publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2012-06-11 | Thermal Stability of Thermoelectric Materials via In Situ Resistivity Measurements | An experimental setup for determining the electrical resistivity of several
types of thermoelectric materials over the temperature range 20 < T < 550 C is
described in detail. One resistivity measurement during temperature cycling is
also explained for Cu0.01Bi2Te2.7Se0.3 while a second measurement is made on
Yb0.35Co4Sb12 as a function of time at 400 C. Both measurements confirm that
the materials are thermally stable for the temperature range and time period
measured. Measurements made during temperature cycling show an irreversible
decrease in the electrical resistivity of Cu0.01Bi2Te2.7Se0.3 when the
measuring temperature exceeds the pressing temperature. Several other possible
uses of such a system include but are not limited to studying the effects of
annealing and/or oxidation as a function of both temperature and time. | 1206.2094v1 |
2022-07-27 | Terahertz microresonators for material characterisation | Terahertz (THz) technology is rapidly evolving, and the advancement of data
and information processing devices is essential. Silicon THz microresonators
provide perfect platforms to develop compact and integrated devices that could
transform THz technology. Here we present a systematic study on the key figure
of merit of silicon THz disc microresonators - the quality factor (Q-factor) -
in dependence on the substrate's resistivity. Our results show that the
Q-factor depends linearly on the resistivity and a variation in resistivity
from 10k$\Omega$cm to 15k$\Omega$cm changes the Q-factor from 50k to 76k at
0.6THz. Moreover, we experimentally determine that the silicon material
absorption is inversely proportional to the substrate's resistivity. In
general, the presented methodology is ideally suited to precisely measure the
material absorption of low-loss materials in the THz domain, which is
challenging using conventional THz spectroscopy. | 2207.13818v1 |
2023-03-24 | Charge-density-wave resistive switching and voltage oscillations in ternary chalcogenide BaTiS3 | Phase change materials, which show different electrical characteristics
across the phase transitions, have attracted considerable research attention
for their potential electronic device applications. Materials with
metal-to-insulator or charge density wave (CDW) transitions such as VO2 and
1T-TaS2 have demonstrated voltage oscillations due to their robust bi-state
resistive switching behavior with some basic neuronal characteristics. BaTiS3
is a small bandgap ternary chalcogenide that has recently reported the
emergence CDW order below 245 K. Here, we report on the discovery of DC voltage
/ current-induced reversible threshold switching in BaTiS3 devices between a
CDW phase and a room temperature semiconducting phase. The resistive switching
behavior is consistent with a Joule heating scheme and sustained voltage
oscillations with a frequency of up to 1 kHz has been demonstrated by
leveraging the CDW phase transition and the associated negative differential
resistance. Strategies of reducing channel sizes and improving thermal
management may further improve the device performance. Our findings establish
BaTiS3 as a promising CDW material for future energy-efficient electronics,
especially for neuromorphic computing. | 2303.14169v1 |
2016-02-24 | Design and optimization of resistive anode for a two-dimensional imaging triple-GEM detector | The optimization of resistive anode for two dimensional imaging detectors
which consists of a series of high resistive square pads surrounding by low
resistive strips has been studied by both numerical simulations and
experimental tests. It has been found that to obtain good detector performance,
the resistance ratio of the pad to the strip should be larger than 5, the
nonuniformity of the pad surface resistivity had better be less than $20\%$, a
smaller pad width leads to a smaller spatial resolution and when the pad width
is $6mm$, the spatial resolution ($\sigma$) can reach about $105{\mu}m$. Based
on the study results, a 2-D GEM detector prototype with the optimized resistive
anode is constructed and a good imaging performance is achieved. | 1602.07438v1 |
2017-09-19 | Considering non-uniform current distributions in magnetoresistive sensor designs and their implications for the resistance transfer function | Non-uniform current distributions of spin valves with disk shaped free layers
are investigated. In the context of spin valves, the vortex state, which is the
ground-state in many disk shaped magnetic bodies, allows for distinct parallel
channels of high and low resistivity. The readout current is thus able to evade
high resistivity regions in favor of low resistivity regions, giving rise to
'conductive inhomogeneities'. Therefore, the total resistance of the spin valve
does not always correspond exactly to the total average magnetization of the
free layer. In addition, the resistance transfer function can be significantly
influenced by the spatial placement of the electrodes, giving rise to
'geometric inhomogeneities'. The resulting deviations from resistance to
magnetization transfer function are investigated for different spin valve
geometries and compared to measurements of comparable devices. | 1709.06394v1 |
2023-09-19 | Effects of plasma resistivity in three-dimensional full-F gyro-fluid turbulence simulations | A full-F, isothermal, electromagnetic, gyro-fluid model is used to simulate
plasma turbulence in a COMPASS-sized, diverted tokamak. A parameter scan
covering three orders of magnitude of plasma resistivity and two values for the
ion to electron temperature ratio with otherwise fixed parameters is setup and
analysed. Simulations are performed with a new version of the FELTOR code,
which is fully parallelized on GPUs. Each simulation covers a couple of
milliseconds.
Two transport regimes for high and low plasma resistivities are revealed.
Beyond a critical resistivity the mass and energy confinement reduces with
increasing resistivity. Further, for high plasma resistivity the direction of
parallel acceleration is swapped compared to low resistivity.
The integration of exact conservation laws over the closed field line region
allows for an identification of numerical errors within the simulations. The
electron force balance and energy conservation show relative errors on the
order of $10^{-3}$ while the particle conservation and ion momentum balance
show errors on the order of $10^{-2}$.
Relative fluctuations amplitudes increase from below $1\%$ in the core to
$15\%$ in the edge and up to $40\%$ in the scrape-off layer.
Finally, three-dimensional visualisations using ray tracing techniques are
displayed and discussed. The field-alignment of turbulent fluctuations in
density and parallel current becomes evident. | 2309.10414v1 |
2016-11-09 | TiO$_2$-based Memristors and ReRAM: Materials, Mechanisms and Models (a Review) | The memristor is the fundamental non-linear circuit element, with uses in
computing and computer memory. ReRAM (Resistive Random Access Memory) is a
resistive switching memory proposed as a non-volatile memory. In this review we
shall summarise the state of the art for these closely-related fields,
concentrating on titanium dioxide, the well-utilised and archetypal material
for both. We shall cover material properties, switching mechanisms and models
to demonstrate what ReRAM and memristor scientists can learn from each other
and examine the outlook for these technologies. | 1611.04456v1 |
2018-10-30 | An alternative to the topological interpretation of the transverse resistivity anomalies in SrRuO3 | We clarify the physical origin of anomalies in transverse resistivity often
observed in exotic materials, such as SrRuO3, in which the Berry curvature is
manifested in the transport properties. The previously attributed mechanism for
the anomalies, the topological Hall effect (THE), is refuted by our thorough
investigations as well as formulation of a model considering inhomogeneous
magnetoelectric properties in the material. Our analyses fully explain every
feature of the anomalies without resorting to the THE. The present results
establish a fundamental understanding, which was previously overlooked, of
magneto-transport properties in such exotic materials. | 1810.12529v1 |
2004-11-26 | The Acceleration Mechanism of Resistive MHD Jets Launched from Accretion Disks | We analyzed the results of non-linear resistive magnetohydrodynamical (MHD)
simulations of jet formation to study the acceleration mechanism of
axisymmetric, resistive MHD jets. The initial state is a constant angular
momentum, polytropic torus threaded by weak uniform vertical magnetic fields.
The time evolution of the torus is simulated by applying the CIP-MOCCT scheme
extended for resistive MHD equations. We carried out simulations up to 50
rotation period at the innermost radius of the disk created by accretion from
the torus. The acceleration forces and the characteristics of resistive jets
were studied by computing forces acting on Lagrangian test particles. Since the
angle between the rotation axis of the disk and magnetic field lines is smaller
in resistive models than in ideal MHD models, magnetocentrifugal acceleration
is smaller. The effective potential along a magnetic field line has maximum
around $z \sim 0.5r_0$ in resistive models, where $r_0$ is the radius where the
density of the initial torus is maximum. Jets are launched after the disk
material is lifted to this height by pressure gradient force. Even in this
case, the main acceleration force around the slow magnetosonic point is the
magnetocentrifugal force. The power of the resistive MHD jet is comparable to
the mechanical energy liberated in the disk by mass accretion. Joule heating is
not essential for the formation of jets. | 0411712v1 |
2016-10-30 | Temperature and Humidity Dependence of Resistance in Nano-Diamond Powder | The electrical resistance of detonation nano-diamond powders was measured
from liquid nitrogen temperature to room temperature and in relative humidity
environments from around 10% to 100%. After sample exposures of several hours
at 100% relative humidity at room temperature (around 295 K), when the
temperature was reduced, the resistance increased to the upper measurement
limit of our apparatus (120 M{\Omega}) at around 240 K. Upon warming, the
resistance dropped back to the room temperature value, with some hysteresis.
For sample exposures after several hours at 100% relative humidity at room
temperature, as the relative humidity was reduced, the sample resistance
increased to the upper range limit of the apparatus. As the relative humidity
was then increased (all at room temperature), the resistance dropped. For
samples exposed to low (~10%) relative humidity for several hours at room
temperature, as the humidity was increased (at room temperature), the
resistance decreased, and then increased when the humidity was reduced. The
temperature behavior was markedly differ from that of powdered graphite and
multi-walled carbon nano tubes. | 1611.02242v2 |
2018-07-04 | Gate controlled large resistance switching driven by charge density wave in 1T-TaS2/2H-MoS2 heterojunction | 1T-TaS2 is a layered material that exhibits charge density wave (CDW) induced
distinct electrical resistivity phases and has attracted a lot of attention for
interesting device applications. However, such resistivity switching effects
are often weak, and cannot be modulated by an external gate voltage - limiting
their widespread usage. Using a back-gated 1T-TaS2/2H-MoS2 heterojunction, here
we show that the usual resistivity switching in TaS2 due to different phase
transitions is accompanied with a surprisingly strong modulation in the
Schottky barrier height (SBH) at the TaS2/MoS2 interface - providing an
additional knob to control the degree of the phase-transition-driven
resistivity switching by an external gate voltage. In particular, the
commensurate (C) to triclinic (T) phase transition results in an increase in
the SBH owing to a collapse of the Mott gap in TaS2. The change in SBH allows
us to estimate an electrical Mott gap opening of ~71 +/- 7 meV in the C phase
of TaS2. On the other hand, the nearly-commensurate (NC) to incommensurate (IC)
phase transition results in a suppression in the SBH, and the heterojunction
shows a gate-controlled resistivity switching up to 17.3, which is ~14.5 times
higher than that of standalone TaS2. The findings mark an important step
forward showing a promising pathway to externally control as well as amplify
the CDW induced resistivity switching. This will boost device applications that
exploit these phase transitions, such as ultra-broadband photodetection,
negative differential conductance, fast oscillator and threshold switching in
neuromorphic circuits. | 1807.01652v2 |
2008-10-08 | Performance Analysis of 60nm gate length III-V InGaAs HEMTs: Simulations vs. experiments | An analysis of recent experimental data for high-performance In0.7Ga0.3As
high electron mobility transistors (HEMTs) is presented. Using a fully quantum
mechanical, ballistic model, we simulate In0.7Ga0.3As HEMTs with gate lengths
of LG = 60nm, 85, and 135 nm and compare the result to the measured I-V
characteristics including draininduced barrier lowering, sub-threshold swing,
and threshold voltage variation with gate insulator thickness, as well as
on-current performance. To first order, devices with three different oxide
thicknesses and channel lengths can all be described by our ballistic model
with appropriate values of parasitic series resistance. For high gate voltages,
however, the ballistic simulations consistently overestimate the measured
on-current, and they do not show the experimentally observed decrease in
on-current with increasing gate length. With no parasitic series resistance at
all, the simulated on-current of the LG = 60 nm device is about twice the
measured current. According to the simulation, the estimated ballistic carrier
injection velocity for this device is about 2.7 x 10^7 cm/s. Because of the
importance of the semiconductor capacitance, the simulated gate capacitance is
about 2.5 times less than the insulator capacitance. Possible causes of the
transconductance degradation observed under high gate voltages in these devices
are also explored. In addition to a possible gate-voltage dependent scattering
mechanism, the limited ability of the source to supply carriers to the channel,
and the effect of nonparabolicity are likely to play a role. The drop in
on-current with increasing gate length is an indication that the devices
operate below the ballistic limit. | 0810.1540v1 |
2008-12-26 | Flux quanta driven by high-density currents in low-impurity V3Si and LuNi2B2C: free flux flow and flux-core size effect | High density direct currents (DC) are used to drive flux quanta via the
Lorentz force towards a highly ordered "free flux flow" (FFF) dynamic state,
made possible by the weak-pinning environment of high-quality, single-crystal
samples of two low-Tc superconducting compounds, V3Si and LuNi2B2C. We report
the effect of the magnetic field-dependent fluxon core size on flux flow
resistivity rho_f. Much progress has been made in minimizing the technical
challenges associated with the use of high currents. Attainment of a FFF phase
is indicated by the saturation at highest currents of flux-flow dissipation
levels that are well below the normal state resistance and have field-dependent
values. The field dependence of the corresponding rho_f is shown to be
consistent with a prediction based on a model for the decrease of flux core
size at higher fields in weak-coupling BCS s-wave materials. | 0812.4715v4 |
2020-06-01 | Radiation hardness of GaAs: Cr and Si sensors irradiated by electron beam | The interest in using the radiation detectors based on high resistive
chromium-compensated GaAs (GaAs:Cr) in high energy physics and others applied
fields has been growing steadily due to its numerous advantages over others
classical materials. High radiation hardness at room temperature stands out and
needs to be systematically investigated. In this paper an experimental study of
the effect of 20.9 MeV electrons generated by the LINAC-200 accelerator on some
properties of GaAs:Cr based sensors is presented. In parallel, Si sensors were
irradiated at the same conditions, measured and analyzed in order to perform a
comparative study. The target sensors were irradiated with the dose up to 1.5
MGy. The current-voltage characteristics, resistivity, charge collection
efficiency and their dependences on the bias voltage and temperature were
measured at different absorbed doses. An analysis of the possible microscopic
mechanisms leading to the observed effects in GaAs:Cr sensors is presented in
the article. | 2006.01254v1 |
2021-02-04 | Quantum Transport in Two-Dimensional WS$_2$ with High-Efficiency Carrier Injection Through Indium Alloy Contacts | Two-dimensional transition metal dichalcogenides (TMDCs) have properties
attractive for optoelectronic and quantum applications. A crucial element for
devices is the metal-semiconductor interface. However, high contact resistances
have hindered progress. Quantum transport studies are scant as low-quality
contacts are intractable at cryogenic temperatures. Here, temperature-dependent
transfer length measurements are performed on chemical vapour deposition grown
single-layer and bilayer WS$_2$ devices with indium alloy contacts. The devices
exhibit low contact resistances and Schottky barrier heights (\sim10
k$\Omega$\si{\micro\metre} at 3 K and 1.7 meV). Efficient carrier injection
enables high carrier mobilities ($\sim$190 cm$^2$V$^{-1}$s$^{-1}$) and
observation of resonant tunnelling. Density functional theory calculations
provide insights into quantum transport and properties of the WS$_2$-indium
interface. Our results reveal significant advances towards high-performance
WS$_2$ devices using indium alloy contacts. | 2102.02489v1 |
2021-08-11 | Single-domain perpendicular magnetization induced by the coherent O 2p-Ru 4d hybridized state in an ultra-high-quality SrRuO3 film | We investigated the Ru 4d and O 2p electronic structure and magnetic
properties of an ultra-high-quality SrRuO3 film on SrTiO3 grown by
machine-learning-assisted molecular beam epitaxy. The high itinerancy and long
quantum lifetimes of the quasiparticles in the Ru 4d t2g-O 2p hybridized
valence band are confirmed by observing the prominent well-screened peak in the
Ru 3d core-level photoemission spectrum, the coherent peak near the Fermi
energy in the valence band spectrum, and quantum oscillations in the
resistivity. The element-specific magnetic properties and the hybridization
between the Ru 4d and O 2p orbitals were characterized by Ru M2,3-edge and O
K-edge soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism
measurements. The ultra-high-quality SrRuO3 film with the residual resistivity
ratio of 86 shows the large orbital magnetic moment of oxygen ions induced by
the strong orbital hybridization of the O 2p states with the spin-polarized Ru
4d t2g states. The film also shows single-domain perpendicular magnetization
with an almost ideal remanent magnetization ratio of 0.97. These results
provide detailed insights into the relevance between orbital hybridization and
the perpendicular magnetic anisotropy in SrRuO3/SrTiO3 systems. | 2108.04980v1 |
2009-08-03 | Resistivity of Mn$_{1-x}$Fe$_x$Si single crystals: Evidence for quantum critical behavior | Resistivity measurements have been made on Mn$_{1-x}$Fe$_x$Si single crystals
between 2 and 300K for $x$ = 0, 0.05, 0.08, 0.12 and 0.15. Fe doping is found
to depress the magnetic ordering temperature from 30K for $x$ = 0 to below 2K
for $x$ = 0.15. Although Fe doping results in a large increase of the
low-temperature residual resistivity, the temperature dependence of the
resistivity above the magnetic transition remains practically unaffected by
increasing Fe content. An analysis of the temperature derivative of the
resistivity provides strong evidence for the existence of a non-Fermi-liquid
ground state near $x$ = 0.15 and thus for a quantum critical point tuned by Fe
content. | 0908.0294v1 |
2012-10-09 | Effect of back-gate on contact resistance and on channel conductance in graphene-based field-effect transistors | We study the contact resistance and the transfer characteristics of
back-gated field effect transistors of mono- and bi-layer graphene. We measure
specific contact resistivity of ~7kohm*um2 and ~30kohm*um2 for Ni and Ti,
respectively. We show that the contact resistance is a significant contributor
to the total source-to-drain resistance and it is modulated by the back-gate
voltage. We measure transfer characteristics showing double dip feature that we
explain as the effect of doping due to charge transfer from the contacts
causing minimum density of states for graphene under the contacts and in the
channel at different gate voltage. | 1210.2531v1 |
2013-07-01 | Magnetic and transport parameters of LSMO and YBCO/LSMO films deposited on sapphire substrates | The La0.7Sr0.3MnO3 (LSMO) layers and YBa2Cu3O7-{\delta}/La0.7Sr0.3MnO3
(YBCO/LSMO) bilayers were grown by magnetron sputtering on sapphire (Al2O3 or
ALO) substrates. Temperature dependences of resistance of single LSMO films,
grown on ALO substrates were typical for polycrystalline manganite materials
and the resistance decreased with decrease of the temperature at medium
temperatures and increased at lower and higher temperatures. Deposition of a
top YBCO layer led to a drastic increase of the sample resistance. These
bilayers did not demonstrate a decreasing of the resistance with decrease of
temperature. Temperature dependence of the resistance of these samples was
interpreted in the framework of a phenomenological model of two intergrain
conduction channels. In framework of this model, parameters of the samples were
determined and discussed. | 1307.0302v1 |
2015-01-27 | Realization of a reversible switching in TaO2 polymorphs via Peierls distortion for resistance random access memory | Transition-metal-oxide based resistance random access memory is a promising
candidate for next-generation universal non-volatile memories. Searching and
designing appropriate new materials used in the memories becomes an urgent
task. Here, a new structure with the TaO2 formula was predicted using
evolutionary algorithms in combination with first-principles calculations. This
new structure having a triclinic symmetry (T-TaO2) is both energetically and
dynamically more favorable than the commonly believed rutile structure
(R-TaO2). Our hybrid functional calculations show that T-TaO2 is a
semiconductor with a band gap of 1.0 eV, while R-TaO2 is a metallic conductor.
This large difference in electrical property makes TaO2 a potential candidate
for resistance random access memory (RRAM). Furthermore, we have shown that
T-TaO2 is actually a Peierls distorted R-TaO2 phase and the transition between
these two structures is via a directional displacement of Ta atoms. The energy
barrier for the reversible phase transition from R-TaO2 to T-TaO2 is 0.19
eV/atom and the other way around is 0.23 eV/atom, suggesting low power
consumption for the resistance switch. The present findings provide a new
mechanism for the resistance switch and will also stimulate experimental work
to fabricate tantalum oxides based RRAM. | 1501.06632v1 |
2015-02-09 | Four-Probe Methods for Measuring the Resistivity of Samples in the Form of Rectangular Parallelepipeds | The problem of measuring the resistivity of isotropic samples of finite
dimensions in the form of rectangular parallelepipeds using the four-probe
technique was considered. Two variants of contact arrangements were studied:
(1) four collinear probes are positioned on one side of a sample symmetrically
with respect to the other sides, and (2) two probes on one side of a sample and
two on the opposite side are placed precisely in opposite positions and
symmetrically with respect to the other sides of the sample (the Schnabel
method). Solutions of the problem of the electric field potential distribution
in a sample for different positions of the current contacts were found. The
solutions were obtained in the form of double series and methods of their
summation are presented. The obtained results are extended to the case of
measuring the resistivity of anisotropic samples when the resistivity tensor
has two independent components. The results of using the developed technique
for measuring the resistivity of such a highly anisotropic material as highly
oriented pyrolitic graphite using the Schnabel method are presented. | 1502.02600v1 |
2019-12-10 | Resistance Drift in Ge2Sb2Te5 Phase Change Memory Line Cells at Low Temperatures and Its Response to Photoexcitation | Resistance drift in phase change materials is characterized in amorphous
phase change memory line-cells from 300 K to 125 K range and is observed to
follow the previously reported power-law behavior with drift coefficients in
the 0.07 to 0.11 range in dark. While these drift coefficients measured in dark
are similar to commonly observed drift coefficients (~0.1) at and above room
temperature, measurements under light show a significantly lower drift
coefficient (0.05 under illumination versus 0.09 in dark at 150K). Periodic
on/off switching of light shows sudden decrease/increase of resistance,
attributed to photo-excited carriers, followed by a very slow response (~30
minutes at 150 K) attributed to contribution of charge traps. Continuation of
the resistance drift at low temperatures and the observed photo-response
suggest that resistance drift in amorphous phase change materials is
predominantly an electronic process. | 1912.04480v2 |
2022-04-04 | Inter- to Intra-Layer Resistivity Anisotropy of NdFeAs(O,H) with Various Hydrogen Concentrations | With molecular beam epitaxy and topotactic chemical reaction, we prepared
NdFeAs(O,H) epitaxial thin films with various hydrogen concentrations on
5{\deg} vicinal cut MgO substrates. By measuring the resistivities along the
longitudinal and transversal directions, the ab plane and the c axis
resistivities (\{rho}_ab and \{rho}_c) were obtained. The resistivity
anisotropy {\gamma}_\{rho}=\{rho}_c \ \{rho}_ab of NdFeAs(O,H) with various
hydrogen concentrations was compared with that of NdFeAs(O,F). At the H
concentrations which led to superconducting transition temperatures Tc over 40
K, {\gamma}_\r{ho} recorded ~100-150 at 50 K. On the other hand, a low
{\gamma}_\{rho} value of 9 was observed with the mostly doped sample. The
exponent \{beta} of the ab plane resistivity obtained by fitting a power law
expression \{rho}_{ab}(T)=\{rho}_0+AT^\{beta} to the data was close to unity
down to low temperature in the vicinity where the second antiferromagnetic
phase locates, which may be related to the quantum critical point discussed at
the over-doped side of the phase diagram. | 2204.01554v1 |
2020-04-28 | A Route to High-Toughness Battery Electrodes | There is increasing interest in materials that combine energy-storing
functions with augmented mechanical properties, ranging from flexibility in
bending to stretchability to structural properties. In the case of lithium-ion
batteries, these mechanical functions could enable their integration in
emerging technologies such as wearable, free-form electronics and ultimately as
structural elements, for example, in transport applications. This work presents
a method to produce flexible LiFePO4 LFP electrodes with an extraordinary
combination of electrochemical and mechanical performance. Such electrodes
exhibit an exceptionally high specific toughness, combined with superior rate
capability and energy density, with respect to reference electrodes with
typical metallic current collectors. These properties are a result of the
strong adhesion of the active material particles to the high surface area
carbon nanotube fiber fabric, used as a lightweight, tough, and highly
conducting current collector. This strong adherence minimizes electrical
resistance, mitigates interfacial failure, and increases ductility through
heterogeneous strain after cohesive failure of the inorganic phase. As a
result, these electrodes can withstand large deformations before fracture, and,
even after fracture, they retain excellent electrochemical performance,
approximately double that of unstretched, Al-supported LFP electrodes with
equivalent loading. | 2004.13350v1 |
2023-02-02 | High-entropy silicide superconductors with W$_{5}$Si$_{3}$-type structure | We report the synthesis, crystal structure and physical properties of two new
high-entropy silicides (HESs), namely
(Nb$_{0.1}$Mo$_{0.3}$W$_{0.3}$Re$_{0.2}$Ru$_{0.1}$)$_{5}$Si$_{3}$ and
(Nb$_{0.2}$Mo$_{0.3}$W$_{0.3}$Re$_{0.1}$Ru$_{0.1}$)$_{5}$Si$_{3}$. Structural
analysis indicates that both HESs consist of a (nearly) single tetragonal
W$_{5}$Si$_{3}$-type phase (space group $I$4/$mcm$) with a disordered cation
distribution. Electrical resistivity, magnetic susceptibility and specific heat
measurements show that
(Nb$_{0.1}$Mo$_{0.3}$W$_{0.3}$Re$_{0.2}$Ru$_{0.1}$)$_{5}$Si$_{3}$ and
(Nb$_{0.2}$Mo$_{0.3}$W$_{0.3}$Re$_{0.1}$Ru$_{0.1}$)$_{5}$Si$_{3}$ are weakly
coupled bulk superconductors, which represent the first superconducting
high-entropy nonoxide ceramics. In particular, these HESs have higher $T_{\rm
c}$ values (3.2-3.3 K) compared with those of the binary counterparts, and
their $B_{\rm c2}$(0)/$T_{\rm c}$ ratios are the largest among superconductors
of the same structural type. | 2302.00844v1 |
2024-01-15 | Fatigue Behavior of High-Entropy Alloys | High-entropy alloys (HEAs) refer to alloys composed of five or more elements
in equal or near-equal amounts or in an atomic concentration range of 5 to 35
atomic percent (at%). Different elemental ratios will affect the
microstructures of HEAs and provide them with unique properties. Based on past
research, HEAs have exhibited superior performance, relative to most
conventional alloys, with respect to many properties, such as strength,
toughness, corrosion resistance, magnetic behavior, etc. Among them, fatigue
behavior has been a topic of focus, due to its importance in industrial
applications. In this article, we summarized the research progress in the
HEA-fatigue behavior in the past ten years, including experimental results and
theoretical studies in subdivisions, such as high-cycle fatigue, low-cycle
fatigue, fatigue-crack growth, fatigue mechanisms, etc. The influence of the
processing and test methods on HEAs is described. The accuracy of several
commonly used prediction models is also outlined. Finally, unresolved issues
and suggestions on the direction of future research efforts are presented. | 2401.07418v1 |
2024-01-26 | Accelerated intermetallic phase amorphization in a Mg-based high-entropy alloy powder | We describe a novel mechanism for the synthesis of a stable high-entropy
alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by
employing high-energy mechanical milling. The presented methodology expedites
the synthesis of amorphous alloy powder by strategically injecting entropic
disorder through the inclusion of multi-principal elements in the alloy
composition. Predictions from first principles and materials theory corroborate
the results from microscopic characterizations that reveal a transition of the
amorphous phase from a precursor intermetallic structure. This transformation,
characterized by the emergence of antisite disorder, lattice expansion, and the
presence of nanograin boundaries, signifies a departure from the precursor
intermetallic structure. Additionally, this phase transformation is accelerated
by the presence of multiple principal elements that induce severe lattice
distortion and a higher configurational entropy. The atomic size mismatch of
the dissimilar elements present in the alloy produces a stable amorphous phase
that resists reverting to an ordered lattice even on annealing. | 2401.15197v2 |
2024-03-28 | High Mobility Charge Transport in a Multicarrier Altermagnet CrSb | A newly identified magnetic phase called altermagnet is being actively
studied because of its unprecedented spin-dependent phenomena. Among the
candidate materials, CrSb has a particularly high transition temperature and a
large spin-splitting energy, but its transport properties have remained
unexplored. In this study, we report the magnetotransport properties of CrSb
measured on single crystals. We found that the Hall resistivity shows a
nonlinear dependence on the magnetic field at low temperatures. From
symmetry-based considerations, however, this behavior can not be attributed to
an anomalous Hall effect, but to a multicarrier effect. A multicarrier fitting
to the in-plane conductivity tensor revealed that there are carriers with high
mobilities in CrSb, probably because of the presence of Weyl points in the
electronic structure. | 2403.19233v1 |
2014-02-26 | MoS2 P-type Transistors and Diodes Enabled by High Workfunction MoOx Contacts | The development of low-resistance source/drain contacts to transition metal
dichalcogenides (TMDCs) is crucial for the realization of high-performance
logic components. In particular, efficient hole contacts are required for the
fabrication of p-type transistors with MoS2, a model TMDC. Previous studies
have shown that the Fermi level of elemental metals is pinned close to the
conduction band of MoS2, thus resulting in large Schottky barrier heights for
holes with limited hole injection from the contacts. Here, we show that
substoichiometric molybdenum trioxide (MoOx, x<3), a high workfunction
material, acts as an efficient hole injection layer to MoS2 and WSe2. In
particular, we demonstrate MoS2 p-type field-effect transistors and diodes by
using MoOx contacts. We also show drastic on-current improvement for p-type
WSe2 FETs with MoOx contacts over devices made with Pd contacts, which is the
prototypical metal used for hole injection. The work presents an important
advance in contact engineering of TMDCs and will enable future exploration of
their performance limits and intrinsic transport properties. | 1402.6632v1 |
2015-03-23 | Electron-Irradiation Induced Nanocrystallization of Pb(II) in Silica Gels Prepared in High Magnetic Field | In a previous study, structure of silica gels prepared in a high magnetic
field was investigated. While a direct application of such anisotropic silica
gels is for an optical anisotropic medium possessing chemical resistance, we
show here their possibility of medium in materials processing. In this
direction, for example, silica hydrogels have so far been used as media of
crystal growth. In this paper, as opposed to the soft-wet state, dried silica
gels have been investigated. We have found that lead (II) nanocrystallites were
formed induced by electron irradiation to lead (II)-doped dried silica gels
prepared in a high magnetic field such as B = 10 T. Hydrogels made from a
sodium metasilicate solution doped with lead (II) acetate were prepared. The
dried specimens were irradiated by electrons in a transmission electron
microscope environment. Electron diffraction patterns indicated the
crystallinity of lead (II) nanocrystallites depending on B. An advantage of
this processing technique is that the crystallinity can be controlled through
the strength of magnetic field B applied during gel preparation. Specific
skills are not required to control the strength of magnetic field. | 1503.06863v1 |
2017-04-07 | Thermopower and thermal conductivity in the Weyl semimetal NbP | The Weyl semimetal NbP exhibits an extremely large magnetoresistance (MR) and
an ultra-high mobility. The large MR originates from a combination of the
nearly perfect compensation between electron- and hole-type charge carriers and
the high mobility, which is relevant to the topological band structure. In this
work we report on temperature- and field-dependent thermopower and thermal
conductivity experiments on NbP. Additionally, we carried out complementary
heat capacity, magnetization, and electrical resistivity measurements. We found
a giant adiabatic magnetothermopower with a maximum of 800 $\mu$V/K at 50 K in
a field of 9 T. Such large effects have been observed rarely in bulk materials.
We suggest that the origin of this effect might be related to the high
charge-carrier mobility. We further observe pronounced quantum oscillations in
both thermal conductivity and thermopower. The obtained frequencies compare
well with our heat capacity and magnetization data. | 1704.02241v2 |
2020-10-29 | Two-dimensional hole gas in organic semiconductors | A highly conductive metallic gas that is quantum mechanically confined at a
solid-state interface is an ideal platform to explore nontrivial electronic
states that are otherwise inaccessible in bulk materials. Although
two-dimensional electron gas (2DEG) has been realized in conventional
semiconductor interfaces, examples of two-dimensional hole gas (2DHG), which is
the counter analogue of 2DEG, are still limited. Here, we report the
observation of a 2DHG in solution-processed organic semiconductors in
conjunction with an electric double-layer using ionic liquids. A molecularly
flat single crystal of high mobility organic semiconductors serves as a
defect-free interface that facilitates two-dimensional confinement of
high-density holes. Remarkably low sheet resistance of 6 k$\Omega$ and high
hole gas density of 10$^{14}$ cm$^{-2}$ result in a metal-insulator transition
at ambient pressure. The measured degenerated holes in the organic
semiconductors provide a broad opportunity to tailor low-dimensional electronic
states using molecularly engineered heterointerfaces. | 2010.15883v1 |
2021-07-29 | Synergetic enhancement of power factor and suppression of lattice thermal conductivity via electronic structure modification and nanostructuring on Ni and B co-doped p-type Si-Ge alloy | For simultaneously achieving the high-power factor and low lattice thermal
conductivity of Si-Ge based thermoelectric materials, we employed, in this
study, constructively modifying the electronic structure near the chemical
potential and nano-structuring by low temperature and high-pressure sintering
on nano-crystalline powders. Nickel was doped to create the impurity states
near the edge of the valence band for enhancing the power factor with boron for
tuning the carrier concentration. The nanostructured samples with the nominal
composition of Si0.65-xGe0.32Ni0.03Bx (x = 0.01, 0.02, 0.03, and 0.04) were
synthesized by the mechanical alloying followed low-temperature and
high-pressure sintering process. A large magnitude of Seebeck coefficient
reaching 321 {\mu}VK-1 together with a small electrical resistivity of 4.49
m{\Omega}cm, leads to a large power factor of 2.3 Wm-1K-2 at 1000 K. With
successfully reduced thermal conductivity down to 1.47 Wm-1K-1, a large value
of ZT ~1.56 was obtained for Si0.65-xGe0.32Ni0.03B0.03 at 1000 K | 2107.13778v1 |
2021-09-03 | Growth and characterization of high-quality single-crystalline SnTe retaining cubic symmetry down to the lowest temperature studied | SnTe, an archetypical topological crystalline insulator, often shows a
transition from a highly symmetric cubic phase to a rhombohedral structure at
low temperatures. In order to achieve the highly symmetric cubic phase at low
temperatures suitable for quantum behaviour, we have employed the modified
Bridgman method to grow a high-quality single-crystalline sample of SnTe.
Analysis of the crystal structure using Laue diffraction and rocking curve
measurements show a very high degree of single crystallinity of the sample.
Resistivity and the specific heat data do not show the signature of structural
transition down to the lowest temperature studied. The magnetic susceptibility
shows diamagnetic behaviour. All these properties manifest the behaviour of a
typical bulk semiconductor with conducting surface states as expected in a
topological material. Detailed powder x-ray diffraction measurements show cubic
structure in the whole temperature range studied. | 2109.01420v2 |
2021-11-22 | High-entropy ceramics: propelling applications through disorder | Disorder enhances desired properties, as well as creating new avenues for
synthesizing materials. For instance, hardness and yield stress are improved by
solid-solution strengthening, a result of distortions and atomic size
mismatches. Thermo-chemical stability is increased by the preference of
chemically disordered mixtures for high-symmetry super-lattices. Vibrational
thermal conductivity is decreased by force-constant disorder without
sacrificing mechanical strength and stiffness. Thus, high-entropy ceramics
propel a wide range of applications: from wear resistant coatings and thermal
and environmental barriers to catalysts, batteries, thermoelectrics and nuclear
energy management. Here, we discuss recent progress of the field, with a
particular emphasis on disorder-enhanced properties and applications. | 2111.11519v1 |
2022-11-08 | Observation of room-temperature ferroelectricity in elemental Te nanowires | Ferroelectrics are essential in low-dimensional memory devices for multi-bit
storage and high-density integration. A polar structure is a necessary premise
for ferroelectricity, mainly existing in compounds. However, it is usually rare
in elemental materials, causing a lack of spontaneous electric polarization.
Here, we report an unexpected room-temperature ferroelectricity in few-chain Te
nanowires. Out-of-plane ferroelectric loops and domain reversal are observed by
piezoresponse force microscopy. Through density functional theory, we attribute
the ferroelectricity to the ion-displacement created by the interlayer
interaction between lone pair electrons. Ferroelectric polarization can induce
a strong field effect on the transport along the Te chain, supporting a
self-gated field-effect transistor. It enables a nonvolatile memory with high
in-plane mobility, zero supply voltage, multilevel resistive states, and a high
on/off ratio. Our work provides new opportunities for elemental ferroelectrics
with polar structures and paves a way towards applications such as low-power
dissipation electronics and computing-in-memory devices. | 2211.04066v1 |
2009-07-17 | Study of timing properties of single gap high-resistive bakelite RPC | The time resolution for several single gap (2 mm) prototype Resistive Plate
Chambers (RPC) made of high resistive (bulk resistivity ~ 10^10 - 10^12 ohm
cm), 2 mm thick matt finished bakelite paper laminates with silicone coating on
the inner surfaces, has been measured. The time resolution for all the modules
has been found to be ~ 2 ns at the plateau region. | 0907.2982v1 |
2003-09-16 | Metal-insulator transition in EuO | It is shown that the spectacular metal-insulator transition in Eu-rich EuO
can be simulated within an extended Kondo lattice model. The different orders
of magnitude of the jump in resistivity in dependence on the concentration of
oxygen vacancies as well as the low-temperature resistance minimum in
high-resistivity samples are reproduced quantitatively. The huge colossal
magnetoresistance (CMR) is calculated and discussed. | 0309369v2 |
2016-08-08 | Quantum Criticality and DBI Magneto-resistance | We use the DBI action from string theory and holography to study the
magneto-resistance at quantum criticality with hyperscaling violation. We find
and analyze a rich class of scaling behaviors for the magneto-resistance. A
special case describes the scaling results found in pnictides by Hayers et al.
in~\cite{analytis}. | 1608.02598v2 |
2023-09-19 | Resistivity of the two-dimensional Bose-Hubbard model at weak coupling | We calculate the weak-coupling resistivity of the two-dimensional Bose
Hubbard model, comparing with the more familiar fermionic case. At high
temperature the resistivity is linear in $T$, while in the low temperature
normal state it is exponentially suppressed. We explore the density dependence
and calculate the momentum relaxation rate. | 2309.10782v1 |
2018-09-24 | Ionic Tuning of Cobaltites at the Nanoscale | Control of materials through custom design of ionic distributions represents
a powerful new approach to develop future technologies ranging from spintronic
logic and memory devices to energy storage. Perovskites have shown particular
promise for ionic devices due to their high ion mobility and sensitivity to
chemical stoichiometry. In this work, we demonstrate a solid-state approach to
control of ionic distributions in (La,Sr)CoO$_{3}$ thin films. Depositing a Gd
capping layer on the perovskite film, oxygen is controllably extracted from the
structure, up-to 0.5 O/u.c. throughout the entire 36 nm thickness. Commensurate
with the oxygen extraction, the Co valence state and saturation magnetization
show a smooth continuous variation. In contrast, magnetoresistance measurements
show no-change in the magnetic anisotropy and a rapid increase in the
resistivity over the same range of oxygen stoichiometry. These results suggest
significant phase separation, with metallic ferromagnetic regions and
oxygen-deficient, insulating, non-ferromagnetic regions, forming percolated
networks. Indeed, X-ray diffraction identifies oxygen-vacancy ordering,
including transformation to a brownmillerite crystal structure. The unexpected
transformation to the brownmillerite phase at ambient temperature is further
confirmed by high-resolution scanning transmission electron microscopy which
shows significant structural - and correspondingly chemical - phase separation.
This work demonstrates room-temperature ionic control of magnetism, electrical
resistivity, and crystalline structure in a 36 nm thick film, presenting new
opportunities for ionic devices that leverage multiple material
functionalities. | 1809.08728v1 |
2020-02-17 | Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys | Understanding the strengthening and deformation mechanisms in refractory
high-entropy alloys (HEAs), proposed as new high-temperature material, is
required for improving their typically insufficient room-temperature ductility.
Here, density-functional theory simulations and a continuum mechanics analysis
were conducted to systematically investigate the competition between cleavage
decohesion and dislocation emission from a crack tip in the body-centered cubic
refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This
crack-tip competition is evaluated for tensile loading and a totality of 15
crack configurations and slip systems. Our results predict that dislocation
plasticity at the crack tip is generally unfavorable -- although the
competition is close for some crack orientations, suggesting intrinsic
brittleness and low crack-tip fracture toughness in these five HEAs at zero
temperature. Fluctuations in local alloy composition, investigated for
HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip
system relative to the configuration average of that slip system, but do not
change the dominant crack-tip response. In the case of single-crystal MoNbTaW,
where an experimental, room-temperature fracture-toughness value is available
for a crack on a \{100\} plane, theoretical and experimental results agree
favorably. Factors that may limit the agreement are discussed. We survey the
effect of material anisotropy on preferred crack tip orientations, which are
found to be alloy specific. Mixed-mode loadings are found to shift the
competition in favor of cleavage or dislocation nucleation, depending on crack
configuration and amplified by the effect of material anisotropy on crack tip
stresses. | 2002.07013v1 |
2019-08-22 | Non-localized states and high hole mobility in amorphous germanium | Covalent amorphous semiconductors, such as amorphous silicon (a-Si) and
germanium (a-Ge), are commonly believed to have localized electronic states at
the top of the valence band and the bottom of the conduction band. Electrical
conductivity is thought to be by the hopping mechanism through localized
states. The carrier mobility of these materials is usually very low, in the
order of ~10^-3 - 10^-2 cm^2/(Vs) at room temperature. In this study, we
present the Hall effect characterization of a-Ge prepared by self-ion
implantation of Ge ions. The a-Ge prepared by this method is highly homogenous
and has a mass density within 98.5% of the crystalline Ge. The material
exhibits an exceptionally high electrical conductivity and carrier mobility
(~100 cm^2/(Vs)) for an amorphous semiconductor. The temperature-dependent
resistivity of the material is very-well defined with two distinctive regions,
extrinsic and intrinsic conductivity, as in crystalline Ge. These results are
direct evidence for a largely-preserved band structure and non-localized states
of the valence band in a-Ge, as proposed by Tauc et al. from optical
characterization alone. This finding is not only significant for the
understanding of electrical conductivity in covalent disordered semiconductors,
but the exceptionally high mobility we have observed in amorphous Ge opens up
device applications not previously considered for amorphous semiconductors. | 1908.08246v1 |
2020-11-20 | StressNet: Deep Learning to Predict Stress With Fracture Propagation in Brittle Materials | Catastrophic failure in brittle materials is often due to the rapid growth
and coalescence of cracks aided by high internal stresses. Hence, accurate
prediction of maximum internal stress is critical to predicting time to failure
and improving the fracture resistance and reliability of materials. Existing
high-fidelity methods, such as the Finite-Discrete Element Model (FDEM), are
limited by their high computational cost. Therefore, to reduce computational
cost while preserving accuracy, a novel deep learning model, "StressNet," is
proposed to predict the entire sequence of maximum internal stress based on
fracture propagation and the initial stress data. More specifically, the
Temporal Independent Convolutional Neural Network (TI-CNN) is designed to
capture the spatial features of fractures like fracture path and spall regions,
and the Bidirectional Long Short-term Memory (Bi-LSTM) Network is adapted to
capture the temporal features. By fusing these features, the evolution in time
of the maximum internal stress can be accurately predicted. Moreover, an
adaptive loss function is designed by dynamically integrating the Mean Squared
Error (MSE) and the Mean Absolute Percentage Error (MAPE), to reflect the
fluctuations in maximum internal stress. After training, the proposed model is
able to compute accurate multi-step predictions of maximum internal stress in
approximately 20 seconds, as compared to the FDEM run time of 4 hours, with an
average MAPE of 2% relative to test data. | 2011.10227v1 |
2022-05-16 | Single Crystalline 2D Material Nanoribbon Networks for Nanoelectronics | The last decade has seen a flurry of studies related to graphene nanoribbons
owing to their potential applications in the quantum realm. However, little
experimental work has been reported towards nanoribbons of other 2D materials
due to the absence of synthesis routes. Here, we propose a universal approach
to synthesize high-quality networks of nanoribbons from arbitrary 2D materials
while maintaining high crystallinity, sufficient yield, narrow size
distribution, and straight-forward device integrability. The wide applicability
of this technique is demonstrated by fabricating MoS2, WS2, WSe2, and graphene
nanoribbon field effect transistors that inherently do not suffer from
interconnection resistances. By relying on self-assembled and self-aligned
organic nanostructures as masks, we demonstrate the possibility of controlling
the predominant crystallographic direction of the nanoribbon's edges.
Electrical characterization shows record mobilities and very high ON currents
for various TMDCs despite extreme width scaling. Lastly, we explore decoration
of nanoribbon edges with plasmonic particles paving the way towards the
development of nanoribbon-based plasmonic sensing and opto-electronic devices. | 2205.09507v1 |
2023-04-18 | Controllable Strain-driven Topological Phase Transition and Dominant Surface State Transport in High-Quality HfTe5 Samples | Controlling materials to create and tune topological phases of matter could
potentially be used to explore new phases of topological quantum matter and to
create novel devices where the carriers are topologically protected. It has
been demonstrated that a trivial insulator can be converted into a topological
state by modulating the spin-orbit interaction or the crystal lattice. However,
there are limited methods to controllably and efficiently tune the crystal
lattice and at the same time perform electronic measurements at cryogenic
temperatures. Here, we use large controllable strain to demonstrate the
topological phase transition from a weak topological insulator phase to a
strong topological insulator phase in high-quality HfTe5 samples. After
applying high strain to HfTe5 and converting it into a strong topological
insulator, we found that the sample's resistivity increased by more than two
orders of magnitude (24,000%) and that the electronic transport is dominated by
the topological surface states at cryogenic temperatures. Our findings show
that HfTe5 is an ideal material for engineering topological properties, and it
could be generalized to study topological phase transitions in van der Waals
materials and heterostructures. These results can pave the way to create novel
devices with applications ranging from spintronics to fault-tolerant
topologically protected quantum computers. | 2304.09072v1 |
2016-12-17 | Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks | Graphene, as a promising material of post-silicon electronics, opens a new
paradigm for the novel electronic properties and device applications. On the
other hand, the 2D feature of graphene makes it technically challenging to be
integrated into 3D transistors with a sufficient processor capacity. Although
there are many attempts to assemble 2D graphene into 3D structures, the
characteristics of massless Dirac fermions cannot be well preserved in these
materials for transistor applications. Here we report a high-performance
graphene transistor by utilizing 3D nanoporous graphene which is comprised of
an interconnected single graphene sheet and a commodious open porosity to
infuse an ionic liquid for a tunable electronic state by applying electric
fields. The 3D nanoporous graphene transistor, with high carrier mobility of
5000-7500 cm$^2$V$^{-1}$s$^{-1}$, exhibits two to three orders of magnitude
higher electric conductance and capacitance than those of 2D graphene devices,
along with preserved ambipolor electronic nature of Dirac cones. Moreover, the
3D graphene networks with Dirac fermions turn out to exhibit a unique nonlinear
Hall resistance in a wide range of the gate voltages. The high quality 3D
nanoporous graphene EDLT may open a new field for utilizing Dirac fermions in
3D network structures for various fundamental and practical applications. | 1612.05716v1 |
2017-11-24 | Stability of Thin Film Refractory Plasmonic Materials Taken to High Temperatures in Air | Materials such as W, TiN, and SrRuO3 (SRO) have been suggested as promising
alternatives to Au and Ag in plasmonic applications owing to their refractory
properties. However, investigation of the reproducibility of the optical
properties after thermal cycling at high operational temperatures is so far
lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, and SrRuO3 are
investigated to assess their viability for robust refractory plasmonic
applications. Films ranging in thickness from 50 - 180 nm are deposited on MgO
and Si substrates by RF magnetron sputtering and, in the case of SrRuO3, pulsed
laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic
ellipsometry, and DC resistivity. Measurements are conducted before and after
annealing in air at temperatures ranging from 300 - 1000{\deg} C for one hour,
to establish the maximum cycling temperature and potential longevity at
temperature for each material. It is found that SrRuO3 retains metallic
behaviour after annealing at 800{\deg} C, however, importantly, the optical
properties of TiN and TiON are degraded as a result of oxidation. Nevertheless,
both TiN and TiON may be better suited than Au or SRO for high temperature
applications operating under vacuum conditions. | 1711.08923v1 |
2016-03-17 | Transport evidence for the three-dimensional Dirac semimetal phase in ZrTe5 | Topological Dirac semimetal is a newly discovered class of materials and has
attracted intense attentions. This material can be viewed as a
three-dimensional (3D) analogue of graphene and has linear energy dispersion in
bulk, leading to a range of exotic transport properties. Here we report direct
quantum transport evidence of 3D Dirac semimetal phase of layered material
ZrTe5 by angular dependent magnetoresistance measurements under high magnetic
fields up to 31 Tesla. We observed very clear negative longitudinal
magnetoresistance induced by chiral anomaly under the condition of the magnetic
field aligned only along the current direction. Pronounced Shubnikov-de Hass
(SdH) quantum oscillations in both longitudinal magnetoresistance and
transverse Hall resistance were observed, revealing anisotropic light cyclotron
masses and high mobility of the system. In particular, a nontrivial {\pi}-Berry
phase in the SdH gives clear evidence for 3D Dirac semimetal phase.
Furthermore, we observed clear Landau Level splitting under high magnetic
field, suggesting possible splitting of Dirac point into Weyl points due to
broken time reversal symmetry. Our results indicate that ZrTe5 is an ideal
platform to study 3D massless Dirac and Weyl fermions in a layered compound. | 1603.05351v2 |
2022-06-16 | Scalable Composites Benefiting from Transition-Metal Oxides as Cathode Materials for Efficient Lithium-Sulfur Batteries | Composite materials achieved by including transition-metal oxides with
different structures and morphologies in sulfur are suggested as scalable
cathodes for high-energy lithium-sulfur (Li-S) batteries. The composites
contain 80 wt.% sulfur and 20 wt.% of either MnO2 or TiO2, leading to a sulfur
content in the electrode of 64 wt.% and revealing a reversible, fast, and lowly
polarized conversion process in the cell with limited interphase resistance.
The S-TiO2 composite exhibits an excellent rate capability between C/10 and 2C,
and a cycle life extended over 400 cycles at 2C, owing to the effects of the
nanometric TiO2 additive in boosting the reaction kinetics. Instead, the
micrometric sized particles of MnO2 partially limit the electrochemical
activity of S-MnO2 to the current rate of 1C. Nevertheless, both S-MnO2 and
S-TiO2 withstand a sulfur loading up to values approaching 6 mgcm-2, and
deliver an areal capacit ranging from about 4.5 to 5.5 mAhcm-2 at C/5. The
excellent performances of the metal oxide-sulfur electrodes, even at high
active material loading, and the possible scalability of the synthetic pathway
adopted in the work suggest that the composites are viable cathodes for
next-generation Li-S batteries with high energy density and efficient
electrochemical process. | 2206.14569v1 |
2024-01-25 | Spatially Resolved High Voltage Kelvin Probe Force Microcopy: A Novel Avenue for Examining Electrical Phenomena at Nanoscale | Kelvin probe microscopy (KPFM) is a well-established scanning probe
technique, used to measure surface potential accurately; it has found extensive
use in the study of a range of materials phenomena. In its conventional form,
KPFM frustratingly precludes imaging samples or scenarios where large surface
potential exists or large surface potential gradients are created outside the
typical +/-10V window. If the potential regime measurable via KPFM could be
expanded, to enable precise and reliable metrology, through a high voltage KPFM
(HV-KPFM) adaptation, it could open up pathways towards a range of novel
experiments, where the detection limit of regular KPFM has so far prevented the
use of the technique. In this work, HV-KPFM has been realised and shown to be
capable of measuring large surface potential and potential gradients with
accuracy and precision. The technique has been employed to study a range of
materials (positive temperature coefficient of resistivity ceramics, charge
storage fluoropolymers and pyroelectrics) where accurate spatially resolved
mapping of surface potential within high voltage regime facilitates novel
physical insight. The results demonstrate that HV-KPFM can be used as an
effective tool to fill in existing gaps in surface potential measurements while
also opening routes for novel studies in materials physics. | 2401.14124v1 |
2024-02-05 | High Strain Engineering of a Suspended WSSe Monolayer Membrane by Indentation and Measured by Tip-enhanced Photoluminescence | Straintronics involves the manipulation and regulation of the electronic
characteristics of 2D materials through the use of macro- and nano-scale strain
engineering. In this study, we utilized an atomic force microscope (AFM)
coupled with an optical system to perform indentation measurements and
tip-enhanced photoluminescence (TEPL), allowing us to extract the local optical
response of a suspended monolayer membrane of ternary WSSe at various levels of
deformation, up to strains of 10%. The photoluminescence signal is modelled
considering the deformation, stress distribution and strain dependence of the
WSSe band structure. We observe an additional TEPL signal that exhibits
significant variation under strain, with 64 meV per percent of elongation. This
peak is linked to the highly strained 2D material lying right underneath the
tip. We discuss the amplification of the signal and its relation to the
excitonic funnelling effect in a more comprehensive model. We will also compare
the diffusion caused by Auger recombination against the radiative excitonic
decay. We use TEPL to examine and comprehend the local physics of 2D
semi-conducting materials subjected to extreme mechanical strain. Chemical
vapour deposition-fabricated 2D ternaries possess high strain resistance,
comparable to the benchmark MoS2, and a high Young's modulus of 273 GPa. | 2402.03061v1 |
2019-08-11 | Magnetotransport as diagnostic of spin reorientation: kagome ferromagnet as a case study | While in most ferro or antiferromagnetic materials there is a unique
crystallographic direction, including crystallographically equivalent
directions, in which the moments like to point due to spin-orbit coupling, in
some, the direction of the spin reorients as a function of a certain physical
parameter such as temperature, pressure etc. Fe3Sn2 is a kagome ferromagnet
with an onset of ferromagnetism below 650 K, and undergoes a spin reorientation
near 150 K. While it is known that the moments in Fe3Sn2 point perpendicular to
the kagome plane at high temperatures and parallel to the kagome plane at low
temperatures, how the distribution of the magnetic domains in the two different
spin orientations evolve throughout the spin reorientation is not well known.
Furthermore, while there have been various reports on the magnetotransport
properties in the Hall configuration, the angular dependence of
magnetoresistance has not been studied so far. In this paper, we have examined
the spin reorientation by using anisotropic magnetoresistivity in detail,
exploiting the dependence of the resistivity on the direction between
magnetization and applied current. We are able to determine the distribution of
the magnetic domains as a function of temperature between 360 K to 2 K and the
reorientation transition to peak at 120 K. We discover that both out of plane
and in plane phases coexist at temperatures around the spin reorientation,
indicative of a first order transition. Although the volume of the magnetic
domains in the different phases sharply changes at the spin reorientation
transition, the electronic structure for a specific magnetization is not
influenced by the spin reorientation. In contrast, we observe an electronic
transition around 40 K, hitherto unreported, and reflected in both the
zero-field resistivity and anisotropic resistivity. | 1908.03927v1 |
2021-11-22 | Shape-Dependent Multi-Weight Magnetic Artificial Synapses for Neuromorphic Computing | In neuromorphic computing, artificial synapses provide a multi-weight
conductance state that is set based on inputs from neurons, analogous to the
brain. Additional properties of the synapse beyond multiple weights can be
needed, and can depend on the application, requiring the need for generating
different synapse behaviors from the same materials. Here, we measure
artificial synapses based on magnetic materials that use a magnetic tunnel
junction and a magnetic domain wall. By fabricating lithographic notches in a
domain wall track underneath a single magnetic tunnel junction, we achieve 4-5
stable resistance states that can be repeatably controlled electrically using
spin orbit torque. We analyze the effect of geometry on the synapse behavior,
showing that a trapezoidal device has asymmetric weight updates with high
controllability, while a straight device has higher stochasticity, but with
stable resistance levels. The device data is input into neuromorphic computing
simulators to show the usefulness of application-specific synaptic functions.
Implementing an artificial neural network applied on streamed Fashion-MNIST
data, we show that the trapezoidal magnetic synapse can be used as a
metaplastic function for efficient online learning. Implementing a
convolutional neural network for CIFAR-100 image recognition, we show that the
straight magnetic synapse achieves near-ideal inference accuracy, due to the
stability of its resistance levels. This work shows multi-weight magnetic
synapses are a feasible technology for neuromorphic computing and provides
design guidelines for emerging artificial synapse technologies. | 2111.11516v2 |
2014-11-04 | Tackling drug resistant infection outbreaks of global pandemic Escherichia coli ST131 using evolutionary and epidemiological genomics | High-throughput molecular screening is required to investigate the origin and
diffusion of antimicrobial resistance in pathogen outbreaks. The most frequent
cause of human infection is Escherichia coli, which is dominated by sequence
type 131 (ST131), a set of rapidly radiating pandemic clones. The highly
infectious clades of ST131 originated firstly by a mutation enhancing virulence
and adhesion. Secondly, single-nucleotide polymorphisms occurred enabling
fluoroquinolone-resistance, which is near-fixed in all ST131. Thirdly, broader
resistance through beta-lactamases has been gained and lost frequently,
symptomatic of conflicting environmental selective effects. This flexible
approach to gene exchange is worrying and supports the proposition that ST131
will develop an even wider range of plasmid and chromosomal elements promoting
antimicrobial resistance. To stymie ST131, deep genome sequencing is required
to understand the origin, evolution and spread of antimicrobial resistance
genes. Phylogenetic methods that decipher past events can predict future
patterns of virulence and transmission based on genetic signatures of
adaptation and gene exchange. Both the effect of partial antimicrobial exposure
and cell dormancy caused by variation in gene expression may accelerate the
development of resistance. High-throughput sequencing can decode measurable
evolution of cell populations within patients associated with systems-wide
changes in gene expression during treatments. A multi-faceted approach can
enhance assessment of antimicrobial resistance in E. coli ST131 by examining
transmission dynamics between hosts to achieve a goal of pre-empting resistance
before it emerges by optimising antimicrobial treatment protocols. | 1411.0905v3 |
2014-09-25 | Recycled nylon fibers as cement mortar reinforcement | We investigate engineering applications of recycled nylon fibers obtained
from waste fishing nets, focusing our attention on the use of recycled nylon
fibers as tensile reinforcement of cementitious mortars. We begin by
characterizing the tensile behavior of both unconditioned and alkali-cured
recycled nylon fibers obtained through manual cutting of waste fishing net
filaments, with the aim of assessing the resistance of such materials to
chemical attacks. Special attention is also given to evaluating the workability
of fresh mortar and the possible impacts of contaminants released by waste
fishing nets into the environment. Next, we deal with compression and bending
tests on cementitious mortars reinforced with recycled nylon fibers, and
establish comparisons with the experimental behavior of the unreinforced
material and with results given in existing literature. In our analysis of
different weight fractions and aspect ratios of the reinforcing fibers, we
observe marked increases in the tensile strength (up to +35%) and toughness (up
to 13 times greater) of the nylon reinforced mortar, as compared with the
unreinforced material. The presented results emphasize the high environmental
and mechanical potential of recycled nylon fibers for the reinforcement of
sustainable cement mortars. | 1409.7258v4 |
2019-05-14 | Ohmic contact engineering in few-layer black Phosphorus field effect transistors | Achieving good quality Ohmic contacts to van der Waals materials is a
challenge, since at the interface between metal and van der Waals material,
different conditions can occur, ranging from the presence of a large energy
barrier between the two materials to the metallization of the layered material
below the contacts. In black phosphorus (bP), a further challenge is its high
reactivity to oxygen and moisture, since the presence of uncontrolled oxidation
can substantially change the behavior of the contacts. In this study, we
investigate the influence of the metal used for the contacts to bP against the
variability between different flakes and different samples, using three of the
most used metals as contacts: Chromium, Titanium, and Nickel. Using the
transfer length method, from an analysis of ten devices, both at room
temperature and at low temperature, Ni results to be the best metal for Ohmic
contacts to bP, providing the lowest contact resistance and minimum scattering
between different devices. Moreover, we investigate the gate dependence of the
current-voltage characteristics of these devices. In the accumulation regime,
we observe good linearity for all metals investigated. | 1905.05649v1 |
2019-06-24 | Conductivity of Dirac-like surface states in correlated honeycomb transition metal oxide Mott insulators | The search for materials with novel and unusual electronic properties is at
the heart of condensed matter physics as well as the basis to develop
conceptual new technologies. In this context, the correlated honeycomb
transition metal oxides attract large attention for both, being a possible
experimental realization of the theoretically predicted magnetic Kitaev
exchange and the theoretical prospect of topological nontriviality. The Mott
insulating sodium iridate is prototypical among these materials with the
promising prospect to bridge the field of strongly correlated systems with
topology, finally opening a path to a wide band gap material with exotic
surface properties. Here, we report a profound study of the electronic
properties of ultra-high-vacuum cleaved surfaces combining transport
measurements with scanning tunneling techniques, showing that multiple
conductive channels with differing nature are simultaneously apparent in this
material. Most importantly, a V-shaped density of states and a low sheet
resistance, in spite of a large defect concentration, point towards a
topologically protected surface conductivity contribution. By incorporating the
issue of the addressability of electronic states in the tunneling process, we
develop a framework connecting previous experimental results as well as
theoretical considerations. | 1906.09809v2 |
2020-07-22 | Impact of Li$_{2.9}$B$_{0.9}$S$_{0.1}$O$_{3.1}$ glass additive on the structure and electrical properties of the LATP-based ceramics | The existing solid electrolytes for lithium ion batteries suffer from low
total ionic conductivity, which restricts its usefulness for the lithium-ion
battery technology. Among them, the NASICON-based materials, such as
Li1.3Al0.3Ti1.7(PO4)3 (LATP) exhibit low total ionic conductivity due to highly
resistant grain boundary phase. One of the possible approaches to efficiently
enhance their total ionic conductivity is the formation of a composite
material. Herein, the Li2.9B0.9S0.1O3.1 glass, called LBSO hereafter, was
chosen as an additive material to improve the ionic properties of the ceramic
Li1.3Al0.3Ti1.7(PO4)3 base material. The properties of this
Li1.3Al0.3Ti1.7(PO4)3-xLi2.9B0.9S0.1O3.1 (0 < x < 0.3) system have been studied
by means of high temperature X-ray diffractometry (HTXRD), 7Li, 11B, 27Al and
31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR),
thermogravimetry (TG), scanning electron microscopy (SEM), impedance
spectroscopy (IS) and density methods. We show here that the introduction of
the foreign LBSO phase enhances their electric properties. This study reveals
several interesting correlations between the apparent density, the
microstructure, the composition, the sintering temperature and the ionic
conductivity. Moreover, the electrical properties of the composites will be
discussed in the terms of the brick-layer model (BLM). The highest value of
{\sigma}tot = 1.5 x 10-4 Scm-1 has been obtained for LATP-0.1LBSO material
sintered at 800{\deg}C. | 2007.11244v2 |
2020-12-16 | Anisotropic phonon-mediated electronic transport in chiral Weyl semimetals | Discovery and observations of exotic, quantized optical and electrical
responses have sparked renewed interest in nonmagnetic chiral crystals. Within
this class of materials, six group V transition metal ditetrelides, that is,
XY$_2$ (X = V, Nb, Ta and Y = Si, Ge), host composite Weyl nodes on
high-symmetry lines, with Kramers-Weyl fermions at time-reversal invariant
momenta. In addition, at least two of these materials, NbGe$_2$ and NbSi$_2$,
exhibit superconducting transitions at low temperatures. The interplay of
strong electron-phonon interaction and complex Fermi surface topology present
an opportunity to study both superconductivity and hydrodynamic electron
transport in these systems. Towards this broader question, we present an ab
initio theoretical study of the electronic transport and electron-phonon
scattering in this family of materials, with a particular focus on NbGe$_2$ vs.
NbSi$_2$, and the other group V ditetrelides. We shed light on the microscopic
origin of NbGe$_2$'s large and anisotropic room temperature resistivity and
contextualize its strong electron-phonon scattering with a presentation of
other relevant scattering lifetimes, both momentum-relaxing and
momentum-conserving. Our work explores the intriguing possibility of observing
hydrodynamic electron transport in these chiral Weyl semimetals. | 2012.09207v1 |
2022-08-15 | Valley-coherent quantum anomalous Hall state in AB-stacked MoTe2/WSe2 bilayers | Moir\'e materials provide fertile ground for the correlated and topological
quantum phenomena. Among them, the quantum anomalous Hall (QAH) effect, in
which the Hall resistance is quantized even under zero magnetic field, is a
direct manifestation of the intrinsic topological properties of a material and
an appealing attribute for low-power electronics applications. The QAH effect
has been observed in both graphene and transition metal dichalcogenide (TMD)
moir\'e materials. It is thought to arise from the interaction-driven valley
polarization of the narrow moir\'e bands. Here, we show surprisingly that the
newly discovered QAH state in AB-stacked MoTe2/WSe2 moir\'e bilayers is not
valley-polarized but valley-coherent. The layer- and helicity-resolved optical
spectroscopy measurement reveals that the QAH ground state possesses
spontaneous spin (valley) polarization aligned (anti-aligned) in two TMD
layers. In addition, saturation of the out-of-plane spin polarization in both
layers occurs only under high magnetic fields, supporting a canted spin
texture. Our results call for a new mechanism for the QAH effect and highlight
the potential of TMD moir\'e materials with strong electronic correlations and
spin-orbit interactions for exotic topological states. | 2208.07452v1 |
2022-09-26 | Evaluating Effects of Geometry and Material Composition on Production of Transversely Shaped Beams from Diamond Field Emission Array Cathodes | Field emission cathodes (FECs) are attractive for the next generation of
injectors due to their ability to provide high current density bright beams
with low intrinsic emittance. One application of FECs worthy of special
attention is to provide transversely shaped electron beams for emittance
exchange that translates a transverse electron beam pattern into a longitudinal
pattern. FECs can be fabricated in a desired pattern and produce transversely
shaped beams without the need for complex masking or laser schemes. However,
reliable and consistent production of transversely shaped beams is affected by
material properties of the FEC. This paper reports the results of testing two
diamond field emitter array (DFEA) FECs with the same lithography pattern and
emitter geometry but different material and tip characteristics. Although both
cathodes were able to sustain gradients of 44 MV/m and produce maximum output
integral charge of 0.5 nC per radiofrequency (rf) pulse, their emission
patterns were quite different. One cathode did not produce a patterned beam
while the other one did. Differences in field emission characteristics and
patterned beam production were explained by the differences in the tip geometry
and the cathode material properties. The main practical takeaway was found to
be that the tip sharpness was not a prerequisite for good patterned beam
production. Instead, other material characteristics, such as the ballast
resistance, determined cathode performance. | 2209.13047v1 |
2023-04-13 | Effect of hirtisation on the roughness and fatigue performance of porous titanium lattice structures | Additive manufacturing (AM) has enabled the fabrication of extremely complex
components such as porous metallic lattices, which have applications in
aerospace, automotive, and in particular biomedical devices. The fatigue
resistance of these materials is currently an important limitation however, due
to manufacturing defects such as semi-fused particles and weld lines. Here
Hirtisation$^\circledR$ is used for post-processing of Ti-6Al-4V lattices,
reducing the strut surface roughness (Sa) from 12 to 6 $\mu$m, removing all
visible semi-fused particles. The evenness of this treatment in lattices with
$\rho /\rho_{s}$ up to 18.3% and treatment depth of 6.5 mm was assessed,
finding no evidence of reduced effectiveness on internal surfaces. After
normalising to quasi-static mechanical properties to account for material
losses during hirtisation (34-37% reduction in strut diameter), the fatigue
properties show a marked improvement due to the reduction in surface roughness.
Normalised high cycle fatigue strength ($\sigma_{f,10^{6}}/\sigma_{y}$)
increased from around 0.1 to 0.16-0.21 after hirtisation, an average increase
of 80%. For orthopaedic implant devices where matching the stiffness of
surrounding bone is crucial, the $\sigma_{f}/E$ ratio is a key metric. After
hirtisation the $\sigma_{f}/E$ ratio increased by 90%, enabling design of
stiffness matched implant materials with greater fatigue strength. This work
demonstrates that hirtisation is an effective method for improving the surface
roughness of porous lattice materials, thereby enhancing their fatigue
performance. | 2304.06621v1 |
2024-03-15 | An inflated dynamic Laplacian to track the emergence and disappearance of semi-material coherent sets | Lagrangian methods continue to stand at the forefront of the analysis of
time-dependent dynamical systems. Most Lagrangian methods have criteria that
must be fulfilled by trajectories as they are followed throughout a given
finite flow duration. This key strength of Lagrangian methods can also be a
limitation in more complex evolving environments. It places a high importance
on selecting a time window that produces useful results, and these results may
vary significantly with changes in the flow duration. We show how to overcome
this drawback in the tracking of coherent flow features. Finite-time coherent
sets (FTCS) are material objects that strongly resist mixing in complicated
nonlinear flows. Like other materially coherent objects, by definition they
must retain their coherence properties throughout the specified flow duration.
Recent work [Froyland and Koltai, CPAM, 2023] introduced the notion of
semi-material FTCS, whereby a balance is struck between the material nature and
the coherence properties of FTCS. This balance provides the flexibility for
FTCS to come and go, merge and separate, or undergo other changes as the
governing unsteady flow experiences dramatic shifts. The purpose of this work
is to illustrate the utility of the inflated dynamic Laplacian introduced in
[Froyland and Koltai, CPAM, 2023] in a range of dynamical systems that are
challenging to analyse by standard Lagrangian means, and to provide an
efficient meshfree numerical approach for the discretisation of the inflated
dynamic Laplacian. | 2403.10360v1 |
2024-03-20 | Tailoring Physical Properties of Crystals through Synthetic Temperature Control: A Case Study for new Polymorphic NbFeTe2 phases | Growth parameters play a significant role in the crystal quality and physical
properties of layered materials. Here we present a case study on a van der
Waals magnetic NbFeTe2 material. Two different types of polymorphic NbFeTe2
phases, synthesized at different temperatures, display significantly different
behaviors in crystal symmetry, electronic structure, electrical transport, and
magnetism. While the phase synthesized at low temperature showing behavior
consistent with previous reports, the new phase synthesized at high
temperature, has completely different physical properties, such as metallic
resistivity, long-range ferromagnetic order, anomalous Hall effect, negative
magnetoresistance, and distinct electronic structures. Neutron diffraction
reveals out-of-plane ferromagnetism below 70K, consistent with the electrical
transport and magnetic susceptibility studies. Our work suggests that simply
tuning synthetic parameters in a controlled manner could be an effective route
to alter the physical properties of existing materials potentially unlocking
new states of matter, or even discovering new materials. | 2403.13596v1 |
2022-07-06 | Proposal for semiconductor-free negative differential resistance tunnel diode with ultra-high peak-to-valley current ratio | The negative differential resistance (NDR) tunnel diodes are promising
alternative devices for beyond-CMOS computing as they offer several potential
applications when integrated with transistors. We propose a novel
semiconductor-free NDR tunnel diode concept that exhibits an ultra-high
peak-to-valley current ratio (PVCR) value. Our proposed NDR diode consists of
two cold metal electrodes separated by a thin insulating tunnel barrier. The
NDR effect stems from the unique electronic band structure of the cold metal
electrodes, i.e., the width of the isolated metallic bands around the Fermi
level as well as the energy gaps separating higher- and lower-lying bands
determine the current-voltage ($I$-$V$) characteristics and the PVCR value of
the tunnel diode. By proper choice of the cold metal electrode materials,
either a conventional N-type or ${\Lambda}$-type NDR effect can be obtained.
Two-dimensional (2D) materials offer a unique platform for the realization of
proposed NDR tunnel diodes. To demonstrate the proof of concept we employ the
nonequilibrium Green function method combined with density functional theory to
calculate the $I$-$V$ characteristic of the lateral (AlI$_2$/MgI$_2$/AlI$_2$)
and vertical (NbS$_2$/h-BN/NbS$_2$) heterojunction tunnel diodes based on 2D
cold metals. For the lateral tunnel diode, we obtain a ${\Lambda}$-type NDR
effect with an ultra-high PVCR value of 10$^{16}$ at room temperature, while
the vertical tunnel diode exhibits a conventional N-type NDR effect with a
smaller PVCR value of about 10$^4$. The proposed concept provides a
semiconductor-free solution for NDR devices to achieve desired $I$-$V$
characteristics with ultra-high PVCR values for memory and logic applications. | 2207.02593v2 |
2001-02-12 | Temperature- and magnetic-field-dependent resistivity of MgB2 sintered at high temperature and high pressure condition | We report the temperature- and magnetic-field-dependent resistivity of MgB2
sintered at high temperature and high pressure condition. The superconducting
transition width for the resistivity measurement was about 0.4 K, and the
low-field magnetization showed a sharp superconducting transition with a
transition width of about 1 K. The resistivity in the normal state roughly
followed T^2 behavior with smaller residual resistivity ratio (RRR) of 3 over
broad temperature region above 100 K rather than reported T^3 behavior with
larger RRR value of ~ 20 in the samples made at lower pressures. Also, the
resistivity did not change appreciably with the applied magnetic field, which
was different from previous report. These differences were discussed with the
microscopic and structural change due to the high-pressure sintering. | 0102215v4 |
2017-03-01 | Size Dependence of Nanoscale Wear of Silicon Carbide | Nanoscale, single-asperity wear of single-crystal silicon carbide (sc-SiC)
and nanocrystalline silicon carbide (nc-SiC) is investigated using
single-crystal diamond nanoindenter tips and nanocrystalline diamond atomic
force microscopy (AFM) tips under dry conditions, and the wear behavior is
compared to that of single-crystal silicon with both thin and thick native
oxide layers. We discovered a transition in the relative wear resistance of the
SiC samples compared to that of Si as a function of contact size. With larger
nanoindenter tips (tip radius around 370 nm), the wear resistances of both
sc-SiC and nc-SiC are higher than that of Si. This result is expected from the
Archard's equation because SiC is harder than Si. However, with the smaller AFM
tips (tip radius around 20 nm), the wear resistances of sc-SiC and nc-SiC are
lower than that of Si, despite the fact that the contact pressures are
comparable to those applied with the nanoindenter tips, and the plastic zones
are well-developed in both sets of wear experiments. We attribute the decrease
in the relative wear resistance of SiC compared to that of Si to a transition
from a wear regime dominated by the materials' resistance to plastic
deformation (i.e., hardness) to a regime dominated by the materials' resistance
to interfacial shear. This conclusion is supported by our AFM studies of
wearless friction, which reveal that the interfacial shear strength of SiC is
higher than that of Si. The contributions of surface roughness and surface
chemistry to differences in interfacial shear strength are also discussed. | 1703.01181v1 |
2022-02-09 | Scalable $\rm Al_2O_3-TiO_2$ Conductive Oxide Interfaces as Defect Reservoirs for Resistive Switching Devices | Resistive switching devices herald a transformative technology for memory and
computation, offering considerable advantages in performance and energy
efficiency. Here we employ a simple and scalable material system of conductive
oxide interfaces and leverage their unique properties for a new type of
resistive switching device. For the first time, we demonstrate an $\rm
Al_2O_3-TiO_2$ based valence-change resistive switching device, where the
conductive oxide interface serves both as the back electrode and as a reservoir
of defects for switching. The amorphous-polycrystalline $\rm Al_2O_3-TiO_2$
conductive interface is obtained following the technological path of
simplifying the fabrication of the two-dimensional electron gases (2DEGs),
making them more scalable for practical mass integration. We combine physical
analysis of the device chemistry and microstructure with comprehensive
electrical analysis of its switching behavior and performance. We pinpoint the
origin of the resistive switching to the conductive oxide interface, which
serves as the bottom electrode and as a reservoir of oxygen vacancies. The
latter plays a key role in valence-change resistive switching devices. The new
device, based on scalable and complementary metal-oxide-semiconductor (CMOS)
technology-compatible fabrication processes, opens new design spaces towards
increased tunability and simplification of the device selection challenge. | 2202.04477v2 |
2019-04-07 | Phase field modelling of crack propagation in functionally graded materials | We present a phase field formulation for fracture in functionally graded
materials (FGMs). The model builds upon homogenization theory and accounts for
the spatial variation of elastic and fracture properties. Several paradigmatic
case studies are addressed to demonstrate the potential of the proposed
modelling framework. Specifically, we (i) gain insight into the crack growth
resistance of FGMs by conducting numerical experiments over a wide range of
material gradation profiles and orientations, (ii) accurately reproduce the
crack trajectories observed in graded photodegradable copolymers and
glass-filled epoxy FGMs, (iii) benchmark our predictions with results from
alternative numerical methodologies, and (iv) model complex crack paths and
failure in three dimensional functionally graded solids. The suitability of
phase field fracture methods in capturing the crack deflections intrinsic to
crack tip mode-mixity due to material gradients is demonstrated. Material
gradient profiles that prevent unstable fracture and enhance crack growth
resistance are identified: this provides the foundation for the design of
fracture resistant FGMs. The finite element code developed can be downloaded
from www.empaneda.com/codes. | 1904.08749v1 |
2009-05-13 | Reliability of resistivity quantification for shallow subsurface water processes | The reliability of surface-based electrical resistivity tomography (ERT) for
quantifying resistivities for shallow subsurface water processes is analysed. A
method comprising numerical simulations of water movement in soil and
forward-inverse modeling of ERT surveys for two synthetic data sets is
presented. Resistivity contrast, e.g. by changing water content, is shown to
have large influence on the resistivity quantification.
An ensemble and clustering approach is introduced in which ensembles of 50
different inversion models for one data set are created by randomly varying the
parameters for a regularisation based inversion routine. The ensemble members
are sorted into five clusters of similar models and the mean model for each
cluster is computed. Distinguishing persisting features in the mean models from
singular artifacts in individual tomograms can improve the interpretation of
inversion results.
Especially in the presence of large resistivity contrasts in high sensitivity
areas, the quantification of resistivities can be unreliable. The ensemble
approach shows that this is an inherent problem present for all models inverted
with the regularisation based routine. The results also suggest that the
combination of hydrological and electrical modeling might lead to better
results. | 0905.2117v1 |
2009-06-17 | Resistive MHD jet simulations with large resistivity | Axisymmetric resistive MHD simulations for radially self-similar initial
conditions are performed, using the NIRVANA code. The magnetic diffusivity
could occur in outflows above an accretion disk, being transferred from the
underlying disk into the disk corona by MHD turbulence (anomalous turbulent
diffusivity), or as a result of ambipolar diffusion in partially ionized flows.
We introduce, in addition to the classical magnetic Reynolds number Rm, which
measures the importance of resistive effects in the induction equation, a new
number Rb, which measures the importance of the resistive effects in the energy
equation. We find two distinct regimes of solutions in our simulations. One is
the low-resistivity regime, in which results do not differ much from ideal-MHD
solutions. In the high-resistivity regime, results seem to show some
periodicity in time-evolution, and depart significantly from the ideal-MHD
case. Whether this departure is caused by numerical or physical reasons is of
considerable interest for numerical simulations and theory of astrophysical
outflows and is currently investigated. | 0906.3254v1 |
2011-12-29 | Magnetospheric Accretion and Ejection of Matter in Resistive Magnetohydrodynamic Simulations | The ejection of matter in the close vicinity of a young stellar object is
investigated, treating the accretion disk as a gravitationally bound reservoir
of matter. By solving the resistive MHD equations in 2D axisymmetry using our
version of the Zeus-3D code with newly implemented resistivity, we study the
effect of magnetic diffusivity in the magnetospheric accretion-ejection
mechanism. Physical resistivity was included in the whole computational domain
so that reconnection is enabled by the physical as well as the numerical
resistivity. We show, for the first time, that quasi-stationary fast ejecta of
matter, which we call {\em micro-ejections}, of small mass and angular momentum
fluxes, can be launched from a purely resistive magnetosphere. They are
produced by a combination of pressure gradient and magnetic forces, in presence
of ongoing magnetic reconnection along the boundary layer between the star and
the disk, where a current sheet is formed. Mass flux of micro-ejection
increases with increasing magnetic field strength and stellar rotation rate,
and is not dependent on the disk to corona density ratio and amount of
resistivity. | 1112.6226v2 |
2016-10-17 | Nonlinear Resistivity for Magnetohydrodynamical Models | A new formulation of the plasma resistivity that arises from the collisional
momentum-transfer rate between electrons and ions is presented. The resistivity
computed herein is shown to depend not only on the temperature and density but
also on all other polynomial velocity-space moments of the distribution
function, such as the pressure tensor and heat flux vector. The exact
expression for the collisional momentum-transfer rate is determined, and is
used to formulate the nonlinear anisotropic resistivity. The new formalism
recovers the Spitzer resistivity, as well as the concept of thermal force if
the heat flux is assumed to be proportional to a temperature gradient.
Furthermore, if the pressure tensor is related to viscous stress, the latter
enters the expression for the resistivity. The relative importance of the
nonlinear term(s) with respect to the well-established electron inertia and
Hall terms is also examined. The subtle implications of the nonlinear
resistivity, and its dependence on the fluid variables, are discussed in the
context of magnetized plasma environments and phenomena such as magnetic
reconnection. | 1610.05193v2 |
2020-03-09 | Quantum mechanical current-to-voltage conversion with quantum Hall resistance array | Accurate measurement of the electric current requires a stable and calculable
resistor for an ideal current to voltage conversion. However, the temporal
resistance drift of a physical resistor is unavoidable, unlike the quantum Hall
resistance directly linked to the Planck constant h and the elementary charge
e. Lack of an invariant high resistance leads to a challenge in making small
current measurements below 1 muA with an uncertainty better than one part in
106. In this work, we demonstrate a current to voltage conversion in the range
from a few nano amps to one microamp with an invariant quantized Hall array
resistance. The converted voltage is directly compared with the Josephson
voltage reference in the framework of Ohm's law. Markedly distinct from the
classical conversion, which relies on an artifact resistance reference, this
current-to-voltage conversion does not demand timely resistance calibrations.
It improves the precision of current measurement down to 8 10 -8 at 1 muA. | 2003.04464v1 |
2021-02-11 | Suppressing evolution through environmental switching | Ecology and evolution under changing environments are important in many
subfields of biology with implications for medicine. Here, we explore an
example: the consequences of fluctuating environments on the emergence of
antibiotic resistance, which is an immense and growing problem. Typically, high
doses of antibiotics are employed to eliminate the infection quickly and
minimize the time under which resistance may emerge. However, this strategy may
not be optimal. Since competition can reduce fitness and resistance typically
has a reproductive cost, resistant mutants' fitness can depend on their
environment. Here we show conditions under which environmental varying fitness
can be exploited to prevent the emergence of resistance. We develop a
stochastic Lotka-Volterra model of a microbial system with competing
phenotypes: a wild strain susceptible to the antibiotic, and a mutant strain
that is resistant. We investigate the impact of various pulsed applications of
antibiotics on population suppression. Leveraging competition, we show how a
strategy of environmental switching can suppress the infection while avoiding
resistant mutants. We discuss limitations of the procedure depending on the
microbe and pharmacodynamics and methods to ameliorate them. | 2102.05813v2 |
2023-12-08 | Electron-hole collision-limited resistance of gapped graphene | Collisions between electrons and holes can dominate the carrier scattering in
clean graphene samples in the vicinity of charge neutrality point. While
electron-hole limited resistance in pristine gapless graphene is well-studied,
its evolution with induction of band gap $E_g$ is less explored. Here, we
derive the functional dependence of electron-hole limited resistance of gapped
graphene $\rho_{eh}$ on the ratio of gap and thermal energy $E_g/kT$. At low
temperatures and large band gaps, the resistance grows linearly with $E_g/kT$,
and possesses a minimum at $E_g \approx 2.5 kT$. This contrast to the Arrhenius
activation-type behaviour for intrinsic semiconductors. Introduction of
impurities restores the Arrhenius law for resistivity at low temperatures
and/or high doping densities. The hallmark of electron-hole collision effects
in graphene resistivity at charge neutrality is the crossover between
exponential and power-law resistivity scalings with temperature. | 2312.05066v1 |
2019-03-18 | Experimental and Theoretical Investigation on the Possible Half-metallic Behaviour of Equiatomic Quaternary Heusler Alloys: CoRuMnGe and CoRuVZ (Z = Al, Ga) | In this report, structural, electronic, magnetic and transport properties of
quaternary Heusler alloys CoRuMnGe and CoRuVZ (Z = Al, Ga) are investigated.
All the three alloys are found to crystallize in cubic structure. CoRuMnGe
exhibits L2$_1$ structure whereas, the other two alloys have B2-type disorder.
For CoRuMnGe and CoRuVGa, the experimental magnetic moments are in close
agreement with the theory as well as those predicted by the Slater-Pauling
rule, while for CoRuVAl, a relatively large deviation is seen. The reduction in
the moment in case of CoRuVAl possibly arises due to the anti-site disorder
between Co and Ru sites as well as V and Al sites. Among these alloys, CoRuMnGe
has the highest T$\mathrm{_C}$ of 560 K. Resistivity variation with temperature
reflects the half-metallic nature in CoRuMnGe alloy. CoRuVAl shows metallic
character in both paramagnetic and ferromagnetic states, whereas the
temperature dependence of resistivity for CoRuVGa is quite unusual. In the last
system, $\rho$ vs. T curve shows an anomaly in the form of a maximum and a
region of negative temperature coefficient of resistivity (TCR) in the
magnetically ordered state. The ab initio calculations predict nearly
half-metallic ferromagnetic state with high spin polarization of 91, 89 and 93
\% for CoRuMnGe, CoRuVAl and CoRuVGa respectively. To investigate the
electronic properties of the experimentally observed structure, the Co-Ru swap
disordered structures of CoRuMnGe alloy are also simulated and it is found that
the disordered structures retain half-metallic nature, high spin polarization
with almost same magnetic moment as in the ideal structure. Nearly
half-metallic character, high T$\mathrm{_C}$ and high spin polarization make
CoRuMnGe alloy promising for room temperature spintronic applications. | 1903.07265v2 |
2021-05-06 | High-sensitivity of initial SrO growth on the residual resistivity in epitaxial thin films of SrRuO$_3$ on SrTiO$_3$ (001) | The growth of SrRuO$_3$ (SRO) thin film with high-crystallinity and low
residual resistivity (RR) is essential to explore its intrinsic properties.
Here, utilizing the adsorption-controlled growth technique, the growth
condition of initial SrO layer on TiO$_2$-terminated SrTiO$_3$ (STO) (001)
substrate was found to be crucial for achieving a low RR in the resulting SRO
film grown afterward. The optimized initial SrO layer shows a $c$(2 x 2)
superstructure that was characterized by electron diffraction, and a series of
SRO films with different thicknesses ($t$s) were then grown. The resulting SRO
films exhibit excellent crystallinity with orthorhombic-phase down to $t
\approx$ 4.3 nm, which was confirmed by high resolution X-ray measurements.
From azimuthal X-ray scan for SRO orthorhombic (021) reflection, we uncover
four structural domains with a dominant domain of orthorhombic SRO [001] along
cubic STO [010] direction. The dominant domain population depends on $t$, STO
miscut angle (${\alpha}$), and miscut direction (${\beta}$), giving a volume
fraction of about 92 $\%$ for $t \approx$ 26.6 nm and (${\alpha}$, ${\beta}$) ~
(0.14$^{\rm o}$, 5$^{\rm o}$). On the other hand, metallic and ferromagnetic
properties were well preserved down to $t \approx$ 1.2 nm. Residual resistivity
ratio (RRR = ${\rho}$(300 K)/${\rho}$(5 K)) reduces from 77.1 for $t \approx$
28.5 nm to 2.5 for $t \approx$ 1.2 nm, while ${\rho}$(5 K) increases from 2.5
$\mu\Omega$cm for $t \approx$ 28.5 nm to 131.0 $\mu\Omega$cm for $t \approx$
1.2 nm. The ferromagnetic onset temperature ($T_c\prime$) of around 151 K
remains nearly unchanged down to $t \approx$ 9.0 nm and decreases to 90 K for
$t \approx$ 1.2 nm. Our finding thus provides a practical guideline to achieve
high crystallinity and low RR in ultra-thin SRO films by simply adjusting the
growth of initial SrO layer. | 2105.02404v1 |
2021-12-01 | Synthesis and study of (Na, Zr) and (Ca, Zr) phosphate-molybdates and phosphate-tungstates: Thermal expansion behavior, radiation test and hydrolytic stability | Thermal expansion behavior at high temperatures of synthesized
Na$_{1-x}$Zr$_2$(PO$_4$)$_{3-x}$(XO$_4$)$_x$, and
Ca$_{1-x}$Zr$_2$(PO$_4$)$_{3-x}$(XO$_4$)$_x$, X = Mo, W compounds has been
investigated. Ceramics with relatively high density (more than 97.5%) were
produced by Spark Plasma Sintering (SPS) of submicron powders obtained by
sol-gel synthesis. The study of strength characteristics has revealed that
hardness the ceramics are greater than 5 GPa, and minimum fracture toughness
factor was 1 MPa*m$^{1/2}$. It was found that ceramics have a high hydrolytic
resistance in the static regime -- the minimum leaching rates for the Mo- and
W-containing specimens were $31\times10^{-6}$ and $3.36\times 10^{-6}$
g/(cm$^2$*day), respectively. The ceramics had a high resistance to the
irradiation by Xe$^{+26}$ multiple-charged ions with the energy 167 MeV up to
the fluences in the range 1*10$^{12}$ - 6*10$^{13}$ cm$^{-2}$. The
Mo-containing Na$_{0.5}$Zr$_2$(PO$_4$)$_{2.5}$(XO$_4$)$_{0.5}$ ceramics were
shown to have a higher radiation resistance that the phosphate-tungstates. | 2112.00373v1 |
2021-02-22 | High T$_C$ ferromagnetic inverse Heusler alloys: A comparative study of Fe$_2$RhSi and Fe$_2$RhGe | We report the results of experimental investigations on structural, magnetic,
resistivity, caloric properties of Fe$_2$RhZ (Z=Si,Ge) along with
\textit{ab-initio} band structure calculations using first principle
simulations. Both these alloys are found to crystallize in inverse Heusler
structure but with disorder in tetrahedral sites between Fe and Rh. Fe$_2$RhSi
has saturation moment of 5.00 $\mu_B$ and while its counterpart has 5.19
$\mu_B$. Resistivity measurement reveals metallic nature in both of them.
Theoretical simulations using generalized gradient approximation(GGA) predict
inverse Heusler structure with ferromagnetic ordering as ground state for both
the alloys. However it underestimates the experimentally observed moments.
GGA+$U$ approach, with Hubbard $U$ values estimated from density functional
perturbation theory helps to improve the comparison of the experimental
results. Fe$_2$RhSi is found to be half metallic ferromagnet while Fe$_2$RhGe
is not. Varying $U$ values on Fe and Rh sites does not change the net moment
much in Fe$_2$RhSi, unlike in Fe$_2$RhGe. Relatively small exchange splitting
of orbitals in Fe$_2$RhGe compared to that of Fe$_2$RhSi is the reason for not
opening the band gap in the minority spin channel in the former. High ordering
temperature and moment make Fe$_2$RhSi useful for spintronics applications. | 2102.10967v1 |
1995-11-10 | Contrasting Dynamic Spin Susceptibility Models and their Relation to High Temperature Superconductivity | We compare the normal-state resistivities $\rho$ and the critical
temperatures $T_c$ for superconducting $d_{x^2-y^2}$ pairing due to
antiferromagnetic (AF) spin fluctuation exchange in the context of the two
phenomenological dynamical spin susceptibility models, recently proposed by
Millis, Monien, and Pines (MMP) and Monthoux and Pines (MP) and, respectively,
by Radtke, Ullah, Levin, and Norman (RULN), for the cuprate high-$T_c$
materials. Assuming comparable electronic bandwidths and resistiviies in both
models, we show that the RULN model gives a much lower d-wave $T_c$
($\lsim20$K) than the MMP model (with $T_c\sim100$K). We demonstrate that these
profound differences in the $T_c$'s arise from fundamental differences in the
spectral weight distributions of the two model susceptibilities and are
{\it{not}} primarily caused by differences in the calculational techniques
employed by MP and RULN. The MMP model, claimed to fit NMR data in YBCO,
exhibits substantial amounts of spin fluctuation spectral weight up to an
imposed cut-off of 400meV, whereas, in the RULN model, claimed to fit YBCO
neutron scattering data, the weight is narrowly peaked and effectively cut-off
by 100meV. Further neutron scattering experiments, to explore the spectral
weight distribution at all wavevectors over a sufficiently large excitation
energy range, will thus be of crucial importance to resolve the question
whether AF spin fluctuation exchange provides a viable mechanism to account for
high-$T_c$ superconductivity. The large high-frequency boson spectral weight,
needed to generate both a high d-wave $T_c$ and a low normal-state resistivity,
also implies large values, of order unity, for the Migdal smallness parameter,
thus casting serious doubt on the validity of the very | 9511051v1 |
2011-11-14 | High Field (14Tesla) Magneto Transport of Sm/PrFeAsO | We report high field magneto transport of Sm/PrFeAsO. Below spin density wave
transition (TSDW), the magneto-resistance (MR) of Sm/PrFeAsO is positive and
increasing with decreasing temperature. The MR of SmFeAsO, is found 16%,
whereas the same is 21.5% in case of PrFeAsO, at 2.5 K under applied magnetic
field of 14 Tesla (T). In case of SmFeAsO, the variation of isothermal MR with
field below 20 K is nonlinear at lower magnetic fields (< 2 Tesla) and the same
is linear at moderately higher magnetic fields (H \geq 3.5 T). On the other
hand PrFeAsO shows almost linear MR at all temperatures below 20 K. The
anomalous behavior of MR being exhibited in PrFeAsO is originated from Dirac
cone states. The stronger interplay of Fe and Pr ordered moments is responsible
for this distinct behavior. PrFeAsO also shows a hump in resistivity (R-T) with
possible conduction band (FeAs) mediated ordering of Pr moments at around 12 K.
However the same is absent in SmFeAsO even down to 2 K. Our results of high
field magneto-transport of up to 14 Tesla brings about clear distinction
between ground states of SmFeAsO and PrFeAsO. | 1111.3143v2 |
2013-02-25 | On the specifics of the electrical conductivity anomalies in PVC nanocomposites | A qualitative model describing the "anomalous" features of the conductivity
of polymer nanocomposites, in particular, switching to the conducting state in
relatively thick (tens of microns or more) of flexible PVC films is considered.
In previously published experimental results, change of conductivity by 10 or
more orders of magnitude occurred both in the absence of external influences
(spontaneously), and under the influence of an applied electric field, as well
as other initiating factors (such as uniaxial pressure) . In a model of hopping
conduction mechanism it is shown, that switching in the conduction states under
the action of external field significantly (by orders of magnitude) below
threshold can be associated with a high-resistance state instability that
results from the sequence of "shorting" (reversible soft breakdown) of narrow
insulating gaps between regions with relatively high conductivity. Increasing
the field strength in the remaining insulating gaps ultimately leads to the
formation of a conducting channel between the external electrodes and switching
conductivity of the composite film sample in a state of high conductivity. This
cascade model is essentially based on the transition from the usual description
of the charge tunneling through single independent insulating gap to take into
account correlations between adjacent gaps. In the frame of developed model
other "anomalies" such as exponential dependence of the resistance on the
sample thickness, pressure, and other influences can be qualitative explained.
An analogy of the model with a cascading breakdown of avalanche transistors is
also considered. | 1302.5993v1 |
2016-12-15 | The properties of ultrapure delafossite metals | Although they were first synthesized in chemistry laboratories nearly fifty
years ago, the physical properties of the metals PdCoO2, PtCoO2 and PdCrO2 have
only more recently been studied in detail. The delafossite structure contains
triangular co-ordinated atomic layers, and electrical transport in the
delafossite metals is strongly two-dimensional. Their most notable feature is
their in-plane conductivity, which is amazingly high for oxide metals. At room
temperature, the conductivity of non-magnetic PdCoO2 and PtCoO2 is higher per
carrier than those of any alkali metal and even the most conductive elements,
copper and silver. At low temperatures the best crystals have resistivities of
a few n{\Omega}cm, corresponding to mean free paths of tens of microns. PdCrO2
is a frustrated antiferromagnetic metal, with magnetic scattering contributing
to the resistivity at high temperatures and small gaps opening in the Fermi
surface below the N\'eel temperature. There is good evidence that electronic
correlations are weak in the Pd/Pt layers but strong in the Co/Cr layers;
indeed the Cr layer in PdCrO2 is thought to be a Mott insulator. The
delafossite metals therefore act like natural heterostructures between strongly
correlated and nearly free electron sub-systems. Combined with the extremely
high conductivity, they provide many opportunities to study electrical
transport and other physical properties in new regimes. The purpose of this
review is to describe current knowledge of these fascinating materials and set
the scene for what is likely to be a considerable amount of future research. | 1612.04948v1 |
2017-10-05 | Dual-wavelength Photo-Hall effect spectroscopy of deep levels in high resistive CdZnTe with negative differential photoconductivity | Photo-Hall effect spectroscopy was used in the study of deep levels in high
resistive CdZnTe. The monochromator excitation in the photon energy range
0.65-1.77 eV was complemented by a laser diode high-intensity excitation at
selected photon energies. A single sample characterized by multiple unusual
features like negative differential photoconductivity and anomalous depression
of electron mobility was chosen for the detailed study involving measurements
at both the steady and dynamic regimes. We revealed that the Hall mobility and
photoconductivity can be both enhanced and suppressed by an additional
illumination at certain photon energies. The anomalous mobility decrease was
explained by an excitation of the inhomogeneously distributed deep level at the
energy Ev+1.0 eV enhancing thus potential non-uniformities. The appearance of
negative differential photoconductivity was interpreted by an intensified
electron occupancy of that level by a direct valence band-to-level excitation.
Modified Shockley-Read-Hall theory was used for fitting experimental results by
a model comprising five deep levels. Properties of the deep levels and their
impact on the device performance were deduced. | 1710.01945v1 |
2020-02-25 | Hydrogenated amorphous silicon detectors for particle detection, beam flux monitoring and dosimetry in high-dose radiation environment | Hydrogenated amorphous silicon (a-Si:H) has remarkable radiation resistance
properties and can be deposited on a lot of different substrates. A-Si:H based
particle detectors have been built since mid 1980s as planar p-i-n or Schottky
diode structures; the thickness of these detectors ranged from 1 to 50 micron.
However MIP detection using planar structures has always been problematic due
to the poor S/N ratio related to the high leakage current at high depletion
voltage and the low charge collection efficiency. The usage of 3D detector
architecture can be beneficial for the possibility to reduce inter-electrode
distance and increase the thickness of the detector for larger charge
generation compared to planar structures. Such a detector can be used for
future hadron colliders for its radiation resistance and also for X-ray
imaging. Furthermore the possibility of a-Si:H deposition on flexible materials
(like kapton) can be exploited to build flexible and thin beam flux measurement
detectors and x-ray dosimeters. | 2002.10848v1 |
2021-01-29 | Wide-range epitaxial strain control of electrical and magnetic properties in high-quality SrRuO3 films | Epitaxial strain in 4d ferromagnet SrRuO3 films is directly linked to the
physical properties through the strong coupling between lattices, electrons,
and spins. It provides an excellent opportunity to tune the functionalities of
SrRuO3 in electronic and spintronic devices. However, a thorough understanding
of the epitaxial strain effect in SrRuO3 has remained elusive due to the lack
of systematic studies. This study demonstrates wide-range epitaxial strain
control of electrical and magnetic properties in high-quality SrRuO3 films. The
epitaxial strain was imposed by cubic or pseudocubic perovskite substrates
having a lattice mismatch of -1.6 to 2.3% with reference to bulk SrRuO3. The
Poisson ratio, which describes the two orthogonal distortions due to the
substrate clamping effect, is estimated to be 0.33. The Curie temperature (TC)
and residual resistivity ratios of the series of films are higher than or
comparable to the highest reported values for SrRuO3 on each substrate,
confirming the high crystalline quality of the films. A TC of 169 K is achieved
in a tensile-strained SrRuO3 film on the DyScO3 (110) substrate, which is the
highest value ever reported for SrRuO3. The TC (146-169 K), magnetic anisotropy
(perpendicular or in-plane magnetic easy axis), and metallic conduction
(residual resistivity at 2 K of 2.10 - 373 {\mu}{\Omega}cm) of SrRuO3 are
widely controlled by epitaxial strain. These results provide guidelines to
design SrRuO3-based heterostructures for device applications. | 2101.12376v1 |
2020-05-16 | Pressure-induced Topological and Structural Phase Transitions in an Antiferromagnetic Topological Insulator | Recently, natural van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n have
been theoretically predicted and experimentally shown to host tunable magnetic
properties and topologically nontrivial surface states. In this work, we
systematically investigate both the structural and electronic responses of
MnBi2Te4 and MnBi4Te7 to external pressure. In addition to the suppression of
antiferromagnetic order, MnBi2Te4 is found to undergo a
metal-semiconductor-metal transition upon compression. The resistivity of
MnBi4Te7 changes dramatically under high pressure and a non-monotonic evolution
of \r{ho}(T) is observed. The nontrivial topology is proved to persists before
the structural phase transition observed in the high-pressure regime. We find
that the bulk and surface states respond differently to pressure, which is
consistent with the non-monotonic change of the resistivity. Interestingly, a
pressure-induced amorphous state is observed in MnBi2Te4, while two high
pressure phase transitions are revealed in MnBi4Te7. Our combined theoretical
and experimental research establishes MnBi2Te4 and MnBi4Te7 as highly tunable
magnetic topological insulators, in which phase transitions and new ground
states emerge upon compression. | 2005.08015v1 |
2020-08-03 | Solute hydrogen and deuterium observed at the near atomic scale in high-strength steel | Observing solute hydrogen (H) in matter is a formidable challenge, yet,
enabling quantitative imaging of H at the atomic-scale is critical to
understand its deleterious influence on the mechanical strength of many
metallic alloys that has resulted in many catastrophic failures of engineering
parts and structures. Here, we report on the APT analysis of hydrogen (H) and
deuterium (D) within the nanostructure of an ultra-high strength steel with
high resistance to hydrogen embrittlement. Cold drawn, severely deformed
pearlitic steel wires (Fe-0.98C-0.31Mn-0.20Si-0.20Cr-0.01Cu-0.006P-0.007S wt.%,
{\epsilon}=3.1) contains cementite decomposed during the pre-deformation of the
alloy and ferrite. We find H and D within the decomposed cementite, and at some
interfaces with the surrounding ferrite. To ascertain the origin of the H/D
signal obtained in APT, we explored a series of experimental workflows
including cryogenic specimen preparation and cryogenic-vacuum transfer from the
preparation into a state-of-the-art atom probe. Our study points to the
critical role of the preparation, i.e. the possible saturation of H-trapping
sites during electrochemical polishing, how these can be alleviated by the use
of an outgassing treatment, cryogenic preparation and transfer prior to
charging. Accommodation of large amounts of H in the under-stoichiometric
carbide likely explains the resistance of pearlite against hydrogen
embrittlement. | 2008.00684v1 |
2021-07-01 | Singular angular magnetoresistance and sharp resonant features in a high-mobility metal with open orbits, ReO3 | We report high-resolution angular magnetoresistance (AMR) experiments
performed on crystals of ReO$_3$ with high mobility (90,000 cm$^2$/Vs at 2 K)
and extremely low residual resistivity (5-8 n$\Omega$cm). The Fermi surface,
comprised of intersecting cylinders, supports open orbits. The resistivity
$\rho_{xx}$ in a magnetic field $B$ = 9 T displays a singular pattern of
behavior. With $\bf E\parallel \hat{x}$ and $\bf B$ initially
$\parallel\bf\hat{z}$, tilting $\bf B$ in the longitudinal $k_z$-$k_x$ plane
leads to a steep decrease in $\rho_{xx}$ by a factor of 40. However, if $\bf B$
is tilted in the transverse $k_y$-$k_z$ plane, $\rho_{xx}$ increases steeply by
a factor of 8. Using the Shockley tube integral approach, we show that, in
ReO$_3$, the singular behavior results from the rapid conversion of closed to
open orbits, resulting in opposite signs for AMR in orthogonal planes. The
floor values of $\rho_{xx}$ in both AMR scans are identified with specific sets
of open and closed orbits. Also, the "completion angle" $\gamma_c$ detected in
the AMR is shown to be an intrinsic geometric feature that provides a new way
to measure the Fermi radius $k_F$. However, additional sharp resonant features
which appear at very small tilt angles in the longitudinal AMR scans are not
explained by the tube integral approach. | 2107.00742v1 |
2021-07-07 | Development and validation of electrical-insulating Al2O3 coatings for high-temperature liquid PbLi applications | Electrical-insulating coatings are of great importance for liquid-metal
breeder/coolant based systems relevant to fusion power plants. In specific to
Pb-16Li eutectic, a candidate breeder material, such coatings are being
actively investigated for their criticality in addressing various
functionalities. For such applications, a candidate coating must be
demonstrated for its compatibility with corrosive media, high operational
temperatures and integrity of electrical-insulation over long durations without
substantial degradation. At present, no relevant in-situ insulation resistance
(IR) data is available for performance assessment of coated substrates within
PbLi environment. To address this shortfall, an experimental study was
performed at IPR towards application of high-purity alumina coatings on SS-316L
substrates and further rigorous validation in static PbLi environment. The
adopted coating process required a low-temperature heat treatment (< 430C) and
could yield average coating thicknesses in the range of 100-500 micron. Coated
samples were validated for their electrical insulation integrity in static PbLi
over two test campaigns for continuous durations of over 700 h and 1360 h,
including thermal cycling, at operational temperature between 300C-400C.
Estimated volumetric electrical-resistivity remained of the order of 109-1011
ohm-cm without significant degradation. In-situ estimations of thermal derating
factors establish excellent electrical-insulation characteristics after long
term exposure to liquid PbLi. This paper presents details of utilized coating
application methods, coating thickness estimations, liquid-metal test set-up,
insulation performance and critical observations from SEM/EDX and XRD analysis
on the tested samples. | 2107.03244v1 |
2021-09-26 | Tomographic Volumetric Additive Manufacturing of Silicon Oxycarbide Ceramics | Ceramics are highly technical materials with properties of interest for
multiple industries. Precisely because of their high chemical, thermal, and
mechanical resistance, ceramics are difficult to mold into complex shapes. A
possibility to make convoluted ceramic parts is to use preceramic polymers
(PCP) in liquid form. The PCP resin is first solidified in a desired geometry
and then transformed into ceramic compounds through a pyrolysis step that
preserves the shape. Light-based additive manufacturing (AM) is a promising
route to achieve solidification of the PCP resin. Different approaches, such as
stereolithography, have already been proposed but they all rely on a
layer-by-layer printing process which sets limitations on the printing speed
and object geometry. Here, we report on the fabrication of complex 3D
centimeter-scale ceramic parts by using tomographic volumetric printing which
is fast, high resolution and offers a lot of freedom in terms of geometrical
design compared to state-of-the-art AM techniques. First, we formulated a
photosensitive preceramic resin that was solidified by projecting light
patterns from multiple angles. Then, the obtained 3D printed parts were
converted into ceramics by pyrolyzing them in a furnace. We demonstrate the
strength of this approach through the fabrication of dense microcomponents
exhibiting overhangs and hollow geometries without the need of supporting
structures, and characterize their resistance to high heat and harsh chemical
treatments. | 2109.12680v1 |
2022-11-16 | Characterisation of Gamma-irradiated MCz-Silicon Detectors with a High-$K$ Negative Oxide as Field Insulator | The high-luminosity operation of the Tracker in the Compact Muon Solenid
(CMS) detector at the Large Hadron Collider (LHC) experiment calls for the
development of silicon-based sensors. This involves implementation of
AC-coupling to micro-scale pixel sensor areas to provide enhanced isolation of
radiation-induced leakage currents. The motivation of this study is the
development of AC-pixel sensors with negative oxides (such as aluminium oxide -
Al$_2$O$_3$ and hafnium oxide - HfO$_2$) as field insulators that possess good
dielectric strength and provide radiation hardness. Thin films of Al$_2$O$_3$
and HfO$_2$ grown by atomic layer deposition (ALD) method were used as
dielectrics for capacitive coupling. A comparison study based on dielectric
material used in MOS capacitors indicate HfO$_2$ as a better candidate since it
provides higher sensitivity (where, the term sensitivity is defined as the
ratio of the change in flat-band voltage to dose) to negative charge
accumulation with gamma irradiation.
Further, space charge sign inversion was observed for sensors processed on
high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates that
were irradiated with gamma rays up to a dose of 1 MGy. The inter-pixel
resistance values of heavily gamma irradiated AC-coupled pixel sensors suggest
that high-$K$ negative oxides as field insulators provide a good electrical
isolation between the pixels. | 2211.09158v2 |
2023-07-12 | Extrinsic Anomalous Hall effect in Mn Doped GeSnTe Semiconductors in the Bad Metal Hopping Regime | We present high field magnetotransport studies of Ge1-x-y(SnxMny)Te bulk
multiferroics with diamagnetic Sn and paramagnetic Mn concentration x = 0.38 to
0.79 and y = 0.02 to 0.086, respectively. The zero field resistivity, {\rho}(T)
takes significant contribution from defects below T = 20 K however, a mixed
scattering contribution from dynamic disorder and unusual sources is estimated
from T = 20 K to 300 K. The carrier mobility shows anomalous temperature
dependence from T0.2 to T0.5 which hints towards possible presence of polaronic
effects resulting from coupling of holes with phonons. This anomalous behavior
cannot be understood in terms of pure phononic scattering mechanism at high
temperature. From point of view of high field results, the transverse component
of magnetoresistivity manifests anomalous Hall effect originating from
extrinsic scattering sources, particularly the side jump mechanism reveals a
larger contribution. We also find that the correlation between the transverse
and longitudinal conductivities follow the universal scaling law {\sigma}xy ~
{\sigma}xxn where n = 1.6 in the low conductivity limit. The values n = 1.5 to
1.8 obtained for the present GSMT alloys justify the bad metal hopping regime
since the results fall in the low conductivity ferromagnetic family with
{\sigma}xx ~ 104 ohmcm-1. The interpretation of the n = 1.6 scaling in the low
conductivity regime is thus far not fully understood. However, the anomalous
Hall resistivity scaling with modified relation by Tian et al is indicative of
the dominant side jump scattering along with noticeable role of skew
scattering. | 2307.06271v1 |
2012-10-07 | Tailoring Magnetism of Perpendicularly Magnetized MnxGa Epitaxial Films on GaAs for Practical Applications | MnxGa films with high perpendicular anisotropy, coercivity and energy product
have great application potential in ultrahigh-density perpendicular recording,
permanent magnets, spin-transfer-torque memory and oscillators,
magneto-resistance sensors and ferromagnetic metal/semiconductor
heterostructure devices. Here we present a comprehensive diagram of effective
magnetism-tailoring of perpendicularly magnetized MnxGa films grown on III-V
semiconductor GaAs by using molecular-beam epitaxy for the first time, by
systematically investigating the wide-range composition and detailed
post-growth annealing effects. We show that the (001)-orientated MnxGa films
with L10 or D022 ordering could be crystallized on GaAs in a very wide
composition range from x=0.76 to 2.6. L10-ordered MnxGa films show robust
magnetization, high remanent ratio, giant perpendicular anisotropy, high
intrinsic and extrinsic coercivity, and large energy product, which make this
kind of material favorable for perpendicular magnetic recording,
high-performance spintronic devices and permanent magnet applications. In
contrast, D022-ordered films exhibit lower perpendicular anisotropy and weaker
magnetism. Post-growth annealing MnxGa films studies reveal high
thermal-stability up to 450 oC, and effective tailoring of magnetic properties
can be realized by prolonging annealing at 450 oC. These results would be
helpful for understanding this kind of material and designing new spintronic
devices for specific practical applications. | 1210.2062v3 |
2012-11-14 | The Critical Current Density of an SNS Josephson-Junction | The critical current density (Jc) through a superconductor in high magnetic
fields is controlled by the inclusions and microstructure of the material that
hold fluxons stationary to keep the resistance zero and is described using
Ginzburg-Landau (G-L) theory. Although the functional form of Jc for
superconducting-normal-superconducting (SNS) Josephson-Junctions (J-Js) is
known in the low field limit, includes the local properties of the junctions
and has been confirmed experimentally in many systems, there are no general
solutions for Jc of J-Js in high fields. Scaling laws describe the functional
form (magnetic field, temperature and strain dependence) of Jc for
polycrystalline superconductors in high fields but do not include local grain
boundary properties. They are derived by considering isolated pinning sites
where at criticality fluxons either depin or free fluxons shear past pinned
fluxons as part of the flux line lattice. However, visualisation of solutions
to the Time Dependent Ginzburg-Landau (TDGL) equations for polycrystalline
materials have shown that fluxons cross the superconductor by flowing along the
grain boundaries. Here we derive clean- and dirty- limit analytic equations for
of SNS J-Js in high fields and verify them using computational solutions to
TDGL theory. We consider SNS J-Js to be the basic building blocks for grain
boundaries in polycrystalline materials since they provide flux-flow channels.
The J-Js description provides a mathematical framework that includes the
utility of scaling laws together with our microscopic understanding of barriers
to supercurrent flow and helps identify the grain boundary engineering that can
improve in low temperature polycrystalline superconductors used in high
magnetic field applications. | 1211.3255v2 |
2013-09-08 | Nanoscale resolution scanning thermal microscopy with thermally conductive nanowire probes | Scanning thermal microscopy (SThM) - a type of scanning probe microscopy that
allows mapping thermal transport and temperatures in nanoscale devices, is
becoming a key approach that may help to resolve heat dissipation problems in
modern processors and develop new thermoelectric materials. Unfortunately,
performance of current SThM implementations in measurement of high thermal
conductivity materials continues to me limited. The reason for these
limitations is two-fold - first, SThM measurements of high thermal conductivity
materials need adequate high thermal conductivity of the probe apex, and
secondly, the quality of thermal contact between the probe and the sample
becomes strongly affected by the nanoscale surface corrugations of the studied
sample. In this paper we develop analytical models of the SThM approach that
can tackle these complex problems - by exploring high thermal conductivity
nanowires as a tip apex, and exploring contact resistance between the SThM
probe and studied surface, the latter becoming particularly important when both
tip and surface have high thermal conductivities. We develop analytical model
supported by the finite element analysis simulations and by the experimental
tests of SThM prototype using carbon nanotube (CNT) at the tip apex as a heat
conducting nanowire. These results elucidate vital relationships between the
performance of the probe in SThM from one side and thermal conductivity,
geometry of the probe and its components from the other, providing pathway for
overcoming current limitations of SThM. | 1309.2010v1 |
2019-09-13 | Electric field and current induced electroforming modes in NbOx | Electroforming is used to initiate the memristive response in
metal/oxide/metal devices by creating a filamentary conduction path in the
oxide film. Here we use a simple photoresist-based detection technique to map
the spatial distribution of conductive filaments formed in Nb/NbOx/Pt devices,
and correlate these with current-voltage characteristics and in-situ
thermoreflectance measurements to identify distinct modes of electroforming in
low and high conductivity NbOx films. In low conductivity films the filaments
are randomly distributed within the oxide film, consistent with a field-induced
weakest-link mechanism, while in high conductivity films they are concentrated
in the center of the film. In the latter case the current-voltage
characteristics and in-situ thermoreflectance imaging show that electroforming
is associated with current bifurcation into regions of low and high current
density. This is supported by finite element modelling of the current
distribution and shown to be consistent with predictions of a simple core-shell
model of the current distribution. These results clearly demonstrate two
distinct modes of electroforming in the same materials system and show that the
dominant mode depends on the conductivity of the film, with field-induced
electroforming dominant in low conductivity films and current-bifurcation
induced electroforming dominant in high conductivity films. Finally, we
demonstrate S-type and snap-back negative differential resistance in the high
conductivity films and explain this behavior in terms of two-zone model. | 1909.06443v2 |
2000-05-25 | Critical Resistivity along the Quantum Hall Liquid--Insulator Transition Line | The critical resistivity measured along the quantum Hall liquid--insulator
transition line indicates a pronounced peak at a critical filling factor close
to 1, which marks the crossover from the high to low magnetic field regime in
the phase diagram. The origin of this behavior is explained in the framework of
classical transport in a puddle network model. The proposed scenario is also
consistent with the behavior of the critical Hall resistance along the
transition line. In addition, a formula is suggested as a fit for isotherms
($\rho_{xx}$ vs. $\nu$) in the moderately high field regime, which exhibits a
violation of duality symmetry as the critical resistivity is evelated from the
`universal' value $h/e^2$. | 0005436v1 |
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