phys. Rev. Lett. 117, 206601
(2016)], we demonstrated that the Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction can produce a classical spin liquid state at finite temperature,
whose resistivity increases with decreasing temperature. The classical spin
liquid exists over a relatively large temperature window because of the
frustrated nature of the RKKY interaction produced by a 2D electron gas. In
this work, we investigate the robustness of the RKKY-induced resistivity upturn
against site dilution, which provides an alternative, and more robust, way of
stabilizing the classical spin liquid state down to T=0. By using series
expansions and stochastic Landau-Lifshitz dynamics simulation, we show that
site dilution competes with thermal fluctuations and further stabilizes the
resistivity upturn, which is accompanied by a negative magnetoresistivity due
to suppression of the electron-spin scattering.
|
2002.03858v2
|
2021-10-06
|
Pinpointing the Dominant Component of Contact Resistance to Atomically Thin Semiconductors
|
Achieving good electrical contacts is one of the major challenges in
realizing devices based on atomically thin two-dimensional (2D) semiconductors.
Several studies have examined this hurdle, but a universal understanding of the
contact resistance and an underlying approach to its reduction are currently
lacking. In this work we expose the shortcomings of the classical contact
resistance model in describing contacts to 2D materials, and offer a correction
based on the addition of a lateral pseudo-junction resistance component (Rjun).
We use a combination of unique contact resistance measurements to
experimentally characterize Rjun for Ni contacts to monolayer MoS2. We find
that Rjun is the dominating component of the contact resistance in undoped 2D
devices and show that it is responsible for most of the back-gate bias and
temperature dependence. Our corrected model and experimental results help
understand the underlying physics of state-of-the-art contact engineering
approaches in the context of minimizing Rjun.
|
2110.02563v1
|
2023-11-14
|
Giant Resistance Switch in Twisted Transition Metal Dichalcogenide Tunnel Junctions
|
Resistance switching in multilayer structures are typically based on
materials possessing ferroic orders. Here we predict an extremely large
resistance switching based on the relative spin-orbit splitting in twisted
transition metal dichalcogenide (TMD) monolayers tunnel junctions. Because of
the valence band spin splitting which depends on the valley index in the
Brillouin zone, the perpendicular electronic transport through the junction
depends on the relative reciprocal space overlap of the spin-dependent Fermi
surfaces of both layers, which can be tuned by twisting one layer. Our quantum
transport calculations reveal a switching resistance of up to $10^6 \%$ when
the relative alignment of TMDs goes from $0^{\circ}$ to $60^{\circ}$ and when
the angle is kept fixed at $60^{\circ}$ and the Fermi level is varied. By
creating vacancies, we evaluate how inter-valley scattering affects the
efficiency and find that the resistance switching remains large ($10^4 \%$) for
typical values of vacancy concentration. Not only this resistance switching
should be observed at room temperature due to the large spin splitting, but our
results show how twist angle engineering and control of van der Waals
heterostructures could be used for next-generation memory and electronic
applications.
|
2311.08397v1
|
2000-10-24
|
Slater Transition in the Pyrochlore Cd2Os2O7
|
Cd2Os2O7 crystallizes in the pyrochlore structure and undergoes a
metal-insulator transition (MIT) near 226 K. We have characterized the MIT in
Cd2Os2O7 using X-ray diffraction, resistivity at ambient and high pressure,
specific heat, magnetization, thermopower, Hall coefficient, and thermal
conductivity. Both single crystals and polycrystalline material were examined.
The MIT is accompanied by no change in crystal symmetry and a change in unit
cell volume of less than 0.05%. The resistivity shows little temperature
dependence above 226 K, but increases by 3 orders of magnitude as the sample is
cooled to 4 K. The specific heat anomaly resembles a mean-field transition and
shows no hysteresis or latent heat. Cd2Os2O7 orders magnetically at the MIT.
The magnetization data is consistent with antiferromagnetic order, with a small
parasitic ferromagnetic component. The Hall and Seebeck coefficients are
consistent with a semiconducting gap opening at the Fermi energy at the MIT. We
have also performed electronic structure calculations on Cd2Os2O7. These
calculations indicate that Cd2Os2O7 is metallic, with a sharp peak in the
density of states at the Fermi energy. We intepret the data in terms of a
Slater transition. In this scenario, the MIT is produced by a doubling of the
unit cell due to the establishment of antiferromagnetic order. A Slater
transition-unlike a Mott transition-is predicted to be continuous, with a
semiconducting energy gap opening much like a BCS gap as the material is cooled
below $T_{MIT}$.
|
0010364v1
|
2004-12-17
|
Origin of Colossal Dielectric Response of Pr(0.6)Ca(0.4)MnO(3)
|
We report the detailed study of dielectric response of Pr(0.6)Ca(0.4)MnO(3)
(PCMO), member of manganite family showing colossal magnetoresistance.
Measurements have been performed on four polycrystalline samples and four
single crystals, allowing us to compare and extract the essence of dielectric
response in the material. High frequency dielectric function is found to be 30,
as expected for the perovskite material. Dielectric relaxation is found in
frequency window of 20Hz-1MHz at temperatures of 50-200K that yields to
colossal low-frequency dielectric function, i.e. static dielectric constant.
Static dielectric constant is always colossal, but varies considerably in
different samples from 1000 until 100000. The measured data can be simulated
very well by blocking (surface barrier) capacitance in series with sample
resistance. This indicates that the large dielectric constant in PCMO arises
from the Schottky barriers at electrical contacts. Measurements in magnetic
field and with d.c. bias support this interpretation. Weak anomaly at the
charge ordering temperature can also be attributed to interplay of sample and
contact resistance. We comment our results in the framework of related studies
by other groups.
|
0412473v3
|
2012-05-14
|
Bi2Te1.6S1.4 - a Topological Insulator in the Tetradymite Family
|
We describe the crystal growth, crystal structure, and basic electrical
properties of Bi2Te1.6S1.4, which incorporates both S and Te in its Tetradymite
quintuple layers in the motif -[Te0.8S0.2]-Bi-S-Bi-[Te0.8S0.2]-. This material
differs from other Tetradymites studied as topological insulators due to the
increased ionic character that arises from its significant S content.
Bi2Te1.6S1.4 forms high quality crystals from the melt and is the S-rich limit
of the ternary Bi-Te-S {\gamma}-Tetradymite phase at the melting point. The
native material is n-type with a low resistivity; Sb substitution, with
adjustment of the Te to S ratio, results in a crossover to p-type and resistive
behavior at low temperatures. Angle resolved photoemission study shows that
topological surface states are present, with the Dirac point more exposed than
it is in Bi2Te3 and similar to that seen in Bi2Te2Se. Single crystal structure
determination indicates that the S in the outer chalcogen layers is closer to
the Bi than the Te, and therefore that the layers supporting the surface states
are corrugated on the atomic scale.
|
1205.2924v1
|
2015-05-26
|
Transport, Magnetic and Vibrational Properties of Chemically Exfoliated Few Layer Graphene
|
We study the vibrational, magnetic and transport properties of Few Layer
Graphene (FLG) using Raman and electron spin resonance spectroscopy and
microwave conductivity measurements. FLG samples were produced using wet
chemical exfoliation with different post-processing, namely ultrasound
treatment, shear mixing, and magnetic stirring. Raman spectroscopy shows a low
intensity D mode which attests a high sample quality. The G mode is present at
$1580$ cm$^{-1}$ as expected for graphene. The 2D mode consists of 2 components
with varying intensities among the different samples. This is assigned to the
presence of single and few layer graphene in the samples. ESR spectroscopy
shows a main line in all types of materials with a width of about $1$ mT and
and a $g$-factor in the range of $2.005-2.010$. Paramagnetic defect centers
with a uniaxial $g$-factor anisotropy are identified, which shows that these
are related to the local sp$^2$ bonds of the material. All kinds of
investigated FLGs have a temperature dependent resistance which is compatible
with a small gap semiconductor. The difference in resistance is related to the
different grain size of the samples.
|
1505.06857v1
|
2017-02-10
|
Highly wear-resistant and low-friction Si3N4 composites by addition of graphene nanoplatelets approaching the 2D limit
|
Graphene nanoplatelets (GNPs) have emerged as one of the most promising
filler materials for improving the tribological performance of ceramic
composites due to their outstanding solid lubricant properties as well as
mechanical and thermal stability. Yet, the addition of GNPs has so far provided
only a very limited improvement in the tribological properties of ceramics,
particularly concerning the reduction of their friction coefficient. This is
most likely due to the challenges of achieving a lubricating and protecting
tribo-film through a high GNP coverage of the exposed surfaces. Here we show
that this can be achieved by efficiently increasing the exfoliation degree of
GNPs down to the few-layer (FL) range. By employing FL-GNPs as filler material,
the wear resistance of Si3N4 composites can be increased by about twenty times,
the friction coefficient reduced to nearly its half, while the other mechanical
properties are also preserved or improved. Using confocal Raman microscopy, we
were able to demonstrate the formation of a continuous FL- GNP tribo-film,
already at 5wt% FL-GNP content.
|
1702.03153v1
|
2017-12-16
|
Stress-dependent electrical transport and its universal scaling in granular materials
|
We experimentally and numerically examine stress-dependent electrical
transport in granular materials to elucidate the origins of their universal
dielectric response. The ac responses of granular systems under varied
compressive loadings consistently exhibit a transition from a resistive plateau
at low frequencies to a state of nearly constant loss at high frequencies. By
using characteristic frequencies corresponding to the onset of conductance
dispersion and measured direct-current resistance as scaling parameters to
normalize the measured impedance, results of the spectra under different stress
states collapse onto a single master curve, revealing well-defined
stress-independent universality. In order to model this electrical transport, a
contact network is constructed on the basis of prescribed packing structures,
which is then used to establish a resistor-capacitor network by considering
interactions between individual particles. In this model the
frequency-dependent network response meaningfully reproduces the experimentally
observed master curve exhibited by granular materials under various normal
stress levels indicating this universal scaling behaviour is found to be
governed by i) interfacial properties between grains and ii) the network
configuration. The findings suggest the necessity of considering contact
morphologies and packing structures in modelling electrical responses using
network-based approaches.
|
1712.05938v2
|
2020-04-06
|
Spin Hall magnetoresistance in antiferromagnetic insulators
|
Antiferromagnetic materials promise improved performance for spintronic
applications, as they are robust against external magnetic field perturbations
and allow for faster magnetization dynamics compared to ferromagnets. The
direct observation of the antiferromagnetic state, however, is challenging due
to the absence of a macroscopic magnetization. Here, we show that the spin Hall
magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic spin
structure via simple electrical transport experiments by investigating the
easy-plane antiferromagnetic insulators $\alpha$-Fe2O3 (hematite) and NiO in
bilayer heterostructures with a Pt heavy metal top electrode. While rotating an
external magnetic field in three orthogonal planes, we record the longitudinal
and the transverse resistivities of Pt and observe characteristic resistivity
modulations consistent with the SMR effect. We analyze both their amplitude and
phase and compare the data to the results from a prototypical collinear
ferrimagnetic Y3Fe5O12/Pt bilayer. The observed magnetic field dependence is
explained in a comprehensive model, based on two magnetic sublattices and
taking into account magnetic field-induced modifications of the domain
structure. Our results show that the SMR allows us to understand the spin
configuration and to investigate magnetoelastic effects in antiferromagnetic
multi-domain materials. Furthermore, in $\alpha$-Fe2O3/Pt bilayers, we find an
unexpectedly large SMR amplitude of $2.5 \times 10^{-3}$, twice as high as for
prototype Y3Fe5O12/Pt bilayers, making the system particularly interesting for
room-temperature antiferromagnetic spintronic applications.
|
2004.02639v2
|
2017-04-11
|
Transfer of Vertical Graphene Nanosheets onto Flexible Substrates towards Supercapacitor Application
|
Vertical graphene nanosheets (VGNs) are the material of choice for
next-generation electronic device applications. The growing demand for flexible
devices in electronic industry brings in restriction on growth temperature of
the material of interest. However, VGNs with better structural quality is
usually achieved at high growth temperatures. The difficulty associated with
the direct growth on flexible substrates can overcome by adopting an effective
strategy of transferring the well grown VGNs onto arbitrary flexible substrates
through soft chemistry route. Hence, we demonstrated a simple, inexpensive and
scalable technique for the transfer of VGNs onto arbitrary substrates without
disrupting its morphology and structural properties. After transfer, the
morphology, chemical structure and electronic properties are analyzed by
scanning electron microscopy, Raman spectroscopy and four probe resistive
methods, respectively. Associated characterization investigation indicates the
retention of morphological, structural and electrical properties of transferred
VGNs compared to as-grown one. Furthermore the storage capacity of the VGNs
transferred onto flexible substrates is also examined. A very lower sheet
resistance of 0.67 kOhm/sq. and excellent supercapacitance of 158
micro-Farrad/cm2 with 91.4% retention after 2000 cycles confirms the great
prospective of this damage-free transfer approach of VGNs for flexible
nanoelectronic device applications
|
1704.03227v1
|
2019-03-26
|
Isostructural Mott Transition in 2D honeycomb antiferromagnet V$_{0.9}$PS$_3$
|
We present the observation of an isostructural Mott insulator-metal
transition in van-der-Waals honeycomb antiferromagnet V$_{0.9}$PS$_3$ through
high-pressure x-ray diffraction and transport measurements. The MPX$_3$ family
of magnetic van-der-Waals materials (M denotes a first row transition metal and
X either S or Se) are currently the subject of broad and intense attention, but
the vanadium compounds have until this point not been studied beyond their
basic properties. We observe insulating variable-range-hopping type resistivity
in V$_{0.9}$PS$_3$, with a gradual increase in effective dimensionality with
increasing pressure, followed by a transition to a metallic resistivity
temperature dependence between 112 and 124 kbar. The metallic state
additionally shows a low-temperature upturn we tentatively attribute to the
Kondo Effect. A gradual structural distortion is seen between 26-80 kbar, but
no structural change at higher pressures corresponding to the insulator-metal
transition. We conclude that the insulator-metal transition occurs in the
absence of any distortions to the lattice - an isostructural Mott transition in
a new class of two-dimensional material, and in strong contrast to the behavior
of the other MPX$_3$ compounds.
|
1903.10971v1
|
2019-03-29
|
Substrate Mediated Synthesis of Ti-Si-N Nano-and-Micro Structures for Optoelectronic Applications
|
Being one of the strongest materials, ternary TiSiN exhibits a very
interesting family of binary transition metal nitride and silicide systems. A
novel technique to fabricate morphologically fascinating nano and micro
structures of TiSiN is reported here. The referred TiSiN films, majorly
constituted with cubic TiN phase, are enriched with crystalline nanoparticles,
micro-flowers and faceted micro-crystals which possess attractive
functionalities towards plasmon mediated optoelectronic applications.
Reactivity of titanium to silicon nitride based dielectric topping on the
substrate at high temperature plays the key role in nitride formation for the
demonstrated protocol. The optoelectronic response for these morphologically
enriched composite films indicates an influential role of photo-induced surface
plasmon polaritons on their dc transport properties. A plasmonically tuned
resistive switching, controlled by the surface morphology in association with
the film thickness, is observed under light illumination. Using Drudes modified
frequency dependent bulk electron scattering rates and surface mediated
SPPs-electron scattering rates, a generic model is proposed for addressing
unambiguously the increased device resistance in response to light. The
featured synthesis process opens a new direction towards the growth of
transition metal nitrides while the proposed model serves as a basic platform
to understand photo-induced electron scattering mechanisms in metal.
|
1903.12376v1
|
2020-01-06
|
Controlled introduction of defects to delafossite metals by electron irradiation
|
The delafossite metals PdCoO$_{2}$, PtCoO$_{2}$ and PdCrO$_{2}$ are among the
highest conductivity materials known, with low temperature mean free paths of
tens of microns in the best as-grown single crystals. A key question is whether
these very low resistive scattering rates result from strongly suppressed
backscattering due to special features of the electronic structure, or are a
consequence of highly unusual levels of crystalline perfection. We report the
results of experiments in which high energy electron irradiation was used to
introduce point disorder to the Pd and Pt layers in which the conduction
occurs. We obtain the cross-section for formation of Frenkel pairs in absolute
units, and cross-check our analysis with first principles calculations of the
relevant atomic displacement energies. We observe an increase of resistivity
that is linear in defect density with a slope consistent with scattering in the
unitary limit. Our results enable us to deduce that the as-grown crystals
contain extremely low levels of in-plane defects of approximately $0.001\%$.
This confirms that crystalline perfection is the most important factor in
realizing the long mean free paths, and highlights how unusual these
delafossite metals are in comparison with the vast majority of other
multi-component oxides and alloys. We discuss the implications of our findings
for future materials research.
|
2001.01471v1
|
2020-01-17
|
Wettability and surface energy of parylene F
|
Parylenes are barrier materials employed as protective layers. However, many
parylenes are unsuitable for applications under harsh conditions. A new
material, parylene F, demonstrates considerable potential for a wide range of
applications due to its high temperature and UV resistance. For the first time,
the wettability and surface energy of parylene F were investigated to determine
the feasibility of parylene F as an alternative to the commonly employed
parylene C. The results show that parylene F has a hydrophobic surface with a
water contact angle of 109.63 degrees. We found that 3.5 ul probe liquid is an
optimal value for the contact angle measurement of parylene F. Moreover, we
found that the Owens-Wendt-Kaelble and the Lifshitz-van der Waals/acid-base
approaches are unsuitable for determining the surface energy of parylene F,
whereas an approach based on the limitless liquid-solid interface wetting
system is compatible. Furthermore, the results show that parylene F has a
surface energy of 39.05 mJ/m2. Considering the improved resistance, relatively
low cost, and the desirable properties, parylene F can replace parylene C for
applications under harsh conditions.
|
2001.06146v2
|
2020-01-24
|
Adaptive hard and tough mechanical response in single-crystal B1 VNx ceramics via control of anion vacancies
|
High hardness and toughness are generally considered mutually exclusive
properties for single-crystal ceramics. Combining experiments and ab initio
molecular dynamics (AIMD) atomistic simulations at room temperature, we
demonstrate that both the hardness and toughness of single-crystal
NaCl-structure VNx/MgO(001) thin films are simultaneously enhanced through the
incorporation of anion vacancies. Nanoindentation results show that VN0.8, here
considered as representative understoichiometric VNx system, is ~20% harder, as
well as more resistant to fracture than stoichiometric VN samples. AIMD
modeling of VN and VN0.8 supercells subjected to [001] and [110] elongation
reveal that the tensile strengths of the two materials are similar.
Nevertheless, while the stoichiometric VN phase systematically cleaves in a
brittle manner at tensile yield points, the understoichiometric compound
activates transformation-toughening mechanisms that dissipate accumulated
stresses. AIMD simulations also show that VN0.8 exhibits an initially greater
resistance to both {110}<1-10> and {111}<1-10> shear deformation than VN.
However, for progressively increasing shear strains, the VN0.8 mechanical
behavior gradually evolves from harder to more ductile than VN. The transition
is mediated by anion vacancies, which facilitate {110}<1-10> and {111}<1-10>
lattice slip by reducing activation shear stresses by as much as 35%.
Electronic-structure analyses show that the two-regime hard/tough mechanical
response of VN0.8 primarily stems from its intrinsic ability to transfer d
electrons between 2nd-neighbor and 4th-neighbor (i.e., across vacancy sites)
V-V metallic states. Our work offers a route for electronic-structure design of
hard materials in which a plastic mechanical response is triggered with
loading.
|
2001.08933v2
|
2020-05-14
|
Gate- and Light-Tunable Negative Differential Resistance with High Peak Current Density in 1T-TaS$_2$/2H-MoS$_2$ T-Junction
|
Metal-based electronics is attractive for fast and radiation-hard electronic
circuits and remains one of the longstanding goals for researchers. The
emergence of 1T-TaS$_2$, a layered material exhibiting strong charge density
wave (CDW) driven resistivity switching that can be controlled by an external
stimulus such as electric field and optical pulses, has triggered a renewed
interest in metal-electronics. Here we demonstrate a negative differential
resistor (NDR) using electrically driven CDW phase transition in an
asymmetrically designed T-junction made up of 1T-TaS$_2$/2H-MoS$_2$ van der
Waals heterostructure. The principle of operation of the proposed device is
governed by majority carrier transport and is distinct from usual NDR devices
employing tunneling of carriers, thus avoids the bottleneck of weak tunneling
efficiency in van der Waals heterojunctions. Consequently, we achieve a peak
current density in excess of $10^5$ nA$\mu$m$^{-2}$, which is about two orders
of magnitude higher than that obtained in typical layered material based NDR
implementations. The peak current density can be effectively tuned by an
external gate voltage as well as photo-gating. The device is robust against
ambiance-induced degradation and the characteristics repeat in multiple
measurements over a period of more than a month. The findings are attractive
for the implementation of active metal-based functional circuits.
|
2005.07146v2
|
2021-05-23
|
Substrate-Versatile Direct-Write Printing of Carbon Nanotube-Based Flexible Conductors, Circuits, and Sensors
|
Printed electronics rely on the deposition of conductive liquid inks,
typically onto polymeric or paper substrates. Among available conductive
fillers for use in electronic inks, carbon nanotubes (CNTs) have high
conductivity, low density, processability at low temperatures, and intrinsic
mechanical flexibility. However, the electrical conductivity of printed CNT
structures has been limited by CNT quality and concentration, and by the need
for nonconductive modifiers to make the ink stable and extrudable. This study
introduces a polymer-free, printable aqueous CNT ink, and presents the
relationships between printing resolution, ink rheology, and ink-substrate
interactions. A model is constructed to predict printed feature sizes on
impermeable substrates based on Wenzel wetting. Printed lines have conductivity
up to 10,000 S/m. The lines are flexible, with < 5% change in DC resistance
after 1,000 bending cycles, and <3% change in DC resistance with a bending
radius down to 1 mm. Demonstrations focus on (i) conformality, via printing
CNTs onto stickers that can be applied to curved surfaces, (ii) interactivity
using a CNT-based button printed onto folded paper structure, and (iii)
capacitive sensing of liquid wicking into the substrate itself. Facile
integration of surface mount components on printed circuits is enabled by the
intrinsic adhesion of the wet ink.
|
2105.10942v1
|
2021-10-05
|
Nanoscale devices with superconducting electrodes to locally channel current in 3D Weyl semimetals
|
We report on the fabrication of nano-devices on the \hkl[-1 0 1] surface of a
Weyl semimetal, a macroscopic crystal of TaAs, and low-temperature transport
measurements. We can implement electron beam lithography by peeling off and
transferring the resist for nanofabrication onto the irregular crystal. We
fabricate the device electrodes with superconducting Niobium nitride (NbN) to
control the current flow through the intended active area of the devices. Our
device structure enables the reduction of the current jetting effect, and we
demonstrate the negative magnetoresistance measurement as a function of angle.
The high field magnetotransport show three distinct oscillation frequencies
corresponding to the three bands at the Fermi level. Resistance measured in the
low magnetic field shows the usual weak anti-localization dip near the
zero-field -- a signature of a Weyl material. Our method of fabricating devices
with superconducting electrodes provides a way to probe the electrical
properties of macroscopic single crystals at the nanoscale. As we use
conventional lithographic techniques for patterning, this method can be
extended to a wide gamut of electrode materials and a large class of 3D quantum
materials.
|
2110.01793v1
|
2021-11-29
|
Doped graphene/carbon black hybrid catalyst giving enhanced oxygen reduction reaction activity with high resistance to corrosion in proton exchange membrane fuel cells
|
Nitrogen doping of the carbon is an important method to improve the
performance and durability of catalysts for proton exchange membrane fuel cells
by platinum-nitrogen and carbon-nitrogen bonds. This study shows that p-phenyl
groups and graphitic N acting bridges linking platinum and the graphene/carbon
black (the ratio graphene/carbon black=2/3) hybrid support materials achieved
the average size of platinum nanoparticles with (4.88 +/- 1.79) nm. It improved
the performance of the lower-temperature hydrogen fuel cell up to 0.934 W cm-2
at 0.60 V, which is 1.55 times greater than that of commercial Pt/C. Doping
also enhanced the interaction between Pt and the support materials, and the
resistance to corrosion, thus improving the durability of the low-temperature
hydrogen fuel cell with a much lower decay of 10 mV at 0.80 A cm-2 after 30k
cycles of an in-situ accelerated stress test of catalyst degradation than that
of 92 mV in Pt/C, which achieves the target of Department of Energy (<30 mV).
Meanwhile, Pt/NrEGO2-CB3 remains 78% of initial power density at 1.5 A cm-2
after 5k cycles of in-situ accelerated stress test of carbon corrosion, which
is more stable than the power density of commercial Pt/C, keeping only 54%
after accelerated stress test.
|
2111.14648v1
|
2022-03-22
|
Traps and transport resistance: the next frontier for stable state-of-the-art non-fullerene acceptor solar cells
|
Stability is one of the most important challenges facing organic solar cells
(OSC) on their path to commercialization. In the high-performance material
system PM6:Y6 studied here, investigate degradation mechanisms of inverted
photovoltaic devices. We have identified two distinct degradation pathways: one
requires presence of both illumination and oxygen and features a short-circuit
current reduction, the other one is induced thermally and marked by severe
losses of open-circuit voltage and fill factor. We focus our investigation on
the thermally accelerated degradation. Our findings show that bulk material
properties and interfaces remain remarkably stable, however, aging-induced
defect state formation in the active layer remains the primary cause of thermal
degradation. The increased trap density leads to higher non-radiative
recombination, which limits open-circuit voltage and lowers charge carrier
mobility in the photoactive layer. Furthermore, we find the trap-induced
transport resistance to be the major reason for the drop in fill factor. Our
results suggest that device lifetimes could be significantly increased by
marginally suppressing trap formation, leading to a bright future for OSC.
|
2203.11905v1
|
2022-07-05
|
Phonons behave like Electrons in the Thermal Hall Effect of the Cuprates
|
The thermal Hall effect, which arises when heat flows transverse to an
applied thermal gradient, has become an important observable in the study of
quantum materials. Recent experiments found a large thermal Hall conductivity
$\kappa_{xy}$ in many high-temperature cuprate superconductors, including deep
inside the Mott insulator, but the underlying mechanism remains unknown. Here,
we uncover a surprising linear temperature dependence for the inverse thermal
Hall resistivity, $1/\rho_H=-\kappa_{xx}^2/\kappa_{xy}$, in the Mott insulating
cuprates $\mathrm{La_2CuO_4}$ and $\mathrm{Sr_2CuO_2Cl_2}$. We also find this
linear scaling in the pseudogap state of Nd-LSCO in the out-of-plane direction,
highlighting the importance of phonons. On the electron-doped side, the linear
inverse thermal Hall signal emerges in NCCO and PCCO at various dopings,
including in the strange metal. Although such dependence arises in the simple
Drude model for itinerant electrons, its origin is unclear in strongly
correlated Mott insulating or pseudogap states. We perform a Boltzmann analysis
for phonons that incorporates skew-scattering, and we are able to identify
regimes where a linear $T$ inverse Hall resistivity appears. Finally, we
suggest future experiments that would further our fundamental understanding of
heat transport in the cuprates, and other quantum materials.
|
2207.02240v3
|
2022-08-28
|
Multiferroic Ti$_3$C$_2$T$_x$ MXene with Tunable Ferroelectric-controlled High Performance Resistive Memory Devices
|
Multiferroic (MF) devices based on simultaneous ferroelectric and
ferromagnetic phenomena are considered to be promising candidates for future
bi-functional micro/nano-electronics. The multiferroic phenomena in
two-dimensional materials is rarely reported in literature. We reported a
simple approach to reveal frequency-dependent ferroelectricity and
mutiferroicity in Ti$_3$C$_2$T$_x$ MXene film at room-temperature. To study the
frequency and poling effect on ferroelectricity as well as multiferroicity, we
performed electric polarization vs. electric field measurement at different
external frequencies measured under zero and non-zero static magnetic fields.
In order to further investigate this effect, the magneto-electric (ME) coupling
was also performed to confirm the multiferroic nature of our synthesized
Ti$_3$C$_2$T$_x$ MXene film. The ferroelectric hysteresis effect was attributed
to the switching of electric domain walls under low frequencies that continue
to respond to at much extent to the higher frequencies. The coupling between
disordered electric dipoles with local spin moments could cause presence of
strong magneto-electric coupling. Moreover, the bipolar resistive switching in
trilayer memory devices also supports the ferroelectric behavior of HT-
Ti$_3$C$_2$T$_x$ MXene film and showed uniform repeatability in switching
behavior due to minimum dielectric loss inside ferroelectric
HT-Ti$_3$C$_2$T$_x$ MXene along with improved on/off ratio in comparison to
non-ferroelectric Ti$_3$C$_2$T$_x$ MXene. The unique multiferroic behavior
along with ferroelectric-tuned memristor devices reported here at room
temperature will help understand the intrinsic nature of 2D materials and will
establish novel data storage devices.
|
2208.13128v1
|
2023-08-05
|
Graphene-based RRAM devices for neural computing
|
Resistive random access memory (RRAM) is very well known for its potential
application in in-memory and neural computing. However, they often have
different types of device-to-device and cycle-to-cycle variability. This makes
it harder to build highly accurate crossbar arrays.Traditional RRAM designs
make use of various filament-based oxide materials for creating a channel which
is sandwiched between two electrodes to form a two-terminal structure. They are
often subjected to mechanical and electrical stress over repeated
read-and-write cycles. The behavior of these devices often varies in practice
across wafer arrays over these stress when fabricated. The use of emerging 2D
materials is explored to improve electrical endurance, long retention In review
time, high switching speed, and fewer power losses. This study provides an
in-depth exploration of neuro-memristive computing and its potential
applications, focusing specifically on the utilization of graphene and 2D
materials in resistive random-access memory (RRAM) for neural computing. The
paper presents a comprehensive analysis of the structural and design aspects of
graphene-based RRAM, along with a thorough examination of commercially
available RRAM models and their fabrication techniques. Furthermore, the study
investigates the diverse range of applications that can benefit from
graphene-based RRAM devices.
|
2308.02767v1
|
2023-08-06
|
Mechanically exfoliated low-layered [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]: A single-crystalline p-type transparent conducting oxide
|
Transparent conducting oxides (TCOs) are essential components of
optoelectronic devices and various materials have been explored for highly
efficient TCOs having a combination of high transmittance and low sheet
resistance. Here, we focus on a misfit thermoelectric oxide
[Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] and fabricate the transparent low-layered
crystals by a mechanical tape-peeling method using the single-crystalline
samples. From the transmittance measurement, we find that the thickness of
low-layered samples is several orders of hundred nanometers, which is
comparable with the estimation from the scanning electron microscopy images.
Compared to the previous results on the polycrystalline and $c$-axis oriented
transparent films, the electrical resistivity is reduced owing to the
single-crystalline nature. The figure of merit for the transparent conducting
materials in the present low-layered samples is then evaluated to be higher
than the values in the previous reports. The present results on the low-layered
single-crystalline [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] may offer a unique class
of multi-functional transparent thermoelectric oxides.
|
2308.03221v1
|
2023-09-06
|
Robust Sandwiched B/TM/B Structures by Metal Intercalating into Bilayer Borophene Leading to Excellent Hydrogen Evolution Reaction
|
Bilayer borophene, very recently synthesized on Ag and Cu, possesses
extremely flat large surface and excellent conductivity. Besides, the van der
Waals gap of bilayer borophene can be intercalated by metal atoms, thereby
tailoring the properties of bilayer borophene. Herein, we propose that
sandwiched B/TM/B (TM=Co, Ni, Cu, Pd) could be a new 2D formation by transiton
metal atoms intercalated into bilayer borophene network, it is quiet robust
with both energetic, structural and thermal stability, and exhibits heat
resistance of at least 1300 K. Besides, it is novel platform for
electrocatalytic hydrogen evolution reaction (HER). The interecalation metal
atom serves as single-atomic catalyst, which acting the nonmetal boron layers.
Beyond that, the transtion metal is protected by outside boron layers from
being corroded by acidic/alkaline solution. B/Cux/B, B/Pdx/B and B/Alx/B with
different metal coverage exhibit defect-independent extremely low HER free
energy in the range of -0.162 ~ 0.179 eV, -0.134 ~ 0.183 eV and -0.082 ~ 0.086
eV which are comparable to noble metal Pt. Combining excellent conduction, high
structural and thermal stability, low resistance to intercalated behaviour,
effortless water splitting process, excellent defect-independent catalytic
performance, cheapness and abundance of raw materials, free of corrodation, 2D
sandwiched B/TM/B (TM=Co, Ni, Cu, Pd) is believed to promising for
electrocatalytic HER applications.
|
2309.02963v1
|
2023-11-22
|
Rashba-splitting-induced topological flat band detected by anomalous resistance oscillations beyond the quantum limit in ZrTe$_5$
|
Topological flat band, on which the kinetic energy of topological electrons
is quenched, represents a platform for investigating the topological properties
of correlated systems. Recent experimental studies on flattened electronic
bands have mainly concentrated on 2-dimensional materials created by van der
Waals heterostructure-based engineering. Here, we report the observation of a
topological flat band formed by polar-distortion-assisted Rashba splitting in a
3-dimensional Dirac material ZrTe$_5$. The polar distortion and resulting
Rashba splitting on the band are directly detected by torque magnetometry and
the anomalous Hall effect, respectively. The local symmetry breaking further
flattens the band, on which we observe resistance oscillations beyond the
quantum limit. These oscillations follow the temperature dependence of the
Lifshitz-Kosevich formula but are evenly distributed in B instead of 1/B in
high magnetic fields. Furthermore, the cyclotron mass anomalously gets enhanced
about 10$^2$ times at field ~20 T. These anomalous properties of oscillations
originate from a topological flat band with quenched kinetic energy. The
topological flat band, realized by polar-distortion-assisted Rashba splitting
in the 3-dimensional Dirac system ZrTe$_5$, signifies an intrinsic platform
without invoking moir\'e or order-stacking engineering, and also opens the door
for studying topologically correlated phenomena beyond the dimensionality of
two.
|
2311.13346v2
|
2024-04-19
|
Machine Learning-guided accelerated discovery of structure-property correlations in lean magnesium alloys for biomedical applications
|
Magnesium alloys are emerging as promising alternatives to traditional
orthopedic implant materials thanks to their biodegradability,
biocompatibility, and impressive mechanical characteristics. However, their
rapid in-vivo degradation presents challenges, notably in upholding mechanical
integrity over time. This study investigates the impact of high-temperature
thermal processing on the mechanical and degradation attributes of a lean
Mg-Zn-Ca-Mn alloy, ZX10. Utilizing rapid, cost-efficient characterization
methods like X-ray diffraction and optical, we swiftly examine microstructural
changes post-thermal treatment. Employing Pearson correlation coefficient
analysis, we unveil the relationship between microstructural properties and
critical targets (properties): hardness and corrosion resistance. Additionally,
leveraging the least absolute shrinkage and selection operator (LASSO), we
pinpoint the dominant microstructural factors among closely correlated
variables. Our findings underscore the significant role of grain size
refinement in strengthening and the predominance of the ternary Ca2Mg6Zn3 phase
in corrosion behavior. This suggests that achieving an optimal blend of
strength and corrosion resistance is attainable through fine grains and reduced
concentration of ternary phases. This thorough investigation furnishes valuable
insights into the intricate interplay of processing, structure, and properties
in magnesium alloys, thereby advancing the development of superior
biodegradable implant materials.
|
2404.13022v1
|
2010-02-08
|
Processing and Characterization of Multiferroic Bi-relaxors
|
We compare chemical solution deposition (CSD), and pulsed-laser-deposition
(PLD), specimens of the new room-temperature, single-phase, multiferroic
magnetoelectric, [PbFe2/3W1/3O3]x[PbZr0.53Ti0.47O3]1-x (PZTFWx ~ 0.40<x<0.20)
with polarization, loss (<1%), and resistivity (typically 108 ohm.cm) equal to
or superior to BiFeO3. Single phase polycrystalline multiferroics PZTFWx thin
films were fabricated on platinized silicon substrate by CSD and as epitaxial
single-crystal films on MgO substrate by PLD. High dielectric constants (1200-
3000), high polarization (30 - 60 micro C/cm2), weak saturation magnetization
(0.48 - 4.53 emu/cm3), a broad dielectric temperature peak, high-frequency
dispersion, low dielectric loss and low leakage current were observed in these
materials, suggesting the family as candidates for room-temperature
multiferroic devices. The ferroelectric switching in these materials can be
suppressed or quenched with applied magnetic field.
|
1002.1637v1
|
2012-08-20
|
Topological insulator Bi2Te3 films synthesized by metal organic chemical vapor deposition
|
Topological insulator (TI) materials such as Bi2Te3 and Bi2Se3 have attracted
strong recent interests. Large scale, high quality TI thin films are important
for developing TI-based device applications. In this work, structural and
electronic properties of Bi2Te3 thin films deposited by metal organic chemical
vapor deposition (MOCVD) on GaAs (001) substrates were characterized via X-ray
diffraction (XRD), Raman spectroscopy, angle-resolved photoemission
spectroscopy (ARPES), and electronic transport measurements. The characteristic
topological surface states (SS) with a single Dirac cone have been clearly
revealed in the electronic band structure measured by ARPES, confirming the TI
nature of the MOCVD Bi2Te3 films. Resistivity and Hall effect measurements have
demonstrated relatively high bulk carrier mobility of ~350 cm^2/Vs at 300K and
~7,400 cm^2/Vs at 15 K. We have also measured the Seebeck coefficient of the
films. Our demonstration of high quality topological insulator films grown by a
simple and scalable method is of interests for both fundamental research and
practical applications of thermoelectric and TI materials.
|
1208.4071v1
|
2017-10-03
|
Large thermoelectric figure of merit in graphene layered devices at low temperature
|
Nanostructured materials have emerged as an alternative to enhance the figure
of merit (ZT) of thermoelectric (TE) devices. Graphene exhibits a high
electrical conductivity (in-plane) that is necessary for a high ZT; however,
this effect is countered by its impressive thermal conductivity. In this work
TE layered devices composed of electrochemically exfoliated graphene (EEG) and
a phonon blocking material such as poly (3,4-ethylenedioxythiophene)polystyrene
sulfonate (PEDOT:PSS), polyaniline (PANI) and gold nanoparticles (AuNPs) at the
interface were prepared. The figure of merit, ZT, of each device was measured
in the cross-plane direction using the Transient Harman Method (THM) and
complemented with AFM-based measurements. The results show remarkable high ZT
values (0.81 < ZT < 2.45) that are directly related with the topography,
surface potential, capacitance gradient and resistance of the devices at the
nanoscale.
|
1710.01152v1
|
2014-08-07
|
A broadband silicon quarter-wave retarder for far-infrared spectroscopic circular dichroism
|
The high brightness, broad spectral coverage and pulsed characteristics of
infrared synchrotron radiation enable time-resolved spectroscopy under
throughput-limited optical systems, as can occur with the high-field magnet
cryostat systems used to study electron dynamics and cyclotron resonance by
far-infrared techniques. A natural extension for magnetospectroscopy is to
sense circular dichroism, i.e. the difference in a material's optical response
for left and right circularly polarized light. A key component for
spectroscopic circular dichroism is an achromatic 1/4 wave retarder functioning
over the spectral range of interest. We report here the development of an
in-line retarder using total internal reflection in high-resistivity silicon.
We demonstrate its performance by distinguishing electronic excitations of
different handednesses for GaAs in a magnetic field. This 1/4 wave retarder is
expected to be useful for far-infrared spectroscopy of circular dichroism in
many materials.
|
1408.1650v1
|
2018-09-05
|
Improving the performance of Ge$_2$Sb$_2$Te$_5$ materials via nickel doping: Towards RF-compatible phase-change devices
|
High-speed electrical switching of Ge2Sb2Te5 (GST) remains a challenging task
due to the large impedance mismatch between the low-conductivity amorphous
state and the high-conductivity crystalline state. In this letter, we
demonstrate an effective doping scheme using nickel to reduce the resistivity
contrast between the amorphous and crystalline states by nearly three orders of
magnitude. Most importantly, our results show that doping produces the desired
electrical performance without adversely affecting the film's optical
properties. The nickel doping level is approximately 2% and the lattice
structure remains nearly unchanged when compared with undoped-GST. The
refractive indices at amorphous and crystalline states were obtained using
ellipsometry which echoes the results from XRD. The material's thermal
transport properties are measured using time-domain thermoreflectance (TDTR),
showing no change upon doping. The advantages of this doping system will open
up new opportunities for designing electrically reconfigurable high speed
optical elements in the near-infrared spectrum.
|
1810.01964v1
|
2012-01-04
|
Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials
|
We found that an optimized mixture of graphene and multilayer graphene -
produced by the high-yield inexpensive liquid-phase-exfoliation technique - can
lead to an extremely strong enhancement of the cross-plane thermal conductivity
K of the composite. The "laser flash" measurements revealed a record-high
enhancement of K by 2300 % in the graphene-based polymer at the filler loading
fraction f =10 vol. %. It was determined that a relatively high concentration
of single-layer and bilayer graphene flakes (~10-15%) present simultaneously
with thicker multilayers of large lateral size (~ 1 micrometer) were essential
for the observed unusual K enhancement. The thermal conductivity of a
commercial thermal grease was increased from an initial value of ~5.8 W/mK to
K=14 W/mK at the small loading f=2%, which preserved all mechanical properties
of the hybrid. Our modeling results suggest that graphene - multilayer graphene
nanocomposite used as the thermal interface material outperforms those with
carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and
lower Kapitza resistance at the graphene - matrix interface.
|
1201.0796v1
|
2016-03-07
|
High-pressure melt growth and transport properties of SiP, SiAs, GeP, and GeAs 2D layered semiconductors
|
Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of
2D layered semiconductors. We have succeeded in growing bulk single crystals of
these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil
hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs
were obtained, and could be exfoliated into 2D flakes. Small and brittle
crystals of SiP were yielded by this method. High-pressure sintered
polycrystalline SiP and GeAs have also been successfully used as a precursor in
the Chemical Vapor Transport growth of these crystals in the presence of
I$_{2}$ as a transport agent. All compounds are found to crystallize in the
expected layered structure and do not undergo any structural transition at low
temperature, as shown by Raman spectroscopy down to T=5K. All materials exhibit
a semiconducting behavior. The electrical resistivity of GeP, GeAs and SiAs is
found to depend on temperature following a 2D-Variable Range Hopping conduction
mechanism. The availability of bulk crystals of these compounds opens new
perspectives in the field of 2D semiconducting materials for device
applications.
|
1603.02134v1
|
2017-05-01
|
High pressure floating-zone growth of perovskite nickelate LaNiO3 single crystals
|
We report the first single crystal growth of the correlated metal LaNiO3
using a high-pressure optical-image floating zone furnace. The crystals were
studied using single crystal/powder x-ray diffraction, resistivity, specific
heat, and magnetic susceptibility. The availability of bulk LaNiO3 crystals
will (i) promote deep understanding in this correlated material, including the
mechanism of enhanced paramagnetic susceptibility, and (ii) provide rich
opportunities as a substrate for thin film growth such as important
ferroelectric and/or multiferroic materials. This study demonstrates the power
of high pO2 single crystal growth of nickelate perovskites and correlated
electron oxides more generally.
|
1705.00570v1
|
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