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2016-12-09 | Characterization of Fully Depleted CMOS Active Pixel Sensors on High Resistivity Substrates for Use in a High Radiation Environment | Depleted CMOS active sensors (DMAPS) are being developed for high-energy
particle physics experiments in high radiation environments, such as in the
ATLAS High Luminosity Large Hadron Collider (HL-LHC). Since charge collection
by drift is mandatory for harsh radiation environment, the application of high
bias voltage to high resistive sensor material is needed. In this work, a
prototype of a DMAPS was fabricated in a 150nm CMOS process on a substrate with
a resistivity of >2 k{\Omega}cm that was thinned to 100 {\mu}m. Full depletion
occurs around 20V, which is far below the breakdown voltage of 110 V. A readout
chip has been attached for fast triggered readout. Presented prototype also
uses a concept of sub-pixel en/decoding three pixels of the prototype chip are
readout by one pixel of the readout chip. Since radiation tolerance is one of
the largest concerns in DMAPS, the CCPD_LF chip has been irradiated with X-rays
and neutrons up to a total ionization dose of 50 Mrad and a fluence of
10E15neq/cm2, respectively. | 1612.03154v1 |
2022-03-14 | Photomultipliers as High Rate Radiation-Resistant In-Situ Sensors in Future Experiments | In the Energy Frontier we suggest developing high rate (100 MHz) finely
segmented forward calorimetry preradiators with time resolution <50 ps which
will survive the first 1-2 Lint of incident high radiation doses, protecting
forward calorimeters 3<y<6; less than 5 degrees to the beam behind them from
radiation damage, with high granularity, high rate capability and 30ps time
resolution (4D calorimetry) providing lepton and photon ID and measurement. In
the Intensity Frontier beam particle selection, such as tagged neutrino and
kaon beams, and lepton violation experiments with muons require very high
rates. Cosmic Frontiers requiring low power, non-cooled calorimetry or optical
detection that can keep track of particles or photons arriving at 100 MHz, and
survivable for years in space radiation may also benefit. The basic research is
to use compact channelized PMTs with quartz or other radiation resistant
windows with metal envelopes as an in-situ sensor, directly coupled to Cerenkov
(or radiation-resistant scintillator) tiles, utilizing the dynode signals as a
potentially compensating 2nd signal, and with no active electronics. If
successful, directions include proposals for high SE yield mesh dynode
activator materials such as GaP or B doped diamond films with 25 SEe at 300 eV
electron energies, and possibly for compact low cost tile SE sensors with no
photocathode, far easier to fabricate than PMTs with all metal final assembly
in air, brazed seals; bakeout 900 C; pump out with tipoff - vacuum 100x higher
than PMTs. Such sensors have many applications beyond HEP, in research,
medicine, industry and defense. | 2203.09941v1 |
2019-01-25 | Current-Induced Torques with Dresselhaus Symmetry Due to Resistance Anisotropy in 2D Materials | We report measurements of current-induced torques in heterostructures of
Permalloy (Py) with TaTe$_2$, a transition-metal dichalcogenide (TMD) material
possessing low crystal symmetry, and observe a torque component with
Dresselhaus symmetry. We suggest that the dominant mechanism for this
Dresselhaus component is not a spin-orbit torque, but rather the Oersted field
arising from a component of current that flows perpendicular to the applied
voltage due to resistance anisotropy within the TaTe$_2$. This type of
transverse current is not present in wires made from a single uniform layer of
a material with resistance anisotropy, but will result whenever a material with
resistance anisotropy is integrated into a heterostructure with materials
having different resistivities, thereby producing a spatially non-uniform
pattern of current flow. This effect will therefore influence measurements in a
wide variety of heterostructures incorporating 2D TMD materials and other
materials with low crystal symmetries. | 1901.08908v1 |
1999-08-13 | Resistive upper critical fields and irreversibility lines of optimally-doped high-T_c cuprates | We present the resistively-determined upper critical field H^{\rho}_{c2}(T)
and the irreversibility lines H^{\rho}_{irr}(T) of various high-T_c cuprates,
deduced from measurements in 61-T pulsed magnetic fields applied parallel to
the c-axis. The SHAPE of both H^{\rho}_{c2}(T) and H^{\rho}_{irr}(T) depends
monotonically on the anisotropy of the material and none of the samples show
saturation of H^{\rho}(T) at low temperatures. The anomalous positive
curvature, d^2 H^{\rho}/dT^2 > 0, is the strongest in materials with the
largest normal-state anisotropy, regardless of whether anisotropy is varied by
changing the carrier concentration or by comparing a variety of optimally-doped
compounds. | 9908190v1 |
2009-04-10 | Transition of stoichiometricSr2VO3FeAs to a superconducting state at 37.2 K | The superconductor Sr4V2O6Fe2As2 with transition temperature at 37.2 K has
been fabricated. It has a layered structure with the space group of p4/nmm, and
with the lattice constants a = 3.9296Aand c = 15.6732A. The observed large
diamagnetization signal and zero-resistance demonstrated the bulk
superconductivity. The broadening of resistive transition was measured under
different magnetic fields leading to the discovery of a rather high upper
critical field. The results also suggest a large vortex liquid region which
reflects high anisotropy of the system. The Hall effect measurements revealed
dominantly electron-like charge carriers in this material. The
superconductivity in the present system may be induced by oxygen deficiency or
the multiple valence states of vanadium. | 0904.1732v5 |
2014-12-25 | Carbon Nanotube Based Delay Model For High Speed Energy Efficient on Chip Data Transmission Using: Current Mode Technique | Speed is a major concern for high density VLSI networks. In this paper the
closed form delay model for current mode signalling in VLSI interconnects has
been proposed with resistive load termination. RLC interconnect line is
modelled using characteristic impedance of transmission line and inductive
effect. The inductive effect is dominant at lower technology node is modelled
into an equivalent resistance. In this model first order transfer function is
designed using finite difference equation, and by applying the boundary
conditions at the source and load termination. It has been observed that the
dominant pole determines system response and delay in the proposed model. Using
CNIA tool (carbon nanotube interconnect analyzer) the interconnect line
parameters has been estimated at 45nm technology node. The novel proposed
current mode model superiority has been validated for CNT type of material. It
superiority factor remains to 66.66% as compared to voltage mode signalling.
And current mode dissipates 0.015pJ energy where as VM consume 0.045pJ for a
single bit transmission across the interconnect over CNT material. Secondly the
damping factor of a lumped RLC circuit is shown to be a useful figure of merit. | 1412.7818v1 |
2015-03-29 | Edge-channel interferometer at the graphene quantum Hall pn junction | We demonstrate a quantum Hall edge-channel interferometer in a high-quality
graphene pn junction under a high magnetic field. The co-propagating p and n
quantum Hall edge channels traveling along the pn interface functions as a
built-in Aharanov-Bohm-type interferometer, the interferences in which are
sensitive to both the external magnetic field and the carrier concentration.
The trajectories of peak and dip in the observed resistance oscillation are
well reproduced by our numerical calculation that assumes magnetic flux
quantization in the area enclosed by the co-propagating edge channels. Coherent
nature of the co-propagating edge channels are confirmed by the
checkerboard-like pattern in the dc-bias and magnetic-field dependences of the
resistance oscillations. | 1503.08385v1 |
2017-11-16 | Anisotropic magnetic properties of the ferromagnetic semiconductor CrSbSe$_3$ | Single crystals of CrSbSe$_3$, a structurally pseudo-one-dimensional
ferromagnetic semiconductor, were grown using a high-temperature solution
growth technique and were characterized by x-ray diffraction, anisotropic,
temperature- and field-dependent magnetization, temperature-dependent
resistivity and optical absorption measurements. A band gap of 0.7 eV was
determined from both resistivity and optical measurements. At high
temperatures, CrSbSe$_3$ is paramagnetic and isotropic with a Curie-Weiss
temperature of $\sim$145 K and an effective moment of $\sim$4.1 $\mu_B$/Cr. A
ferromagnetic transition occurs at $T_c$ = 71 K. The $a$-axis, perpendicular to
the chains in the structure, is the magnetic easy axis, while the chain axis
direction, along $b$, is the hard axis. Magnetic isotherms measured around
$T_c$ do not follow the behavior predicted by simple mean field critical
exponents for a second order phase transition. A tentative set of critical
exponents is estimated based on a modified Arrott plot analysis, giving
$\beta\sim$0.25, $\gamma\sim$1.38 and $\delta\sim$6.6. | 1711.06342v1 |
2018-05-18 | Search for alternative magnetic tunnel junctions based on all-Heusler stacks | By imposing the constraints of structural compatibility, stability and a
large tunneling magneto-resistance, we have identified the
Fe$_3$Al/BiF$_3$/Fe$_3$Al stack as a possible alternative to the
well-established FeCoB/MgO/FeCoB in the search for a novel materials platform
for high-performance magnetic tunnel junctions. Various geometries of the
Fe$_3$Al/BiF$_3$/Fe$_3$Al structure have been analyzed, demonstrating that a
barrier of less than 2~nm yields a tunneling magneto-resistance in excess of
25,000~\% at low bias, without the need for the electrodes to be half-metallic.
Importantly, the presence of a significant spin gap in Fe$_3$Al for states with
$\Delta_1$ symmetry along the stack direction makes the TMR very resilient to
high voltages. | 1805.08603v1 |
2019-09-23 | High Throughput Production of Transparent Conductive Single-Walled Carbon Nanotube Films via Advanced Floating Catalyst Chemical Vapor Deposition | Single-walled carbon nanotube (SWCNT) films are promising materials for
transparent conductive films (TCFs) with potential applications in flexible
displays, touch screens, solar cells and solid-state lighting1,2. However,
further reductions in resistivity and in cost of SWCNT films are necessary for
high quality TCF products3. Here, we report an improved floating catalyst
chemical vapor deposition method to directly and continuously produce ultrathin
and freestanding SWCNT films at the hundred meter-scale. Both carbon conversion
efficiency and SWCNT TCF yield are increased by three orders of magnitude
relative to the conventional floating catalyst chemical vapor deposition. After
doping, the film manifests a sheet resistance of 40 ohm/sq. at 90%
transmittance, representing record performance for large-scale SWCNT films. Our
work provides a new avenue to accelerate the industrialization of SWCNT films
as TCFs. | 1909.10189v1 |
2020-03-24 | XUV Induced Bleaching of a Tin Oxo Cage Photoresist Studied by High Harmonic Absorption Spectroscopy | Inorganic molecular materials such as tin oxo cages are a promising
generation of photoresists compatible with the demands of the recently
developed Extreme UltraViolet (EUV) lithography technology. Therefore, a
detailed understanding of the photon-induced reactions which occur in
photoresists after exposure is important. We used XUV broadband laser pulses in
the range of 25-40 eV from a table-top high-harmonic source to expose thin
films of the tin oxo cage resist to shed light on some of the photo-induced
chemistry via XUV absorption spectroscopy. During the exposure, the transmitted
spectra were recorded and a noticeable absorbance decrease was observed in the
resist. Dill parameters were extracted to quantify the XUV induced conversion
and compared to EUV exposure results at 92 eV. Based on the absorption changes,
we estimate that approximately 60% of tin-carbon bonds are cleaved at the end
of the exposure. | 2003.10961v1 |
2017-03-18 | Discovering the Building Blocks of Atomic Systems using Machine Learning | Machine learning has proven to be a valuable tool to approximate functions in
high-dimensional spaces. Unfortunately, analysis of these models to extract the
relevant physics is never as easy as applying machine learning to a large
dataset in the first place. Here we present a description of atomic systems
that generates machine learning representations with a direct path to physical
interpretation. As an example, we demonstrate its usefulness as a universal
descriptor of grain boundary systems. Grain boundaries in crystalline materials
are a quintessential example of a complex, high-dimensional system with broad
impact on many physical properties including strength, ductility, corrosion
resistance, crack resistance, and conductivity. In addition to modeling such
properties, the method also provides insight into the physical "building
blocks" that influence them. This opens the way to discover the underlying
physics behind behaviors by understanding which building blocks map to
particular properties. Once the structures are understood, they can then be
optimized for desirable behaviors. | 1703.06236v1 |
2019-06-06 | Modeling the effect of microstructure on elastic wave propagation in platelet-reinforced composites and ceramics | Dense ceramics are irreplaceable in applications requiring high mechanical
stiffness, chemical and temperature resistance and low weight. To improve their
toughness, ceramics can be reinforced with elongated inclusions. Recent
manufacturing strategies have been developed to control the orientations of
disc-like micro-particles in polymeric and ceramic matrices and to build
periodic microstructures. Given the infinite number of possible microstructures
available, modeling tools are required to select the potentially best design.
Periodic microstructures can be involved in elastic wave scattering to
dissipate mechanical energy from vibrations. In this paper, a model is proposed
to determine the frequency bandgaps associated to periodic architectures in
composites and ceramics and the influence of microstructural parameters are
investigated. The results are used to define guidelines for the future
fabrication of hard bulk ceramic materials that combine traditional ceramic
properties with high vibration resistance. | 1906.02582v1 |
2020-08-28 | Tunnel magnetoresistance in scandium nitride magnetic tunnel junctions using first principles | The magnetic tunnel junction is a cornerstone of spintronic devices and
circuits, providing the main way to convert between magnetic and electrical
information. In state-of-the-art magnetic tunnel junctions, magnesium oxide is
used as the tunnel barrier between magnetic electrodes, providing a uniquely
large tunnel magnetoresistance at room temperature. However, the wide bandgap
and band alignment of magnesium oxide-iron systems increases the
resistance-area product and causes challenges of device-to-device variability
and tunnel barrier degradation under high current. Here, we study using first
principles narrower-bandgap scandium nitride tunneling properties and transport
in magnetic tunnel junctions in comparison to magnesium oxide. These
simulations demonstrate a high tunnel magnetoresistance in Fe/ScN/Fe MTJs via
{\Delta}_1 and {\Delta}_2' symmetry filtering with low wavefunction decay
rates, allowing a low resistance-area product. The results show that scandium
nitride could be a new tunnel barrier material for magnetic tunnel junction
devices to overcome variability and current-injection challenges. | 2008.12770v1 |
2020-11-07 | Thickness-dependent quantum transport of Weyl fermions in ultra-high-quality SrRuO3 films | The recent observation of Weyl fermions in the itinerant 4d ferromagnetic
perovskite SrRuO3 points to this material being a good platform for exploring
novel physics related to a pair of Weyl nodes in epitaxial heterostructures. In
this letter, we report the thickness-dependent magnetotransport properties of
ultra-high-quality epitaxial SrRuO3 films grown under optimized conditions on
SrTiO3 substrates. Signatures of Weyl fermion transport, i.e., unsaturated
linear positive magnetoresistance accompanied by a quantum oscillation having a
{\pi} Berry phase, were observed in films with thicknesses as small as 10 nm.
Residual resistivity increased with decreasing film thickness, indicating
disorder near the interface between SrRuO3 and the SrTiO3 substrate. Since this
disorder affects the magnetic and electrical properties of the films, the Curie
temperature decreases and the coercive field increases with decreasing
thickness. Thickness-dependent magnetotransport measurements revealed that the
threshold residual resistivity ratio (RRR) to observe Weyl fermion transport is
21. These results provide guidelines for realizing quantum transport of Weyl
fermions in SrRuO3 near heterointerfaces. | 2011.03670v1 |
2021-05-11 | Exploring the Correlation between Solvent Diffusion and Creep Resistance of Mg-Ga HCP Alloys from High Throughput Liquid-Solid Diffusion Couple | The liquid-solid diffusion couple technique, supported by phenomenological
analysis and nano-indentation tests, is proposed on account of the relatively
low melting points of Mg to explore the diffusion mobility and creep
deformation. The potential of this strategy is demonstrated in Mg-Ga hcp alloys
where Ga solute (i.e. impurity) and Mg solvent diffusions in hcp Mg-Ga alloys
were both unveiled. It was followed by mapping the compressive creep behavior
via nanoindentation along the composition arrays within the same Mg-Ga couple
sample. The compressive creep resistance of Mg-Ga hcp alloys increased with the
Ga content, and this enhancement was similar to the one found in Mg-Zn alloys
and superior to the one reported in Mg-Al alloys though Al is a slower impurity
diffuser in hcp-Mg than Zn and Ga. Thereby, the solvent diffusion and its
variation with the composition, rather than the solute diffusion, was suggested
to govern the creep properties at high temperatures and low stresses. | 2105.05096v1 |
2021-08-30 | Out-of-Plane Resistance Switching of 2D Bi2O2Se at Nanoscale | 2D bismuth oxyselenide (Bi2O2Se) with high electron mobility shows great
potential for nanoelectronics. Although in-plane properties of Bi2O2Se have
been widely studied, its out-ofplane electrical transport behavior remains
elusive, despite its importance in fabricating devices with new functionality
and high integration density. Here, we study the out-of-plane electrical
properties of 2D Bi2O2Se at nanoscale by conductive atomic force microscope. We
find that hillocks with tunable heights and sizes are formed on Bi2O2Se after
applying vertical electrical field. Intriguingly, such hillocks are conductive
in vertical direction, resulting in a previously unknown out-of-plane
resistance switching in thick Bi2O2Se flakes while ohmic conductive
characteristic in thin ones. Furthermore, we observe the transformation from
bipolar to stable unipolar conduction in thick Bi2O2Se flake possessing such
hillocks, suggesting its potential to function as a selector in vertical
devices. Our work reveals unique out-of-plane transport behavior of 2D Bi2O2Se,
providing the basis for fabricating vertical devices based on this emerging 2D
material. | 2108.13240v1 |
2004-07-07 | Properties of MgB2 thin films with carbon doping | We have studied structural and superconducting properties of MgB2 thin films
doped with carbon during the hybrid physical-chemical vapor deposition process.
A carbon-containing metalorganic precursor bis(cyclopentadienyl)magnesium was
added to the carrier gas to achieve carbon doping. As the amount of carbon in
the films increases, the resistivity increases, Tc decreases, and the upper
critical field increases dramatically as compared to the clean films. The
self-field Jc in the carbon-doped films is lower than that in the clean films,
but Jc remains relatively high to much higher magnetic fields, indicating
stronger pinning. Structurally, the doped films are textured with nano-grains
and highly resistive amorphous areas at the grain boundaries. The carbon doping
approach can be used to produce MgB2 materials for high magnetic field
applications. | 0407146v1 |
2006-01-30 | Growth of high quality large area MgB2 thin films by reactive evaporation | We report a new in-situ reactive deposition thin film growth technique for
the production of MgB2 thin films which offers several advantages over all
existing methods and is the first deposition method to enable the production of
high-quality MgB2 films for real-world applications. We have used this growth
method, which incorporates a rotating pocket heater, to deposit MgB2 films on a
variety of substrates, including single-crystalline, polycrystalline, metallic,
and semiconductor materials up to 4" in diameter. This technique allows growth
of double-sided, large-area films in the intermediate temperature range of 400
to 600 degrees C. These films are clean, well-connected, and consistently
display Tc values of 38 to 39 K with low resistivity and residual resistivity
values. They are also robust and uncommonly stable upon exposure to atmosphere
and water. | 0601669v1 |
2017-03-27 | Machining of Spherical Component Fabricated by Selected Laser Melting, Part II: Application of Ti in Biomedical | Ti and Ti-Based alloys have unique properties such as high strength, low
density and excellent corrosion resistance. These properties are essential for
the manufacture of lightweight and high strength components for biomedical
applications. In this paper, Ti properties such as metallurgy, mechanical
properties, surface modification, corrosion resistance, biocompatibility and
osseointegration in biomedical applications have been discussed. This paper
also analyses the advantages and disadvantages of various Ti manufacturing
processes for biomedical applications such as casting, powder metallurgy, cold
and hot working, machining, laser engineering net shaping, superplastic
forming, forging and ring rolling. The contributions of this research are
twofold, firstly scrutinizing the behaviour of Ti and Ti-Based alloys in-vivo
and in-vitro experiments in biomedical applications to determine the factors
leading to failure, and secondly strategies to achieve desired properties
essential to improving the quality of patient outcomes after receiving surgical
implants. Future research will be directed toward manufacturing of Ti for
medical applications by improving the production process, for example using
optimal design approaches in additive manufacturing and investigating alloys
containing other materials in order to obtain better medical and mechanical
characteristics. | 1703.10045v1 |
2021-10-28 | Analysis of Prospective Elements and Crystal Lattice Structures via Computer Algorithms to Identify Standard Temperature Pressure (STP) Superconductors | Superconductors have the potential to revolutionize technology due to their
ability to have zero electrical resistance. However, superconductor materials
require either low temperatures or high pressures to function in a
superconductive state. Thus, researchers are now on the search for the
first-ever room temperature, ambient pressure superconductor. Yet, recent
discoveries have only shown superconductors that work at low temperatures with
ambient pressure or room temperature with high pressures. The region between
these two extremes has not been identified due to the number of variables that
affect superconductivity. To reduce the number of permutations that need to be
tested to identify the first STP superconductor I propose the use of a computer
algorithm designed to test various crystal structures of superconducting
materials and combinations of elements that will have zero electrical
resistance and exhibit the Meisner effect. Some elemental superconductors that
have the highest critical temperature at standard pressure are V, Zr, La, Hf,
Re, Th, Pa, U, and Am. The elements once combined with other elements in the
right crystalline structure can produce a metastable state where the
superconductors will keep their physical characteristics once they form. | 2110.15201v1 |
2022-07-28 | Pressure induced 3D strain in 2D Graphene | Two-dimensional (2D) materials such as graphene offer a variety of
outstanding properties for a wide range of applications. Their transport
properties in particular present a rich field of study. However, the studies of
transport properties of graphene under pressure are mostly limited to $\sim$1
GPa, largely due to the technical challenges and difficulties of placing
graphene inside a diamond anvil cell (DAC) and maintaining good electrical
contacts under pressure. We developed a novel technique allowing for direct
measurements of the transport properties of high quality chemical vapor
deposition (CVD) monolayer graphene under pressures. Combined Raman
spectroscopic and direct resistivity measurements on pure monolayer graphene up
to 40 GPa shows an effective out of plane stiffness of
$c_{33}$=0.26$\pm_{.09}^{.11}$ GPa, and observe relatively constant resistances
with pressure, suggesting high pressure as a useful technique for producing
large biaxial strains within graphene. | 2207.14183v1 |
2023-07-12 | The Collaborative Effects of Intrinsic and Extrinsic Impurities in Low RRR SRF Cavities | The superconducting radio-frequency (SRF) community has shown that
introducing certain impurities into high-purity niobium can improve quality
factors and accelerating gradients. We question why some impurities improve RF
performance while others hinder it. The purpose of this study is to
characterize the impurity profile of niobium with a low residual resistance
ratio (RRR) and correlate these impurities with the RF performance of low RRR
cavities so that the mechanism of impurity-based improvements can be better
understood and improved upon. The combination of RF testing and material
analysis reveals a microscopic picture of why low RRR cavities experience low
temperature-dependent BCS resistance behavior more prominently than their high
RRR counterparts. We performed surface treatments, low temperature baking and
nitrogen-doping, on low RRR cavities to evaluate how the intentional addition
of oxygen and nitrogen to the RF layer further improves performance through
changes in the mean free path and impurity profile. The results of this study
have the potential to unlock a new understanding on SRF materials and enable
the next generation of SRF surface treatments. | 2307.06259v1 |
2023-02-15 | An experimental high-throughput to high-fidelity study towards discovering Al-Cr containing corrosion-resistant compositionally complex alloys | Compositionally complex alloys hold the promise of simultaneously attaining
superior combinations of properties, such as corrosion resistance,
light-weighting, and strength. Achieving this goal is a challenge due in part
to a large number of possible compositions and structures in the vast alloy
design space. High-throughput methods offer a path forward, but a strong
connection between the synthesis of an alloy of a given composition and
structure with its properties has not been fully realized to date. Here, we
present the rapid identification of corrosion-resistant alloys based on
combinations of Al and Cr in a base Al-Co-Cr-Fe-Ni alloy. Previously unstudied
alloy stoichiometries were identified using a combination of high-throughput
experimental screening coupled with key metallurgical and electrochemical
corrosion tests, identifying alloys with excellent passivation behavior. The
alloy native oxide performance and its self-healing attributes were probed
using rapid tests in deaerated 0.1 mol/L H2SO4. Importantly, a correlation was
found between the electrochemical impedance modulus of the exposure-modified
air-formed film and self-healing rate of the CCAs. Multi-element extended x-ray
absorption fine structure analyses connected more ordered type chemical
short-range order in the Ni-Al 1st nearest-neighbor shell to poorer corrosion
resistance. This report underscores the utility of high throughput exploration
of compositionally complex alloys for the identification and rapid screening of
a vast stoichiometric space. | 2302.07988v2 |
2021-04-06 | In-situ dispersion of electrospun nanofibers in PDMS for fabrication of high strength, transparent nanocomposites | The polymer nanocomposites find applications in diverse areas ranging from
smart materials to bioengineering. They are developed by dispersion of
nanomaterials in a bulk phase of a polymeric material. Although several methods
facilitate efficient dispersion of nanomaterials in a bulk polymer matrix to
create nanocomposites, majority of them follows heat, beat and treat processes.
These processes are high energy demanding processes. Moreover, the challenge
increases when nanomaterials need to be dispersed in a viscous polymeric
material. This results in spatial heterogeneity in the dispersion of
nanomaterials, eventually leading to compromised mechanical properties of a
nanocomposite. Therefore, in the current work, we propose an in-situ, on-step
fabrication process of polydimethylsiloxane (PDMS) nanocomposites. Electrospun
polyvinyl alcohol (PVA) nanofibers are homogenously dispersed in a PDMS matrix
to create a high strength, transparent PDMS nanocomposite. The homogenous
dispersion of nanofibers in PDMS matrix is characterised by scanning electron
microscopy (SEM), confocal imaging and rheological studies. Further, the
prepared PDMS nanocomposite exhibits improved mechanical strength and
comparable optical transparency in comparison to native PDMS. Hence, the
fabricated PDMS nanocomposites, being resistant to mechanical stress and
optically transparent, will find applications as transdermal patches, flexible
electronics, microfluidic devices and others. | 2104.02418v1 |
2022-04-12 | Bayesian optimization with experimental failure for high-throughput materials growth | A crucial problem in achieving innovative high-throughput materials growth
with machine learning and automation techniques, such as Bayesian optimization
(BO) and robotic experimentation, has been a lack of an appropriate way to
handle missing data due to experimental failures. Here, we propose a new BO
algorithm that complements the missing data in the optimization of materials
growth parameters. The proposed method provides a flexible optimization
algorithm capable of searching a wide multi-dimensional parameter space. We
demonstrate the effectiveness of the method with simulated data as well as in
its implementation for actual materials growth, namely
machine-learning-assisted molecular beam epitaxy (ML-MBE) of SrRuO3, which is
widely used as a metallic electrode in oxide electronics. Through the
exploitation and exploration in a wide three-dimensional parameter space, while
complementing the missing data, we attained tensile-strained SrRuO3 film with a
high residual resistivity ratio of 80.1, the highest among tensile-strained
SrRuO3 films ever reported, in only 35 MBE growth runs. | 2204.05452v1 |
2023-08-30 | Target tests for the ILC positron source Talk presented at the International Workshop on Future Linear Colliders (LCWS2023) | The positron source is an essential component of the International Linear
Collider (ILC) and is an area that poses some design challenges. One
consideration is the material for the target, where the 1014 positrons per
second for the ILC are generated. The potential material would need to be able
to resist the high load created by the intense high energy photon beam. One of
such candidates is the titanium alloy Ti-6Al-4V, for which the results of
material tests with 3.5 MeV electrons are shown. The material was characterized
after the irradiation by high-energy X-ray diffraction (HE-XRD) and changes
caused by the irradiation to the crystal structure were studied. These tests
revealed there was only minimal change in the phase fractions and crystal
structure of the material under conditions as expected for the ILC. | 2308.15916v1 |
2019-08-16 | Ab initio phonon transport across grain boundaries in graphene using machine learning based on small dataset | Establishing the structure-property relationship for grain boundaries (GBs)
is critical for developing next generation functional materials, but has been
severely hampered due to its extremely large configurational space. Atomistic
simulations with low computational cost and high predictive power are strongly
desirable, but the conventional simulations using empirical interatomic
potentials and density functional theory suffer from the lack of predictive
power and high computational cost, respectively. A machine learning interatomic
potential (MLIP) recently emerged but often requires an extensive size of the
training dataset, making it a less feasible approach. Here we demonstrate that
an MLIP trained with a rationally designed small training dataset can predict
thermal transport across GBs in graphene with ab initio accuracy at an
affordable computational cost. In particular, we employed a rational approach
based on the structural unit model to find a small set of GBs that can
represent the entire configurational space and thus can serve as a
cost-effective training dataset for the MLIP. Only 5 GBs were found to be
enough to represent the entire configurational space of graphene GBs. Using the
atomistic Green's function approach and the MLIP, we revealed that the
structure-thermal resistance relation in graphene does not follow the common
understanding that large dislocation density causes larger thermal resistance.
In fact, thermal resistance is nearly independent of dislocation density at
room temperature and is higher when the dislocation density is small at
sub-room temperature. We explain this intriguing behavior with the buckling
near a GB causing a strong scattering of flexural phonon modes. | 1909.02386v3 |
2022-02-18 | Synergism between B and Nb improves fire resistance in microalloyed steels | The development of new fire-resistant steels represents a challenge in
materials science and engineering of utmost importance. Alloying elements such
as Nb and Mo are generally used to improve the strength at both room- and
high-temperatures due to, for example, the formation of precipitates and harder
microconstituents. In this study we show alternatively that the addition of
small amounts of boron in Nb-microalloyed steels may play a crucial role in
maintaining the mechanical properties at high temperatures. The 66\,\%
yield-strength criteria for fire resistance is achieved at $\approx
574$\,{\deg}C for a boron steel, whereas without boron this value reaches
$\approx 460$\,{\deg}C, a remarkable boron-induced mechanical strengthening
enhancement. DFT calculations show that boron additions can lower the vacancy
formation energy when compared to pure ferrite and, for Nb-B steels, there is a
further 24\,\% reduction, suggesting that the boron-niobium combination acts as
an effective pinning-based strengthening agent. | 2202.09197v1 |
2020-07-28 | Good Practice Guide on the electrical characterization of graphene using non-contact and high-throughput methods | The electrical characterisation of graphene, either in plane sheets or in
properly geometrised form can be approached using non-contact methods already
employed for thin film materials. The extraordinary thinness (and,
correspondingly, the volume) of graphene, however, makes the proper application
of these methods difficult. The electrical properties of interest (sheet
electrical resistivity/conductivity, concentration and mobility of charge
carriers) must be indirectly derived from the measurement outcome by
geometrical and electrical modelling; the assumptions behind such models (e.g.,
uniformity and isotropy, effective value of the applied fields, etc.) require
careful consideration. The traceability of the measurement to the International
System of units and a proper expression of measurement uncertainty is an issue.
This guide focuses on non-contact and high-throughput methods, that are
methods where the graphene sample surface is not physically contacted with any
metallic electrodes at any stage. A companion guide about contact methods is
also available. The methods discussed are:
- Measurement of surface potential and work function using Scanning Kelvin
Probe Microscopy (SKPM); - Measurement of sheet resistance by Microwave
Resonant Cavity; - Measurement of sheet resistance by Terahertz time-domain
spectroscopy (THz-TDS); For each method, a corresponding measurement protocol
is discussed, which describes: - The measurement principle; - Sample
requirements and preparation; - A description of the measurement equipment /
apparatus; - Calibration standards and ways to achieve a traceable measurement; | 2007.14047v1 |
2020-12-08 | The Competing Effect of Initial Crack Depth Versus Chemical Strengthening Parameters on Apparent Fracture Toughness of Sodium Aluminosilicate Glass | The widespread use of sodium aluminosilicate glass in many engineering
applications due to its mechanical and optical properties (transparency,
dielectric, etc.), has become common in recent years. However, glass, a brittle
material, has its vulnerability to fracture. Processes such as heat treatment
(heat tempering) or chemical strengthening through ion-exchange have been used
to create residual stress profiles on the glass, in a bid to improve its
fracture strength. However, failure still occurs, which is mostly catastrophic
and expensive to repair. Therefore understanding, predicting, and eventually
improving the resistance to damage or fracture of chemically strengthened glass
is important to designing new glasses that would be tougher while retaining
their transparency. The relationship between the glass residual stress
parameters such as the compressive stress (CS), depth of compression layer
(DOL), and central tension (CT) versus apparent (effective) fracture toughness
for different crack depth was investigated in this study using a Silicon
Carbide particle blast plus ring-on-ring (RoR) test method. The results also
showed that improving the fracture resistance of glass via chemical
strengthening requires a proper combination of CS, DOL, and CT, which is
particularly dependent on the initial/existing crack (flaw) depth. It was
determined that for a damage event involving the introduction of a shallow
crack depth, the criterion for optimal resistance to fracture, in terms of
apparent fracture toughness, is weighted more towards a high CS, than deep DOL
while for a deep flaw damage event, it is more weighted towards deep DOL, than
a high CS. These results provide a valuable piece of information in the design
of a more robust glass in engineering applications. | 2012.04732v1 |
2021-04-07 | Ultra-Thin Lubricant-Infused Vertical Graphene Nanoscaffolds for High-Performance Dropwise Condensation | Lubricant-infused surfaces (LIS) are highly efficient in repelling water and
constitute a very promising family of materials for condensation processes
occurring in a broad range of energy applications. However, the performance of
LIS in such processes is limited by the inherent thermal resistance imposed by
the thickness of the lubricant and supporting surface structure, as well as by
the gradual depletion of the lubricant over time. Here we present a remarkable,
ultra-thin (~70 nm) and conductive LIS architecture, obtained by infusing
lubricant into a vertically grown graphene nanoscaffold on copper. The
ultra-thin nature of the scaffold, combined with the high in-plane thermal
conductivity of graphene, drastically minimize earlier limitations, effectively
doubling the heat transfer performance compared to a state-of-the-art CuO LIS
surface. We show that the effect of the thermal resistance to the heat transfer
performance of a LIS surface, although often overlooked, can be so detrimental
that a simple nanostructured CuO surface can outperform a CuO LIS surface,
despite film condensation on the former. The present vertical graphene LIS is
also found to be resistant to lubricant depletion, maintaining stable dropwise
condensation for at least ~7 hours with no significant change of advancing
contact angle and contact angle hysteresis. The lubricant consumed by the
vertical graphene LIS is 52.6% less than the existing state-of-the-art CuO LIS,
making also the fabrication process more economical. | 2104.03091v1 |
2023-07-24 | Large negative magnetoresistance and pseudogap phase in superconducting A15-type La$_4$H$_{23}$ | High pressure plays a crucial role in the field of superconductivity.
Compressed hydride superconductors are leaders in the race for a material that
can conduct electricity without resistance at high or even room temperature. In
the present work, we have discovered new lanthanum superhydride, cubic A15-type
La$_4$H$_{23}$, with lower stabilization pressure compared to the reported
$\textit{fcc}$ LaH$_{10}$. Superconducting La$_4$H$_{23}$ was obtained by laser
heating of LaH$_3$ with ammonia borane at about 120 GPa. Transport measurements
reveal the maximum critical temperature $\textit{T}$$_{C}$(onset) = 105 K and
the critical field $\textit{H}$$_{C2}$(0) = 32 T at 118 GPa, as evidenced by
the sharp drop of electrical resistance and the displacement of superconducting
transitions in applied magnetic fields. Moreover, we provide evidence for
unconventional transport associated with a pseudogap phase in La$_4$H$_{23}$
using pulsed magnetic fields up to 68 T. A large negative magnetoresistance in
the non-superconducting state below 40 K, quasi $\textit{T}$-linear electrical
resistance, and a sign-change of its temperature dependence mark the emergence
of pseudogap in this hydride. Discovered lanthanum hydride is a new member of
the A15 family of superconductors with $\textit{T}$$_C$ exceeding the boiling
point of liquid nitrogen. | 2307.13067v3 |
2019-07-04 | Contact Engineering High Performance n-Type MoTe2 Transistors | Semiconducting MoTe2 is one of the few two-dimensional (2D) materials with a
moderate band gap, similar to silicon. However, this material remains
under-explored for 2D electronics due to ambient instability and predominantly
p-type Fermi level pinning at contacts. Here, we demonstrate unipolar n-type
MoTe2 transistors with the highest performance to date, including high
saturation current (>400 ${\mu}A/{\mu}m$ at 80 K and >200 ${\mu}A/{\mu}m$ at
300 K) and relatively low contact resistance (1.2 to 2 $k{\Omega}\cdot{\mu}m$
from 80 to 300 K), achieved with Ag contacts and AlOx encapsulation. We also
investigate other contact metals, extracting their Schottky barrier heights
using an analytic subthreshold model. High-resolution X-ray photoelectron
spectroscopy reveals that interfacial metal-Te compounds dominate the contact
resistance. Among the metals studied, Sc has the lowest work function but is
the most reactive, which we counter by inserting monolayer h-BN between MoTe2
and Sc. These metal-insulator-semiconductor (MIS) contacts partly de-pin the
metal Fermi level and lead to the smallest Schottky barrier for electron
injection. Overall, this work improves our understanding of n-type contacts to
2D materials, an important advance for low-power electronics. | 1907.02587v1 |
2011-03-11 | Optimized fabrication of high quality La0.67Sr0.33MnO3 thin films considering all essential characteristics | In this article, an overview of the fabrication and properties of high
quality La0.67Sr0.33MnO3 (LSMO) thin films is given. A high quality LSMO film
combines a smooth surface morphology with a large magnetization and a small
residual resistivity, while avoiding precipitates and surface segregation. In
literature, typically only a few of these issues are adressed. We therefore
present a thorough characterization of our films, which were grown by pulsed
laser deposition. The films were characterized with reflection high energy
electron diffraction, atomic force microscopy, x-ray diffraction, magnetization
and transport measurements, x-ray photoelectron spectroscopy and scanning
transmission electron microscopy. The films have a saturation magnetization of
4.0 {\mu}B/Mn, a Curie temperature of 350 K and a residual resistivity of 60
{\mu}{\Omega}cm. These results indicate that high quality films, combining both
large magnetization and small residual resistivity, were realized. A comparison
between different samples presented in literature shows that focussing on a
single property is insufficient for the optimization of the deposition process.
For high quality films, all properties have to be adressed. For LSMO devices,
the thin film quality is crucial for the device performance. Therefore, this
research is important for the application of LSMO in devices. | 1103.2267v1 |
2022-10-24 | Nanomolding of Metastable Mo$_{4}$P$_{3}$ | Reduced dimensionality leads to emergent phenomena in quantum materials and
there is a need for accelerated materials discovery of nanoscale quantum
materials in reduced dimensions. Thermomechanical nanomolding is a rapid
synthesis method that produces high quality single-crystalline quantum
nanowires with controlled dimensions over wafer-scale sizes. Herein, we apply
nanomolding to fabricate nanowires from bulk feedstock of MoP, a triple-point
topological metal with extremely high conductivity that is promising for
low-resistance interconnects. Surprisingly, we obtained single-crystalline
Mo$_{4}$P$_{3}$ nanowires, a metastable phase at room temperature in
atmospheric pressure. We thus demonstrate nanomolding can create metastable
phases inaccessible by other nanomaterial syntheses and can explore a
previously inaccessible synthesis space at high temperatures and pressures.
Furthermore, our results suggest that the current understanding of interfacial
solid diffusion for nanomolding is incomplete, providing opportunities to
explore solid-state diffusion at high-pressure and high-temperature regimes in
confined dimensions. | 2210.13392v1 |
2024-02-02 | Nano-ironing van der Waals Heterostructures Towards Electrically Controlled Quantum Dots | Assembling two-dimensional van der Waals layered materials into
heterostructures is an exciting development that sparked the discovery of rich
correlated electronic phenomena and offers possibilities for designer device
applications. However, resist residue from fabrication processes is a major
limitation. Resulting disordered interfaces degrade device performance and mask
underlying transport physics. Conventional cleaning processes are inefficient
and can cause material and device damage. Here, we show that thermal scanning
probe based cleaning can effectively eliminate resist residue to recover
pristine material surfaces. Our technique is compatible at both the material-
and device-level, and we demonstrate the significant improvement in the
electrical performance of 2D WS2 transistors. We also demonstrate the cleaning
of van der Waals heterostructures to achieve interfaces with low disorder. This
enables the electrical formation and control of quantum dots that can be tuned
from macroscopic current flow to the single-electron tunnelling regime. Such
material processing advances are crucial for constructing high-quality vdW
heterostructures that are important platforms for fundamental studies and
building blocks for quantum and nano-electronics applications. | 2402.01185v1 |
2024-02-13 | Plasma-wall interaction in laser inertial fusion reactors: novel proposals for radiation tests of first wall materials | Dry-wall laser inertial fusion (LIF) chambers will have to withstand strong
bursts of fast charged particles which will deposit tens of kJ m$^{-2}$ and
implant more than 10$^{18}$ particles m$^{-2}$ in a few microseconds at a
repetition rate of some Hz. Large chamber dimensions and resistant
plasma-facing materials must be combined to guarantee the chamber performance
as long as possible under the expected threats: heating, fatigue, cracking,
formation of defects, retention of light species, swelling and erosion. Current
and novel radiation resistant materials for the first wall need to be validated
under realistic conditions. However, at present there is a lack of facilities
which can reproduce such ion environments.
This contribution proposes the use of ultra-intense lasers and high-intense
pulsed ion beams (HIPIB) to recreate the plasma conditions in LIF reactors. By
target normal sheath acceleration, ultra-intense lasers can generate very short
and energetic ion pulses with a spectral distribution similar to that of the
inertial fusion ion bursts, suitable to validate fusion materials and to
investigate the barely known propagation of those bursts through background
plasmas/gases present in the reactor chamber. HIPIB technologies, initially
developed for inertial fusion driver systems, provide huge intensity pulses
which meet the irradiation conditions expected in the first wall of LIF
chambers and thus can be used for the validation of materials too. | 2402.10235v1 |
2002-03-25 | Photo-response of the conductivity in functionalized pentacene compounds | We report the first investigation of the photo-response of the conductivity
of a new class of organic semiconductors based on functionalized pentacene.
These materials form high quality single crystals that exhibit a thermally
activated resistivity. Unlike pure pentacene, the functionalized derivatives
are readily soluble in acetone, and can be evaporated or spin-cast as thin
films for potential device applications. The electrical conductivity of the
single crystal materials is noticeably sensitive to ambient light changes. The
purpose, therefore, of the present study, is to determine the nature of the
photo-response in terms of carrier activation vs. heating effects, and also to
measure the dependence of the photo-response on photon energy. We describe a
new method, involving the temperature dependent photo-response, which allows an
unambiguous identification of the signature of heating effects in materials
with a thermally activated conductivity. We find strong evidence that the
photo-response in the materials investigated is predominantly a highly
localized heating mechanism. Wavelength dependent studies of the photo-response
reveal resonant features and cut-offs that indicate the photon energy
absorption is related to the electronic structure of the material. | 0203522v1 |
2016-04-19 | Tuning the work function in transition metal oxides and their heterostructures | The development of novel functional materials in experimental labs combined
with computer-based compound simulation brings the vision of materials design
on a microscopic scale continuously closer to reality. For many applications
interface and surface phenomena rather than bulk properties are key. One of the
most fundamental qualities of a material-vacuum interface is the energy
required to transfer an electron across this boundary, i.e. the work function.
It is a crucial parameter for numerous applications, including organic
electronics, field electron emitters, and thermionic energy converters. Being
generally very resistant to degradation at high temperatures, transition metal
oxides present a promising materials class for such devices. We have performed
a systematic study for perovskite oxides that provides reference values and,
equally important, reports on materials trends and the tunability of work
functions. Our results identify and classify dependencies of the work function
on several parameters including specific surface termination, surface
reconstructions, oxygen vacancies, and heterostructuring. | 1604.05615v1 |
2020-04-15 | Featureless adaptive optimization accelerates functional electronic materials design | Electronic materials exhibiting phase transitions between metastable states
(e.g., metal-insulator transition materials with abrupt electrical resistivity
transformations) are challenging to decode. For these materials, conventional
machine learning methods display limited predictive capability due to data
scarcity and the absence of features impeding model training. In this article,
we demonstrate a discovery strategy based on multi-objective Bayesian
optimization to directly circumvent these bottlenecks by utilizing latent
variable Gaussian processes combined with high-fidelity electronic structure
calculations for validation in the chalcogenide lacunar spinel family. We
directly and simultaneously learn phase stability and band gap tunability from
chemical composition alone to efficiently discover all superior compositions on
the design Pareto front. Previously unidentified electronic transitions also
emerge from our featureless adaptive optimization engine. Our methodology
readily generalizes to optimization of multiple properties, enabling co-design
of complex multifunctional materials, especially where prior data is sparse. | 2004.07365v2 |
2022-11-08 | Extraordinary magnetometry -- a review on extraordinary magnetoresistance | Extraordinary magnetoresistance (EMR) is a geometric magnetoresistance effect
occurring in hybrid devices consisting of a high-mobility material joined by a
metal. The change in resistance can exceed 107% at room temperature when a
magnetic field of 5 T is applied. Magnetic field sensors based on EMR hold the
potential formeasuring weak magnetic fields with an unprecedented sensitivity,
yet, to date this potential is largely unmet. In this work, we provide an
extensive review of the current state-of-the-art in EMR sensors with a focus on
the hybrid device geometries, the constituent material properties and
applications of EMR. We present a direct comparison of the best devices in
literature across magnetoresistance, sensitivity and noise equivalent field for
different materials and geometric designs. The compilation of studies collected
in this review illustrates the extremely rich possibilities for tuning the
magnetoresistive behavior varying the device geometry and material properties.
In addition, we aim to improve the understanding of the EMR effect and its
interplay with geometry and material properties. Finally, we discuss recent
trends in the field and future perspectives for EMR. | 2211.04308v1 |
2015-07-24 | Measurements of the Rate Capability of Various Resistive Plate Chambers | Resistive Plate Chambers (RPCs) exhibit a significant loss of efficiency for
the detection of particles, when subjected to high particle fluxes. This rate
limitation is related to the usually high resistivity of the resistive plates
used in their construction. This paper reports on measurements of the
performance of three different glass RPC designs featuring a different total
resistance of the resistive plates. The measurements were performed with 120
GeV protons at varying beam intensities | 1507.06968v2 |
2006-06-17 | Elastomeric carbon nanotube circuits for local strain sensing | We use elastomeric polydimethylsiloxane substrates to strain single-walled
carbon nanotubes and modulate their electronic properties, with the aim of
developing flexible materials that can sense local strain. We demonstrate
micron-scale nanotube devices that can be cycled repeatedly through strains as
high as 20% while providing reproducible local strain transduction by via the
device resistance. We also compress individual nanotubes, and find they undergo
an undulatory distortion with a characteristic spatial period of 100-200 nm.
The observed period can be understood by the mechanical properties of nanotubes
and the substrate in conjunction with continuum elasticity theory. These could
potentially be used to create superlattices within individual nanotubes,
enabling novel devices and applications. | 0606463v1 |
2007-06-12 | Very large spontaneous electric polarization in BiFeO3 single crystals at room temperature and its evolution under cycling fields | Electric polarization loops are measured at room temperature on highly pure
BiFeO3 single crystals synthesized by a flux growth method. Because the
crystals have a high electrical resistivity, the resulting low leakage currents
allow us to measure a large spontaneous polarization reaching 100
microC.cm^{-2}, a value never reported in the bulk. During electric cycling,
the slow degradation of the material leads to an evolution of the hysteresis
curves eventually preventing full saturation of the crystals. | 0706.1681v1 |
2008-04-23 | Giant Carrier Mobility in Single Crystals of FeSb2 | We report the giant carrier mobility in single crystals of FeSb2. Nonlinear
field dependence of Hall resistivity is well described with the two-carrier
model. Maximum mobility values in high mobility band reach ~10^5 cm^2/Vs at 8
K, and are ~10^2 cm^2/Vs at the room temperature. Our results point to a class
of materials with promising potential for applications in solid state
electronics. | 0804.3625v1 |
2011-01-30 | Thermodynamics of second phase conductive filaments | We present a theory of second phase conductive filaments in phase
transformable systems; applications include threshold switches, phase change
memory, and shunting in thin film structures. We show that the average filament
parameters can be described thermodynamically. In agreement with the published
data, the predicted filament current voltage characteristics exhibit negative
differential resistance vanishing at high currents where the current density
becomes a bulk material property. Our description is extendible to filament
transients and allows for efficient numerical simulation. | 1101.5737v2 |
2012-08-30 | Calculation of thermal parameters of SiGe microbolometers | The thermal parameters of a SiGe microbolometer were calculated using
numerical modeling. The calculated thermal conduction and thermal response time
are in good agreement with the values found experimentally and range between
2x10$^-7$ and 7x10$^-8$ W/K and 1.5 and 4.5 ms, respectively. High sensitivity
of microbolometer is achieved due to optimization of the thermal response time
and thermal conduction by fitting the geometry of supporting heat-removing legs
or by selection of a suitable material providing boundary thermal resistance
higher than 8x10$^-3$ cm$^2$K/W at the SiGe interface. | 1208.6147v1 |
2022-02-22 | Superconductivity and weak anti-localization in nodal-line semimetal SnTaS_2 | Topological semimetals with superconducting properties provide an emergent
platform to explore the properties of topological superconductors. We report
magnetization, and magneto-transport measurements on high quality single
crystals of transition metal dichalcogenide SnTaS2. It is a nodal line
semimetal with superconducting transition below Tc = 2.9 K. Moderate anisotropy
(3.1) is observed in upper critical fields along H||c and H||ab plane. In the
normal state we observe large magneto-resistance and weak anti-localization
effect that provide unambiguous confirmation of topological features in SnTaS2.
Therefore, genuine topological characteristics can be studied in this material,
particularly with regard to microscopic origin of order parameter symmetry. | 2202.10711v1 |
2020-05-07 | HVDC Surface Flashover in Compressed Air for Various Dielectrics | This study measures the voltage at which flashover occurs in compressed air
for a variety of dielectric materials and lengths in a uniform field for DC
voltages up to 100 kV. Statistical time lag is recorded and characterized,
displaying a roughly exponential dependence on breakdown voltage. Of the
materials tested, acrylic is observed to be the most resistant to flashover.
These data are intended to facilitate the design of compressed-air insulated
high voltage systems as an alternative to SF6 insulated systems. | 2006.12615v2 |
2023-07-30 | Non-Equilibrium Nature of Fracture Determines the Crack Paths | A high-fidelity neural network-based force field, NN-F$^{3}$, is developed to
cover the strain states up to material failure and the non-equilibrium,
intermediate nature of fracture. Simulations of fracture in 2D crystals using
NN-F$^{3}$ reveal spatial complexities from lattice-scale kinks to sample-scale
patterns. We find that the fracture resistance cannot be quantified by the
energy densities of relaxed edges as in the literature. Instead, the fracture
patterns, critical stress intensity factors at the kinks, and energy densities
of edges in the intermediate, unrelaxed states offer reasonable measures for
the fracture toughness and its anisotropy. | 2307.16126v1 |
2004-09-30 | Scaling theory of magneto-resistance in disordered local moment ferromagnets | We present a scaling theory of magneto-transport in Anderson-localized
disordered ferromagnets. Within our framework a pronounced
magnetic-field-sensitive resistance peak emerges naturally for temperatures
near the magnetic phase transition. We find that the resistance anomaly is a
direct consequence of the change in localization length caused by the magnetic
transition. For increasing values of the external magnetic field, the
resistance peak is gradually depleted and pushed towards higher temperatures.
Our results are in good agreement with magneto-resistance measurements on a
variety of disordered magnets. | 0410003v2 |
2009-02-08 | Pulse width controlled resistivity switching at room temperature in Bi0.8Sr0.2MnO3 | We report pulsed as well as direct current/voltage induced electroresistance
in Bi0.8Sr0.2MnO3 at room temperature. It is shown that bi-level and
multi-level resistivity switching can be induced by a sequence of pulses of
varying pulse width at fixed voltage amplitude. Resistivity increases abruptly
(= 55 % at 300 K) upon reducing pulse width from 100 ms to 25 ms for a fixed
electric field (E = 2 V/cm2) of 200 ms pulse period. The resistivity switching
is accompanied by a periodic change in temperature which alone can not explain
the magnitude of the resistivity change. | 0902.1281v1 |
2010-01-05 | Mechanism for bipolar resistive switching in transition metal oxides | We introduce a model that accounts for the bipolar resistive switching
phenomenom observed in transition metal oxides. It qualitatively describes the
electric field-enhanced migration of oxygen vacancies at the nano-scale. The
numerical study of the model predicts that strong electric fields develop in
the highly resistive dielectric-electrode interfaces, leading to a spatially
inhomogeneous oxygen vacancies distribution and a concomitant resistive
switching effect. The theoretical results qualitatively reproduce non-trivial
resistance hysteresis experiments that we also report, providing key validation
to our model. | 1001.0703v1 |
2011-05-19 | Nonvolatile bipolar resistive switching in Au/BiFeO3/Pt | Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO3/Pt
structure, where a Schottky contact and a quasi-Ohmic contact were formed at
the Au/BiFeO3 and BiFeO3/Pt interface, respectively. By changing the polarity
of the external voltage, the Au/BiFeO3/Pt is switched between two stable
resistance states without an electroforming process. The resistance ratio is
larger than two orders of magnitude. The resistive switching is understood by
the electric field - induced carriers trapping and detrapping, which changes
the depletion layer thickness at the Au/BiFeO3 interface. | 1105.3827v1 |
2011-07-30 | Polaronic transport in the ferromagnetic phase of Gd1-xCaxBaCo2O5.53 | Temperature dependent electrical resistivity and thermopower measurements
were carried out on Gd1-xCaxBaCo2O5.53 with x varying between 0 and 0.25. Ca
subsitution leads to the incorporation of holes (Co4+) into the system that
leads to a reduction in resistivity and a stabilisation of the ferromagnetic
phase at low temperatures. The temperature dependence of resistivity and
thermopower are markedly different in the Ca doped sample, with a dramatic
reduction in the resistivity, as compared to that in the pristine sample. The
variation in both the resistivity and thermopower with temperature is explained
in terms of the transport of polarons in the ferromagnetic phase of Ca doped
system. | 1108.0059v1 |
2017-06-20 | Scaling of the Hall effects beyond the quantum resistance threshold in oxidized CoFeB | The ordinary and the extraordinary Hall effects were studied in gradually
oxidized amorphous CoFeB ferromagnets over six orders of resistivity from the
metallic to the strongly insulating regime. Polarity of the extraordinary Hall
effect reverses, and the amplitude of both the ordinary and the extraordinary
Hall effects increases quadratically with resistivity when resistance exceeds
the quantum resistance threshold. The absolute value of the extraordinary Hall
effect scales linearly with the ordinary one in the entire range over eight
orders of magnitude between the metallic and the insulating states. The
behavior differs qualitatively and quantitatively from theoretically predicted
and experimentally known in other materials. | 1706.06392v1 |
2016-03-11 | Measurement of the $B_{1g}$ and $B_{2g}$ components of the elastoresistivity tensor for tetragonal materials via transverse resistivity configurations | The elastoresistivity tensor $m_{ij,kl}$ relates changes in resistivity to
strains experienced by a material. As a fourth-rank tensor, it contains
considerably more information about the material than the simpler (second-rank)
resistivity tensor; in particular, for a tetragonal material, the $B_{1g}$ and
$B_{2g}$ components of the elastoresistivity tensor ($m_{xx,xx}-m_{xx,yy}$ and
$2m_{xy,xy}$, respectively) can be related to its nematic susceptibility.
Previous experimental probes of this quantity have focused exclusively on
differential longitudinal elastoresistance measurements, which determine the
induced resistivity anisotropy arising from anisotropic in-plane strain based
on the difference of two longitudinal resistivity measurements. Here we
describe a complementary technique based on \textit{transverse}
elastoresistance measurements. This new approach is advantageous because it
directly determines the strain-induced resistivity anisotropy from a single
transverse measurement. To demonstrate the efficacy of this new experimental
protocol, we present transverse elastoresistance measurements of the
$2m_{xy,xy}$ elastoresistivity coefficient of BaFe$_2$As$_2$, a representative
iron-pnictide that has previously been characterized via differential
longitudinal elastoresistance measurements. | 1603.03537v1 |
2017-04-13 | Low temperature physical properties of Co-35Ni-20Mo-10Cr alloy MP35N | Multiphase Co-35Ni-20Mo-10Cr alloy MP35N is a high strength alloy with
excellent corrosion resistance. Its applications span chemical, medical, and
food processing industries. Thanks to its high modulus and high strength, it
found applications in reinforcement of ultra-high field pulsed magnets.
Recently, it has also been considered for reinforcement in superconducting
wires used in ultra-high field superconducting magnets. For these applications,
accurate measurement of its physical properties at cryogenic temperatures is
very important. In this paper, physical properties including electrical
resistivity, specific heat, thermal conductivity, and magnetization of
as-received and aged samples are measured from 2 to 300 K. The electrical
resistivity of the aged sample is slightly higher than the as-received sample,
both showing a weak linear temperature dependence in the entire range of 2 -
300 K. The measured specific heat Cp of 0.43 J/g-K at 295 K agrees with a
theoretical prediction, but is significantly smaller than the values in the
literature. The thermal conductivity between 2 and 300 K is in good agreement
with the literature which is only available above 77 K. Magnetic property of
MP35N changes significantly with aging. The as-received sample exhibits Curie
paramagnetism with a Curie constant C = 0.175 K. While the aged sample contains
small amounts of a ferromagnetic phase even at room temperature. The measured
MP35N properties will be useful for the engineering design of pulsed magnets
and superconducting magnets using MP35N as reinforcement. | 1704.04275v1 |
2024-02-20 | Molten Salt Flux Liquid Transport Method for Ultra Clean Single Crystals UTe2 | Various single crystal growth techniques are presented for the unconventional
superconductor UTe2. The molten salt flux liquid transport (MSFLT) method is
employed to grow high-quality and large single crystals, exhibiting a high
residual resistivity ratio (RRR = 200-800). On the other hand, the Te self-flux
and chemical vapor transport (CVT) method produces samples of lower quality.
The MSFLT method is a hybrid approach that combines the molten salt flux (MSF)
and CVT methods. One significant advantage is that the materials gradually
crystallize at the relatively low temperature which is fixed during the main
process. This might be crucial for preventing U deficiency and obtaining
high-quality and large single crystals of UTe2. Many different single crystals
obtained by different technique were characterized by resistivity, specific
heat measurements. The superconducting transition temperature decreases with
the residual resistivity, followed by the Abrikosov-Gor'kov pair breaking
theory. The highest quality sample reaches Tc=2.1K. The residual gamma-value of
specific heat for the highest quality sample is only 3 percents of the normal
state gamma-value. The specific heat jump, Delta C/(gamma Tc) reaches about 2.7
for high quality samples, indicating a strong coupling superconductor.
Furthermore, the magnetic susceptibility for the field along a-axis in a high
quality single crystal does not show an up-turn behavior on cooling, which is
consistent with the results of NMR Knight shift and muSR experiments. | 2402.12740v2 |
2023-12-29 | Bilayer Vanadium Dioxide Thin Film with Elevated Transition Temperatures and High Resistance Switching | Despite widespread interest in the phase-change applications of vanadium
dioxide (VO$_2$), the fabrication of high-quality VO$_2$ thin films with
elevated transition temperatures (TIMT) and high Insulator-Metal-Transition
resistance switching still remains a challenge. This study introduces a
two-step atmospheric oxidation approach to fabricate bilayer VO$_{2-x}$/VO$_2$
films on a c-plane sapphire substrate. To quantify the impact of the VO$_2$
buffer layer, a single-layer VO$_2$ film of the same thickness was also
fabricated. The bilayer VO$_{2-x}$/VO$_2$ films wherein the top VO$_{2-x}$ film
was under-oxidized demonstrated an elevation in TIMT reaching ~97 $^\circ$C,
one of the highest reported to date for VO$_2$ films and is achieved in a
doping-free manner. Our results also reveal a one-order increase in resistance
switching, with the optimum bilayer VO$_2$/VO$_2$ film exhibiting ~3.6 orders
of switching from 25 $^\circ$C to 110 $^\circ$C, compared to the optimum
single-layer VO$_2$ reference film. This is accompanied by a one-order decrease
in the on-state resistance in its metallic phase. The elevation in TIMT,
coupled with increased strain extracted from the XRD characterization of the
bilayer film, suggests the possibility of compressive strain along the c-axis.
These VO$_{2-x}$/VO$_2$ films also demonstrate a significant change in the
slope of their resistance vs temperature curves contrary to the conventional
smooth transition. This feature was ascribed to the rutile/monoclinic
quasi-heterostructure formed due to the top VO$_{2-x}$ film having a reduced
TIMT. Our findings carry significant implications for both the lucid
fabrication of VO$_2$ thin film devices as well as the study of phase
transitions in correlated oxides. | 2312.17437v1 |
2024-01-31 | Spark Plasma Sintering for high-speed diffusion welding of the ultrafine grained near-a Ti-5Al-2V alloy with high strength and corrosion resistance for nuclear engineering | The paper demonstrates the prospects of Spark Plasma Sintering (SPS) for the
high-speed diffusion welding of the high-strength ultrafine-grained (UFG)
near-a Ti-5Al-2V alloy. The effect of increased diffusion welding intensity in
the UFG Ti alloys is discussed also. The welds of the UFG near-a-Ti-5Al-2V
alloy obtained by SPS are featured by high density, strength, and corrosion
resistance. The rate of weld sealing in the UFG alloys has been shown to depend
on the heating rate non-monotonously (with a pronounced maximum). At the stage
of continuous heating and isothermic holding, the kinetics of the weld sealing
was found to be determined by the exponential creep rate, the intensity of
which in the coarse-grained (CG) alloys is limited by the diffusion rate in the
crystal lattice whereas in the UFG alloys it is limited by the grain boundary
diffusion rate. | 2401.17718v1 |
2018-01-29 | Memristor properties of high temperature superconductors | The review of studies on memristive properties or effect of resistive
switchings in four classes of high temperature superconductors is presented in
order to reveal functional properties of HTSCs which become apparent in the
effects under discussion, prospects of usage of high temperature
superconductors based memristors in applications and search for new mechanisms
of strongly correlated nature to realize new generation memristors. The
properties are: undergoing metal insulator transition at oxygen doping,
transport anisotropy, existence of charge reservoirs through which doping of
conductive copper oxygen layers is carried out. These are the main functional
properties of HTSCs which permit to use them in memristors. By the example of
study of bipolar effect of resistive switching in high temperature
superconductors based heterojunctions it is shown how one can form memristor
structures based on high temperature superconductors using their functional
properties. | 1801.09428v1 |
2016-03-07 | Prediction of a Two-dimensional Phosphorus Nitride Monolayer | Today, 2D semiconductor materials have been extended into the nitrogen group:
phosphorene, arsenene, antimonene and even nitrogene. Motivated by them, based
upon first-principles density functional calculations, we propose a new
two-dimensional phosphorus nitride (PN) structure that is stable well above the
room temperature, due to its extremely high cohesive energy. Unlike
phosphorene, PN structure is resistant to high temperature oxidation. The
structure is predicted to be a semiconductor with a wide, indirect band gap of
2.64 eV. More interestingly, the phosphorus nitride monolayer experiences an
indirect-to-direct band-gap transition at a relatively small tensile strain.
Such dramatic transformation in the electronic structure combined with
structural stability and oxidation resistance at high temperature could pave
the way for exciting innovations in high-speed ultrathin transistors, power
electronic modules, ultra-high efficiency LEDs and semiconductor lasers. | 1603.01957v2 |
2023-04-12 | Crack-free high composition (>35%) thick (>30 nm) barrier AlGaN/AlN/GaN HEMT on sapphire with record low sheet resistance | In this article, high composition (>35%) thick (>30 nm) barrier AlGaN/AlN/GaN
HEMT structure grown on a sapphire substrate with ultra-low sheet resistivity
(<250 \Omega / \Box ) is reported. Optimization of growth conditions, such as
reduced growth rate, low carbon incorporation, and thickness optimization of
different epitaxial layers allowed to grow a crack-free high composition and
thick AlGaN barrier layer HEMT structure. A significantly high two-dimensional
electron gas (2DEG) density of 1.46 \times 10^{13} cm^{-2} with a room
temperature mobility of 1710 cm^{2}/V.s is obtained by Hall measurement using
the Van-Der-Pauw method. These state-of-the-art results show great potential
for high-power Ga-polar HEMT design on the sapphire substrate. | 2304.05593v1 |
2015-02-06 | Long-term stability of phase-separated Half-Heusler compounds | Half-Heusler (HH) compounds have shown high Figure of merits up to 1.5. The
key to these high thermoelectric efficiencies is an intrinsic phase separation,
which occurs in multicomponent Half-Heusler compounds and leads to an
significantly reduction of the thermal conductivity. For commercial
applications, compatible n- and p-type materials are essential and their
thermal stability under operating conditions, e.g. for an automotive up to 873
K, needs to be guaranteed. For the first time, the long-term stability of n-
and p-type HH materials is proved. We investigated HH materials based on the
Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both
compounds exhibit a maximum Seebeck coefficient of S around 210 muV/K and an
intrinsic phase separation into two HH phases. The dendritic microstructure is
temperature resistant and maintained the low thermal conductivity values (kappa
less than 4 W/Km). Our results emphasize that phase-separated HH compounds are
suitable low cost materials and can lead to enhanced thermoelectric
efficiencies beyond the set benchmark for industrial applications. | 1502.01828v1 |
2020-08-12 | Helium effects and bubbles formation in irradiated Ti3SiC2 | Ti3SiC2 is a potential structural material for nuclear reactor applications.
However, He irradiation effects in this material are not well understood,
especially at high temperatures. Here, we compare the effects of He irradiation
in Ti3SiC2 at room temperature (RT) and at 750 {\deg}C. Irradiation at 750
{\deg}C was found to lead to extremely elongated He bubbles that are
concentrated in the nano-laminate layers of Ti3SiC2, whereas the overall
crystal structure of the material remained intact. In contrast, at RT, the
layered structure was significantly damaged and highly disordered after
irradiation. Our study reveals that at elevated temperatures, the unique
structure of Ti3SiC2 can accommodate large amounts of He atoms in the
nano-laminate layer, without compromising the structural stability of the
material. The structure and the mechanical tests results show that the
irradiation induced swelling and hardening at 750 {\deg}C are much smaller than
those at RT. These results indicate that Ti3SiC2 has an excellent resistance to
accumulation of radiation-induced He impurities and that it has a considerable
tolerance to irradiation-induced degradation of mechanical properties at high
temperatures. | 2008.05468v1 |
2023-09-05 | Control of Mechanical and Fracture Properties in Two-phase Materials Reinforced by Continuous, Irregular Networks | Composites with high strength and high fracture resistance are desirable for
structural and protective applications. Most composites, however, suffer from
poor damage tolerance and are prone to unpredictable fractures. Understanding
the behavior of materials with an irregular reinforcement phase offers
fundamental guidelines for tailoring their performance. Here, we study the
fracture nucleation and propagation in two phase composites, as a function of
the topology of their irregular microstructures. We use a stochastic algorithm
to design the polymeric reinforcing network, achieving independent control of
topology and geometry of the microstructure. By tuning the local connectivity
of isodense tiles and their assembly into larger structures, we tailor the
mechanical and fracture properties of the architected composites, at the local
and global scale. Finally, combining different reinforcing networks into a
spatially determined meso-scale assembly, we demonstrate how the spatial
propagation of fractures in architected composite materials can be designed and
controlled a priori. | 2309.01888v1 |
2020-01-21 | Mechanical behavior, enhanced dc resistivity, energy band gap and high temperature magnetic properties of Y-substituted Mg-Zn ferrites | We report the synthesis of Y-substituted Mg-Zn ferrites using conventional
standard ceramic technique. XRD patterns confirm the single phase cubic spinel
structure up to x = 0.03 and appearance of a secondary phase of YFeO3for higher
Y contents. FESEM images depict the distribution of grains and EDS spectra
confirmed the absence of any unwanted element. Completion of solid state
reaction and formation of spinel structure has been revealed from FTIR spectra.
The FTIR data along with lattice constant, bulk density and porosity were
further used to calculate the stiffness constant (Cij), elastic constant and
Debye temperatures. Mechanical stability of all studied compositions is
confirmed from Cij using Born stability conditions. Brittleness and isotropic
nature are also confirmed using Poisson ratio and anisotropy constants,
respectively. The enhancement of dc electrical resistivity with Y content is
observed. The energy band gap (increased with Y contents) is found in good
agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase
change has been observed from the field dependent high temperature
magnetization curves. The magnetic moments and saturation magnetization were
found to be decreased with increasing temperature. The Curie temperature (Tc)
has been measured from temperature dependent magnetic moment (M-T) and initial
permeability and found to be in good agreement with each other. Decrease in Tc
with Y content is due to redistribution of cations and weakening of the
exchange coupling constant. The magnetic phase transition has been analyzed by
Arrott plot and found to have second order phase transition. The dc resistivity
endorses the prepared ferrites are suitable for high frequency and high
temperature magnetic device applications as well. | 2001.07313v1 |
2023-01-07 | Impact of Severe Plastic Deformation on Kinetics and Thermodynamics of Hydrogen Storage in Magnesium and Its Alloys | Magnesium and its alloys are the most investigated materials for solid-state
hydrogen storage in the form of metal hydrides, but there are still unresolved
problems with the kinetics and thermodynamics of hydrogenation and
dehydrogenation of this group of materials. Severe plastic deformation (SPD)
methods, such as equal-channel angular pressing (ECAP), high-pressure torsion
(HPT), intensive rolling and fast forging, have been widely used to enhance the
activation, air resistance, and hydrogenation/dehydrogenation kinetics of
Mg-based hydrogen storage materials by introducing ultrafine/nanoscale grains
and crystal lattice defects. These severely deformed materials, particularly in
the presence of alloying additives or second-phase nanoparticles, can show not
only fast hydrogen absorption/desorption kinetics but also good cycling
stability. It was shown that some materials that are apparently inert to
hydrogen can absorb hydrogen after SPD processing. Moreover, the SPD methods
were effectively used for hydrogen binding-energy engineering and synthesizing
new magnesium alloys with low thermodynamic stability for reversible
low/room-temperature hydrogen storage, such as nanoglasses, high-entropy
alloys, and metastable phases including the high-pressure {\gamma}-MgH2
polymorph. This article reviews recent advances in the development of Mg-based
hydrogen storage materials by SPD processing and discusses their potential in
future applications. | 2301.05009v1 |
2021-07-26 | Massive electrons and unconventional room-temperature superconductivity in superhydrides | The search for room-temperature superconducting materials has been at the
center of modern research for decades. The recent discovery of high-temperature
superconductivity, under extreme pressure in hydrogen-rich materials, is a
tremendous achievement in this research front. This discovery offers a route in
the search for room temperature superconductivity at ambient pressure. The
superconductivity of these hydrogen-rich materials was confirmed by the
observation of zero-resistance, isotope effects, effect of magnetic field, and
other standard properties. However, some of the experimental features were
puzzling as they were not consistent with the known superconductivity theories.
These debatable features have lead to a series of recent publications
downplaying the existence of superconductivity in these superhydrides. Here we
propose a concept of massive electrons under pressure and successfully explain
all non-standard experimental observations. Our massive electron concept
explains the large effective mass of the quasiparticles, the reason for the
high critical temperatures for moderate electron-phonon couplings, and a 3-5
orders of magnitude larger conductivity causing a narrow resistivity broadening
at the transition in the presence of magnetic field. We anticipate our findings
will lead to a new directions and tweaks in current research in the search for
ambient-pressure, room-temperature superconductors. | 2107.12255v1 |
2010-04-21 | Superconductor-insulator quantum phase transition | The current understanding of the superconductor-insulator transition is
discussed level by level in a cyclic spiral-like manner. At the first level,
physical phenomena and processes are discussed which, while of no formal
relevance to the topic of transitions, are important for their implementation
and observation; these include superconductivity in low electron density
materials, transport and magnetoresistance in superconducting island films and
in highly resistive granular materials with superconducting grains, and the
Berezinskii-Kosterlitz-Thouless transition. The second level discusses and
summarizes results from various microscopic approaches to the problem, whether
based on the Bardeen-Cooper-Schrieffer theory (the disorder-induced reduction
in the superconducting transition temperature; the key role of Coulomb blockade
in high-resistance granular superconductors; superconducting fluctuations in a
strong magnetic field) or on the theory of the Bose-Einstein condensation. A
special discussion is given to phenomenological scaling theories. Experimental
investigations, primarily transport measurements, make the contents of the
third level and are for convenience classified by the type of material used
(ultrathin films, variable composition materials, high-temperature
superconductors, superconductor-poor metal transitions). As a separate topic,
data on nonlinear phenomena near the superconductor-insulator transition are
presented. At the final, summarizing, level the basic aspects of the problem
are enumerated again to identify where further research is needed and how this
research can be carried out. Some relatively new results, potentially of key
importance in resolving the remaining problems, are also discussed. | 1004.3761v1 |
2016-03-30 | Butterfly Magnetoresistance, Quasi-2D Dirac Fermi Surfaces, and a Topological Phase Transition in ZrSiS | Magnetoresistance (MR), the change of a material's electrical resistance in
response to an applied magnetic field, is a technologically important property
that has been the topic of intense study for more than a quarter century. Here
we report the observation of an unusual "butterfly" shaped titanic angular
magnetoresistance (AMR) in the non-magnetic, Dirac material, ZrSiS. The MR is
large and positive, reaching nearly 1.8 x 10^5 percent at 9 T and 2 K at an
angle of 45o between the applied current (along the a-axis) and the applied
field (90o is H parallel to the c-axis). Approaching 90o, a "dip" is seen in
the AMR which can be traced to an angle dependent deviation from the H^2 law.
By analyzing the SdH oscillations at different angles, we find that ZrSiS has a
combination of 2D and 3D Dirac pockets comprising its Fermi surface and that
the anomalous transport behavior coincides with a topological phase transition
whose robust signature is evident despite transport contributions from other
parts of the Fermi surface. We also find that as a function of angle, the
temperature dependent resistivity in high field displays a broad peak-like
behavior, unlike any known Dirac/Weyl material. The combination of very high
mobility carriers and multiple Fermi surfaces in ZrSiS allow for large bulk
property changes to occur as a function of angle between applied fields makes
it a promising platform to study the physics stemming from the coexistence of
2D and 3D Dirac electrons. | 1603.09318v2 |
2020-08-27 | Large-Scale and Robust Multifunctional Vertically-Aligned MoS$_2$ Photo-Memristors | Memristive devices have drawn considerable research attention due to their
potential applications in non-volatile memory and neuromorphic computing. The
combination of resistive switching devices with light-responsive materials is
considered a novel way to integrate optical information with electrical
circuitry. On the other hand, 2D materials have attracted substantial
consideration thank to their unique crystal structure, as reflected in their
chemical and physical properties. Although not the major focus, van der Waals
solids were proven to be potential candidates in memristive devices. In this
scheme, the majority of the resistive switching devices were implemented on
planar flakes, obtained by mechanical exfoliation. Here we utilize a facile and
robust methodology to grow large-scale vertically aligned MoS$_2$ (VA-MoS$_2$)
films on standard silicon substrates. Memristive devices with the structure
silver/VA-MoS$_2$/Si are shown to have low set-ON voltages (<0.5V),
large-retention times ($>2\times10^4$ s) and high thermal stability (up to 350
$^\circ$C). The proposed memristive device also exhibits long term potentiation
/ depression (LTP/LTD) and photo-active memory states. The large-scale
fabrication, together with the low operating voltages, high thermal stability,
light-responsive behaviour and long-term potentiation/depression, makes this
approach very appealing for real-life non-volatile memory applications. | 2008.11950v1 |
2002-08-15 | High Ferromagnetic Transition Temperature (172K) in Mn delta-doped GaAs with p-type Selective Doping | We have found high ferromagnetic transition temperature in Mn delta-doped
GaAs-based heterostructures grown on GaAs(001) substrates by molecular beam
epitaxy. A 0.3 ML Mn d-doped GaAs samples showed high resistivity at low
temperature and did not show a ferromagnetic behavior. However, in a
selectively doped heterostructure (Mn delta-doped GaAs / Be-doped AlGaAs),
where holes were supplied from the Be-doped AlGaAs layer, clear ferromagnetic
order was observed. The ferromagnetic transition temperature of the selectively
doped heterostructure was as high as 172K with suitable low-temperature (LT)
annealing treatment. | 0208299v1 |
2013-10-30 | Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6 | SmB6 has recently been predicted to be a Topological Kondo Insulator, the
first strongly correlated heavy fermion material to exhibit topological surface
states. High quality crystals are necessary to investigate the topological
properties of this material. Single crystal growth of the rare earth
hexaboride, SmB6, has been carried out by the floating zone technique using a
high power xenon arc lamp image furnace. Large, high quality single-crystals
are obtained by this technique. The crystals produced by the floating zone
technique are free of contamination from flux materials and have been
characterised by resistivity and magnetisation measurements. These crystals are
ideally suited for the investigation of both the surface and bulk properties of
SmB6. | 1310.8189v1 |
2019-11-05 | Metal$/BaTiO_{3}/β-Ga_{2}O_{3}$ Dielectric Heterojunction Diode with 5.7 MV/cm Breakdown Field | Wide and ultra-wide band gap semiconductors can provide excellent performance
due to their high energy band gap, which leads to breakdown electric fields
that are more than an order of magnitude higher than conventional silicon
electronics. In materials where p-type doping is not available, achieving this
high breakdown field in a vertical diode or transistor is very challenging. We
propose and demonstrate the use of dielectric heterojunctions that use extreme
permittivity materials to achieve high breakdown field in a unipolar device. We
demonstrate the integration of a high permittivity material BaTiO3 with n-type
$\beta$-Ga2O3 to enable 5.7 MV/cm average electric field and 7 MV/cm peak
electric field at the device edge, while maintaining forward conduction with
relatively low on-resistance and voltage loss. The proposed dielectric
heterojunction could enable new design strategies to achieve theoretical device
performance limits in wide and ultra-wide band gap semiconductors where bipolar
doping is challenging. | 1911.02068v1 |
2009-03-17 | In search for the superconducting spin-switch: Magnetization induced resistance switching effects in La$_{0.67}$Sr$_{0.33}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ bi- and trilayers | We have studied the influence of the magnetization on the superconducting
transition temperature ($T_c$) in bi- and trilayers consisting of the
half-metallic ferromagnet La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) and the
high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO). We have
made use of tilted epitaxial growth in order to achieve contacts between the
two materials that are partly in the crystallographic $ab$-plane of the YBCO.
As a result of uniaxial magnetic anisotropy in the tilted structures, we
observe sharp magnetization switching behavior. At temperatures close to $T_c$,
the magnetization switching induces resistance jumps in trilayers, resulting in
a magnetization dependence of $T_c$. In bilayers, this switching effect can be
observed as well, provided that the interface to the ferromagnetic layer is
considerably rough. Our results indicate that the switching behavior arises
from magnetic stray fields from the ferromagnetic layers that penetrate into
the superconductor. A simple model describes the observed behavior well. We
find no evidence that the switching behavior is caused by a so-called
superconducting spin-switch, nor by accumulation of spin-polarized electrons.
Observation of magnetic coupling of the ferromagnetic layers, through the
superconductor, supports the idea of field induced resistance switching. | 0903.2993v1 |
2016-12-13 | Bad Metals from Fluctuating Density Waves | Bad metals have a large resistivity without being strongly disordered. In
many bad metals the Drude peak moves away from zero frequency as the
resistivity becomes large at increasing temperatures. We catalogue the position
and width of the `displaced Drude peak' in the observed optical conductivity of
several families of bad metals, showing that $\omega_\text{peak} \sim \Delta
\omega \sim k_BT/\hbar$. This is the same quantum critical timescale that
underpins the $T$-linear dc resistivity of many of these materials. We provide
a unified theoretical description of the optical and dc transport properties of
bad metals in terms of the hydrodynamics of short range quantum critical
fluctuations of incommensurate density wave order. Within hydrodynamics, pinned
translational order is essential to obtain the nonzero frequency peak. | 1612.04381v5 |
2017-03-11 | On the isotope effect in compressed superconducting H$_\textrm{3}$S and D$_\textrm{3}$S | A maximum superconductive transition temperature $T_\textrm{C}$ = 203.5 K has
recently been reported for a sample of the binary compound tri-hydrogen sulfide
(H$_\textrm{3}$S) prepared at high pressure and with room temperature
annealing. Measurements of $T_\textrm{C}$ for H$_\textrm{3}$S and its deuterium
counterpart D$_\textrm{3}$S have suggested a mass isotope effect exponent
${\alpha}$ with anomalous enhancements for reduced applied pressures. While
widely cited for evidence of phonon-based superconductivity, the measured
$T_\textrm{C}$ is shown to exhibit important dependences on the quality and
character of the H$_\textrm{3}$S and D$_\textrm{3}$S materials under study;
examination of resistance versus temperature data shows that variations in
$T_\textrm{C}$ and apparent ${\alpha}$ are strongly correlated with residual
resistance ratio, indicative of sensitivity to metallic order. Correlations
also extend to the fractional widths of the superconducting transitions. Using
resistance data to quantify and compensate for the evident materials
differences between H$_\textrm{3}$S and D$_\textrm{3}$S samples, a value of
${\alpha}$ = 0.043 $\pm$ 0.140 is obtained. Thus, when corrected for the
varying levels of disorder, the experimental upper limit ($\leq$0.183) lies
well below ${\alpha}$ derived in phonon-based theories. | 1703.04034v1 |
2019-07-17 | Quasi 2-D magnetism in the Kagome layer compound FeSn | Single crystals of the single Kagome layer compound FeSn are investigated
using x-ray and neutron scattering, magnetic susceptibility and magnetization,
heat capacity, resistivity, Hall, Seebeck, thermal expansion, thermal
conductivity measurements and density functional theory (DFT). FeSn is a planar
antiferromagnet below TN = 365 K and exhibits ferromagnetic magnetic order
within each Kagome layer. The in-plane magnetic susceptibility is sensitive to
synthesis conditions. Resistivity, Hall and Seebeck results indicate multiple
bands near the Fermi energy. The resistivity of FeSn is about 3 times lower for
current along the stacking direction than in the plane, suggesting that
transport and the bulk electronic structure of FeSn is not quasi 2D. FeSn is an
excellent metal with Rho(300K)/Rho(2K) values about 100 in both directions.
While the ordered state is antiferromagnetic, high temperature susceptibility
measurements indicate a ferromagnetic Curie-Weiss temperature of 173 K,
reflecting the strong in-plane ferromagnetic interactions. DFT calculations
show a 3D electronic structure with the Dirac nodal lines along the K-H
directions in the magnetic Brillouin zone about 0.3 eV below the Fermi energy,
with the Dirac dispersions at the K points gapped by spin-orbit coupling except
at the H point. The magnetism, however, is highly 2D with
Jin-plane/Jout-of-plane = 10. The predicted spin-wave spectrum is presented. | 1907.07719v1 |
2019-06-25 | Spin-split band hybridization in graphene proximitized with $α$-RuCl$_3$ nanosheets | Proximity effects induced in the 2D Dirac material graphene potentially open
access to novel and intriguing physical phenomena. Thus far, the coupling
between graphene and ferromagnetic insulators has been experimentally
established. However, only very little is known about graphene's interaction
with antiferromagnetic insulators. Here, we report a low temperature study of
the electronic properties of high quality van der Waals heterostructures
composed of a single graphene layer proximitized with $\alpha$-RuCl$_3$. The
latter is known to become antiferromagnetically ordered below 10 K. Shubnikov
de Haas oscillations in the longitudinal resistance together with Hall
resistance measurements provide clear evidence for a band realignment that is
accompanied by a transfer of electrons originally occupying the graphene's spin
degenerate Dirac cones into $\alpha$-RuCl$_3$ band states with in-plane spin
polarization. Left behind are holes in two separate Fermi pockets, only the
dispersion of one of which is distorted near the Fermi energy due to spin
selective hybridization with these spin polarized $\alpha$-RuCl$_3$ band
states. This interpretation is supported by our DFT calculations. An unexpected
damping of the quantum oscillations as well as a zero field resistance upturn
close to the N$\'e$el temperature of $\alpha$-RuCl$_3$ suggests the onset of
additional spin scattering due to spin fluctuations in the $\alpha$-RuCl$_3$. | 1906.10405v1 |
2020-01-17 | A back-end, CMOS compatible ferroelectric Field Effect Transistor for synaptic weights | Neuromorphic computing architectures enable the dense co-location of memory
and processing elements within a single circuit. This co-location removes the
communication bottleneck of transferring data between separate memory and
computing units as in standard von Neuman architectures for data-critical
applications including machine learning. The essential building blocks of
neuromorphic systems are non-volatile synaptic elements such as memristors. Key
memristor properties include a suitable non-volatile resistance range,
continuous linear resistance modulation and symmetric switching. In this work,
we demonstrate voltage-controlled, symmetric and analog potentiation and
depression of a ferroelectric Hf$_{57}$Zr$_{43}$O$_{2}$ (HZO) field effect
transistor (FeFET) with good linearity. Our FeFET operates with a low writing
energy (fJ) and fast programming time (40 ns). Retention measurements have been
done over 4-bits depth with low noise (1%) in the tungsten oxide (WO$_{x}$)
read out channel. By adjusting the channel thickness from 15nm to 8nm, the
on/off ratio of the FeFET can be engineered from 1% to 200% with an
on-resistance ideally >100 kOhm, depending on the channel geometry. The device
concept is using earth-abundant materials, and is compatible with a back end of
line (BEOL) integration into complementary metal-oxidesemiconductor (CMOS)
processes. It has therefore a great potential for the fabrication of high
density, large-scale integrated arrays of artificial analog synapses. | 2001.06475v1 |
2020-05-16 | Switching friction at a manganite surface using electric fields | We report active control of the friction force at the contact between a
nanoscale asperity and a La$_{0.55}$Ca$_{0.45}$MnO$_3$ (LCMO) thin film using
electric fields. We use friction force microscopy under ultrahigh vacuum
conditions to measure the friction force as we change the film resistive state
by electric field-induced resistive switching. Friction forces are high in the
insulating state and clearly change to lower values when the probed local
region is switched to the conducting state. Upon switching back to an
insulating state, the friction forces increase again. Thus, we demonstrate
active control of friction without having to change the contact temperature or
pressure. By comparing with measurements of friction at the metal-to-insulator
transition and with the effect of applied voltage on adhesion, we rule out
electronic excitations, electrostatic forces and changes in contact area as the
reasons for the effect of resistive switching on friction. Instead, we argue
that friction is limited by phonon relaxation times which are strongly coupled
to the electronic degrees of freedom through distortions of the MnO6 octahedra.
The concept of controlling friction forces by electric fields should be
applicable to any materials where the field produces strong changes in phonon
lifetimes. | 2005.08949v1 |
2020-08-17 | Enhancement of spin Hall conductivity in W-Ta alloy | Generating pure spin currents via the spin Hall effect in heavy metals has
been an active topic of research in the last decade. In order to reduce the
energy required to efficiently switch neighbouring ferromagnetic layers for
applications, one should not only increase the charge- to-spin conversion
efficiency but also decrease the longitudinal resistivity of the heavy metal.
In this work, we investigate the spin Hall conductivity in W_{1-x}Ta_{x} /
CoFeB / MgO (x = 0 - 0.2) using spin torque ferromagnetic resonance
measurements. Alloying W with Ta leads to a factor of two change in both the
damping-like effective spin Hall angle (from - 0.15 to - 0.3) and longitudinal
resistivity (60 - 120 {\mu}W cm). At 11% Ta concentration, a remarkably high
spin Hall angle value of - 0.3 is achieved with a low longitudinal resistivity
100 {\mu}W cm, which could lead to a very low power consumption for this
W-based alloy. This work demonstrates sputter-deposited W-Ta alloys could be a
promising material for power-efficient spin current generation. | 2008.07572v1 |
2020-12-23 | Resistivity, Hall effect, and anisotropic superconducting coherence lengths of HgBa$_2$CaCu$_2$O$_{6+δ}$ thin films with different morphology | Thin films of the high-temperature superconductor
HgBa$_2$CaCu$_2$O$_{6+\delta}$ have been prepared on SrTiO$_3$ substrates by
pulsed-laser deposition of precursor films and subsequent annealing in
mercury-vapor atmosphere. The microstructural properties of such films can vary
considerably and have been analyzed by x-ray diffraction and atomic force
microscopy. Whereas the resistivity is significantly enhanced in samples with
coarse-grained structure, the Hall effect shows little variation. This
disparity is discussed based on models for transport properties in granular
materials. We find that, despite of the morphological variation, all samples
have similar superconducting properties. The critical temperatures $T_c \sim
121.2$ K $\dots 122.0$ K, resistivity, and Hall data indicate that the samples
are optimally doped. The analyses of superconducting order parameter
fluctuations in zero and finite magnetic fields yield the in-plane $\xi_{ab}(0)
\sim 2.3$ nm $\dots 2.8$ nm and out-of-plane $\xi_{c}(0) \sim 0.17$ nm $ \dots
0.24$ nm Ginzburg-Landau coherence lengths at zero temperature. Hall
measurements provide estimates of carrier scattering defects in the normal
state and vortex pinning properties in the superconducting state inside the
grains. | 2012.12539v1 |
2021-05-03 | Fingerprints of quantum criticality in locally resolved transport | Understanding electrical transport in strange metals, including the seeming
universality of Planckian $T$-linear resistivity, remains a longstanding
challenge in condensed matter physics. We propose that local imaging
techniques, such as nitrogen vacancy center magnetometry, can locally identify
signatures of quantum critical response which are invisible in measurements of
a bulk electrical resistivity. As an illustrative example, we use a minimal
holographic model for a strange metal in two spatial dimensions to predict how
electrical current will flow in regimes dominated by quantum critical dynamics
on the Planckian length scale. We describe the crossover between quantum
critical transport and hydrodynamic transport (including Ohmic regimes), both
in charge neutral and finite density systems. We compare our holographic
predictions to experiments on charge neutral graphene, finding quantitative
agreement with available data; we suggest further experiments which may
determine the relevance of our framework to transport on Planckian scales in
this material. More broadly, we propose that locally imaged transport be used
to test the universality (or lack thereof) of microscopic dynamics in the
diverse set of quantum materials exhibiting $T$-linear resistivity. | 2105.01075v4 |
2022-06-16 | Size-Dependent Grain Boundary Scattering in Topological Semimetals | We assess the viability of topological semimetals for application in advanced
interconnect technology, where conductor size is on the order of a few
nanometers and grain boundaries are expected to be prevalent. We investigate
the electron transport properties and grain boundary scattering in thin films
of the topological semimetals CoSi and CoGe using first-principles calculations
combined with the Non-Equilibrium Green's Function (NEGF) technique. Unlike
conventional interconnect metals like Cu and Al, we find that CoSi and CoGe
conduct primarily through topologically-protected surface states in thin film
structures even in the presence of grain boundaries. The area-normalized
resistance decreases with decreasing film thickness for CoSi and CoGe thin
films both with and without grain boundaries; a trend opposite to that of the
conventional metals Cu and Al. The surface-dominated transport mechanisms in
thin films of topological semimetals with grain boundaries demonstrates a
fundamentally new paradigm of the classical resistivity size-effect, and
suggests that these materials may be promising candidates for applications as
nano-interconnects where high electrical resistivity acts as a major bottleneck
limiting semiconductor device performance. | 2206.08214v2 |
2023-03-06 | Thermal hysteretic behavior and negative magnetoresistance in an unusual charge-density-wave material EuTe4 | EuTe4 is a newly-discovered van der Waals material exhibiting a novel
charge-density wave (CDW) with a large thermal hysteresis in the resistivity
and CDW gap. In this work, we systematically study the electronic structure and
transport properties of EuTe4 using high-resolution angle-resolved
photoemission spectroscopy (ARPES), magnetoresistance measurements, and
scanning tunneling microscopy (STM). We observe a CDW gap of about 200 meV at
low temperatures that persists up to 400 K, suggesting that the CDW transition
occurs at a much higher temperature. We observe a large thermal hysteretic
behavior of the ARPES intensity near the Fermi level, consistent with the
resistivity measurement. The hysteresis in the resistivity measurement does not
change under a magnetic field up to 7 T, excluding the thermal magnetic
hysteresis mechanism. Instead, the surface topography measured with STM shows
surface domains with different CDW trimerization directions, which may be
important for the thermal hysteretic behavior of EuTe4. Interestingly, we
observe a large negative magnetoresistance at low temperatures that can be
associated with the canting of magnetically ordered Eu spins. Our work shed
light on the understanding of magnetic, transport, and electronic properties of
EuTe4. | 2303.02848v1 |
2023-05-10 | Doubling of the superconducting transition temperature in ultra-clean wafer-scale aluminum nanofilms | Superconducting properties of thin films can be vastly different from those
of bulk materials. Seminal work has shown the critical temperature Tc of
elemental superconductors decreases with decreasing film thickness when the
normal-state sheet resistance is lower than the quantum resistance h/(4e2).
Sporadic examples on disordered films, however, hinted an enhancement in Tc
although, structural and strain characterization was not possible since samples
were prepared on a cold substrate in situ. To clarify the role of reduced
dimensionality and disorder on the superconducting properties of thin films we
employed molecular beam epitaxy to grow wafer-scale high-quality aluminum (Al)
nanofilms with normal-state sheet resistance at least 20 times lower than
h/(4e2) and investigated their electronic and structural properties ex situ.
Defying general expectations, Tc increases with decreasing Al film thickness,
reaching 2.4 K for 3.5-nm-thick Al film grown on GaAs: twice that of bulk Al
(1.2 K). DFT calculations indicate surface phonon softening impacts
superconductivity in pure ultra-thin films, offering a new route for materials
engineering in two dimensions. | 2305.06084v1 |
1999-06-17 | Anomalous c-axis charge dynamics in copper oxide materials | Within the t-J model, the c-axis charge dynamics of the copper oxide
materials in the underdoped and optimally doped regimes is studied by
considering the incoherent interlayer hopping. It is shown that the c-axis
charge dynamics is mainly governed by the scattering from the in-plane
fluctuation. In the optimally doped regime, the c-axis resistivity is a linear
in temperatures, and shows the metallic-like behavior for all temperatures,
while the c-axis resistivity in the underdoped regime is characterized by a
crossover from the high temperature metallic-like behavior to the low
temperature semiconducting-like behavior, which are consistent with experiments
and numerical simulations. | 9906260v2 |
2001-07-04 | Crystal Growth and Characterization of Doped CZT Crystals | Cd1-xZnxTe crystals with x in the range of 0.1-0.2 were grown by the
high-pressure vertical Bridgman method from pre-synthesized CZT. Resistive
graphite heaters were used to control the temperature profiles within the
furnaces, and an argon overpressure was used to reduce the cadmium loss. The
crystals were doped with either Al, Ni, In, Ga, Ge or Sn. The doping was
carried out by three different ways: 1) by adding of the pure metals during
growth runs; 2) by adding of the tellurides of the metals during growth runs;
or 3) by inserting of the metal tellurides during synthesis of the starting CZT
material. Some of the growth process parameters were also varied. The as-grown
CZT ingots had diameters of either 15 or 38 mm. The influence of the doping on
CZT properties, particularly the conductivity type and specific electrical
resistivity, will be discussed. Energy spectra from alpha particles (U-233,
Ra-226, and U-233+Pu-239+Pu-238) and from different gamma sources (Cs-137,
Co-60, Co-57, Am-241) will be reported. | 0107081v1 |
2007-05-29 | Sliding charge density wave in manganites | The so-called stripe phase of the manganites is an important example of the
complex behaviour of metal oxides, and has long been interpreted as the
localisation of charge at atomic sites. Here, we demonstrate via resistance
measurements on La_{0.50}Ca_{0.50}MnO_3 that this state is in fact a
prototypical charge density wave (CDW) which undergoes collective transport.
Dramatic resistance hysteresis effects and broadband noise properties are
observed, both of which are typical of sliding CDW systems. Moreover, the high
levels of disorder typical of manganites result in behaviour similar to that of
well-known disordered CDW materials. Our discovery that the manganite
superstructure is a CDW shows that unusual transport and structural properties
do not require exotic physics, but can emerge when a well-understood phase (the
CDW) coexists with disorder. | 0705.4310v2 |
2009-02-23 | Superconductivity at 22.3 K in SrFe2-xIrxAs2 | By substituting the Fe with the 5d-transition metal Ir in SrFe2As2, we have
successfully synthesized the superconductor SrFe2-xIrxAs2 with Tc = 22.3 K at x
= 0.5. X-ray diffraction indicates that the material has formed the
ThCr2Si2-type structure with a space group I4/mmm. The temperature dependence
of resistivity and dc magnetization both reveal sharp superconducting
transitions at around 22 K. An estimate on the diamagnetization signal reveals
a high Meissner shielding volume. Interestingly, the normal state resistivity
exhibits a roughly linear behavior up to 300 K. The superconducting transitions
at different magnetic fields were also measured yielding a slope of -dHc2/dT =
3.8 T/K near Tc. Using the Werthamer-Helfand-Hohenberg (WHH) formula, the upper
critical field at zero K is found to be about 58 T. Counting the possible
number of electrons doped into the system in SrFe2-xIrxAs2, we argue that the
superconductivity in the Ir-doped system is different from the Co-doped case,
which should add more ingredients to the underlying physics of the iron
pnictide superconductors. | 0902.3957v2 |
2009-09-07 | SiC Graphene Suitable For Quantum Hall Resistance Metrology | We report the first observation of the quantum Hall effect in epitaxial
graphene. The result described in the submitted manuscript fills the yawning
gap in the understanding of the electronic properties of this truly remarkable
material and demonstrate suitability of the silicon carbide technology for
manufactiring large area high quality graphene. Having found the quantum Hall
effect in several devices produced on distant parts of a single large-area
wafer, we can confirm that material synthesized on the Si-terminated face of
SiC promises a suitable platform for the implementations of quantum resistance
metrology at elevated temperatures and, in the longer term, opens bright
prospects for scalable electronics based on graphene. | 0909.1193v1 |
2010-07-07 | Unusual Resistance Hysteresis in n-Layer Graphene Field Effect Transistors Fabricated on Ferroelectric Pb(Zr_0.2Ti_0.8)O_3 | We have fabricated n-layer graphene field effect transistors on epitaxial
ferroelectric Pb(Zr_0.2Ti_0.8)O_3 (PZT) thin films. At low gate voltages, PZT
behaves as a high-k dielectric with k up to 100. An unusual resistance
hysteresis occurs in gate sweeps at high voltages, with its direction opposite
to that expected from the polarization switching of PZT. The relaxation of the
metastable state is thermally activated, with an activation barrier of 50-110
meV and a time constant of 6 hours at 300 K. We attribute its origin to the
slow dissociation/recombination dynamics of water molecules adsorbed at the
graphene-PZT interface. This robust hysteresis can potentially be used to
construct graphene-ferroelectric hybrid memory devices. | 1007.1240v1 |
2011-01-15 | Theory of anomalous Hall effect for type-II high-Tc and conventional superconductors | The anomalous Hall effect for type-II superconductors is investigated by
random walk theorem. It is shown that the origin of Hall anomaly is induced by
the thermally activated vortex bundle flow (TAVBF) over the
directional-dependent energy barrier formed by the Magus force, random
collective pinning force, and strong pinning force inside the vortex bundles.
The directional-dependent potential barrier of the vortex bundles renormalizes
the Hall and longitudinal resistivities strongly. Under the framework of
present theory, it is also shown that the Hall anomaly is universal for type-II
superconductors, either high- or conventional as well as bulk materials or thin
films. The conditions for Hall anomaly and reentry phenomenon are derived, the
Hall and longitudinal resistivities as well as Hall angle for type-II
superconducting films and bulk materials versus temperature and applied
magnetic field are calculated. All the results are in agreement with the
experiments. | 1101.2943v1 |
2011-12-08 | Circuit Modeling of Tunneling Real-Space Transfer Transistors: Toward Terahertz Frequency Operation | High frequency operation of tunneling real-space transfer transistor (TRSTT)
in the negative differential resistance (NDR) regime is assessed by calculating
the device common source unity current gain frequency (fT) range with a small
signal equivalent circuit model including tunneling. Our circuit model is based
on an In0.2Ga0.8As and delta-doped GaAs dual channel structure with various
gate lengths. The calculated TRSTT fT agrees very well with experimental data,
limiting factor being the resistance of the delta-doped GaAs layer. By
optimizing the gate dimensions and channel materials, we find fT in the NDR
region approaches terahertz range, which anticipates potential use of TRSTT as
terahertz sources. | 1112.1980v1 |
2013-01-24 | Spin transport parameters in metallic multilayers determined by ferromagnetic resonance measurements of spin pumping | We measured spin transport in nonferromagnetic (NM) metallic multilayers from
the contribution to damping due to spin pumping from a ferromagnetic Co90Fe10
thin film. The multilayer stack consisted of NM1/NM2/Co90Fe10(2 nm)/NM2/NM3
with varying NM materials and thicknesses. Using conventional theory for one
dimensional diffusive spin transport in metals, we show that the effective
damping due to spin pumping can be strongly affected by the spin transport
properties of each NM in the multilayer, which permits the use of damping
measurements to accurately determine the spin transport properties of the
various NM layers in the full five-layer stack. We find that due to its high
electrical resistivity, amorphous Ta is a poor spin conductor, in spite of a
short spin-diffusion length of 1.0 nm, and that Pt is an excellent spin
conductor by virtue of its low electrical resistivity and a spin diffusion
length of only 0.5 nm. Spin Hall effect measurements may have underestimated
the spin Hall angle in Pt by assuming a much longer spin diffusion length. | 1301.5861v1 |
2014-11-01 | Manipulating electronic states at oxide interfaces using focused micro X-rays from standard lab-sources | Recently, x-ray illumination, using synchrotron radiation, has been used to
manipulate defects, stimulate self-organization and to probe their structure.
Here we explore a method of defect-engineering low-dimensional systems using
focused laboratory-scale X-ray sources. We demonstrate an irreversible change
in the conducting properties of the 2-dimensional electron gas at the interface
between the complex oxide materials LaAlO3 and SrTiO3 by X-ray irradiation. The
electrical resistance is monitored during exposure as the irradiated regions
are driven into a high resistance state. Our results suggest attention shall be
paid on electronic structure modification in X-ray spectroscopic studies and
highlight large-area defect manipulation and direct device patterning as
possible new fields of application for focused laboratory X-ray sources. | 1411.0177v1 |