publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2018-12-18 | An application of extensions of the Ramo-Shockley theorem to signals in silicon sensors | We discuss an extension of the Ramo-Shockley theorem that allows the
calculation of signals in detectors that contain non-linear materials of
arbitrary permittivity and finite conductivity (volume resistivity) as well as
a static space-charge. The readout-electrodes can be connected by an arbitrary
impedance network. This formulation is useful for the treatment of
semiconductor sensors where the finite volume resistivity in the sensitive
detector volume cannot be neglected. The signals are calculated by means of
time dependent weighting fields and weighting vectors. These are calculated by
adding voltage or current signals to the electrodes in question, which has a
very practical application when using semiconductor device simulation programs.
An analytic example for an un-depleted silicon sensor is given. | 1812.07570v2 |
2018-12-19 | Blue (In,Ga)N Light-Emitting Diodes with Buried n+-p+ Tunnel Junctions by Plasma-Assisted Molecular Beam Epitaxy | Blue light-emitting diodes (LEDs) consisting of a buried n+-p+ GaN tunnel
junction, (In,Ga)N multiple quantum wells (MQWs) and a n+-GaN top layer are
grown on single-crystal Ga-polar n+-GaN bulk wafers by plasma-assisted
molecular beam epitaxy. The (In,Ga)N MQW active regions overgrown on the p+-GaN
show chemically abrupt and sharp interfaces in a wide range of compositions and
are seen to have high structural and optical properties as verified by X-ray
diffraction and spatially resolved cathodoluminescence measurements. The
processed LEDs reveal clear rectifying behavior with a low contact and buried
tunnel junction resistivity. By virtue of the top n+-GaN layer with a low
resistance, excellent current spreading in the LEDs is observed at low currents
in this device structure. A few of new device possibilities based on this
unique design are discussed. | 1812.07708v1 |
2019-01-07 | Growth and Characterization of Fe0.95Se0.6Te0.4 Single Crystal | In this paper we present the single crystal growth of Fe0.95Se0.6Te0.4 high
TC superconducting sample by the modified Bridgman technique. The x-ray
diffraction pattern shows the single crystal nature of the sample, as only
(00l) peaks are detectable. The stoichiometric composition has been verified by
energy dispersive x-ray analysis. The superconducting transition temperature at
14 K was confirmed through DC magnetization (ZFC-FC) and resistivity
measurements. By analyzing the isothermal M-H curves, we determined the value
of H_c1 (0) ~360 Oe by extrapolating the data. The temperature coefficient of
resistivity obtained using the power law fitting was found to be 0.6. The
obtained Raman spectra at room temperature can be interpreted with the
tetragonal crystal structure and space group P4/nmm. | 1901.01955v1 |
2019-11-06 | Low frequency imaginary impedance at the superconducting transition of 2H-NbSe$_2$ | The superconducting transition leads to a sharp resistance drop in a
temperature interval that can be a small fraction of the critical temperature
T$_c$. A superconductor exactly at T$_c$ is thus very sensitive to all kinds of
thermal perturbations, including the heat dissipated by the measurement
current. We show that the interaction between electrical and thermal currents
leads to a sizeable imaginary impedance at frequencies of order of tens of Hz
at the resistive transition of single crystals of the layered material
2H-NbSe$_2$. We explain the result using models developed for transition edge
sensors. By measuring under magnetic fields and at high currents, we find that
the imaginary impedance is strongly influenced by the heat associated with
vortex motion and out-of-equilibrium quasiparticles. | 1911.02340v2 |
2020-01-15 | Enhanced Carrier Transport by Transition Metal Doping in WS2 Field Effect Transistors | High contact resistance is one of the primary concerns for electronic device
applications of two-dimensional (2D) layered semiconductors. Here, we explore
the enhanced carrier transport through metal-semiconductor interfaces in WS2
field effect transistors (FETs) by introducing a typical transition metal, Cu,
with two different doping strategies: (i) a "generalized" Cu doping by using
randomly distributed Cu atoms along the channel and (ii) a "localized" Cu
doping by adapting an ultrathin Cu layer at the metal-semiconductor interface.
Compared to the pristine WS2 FETs, both the generalized Cu atomic dopant and
localized Cu contact decoration can provide a Schottky-to-Ohmic contact
transition owing to the reduced contact resistances by 1 - 3 orders of
magnitude, and consequently elevate electron mobilities by 5 - 7 times higher.
Our work demonstrates that the introduction of transition metal can be an
efficient and reliable technique to enhance the carrier transport and device
performance in 2D TMD FETs. | 2001.05105v1 |
2020-01-20 | Electrical conduction mechanisms of metal / high-Tc superconductor (YBCO) interfaces | Current-voltage characteristics of Au~/~YBa$_2$Cu$_3$O$_{7-\delta}$
interfaces (Au/YBCO), built on optimally-doped YBCO thin films, grown by pulsed
laser deposition, were measured as a function of temperature in the 50 K to 270
K range, for two different resistance states. A non-trivial equivalent circuit
model is proposed, which reveals the existence of a highly inhomogeneous
scenario composed by two complex layers: one presenting both a non-linear
Poole-Frenkel conduction as well as Variable Range Hopping localization effects
(probably associated with YBa$_2$Cu$_3$O$_{6}$) mixed with a minor metallic
phase, while the other is also composed by a mixture of YBCO with different
oxygen contents, where a metallic ohmic phase still percolates. A microscopic
description of the effects produced by the resistance switching is given,
showing the evolution of carrier traps, localization effects and dielectric
behavior for each state. The dielectric behavior is interpreted in terms of a
Maxwell-Wagner scenario. | 2001.07237v1 |
2020-06-09 | Fluctuations superconductivity and giant negative magnetoresistance in a gate voltage tuned 2D electron liquid with strong spin-orbit impurity scattering | We present a quantitative theory of the gate-voltage tuned
superconductor-to-insulator transition (SIT) observed experimentally in the 2D
electron liquid created in the (111) interface between crystalline SrTiO_3 and
LaAlO_3 . Considering two fundamental opposing effects of Cooper-pair
fluctuations; the critical conductivity enhancement, known as
para-conductivity, and its suppression associated with the loss of unpaired
electrons due to Cooper-pairs formation, we employ the standard thermal
fluctuations theory, modified to include quantum fluctuations within a novel
phenomenological approach. Relying on the quantitative agreement found between
our theory and a large body of experimental sheet-resistance data, we conclude
that spin-orbit scatterings, via significant enhancement of the interaction
between fluctuations, strongly enhance the sheet resistance peak at high
fields, and reveal anomalous metallic behavior at low fields, due to mixing of
relatively heavy electron bands with a light electron band near a Lifshitz
point. | 2006.05098v3 |
2020-08-15 | Ultrahigh Doping of Graphene Using Flame-Deposited MoO3 | The expected high performance of graphene-based electronics is often hindered
by lack of adequate doping, which causes low carrier density and large sheet
resistance. Many reported graphene doping schemes also suffer from instability
or incompatibility with existing semiconductor processing. Here we report
ultrahigh and stable p-type doping up to ~7x10^13 1/cm^2 (~2x10^21 1/cm^3}) of
monolayer graphene grown by chemical vapor deposition. This is achieved by
direct polycrystalline MoO3 growth on graphene using a rapid flame synthesis
technique. With this approach, the metal-graphene contact resistance for holes
is reduced to ~200 Ohm-um. We also demonstrate that flame-deposited MoO3
provides over 5x higher doping of graphene, as well as superior thermal and
long-term stability, compared to electron-beam deposited MoO3. | 2008.06794v1 |
2020-11-13 | Large anomalous Hall angle in a topological semimetal candidate TbPtBi | The magnetotransport properties in antiferromagnetic half-Heusler single
crystals of TbPtBi, a magnetic-field-induced topological semimetal with simple
band structure, are investigated. We found that a nonmonotonic magnetic field
dependence of the anomalous Hall resistivity in a high magnetic field (B>7T),
which come from the change of band structure induced by the Zeeman-like
splitting when applying the external magnetic field. The experiment results
show that credible anomalous Hall resistivity and conductivity reach up to
0.6798m{\Omega}cm and 125{\Omega}-1cm-1, respectively. A large AHA up to 33% is
obtained in TbPtBi, which is comparable to typical ferromagnetic Weyl
semimetal. The analysis of results show it should be attributed to topological
band around EF and low carrier density. | 2011.06864v1 |
2021-03-09 | Anisotropy of the In-Plane and Out-of-Plane Resistivity and the Hall Effect in the Normal State of Vicinal-Grown YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin Films | The resistivity and the Hall effect in the copper-oxide high-temperature
superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ (YBCO) are remarkably
anisotropic. Using a thin film of YBCO grown on an off-axis cut SrTiO$_3$
substrate allows one to investigate these anisotropic transport properties in a
planar and well-defined sample geometry employing a homogeneous current
density. In the normal state, the Hall voltage probed parallel to the
copper-oxide layers is positive and strongly temperature dependent, whereas the
out-of-plane Hall voltage is negative and almost temperature independent. The
results confirm previous measurements on single crystals by an entirely
different measurement method and demonstrate that vicinal thin films might be
also useful for investigations of other layered nanomaterials. | 2103.05511v1 |
2021-06-24 | Erasable superconductivity in topological insulator Bi2Se3 induced by voltage pulse | Three-dimensional topological insulators (TIs) attract much attention due to
its topologically protected Dirac surface states. Doping into TIs or their
proximity with normal superconductors can promote the realization of
topological superconductivity(SC) and Majorana fermions with potential
applications in quantum computations. Here, an emergent superconductivity was
observed in local mesoscopic point-contacts on the topological insulator Bi2Se3
by applying a voltage pulse through the contacts, evidenced by the Andreev
reflection peak in the point-contact spectra and a visible resistance drop in
the four-probe electrical resistance measurements. More intriguingly, the
superconductivity can be erased with thermal cycles by warming up to high
temperatures (300 K) and induced again by the voltage pulse at the base
temperature (1.9 K), suggesting a significance for designing new types of
quantum devices. Nematic behaviour is also observed in the superconducting
state, similar to the case of CuxBi2Se3 as topological superconductor
candidates. | 2106.13207v1 |
2021-06-29 | Low Resistance III-V Hetero-contacts to N-Ge | We experimentally study III-V/Ge heterostructure and demonstrate InGaAs
hetero-contacts to n-Ge with a wide range of In % and achieve low contact
resistivity ($\rho_C$) of $5\times10^{-8} \Omega\cdot cm^2$ for Ge doping of $3
\times 10^{19} cm^{-3}$. This results from re-directing the charge neutrality
level (CNL) near the conduction band and benefiting from low effective mass for
high electron transmission. For the first time, we observe that the
heterointerface presents no temperature dependence despite the two different
conduction minimum valley locations of III-V ($\Gamma$-valley) and Ge
(L-valley), which potentially stems from elastic trap-assisted tunneling
through defect states at the interface generated by dislocations. The
hetero-interface plays a dominant role in the overall $\rho_C$ below $\approx 1
\times 10^{-7} \Omega \cdot cm^2$, which can be further improved with large
active dopant concentration in Ge by co-doping. | 2106.15099v1 |
2021-09-08 | Unusual Magnetic Properties in Layered Magnetic Topological Insulator EuSn2As2 | EuSn2As2 with layered rhombohedral crystal structure is proposed to be a
candidate of intrinsic antiferromagnetic (AFM) topological insulator. Here, we
have investigated systematic magnetoresistance (MR) and magnetization
measurements on the high quality EuSn2As2 single crystal with the magnetic
field both parallel and perpendicular to (00l) plane. Both the kink of magnetic
susceptibility and longitudinal resistivity reveal that EuSn2An2 undergoes an
AFM transition at TN = 21 K. At T = 2 K, the magnetization exhibits two
successive plateaus of ~ 5.6 {\mu}B/Eu and ~ 6.6 {\mu}B/Eu at the corresponding
critical magnetic fields. Combined with the negative longitudinal MR and
abnormal Hall resistance, we demonstrate that EuSn2An2 undergoes complicated
magnetic transitions from an AFM state to a canted ferromagnetic (FM) state at
Hc and then to a polarized FM state at Hs as the magnetic field increase. | 2109.03414v1 |
2022-05-12 | Shubnikov-de Haas and de Haas-van Alphen oscillation in Czochralski grown CoSi single crystal | Anisotropic transport, Shubnikov-de Haas (SdH), and de Haas-van Alphen (dHvA)
quantum oscillations studies are reported on a high-quality CoSi single crystal
grown by the Czochralski method. Temperature-dependent resistivities indicate
the dominating electron-electron scattering. Magnetoresistance (MR) at 2 K
reaches 610% for I||[111] and B||[01-1], whereas it is 500% for I||[01-1] and
B||[111]. A negative slope in field-dependent Hall resistivity suggests
electrons are the majority carriers. The carrier concentration extracted from
Hall conductivity indicates no electron-hole compensation. In 3D CoSi, the
electron transport lifetime is found to be approximately in the same order as
quantum lifetime, whereas in 2D electron gas the long-range scattering drives
the transport life much larger than the quantum lifetime. From linear and Hall
SdH oscillations the effective masses and Dingle temperatures have been
calculated. The dHvA oscillation reveals three frequencies at 18 ($\gamma$),
558 ($\alpha$) and 663 T ($\beta$)), whereas, SdH oscillation results in only
two frequencies $\alpha$ and $\beta$. The $\gamma$ frequency observed in dHvA
oscillation is a tiny hole pocket at the $\Gamma$ point. | 2205.05881v1 |
2022-07-05 | Anderson localization crossover in 2D Si systems: The past and the present | Using Ioffe-Regel-Mott (IRM) criterion for strong localization crossover in
disordered doped 2D electron systems, we theoretically study the relationships
among the three key experimentally determined localization quantities: critical
density ($n_\mathrm{c}$), critical resistance ($\rho_\mathrm{c}$), and sample
quality defined by the effective impurity density (as experimentally diagnosed
by the sample mobility, $\mu_\mathrm{m}$, at densities much higher than
critical densities). Our results unify experimental results for 2D
metal-insulator transitions (MIT) in Si systems over a 50-year period
(1970-2020), showing that $n_\mathrm{c}$ ($\rho_\mathrm{c}$) decrease
(increase) with increasing sample quality, explaining why the early experiments
in the 1970s, using low-quality samples ($\mu_\mathrm{m} \sim 10^3
\mathrm{cm}^2/Vs$) reported strong localization crossover at $n_c \sim 10^{12}
\mathrm{cm}^{-2}$ with $\rho_c \sim 10^3\Omega$ whereas recent experiments
(after 1995), using high-quality samples ($\mu_\mathrm{m} >10^4
\mathrm{cm}^2/Vs$), report $n_c \sim 10^{11} \mathrm{cm}^{-2}$ with
$\rho_c>10^4\Omega$. Our theory establishes the 2D MIT to be primarily a
screened Coulomb disorder-driven strong localization crossover phenomenon,
which happens at different sample-dependent critical density and critical
resistance, thus unifying Si 2D MIT phenomena over a 50-year period. | 2207.02220v1 |
2022-08-22 | Electronic structure and physical properties of EuAuAs single crystal | High-quality single crystals of EuAuAs were studied by means of powder x-ray
diffraction, magnetization, magnetic susceptibility, heat capacity, electrical
resistivity and magnetoresistance measurements. The compound crystallizes with
a hexagonal structure of the ZrSiBe type (space group $P6_3/mmc$). It orders
antiferromagnetically below 6 K due to the magnetic moments of divalent Eu
ions. The electrical resistivity exhibits metallic behavior down to 40 K,
followed by a sharp increase at low temperatures. The magnetotransport
isotherms show a distinct metamagnetic-like transition in concert with the
magnetization data. The antiferromagnetic ground state in \mbox{EuAuAs} was
corroborated in the \textit{ab initio} electronic band structure calculations.
Most remarkably, the calculations revealed the presence of nodal line without
spin-orbit coupling and Dirac point with inclusion of spin-orbit coupling. The
\textit{Z}$_2$ invariants under the effective time reversal and inversion
symmetries make this system nontrivial topological material. Our findings,
combined with experimental analysis, makes EuAuAs a plausible candidate for an
antiferromagnetic topological nodal-line semimetal. | 2208.10405v1 |
2022-09-18 | Superparamagnetic and metal-like Ru2TiGe: a propitious thermoelectric material | We report a study of structural, magnetic, heat capacity and thermoelectric
properties of a Rubased Heusler alloy, Ru2TiGe. The magnetic measurements
reveal that at higher temperatures, diamagnetic and Pauli paramagnetic
contributions dominate the magnetic behaviour whereas, at lower temperatures
(T<= 20 K), superparamagnetic interaction among clusters is observed. Effect of
such magnetic defects is also evident in the electrical resistivity behaviour
at lower temperatures. Though the temperature dependence of resistivity
exhibits a metal-like nature, the large value of Seebeck coefficient leads to
an appreciable power factor of the order of 1 mW/mK2 at 300 K. Large power
factor as well as low thermal conductivity results in a value of ZT = 0.025 at
390 K for Ru2TiGe that is orders of magnitude higher than that of the other
pure Heusler alloys and point towards its high potential for practical
thermoelectric applications. | 2209.08474v1 |
2022-11-02 | Umklapp electron-electron scattering in bilayer graphene moiré superlattice | Recent experimental advances have been marked by the observations of
ballistic electron transport in moir\'e superlattices in highly aligned
heterostructures of graphene and hexagonal boron nitride (hBN). Here, we
predict that a high-quality graphene bilayer aligned with an hBN substrate
features $T^2$-dependent resistivity caused by umklapp electron-electron (Uee)
scattering from the moir\'e superlattice, that is, a momentum kick by Bragg
scattering experienced by a pair of electrons. Substantial Uee scattering
appears upon $p$-doping of the bilayer above a threshold density, which depends
on the twist angle between graphene and hBN, and its contribution towards the
resistivity grows rapidly with hole density until it reaches a peak value,
whose amplitude changes non-monotonically with the superlattice period. We also
analyse the influence of an electrostatically induced bandgap in the bilayer
and trigonal warping it enhances in the electron dispersion on the
electron-electron umklapp scattering. | 2211.01005v1 |
2023-01-11 | Application of the partial Dirichlet-Neumann contact algorithm to simulate low-velocity impact events on composite structures | Impact simulations for damage resistance analysis are computationally
intensive due to contact algorithms and advanced damage models. Both methods,
which are the main ingredients in an impact event, require refined meshes at
the contact zone to obtain accurate predictions of the contact force and damage
onset and propagation through the material. This work presents the application
of the partial Dirichlet-Neumann contact algorithm to simulate low-velocity
impact problems on composite structures using High-Performance Computing. This
algorithm is devised for parallel finite element codes running on
supercomputers, and it is extended to explicit time integration schemes to
solve impact problems including damage. The proposed framework is validated
with a standard test for damage resistance on fiber-reinforced polymer matrix
composites. Moreover, the parallel performance of the proposed algorithm has
been evaluated in a mesh of 74M of elements running with 2400 processors. | 2301.05552v2 |
2023-01-19 | Unusual anisotropic magnetoresistance due to magnetization-dependent spin-orbit interactions | One of recent surprising discoveries is the unusual anisotropic
magnetoresistance (UAMR) that depends on two magnetization components
perpendicular to the current differently, in contrast to the conventional
anisotropic magnetoresistance (AMR) that predicts no change in resistance when
the magnetization varies in the plane perpendicular to the current. Using
density functional theory and Boltzmann transport equation calculations for bcc
Fe, hcp Co, and bcc FeCo alloys, we show that UAMR can be accounted by the
magnetization-dependent spin-orbit interactions (SOI): Magnetization-dependent
SOI modifies electron energy bands that, in turn, changes resistance. A
phenomenological model reveals the intrinsic connection between SOI and
order-parameters. Such a mechanism is confirmed by the strong biaxial stain
effect on UAMR. Our findings provide an efficient way of searching and
optimizing materials with large UAMR, important in the design of
high-performance spintronic devices. | 2301.07886v1 |
2023-03-06 | Timing resistive plate chambers for thermal neutron detection with 3D position sensitivity | An optimized design of a neutron detector based on timing RPCs (Resistive
Plate Chambers) with boron-10 neutron converters is presented. The detector is
composed of a stack of ten double gap RPCs with aluminium cathode plates coated
on both sides with $^{10}B_{4}C$. This design enables simultaneous
determination with high accuracy of both the neutron time-of-flight (down to ns
resolution) and the interaction position in 3D (down to 0.25 mm resolution
across and ~1 mm along the beam). It is shown that the detection efficiency can
approach 60% for neutrons with $\lambda$ = 4.7 \.A. A new geometry with less
material budget is introduced for the signal pick-up strip arrays. The results
of simulation-based optimization of the design are reported considering the
trade-off between the detection efficiency, the count rate capability and the
amount of elastic scattering on the detector components. | 2303.03461v1 |
2023-03-22 | Effect of gamma radiation on electrical properties of diffusive memristor devices | Diffusive memristors continue to receive tremendous interest due to their
ability to emulate biological neurons and thus aid the development of
bio-inspired computation technology. A major issue with the diffusive memristor
is the inability to reliably control the formation of the conduction filaments
which affects both the device functionality and reproducibility of regimes
after each application of voltage. Here we investigate the effect of gamma
radiation on the electrical properties of the diffusive memristors based on
metallic nanoparticles in dielectric matrix. Our experiments show that after
exposing to radiation, the memristors demonstrate much sharper (and less noisy)
hysteresis in the current-voltage characteristics while preserving the same
low- and high-resistive states as in the pristine samples. Additionally, the
radiation lowers both threshold and hold voltages that correspond to onset of
low- and high- resistive states, respectively. The proposed mechanism involves
radiation-induced defects in the silica matrix which help to establish dominant
pathways for nanoparticles to form conduction filaments. Our findings suggest
an efficient way to enhance working characteristics of diffusive memristors and
to improve their reproducibility. | 2303.12762v1 |
2023-07-18 | Universal scaling near band-tuned metal-insulator phase transitions | We present a theory for band-tuned metal-insulator transitions based on the
Kubo formalism. Such a transition exhibits scaling of the resistivity curves,
in the regime where $T\tau >1$ or $\mu \tau>1$, where $\tau$ is the scattering
time and $\mu$ the chemical potential. At the critical value of the chemical
potential, the resistivity diverges as a power law, $R_c \sim 1/T$.
Consequently, on the metallic side there is a regime with negative $dR/dT$,
which is often misinterpreted as insulating. We show that scaling and this
`fake insulator' regime is observed in a wide range of experimental systems. In
particular, we show that Mooij correlations in high-temperature metals with
negative $dR/dT$ can be quantitatively understood with our scaling theory in
the presence of $T$-linear scattering. | 2307.09292v1 |
2023-10-10 | The black hole to black hole phase transition probed by the D3-D7 model fermionic spectral functions | We consider the D3-D7 model and analyze the phase transition from the
black-hole phase to another black-hole phase using the spectral function of a
probe fermion on D7 in the presence of the finite density and temperature. From
the fermionic spectral functions, we study the temperature dependence of the
decay rate and we observe a jump in it at the critical temperature that
corresponds to the first order phase transition. We found that if we assume
that the Drude model works in this case so that the resistivity is proportional
to the fermion decay rate, the jump matches the resistivity data in a heavy
fermion material. | 2310.06317v1 |
2023-10-22 | Electrical conductivity enhancement of epitaxially grown TiN thin films | Titanium nitride (TiN) presents superior electrical conductivity with
mechanical and chemical stability and compatibility with the semiconductor
fabrication process. Here, we fabricated epitaxial and polycrystalline TiN
(111) thin films on MgO (111), sapphire (001), and mica substrates at 640oC and
room temperature by using a DC sputtering, respectively. The epitaxial films
show less amount of surface oxidation than the polycrystalline ones grown at
room temperature. The epitaxial films show drastically reduced resistivity (~30
micro-ohm-cm), much smaller than the polycrystalline films.
Temperature-dependent resistivity measurements show a nearly monotonic
temperature slope down to low temperature. These results demonstrate that high
temperature growth of TiN thin films leads to significant enhancement of
electrical conductivity, promising for durable and scalable electrode
applications. | 2310.14208v1 |
2023-11-20 | Magnetic-field-induced nonlinear transport in HfTe5 | The interplay of electron correlations and topological phases gives rise to
various exotic phenomena including fractionalization, excitonic instability,
and axionic excitation. Recently-discovered transition-metal pentatellurides
can reach the ultra-quantum limit in low magnetic fields and serve as good
candidates for achieving such a combination. Here, we report evidences of
density wave and metal-insulator transition in HfTe5 induced by intense
magnetic fields. Using the nonlinear transport technique, we detect a distinct
nonlinear conduction behavior in the longitudinal resistivity within the a-c
plane, corresponding to the formation of a density wave induced by magnetic
fields. In high fields, the onset of the nonlinear conduction in the Hall
resistivity indicates an impurity-pinned magnetic freeze-out as the possible
origin of the insulating behavior. These frozen electrons can be gradually
re-activated into mobile states above a threshold electric field. These
experimental evidences call for further investigations into the underlying
mechanism for the bulk quantum Hall effect and field-induced phase transtions
in pentatellurides. | 2311.11517v1 |
2023-11-29 | Lateral NbS$_2$/MoS$_2$/NbS$_2$ transistors: physical modeling and performance assessment | Reducing the contact resistance of field-effect transistors based on
two-dimensional materials is one of the key improvements required to to enable
the integration of such transistors in an industrially relevant process.
Suitably designed lateral heterojunctions provide an opportunity to
independently tailor the contact and channel properties and to mitigate the
problem of high contact resistance. Inspired by the recent experimental
demonstration of a two-dimensional $p$-type Schottky barrier, here we use
quantum transport simulations to estimate the performance of $p$-type
transistors in which the channel consists of a lateral heterostructure of
NbS$_2$/MoS$_2$/NbS$_2$ (semimetal-semiconductor-semimetal). We find that the
gate alignment with the channel is a critical design parameter, strongly
influencing the capability of the gate to modulate the Schottky barrier at the
MoS$_2$/NbS$_2$ interfaces. This effect is also found to significantly affect
the scaling behavior of the device. | 2311.18031v1 |
2024-02-23 | Electrical Scanning Probe Microscope Measurements Reveal Surprisingly High Dark Conductivity in Y6 and PM6:Y6 and Non-Langevin Recombination in PM6:Y6 | We used broadband local dielectric spectroscopy (BLDS), an electric force
microscopy technique, to make non-contact measurements of conductivity in the
dark and under illumination of PM6:Y6 and Y6 prepared on ITO and PEDOT:PSS/ITO.
Over a range of illumination intensities, BLDS spectra were acquired and fit to
an impedance model of the tip-sample interaction to obtain a sample resistance
and capacitance. By comparing two descriptions of cantilever friction, an
impedance model and a microscopic model, we connected the sample resistance
inferred from impedance modeling to a microscopic sample conductivity. A charge
recombination rate was estimated from plots of the conductivity versus light
intensity and found to be sub-Langevin. The dark conductivity was orders of
magnitude higher than expected from Fermi-level equilibration of the PM6:Y6
with the substrate, suggesting that dark carriers may be a source of
open-circuit voltage loss in PM6:Y6. | 2402.15501v1 |
2021-05-07 | Integrating van der Waals materials on paper substrates for electrical and optical applications | Paper holds the promise to replace silicon substrates in applications like
internet of things or disposable electronics that require ultra-low-cost
electronic components and an environmentally friendly electronic waste
management. In the last years, spurred by the abovementioned properties of
paper as a substrate and the exceptional electronic, mechanical and optical
properties of van der Waals (vdW) materials, many research groups have worked
towards the integration of vdW materials-based devices on paper. Recently, a
method to deposit a continuous film of densely packed interconnects of vdW
materials on paper by simply rubbing the vdW crystals against the rough surface
of paper has been presented. This method utilizes the weak interlayer vdW
interactions and allows cleaving of the crystals into micro platelets through
the abrasion against the paper. Here, we aim to illustrate the general
character and the potential of this technique by fabricating films of 39
different vdW materials (including superconductors, semi-metals,
semiconductors, and insulators) on standard copier paper. We have thoroughly
characterized their optical properties showing their high optical quality: one
can easily resolve the absorption band edge of semiconducting vdW materials and
even the excitonic features present in some vdW materials with high exciton
binding energy. We also measured the electrical resistivity for several vdW
materials films on paper finding exceptionally low values, which are in some
cases, orders of magnitude lower than those reported for analogous films
produced by inkjet printing. We finally demonstrate the fabrication of
field-effect devices with vdW materials on paper using the paper substrate as
an ionic gate. | 2105.03486v1 |
2017-06-29 | Origin of Contact Resistance at Ferromagnetic Metal-Graphene Interfaces | Edge contact geometries are thought to yield ultralow contact resistances in
most non-ferromagnetic metal-graphene interfaces owing to their large
metal-graphene coupling strengths. Here, we examine the contact resistance of
edge- versus surface-contacted ferromagnetic metal-graphene interfaces (i.e.
nickel- and cobalt-graphene interfaces) using both single-layer and few-layer
graphene. Good qualitative agreement is obtained between theory and experiment.
In particular, in both theory and experiment, we observe that the contact
resistance of edge-contacted ferromagnetic metal-graphene interfaces is much
lower than that of surface-contacted ones, for all devices studied and
especially for the single-layer graphene systems. We show that this difference
in resistance is not due to differences in the metal-graphene coupling
strength, which we quantify using Hamiltonian matrix elements. Instead, the
larger contact resistance in surface contacts results from spin filtering at
the interface, in contrast to the edge-contacted case where both spins are
transmitted. Temperature-dependent resistance measurements beyond the Curie
temperature TC show that the spin degree of freedom is indeed important for the
experimentally measured contact resistance. These results show that it is
possible to induce a large change in contact resistance by changing the
temperature in the vicinity of TC, thus paving the way for
temperature-controlled switches based on spin. | 1706.09591v1 |
2023-09-22 | Non-equilibrium Thermal Resistance of Interfaces Between III-V Compounds | Interfacial thermal resistance has been often estimated and understood using
the Landauer formalism that assumes incident phonons with equilibrium
distribution. However, previous studies suggest that phonons are
out-of-equilibrium near the interface because of the heat flow through the
leads and the scattering of phonons by the interface. In this paper, we report
a systematic study on how vibrational spectra mismatch affects the degree of
phonon non-equilibrium near an interface, how fast it is relaxed as the phonons
diffuse into a lead, and the overall interfacial thermal resistance from the
non-equilibrium phonons. Our discussion is based on the solution of the
Peierls-Boltzmann transport equation with ab initio inputs for 36 interfaces
between semi-infinite group-III (Al, Ga, In) and group-V (P, As, Sb) compound
semiconductor leads. The simulation reveals that the non-equilibrium phonons
cause significant interfacial thermal resistance for all 36 interfaces, making
the overall interfacial thermal resistance two to three times larger than that
predicted by the Landauer formalism. We observe a clear trend that the degree
of phonon non-equilibrium near an interface and the interfacial thermal
resistance from the non-equilibrium phonons increase as the mismatch of the
Debye temperature of two lead materials increases. This contrasts with Landauer
formalism's predictions, which show no correlation with the Debye temperature
mismatch. The relaxation length of the phonon non-equilibrium varies
significantly from 50nm to 1.5um depending on the combination of the lead
materials. The relaxation length is proportional to the phonon mean free path
of the corresponding lead material but also largely depends on the material in
the opposite lead. This suggests the relaxation length cannot be considered an
intrinsic property of the corresponding lead material. | 2309.13187v1 |
2003-10-28 | On magnetic field generation in Kolmogorov turbulence | We analyze the initial, kinematic stage of magnetic field evolution in an
isotropic and homogeneous turbulent conducting fluid with a rough velocity
field, v(l) ~ l^alpha, alpha<1. We propose that in the limit of small magnetic
Prandtl number, i.e. when ohmic resistivity is much larger than viscosity, the
smaller the roughness exponent, alpha, the larger the magnetic Reynolds number
that is needed to excite magnetic fluctuations. This implies that numerical or
experimental investigations of magnetohydrodynamic turbulence with small
Prandtl numbers need to achieve extremely high resolution in order to describe
magnetic phenomena adequately. | 0310780v2 |
1999-08-04 | Polarization fields in nitride nanostructures: ten points to think about | Macroscopic polarization, both of intrinsic and piezoelectric nature, is
unusually strong in III-V nitrides, and the built in electric fields in the
layers of nitride-based nanostructures, stemming from polarization changes at
heterointerfaces, have a major impact on the properties of single and multiple
quantum wells, high mobility transistors, and thin films. The concepts involved
in the theory and applications of polarization in nitrides have encountered
some resistance in the field. Here we discuss critically ten ``propositions''
aimed at clarifying the main controversial issues. | 9908060v1 |
2001-02-06 | Observation of superconductivity in Y$_2$PdGe$_3$, structurally same as MgB$_2$ | The results of electrical resistance (1.4 - 300 K), magnetization (2-300 K)
and heat-capacity (2 - 50 K) measurements in Y$_2$PdGe$_3$, found to
crystallize in a AlB$_2$-derived hexagonalstructure, are reported. The results
establish that this compound is superconducting below 3 K. This obervation is
interesting considering that this compound is the first superconductor among
the ternary members derived from the hexagonal AlB$_2$ structure. With
superconductivity being uncommon even among binary alloys derived from AlB$_2$
structure and with recent excitement on the observation of high temperature
superconductivity in Mg$B_2$, this finding gains importance. | 0102110v1 |
2002-05-08 | Complex Quantum Phenomena in a Bilayered Calcium Ruthenate | Ca$_3$Ru$_2$O$_7$ undergoes an antiferromagnetic transition at
$T_{\text{N}}=56 $K, followed by a Mott-like (MI) transition at
$T_{\text{MI}}=48$ K. This nonmetallic ground state, with a charge gap of 0.1
eV, is suppressed by a highly anisotropic metamagnetic transition that leads to
a fully spin-polarized metallic state. We report the observation of
Shubnikov-de Haas oscillations in the \textit{gapped} state, colossal
magnetoresistance in the inter-plane resistivity with a large anisotropy
different from that observed in the magnetization, and non-Fermi liquid
behavior in the metallic state at high magnetic fields. | 0205151v1 |
2002-06-10 | Realization of La2MnVO6: Search for half-metallic antiferromagnetism? | Single-phase polycrystalline La2MnVO6 samples were synthesized by arc melting
and characterized by X-ray diffraction, magnetization and resistivity
measurements. We find that the compound has cubic (space group), partly ordered
double perovskite structure. The sample exhibits ferrimagnetic behavior and
variable-range hopping conductivity. We conclude based on the magnetic
properties that both Mn and V ions are trivalent; moreover, the Mn3+ ions are
in a high-spin state, which is the reason that the compound is not a
half-metallic antiferromagnet. | 0206146v1 |
2002-07-09 | Perspectives of superconducting MgB2 for microwave applications | We discuss the temperature, frequency, and power-dependent surface resistance
of the boride superconductor MgB2 in relation to possible applications for
passive microwave devices. The data available in the literature are compared
with results for polycrystalline Nb3Sn and epitaxial YBa2Cu3O7-x, which are
representative of the classical and cuprate superconductors. MgB2 displays all
specific features that make superconductors attractive for high-performance
devices, even though the fabrication technology is not yet mature. We attempt
to identify promising areas of applications, as well as material requirements,
which could further promote the attractiveness of the new superconductor in
this field. | 0207226v1 |
2002-08-15 | Superconductivity in Ba_2Sn_3Sb_6 and SrSn_3Sb_4 | Resistivity and ac magnetic susceptibility measurements on Ba2Sn3Sb6 and
SrSn3Sb4 indicate that these Zintl compounds display a transition to a
superconducting phase at Tc = 3.9 K. The Meissner effect was observed for
Ba2Sn3Sb6 under an applied field of 25 Oe. The signatures for
superconductivity, such as high and low velocity conduction electrons and lone
pairs, are present for both of these compounds. | 0208313v1 |
2002-11-22 | Correlations and Semimetallic Behaviors in Pyrochlore Oxide Cd2Re2O7 | Electronic properties of the metallic pyrochlore oxide Cd2Re2O7 are studied
by means of electrical resistivity and Hall measurements. Semimetallic band
structures are revealed as expected from band structure calculations. It is
found that large changes in carrier density and mass occur at the structural
phase transition at Ts1 = 200 K. A large mass enhancement is observed,
particularly for the high-temperature phase with the ideal pyrochlore
structure, suggesting that an anomalous correlation has an important effect on
the itinerant electrons in the pyrochlore lattice. | 0211517v1 |
2004-02-02 | Dielectric responses of the layered cobalt oxysulfide Sr_2Cu_2CoO_2S_2 with CoO_2 square-planes | We have studied the dielectric responses of the layered cobalt oxysulfide
Sr$_2$Cu$_2$CoO$_2$S$_2$ with the CoO$_2$ square-planes. With decreasing
temperature below the N\'eel temperature, the resistivity increases like a
semiconductor, and the thermopower decreases like a metal. The dielectric
constant is highly dependent on temperature, and the dielectric relaxation is
systematically changed with temperature, which is strongly correlated to the
magnetic states. These behaviors suggest that carriers distributed
homogeneously in the paramagnetic state at high temperatures are expelled from
the antiferromagnetically ordered spin domain below the N\'eel temperature. | 0402034v1 |
2005-01-28 | Ce doping in T-La2CuO4 films: Broken electron-hole symmetry for high-Tc superconductivity | We attempted Ce doping in La2CuO4 with the K2NiF4 (T) structure by molecular
beam epitaxy. At low growth temperature and with an appropriate substrate
choice, we found that Ce can be incorporated into the K2NiF4 lattice up to x ~
0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes
T-La2-xCexCuO4 more insulating, which is in sharp contrast to Ce doping in
La2CuO4 with the Nd2CuO4 structure, which makes the compounds superconducting.
The observed smooth increase in resistivity from hole-doped side
(T-La2-xSrxCuO4) to electron-doped side (T-La2-xCexCuO4) indicates that
electron-hole symmetry is broken in the T-phase materials. | 0501703v1 |
2005-09-05 | Large magnetoresistance and magnetocaloric effect above 70 K in Gd2Co2Al, Gd2Co2Ga and Gd7Rh3 | The electrical resistivity, magnetization and heat-capacity behavior of the
Gd-based compounds, Gd2Co2Al, Gd2Co2Ga and Gd7Rh3, ordering magnetically at TC=
78 K, TC= 76 K and TN= 140 K have been investigated as a function of
temperature and magnetic field. All these compounds are found to show large
magnetoresistance (with a negative sign) in the paramagnetic state at rather
high temperatures with the magnitude peaking at respective magnetic ordering
temperatures. There is a corresponding behavior in the magnetocaloric effect as
inferred from the entropy derived from these data. | 0509107v1 |
2006-10-11 | Intergrain connectivity and resistive broadening in vortex state: a comparison between MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10 superconductors | Magnetoresistance and radio frequency penetration depth techniques are used
to study grain connectivity and broadening of superconducting transition. We
study and compare these issues in clean polycrytalline samples of three
different superconducting systems e.g. MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10. From
the rf response, the bulk pinning force constant is evaluated. From high field
transport measurements, H-T phase diagram is ascertained for the three systems
with varying degrees of fluctuation and connectivity. | 0610295v1 |
2007-03-25 | Novel dynamical effects and glassy response in strongly correlated electronic system | We find an unconventional nucleation of low temperature paramagnetic metal
(PMM) phase with monoclinic structure from the matrix of high-temperature
antiferromagnetic insulator (AFI) phase with tetragonal structure in strongly
correlated electronic system $BaCo_{0.9}Ni_{0.1}S_{1.97}$. Such unconventional
nucleation leads to a decease in resistivity by several orders with relaxation
at a fixed temperature without external perturbation. The novel dynamical
process could arise from the competition of strain fields, Coulomb
interactions, magnetic correlations and disorders. Such competition may
frustrate the nucleation, giving rise to a slow, nonexponential relaxation and
"physical aging" behavior. | 0703647v1 |
2007-07-05 | Anomalous exchange coupling in transition-metal-oxide based superlattices with antiferromagnetic spacer layers | A direct correlation is seen between the coercive field (HC) and the
magnetic-field-dependent resistivity (MR) in SrMnO3/SrRuO3 superlattices of
perpendicular magnetic anisotropy. The magnetoresistance shows a sharp jump at
Hc for in-plane current and the out-of-plane magnetic field. Both HC and
high-field MR also oscillate with the thickness of the SrMnO3 spacer layers
separating the metallic ruthenate. Since the spacer in these superlattices has
no mobile carriers to facilitate an oscillatory coupling, we attribute the
observed behavior to the spin-polarized quantum tunneling of electrons between
the ferromagnetic layers and antiferromagnetically ordered t2g spins of SrMnO3. | 0707.0768v1 |
2007-08-10 | Coherent quasiparticle transport in grain boundary junctions employing high-Tc superconductors | Magneto-fluctuations of the normal resistance RN have been reproducibly
observed in YBa2Cu3O7-d biepitaxial grain boundary junctions at low
temperatures. We attribute them to mesoscopic transport in narrow channels
across the grain boundary line, occurring in an unusual energy regime. The
Thouless energy appears to be the relevant energy scale. Possible implications
on the understanding of coherent transport of quasiparticles in HTS and of the
dissipation mechanisms are discussed. | 0708.1448v1 |
2007-09-26 | Single crystal growth and anisotropy of CeRuPO | We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction. | 0709.4144v2 |
2007-11-30 | Large voltage from spin pumping in magnetic tunnel junctions | We studied the response of a ferromagnet-insulator-normal metal tunnel
structure under an external oscillating radio frequency (R.F.) magnetic field.
The D. C. voltage across the junction is calculated and is found not to
decrease despite the high resistance of the junction; instead, it is of the
order of $\mu V$ to $100\mu V$, much larger than the experimentally observed
value (100 nano-V) in the "strong coupled" ohmic ferromagnet-normal metal
bilayers. This is consistent with recent experimental results in tunnel
structures, where the voltage is larger than $\mu V$s. The damping and loss of
an external RF field in this structure is calculated. | 0711.4939v1 |
2008-01-07 | High Performance Thermal Interface Technology Overview | An overview on recent developments in thermal interfaces is given with a
focus on a novel thermal interface technology that allows the formation of 2-3
times thinner bondlines with strongly improved thermal properties at lower
assembly pressures. This is achieved using nested hierarchical surface channels
to control the particle stacking with highly particle-filled materials.
Reliability testing with thermal cycling has also demonstrated a decrease in
thermal resistance after extended times with longer overall lifetime compared
to a flat interface. | 0801.1046v1 |
2008-01-17 | Stability of RVB hole stripes in high-temperature superconductors | Indications of density-wave states in underdoped cuprates, coming from recent
STM (scanning tunneling microscopy) and Hall-resistance measurements, have
raised new concerns whether stripes could be stabilized in the superconducting
phase of cuprate materials, even in the absence of antiferromagnetism. Here, we
investigate this issue using state-of-the-art quantum Monte Carlo calculations
of a $t-J$ model. In particular we consider the stability of unidirectional
hole domains in a modulated superconducting background, by taking into account
the effect of tetragonal-lattice distortions, next-nearest neighbor hopping and
long-range Coulomb repulsion. | 0801.2722v2 |
2008-08-03 | Superconductivity in Yttrium Iron Oxyarsenide System | Iron-based oxypnictides substituted with yttrium have been prepared via a
conventional solid state reaction. The product after first 50 hours of reaction
showed diamagnetic-like transition at around 10 K but was not superconducting,
while additional 72 hours of high temperature heat treatment was required to
yield superconducting sample which was doped with fluoride. Temperature
dependence of the susceptibility shows both screening and Meissner effect at
around 10 K, while resistance as a function of temperature displayed a drop at
around the same temperature. | 0808.0288v2 |
2008-09-16 | Interface heat transfer between crossing carbon nanotubes, and the thermal conductivity of nanotube pellets | We theoretically compute the interface thermal resistance between crossing
single walled carbon nanotubes of various chiralities, using an atomistic
Green's function approach with semi-empirical potentials. The results are then
used to model the thermal conductivity of three dimensional nanotube pellets in
vacuum. For an average nanotube length of 1 $\mu$m, the model yields an upper
bound for the thermal conductivity of densely compacted pellets, of the order
of a few W/m-K. This is in striking contrast with the ultra-high thermal
conductivity reported on individually suspended nanotubes. The results suggest
that nanotube pellets might have an application as thermal insulators. | 0809.2660v1 |
2008-10-29 | High-Mobility Few-Layer Graphene Field Effect Transistors Fabricated on Epitaxial Ferroelectric Gate Oxides (Supplementary Information) | Supplementary Information to arXiv:0810.4466: 1. Characterizations of
Pb(Zr_0.2Ti_0.8)O_3 (PZT) films. 2. Substrate preparation before the
exfoliation of graphene. 3. The band structure of FLG. 4. Dielectric constant
measurements of PZT. 5. rho(V_g) and R_H(V_g) fitting inside the band overlap
regime. 6. The deformation potential of longitudinal acoustic (LA) phonons in
graphene. 7. Resistivity and Hall measurements of a SiO_2-gated FLG. | 0810.5339v1 |
2008-12-20 | Mobility Extraction and Quantum Capacitance Impact in High Performance Graphene Field-effect Transistor Devices | The field-effect mobility of graphene devices is discussed. We argue that the
graphene ballistic mean free path can only be extracted by taking into account
both, the electrical characteristics and the channel length dependent mobility.
In doing so we find a ballistic mean free path of 300nm at room-temperature for
a carrier concentration of ~1e12/cm2 and that a substantial series resistance
of around 300ohmum has to be taken into account. Furthermore, we demonstrate
first quantum capacitance measurements on single-layer graphene devices. | 0812.3927v1 |
2009-01-07 | Electrically Controlled Magnetic Memory and Programmable Logic based on Graphene/Ferromagnet Hybrid Structures | It has been shown that the combining of the electrical effect on the exchange
bias field with giant magneto-resistance effect of the graphene/ferromagnet
hybrid structures reveals a new non-volatile magnetic random access memory
device conception. In such device an electric bias realizes the writing bits
instead a magnetic field of remote word line with high energy consumption.
Interplay of two graphene mediated exchange bias fields applied to different
sides of free ferromagnet results in programable logic operations that depends
on specific realization of the structure. | 0901.0926v1 |
2009-03-21 | Graphite in the bi-layer regime: in-plane transport | An interplay between the increase in the number of carriers and the decrease
in the scattering time is expected to result in a saturation of the in-plane
resistivity, $\rho_{ab}$, in graphite above room temperature. Contrary to this
expectation, we observe a pronounced increase in $\rho_{ab}$ in the interval
between 300 and 900 K. We provide a theory of this effect based on intervalley
scattering of charge carriers by high-frequency, graphene-like optical phonons. | 0903.3646v2 |
2009-04-22 | Emergence of dissipative structures in current-carrying superconducting wires | We discuss the emergence of a spontaneous temperature and critical current
spatial modulation in current-carrying high temperature superconducting wire.
The modulation of the critical current along the wire on a scale of 3 - 10 mm
forces a fraction of the transport current to crisscross the resistive
interface between the superconducting film and normal metal stabilizer attached
to it. This generates additional heat that allows such a structure to be self
sustainable. Stability and the conditions for experimental observation of this
phenomenon are also discussed. | 0904.3474v1 |
2009-04-23 | Crystal growth, structure and ferromagnetic properties of a Ce3Pt23Si11 single crystal | A high-quality single crystal of Ce3Pt23Si11 has been grown using the
Czochralski method. The crystal structure is presented and the chemical
composition has been checked using an electron microprobe analyzer.
Measurements of the electrical resistivity and magnetic susceptibility
performed at low temperature show a ferromagnetic transition at Tc = 0.44 K. | 0904.3720v1 |
2009-05-29 | Growth of Sr1-xCaxRuO3 thin films by metalorganic aerosol deposition | We report the growth of thin films of Sr1-xCaxRuO3 on SrTiO3 and MgO
substrates by metalorganic aerosol deposition. The structure and microstructure
is characterized by X-ray diffraction and room-temperature scanning tunnelling
microscopy (STM), respectively. STM indicates in-plane epitaxy and a small
surface roughness for films on SrTiO3. The high-quality of the films is
supported by large residual resistivity ratios up to 29. | 0905.4896v2 |
2009-09-07 | Anomalous magnetotransport and cyclotron resonance of high mobility magnetic 2DHGs in the quantum Hall regime | Low temperature magnetotransport measurements and far infrared transmission
spectroscopy are reported in molecular beam epitaxial grown two-dimensional
hole systems confined in strained InAs quantum wells with magnetic impurities
in the channel. The interactions of the free holes spin with the magnetic
moment of 5/2 provided by manganese features intriguing localization phenomena
and anomalies in the Hall and the quantum Hall resistance. In magnetic field
dependent far infrared spectroscopy measurements well pronounced cyclotron
resonance and an additional resonance are found that indicates an anticrossing
with the cyclotron resonance. | 0909.1124v1 |
2010-08-15 | Unconventional Anomalous Hall Effect in the Metallic Triangular-Lattice Magnet PdCrO2 | We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a
quasi-two-dimensional triangular-lattice antiferromagnet PdCrO2. Using high
quality single crystals of PdCrO2, we found that the Hall resistivity deviates
from the conventional behavior below T* = 20 K, noticeably lower than TN = 37.5
K, at which Cr^{3+} (S=3/2) spins order in a 120 degree structure. In view of
the theoretical expectation that the spin chirality cancels out in the simplest
120 degree spin structure, we discuss required conditions for the emergence of
UAHE within Berry-phase mechanisms. | 1008.2503v1 |
2010-08-27 | Metal-nonmetal transition in LixCoO2 thin film and thermopower enhancement at high Li concentration | We investigate the transport properties of LixCoO2 thin films whose
resistivities are nearly an order of magnitude lower than those of the bulk
polycrystals. A metal-nonmetal transition occurs at ~0.8 in a biphasic domain,
and the Seebeck coefficient (S) is drastically increased at ~140 K (= T*) with
increasing the Li concentration to show a peak of magnitude ~120 \muV/K in the
S-T curve of x = 0.87. We show that T* corresponds to a crossover temperature
in the conduction, most likely reflecting the correlation-induced temperature
dependence in the low-energy excitations. | 1008.4635v1 |
2010-10-21 | Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions | We calculate quantum transport for metal-graphene nanoribbon heterojunctions
within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is
paid on both the chemical aspects of the interface bonding as well the
one-dimensional electrostatics along the ribbon length. Band-bending and doping
effects strongly influence the transport properties, giving rise to conductance
asymmetries and a selective suppression of the subband formation. Junction
electrostatics and p-type characteristics drive the conduction mechanism in the
case of high work function Au, Pd and Pt electrodes, while contact resistance
becomes dominant in the case of Al. | 1010.4393v1 |
2010-11-02 | Spin connection and boundary states in a topological insulator | We study the surface resistivity of a three-dimensional topological insulator
when the boundaries exhibit a non trivial curvature. We obtain an analytical
solution for a spherical topological insulator, and we show that a non trivial
quantum spin connection emerges from the three dimensional band structure. We
analyze the effect of the spin connection on the scattering by a bump on a flat
surface. Quantum effects induced by the geometry lead to resonances when the
electron wavelength is comparable to the size of the bump. | 1011.0565v1 |
2010-11-20 | Imaging Dissipation and Hot Spots in Carbon Nanotube Network Transistors | We use infrared thermometry of carbon nanotube network (CNN) transistors and
find the formation of distinct hot spots during operation. However, the average
CNN temperature at breakdown is significantly lower than expected from the
breakdown of individual nanotubes, suggesting extremely high regions of power
dissipation at the nanotube junctions. Statistical analysis and comparison with
a thermal model allow the extraction of the average tube-tube junction thermal
resistance, ~4.4x10^11 K/W (thermal conductance ~2.27 pW/K). This indicates
that nanotube junctions have a much greater impact on CNN transport,
dissipation, and reliability than extrinsic factors such as low substrate
thermal conductivity. | 1011.4551v2 |
2011-05-16 | Coulomb drag in graphene | We calculate theoretically the Coulomb drag resistivity for two graphene
monolayers spatially separated by a distance "$d$". We show that the frictional
drag induced by inter-layer electron-electron interaction goes asymptotically
as $T^2/n^3$ and $T^2 \ln(n)/n$ in the high-density ($k_F d \gg 1$) and
low-density ($k_F d \ll 1$) limits, respectively. | 1105.3203v2 |
2011-07-23 | Modified exponential I(U) dependence and optical efficiency of AlGaAs SCH lasers in computer modeling with Synopsys TCAD | Optical and electrical characteristics of AlGaAs lasers with separate
confinement heterostructures are modeled by using Synopsys's Sentaurus TCAD,
and open source software. We propose a modified exponential $I-V$ dependence to
describe electrical properties. A simple analytical, phenomenological model is
found to describe optical efficiency, $\eta$, with a high accuracy, by using
two parameters only. A link is shown between differential electrical
resistivity $r=dU/dI$ just above the lasing offset voltage, and the functional
$\eta(U)$ dependence. | 1107.4668v1 |
2011-08-20 | Demonstration of Forward Inter-band Tunneling in GaN by Polarization Engineering | We report on the design, fabrication, and characterization of GaN interband
tunnel junction showing forward tunneling characteristics. We have achieved
very high forward tunneling currents (153 mA/cm2 at 10 mV, and 17.7 A/cm2 peak
current) in polarization-engineered GaN/InGaN/GaN heterojunction diodes grown
by plasma assisted molecular beam epitaxy. We also report the observation of
repeatable negative differential resistance in interband III-Nitride tunnel
junctions, with peak-valley current ratio (PVCR) of 4 at room temperature. The
forward current density achieved in this work meets the typical current drive
requirements of a multi-junction solar cell. | 1108.4075v1 |
2012-04-10 | Tunneling conduction in graphene/(poly)vinyl alcohol composites | Graphene/(Poly)vinyl alcohol (PVA) composite film with thickness $60 \mu m$
were synthesized by solidification of a PVA solution comprising of dispersed
graphene nanosheets. The close proximity of the graphene sheets enables the
fluctuation induced tunneling of electrons to occur from one sheet to another.
The dielectric data show that the present system can be simulated to a parallel
resistance-capacitor network. The high frequency exponent of the frequency
variation of the ac conductivity indicates that the charge carriers move in a
two-dimensional space. The sample preparation technique will be helpful for
synthesizing flexible conductors. | 1204.2126v2 |
2012-07-27 | Theoretical model of structure-dependent conductance crossover in disordered carbon | We analyze the effects of sp^2/sp^3 bond-aspect ratio on the transport
properties of amorphous carbon quasi-1D structures where structural disorder
varies in a very non-linear manner with the effective bandgap. Using a
tight-binding approach the calculated electron transmission showed a high
probability over a wide region around the Fermi-level for sp^2-rich carbon and
also distinct peaks close to the band edges for sp^3-rich carbon structures.
This model shows a sharp rise of the structure resistance with the increase of
sp^3C % followed by saturation in the wide bandgap regime for carbon
superlattice-like structures and suggests the tuneable characteristic time of
carbon-based devices. | 1207.6478v1 |
2012-11-22 | Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO$_{2\pm x}$ | We have conducted a detailed thin film growth structure of oxygen engineered
monoclinic HfO$_{2\pm x}$ grown by reactive molecular beam epitaxy (MBE). The
oxidation conditions induce a switching between ($\bar{1}11$) and (002) texture
of hafnium oxide. The band gap of oxygen deficient hafnia decreases with
increasing amount of oxygen vacancies by more than 1 eV. For high oxygen
vacancy concentrations, defect bands form inside the band gap that induce
optical transitions and $p$-type conductivity. The resistivity changes by
several orders of magnitude as a function of oxidation conditions. Oxygen
vacancies do not give rise to ferromagnetic behavior. | 1211.5215v1 |
2013-05-21 | High sensitive quasi freestanding epitaxial graphene gassensor on 6H-SiC | We have measured the electrical response to NO$_2$, N$_2$, NH$_3$ and CO for
epitaxial graphene and quasi freestanding epitaxial graphene on 6H-SiC
substrates. Quasi freestanding epitaxial graphene shows a 6 fold increase in
NO2 sensitivity compared to epitaxial graphene. Both samples show a sensitivity
better than the experimentally limited 1 ppb. The strong increase in
sensitivity of quasi freestanding epitaxial graphene can be explained by a
Fermi-energy close to the Dirac Point leading to a strongly surface doping
dependent sample resistance. Both sensors show a negligible sensitivity to
N$_2$, NH$_3$ and CO. | 1305.4737v1 |
2013-09-04 | Enhancing high-temperature thermoelectric properties of PtAs2 by Rh doping | The effects of Rh doping on the thermoelectric properties of Pt1-xRhxAs2 (x =
0, 0.005, and 0.01) with pyrite structure were studied by conducting
measurements of electrical resistivity rho, Seebeck coefficient S, and thermal
conductivity kappa. The sample with x = 0.005 exhibited large S and low rho,
resulting in a maximum power factor (S^2/rho) of 65 muW/cmK^2 at 440 K. The
peculiarly shaped "corrugated flat band" predicted for PtSb2 might explain the
enhanced thermoelectric properties of doped PtAs2. | 1309.0939v1 |
2013-10-06 | Charge transport through graphene junctions with wetting metal leads | Graphene is believed to be an excellent candidate material for
next-generation electronic devices. However, one needs to take into account the
nontrivial effect of metal contacts in order to precisely control the charge
injection and extraction processes. We have performed transport calculations
for graphene junctions with wetting metal leads (metal leads that bind
covalently to graphene) using nonequilibrium Green's functions and density
functional theory. Quantitative information is provided on the increased
resistance with respect to ideal contacts and on the statistics of current
fluctuations. We find that charge transport through the studied two-terminal
graphene junction with Ti contacts is pseudo-diffusive up to surprisingly high
energies. | 1310.1640v1 |
2013-11-17 | Giant magnetothermopower in charge ordered Nd0.75Na0.25MnO3 | We report magnetization, resistivity and thermopower in the charge-orbital
ordered antiferromagnet Nd0.75Na0.25MnO3. Magnetic-field induced collapse of
antiferromagnetism is found to be accompanied by a giant negative
magnetothermopower (= 80-100% for a field change of 5T) over a wide temperature
(T = 60-225K) and giant magnetoresistance. While the field-induced metamagnetic
transition in magnetization is reversible upon field-cycling at T > 40 K, it is
irreversible at lower temperatures and this has impact on magnetoresistance,
magnetothermopower as well as change in the temperature of the sample. Our
results indicate high sensitivity of thermopower to changes in the magnetic
state of the sample. | 1311.4165v1 |
2014-02-05 | Selective molecular capture mechanism in carbon nanotube networks | Recent air pollution issues have raised significant attention to develop
efficient air filters, and one of the most promising candidates is that enabled
by nanofibers. We explore here selective molecular capture mechanism for
volatile organic compounds in carbon nanotube networks by performing atomistic
simulations. The results are discussed with respect to the two key parameters
that define the performance of nanofiltration, i.e. the capture efficiency and
flow resistance, which validate the advantage of carbon nanotube networks with
high surface-to-volume ratio and atomistically smooth surfaces. We also reveal
the important roles of interfacial adhesion and diffusion that govern selective
gas transport through the network. | 1402.1011v1 |
2016-01-06 | Effect of SW defect on structural and transport properties of silicene nanoribbons | Using density functional theory and non-equilibrium Greens function
technique, we performed theoretical investigations on the structural and
transport properties of zigzag silicene nanoribbons with Stone-Wales defect.
The calculated formation energy is significantly lower than that of graphene
and silicene, which implies the high stability of such defect in SiNRs.
Negative differential resistance can be observed within certain bias voltage
range in both perfect and SW defected SiNRs. In order to elucidate the
mechanism the NDR behavior,the transmission spectra and molecular projected
self-consistent Hamiltonian states are discussed in details. | 1601.01053v1 |
2016-01-30 | Slippery but tough - the rapid fracture of lubricated frictional interfaces | We study the onset of friction for rough contacting blocks whose interface is
coated with a thin lubrication layer. High speed measurements of the real
contact area and stress fields near the interface reveal that propagating shear
cracks mediate lubricated frictional motion. While lubricants reduce interface
resistances, surprisingly, they significantly increase energy dissipated,
$\Gamma$, during rupture. Moreover, lubricant viscosity affects the onset of
friction but has no effect on $\Gamma$. Fracture mechanics provide a new way to
view the otherwise hidden complex dynamics of the lubrication layer. | 1602.00085v2 |
2016-10-09 | Physical properties of KMgBi single crystals | KMgBi single crystals are grown by using the Bi flux successfully. KMgBi
shows semiconducting behavior with a metal-semiconductor transition at high
temperature region and a resistivity plateau at low temperature region,
suggesting KMgBi could be a topological insulator with a very small band gap.
Moreover, KMgBi exhibits multiband feature with strong temperature dependence
of carrier concentrations and mobilities. | 1610.02699v2 |
2017-06-27 | Influence of Heat Treatment on the Corrosion Behavior of Purified Magnesium and AZ31 Alloy | Magnesium and its alloys are ideal for biodegradable implants due to their
biocompatibility and their low-stress shielding. However, they can corrode too
rapidly in the biological environment. The objective of this research was to
develop heat treatments to slow the corrosion of high purified magnesium and
AZ31 alloy in simulated body fluid at 37{\deg}C. Heat treatments were performed
at different temperatures and times. Hydrogen evolution, weight loss, PDP, and
EIS methods were used to measure the corrosion rates. Results show that heat
treating can increase the corrosion resistance of HP-Mg by 2x and AZ31 by 10x. | 1706.08663v1 |
2017-12-06 | Superconductivity in the ternary compound SrPt$_{10}$P$_4$ with complex new structure | We report superconductivity at 1.4K in the ternary SrPt$_{10}$P$_4$ with a
complex new structure. SrPt$_{10}$P$_4$ crystallizes in a monoclinic
space-group C2/c (\#15) with lattice parameters a= 22.9151(9)$\AA$, b=
13.1664(5)$\AA$, c=13.4131(5)$\AA$, and $\beta$= 90.0270(5)${^\circ}$. Bulk
superconductivity in the samples has been demonstrated through resistivity, ac
susceptibility, and heat capacity measurements. High pressure measurements have
shown that the superconducting T$_C$ is systematically suppressed upon
application of pressure, with a dT$_C$/dP coefficient of -0.016 K/GPa. | 1712.02010v1 |
2018-03-06 | Comparative study on magnetoresistance of carbon-cobalt nanocomposite thin films grown by pulsed laser deposition | We present a comparative study on the influence of applied magnetic field on
the resistance of $C_{1-x}Co_x$ thin films (with $x=0.1$, $0.15$ and $0.2$)
grown on $Si$ substrate by pulsed laser deposition technique. It is found that
the behavior of magnetoresistance (MR) drastically depends on the temperature.
Namely, at low temperatures MR is positive and its behavior is governed by the
field mediated weak localization scenario. While at high temperatures MR turns
negative and its behavior is dominated by electron scattering on ferromagnetic
cobalt atoms. | 1803.02064v1 |
2018-04-27 | Emergent antiferromagnetism of YTiO3 in YTiO3-CaTiO3 superlattices | Transport and magnetoresistance measurements are performed on metallic,
high-carrier density YTiO3-CaTiO3 superlattices as a probe towards the
investigation of an emergent magnetic order of YTiO3. On varying the thickness
of YTiO3 while keeping the CaTiO3 layer thickness constant in the
superlattices, a low-temperature upturn in sheet-resistance, a non-Fermi
liquid-like charge transport and positive magnetoresistance are observed.
Analyses of the origin of such effects suggest that a unique antiferromagnetic
order is realized in the ultra-thin, epitaxially strained YTiO3 layers, which
corroborates well with some recent theoretical predictions in this regard. | 1804.10333v1 |
2018-10-01 | Poly(ionic liquid)-Derived Carbon with Site-Specific N-Doping and Biphasic Heterojunction for Enhanced CO2 Capture and Sensing | CO2 capture is a pressing global environmental issue that drives scientists
to develop creative strategies for tackling this challenge. The concept in this
contribution is to produce site specific nitrogen doping in microporous carbon
fibers. It creates a carbon/carbon heterojunction by using poly(ionic liquid)
(PIL) as soft activation agent that deposits nitrogen species exclusively on
the skin of commercial microporous carbon fibers. Such carbon-based biphasic
heterojunction amplifies the interaction between carbon fiber and CO2 molecule
for unusually high CO2 uptake and resistive sensing. | 1810.06418v1 |
2020-09-13 | Adiabatic theory of SET and RESET transitions | We develop a phenomenological theory of pulse induced phase transformations
behind the SET (from high to low resistive state) and RESET (backward)
processes in nonvolatile memory. We show that in modern era devices, both
evolve in the adiabatic regime with energy deposition time much shorter than
that of thermalization. They are however different by the operating modes:
voltage source driven for SET and current source driven for RESET. The
characteristic temperatures and transition rates are expressed through material
and process parameters. | 2009.06057v2 |
2007-10-29 | Thermoelectrical manipulation of nano-magnets | We propose a device that can operate as a magneto-resistive switch or
oscillator. The device is based on a spin-thermo-electronic control of the
exchange coupling of two strong ferromagnets through a weakly ferromagnetic
spacer. We show that the local Joule heating due to a high concentration of
current in a magnetic point contact or a nanopillar can be used to reversibly
drive the weak ferromagnet through its Curie point and thereby
exchange-decouple the strongly ferromagnetic layers, which have an antiparallel
ground state. Such a spin-thermionic parallel-to-antiparallel switching causes
magnetoresistance oscillations where the frequency can be controlled by proper
biasing from essentially DC to GHz. | 0710.5477v1 |
2007-10-30 | Devitrification of a glass-like arrested ferromagnetic phase in La0.5Ca0.5MnO3 | Magnetization measurements in La0.5Ca0.5MnO3 manganite show that the
high-temperature long-range ferromagnetic-metallic phase transforms to
antiferromagnetic-insulating phase, although a fraction of
ferromagnetic-metallic phase undergoes glass-like kinetic arrest and coexists
at low temperature with the equilibrium antiferromagnetic-insulating phase. We
show here through resistivity measurements that the residual arrested
ferromagnetic-metallic fraction can be converted to the equilibrium
antiferromagnetic-insulating phase by successive annealing at higher
temperatures, possibly through heterogeneous nucleation of equilibrium phase.
Significantly, larger fractions of this glassy ferromagnetic-metallic phase can
be obtained by cooling in higher fields and larger conversion to equilibrium
antiferromagnetic-insulating phase results. | 0710.5585v1 |
2019-03-26 | Patterning of diamond with 10 nm resolution by electron-beam-induced etching | We report on mask-less, high resolution etching of diamond surfaces,
featuring sizes down to 10 nm. We use a scanning electron microscope (SEM)
together with water vapor, which was injected by a needle directly onto the
sample surface. Using this versatile and low-damage technique, trenches with
different depths were etched. Cross sections of each trench were obtained by
focused ion beam milling and used to calculate the achieved aspect ratios. The
developed technique opens up the possibility of mask- and resist-less
patterning of diamond for nano-optical and electronic applications. | 1903.10824v1 |
2015-07-11 | Insulator/metal phase transition and colossal magnetoresistance in holographic model | Within massive gravity, we construct a gravity dual for insulator/metal phase
transition and colossal magnetoresistance (CMR) effect found in some manganese
oxides materials. In heavy graviton limit, a remarkable
magnetic-field-sensitive DC resistivity peak appears at the Curie temperature,
where an insulator/metal phase transition happens and the magnetoresistance is
scaled with the square of field-induced magnetization. We find that metallic
and insulating phases coexist below the Curie point and the relation with the
electronic phase separation is discussed. | 1507.03105v2 |
2019-10-23 | Percolation with plasticity for neuromorphic computing | We introduce the percolation with plasticity (PWP) systems that exhibit
neuromorphic functionalities including multi-valued memory, random number
generation, matrix-vector multiplication, and associative learning. PWP systems
have multiple (N >> 1) interfaces with external circuitry (electrodes) allowing
N! >> 1 measurable interelectrode resistances. Due to the underlying material
properties, they undergo successive nonvolatile modifications in response to
electric pulses. PWP networks offer some advantages over the existing neural
network architectures. Overall, random self-tuning PWP systems with high degree
of parallelism, multiple inputs and outputs present close similarities to the
cortex of mammalian brain. Understanding their topology, electrodynamics, and
statistics opens a field of its own calling upon new theoretical and
experimental insights. | 1910.10535v1 |
2019-11-04 | Closed-loop electric currents and non-local resistance measurements with wide F/I/N tunnel contacts | Lateral spin valves are used to generate and characterize pure spin currents.
Non-local voltage measured in such structures provides information about spin
polarization and spin decay rates. For wide high-transparency F/N contacts it
was shown that the Johnson-Silsbee non-local effect is substantially enriched
by closed-loop electric currents driven by local spin injection in the
electrically dangling part of the valve. For valves with low-transparency F/I/N
tunnel contacts such circular currents are strongly suppressed, yet we show
that the voltage modifications persist, may be significant, and must be
accounted for in the data analysis. | 1911.01034v1 |
2020-01-08 | Electrical and optical properties of hydrated amorphous vanadium oxide | Electrical and optical properties of amorphous vanadium oxide thin films
obtained by electrochemical anodic oxidation are studied. It is shown that
under cathodic polarization the hydrogen insertion into vanadium oxide from an
electrolyte occurs. Metal-insulator transition in amorphous HxVO2 is found to
be preserved up to high concentration (x ~ 1.5) of hydrogen. Memory switching
with the N-type negative differential resistance, associated with the H+ ionic
transfer, is observed in "V/hydrated amorphous vanadium oxide/Au" sandwich
structures. | 2001.02418v1 |
2020-01-08 | Electrical conductivity of vanadium dioxide switching channel | The electrical conductivity of the switching channel of vanadium dioxide
thin-film sandwich structures is studied over a wide temperature range (15-300
K). It is shown that the electrical resistance of the channel varies with
temperature as R~exp(aT-b/T) in the high-temperature region (above 70 K). The
experimental results are discussed from the viewpoint of the small polaron
hopping conduction theory which takes into account the influence of thermal
lattice vibrations onto the resonance integral. | 2001.03053v1 |
2021-03-19 | Side-leakage of facemask | Face masks are used to trap particles (or fluid drops) in a porous material
(filter) in order to avoid or reduce the transfer of particles between the
human lungs (or mouth and nose) and the external environment. The air exchange
between the lungs and the environment is assumed to occur through the facemask
filter. However, if the resistance to air flow through the filter is high some
air (and accompanied particles) will leak through the filter-skin interface. In
this paper I will present a model study of the side-leakage problem. | 2103.10970v1 |
2021-04-25 | High Pressure RTSC-Hydrides are Extreme Hard Type-II Superconductors | It is argued that most of the RTSC hydrides are intrinsic hard type-II
superconductors with strong pinning effects. The pinning centers are long
columnar-like defects, with the radius of the order of the superconducting
coherence length. The core and electromagnetic pinning are both equally
operative, thus giving maximal pinning potential when vortices are oriented
along the columnar axis. The theory predicts: (i) large critical currents, (ii)
huge decrease of the temperature broadening of the resistance in magnetic field
compared with standard superconductors, (iii) large magnetization hysteresis,
(iv) the magnetic irreversible line is pushed toward the second critical field
and magnetization relaxation is much slower. That the RTSC-hydrides are hard
type-II SC can give rise to new physics in these materials. | 2104.12214v1 |
2022-11-19 | A Large-Area RPC Detector for Muography | A muon telescope equipped with four Resistive Plate Chambers of 2 m$^{2}$ per
plane was tested with the muon scattering tomography technique. The telescope
was operated during several hours with high atomic number materials located at
its center with two detector planes on each side. With an intrinsic efficiency
above 98%, spatial resolution around 1 cm and detector planes spaced by 45 cm,
it was possible to identify the presence of a 5 cm thick tungsten block in 10
minutes of acquisition. The results obtained after five hours of acquisition
are also presented in this communication. | 2211.10795v1 |
2023-05-22 | Microcontroller Based AVR Hazardous Gas Detection System using IoT | MQ-6 Semiconductor Sensor for Combustible Gas detection is a Sensitive Gas
sensor. The sensitive material of this MQ-6 gas sensor is SnO2, which works
with lower conductivity in clean air. When the target combustible gas exist,
the sensors conductivity is higher along with the gas concentration rising. As
the conductivity increases the current in the circuit of the sensor increases
which results in lower sensor resistance. This change is used to correspond,
the output signal of gas concentration. MQ-6 gas sensor has high sensitivity to
Methane, Propane and Butane and could be used to detect both Methane and
Propane. The sensor could be used to detect different combustible gas
especially Methane, it is with low cost and suitable for different application. | 2305.12855v1 |
2017-10-25 | High-temperature cyclic oxidation kinetics and microstructural transition mechanisms of Ti-6Al-4V composites reinforced with hybrid (TiC+TiB) networks | The microstructural features and high-temperature oxidation resistance of
hybrid (TiC+TiB) networks reinforced Ti-6Al-4V composites were investigated
after fabricated with reaction hot pressing technique. The inhomogeneous
distribution of hybrid reinforcers resulted in a sort of stress-induced grain
refinement for {\alpha}-Ti matrix phase, which was further facilitated by
heterogeneous nucleation upon additive interfaces. HRTEM analyses revealed the
crystallographic orientation relation between TiB and alpha-Ti phases as
(201)TiB//(-1100)alpha-Ti plus [11-2]//[0001] alpha-Ti, while TiC and
{\alpha}-Ti phases maintained the interrelation of (-200)TiC//(-2110)
{\alpha}-Ti and [001]TiC//[01-10] alpha-Ti. The hybridly reinforced
Ti-6Al-4V/(TiC+TiB) composites displayed superior oxidation resistance to both
the sintered matrix alloy and the two composites reinforced solely with TiC or
TiB addition during the cyclic oxidation at 873, 973 and 1073 K respectively
for 100 h. The hybrid reinforcers volume fraction was a more influential factor
to improve oxidation resistance than the matrix alloy powder size. As
temperature rose from 873 to 1073 K, the oxidation kinetics transferred from
the nearly parabolic type through qusilinear tendency into the finally linear
mode. This corresponded to the morphological transition of oxide scales from a
continuous protective film to a partially damaged layer and ended up with the
complete spallation of alternating alumina and rutile multilayers. A
phenomenological model was proposed to elucidate the growth process of oxides
scales. The release of thermal stress, the suppression of oxygen diffusion and
the fastening of oxide adherence were found as the three major mechanisms to
enhance the oxidation resistance of hybrid reinforced composites. | 1710.09315v1 |
2007-07-20 | A mechanism for unipolar resistance switching in oxide non-volatile memory devices | Building on a recently introduced model for non-volatile resistive switching,
we propose a mechanism for unipolar resistance switching in
metal-insulator-metal sandwich structures. The commutation from the high to low
resistance state and back can be achieved with successive voltage sweeps of the
same polarity. Electronic correlation effects at the metal-insulator interface
are found to play a key role to produce a resistive commutation effect in
qualitative agreement with recent experimental reports on binary transition
metal oxide based sandwich structures. | 0707.3077v1 |
2013-08-02 | Precision Quantum Hall Resistance Measurement on Epitaxial Graphene Device in Low Magnetic Field | Precision quantum Hall resistance (QHR) measurements were performed on
large-area epitaxial graphene device at low magnetic fields (B = 2 T - 8 T) at
temperature T = 1.5 K. Hall resistance was measured using Cryogenic Current
Comparator resistance bridge with high biasing current Isd = 40 micro ampere.
The results showed that at B = 8 T the relative deviation of Hall resistance
from the expected quantized value h/2e2 is within experimental uncertainty of
3.5 parts in 108 and remained below 0.35 parts per million (ppm) down to B = 3
T. | 1308.0456v1 |
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