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2010-11-05 | Interplay between the electrical transport properties of GeMn thin films and Ge substrates | We present evidence that electrical transport studies of epitaxial p-type
GeMn thin films fabricated on high resistivity Ge substrates are severely
influenced by parallel conduction through the substrate, related to the large
intrinsic conductivity of Ge due to its small bandgap. Anomalous Hall
measurements and large magneto resistance effects are completely understood by
taking a dominating substrate contribution as well as the measurement geometry
into account. It is shown that substrate conduction persists also for well
conducting, degenerate, p-type thin films, giving rise to an effective
two-layer conduction scheme. Using n-type Ge substrates, parallel conduction
through the substrate can be reduced for the p-type epi-layers, as a
consequence of the emerging pn-interface junction. GeMn thin films fabricated
on these substrates exhibit a negligible magneto resistance effect. Our study
underlines the importance of a thorough characterization and understanding of
possible substrate contributions for electrical transport studies of GeMn thin
films. | 1011.1450v1 |
2011-08-31 | Local Tunneling Magnetoresistance probed by Low-Temperature Scanning Laser Microscopy | Tunneling magnetoresistance (TMR) in a vertical manganite junction was
investigated by low-temperature scanning laser microscopy (LTSLM) allowing to
determine the local relative magnetization M orientation of the two electrodes
as a function of magnitude and orientation of the external magnetic field H.
Sweeping the field amplitude at fixed orientation revealed magnetic domain
nucleation and propagation in the junction electrodes. For the high-resistance
state an almost single-domain antiparallel magnetization configuration was
achieved, while in the low-resistance state the junction remained in a
multidomain state. Calculated resistance $R_\mathrm{calc}(H)$ based on the
local M configuration obtained by LTSLM is in quantitative agreement with R(H)
measured by magnetotransport. | 1108.6159v1 |
2012-04-16 | Experimental investigation of the magnetic field driven superconductor/ insulator transition in underdoped $La_{2-x}Sr_xCuO_4$ thin films | The magnetic field driven superconductor/insulator transition is studied in a
large variety of $La_{2-x}Sr_xCuO_4$ thin films of various Sr dopings.
Temperature dependence of the resistivity down to 4.2 or 1.5 K under high
pulsed magnetic field (up to 57 T) is analyzed. In particular, the existence of
plateaus in the resistance versus temperature curves, in a limited range of
temperature, for given values of the magnetic field is carefully investigated.
It is shown to be associated to scaling behaviour of the resistance versus
magnetic field curves, evocative of the presence of a quantum critical point. A
three-dimensional (H,x,T) phase diagram is proposed, taking into account the
intrinsic lamellar nature of the materials by the existence of a temperature
crossover from quantum-two-dimensional to three-dimensional behavior. | 1204.3493v1 |
2012-08-20 | Universal linear in temperature resistivity from black hole superradiance | Observations across many families of unconventional materials motivative the
search for robust mechanisms producing linear in temperature d.c. resistivity.
BKT quantum phase transitions are commonplace in holographic descriptions of
finite density matter, separating critical and ordered phases. We show that at
a holographic BKT critical point, if the unstable operator is coupled to the
current via irrelevant operators, then a linear contribution to the resistivity
is universally obtained. We also obtain broad power law tails in the optical
conductivity, that shift spectral weight from the Drude peak as well as
interband energy scales. We give a partial realization of this scenario using
an Einstein-Maxwell-pseudoscalar bulk theory. The instability is a vectorial
mode at nonzero wavevector, which is communicated to the homogeneous current
via irrelevant coupling to an ionic lattice. | 1208.4102v1 |
2012-11-12 | Magnetic and transport properties of tetragonal- or cubic-Heusler-type Co-substituted Mn-Ga epitaxial thin films | The composition dependence of the structural, magnetic, and transport
properties of epitaxially grown Mn-Co-Ga films were investigated. The crystal
structure was observed to change from tetragonal to cubic as the Co content was
increased. In terms of the dependence of saturation magnetization on the Co
content, relatively small value was obtained for the
Mn$_{2.3}$Co$_{0.4}$Ga$_{1.3}$ film at a large {\it K}$_\textrm u$ value of 9.2
Merg/cm$^3$. Electrical resistivity of Mn-Co-Ga films was larger than that of
pure Mn-Ga film. The maximum value of the resistivity was 490 $\mu\Omega$cm for
Mn$_{2.2}$Co$_{0.6}$Ga$_{1.2}$ film. The high resistivity of Mn-Co-Ga might be
due to the presence of localized electron states in the films due to chemical
disordering caused by the Co substitution. | 1211.2524v1 |
2013-03-19 | Self-Formation of Sub-10-nm Nanogaps by Silicidation for Resistive Switch in Air | We developed a simple and reliable method for the fabrication of sub-10-nm
wide nanogaps. The self-formed nanogap is based on the stoichiometric
solid-state reaction between metal and Si atoms during silicidation process.
The nanogap width is deter- mined by the metal layer thickness. Our proposed
method produces nanogaps either symmetric or asymmetric electrodes, as well as,
multiple nanogaps within one unique process step for application to complex
circuits. Therefore, this method provides high throughput and it is suitable
for large-scale production. To demonstrate the feasibil- ity of the proposed
fabrication method, nanogap resistive switches have been built and
characterized. They exhibit a pronounced hysteresis with up to 103 on/off
conductance ratios in air. Our results indicate that the voltages for initially
electroforming the de- vice to the switch state are determinated by the nanogap
sizes. However, the set and reset voltages of the device do not strongly
dependent on the nanogap widths. These phenomena could be helpful to understand
how the resistive switching is established. | 1303.4586v1 |
2013-10-13 | Origin of the energy gap in the narrow-gap semiconductor FeSb2 revealed by high-pressure magnetotransport measurements | To elucidate an origin of the two energy gaps in the narrow-gap semiconductor
FeSb2, we have investigated the effects of hydrostatic pressure on the
resistivity, Hall resistance and magnetoresistance at low temperatures. The
larger energy gap evaluated from the temperature dependence of resistivity
above 100 K is enhanced from 30 to 40 meV with pressure from 0 to 1.8 GPa, as
generally observed in conventional semiconductors. In the low-temperature range
where a large Seebeck coefficient was observed, we evaluate the smaller energy
gap from the magnetotransport tensor using a two-carrier model and find that
the smaller gap exhibits a weak pressure dependence in contrast to that of the
larger gap. To explain the pressure variations of the energy gaps, we propose a
simple model that the smaller gap is a gap from the impurity level to the
conduction band and the larger one is a gap between the valence and conduction
bands, suggesting that the observed large Seebeck coefficient is not relevant
to electron correlation effects. | 1310.3451v1 |
2013-10-30 | Analysis of post wet chemistry heat treatment effects on Nb SRF surface resistance | Most of the current research in superconducting radio frequency (SRF)
cavities is focused on ways to reduce the construction and operating cost of
SRF based accelerators as well as on the development of new or improved cavity
processing techniques. The increase in quality factors is the result of the
reduction of the surface resistance of the materials. A recent test on a 1.5
GHz single cell cavity made from ingot niobium of medium purity and heat
treated at 1400 C in a ultra-high vacuum induction furnace resulted in a
residual resistance of about 1nanoohm and a quality factor at 2.0 K increasing
with field up to 5x10^10 at a peak magnetic field of 90 mT. In this
contribution, we present some results on the investigation of the origin of the
extended Q0-increase, obtained by multiple HF rinses, oxypolishing and heat
treatment of all Nb cavities. | 1310.8159v1 |
2014-02-04 | Multilevel recording in Bi-deficient Pt/BFO/SRO heterostructures based on ferroelectric resistive switching targeting high-density information storage in nonvolatile memories | We demonstrate the feasibility of multilevel recording in
Pt/Bi(1-d)FeO3/SrRuO3 capacitors using the ferroelectric resistive switching
phenomenon exhibited by the Pt/Bi(1-d)FeO3 interface. A tunable population of
up and down ferroelectric domains able to modulate the Schottky barrier height
at the Pt/Bi(1-d)FeO3 interface can be achieved by means of either a collection
of SET/RESET voltages or current compliances. This programming scheme gives
rise to well defined resistance states, which form the basis for a multilevel
storage nonvolatile memory. | 1402.0739v1 |
2014-05-06 | Effect of realistic metal electronic structure on the lower limit of contact resistivity of epitaxial metal-semiconductor contacts | The effect of realistic metal electronic structure on the lower limit of
resistivity in [100] oriented n-Si is investigated using full band Density
Functional Theory and Semi-Empirical Tight Binding (TB) calculations. Using
simulation unit cells guided by the interface chemistry of epitaxial CoSi2 on
[100] oriented Si observed experimentally, it is shown that the 'ideal metal'
assumption fails in some situations and consequently underestimates the lower
limit of contact resistivity in n-Si by at least an order of magnitude at high
doping concentrations. The mismatch in transverse momentum space in the metal
and the semiconductor, the so-called 'valley filtering effect', is shown to be
dependent on the interface chemistry simulated. The results emphasize the need
for explicit inclusion of the metal atomic and electronic structure in the
atomistic modeling of transport across metal-semiconductor contacts | 1405.1317v1 |
2014-11-16 | Laser doping for ohmic contacts in n-type Ge | We achieved ohmic contacts down to 5 K on standard n-doped Ge samples by
creating a strongly doped thin Ge layer between the metallic contacts and the
Ge substrate. Thanks to the laser doping technique used, Gas Immersion Laser
Doping, we could attain extremely large doping levels above the solubility
limit, and thus reduce the metal/doped Ge contact resistance. We tested
independently the influence of the doping concentration and doped layer
thickness, and showed that the ohmic contact improves when increasing the
doping level and is not affected when changing the doped thickness.
Furthermore, we characterised the doped Ge/Ge contact, showing that at high
doping its contact resistance is the dominant contribution to the total contact
resistance. | 1411.4325v1 |
2015-02-19 | Anomalous impact of hydrostatic pressure on superconductivity of polycrystalline LaO0.5F0.5BiSe2 | We report bulk superconductivity at 2.5K in LaO0.5F0.5BiSe2 compound through
the DC magnetic susceptibility and electrical resistivity measurements. The
synthesized LaO0.5F0.5BiSe2 compound is crystallized in tetragonal structure
with space group P4/nmm and Reitveld refined lattice parameters are a= 4.15(1)A
and c=14.02(2)A. The lower critical field of Hc1= 40Oe, at temperature 2K is
estimated through the low field magnetization measurements. The LaO0.5F0.5BiSe2
compound showed metallic normal state electrical resistivity with residual
resistivity value of 1.35m{\Omega}-cm. The compound is type-II superconductor,
and the estimated Hc2(0) value obtained by WHH formula is above 20kOe for
90percent Rn criteria. The superconducting transition temperature decreases
with applied pressure till around 1.68GPa and with further higher pressures a
high Tc phase emerges with possible onset Tc of above 5K for 2.5GPa. | 1502.05502v3 |
2016-06-13 | Performance studies of MRPC prototypes for CBM | Multi-gap Resistive Plate Chambers (MRPCs) with multi-strip readout are
considered to be the optimal detector candidate for the Time-of-Flight (ToF)
wall in the Compressed Baryonic Matter (CBM) experiment. In the R&D phase MRPCs
with different granularities, low-resistive materials and high voltage stack
configurations were developed and tested. Here, we focus on two prototypes
called HD-P2 and THU-strip, both with strips of 27 cm$^2$ length and
low-resistive glass electrodes. The HD-P2 prototype has a single-stack
configuration with 8 gaps while the THU-strip prototype is constructed in a
double-stack configuration with 2 $\times$ 4 gaps. The performance results of
these counters in terms of efficiency and time resolution carried out in a test
beam time with heavy-ion beam at GSI in 2014 are presented in this proceeding. | 1606.04917v1 |
2016-06-28 | Observation of quantum Hall effect in a microstrained Bi$_2$Se$_3$ single crystal | We report the observation of quantum Hall effect (QHE) in a Bi$_2$Se$_3$
single crystal having carrier concentration ($n$)
$\sim1.13\times10^{19}$cm$^{-3}$, three dimensional Fermi surface and bulk
transport characteristics. The plateaus in Hall resistivity coincide with
minima of Shubnikov de Haas oscillations in resistivity. Our results
demonstrate that the presence of perfect two dimensional transport is not an
essential condition for QHE in Bi$_2$Se$_3$. The results of high resolution
x-ray diffraction (HRXRD), energy-dispersive x-ray spectroscopy (EDX), and
residual resistivity measurements show the presence of enhanced crystalline
defects and microstrain. We propose that the formation of localized state at
the edge of each Landau level due to resonance between the bulk and defect band
of Bi$_2$Se$_3$ causes the quantum Hall effect. | 1606.08576v1 |
2016-07-20 | Nonlocal topological valley transport at large valley Hall angles | Berry curvature hot spots in two-dimensional materials with broken inversion
symmetry are responsible for the existence of transverse valley currents, which
give rise to giant nonlocal dc voltages. Recent experiments in high-quality
gapped graphene have highlighted a saturation of the nonlocal resistance as a
function of the longitudinal charge resistivity $\rho_{{\rm c}, xx}$, when the
system is driven deep into the insulating phase. The origin of this saturation
is, to date, unclear. In this work we show that this behavior is fully
compatible with bulk topological transport in the regime of large valley Hall
angles (VHAs). We demonstrate that, for a fixed value of the valley diffusion
length, the dependence of the nonlocal resistance on $\rho_{{\rm c}, xx}$
weakens for increasing VHAs, transitioning from the standard $\rho^3_{{\rm c},
xx}$ power-law to a result that is independent of $\rho_{{\rm c}, xx}$. | 1607.05902v1 |
2016-10-26 | Resistive Switching and Voltage Induced Modulation of Tunneling Magnetoresistance in Nanosized Perpendicular Organic Spin Valves | Nanoscale multifunctional perpendicular organic spin valves have been
fabricated. The devices based on an La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/Co
trilayer show resistive switching of up to 4-5 orders of magnitude and
magnetoresistance as high as -70% the latter even changing sign when voltage
pulses are applied. This combination of phenomena is typically observed in
multiferroic tunnel junctions where it is attributed to magnetoelectric
coupling between a ferromagnet and a ferroelectric material. Modeling indicates
that here the switching originates from a modification of the
La$_{0.7}$Sr$_{0.3}$MnO$_3$ surface. This modification influences the tunneling
of charge carriers and thus both the electrical resistance and the tunneling
magnetoresistance which occurs at pinholes in the organic layer. | 1610.08218v1 |
2016-11-03 | Current crowding mediated large contact noise in graphene field-effect transistors | The impact of the intrinsic time-dependent fluctuations in the electrical
resistance at the graphene-metal interface or the contact noise, on the
performance of graphene field effect transistors, can be as adverse as the
contact resistance itself, but remains largely unexplored. Here we have
investigated the contact noise in graphene field effect transistors of varying
device geometry and contact configuration, with carrier mobility ranging from
5,000 to 80,000$~$cm$^{2}$V$^{-1}$s$^{-1}$. Our phenomenological model for
contact noise due to current crowding in purely two dimensional conductors,
confirms that the contacts dominate the measured resistance noise in all
graphene field effect transistors in the two-probe or invasive four probe
configurations, and surprisingly, also in nearly noninvasive four probe (Hall
bar) configuration in the high mobility devices. The microscopic origin of
contact noise is directly linked to the fluctuating electrostatic environment
of the metal-channel interface, which could be generic to two dimensional
material-based electronic devices. | 1611.01181v2 |
2017-09-02 | Signatures of the Kondo effect in VSe2 | VSe2 is a transition metal dichaclogenide which has a charge-density wave
transition that has been well studied. We report on a low-temperature upturn in
the resistivity and, at temperatures below this resistivity minimum, an unusual
magnetoresistance which is negative at low fields and positive at higher
fields, in single crystals of VSe2. The negative magnetoresistance has a
parabolic dependence on the magnetic field and shows little angular dependence.
The magnetoresistance at temperatures above the resistivity minimum is always
positive. We interpret these results as signatures of the Kondo effect in VSe2.
An upturn in the susceptibility indicates the presence of interlayer V ions
which can provide the localized magnetic moments required for scattering the
conduction electrons in the Kondo effect. The low-temperature behaviour of the
heat capacity, including a high value of gamma, along with a deviation from a
Curie-Weiss law observed in the low-temperature magnetic susceptibility, are
consistent with the presence of magnetic interactions between the paramagnetic
interlayer V ions and a Kondo screening of these V moments. | 1709.00594v1 |
2017-11-20 | Computational analysis of short-range interactions between an edge dislocation and an array of equally-spaced identical shearable or non-shearable precipitates | The interaction between dislocations and precipitates plays an important role
in the mechanical behavior of alloys. To provide more insight into the physics
of this interaction, this research analyzes short-range interactions of an edge
dislocation with an array of equally-spaced identical precipitates. We use a
modified dislocation dynamics approach accounting for penetrable and
impenetrable precipitates. This research quantifies the effects of precipitate
resistance on the geometry of the dislocation-precipitation interaction and the
local distribution of plastic strain near a precipitate. The results show that
a precipitate with a higher resistance causes an increase in the maximum value
of dislocation curvature during the bypass. In addition, a higher level of
precipitate resistance leads to a lower level of plastic deformation. Moreover,
we observed a high plastic strain gradient at the interface of non-shearable
precipitates. | 1711.07428v2 |
2018-01-25 | Non-volatile bipolar resistive switching in sol-gel derived BiFeO3 thin films | BiFeO3 thin films are deposited on FTO coated glass substrates using a simple
sol-gel deposition technique, limiting thickness about 70 nm and Ag/BiFeO3/FTO
RRAM devices are prepared. The devices showed low-voltage bipolar switching
with the maximum Ion/Ioff ~ 450, and low set and reset voltages ~ 1.1 V and
-1.5 V, respectively. The devices are stable against on-off cycles with ~ 104 s
retention time without any significant degradation. The variations in the set
and reset voltages are 0.4 V and 0.6 V, respectively. We found that ohmic and
trap-controlled space charge limited conductions are responsible for low and
high resistance states, respectively. The resistive switching mechanism is
attributed to the formation and rupturing of the metal filament during the
oxidation and reduction of Ag ions for the set and reset states. | 1801.08502v1 |
2017-03-22 | A comparative study of resists and lithographic tools using the Lumped Parameter Model | A comparison of the performance of high resolution lithographic tools is
presented here. We use extreme ultraviolet interference lithography, electron
beam lithography, and He ion beam lithography tools on two different resists
that are processed under the same conditions. The dose-to-clear and the
lithographic contrast are determined experimentally and are used to compare the
relative efficiency of each tool. The results are compared to previous studies
and interpreted in the light of each tool-specific secondary electron yield. In
addition, the patterning performance is studied by exposing dense line/spaces
patterns and the relation between critical dimension and exposure dose is
discussed. Finally, the Lumped Parameter Model is employed in order to
quantitatively estimate the critical dimension of line/spaces, using each tool
specific aerial image. Our implementation is then validated by fitting the
model to the experimental data from interference lithography exposures, and
extracting the resist contrast. | 1703.08229v1 |
2020-04-15 | Radiation reaction friction: Resistive material medium | We explore a novel method of describing the radiation friction of particles
traveling through a mechanically resistive medium. We introduce a particle
motion induced matter warping along the path in a manner assuring that charged
particle dynamics occurs subject to radiative energy loss described by the
Larmor formula. We compare our description with the Landau-Lifshitz-like model
for the radiation friction and show that the established model exhibits
non-physical behavior. Our approach predicts in the presence of large
mechanical friction an upper limit on radiative energy loss being equal to the
energy loss due to the mechanical medium resistance. We demonstrate that
mechanical friction due to strong interactions, for example of quarks in
quark-gluon plasma, can induce significant soft photon radiation. | 2004.09634v2 |
2020-04-28 | Temperature-Dependent Resistivity of Alternative Metal Thin Films | The temperature coefficients of the resistivity (TCR) of Cu, Ru, Co, Ir, and
W thin films have been investigated as a function of film thickness below 10
nm. Ru, Co, and Ir show bulk-like TCR values that are rather independent of the
thickness whereas the TCR of Cu increases strongly with decreasing thickness.
Thin W films show negative TCR values, which can be linked to high disorder.
The results are qualitatively consistent with a temperature-dependent
semiclassical thin film resistivity model that takes into account phonon,
surface, and grain boundary scattering. | 2004.13854v3 |
2007-10-26 | Transport and magnetic properties in YBaCo2O5.45: Focus on the high-temperature transition | The electronic transport properties and the magnetic susceptibility were
measured in detail in $YBaCo_2O_{5.45}$. Close to the so-called metal-insulator
transition, strong effects of resistance relaxation, a clear thermal hysteresis
and a sudden increase of the resistance noise are observed. This is likely due
to the first order character of the transition and to the underlying phases
coexistence. Despite these out of equilibrium features, a positive and linear
magneto-resistance is also observed, possibly linked to the heterogeneity of
the state. From a magnetic point of view, the paramagnetic to ordered magnetic
state transition is observed using non linear susceptibilty. This transition
shows the characteristics of a continuous transition, and time dependent
effects can be linked with the dynamics of magnetic domains in presence of
disorder. Thus, when focusing on the order of the transitions, the electronic
one and the magnetic one can not be directly associated. | 0710.5008v1 |
2017-04-24 | Near-perfect spin filtering and negative differential resistance in an Fe(II)S complex | Density functional theory and nonequilibrium Green's function calculations
have been used to explore spin-resolved transport through the high-spin state
of an iron(II)sulfur single molecular magnet. Our results show that this
molecule exhibits near-perfect spin filtering, where the spin-filtering
efficiency is above 99%, as well as significant negative differential
resistance centered at a low bias voltage. The rise in the spin-up conductivity
up to the bias voltage of 0.4 V is dominated by a conductive lowest unoccupied
molecular orbital, and this is accompanied by a slight increase in the magnetic
moment of the Fe atom. The subsequent drop in the spin-up conductivity is
because the conductive channel moves to the highest occupied molecular orbital
which has a lower conductance contribution. This is accompanied by a drop in
the magnetic moment of the Fe atom. These two exceptional properties, and the
fact that the onset of negative differential resistance occurs at low bias
voltage, suggests the potential of the molecule in nanoelectronic and
nanospintronic applications. | 1704.07327v1 |
2017-07-08 | Electron and thermal transport via Variable Range Hopping in MoSe$_{2}$ single crystals | Bulk single crystal Molybdenum diselenide has been studied for its electronic
and thermal transport properties. We perform resistivity measurements with
current in-plane (CIP) and current perpendicular to plane (CPP) as a function
of temperature. The CIP measurements exhibit metal to semiconductor transition
at $\simeq 31$ K. In the semiconducting phase ($T > 31$ K), the transport is
best explained by variable range hopping (VRH) model. Large magnitude of
resistivity in CPP mode indicates strong structural anisotropy. Seebeck
coefficient as a function of temperature measured in the range $90 - 300$ K,
also agrees well with the VRH model. The room temperature Seebeck coefficient
is found to be $139$ $\mu$V/K. VRH fittings of the resistivity and Seebeck
coefficient data indicate high degree of localization. | 1707.02426v1 |
2015-04-14 | Voltage equilibration for reactive atomistic simulations of electrochemical processes | We introduce EChemDID, a model to describe electrochemical driving force in
reactive molecular dynamics simulations. The method describes the equilibration
of external electrochemical potentials (voltage) within metallic structures and
their effect on the self consistent partial atomic charges used in reactive
molecular dynamics. An additional variable assigned to each atom denotes the
local potential in its vicinity and we use fictitious, but computationally
convenient, dynamics to describe its equilibration within not-simply connected
metallic structures on-the-fly during the molecular dynamics simulation. This
local electrostatic potential is used to dynamically modify the atomic
electronegativities used to compute partial atomic changes via charge
equilibration. Validation tests show that the method provides an accurate
description of the electric fields generated by the applied voltage and the
driving force for electrochemical reactions. We demonstrate EChemDID via
simulations of the operation of electrochemical metallization cells. The
simulations predict the switching of the device between a high-resistance to a
low-resistance state as a conductive metallic bridge is formed and resistive
currents that can be compared with experimental measurements. In addition to
applications in nanoelectronics, EChemDID could be useful to model
electrochemical energy conversion devices. | 1504.03621v1 |
2016-09-29 | Magnetotransport properties and evidence of topological insulating state in LaSbTe | In this report, we present the magnetotransport and magnetization properties
of LaSbTe single crystals. Magnetic field-induced turn-on behavior and
low-temperature resistivity plateau have been observed. By adopting both
metal-semiconductor crossover and Kohler scaling analysis, we have discussed
the possible origin of the temperature and magnetic field dependence of
resistivity. At 5 K and 9 T, a large, non-saturating transverse
magnetoresistance (MR) $\sim$ 5$\times$10$^{3}$ \% has been obtained. The MR
shows considerable anisotropy, when the magnetic field is applied along
different crystallographic directions. The non-linear field dependence of the
Hall resistivity confirms the presence of two types of charge carriers. From
the semiclassical two-band fitting of Hall conductivity and longitudinal
conductivity, very high carrier mobilities and almost equal electron and hole
densities have been deduced, which result in large MR. The Fermi surface
properties have been analyzed from de Haas-van Alphen oscillation. From the
magnetization measurement, the signature of non-trivial surface state has been
detected, which confirms that LaSbTe is a topological insulator, consistent
with the earlier first-principles calculations. | 1609.09397v3 |
2019-11-20 | Investigation of the phase separation property in La$_{0.2}$Pr$_{0.4}$Ca$_{0.4}$MnO$_3$ manganite | We report a comprehensive investigation of La0.2Pr0.4Ca0.4MnO3 to clarify the
micrometre scale phase separation phenomenon in the mixed valent manganite
(La,Pr,Ca)MnO3. The compound shows multiple magnetic transitions, in which the
charge-ordered state is converted into a ferromagnetic state in steps with the
application of a magnetic field. The ac susceptibility measurements show that
the glassy transition at low temperatures does not depend on the frequency,
thus indicating the absence of any spin glass behaviour. Magnetization as well
as heat capacity measurements indicate that this low temperature transition is
magnetic field dependent. The field dependent resistivity at 2K shows a sharp
drop indicating that the sample behaviour changes from a high resistive state
to a low resistive state, corroborating the conversion of charge-ordered
insulating (COI) phase to a ferromagnetic metallic (FMM) phase. Our results
point towards the existence of phase separation, rigidity of the low
temperature glassy-like phase as well as the conversion of COI phase to FMM
phase by the application of magnetic fields. | 1911.08881v1 |
2021-02-01 | Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets | Measurements of the transverse Hall resistance are widely used to investigate
electron transport, magnetization phenomena, and topological quantum states.
Owing to the difficulty of probing transient changes of the transverse
resistance, the vast majority of Hall effect experiments are carried out in
stationary conditions using either dc or ac currents. Here we present an
approach to perform time-resolved measurements of the transient Hall resistance
during current-pulse injection with sub-nanosecond temporal resolution. We
apply this technique to investigate in real-time the magnetization reversal
caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall
effect measurements show that the current-induced switching of GdFeCo is widely
distributed in time and characterized by significant activation delays, which
limit the total switching speed despite the high domain-wall velocity typical
of ferrimagnets. Our method applies to a broad range of current-induced
phenomena and can be combined with non-electrical excitations to perform
pump-probe Hall effect measurements. | 2102.00716v1 |
2021-04-23 | Deformation and tearing of graphene-reinforced elastomer nanocomposites | The resistance to failure through tearing is a crucial mechanical property
for the application of different elastomers. In this work, graphene
nanoplatelets (GNPs) were introduced into a fluoroelastomer (FKM) matrix with
the aim of improving its tear resistance. The fracture energy through tearing
was evaluated using the pure shear test. It was found that the tearing energy
increased linearly with the volume fraction of the GNPs. At the maximum GNP
content, the tearing resistance was 3 times higher, suggesting efficient
toughening from the GNPs. Theoretical analysis of the micromechanics was
conducted by considering debonding and pull-out of the nanoplatelets as
possible toughening mechanisms. It was determined quantitatively that the main
toughening mechanism was debonding of the interface rather than pull-out. The
formation of cavities at flake ends during the deformation, as confirmed by
scanning electron microscopy, was found to contribute to the remarkably high
interfacial debonding energy (~1 kJ/m2). | 2104.11535v1 |
2021-04-27 | Electronegative metal dopants improve switching consistency in Al2O3 resistive switching devices | Resistive random access memories are promising for non-volatile memory and
brain-inspired computing applications. High variability and low yield of these
devices are key drawbacks hindering reliable training of physical neural
networks. In this study, we show that doping an oxide electrolyte, Al2O3, with
electronegative metals makes resistive switching significantly more
reproducible, surpassing the reproducibility requirements for obtaining
reliable hardware neuromorphic circuits. The underlying mechanism is the ease
of creating oxygen vacancies in the vicinity of electronegative dopants, due to
the capture of the associated electrons by dopant mid-gap states, and the
weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind
significantly to the dopant, thereby serving as preferential sites and building
blocks in the formation of conducting paths. We validate this theory
experimentally by implanting multiple dopants over a range of
electronegativities, and find superior repeatability and yield with highly
electronegative metals, Au, Pt and Pd. These devices also exhibit a gradual SET
transition, enabling multibit switching that is desirable for analog computing. | 2104.13301v2 |
2021-05-06 | Contact resistance of various metallisation schemes to superconducting boron doped diamond between 1.9 and 300 K | Diamond is a material that offers potential in numerous device applications.
In particular, highly boron doped diamond is attractive due to its
superconductivity and high Young's Modulus. The fabrication of stable, low
resistance, ohmic contacts is essential to ensure proper device function.
Previous work has established the efficacy of several methods of forming
suitable contacts to diamond at room temperature and above, including carbide
forming and carbon soluble metallisation schemes. Herein, the stability of
several contact schemes (Ti, Cr, Mo, Ta and Pd) to highly boron doped
nanocrystalline diamond was verified down to the cryogenic temperatures with
modified Transmission Line Model (TLM) measurements. While all contact schemes
remained ohmic, a significant temperature dependency is noted at Tc and at the
lowest temperatures the contact resistances ranged from Ti/Pt/Au with ${(8.83
\pm 0.10)\times 10^{-4} \:{\Omega}.cm}$ to Ta/Pt/Au with ${(8.07 \pm 0.62)
\times 10^{-6} \:{\Omega}.cm}$. | 2105.02839v1 |
2021-08-10 | Giant Piezospintronic Effect in a Noncollinear Antiferromagnetic Metal | One of the main bottleneck issues for room-temperature antiferromagnetic
spintronic devices is the small signal read-out owing to the limited
anisotropic magnetoresistance in antiferromagnets. However, this could be
overcome by either utilizing the Berry-curvature-induced anomalous Hall
resistance in noncollinear antiferromagnets or establishing tunnel junction
devices based on effective manipulation of antiferromagnetic spins. In this
work, we demonstrate the giant piezoelectric strain control of the spin
structure and the anomalous Hall resistance in a noncollinear antiferromagnetic
metal - D019 hexagonal Mn3Ga. Furthermore, we built tunnel junction devices
with a diameter of 200 nm to amplify the maximum tunneling resistance ratio to
more than 10% at room-temperature, which thus implies significant potential of
noncollinear antiferromagnets for large signal-output and high-density
antiferromagnetic spintronic device applications. | 2108.04439v1 |
2021-09-07 | Strain-dependent resistance and giant gauge factor in monolayer WSe2 | We report the strong dependence of resistance on uniaxial strain in monolayer
WSe2 at various temperatures, where the gauge factor can reach as large as
2400. The observation of strain-dependent resistance and giant gauge factor is
attributed to the emergence of nonzero Berry curvature dipole. Upon increasing
strain, Berry curvature dipole can generate net orbital magnetization, which
would introduce additional magnetic scattering, decreasing the mobility and
thus conductivity. Our work demonstrates the strain engineering of Berry
curvature and thus the transport properties, making monolayer WSe2 potential
for the application in the high-performance flexible and transparent
electronics. | 2109.02980v1 |
2021-09-12 | Coexistence of resistance oscillations and the anomalous metal phase in a lithium intercalated TiSe$_2$ superconductor | Superconductivity and charge density wave (CDW) appear in the phase diagram
of a variety of materials including the high - $T$$_c$ cuprate family and many
transition metal dichalcogenides (TMDs). Their interplay may give rise to
exotic quantum phenomena. Here, we show that superconducting arrays can
spontaneously form in TiSe$_2$ - a TMD with coexisting superconductivity and
CDW - after lithium ion intercalation. We induce a superconducting dome in the
phase diagram of Li$_x$TiSe$_2$ by using the ionic solid-state gating
technique. Around optimal doping, we observe magnetoresistance oscillations,
indicating the emergence of periodically arranged domains. In the same
temperature, magnetic field and carrier density regime where the resistance
oscillations occur, we observe signatures for the anomalous metal - a state
with a resistance plateau across a wide temperature range below the
superconducting transition. Our study not only sheds further insight into the
mechanism for the periodic electronic structure, but also reveals the interplay
between the anomalous metal and superconducting fluctuations. | 2109.05450v1 |
2021-10-11 | Observation of Exchange Bias in Antiferromagnetic Cr$_{0.79}$Se due to the Coexistence of Itinerant Weak Ferromagnetism at Low-temperatures | We report on the structural, electrical transport, and magnetic properties of
antiferromagnetic transition-metal monochalcogenide Cr$_{0.79}$Se. Different
from the existing off-stoichiometric compositions, Cr$_{0.79}$Se is found to be
synthesised into the same NiAs-type hexagonal crystal structure of CrSe.
Resistivity data suggest Cr$_{0.79}$Se to be a Fermi-liquid-type metal at low
temperatures, while at intermediate temperatures the resistivity depends
sublinearly on the temperature. Eventually, at the elevated temperatures the
rate of change of resistivity rapidly decreases with increasing temperature.
Magnetic measurements suggest a transition from paramagnetic phase to an
antiferromagnetic phase at a N$\acute{e}$el temperature of 225 K. Further
reduction of the sample temperature results into coexistance of weak
ferromagnetism along with the antiferromagnetic phase below 100 K. As a result,
below 100 K, we identify significant exchange bias due to the interaction
between the ferro- and antiferromagnetic phases. In addition, from the
temperature dependent X-ray diffraction measurements we observe that the
NiAs-type structure is stable up to as high as 600$^o$C. | 2110.05058v1 |
2022-06-16 | Fill Factor Losses and Deviations from the Superposition Principle in Lead-Halide Perovskite Solar Cells | The enhancement of the fill factor in the current generation of perovskite
solar cells is the key for further efficiency improvement. Thus, methods to
quantify the fill factor losses are urgently needed. A classical method to
quantify Ohmic and non-Ohmic resistive losses in solar cells is based on the
comparison between the voltage in the dark and under illumination analysed at
equal recombination current density. Applied to perovskite solar cells, we
observe a combination of an Ohmic series resistance with a voltage-dependent
resistance that is most prominent at short circuit and low forward bias. The
latter is most likely caused by the poor transport properties of the electron
and/or hole transport layers. By measuring the photoluminescence of perovskite
solar cells as a function of applied voltage, we provide direct evidence for a
high quasi-Fermi level splitting at low and moderate forward bias that
substantially exceeds the externally applied voltage. This quasi-Fermi level
splitting causes recombination losses and, thus, reduces both the short-circuit
current and the fill factor of the solar cell. | 2207.02297v1 |
2022-12-07 | Self-assembled neuromorphic networks at self-organized criticality in Ag-hBN platform | Networks and systems which exhibit brain-like behavior can analyze
information from intrinsically noisy and unstructured data with very low power
consumption. Such characteristics arise due to the critical nature and complex
interconnectivity of the brain and its neuronal network. We demonstrate that a
system comprising of multilayer hexagonal Boron Nitride (hBN) films contacted
with Silver (Ag), that can uniquely host two different self-assembled networks,
which are self-organized at criticality (SOC). This system shows bipolar
resistive switching between high resistance (HRS) and low resistance states
(LRS). In the HRS, Ag clusters (nodes) intercalate in the van der Waals gaps of
hBN forming a network of tunnel junctions, whereas the LRS contains a network
of Ag filaments. The temporal avalanche dynamics in both these states exhibit
power-law scaling, long-range temporal correlation, and SOC. These networks can
be tuned from one to another with voltage as a control parameter. For the first
time, different neuron-like networks are realized in a single CMOS compatible,
2D materials platform. | 2301.01619v1 |
2023-06-13 | An Evaluation of Multi-Component Weft-Knitted Twill Structures for Sensing Tensile Force | We present multi-component knitted resistive sensors for tracking tensile
force. The knits were fabricated using a Twill structure, which is a simple
pattern featuring anisotropic elastic behavior, providing high stability along
course-direction. Our sensors are made of two commercially available conductive
yarn types, with highly different linear resistance. We present a variety of
integration methods using the proposed Twill structure, all of which can be
easily replicated on a two-bed weft-knitting machine. We evaluate the
performance of the resulting sensor variations, with respect to consistency,
hysteresis, short-term and long-term relaxation and drift, among other metrics.
We found that particulars of the knit's loop composition have a crucial effect
on the consistency of the sensor readings. Furthermore, we show that knitting
resistive yarn more tightly than the substrate material gives superior results
and that improving elastic recoil by adding Lycra to the supporting substrate
can considerably improve performance. | 2306.07612v1 |
2024-04-13 | Combinatorial Printing of Functionally Graded Solid-State Electrolyte for High-Voltage Lithium Metal Batteries | Heterogeneous multilayered solid-state electrolyte (HMSSE) has been widely
explored for their broadened working voltage range and compatibility with
electrodes. However, due to the limitations of traditional manufacturing
methods such as casting, the interface between electrolyte layers in HMSSE can
decrease the ionic conductivity severely. Here, a novel combinatory aerosol jet
printing (CAJP) is introduced to fabricate functionally graded solid-state
electrolyte (FGSSE) without sharp interface. Owing to the unique ability of
CAJP (in-situ mixing and instantaneous tuning of the mixing ratio), FGSSE with
smooth microscale compositional gradation is achieved. Electrochemical tests
show that FGSSE has excellent oxidative stability exceeding 5.5 V and improved
conductivity (>7 times of an analogous HMSSE). By decoupling the total
resistance, we show that the resistance from the electrolyte/electrolyte
interface of HMSSE is 5.7 times of the total resistance of FGSSE. The
Li/FGSSE/NCM622 cell can be stably run for more than 200 cycles along with
improved rate performance. | 2404.09008v1 |
2024-05-29 | Multipacting mitigation by atomic layer deposition: the case study of Titanium Nitride | This study investigates the use of Atomic Layer deposition (ALD) to mitigate
multipacting phenomena inside superconducting radio frequency (SRF) cavities
used in particle accelerators. The unique ALD capability to control the film
thickness down to the atomic level on arbitrary complex shape objects enable
the fine tuning of TiN film resistivity and total electron emission yield
(TEEY) from coupons to devices. This level of control allows us to adequately
choose a TiN film thickness that provide both a high resistivity to prevent
Ohmic losses and low TEEY to mitigate multipacting for the application of
interest. The methodology presented in this work can be scaled to other domain
and devices subject to RF fields in vacuum and sensitive to multipacting or
electron discharge processes with their own requirements in resistivities and
TEEY values | 2405.18949v1 |
2015-05-29 | Few Layer HfS2 FET | 2D materials are expected to be favorable channel materials for field-effect
transistor (FET) with extremely short channel length because of their superior
immunity to short-channel effects (SCE). Graphene, which is the most famous 2D
material, has no bandgap without additional techniques and this property is
major hindrance in reducing the drain leakage. Therefore, 2D materials with
finite band gap, such as transition metal dichalcogenides (TMDs, e.g. MoS2
WSe2) or phosphorene, are required for the low power consumption FETs. Hafnium
disulfide (HfS2) is a novel TMD, which has not been investigated as channel
material. We focused on its potential for well-balanced mobility and bandgap
properties. The higher electron affinity of Hf dichalcogenides compared with Mo
or W chalcogenides facilitates the formation of low resistance contact and
staggered heterojunction with other 2D materials. Here we demonstrate the first
few layer HfS2 FET with robust current saturation and high current on/off ratio
of more than 10^4. | 1505.07970v1 |
2011-10-29 | From mixed valence to the Kondo lattice regime | Many heavy fermion materials are known to crossover from the Kondo lattice
regime to the mixed-valent regime or vice-versa as a function of pressure or
doping. We study this crossover theoretically by employing the periodic
Anderson model within the framework of the dynamical mean field theory. Changes
occurring in the dynamics and transport across this crossover are highlighted.
As the valence is decreased (increased) relative to the Kondo lattice regime,
the Kondo resonance broadens significantly, while the lower (upper) Hubbard
band moves closer to the Fermi level. The resistivity develops a two peak
structure in the mixed valent regime: a low temperature coherence peak and a
high temperature 'Hubbard band' peak. These two peaks merge yielding a broad
shallow maximum upon decreasing the valence further. The optical conductivity,
likewise exhibits an unusual absorption feature (shoulder) in the deep
mid-infrared region, which grows in intensity with decreasing valence. The
involvement of the Hubbard bands in dc transport, and of the effective f-level
in the optical conductivity are shown to be responsible for the anomalous
transport properties. A two-band hybridization-gap model, which neglects
incoherent effects due to many-body scattering, commonly employed to understand
the optical response in these materials is shown to be inadequate, especially
in the mixed-valent regime. Comparison of theory with experiment carried out
for (a) dc resistivities of CeRhIn5, Ce2Ni3Si5, CeFeGe3 and YbIr2Si2; (b)
pressure dependent resistivity of YbInAu2 and CeCu6; and (c) optical
conductivity measurements in YbIr2Si2 yields excellent agreement. | 1110.6498v1 |
2021-04-01 | Enhanced spin injection in molecularly functionalized graphene via ultra-thin oxide barriers | Realisation of practical spintronic devices relies on the ability to create
and detect pure spin currents. In graphene-based spin valves this is usually
achieved by injection of spin-polarized electrons from ferromagnetic contacts
via a tunnel barrier, with Al2O3 and MgO used most widely as barrier materials.
However, the requirement to make these barriers sufficiently thin often leads
to pinholes and low contact resistances which in turn results in low spin
injection efficiencies, typically 5% at room temperature, due to the so-called
resistance mismatch problem. Here we demonstrate an alternative approach to
fabricate ultra-thin tunnel barrier contacts to graphene. We show that
laser-assisted chemical functionalization of graphene with sp3-bonded phenyl
groups effectively provides a seed layer for growth of ultrathin Al2O3 films,
ensuring smooth, high quality tunnel barriers and an enhanced spin injection
efficiency. Importantly, the effect of functionalization on spin transport in
the graphene channel itself is relatively weak, so that the enhanced spin
injection dominates and leads to an order of magnitude increase in spin
signals. Furthermore, spatial control of functionalization using a focused
laser beam and lithographic techniques can in principle be used to limit
functionalization to contact areas only, further reducing the effect on the
graphene channel. Our results open a new route towards circumventing the
resistance mismatch problem in graphene-based spintronic devices based on the
easily available and highly stable Al2O3, and facilitate a step forward in the
development of their practical applications. | 2104.00709v1 |
2017-05-16 | Application of flash method in the measurements of interfacial thermal resistance in layered and particulate composite materials | Presented study concerns the possibility of evaluation of interfacial thermal
resistance (ITR) between the constituents in composite materials with the use
of flash technique. Two variants of such measurement are considered, the first
of which is the measurement of ITR between two bonded layers of different
materials which had been studied before by various researchers. The second
tested measurement method is targeted at determination of ITR in particulate
composites with low and moderate filler content based on their effective
thermal conductivity. Method of such measurement is proposed and tested on two
cases of particle-filled polymer composites. Positive verification results were
obtained for polymer/glass composite in which the difference between thermal
conductivities of matrix and filler is low. For a polymer filled with aluminum
particles the evaluation of average ITR in the samples was impossible as the
effective medium models applied in the method strongly underestimated the
thermal conductivity of that material. The investigation confirmed the need for
more accurate methods of macroscopic thermal properties prediction for
composite media with high contrast of thermal conductivities of the
constituents. Extended literature study suggests that the method can be
applicable to selected classes of engineering materials. | 1705.05621v1 |
1998-12-23 | Temperature dependence of electric resistance and magnetoresistance of pressed nanocomposites of multilayer nanotubes with the structure of nested cones | Bulk samples of carbon multilayer nanotubes with the structure of nested
cones (fishbone structure) suitable for transport measurements, were prepared
by compressing under high pressure (~25 kbar) a nanotube precursor synthesized
through thermal decomposition of polyethylene catalyzed by nickel. The
structure of the initial nanotube material was studied using high-resolution
transmission electron microscopy. In the low-temperature range (4.2 - 100 K)
the electric resistance of the samples changes according to the law ln \rho ~
(T_0/T)^{1/3}, where T_0 ~ 7 K. The measured magnetoresistance is quadratic in
the magnetic field and linear in the reciprocal temperature. The measurements
have been interpreted in terms of two-dimensional variable-range hopping
conductivity. It is suggested that the space between the inside and outside
walls of nanotubes acts as a two-dimensional conducting medium. Estimates
suggest a high value of the density of electron states at the Fermi level of
about 5 10^{21} eV^{-1} cm^{-3}. | 9812384v1 |
2017-01-07 | Spatially uniform resistance switching of low current, high endurance titanium-niobium-oxide memristors | We analyzed micrometer-scale titanium-niobium-oxide prototype memristors,
which exhibited low write-power (<3 {\mu}W) and energy (<200 fJ/bit/{\mu}m2),
low read-power (~nW), and high endurance (>millions of cycles). To understand
their physico-chemical operating mechanisms, we performed in-operando
synchrotron x-ray transmission nanoscale spectromicroscopy using an
ultra-sensitive time-multiplexed technique. We observed only spatially uniform
material changes during cell operation, in sharp contrast to the frequently
detected formation of a localized conduction channel in transition-metal-oxide
memristors. We also associated the response of assigned spectral features
distinctly to non-volatile storage (resistance change) and writing of
information (application of voltage and Joule heating). These results provide
critical insights into high-performance memristors that will aid in device
design, scaling and predictive circuit-modeling, all of which are essential for
the widespread deployment of successful memristor applications. | 1701.01784v1 |
2001-02-09 | Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering | High-density bulk materials of a newly discovered 40K intermetallic MgB2
superconductor were prepared by high pressure sintering. Superconducting
transition with the onset temperature of 39K was confirmed by both magnetic and
resistive measurements. Magnetization versus field (M-H) curve shows the
behavior of a typical Type II superconductor and the lower critical field
Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good
connection between grains and critical current density Jc estimated from the
magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper
critical field Hc2(0) determined by extrapolating the onset of resistive
transition and assuming a dirty limit is 18T. | 0102167v1 |
2018-09-17 | High quality factor graphene-based 2D heterostructure mechanical resonator | Ultralight mechanical resonators based on low-dimensional materials are well
suited as exceptional transducers of minuscule forces or mass changes. However,
the low dimensionality also provides a challenge to minimize resistive losses
and heating. Here, we report on a novel approach that aims to combine different
2D materials to tackle this challenge. We fabricated a heterostructure
mechanical resonator consisting of few layers of niobium diselenide (NbSe$_2$)
encapsulated by two graphene sheets. The hybrid membrane shows high quality
factors up to 245'000 at low temperatures, comparable to the best few-layer
graphene mechanical resonators. In contrast to few-layer graphene resonators,
the device shows reduced electrical losses attributed to the lower resistivity
of the NbSe$_2$ layer. The peculiar low temperature dependence of the intrinsic
quality factor points to dissipation over two-level systems which in turn relax
over the electronic system. Our high sensitivity readout is enabled by coupling
the membrane to a superconducting cavity which allows for the integration of
the hybrid mechanical resonator as a sensitive and low loss transducer in
future quantum circuits. | 1809.06169v1 |
2022-04-22 | Comparison of different sensor thicknesses and substrate materials for the monolithic small collection-electrode technology demonstrator CLICTD | Small collection-electrode monolithic CMOS sensors profit from a high
signal-to-noise ratio and a small power consumption, but have a limited active
sensor volume due to the fabrication process based on thin high-resistivity
epitaxial layers. In this paper, the active sensor depth is investigated in the
monolithic small collection-electrode technology demonstrator CLICTD. Charged
particle beams are used to study the charge-collection properties and the
performance of devices with different thicknesses both for perpendicular and
inclined particle incidence. In CMOS sensors with a high-resistivity
Czochralski substrate, the depth of the sensitive volume is found to increase
by a factor two in comparison with standard epitaxial material and leads to
significant improvements in the hit-detection efficiency and the spatial and
time resolution. | 2204.10569v2 |
2021-11-01 | A New Class of Alumina-Forming Superalloy for 3D Printing | A new class of crack-resistant nickel-based superalloy containing high
$\gamma^\prime$ fraction is studied for the laser-powder bed fusion (L-PBF)
process. The effects of the (Nb+Ta)/Al ratio is emphasised, a strategy that is
shown to confer excellent low-temperature strength whilst maintaining oxidation
resistance at high temperatures via stable alumina scale formation. The
processability of the new alloys is characterised with respect to defect
assessment by micro-focus x-ray computed tomography; use is made of a prototype
turbine blade geometry and the heritage alloy CM247LC as a benchmark. In all
cases, some processing-related porosity is present in thin wall sections such
as the trailing edge, but this can be avoided by judicious processing. The
cracking seen in CM247LC -- in solid-state, liquation and solidification forms
-- is avoided. A novel sub-solvus heat treatment strategy is proposed which
takes advantage of AM not requiring solutioning; super-solvus heat treatment is
inappropriate since it embrittles the material by deterioration of the texture
and coarsening of grain boundary carbides. The tensile strength of the new
superalloy is greatest when the Nb+Ta content is highest and exceeds that of
CM247LC up to $\sim$900$\,$$^\circ$C. The oxidation resistance is best when Al
content is highest, and oxidation-assisted cracking resistance maximized when
the (Nb+Ta)/Al ratio is balanced. In all cases these are equivalent or superior
to that of CM247LC. Nevertheless, the creep resistance of the new alloys is
somewhat inferior to that of CM247LC for which the $\gamma^\prime$, C, and B
contents are higher; this implies a processing/property trade-off which
requires further clarification. | 2111.01049v1 |
2005-11-08 | Development of the Charge Particle Detector Based on CVD - Diamond | High radiation hardness, chemical resistance, high temperature operation
capabilities stimulate a growing interest to use diamond materials as detectors
of ionizing radiation. Samples of CVD-diamond materials in sizes 12 square mm
and 4 square mm with thickness from 50 microns up to 500 microns have been
grown in INR RAS using a DC glow discharge in a mixture of gases CH4/H2 on
molybdenum substrates. | 0511068v1 |
2018-10-24 | High Strain Rate Behaviour of Nano-quasicrystalline Al93Fe3Cr2Ti2 Alloy and Composites | In the present work, we demonstrate for the first time the outstanding
dynamic mechanical properties of nano-quasicrystalline Al93Fe3Cr2Ti2 at.% alloy
and composites. Unlike most crystalline aluminium-based alloys, this alloy and
composites exhibit substantial strain rate sensitivity and retain much of their
ductility at high rates of strain. This opens new pathways for use in
safety-critical materials where impact resistance is required. | 1810.10476v2 |
2019-12-24 | Large spin Hall angle and spin mixing conductance in highly resistive antiferromagnetic Mn2Au | Antiferromagnetic (AFM) materials recently have shown interest in the
research in spintronics due to its zero stray magnetic field, high anisotropy,
and spin orbit coupling. In this context, the bi-metallic AFM Mn2Au has drawn
attention because it exhibits unique properties and its Neel temperature is
very high. Here, we report spin pumping and inverse spin Hall effect
investigations in Mn2Au and CoFeB bilayer system using ferromagnetic resonance.
We found large spin Hall angle {\theta}_SH = 0.22 | 1912.11522v2 |
2008-09-09 | Printed Graphene Circuits | we have fabricated transparent electronic devices based on graphene materials
with thickness down to one single atomic layer by the transfer printing method.
The resulting printed graphene devices retain high field effect mobility and
have low contact resistance. The results show that the transfer printing method
is capable of high-quality transfer of graphene materials from silicon dioxide
substrates, and the method thus will have wide applications in manipulating and
delivering graphene materials to desired substrate and device geometries. Since
the method is purely additive, it exposes graphene (or other functional
materials) to no chemical preparation or lithographic steps, providing greater
experimental control over device environment for reproducibility and for
studies of fundamental transport mechanisms. Finally, the transport properties
of the graphene devices on the PET substrate demonstrate the non-universality
of minimum conductivity and the incompleteness of the current transport theory. | 0809.1634v1 |
2021-08-29 | A graph based workflow for extracting grain-scale toughness from meso-scale experiments | We introduce a novel machine learning computational framework that aims to
compute the material toughness, after subjected to a short training process on
a limited meso-scale experimental dataset. The three part computational
framework relies on the ability of a graph neural network to perform high
accuracy predictions of the micro-scale material toughness, utilizing a limited
size dataset that can be obtained from meso-scale fracture experiments. We
analyze the functionality of the different components of the framework, but the
focus is on the capabilities of the neural network. The minimum size of the
dataset required for the network training is investigated. The results
demonstrate the high efficiency of the algorithm in predicting the crack growth
resistance in micro-scale level, using a crack path trajectory limited to
200-300 grains for the network training. The merit of the proposed framework
arises from the capacity to enhance its performance in different material
systems with a limited additional training on data obtained from experiments
that do not require complex or cumbersome measurements. The main objective is
the development of an efficient computational tool that enables the study of a
wide range of material microstructure properties and the investigation of their
influence on the material toughness. | 2108.12783v1 |
2022-08-25 | Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion | Severe plastic deformation using high-pressure torsion of ternary Cu-based
materials (CuFeCo and CuFeNi) was used to fabricate bulk samples with a
nanocrystalline microstructure. The goal was to produce materials featuring the
granular giant magnetoresistance effect, requiring interfaces between ferro-
and nonmagnetic materials. This magnetic effect was found for both ternary
systems; adequate subsequent annealing had a positive influence. The
as-deformed states, as well as microstructural changes upon thermal treatments,
were studied using scanning electron microscopy and X-ray diffraction
measurements. Deducing from electron microscopy, a single-phase structure was
observed for all as-deformed samples, indicating the formation of a
supersaturated solid solution. However, judging from the presence of the
granular giant-magnetoresistive effect, small ferromagnetic particles have to
be present. The highest drop in room temperature resistivity (2.45% at 1790
kA/m) was found in Cu62Fe19Ni19 after annealing for 1 h at 400 {\deg}C.
Combining the results of classical microstructural studies and magnetic
measurements, insights into the evolution of ferromagnetic particles are
accessible. | 2208.11895v1 |
2023-03-28 | Electrolyte Coatings for High Adhesion Interfaces in Solid-state Batteries from First Principles | We introduce an adhesion parameter that enables rapid screening for materials
interfaces with high adhesion. This parameter is obtained by density functional
theory calculations of individual single-material slabs rather than slabs
consisting of combinations of two materials, eliminating the need to calculate
all configurations of a prohibitively vast space of possible interface
configurations. Cleavage energy calculations are used as an upper bound for
electrolyte and coating energies and implemented in an adapted contact angle
equation to derive the adhesion parameter. In addition to good adhesion, we
impose further constraints in electrochemical stability window, abundance, bulk
reactivity, and stability to screen for coating materials for next-generation
solid-state batteries. Good adhesion is critical in combating delamination and
resistance to Lithium diffusivity in solid-state batteries. Here, we identify
several promising coating candidates for the Li7La3Zr2O12 and sulfide
electrolyte systems including the previously investigated electrode coating
materials LiAlSiO4 and Li5AlO8, making them especially attractive for
experimental optimization and commercialization. | 2303.16350v1 |
2014-12-12 | High-T_c superconductivity in ultrathin Bi_2Sr_2CaCu_2O_8+x down to halfunit-cell thickness by protection with graphene | High-T_c superconductors confined to two dimension exhibit novel physical
phenomena, such as superconductor-insulator transition. In the
Bi_2Sr_2CaCu_2O_8+x (Bi2212) model system, despite extensive studies, the
intrinsic superconducting properties at the thinness limit have been difficult
to determine. Here we report a method to fabricate high quality single-crystal
Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212
van der Waals heterostructure, in which sharp superconducting transitions are
observed. The heterostructure also exhibits a nonlinear current-voltage
characteristic due to the Dirac nature of the graphene band structure. More
interestingly, although the critical temperature remains essentially the same
with reduced thickness of Bi2212, the slope of the normal state T-linear
resistivity varies by a factor of 4-5, and the sheet resistance increases by
three orders of magnitude, indicating a surprising decoupling of the normal
state resistance and superconductivity. The developed technique is versatile,
applicable to investigate other two-dimensional (2D) superconducting materials. | 1412.3896v1 |
2019-08-18 | Maximizing the spin-orbit torque efficiency of Pt/Ti multilayers by optimization of the tradeoff between the intrinsic spin Hall conductivity and carrier lifetime | We report a comprehensive study of the maximization of the spin Hall ratio
({\theta}SH) in Pt thin films by the insertion of sub-monolayer layers of Ti to
decrease carrier lifetime while minimizing the concurrent reduction in the spin
Hall conductivity. We establish that the intrinsic spin Hall conductivity of
Pt, while robust against the strain and the moderate interruption of crystal
order caused by these insertions, begins to decrease rapidly at high
resistivity level because of the shortening carrier lifetime. The unavoidable
trade-off between the intrinsic spin Hall conductivity and carrier lifetime
sets a practical upper bound of {\theta}SH >=0.8 for heterogeneous materials
where the crystalline Pt component is the source of the spin Hall effect and
the resistivity is increased by shortening carrier lifetime. This work also
establishes a very promising spin-Hall metal of [Pt 0.75 nm/Ti 0.2 nm]7/Pt 0.75
nm for energy-efficient, high-endurance spin-orbit torque technologies (e.g.,
memories, oscillators, and logic) due to its combination of a giant {\theta}SH
of 0.8, or equivalently a dampinglike spin torque efficiency per unit current
density of 0.35, with a relatively low resistivity (90 uOhm cm) and high
suitability for practical technology integration. | 1908.06528v1 |
2019-10-22 | Transverse Beam Stability with Low-Impedance Collimators in the High Luminosity Large Hadron Collider: Status and Challenges | The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will double
its beam intensity for the needs of High Energy Physics frontier. In order to
ensure coherent stability until the beams are put in collision, the transverse
impedance has to be reduced. As the major portion of the ring impedance is
supplied by its collimation system, several low resistivity jaw materials have
been proposed to lower the collimator impedance and a special collimator has
been built and installed in the machine to study their effect. The results show
a significant reduction of the resistive wall tune shift with novel materials,
in agreement with the impedance model and the bench impedance and resistivity
measurements. The largest improvement is obtained with a 5 {\mu}m Molybdenum
coating of a Molybdenum-Graphite jaw. This coating can lower the machine
impedance by up to 30% and the stabilizing Landau octupole threshold by up to
120 A. The collimators to be upgraded have been chosen based on the improvement
of the octupole threshold, as well as the tolerance to steady state losses and
failure scenarios. A half of the overall improvement can be obtained by coating
the jaws of a subset of 4 out of 11 collimators identified as the highest
contributors to machine impedance. This subset of low-impedance collimators is
being installed during the Long Shutdown 2 in 2019-2020. | 1910.09974v2 |
2020-11-05 | Preparation of the AlTiNiCuCox system high-entropy alloys and structural analysis | This study aimed to explore and develop a new material with high
cost-effectiveness, excellent strength, light weight, high hardness, great wear
resistance, corrosion resistance, and favorable oxidation resistance.
Structural analysis suggested that, with the change in Co addition amount, the
surface morphology and structure of the alloy system changed. XRD analysis
indicated that, the alloy system was the FCC+BCC mixed structure. In addition,
metallographical demonstrated that, with the increase in Co content, the
dendritic crystal transformed from big block to dendritic structure, then to
snowflake, gradually to petal-like, and finally to petal shape. SEM-EDS
analysis revealed that, Cu element was enriched in interdendritic site, while
Ti, Ni, Al and Co elements were enriched in dendrite. Besides, TEM and TEM-EDS
analysis indicated that, there was nano-size precipitate of small particles in
the Cu-enriched block region, along with dislocation; further, there was twin
structure inside the dendrite, as well as the second phase with different
morphology, and the second phase showed coherency with the matrix. The above
analysis suggested that, the intercrystalline structure was the Cu-enriched
phase of FCC structure; the internal matrix of grain was the NiTi and TiCo
phases of BCC structure; and the second phases inside the grain were the
AlCu2Ti,AlNi2Ti,AlCo2Ti and CuNi phases of FCC structure. Taken together, the
AlTiNiCuCox system novel alloys have changed phase structures and phase types
of the alloy system. | 2011.02799v1 |
2022-01-19 | Secondary Phase Limited Metal-Insulator Phase Transition in Chromium Nitride Thin Films | Chromium nitride (CrN) is a well-known hard coating material that has found
applications in abrasion and wear-resistant cutting tools, bearings, and
tribology applications due to its high hardness, high-temperature stability,
and corrosion-resistant properties. In recent years, CrN has also attracted
significant interest due to its high thermoelectric power factor, and for its
unique and intriguing metal-insulator phase transition. While CrN bulk
single-crystals exhibit the characteristic metal-insulator transition
accompanied with structural (orthorhombic-to-rocksalt) and magnetic
(antiferromagnetic-to-paramagnetic) transition at ~260-280K, observation of
such phase transition in thin-film CrN has been scarce and highly debated. In
this work, the formation of the secondary metallic Cr2N phase during the growth
is demonstrated to inhibit the observation of metal-insulator phase transition
in CrN thin films. When the Cr-flux during deposition is reduced below a
critical limit, epitaxial and stoichiometric CrN thin film is obtained that
reproducibly exhibits the phase transition. Annealing of the mixed-phase film
inside reducing NH3 environment converts the Cr2N into CrN, and a discontinuity
in the electrical resistivity at ~ 277 K appears which supports the underlying
hypothesis. A clear demonstration of the origin behind the controversy of the
metal-insulator transition in CrN thin films marks significant progress and
would enable its nanoscale device realization. | 2201.07442v1 |
2022-01-22 | High-throughput calculations combining machine learning to investigate the corrosion properties of binary Mg alloys | Magnesium (Mg) alloys have shown great prospects as both structural and
biomedical materials, while poor corrosion resistance limits their further
application. In this work, to avoid the time-consuming and laborious experiment
trial, a high-throughput computational strategy based on first-principles
calculations is designed for screening corrosion-resistant binary Mg alloy with
intermetallics, from both the thermodynamic and kinetic perspectives. The
stable binary Mg intermetallics with low equilibrium potential difference with
respect to the Mg matrix are firstly identified. Then, the hydrogen adsorption
energies on the surfaces of these Mg intermetallics are calculated, and the
corrosion exchange current density is further calculated by a hydrogen
evolution reaction (HER) kinetic model. Several intermetallics, e.g. Y3Mg, Y2Mg
and La5Mg, are identified to be promising intermetallics which might
effectively hinder the cathodic HER. Furthermore, machine learning (ML) models
are developed to predict Mg intermetallics with proper hydrogen adsorption
energy employing work function (W_f) and weighted first ionization energy
(WFIE). The generalization of the ML models is tested on five new binary Mg
intermetallics with the average root mean square error (RMSE) of 0.11 eV. This
study not only predicts some promising binary Mg intermetallics which may
suppress the galvanic corrosion, but also provides a high-throughput screening
strategy and ML models for the design of corrosion-resistant alloy, which can
be extended to ternary Mg alloys or other alloy systems. | 2201.09059v1 |
2019-10-17 | High electrical conductivity in the epitaxial polar metals LaAuGe and LaPtSb | Polar metals are an intriguing class of materials that simultaneously host
free carriers and polar structural distortions. Despite the name "polar metal,"
however, most well-studied polar metals are poor electrical conductors. Here,
we demonstrate the molecular beam epitaxial (MBE) growth of LaPtSb and LaAuGe,
two polar metal compounds whose electrical resistivity is an order of magnitude
lower than the well studied oxide polar metals. These materials belong to a
broad family of $ABC$ intermetallics adopting the stuffed wurtzite structure,
also known as hexagonal Heusler compounds. Scanning transmission electron
microscopy (STEM) reveals a polar structure with unidirectionally buckled $BC$
(PtSb, AuGe) planes. Magnetotransport measurements demonstrate good metallic
behavior with low residual resistivity ($\rho_{LaAuGe}=59.05$
$\mu\Omega\cdot$cm and $\rho_{LaAPtSb}=27.81$ $\mu\Omega\cdot$cm at 2K) and
high carrier density ($n_h\sim 10^{21}$ cm$^{-3}$). Photoemission spectroscopy
measurements confirm the band metallicity and are in quantitative agreement
with density functional theory (DFT) calculations. Through DFT-Chemical
Pressure and Crystal Orbital Hamilton Population analyses, the atomic packing
factor is found to support the polar buckling of the structure, though the
degree of direct interlayer $B-C$ bonding is limited by repulsion at the $A-C$
contacts. When combined with insulating hexagonal Heuslers, these materials
provide a new platform for fully epitaxial, multiferroic heterostructures. | 1910.07685v1 |
2024-02-06 | Physics-based Modeling of Pulse and Relaxation of High-rate Li/CF$_{x}$-SVO batteries in Implantable Medical Devices | We present a physics-based model that accurately predicts the performance of
Medtronic's implantable medical device battery lithium/carbon monofluoride
(CF$_x$) - silver vanadium oxide (SVO) under both low-rate background
monitoring and high-rate pulsing currents. The distinct properties of multiple
active materials are reflected by parameterizing their thermodynamics,
kinetics, and mass transport properties separately. Diffusion limitations of
Li$^+$ in SVO are used to explain cell voltage transient behavior during pulse
and post-pulse relaxation. We also introduce change in cathode electronic
conductivity, Li metal anode surface morphology, and film resistance buildup to
capture evolution of cell internal resistance throughout multi-year electrical
tests. We share our insights on how the Li$^+$ redistribution process between
active materials can restore pulse capability of the hybrid electrode, allow
CF$_x$ to indirectly contribute to capacity release during pulsing, and affect
the operation protocols and design principles of batteries with other hybrid
electrodes. We also discuss additional complexities in porous electrode model
parameterization and electrochemical characterization techniques due to
parallel reactions and solid diffusion pathways across active materials. We
hope our models implemented in the Hybrid Multiphase Porous Electrode Theory
(Hybrid-MPET) framework can complement future experimental research and
accelerate development of multi-active material electrodes with targeted
performance. | 2402.03677v1 |
2020-04-25 | Reconciliation of experiments and theory on transport properties of iron and the geodynamo | The amount of heat transport from the core, which constrains the dynamics and
thermal evolution of the region, depends on the transport properties of iron.
Ohta et al.(2016) and Konopkova et al.(2016) measured electrical resistivity
and thermal conductivity of iron, respectively, in laser-heated diamond anvil
cells (DACs) at relevant Earth's core pressure-temperature (P-T) conditions,
and obtained dramatically contradictory results. Here we measure the electrical
resistivity of hcp-iron up to ~170 GPa and ~3,000 K using a four-probe van der
Pauw method coupled with homogeneous flat-top laser-heating in a DAC. We also
compute its electrical and thermal conductivity by first-principles methods
including electron-phonon and electron-electron scattering. We find that the
measured resistivity of hcp-iron increases almost linearly with increasing
temperature, and is consistent with current first-principles computations. The
proportionality coefficient between resistivity and thermal conductivity (the
Lorenz number) in hcp-iron differs from the ideal value (2.44*10^-8 W Omega
K^-2), so a non-ideal Lorenz number of ~(2.0-2.1)*10^-8 W Omega K^-2 is used to
convert the experimental resistivity to the thermal conductivity of hcp-Fe at
high P-T. The results constrain the resistivity and thermal conductivity of
hcp-iron to ~80(5) u Omega cm and ~100(10) W/mK, respectively, at conditions
near core-mantle boundary. Our results indicate an adiabatic heat flow of
~10(1) TW through the core-mantle boundary for a liquid Fe alloy outer core,
supporting a present-day geodynamo driven by thermal convection through the
core's secular cooling and by compositional convection through the latent heat
and gravitational energy during the inner core's solidification. | 2004.12035v1 |
2020-08-26 | Understanding the role of Ca segregation on thermal stability, electrical resistivity and mechanical strength of nanostructured aluminum | Achieving a combination of high mechanical strength and high electrical
conductivity in low-weight Al alloys requires a full understanding of the
relationships between nanoscaled features and physical properties. Grain
boundary strengthening through grain size reduction offers some interesting
possibilities but is limited by thermal stability issues. Zener pinning by
stable nanoscaled particles or grain boundary segregation are well-known
strategies for stabilizing grain boundaries. In this study, the Al-Ca system
has been selected to investigate the way segregation affects the combination of
mechanical strength and electrical resistivity. For this purpose, an Al-Ca
composite material was severely deformed by high-pressure torsion to achieve a
nanoscaled structure with a mean grain size of only 25 nm. X-ray diffraction,
transmission electron microscopy and atom probe tomography data revealed that
the fcc Ca phase was dissolved for large levels of plastic deformation leading
mainly to Ca segregations along crystalline defects. The resulting
microhardness of about 300 HV is much higher than predictions based on Hall and
Petch Law and is attributed to limited grain boundary mediated plasticity due
to Ca segregation. The electrical resistivity is also much higher than that
expected for nanostructured Al. The main contribution comes from Ca
segregations that lead to a fraction of electrons reflected or trapped by grain
boundaries twice larger than in pure Al. The two-phase state was investigated
by in-situ and ex-situ microscopy after annealing at 200{\textdegree}C for 30
min, where precipitation of nanoscaled Al4Ca particles occurred and the mean
grain size reached 35 nm. Annealing also significantly decreased electrical
resistivity, but it remained much higher than that of nanostructured pure Al,
due to Al/Al4Ca interfaces that reflect or trap more than 85% of electrons. | 2008.11405v1 |
2021-02-15 | High-entropy van der Waals materials formed from mixed metal dichalcogenides, halides and phosphorus trisulfides | The charge, spin, and composition degrees of freedom in high-entropy alloy
endow it with tunable valence and spin states, infinite combinations and
excellent mechanical performance. Meanwhile, the stacking, interlayer, and
angle degrees of freedom in van der Waals material bring it with exceptional
features and technological applications. Integration of these two distinct
material categories while keeping their merits would be tempting. Based on this
heuristic thinking, we design and explore a new range of materials (i.e.,
dichalcogenides, halides and phosphorus trisulfides) with multiple metallic
constitutions and intrinsic layered structure, which are coined as high-entropy
van der Waals materials. Millimeter-scale single crystals with homogeneous
element distribution can be efficiently acquired and easily exfoliated or
intercalated in this materials category. Multifarious physical properties like
superconductivity, magnetic ordering, metal-insulator transition and corrosion
resistance have been exploited. Further research based on the concept of
high-entropy van der Waals materials will enrich the high-throughput design of
new systems with intriguing properties and practical applications. | 2102.07493v2 |
2014-12-01 | Conventional superconductivity at 190 K at high pressures | The highest critical temperature of superconductivity Tc has been achieved in
cuprates: 133 K at ambient pressure and 164 K at high pressures. As the nature
of superconductivity in these materials is still not disclosed, the prospects
for a higher Tc are not clear. In contrast the Bardeen-Cooper-Schrieffer (BCS)
theory gives a clear guide for achieving high Tc: it should be a favorable
combination of high frequency phonons, strong coupling between electrons and
phonons, and high density of states. These conditions can be fulfilled for
metallic hydrogen and covalent hydrogen dominant compounds. Numerous followed
calculations supported this idea and predicted Tc=100-235 K for many hydrides
but only moderate Tc~17 K has been observed experimentally. Here we found that
sulfur hydride transforms at P~90 GPa to metal and superconductor with Tc
increasing with pressure to 150 K at ~200 GPa. This is in general agreement
with recent calculations of Tc~80 K for H2S. Moreover we found
superconductivity with Tc~190 K in a H2S sample pressurized to P>150 GPa at
T>220 K. This superconductivity likely associates with the dissociation of H2S,
and formation of SHn (n>2) hydrides. We proved occurrence of superconductivity
by the drop of the resistivity at least 50 times lower than the copper
resistivity, the decrease of Tc with magnetic field, and the strong isotope
shift of Tc in D2S which evidences a major role of phonons in the
superconductivity. H2S is a substance with a moderate content of hydrogen
therefore high Tc can be expected in a wide range of hydrogen-contain
materials. Hydrogen atoms seem to be essential to provide the high frequency
modes in the phonon spectrum and the strong electron-phonon coupling. | 1412.0460v1 |
2021-04-12 | High-speed ionic synaptic memory based on two-dimensional titanium carbide MXene | Synaptic devices with linear high-speed switching can accelerate learning in
artificial neural networks (ANNs) embodied in hardware. Conventional resistive
memories however suffer from high write noise and asymmetric conductance
tuning, preventing parallel programming of ANN arrays as needed to surpass
conventional computing efficiency. Electrochemical random-access memories
(ECRAMs), where resistive switching occurs by ion insertion into a redox-active
channel address these challenges due to their linear switching and low noise.
ECRAMs using two-dimensional (2D) materials and metal oxides suffer from slow
ion kinetics, whereas organic ECRAMs enable high-speed operation but face
significant challenges towards on-chip integration due to poor temperature
stability of polymers. Here, we demonstrate ECRAMs using 2D titanium carbide
(Ti3C2Tx) MXene that combines the high speed of organics and the integration
compatibility of inorganic materials in a single high-performance device. Our
ECRAMs combine the speed, linearity, write noise, switching energy and
endurance metrics essential for parallel acceleration of ANNs, and importantly,
they are stable after heat treatment needed for back-end-of-line integration
with Si electronics. The high speed and performance of these ECRAMs introduces
MXenes, a large family of 2D carbides and nitrides with more than 30
compositions synthesized to date, as very promising candidates for devices
operating at the nexus of electrochemistry and electronics. | 2104.05396v4 |
2022-12-06 | Novel superhard structures of high-pressure C-N compounds | Through machine learning force field accelerated structure search combined
with first-principles calculations, we have studied the structures of new C-N
compounds with different stoichiometric ratios, and found twelve new superhard
C-N compounds, the energies of these structures are similar to c-C3N4 , which
is possibly synthesized by high pressure experiment, the XRD of Pa-3(C4N)
P3(C4N) and C2/m(C2N) are consistent with previous experimental data and can be
used as the structural candidate. According to the macro hardness model, they
are all superhard structures, with Vickers hardness over 40GPa, even, the
hardness of Pa-3 (C4N) as high as 82.2GPa, and Pa-3 (C4N) combines high tensile
and shear resistance. Compared with the hardness calculated by macro hardness
model and bond resistance model, we obtained the relationship between the
hardness and chemical concentration of C-N compounds under the two models,
besides that, we also calculated the fracture toughness of these structures.
According to Niu's model, P2_1/c(C4N) has the best fracture toughness, which is
higher than WC in calculation, This also indicated the superior mechanical
properties of the novel C-N compounds. Moreover, for nitrogen-rich structures,
they have the potential to be used as high energy density, the energy density
of Pa-3(CN3), P-3c1 (CN4), and I-42d (CN4) are 7.076kJ/g, 7.742kJ/g and
8.045kJ/g, which is close or higher than CL-20, therefore, the C-N compounds
synthesized under high pressure have great potential as ideally superhard
materials and high energy density materials(HEDMs). | 2212.03009v3 |
2004-03-19 | Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy | Magnetic, transport, and x-ray diffraction measurements of ferromagnetic
shape memory alloy Ni$_{2.16}$Mn$_{0.84}$Ga revealed that this alloy undergoes
an intermartensitic transition upon cooling, whereas no such a transition is
observed upon subsequent heating. The difference in the modulation of the
martensite forming upon cooling from the high-temperature austenitic state
[5-layered (5M) martensite], and the martensite forming upon the
intermartensitic transition [7-layered (7M) martensite] strongly affects the
magnetic and transport properties of the alloy and results in a large thermal
hysteresis of the resistivity $\rho$ and magnetization $M$. The
intermartensitic transition has an especially marked influence on the transport
properties, as is evident from a large difference in the resistivity of the 5M
and 7M martensite, $(\rho_{\mathrm{5M}} - \rho_{\mathrm{7M}})/\rho
_{\mathrm{5M}} \approx 15%$, which is larger than the jump of resistivity at
the martensitic transition from the cubic austenitic phase to the monoclinic 5M
martensitic phase. We assume that this significant difference in $\rho$ between
the martensitic phases is accounted for by nesting features of the Fermi
surface. It is also suggested that the nesting hypothesis can explain the
uncommon behavior of the resistivity at the martensitic transition, observed in
stoichiometric and near-stoichiometric Ni-Mn-Ga alloys. | 0403495v1 |
2004-10-10 | Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics | We have produced ultrathin epitaxial graphite films which show remarkable 2D
electron gas (2DEG) behavior. The films, composed of typically 3 graphene
sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC,
and characterized by surface-science techniques. The low-temperature
conductance spans a range of localization regimes according to the structural
state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive
magnetoconductance). Low resistance samples show characteristics of
weak-localization in two dimensions, from which we estimate elastic and
inelastic mean free paths. At low field, the Hall resistance is linear up to
4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2}
per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas
oscillations which correspond to nonlinearities observed in the Hall
resistance, indicating a potential new quantum Hall system. We show that the
high-mobility films can be patterned via conventional lithographic techniques,
and we demonstrate modulation of the film conductance using a top-gate
electrode. These key elements suggest electronic device applications based on
nano-patterned epitaxial graphene (NPEG), with the potential for large-scale
integration. | 0410240v1 |
2005-04-29 | Electromigration in thin tunnel junctions with ferromagnetic/nonmagnetic: nanoconstrictions, local heating, and direct and wind forces | Current Induced Resistance Switching (CIS) was recently observed in thin
tunnel junctions with ferromagnetic (FM) electrodes \emph{i.e} FM/I/FM. This
effect was attributed to electromigration of metallic atoms in
nanoconstrictions in the insulating barrier (I). Here we study how the CIS
effect is influenced by a thin non-magnetic (NM) Ta layer, deposited just below
the AlO$_x$ insulating barrier in tunnel junctions of the type FM/NM/I/FM
(FM=CoFe). Enhanced resistance switching occurs with increasing maximum applied
current ($\Imax$), until a plateau of constant CIS is reached for $\Imax\sim65$
mA (CIS$\sim$60%) and above. However, such high electrical currents also lead
to a large ($\sim$9%) irreversible resistance decrease, indicating barrier
degradation. Anomalous voltage-current characteristics with negative derivative
were also observed near $\pm\Imax$ and this effect is here attributed to
heating in the tunnel junction. One observes that the current direction for
which resistance switches in FM/NM/I/FM (clockwise) is opposite to that of
FM/I/FM tunnel junctions (anti-clockwise). This effect will be discussed in
terms of a competition between the electromigration contributions due to the so
called direct and wind forces. It will be shown that the direct force is likely
to dominate electromigration in the Ta (NM) layers, while the wind contribution
likely dominates in the CoFe (FM) layers. | 0504772v6 |
2007-02-05 | Effect of Ir substitution in the ferromagnetic superconductor RuSr2GdCu2O8 | A detailed study of the effect caused by the partial substitution of Ru by Ir
on the magnetic and superconducting properties of the ruthenocuprate
Ru(1-x)Ir(x)Sr2GdCu2o8; 0 <= x <= 0.10; is presented. The combined experimental
results of structural, electrical, and magnetic measurements indicate that Ir
substitutes Ru for x <= 0.10 with no significant structural distortions.
Ir-doping gradually suppresses both the magnetic and the superconducting
states. However, all samples were observed to attain the zero-resistance state
at temperatures >= 2 K up to the highest applied magnetic field of 18 T. The
resistive upper-critical field Hc2 as a function of temperature has been
determined for these polycrystalline samples. Values of Hc2(0) were found to be
\~ 52 T, and weakly dependent on the Ir concentration. We have also observed
that the superconducting transition width decreases and the slope of the
resistive transition increases with increasing Ir doping, a feature which is
much more pronounced at high applied magnetic fields. The double-peak structure
observed in the derivative of the resistive curves has been related to an
inhomogeneous nature of the physical grains which is enhanced due to the Ru
substitution by Ir. This indicates that the Josephson-junction-array (JJA)
model seems to be appropriated to describe the superconducting state in these
ruthenocuprates. The low temperature rho(T) data along with the determined
vortex thermal activation energy are consistent with a 2D vortex dynamics in
these materials. | 0702078v1 |
1997-04-04 | Radiation damage to neutron and proton irradiated GaAs particle detectors | The radiation damage in 200 um thick Schottky diodes made on semi-insulating
(SI) undoped GaAs Liquid Encapsulated Czochralski (LEC) bulk material with
resistivities between 0.4 and 8.9*10E7 Ohm*cm were studied using
alpha-spectroscopy, signal response to minimum ionising particles (MIP), I-V
and CV-measurements. The results have been analysed to investigate the
influence of the substrate resistivity on the detector performance after
neutron and proton irradiation. The leakage current density, signal response to
alpha-particles and MIPs show a strong dependence on the resistivity before and
after irradiation. An observed decrease of the electron mean free drift length
before and after irradiation with increasing substrate resistivity can be
explained by a model involving the different ionisation ratios of defects,
which are introduced by the irradiation. Comparison of the radiation damage due
to neutrons and protons gives a hardness factor of 7+-0.9 for 24 GeV/c protons.
The best detectors show a response to MIPs of 5250 e- at 200 V reverse bias
after a irradiation level of 2*10E14 p/cm^2. | 9704002v1 |
2003-04-10 | Students' Understanding of Direct Current Resistive Electrical Circuits | Research has shown that both high school and university students' reasoning
patterns regarding direct current resistive electric circuits often differ from
the currently accepted explanations. At present, there are no standard
diagnostic examinations in electric circuits. Two versions of a diagnostic
instrument called Determining and Interpreting Resistive Electric circuits
Concepts Tests (DIRECT) were developed, each consisting of 29 questions. The
information provided by the exam provides classroom instructors a means with
which to evaluate the progress and conceptual difficulties of their students
and their instructional methods. It can be used to evaluate curricular packages
and/or other supplemental materials for their effectiveness in overcoming
students' conceptual difficulties. The analyses indicate that students,
especially females, tend to hold multiple misconceptions, even after
instruction. During interviews, the idea that the battery is a constant source
of current was used most often in answering the questions. Students tended to
focus on current in solving the problems and to confuse terms, often assigning
the properties of current to voltage and/or resistance. Results indicated that
students do not have a clear understanding of the underlying mechanisms of
electric circuit phenomena. On the other hand, students were able to translate
easily from a "realistic" representation of a circuit to the corresponding
schematic diagram. | 0304040v2 |
2013-05-15 | Structural ordering driven anisotropic magnetoresistance, anomalous Hall resistance and its topological overtones in full-Heusler Co2MnSi thin films | We report the evolution of crystallographic structure, magnetic ordering and
electronic transport in thin films of full-Heusler alloy Co$_2$MnSi deposited
on (001) MgO with annealing temperatures ($T_A$). By increasing the $T_A$ from
300$^\circ$C to 600$^\circ$C, the film goes from a disordered nanocrystalline
phase to $B2$ ordered and finally to the $L2_1$ ordered alloy. The saturation
magnetic moment improves with structural ordering and approaches the
Slater-Pauling value of $\approx 5.0 \mu_B$ per formula unit for $T_A$ =
600$^\circ$C. At this stage the films are soft magnets with coercive and
saturation fields as low as $\approx$ 7 mT and 350 mT, respectively. Remarkable
effects of improved structural order are also seen in longitudinal resistivity
($\rho_{xx}$) and residual resistivity ratio. A model based upon electronic
transparency of grain boundaries illucidates the transition from a state of
negative $d\rho/dT$ to positive $d\rho/dT$ with improved structural order. The
Hall resistivity ($\rho_{xy}$) derives contribution from the normal scattering
of charge carriers in external magnetic field, the anomalous effect originating
from built-in magnetization and a small but distinct topological Hall effect in
the disordered phase. The carrier concentration ($n$) and mobility ($\mu$) have
been extracted from the high field $\rho_{xy}$ data. The highly ordered films
are characterized by $n$ and $\mu$ of 1.19$\times$ 10$^{29}$ m$^{-3}$ and 0.4
cm$^2V^{-1}s^{-1}$ at room temperature. The dependence of $\rho_{xy}$ on
$\rho_{xx}$ indicates the dominance of skew scattering in our films, which
shows a monotonic drop on raising the $T_A$. The topological Hall effect is
analyzed for the films annealed at 300$^\circ$C. ...... | 1305.3453v1 |
2013-05-21 | Observation of even denominator fractional quantum Hall effect in suspended bilayer graphene | We investigate low-temperature magneto-transport in recently developed,
high-quality multi-terminal suspended bilayer graphene devices, enabling the
independent measurement of the longitudinal and transverse resistance. We
observe clear signatures of the fractional quantum Hall effect, with different
states that are either fully developed, and exhibit a clear plateau in the
transverse resistance with a concomitant dip in longitudinal resistance, or
incipient, and exhibit only a longitudinal resistance minimum. All observed
states scale as a function of filling factor nu, as expected. An unprecedented
even-denominator fractional state is observed at nu = -1/2 on the hole side,
exhibiting a clear plateau in Rxy quantized at the expected value of 2h/e^2
with a precision of ~0.5%. Many of our observations, together with a recent
electronic compressibility measurement performed in graphene bilayers on
hexagonal boron-nitride (hBN) substrates, are consistent with a recent theory
that accounts for the effect of the degeneracy between the N=0 and N=1 Landau
levels in the fractional quantum Hall effect, and predicts the occurrence of a
Moore-Read type nu = -1/2 state. Owing to the experimental flexibility of
bilayer graphene --which has a gate-dependent band structure, can be easily
accessed by scanning probes, and can be contacted with materials such as
superconductors--, our findings offer new possibilities to explore the
microscopic nature of even-denominator fractional quantum Hall effect. | 1305.4761v3 |
2014-11-07 | Resistance noise at the metal-insulator transition in thermochromic VO2 films | Thermochromic VO2 films were prepared by reactive DC magnetron sputtering
onto heated sapphire substrates and were used to make 100-nm-thick samples that
were 10 {\mu}m wide and 100 micron long. The resistance of these samples
changed by a factor of about 2000 in the 50 < Ts < 70 C range of temperature Ts
around the "critical" temperature Tc between a low-temperature semiconducting
phase and a high-temperature metallic-like phase of VO2. Power density spectra
S(f) were extracted for resistance noise around Tc and demonstrated unambiguous
1/f behavior. Data on S(10Hz)/Rs^2 scaled as Rs^x, where Rs is sample
resistance; the noise exponent x was -2.6 for Ts < Tc and +2.6 for Ts > Tc.
These exponents can be reconciled with the Pennetta-Trefan-Reggiani theory [C.
Pennetta, G. Trefanan, and L. Reggiani, Phys. Rev. Lett. 85, 5238 (2000)] for
lattice percolation with switching disorder ensuing from random defect
generation and healing in steady state. Our work hence highlights the dynamic
features of the percolating semiconducting and metallic-like regions around Tc
in thermochromic VO2 films. | 1411.2026v1 |
2015-02-18 | Anomalous electrical conductivity in rapidly crystallized Cu${}_{50-x}$Zr${}_{x}$ (x = 50 - 66.6) alloys | Cu${}_{50-x}$Zr${}_{x}$ (x = 50, 54, 60 and 66.6) polycrystalline alloys were
prepared by arc-melting. The crystal structure of the ingots has been examined
by X-ray diffraction. Non-equilibrium martensitic phases with monoclinic
structure were detected in all the alloys except Cu${}_{33.4}$Zr${}_{66.6}$.
Temperature dependencies of electrical resistivity in the temperature range of
T = 4 - 300 K have been measured as well as room temperature values of Hall
coefficients and thermal conductivity. Electrical resistivity demonstrates
anomalous behavior. At the temperatures lower than 20 K, their temperature
dependencies are non-monotonous with pronounced minima. At elevated
temperatures they have sufficiently non-linear character which cannot be
described within framework of the standard Bloch--Gr\"{u}neisen model. We
propose generalized Bloch--Gr\"{u}neisen model with variable Debye temperature
which describes experimental resistivity dependencies with high accuracy. We
found that both the electrical resistivity and the Hall coefficients reveal
metallic-type conductivity in the Cu-Zr alloys. The estimated values of both
the charge carrier mobility and the phonon contribution to thermal and electric
conductivity indicate the strong lattice defects and structure disorder. | 1502.05297v1 |
2016-05-24 | Thermoelectric transport in the layered Ca$_3$Co$_{4-x}$Rh$_x$O$_9$ single crystals | We have examined an isovalent Rh substitution effect on the transport
properties of the thermoelectric oxide Ca$_3$Co$_{4}$O$_9$ using
single-crystalline form. With increasing Rh content $x$, both the electrical
resistivity and the Seebeck coefficient change systematically up to $x=0.6$ for
Ca$_3$Co$_{4-x}$Rh$_{x}$O$_9$ samples. In the Fermi-liquid regime where the
resistivity behaves as $\rho=\rho_0+AT^2$ around 120 K, the $A$ value decreases
with increasing Rh content, indicating that the correlation effect is weakened
by Rh $4d$ electrons with extended orbitals. We find that, in contrast to such
a weak correlation effect observed in the resistivity of Rh-substituted
samples, the low-temperature Seebeck coefficient is increased with increasing
Rh content, which is explained with a possible enhancement of a pseudogap
associated with the short-range order of spin density wave. In high-temperature
range above room temperature, we show that the resistivity is largely
suppressed by Rh substitution while the Seebeck coefficient becomes almost
temperature-independent, leading to a significant improvement of the power
factor in Rh-substituted samples. This result is also discussed in terms of the
differences in the orbital size and the associated spin state between Co $3d$
and Rh $4d$ electrons. | 1605.07682v1 |
2017-10-25 | Engineering physics of superconducting hot-electron bolometer mixers | Superconducting hot-electron bolometers are presently the best performing
mixing devices for the frequency range beyond 1.2 THz, where good quality
superconductor-insulator-superconductor (SIS) devices do not exist. Their
physical appearance is very simple: an antenna consisting of a normal metal,
sometimes a normal metal-superconductor bilayer, connected to a thin film of a
narrow, short superconductor with a high resistivity in the normal state. The
device is brought into an optimal operating regime by applying a dc current and
a certain amount of local- oscillator power. Despite this technological
simplicity its operation has been found to be controlled by many different
aspects of superconductivity, all occurring simultaneously. A core ingredient
is the understanding that there are two sources of resistance in a
superconductor: a charge conversion resistance occurring at an
normal-metal-superconductor interface and a resistance due to time- dependent
changes of the superconducting phase. The latter is responsible for the actual
mixing process in a non-uniform superconducting environment set up by the
bias-conditions and the geometry. The present understanding indicates that
further improvement needs to be found in the use of other materials with a
faster energy-relaxation rate. Meanwhile several empirical parameters have
become physically meaningful indicators of the devices, which will facilitate
the technological developments. | 1710.09136v1 |
2018-02-13 | Multiple-Modes Scanning Probe Microscopy Characterization of Copper doped Zinc Oxide (ZnO:Cu) Thin Films | This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on
characterize resistance switching (RS), polarization rotation (PO) and surface
potential changes in copper doped ZnO (ZnO:Cu) thin films. The bipolar RS
behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PO
with almost 180{\deg} phase angle is confirmed by using the vertical and
lateral Piezoresponse Force Microscopy (PFM). In addition, it elucidates that
obvious polarization rotation behavior can be observed in the sample with
increasing Cu concentration. Furthermore, correlation of the RS behavior with
PO behavior has been studied by performing various mode SPM measurements on the
same location. The electric field resulted from the opposite polarization
orientation are corresponded to the different resistance states. It is found
that the region with the polarization in downward direction has low resistance
state (LRS), whereas the region with upward polarization has high resistance
state (HRS). In addition, the Piezoresponse Force Spectroscopy (PFS) and
Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the
existence of the built-in field due to the uncomplemented polarization may
affect the depletion region and hence contribute to the RS behavior. In
addition, Kelvin Probe Force Microscopy (KPFM) results show that, when
ZnO-based thin films is subjected to negative and then followed by positive
sample bias, injection charge limit current is dominated. | 1802.04494v1 |
2019-02-11 | Electrical percolation in metal wire network based strain sensors | Metal wire networks rely on percolation paths for electrical conduction, and
by suitably introducing break-make junctions on a flexible platform, a network
can be made to serve as a resistive strain sensor. Several experimental designs
have been proposed using networks made of silver nanowires, carbon nanotubes
and metal meshes with high sensitivities. However, there is limited theoretical
understanding; the reported studies have taken the numerical approach and only
consider rearrangement of nanowires with strain, while the critical break-make
property of the sensor observed experimentally has largely been ignored.
Herein, we propose a generic geometrical based model and study distortion,
including the break-make aspect, and change in electrical percolation of the
network on applying strain. The result shows that when a given strain is
applied, wire segments below a critical angle with respect to the applied
strain direction end up breaking, leading to increased resistance of the
network. The percolation shows interesting attributes; the calculated
resistance increases linearly in the beginning and at a higher rate for higher
strains, consistent with the experimental findings. In a real scenario, the
strain direction need not necessarily be in the direction of measurement, and
therefore, strain value and its direction both are incorporated into the
treatment. The study reveals interesting anisotropic conduction features;
strain sensitivity is higher parallel to the strain, while strain range is
wider for perpendicular measurement. The percolation is also investigated on
direct microscopic images of metal networks to obtain resistance-strain
characteristics and identification of current percolation pathways. The
findings will be important for electrical percolation in general, particularly
in predicting characteristics and improvising metal network-based strain
sensors. | 1902.03746v1 |
2019-12-16 | Electrical Characterization of CIGS Thin Film Solar Cells by Two and Four-Wires Probe Technique | The characterization of thin film solar cells is of huge importance for
obtaining high open circuit voltage and low recombination rates from the
interfaces or within the bulk of the main materials. Among the many electrical
characterization techniques, the two and four wire probe using the Cascade
instrument is of interest since the resistance of the wires, and the electrical
contacts can be excluded by the additional two wires in 4 wire probe
configuration. In this paper, both two and four-point probes configuration are
employed to characterize the CIGS chalcogenide thin film solar cells. The two
wire probe has been used to measure the current-voltage characteristics of the
cell which results in a huge internal resistance. Therefore, the four wire
connection are also used to eliminate the lead resistance to enhance the
characterization accuracy. The load resistance in the twowire probe diminishes
the photogenerated current density at smaller voltage ranges. In contrast, the
proposed four wire probe collects more current at higher voltages due to
enhanced carrier collection efficiency from contact electrodes. The current
conduction mechanism is also identified at every voltage region represented by
the value of the ideality factor of that voltage region. | 2002.07391v1 |
2020-03-31 | Design and Simulation of Memristor-Based Artificial Neural Network for Bidirectional Adaptive Neural Interface | This article proposes a general approach to the simulation and design of a
multilayer perceptron (MLP) network on the basis of cross-bar arrays of
metal-oxide memristive devices. The proposed approach uses the ANNM theory,
tolerance theory, simulation methodology and experiment design. The tolerances
analysis and synthesis process is performed for the ANNM hardware
implementation on the basis of two arrays of memristive microdevices in the
original 16x16 cross-bar topology being a component of bidirectional adaptive
neural interface for automatic registration and stimulation of bioelectrical
activity of a living neuronal culture used in robotics control system. The ANNM
is trained for solving a nonlinear classification problem of stable information
characteristics registered in the culture grown on a multi-electrode array.
Memristive devices are fabricated on the basis of a newly engineered
Au/Ta/ZrO2(Y)/Ta2O5/TiN/Ti multilayer structure, which contains self-organized
interface oxide layers, nanocrystals and is specially developed to obtain
robust resistive switching with low variation of parameters. An array of
memristive devices is mounted into a standard metal-ceramic package and can be
easily integrated into the neurointerface circuit. Memristive devices
demonstrate bipolar switching of anionic type between the high-resistance state
and low-resistance state and can be programmed to set the intermediate
resistive states with a desired accuracy. The ANNM tuning, testing and control
are implemented by the FPGA-based control subsystem. All developed models and
algorithms are implemented as Python-based software. | 2004.00154v1 |
2017-04-29 | Wear-resistant thin films of MRI-230D-Mg alloy using plasma-driven electrolytic oxidation | Wear resistant coatings were produced on a permanent mould cast MRI 230D Mg
alloy by (a) PEO in silicate based electrolyte, (b) PEO in phosphate based
electrolyte, (c) hybrid coatings of silicate PEO followed by laser surface
alloying (LSA) with Al and Al2O3, and (d) hybrid coatings of phosphate PEO
followed by LSA with Al and Al2O3. Microstructural characterization of the
coatings was carried out by scanning electron microscopy (SEM) and X(ray
diffraction. The tribological behavior of the coatings was investigated under
dry sliding condition using linearly reciprocating ball-on-flat wear test. Both
the PEO coatings exhibited a friction coefficient of about 0.8 and hybrid
coatings exhibited a value of about 0.5 against the AISI 52100 steel ball as
the friction partner, which were slightly reduced with the increase in applied
load. The PEO coatings sustained the test without failure at 2 N load but
failed at 5 N load due to micro-fracture caused by high contact stresses. The
hybrid coatings did not get completely worn off at 2 N load but were completely
removed exposing the substrate at 5 N load. The PEO coatings exhibited better
wear resistance than the hybrid coatings and silicate PEO coatings exhibited
better wear resistance than the phosphate PEO coatings. Both the PEO coatings
melted/decomposed on laser irradiation and all the hybrid coatings exhibited
similar microstructure and wear behavior irrespective of the nature of the
primary PEO coating or laser energies. SEM examination of worn surfaces
indicated abrasive wear combined with adhesive wear for all the specimens. The
surface of the ball exhibited a discontinuous transfer layer after the wear
test. | 1705.00116v1 |
2018-08-01 | Effect of multiband transport on charge carrier density fluctuations at the LaAlO$_3$/SrTiO$_3$ interface | Multiband transport in superconductors is interesting both from an academic
as well as an application point of view. It has been postulated that interband
scattering can significantly affect the carrier dynamics in these materials. In
this article we present a detailed study of the electrical transport properties
of the high-mobility two-dimensional electron gas residing at the interface of
LaAlO$_3$/SrTiO$_3$, a prototypical multi-band superconductor. We show, through
careful measurements of the gate dependence of the magnetoresistance and
resistance fluctuations at ultra-low temperatures, that transport in the
superconducting regime of this system has contributions from two bands which
host carriers of very different characters. We identify a gate-voltage tunable
Lifshitz transition in the system and show that the resistance fluctuations
have strikingly different features on either side of it. At low carrier
densities, resistance noise is dominated by number-density fluctuations arising
from trapping-detrapping of charge carriers from defects in the underlying
SrTiO$_3$ substrate, characteristic of a single-band semiconductor. Above the
Lifshitz transition, the noise presumably originates from inter-band
scattering. Our work highlights the importance of inter-band scattering
processes in determining the transport properties of low-dimensional systems
and projects resistance fluctuation spectroscopy as a viable technique for
probing the charge carrier dynamics across a Lifshitz transition. | 1808.00246v1 |
2016-09-06 | Interlayer Transport through a Graphene / Rotated-Boron-Nitride / Graphene Heterostructure | Interlayer electron transport through a graphene / hexagonal boron-nitride
(h-BN) / graphene heterostructure is strongly affected by the misorientation
angle $\theta$ of the h-BN with respect to the graphene layers with different
physical mechanisms governing the transport in different regimes of angle,
Fermi level, and bias. The different mechanisms and their resulting signatures
in resistance and current are analyzed using two different models, a
tight-binding, non-equilibrium Green function model and an effective continuum
model, and the qualitative features resulting from the two different models
compare well. In the large-angle regime ($\theta > 4^\circ$), the change in the
effective h-BN bandgap seen by an electron at the $K$ point of the graphene
causes the resistance to monotonically increase with angle by several orders of
magnitude reaching a maximum at $\theta = 30^\circ$. It does not affect the
peak-to-valley current ratios in devices that exhibit negative differential
resistance. In the small-angle regime ($\theta < 4^\circ$), Umklapp processes
open up new conductance channels that manifest themselves as non-monotonic
features in a plot of resistance versus Fermi level that can serve as
experimental signatures of this effect. For small angles and high bias, the
Umklapp processes give rise to two new current peaks on either side of the
direct tunneling peak. | 1609.01369v1 |
2018-12-13 | Search for power-efficient wide-range reversible resistance modulation of $VO_2$ single crystals | The abrupt metal insulator transition in $VO_2$ is attracting considerable
interest from both fundamental and applicative angles. We report on DC I-V
characteristics measured on $VO_2$ single crystals in the two-probe
configuration at several ambient temperatures below the insulator-metal
transition. The insulator-mixed-metal-insulator transition is induced by Joule
heating above ambient temperature in the range of negative differential
resistivity (NDR). In this range the stability of V(I) is governed by the load
resistance $R_L$. Steady state I(V) is obtained for $R_L> |dV/dI|_{max}$ in the
NDR regime. For $R_L< |dV/dI|_{max}$ there is switching between initial and
final steady states associated with peaks in the Joule power, that are higher
the lower $R_L$ is. The peaks caused by steep switching are superfluous and
damaging the samples. On the other hand, the large $R_L$ needed for steady
state is the main power consumer in the circuit at high currents. The present
work is motivated by the need to avoid damaging switching in the NDR regime
while reducing the power consumption in the circuit. It is shown here that
large resistance modulation can be obtained under steady state conditions with
reduced power consumption by increasing the ambient temperature of the device
above room temperature. | 1812.05702v1 |
2020-01-28 | Pressure tuning of structural and magnetic transitions in EuAg$_4$As$_2$ | We report temperature dependent measurements of ambient pressure specific
heat, magnetic susceptibility, anisotropic resistivity and thermal expansion as
well as in-plane resistivity under pressure up to 20.8 kbar on single crystals
of EuAg$_4$As$_2$. Based on thermal expansion and in-plane electrical transport
measurements at ambient pressure this compound has two, first order, structural
transitions in 80 - 120 K temperature range. Ambient pressure specific heat,
magnetization and thermal expansion measurements show a cascade of up to seven
transitions between 8 and 16 K associated with the ordering of the Eu$^{2+}$
moments. In-plane electrical transport is able to detect more prominent of
these transitions: at 15.5, 9.9, and 8.7 K as well as a weak feature at 11.8 K
at ambient pressure. Pressure dependent electrical transport data show that the
magnetic transitions shift to higher temperatures under pressure, as does the
upper structural transition, whereas the lower structural transition is
suppressed and ultimately vanishes. A jump in resistivity, associated with the
upper structural transition, decreases under pressure with an extrapolated
disappearance (or a change of sign) by 30-35 kbar. In the 10 - 15 kbar range a
kink in the pressure dependence of the upper structural transition temperature
as well as the high and low temperature in-plane resistivities suggest that a
change in the electronic structure may occur in this pressure range. The
results are compared with the literature data for SrAg$_4$As$_2$. | 2001.10574v1 |
2020-08-07 | Dependable contact related parameter extraction in graphene-metal junctions | The accurate extraction and the reliable, repeatable reduction of graphene -
metal contact resistance (R$_{C}$) are still open issues in graphene
technology. Here, we demonstrate the importance of following clear protocols
when extracting R$_{C}$ using the transfer length method (TLM). We use the
example of back-gated graphene TLM structures with nickel contacts, a
complementary metal oxide semiconductor compatible metal. The accurate
extraction of R$_{C}$ is significantly affected by generally observable Dirac
voltage shifts with increasing channel lengths in ambient conditions. R$_{C}$
is generally a function of the carrier density in graphene. Hence, the position
of the Fermi level and the gate voltage impact the extraction of R$_{C}$.
Measurements in high vacuum, on the other hand, result in dependable extraction
of R$_{C}$ as a function of gate voltage owing to minimal spread in Dirac
voltages. We further assess the accurate measurement and extraction of
important parameters like contact-end resistance, transfer length, sheet
resistance of graphene under the metal contact and specific contact resistivity
as a function of the back-gate voltage. The presented methodology has also been
applied to devices with gold and copper contacts, with similar conclusions. | 2008.03218v1 |
2021-05-18 | On the role of boron, carbon and zirconium on hot cracking and creep resistance of additively manufactured polycrystalline superalloys | We investigate the hot cracking susceptibility and creep resistance of three
versions of a nickel-based superalloy with different contents of boron, carbon
and zirconium fabricated by laser powder bed fusion. Crack-free and creep
resistant components are achieved for alloys with boron, carbon and no
zirconium. We then rationalize this result by evaluating how boron, carbon and
zirconium are distributed at grain boundaries in the as-built and heat-treated
microstructures of an alloy containing all these elements. Observations are
conducted by scanning and transmission electron microscopy, and atom probe
tomography. In the as-built microstructure, boron, carbon and zirconium
segregate at high-angle grain boundaries as a result of solute partitioning to
the liquid and limited solid-state diffusion during solidification and cooling.
After heat-treatment, the amount of boron and carbon segregating at grain
boundaries increases significantly. In contrast, zirconium is not found at
grain boundaries but it partitions at the gamma' precipitates formed during the
heat treatment. The presence of zirconium at grain boundaries in the as-built
condition is known to be susceptible to enhance hot cracking, while its absence
in the heat-treated microstructure strongly suggests that this element has no
major effect on the creep resistance. Based on our observations, we propose
alloy design guidelines to at the same time avoid hot cracking during
fabrication and achieve the required creep performance after heat-treatment. | 2105.08307v1 |
2021-07-13 | Reactivity of the Si(100)-2$\times$1-Cl surface with respect to PH$_3$, PCl$_3$, and BCl$_3$: Comparison with PH$_3$ on Si(100)-2$\times$1-H | Despite the interest in a chlorine monolayer on Si(100) as an alternative to
hydrogen resist for atomic-precision doping, little is known about its
interaction with dopant-containing molecules. We used the density functional
theory to evaluate whether a chlorine monolayer on Si(100) is suitable as a
resist for \ce{PH3}, \ce{PCl3}, and \ce{BCl3} molecules. We calculated reaction
pathways for \ce{PH3}, \ce{PCl3}, and \ce{BCl3} adsorption on a bare and
Cl-terminated Si(100)-2$\times$1 surface, as well as for \ce{PH3} adsorption on
H-terminated Si(100)-2$\times$1, which is widely used in current technologies
for atomically precise doping of Si(100) with phosphorus. It was found that the
Si(100)-2$\times$1-Cl surface has a higher reactivity towards phosphine than
Si(100)-2$\times$1-H, and, therefore, unpatterned areas are less protected from
undesirable incorporation of \ce{PH3} fragments. On the contrary, the
resistance of the Si(100)-2$\times$1-Cl surface against the chlorine-containing
molecules turned out to be very high. Several factors influencing reactivity
are discussed. The results reveal that phosphorus and boron trichlorides are
well-suited for doping a patterned Cl-resist by donors and acceptors,
respectively. | 2107.06168v1 |
2022-10-18 | In-plane electronic anisotropy revealed by interlayer resistivity measurements on the iron-based superconductor parent compound CaFeAsF | Both cuprates and iron-based superconductors demonstrate nematicity, defined
as the spontaneous breaking of rotational symmetry in electron systems. The
nematic state can play a role in the high-transition-temperature
superconductivity of these compounds. However, the microscopic mechanism
responsible for the transport anisotropy in iron-based compounds remains
debatable. Here, we investigate the electronic anisotropy of CaFeAsF by
measuring its interlayer resistivity under magnetic fields with varying field
directions. Counterintuitively, the interlayer resistivity was larger in the
longitudinal configuration ($B \parallel I \parallel c$) than in the transverse
one ($B \perp I \parallel c$). The interlayer resistivity exhibited a so-called
coherence peak under in-plane fields and was highly anisotropic with respect to
the in-plane field direction. At $T$ = 4 K and $B$ = 14 T, the
magnetoresistance $\Delta\rho/\rho_0$ was seven times larger in the $B
\parallel b_o$ than in the $B \parallel a_o$ configuration. Our theoretical
calculations of the conductivity based on the first-principles electronic band
structure qualitatively reproduced the above observations but underestimated
the magnitudes of the observed features. The proposed methodology can be a
powerful tool for probing the nematic electronic state in various materials. | 2210.09533v2 |
2023-11-15 | Transport properties of strongly correlated Fermi systems | In our short review, we consider the transport properties of strongly
correlated Fermi systems like heavy fermion metals and high-$T_c$
superconductors. Their transport properties are defined by strong
inter-particle interaction forming flat bands in these compounds. Indeed, in
contrast to the behavior of the transport properties of conventional metals,
the strongly correlated compounds exhibit the linear in temperature
resistivity, $\rho(T)\propto T$. We analyze the magnetoresistance and show that
it under the application of magnetic field becomes negative. It is shown that
near a quantum phase transition, when the density of electronic states
diverges, semiclassical physics remains applicable to describe the resistivity
$\rho$ of strongly correlated metals due to the presence of a transverse
zero-sound collective mode, representing the phonon mode in solids. We
demonstrate that when $T$ exceeds the extremely low Debye temperature $T_D$,
the resistivity $\rho(T)$ changes linearly with $T$, since the mechanism of
formation of the $T$-dependence $\rho(T)$ is similar electron-phonon mechanism,
which predominates at high temperatures in ordinary metals. Thus, in the region
of $T$-linear resistance, electron-phonon scattering leads to a lifetime of
$\tau$ quasiparticles practically independent of the material, which is
expressed as the ratio of the Planck constant $\hbar$ to the Boltzmann constant
constant $k_B$, $T\tau\sim \hbar/k_B$. We explain that due to the
non-Fermi-liquid behavior the real part of the frequency-dependent optical
conductivity $\sigma^R_{opt}(\omega)$ exhibits a scaling behavior, and
demonstrates the unusual power law behavior
$\sigma^R_{opt}(\omega)\propto\omega^{-1}$, rather than the well-known one
shown by conventional metals, $\sigma^R_{opt}(\omega)\propto\omega^{-2}$. | 2311.08974v1 |
2024-01-26 | First-principles methodology for studying magnetotransport in narrow-gap semiconductors: an application to Zirconium Pentatelluride ZrTe5 | The origin of anomalous resistivity peak and accompanied sign reversal of
Hall resistivity of ZrTe$_5$ has been under debate for a long time. Although
various theoretical models have been proposed to account for these intriguing
transport properties, a systematic study from first principles view is still
lacking. In this work, we present a first principles calculation combined with
Boltzmann transport theory to investigate the transport properties in
narrow-gap semiconductors at different temperatures and doping densities within
the relaxation time approximation. Regarding the sensitive
temperature-dependent chemical potential and relaxation time of semiconductors,
we take proper approximation to simulate these two variables, and then
comprehensively study the transport properties of ZrTe$_5$ both in the absence
and presence of an applied magnetic field. Without introducing topological
phases and correlation interactions, we qualitatively reproduced crucial
features observed in experiments, including zero-field resistivity anomaly,
nonlinear Hall resistivity with sign reversal, and non-saturating
magnetoresistance at high temperatures. Our calculation allows a systematic
interpretation of the observed properties in terms of multi-carrier and Fermi
surface geometry. Our method can be extended to other narrow-gap semiconductors
and further pave the way to explore interesting and novel transport properties
of this field. | 2401.15151v1 |
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