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2017-02-24 | Elemental Analysis of Glass and Bakelite Electrodes Using PIXE Facility | The evolution of particle detectors dates back to the discovery of X-rays and
radioactivity in 1890s. In detector history, the Resistive Plate Chambers
(RPCs) are introduced in early 1980s. An RPC is a gaseous detector made up of
two parallel electrodes having high resistivity like that of glass and
bakelite. Currently several high energy physics experiments are using RPC-based
detector system due to robustness and simplicity of construction. In each and
every experiment, RPCs have to run continuously for several years. So, it
demands an in-depth characterization of the electrode materials. In the present
study, an elemental analysis of locally available glass and bakelite samples is
done using PIXE facility available at Panjab University Cyclotron, Chandigarh.
PIXE measurements are done using 2.7 MeV proton beam incident on the electrode
sample target. The constituent elements present in these electrode samples are
reported. | 1702.08480v3 |
2014-08-12 | Collapse of CuO Double Chains and Suppression of Superconductivity in High-Pressure Phase of YBa$_2$Cu$_4$O$_8$ | The crystal structure and electrical resistivity of YBa$_2$Cu$_4$O$_8$ (Y124)
were studied under high pressure up to 18 GPa using diamond-anvil cells,
respectively, in order to clarify its conduction mechanism. Y124 causes the
first-order phase-transition into the orthorhombic Immm at pressure around 11
GPa. The high-pressure phase (HPP) also shows the superconductivity, while the
manner of temperature dependence of electrical resistance and the pressure
dependence of transition temperature, Tc, drastically change above 11 GPa. The
CuO$_2$ plane persists in HPP but the CuO double chains collapse with the phase
transition and transform into three-dimensional Cu-O network, resulting in the
renewal of conduction system. | 1408.2613v1 |
2019-02-11 | Improved oxidation resistance of high emissivity coatings on fibrous ceramic for reusable space system | To develop high emissivity coatings on fibrous ceramic substrates with
improved thermal resistance for reusable space systems,
WSi2-MoSi2-Si-SiB6-borosilicate glass coatings were prepared on fibrous ZrO2 by
slurry dipping and subsequent high temperature rapid sintering. A coating with
50 wt% WSi2 and 50 wt% MoSi2 presents optimal thermal stability with only 10.06
mg/cm2 mass loss and 4.0 % emissivity decrease in the wavelength regime of 1.27
to 1.73 microns after 50 h oxidation at 1773 K. The advantages of double phase
metal silicide coatings combining WSi2 and MoSi2 include improved thermal
compatibility with the substrate and an enhanced glass mediated self healing
ability. | 1902.03943v2 |
2018-08-16 | Investigating Unipolar Switching in Niobium Oxide Resistive Switches: Correlating Quantized Conductance and Mechanism | Memory devices based on resistive switching (RS) have not been fully realised
due to lack of understanding of the underlying switching mechanisms. Nature of
ion transport responsible for switching and growth of conducting filament in
transition metal oxide based RS devices is still in debate. Here, we
investigated the mechanism in Niobium oxide based RS devices, which shows
unipolar switching with high ON/OFF ratio, good endurance cycles and high
retention times. We controlled the boundary conditions between low-conductance
insulating and a high-conductance metallic state where conducting filament (CF)
can form atomic point contact and exhibit quantized conductance behaviour.
Based on the statistics generated from quantized steps data, we demonstrated
that the CF is growing atom by atom with the applied voltage sweeps. We also
observed stable quantized states, which can be utilized in multistate
switching. | 1808.05600v1 |
2019-12-19 | A high-throughput structural and electrochemical study of metallic glass formation in Ni-Ti-Al | Based on a set of machine learning predictions of glass formation in the
Ni-Ti-Al system, we have undertaken a high-throughput experimental study of
that system. We utilized rapid synthesis followed by high-throughput structural
and electrochemical characterization. Using this dual-modality approach, we are
able to better classify the amorphous portion of the library, which we found to
be the portion with a full-width-half-maximum (FWHM) of 0.42 A$^{-1}$ for the
first sharp x-ray diffraction peak. We demonstrate that the FWHM and corrosion
resistance are correlated but that, while chemistry still plays a role, a large
FWHM is necessary for the best corrosion resistance. | 1912.09330v1 |
2011-04-22 | High purity semi-insulating 4H-SiC epitaxial layers by Defect-Competition Epitaxy | Thick, high-purity semi-insulating (SI)homoepitaxial layers on Si-face 4H-SiC
weregrownsystematically, with resistivity \geq 109{\Omega}-cmby maintaining
high C/Si ratios 1.3-15 during growth.Comparison of secondary ion mass spectra
betweenlow-dopedepilayers grown at C/Si ratio<1.3andSI-epilayers grown at C/Si
ratio>1.3 showed little difference in residual impurity concentrations. A
reconciliation of impurity concentration with measured resistivity indicated a
compensating trap concentration of ~1015cm-3present only in the SI-epilayers.
High- resolution photo induced transient spectroscopy (HRPITS) identified
themas Si-vacancy related deep centers, with no detectable EH6/7 and
Z1/2levels. Recombination lifetimes ~5ns suggest application in fast-switching
power devices. | 1104.4509v1 |
2020-05-22 | Sharp negative differential resistance from vibrational mode softening in molecular junctions | We unravel the critical role of vibrational mode softening in single-molecule
electronic devices at high bias. Our theoretical analysis is carried out with a
minimal model for molecular junctions, with mode softening arising due to
quadratic electron-vibration couplings, and by developing a mean-field
approach. We discover that the negative sign of the quadratic
electron-vibration coupling coefficient can realize at high voltage a sharp
negative differential resistance (NDR) effect with a large peak-to-valley
ratio. Calculated current-voltage characteristics, obtained based on ab initio
parameters for a nitro-substituted oligo(phenylene ethynylene) junction, agree
very well with measurements. Our results establish that vibrational mode
softening is a crucial effect at high voltage, underlying NDR, a substantial
diode effect, and the breakdown of current-carrying molecular junctions. | 2005.11365v1 |
2023-02-28 | ZrNb(CO) RF superconducting thin film with high critical temperature in the theoretical limit | Superconducting radio-frequency (SRF) resonators are critical components for
particle accelerator applications, such as free-electron lasers, and for
emerging technologies in quantum computing. Developing advanced materials and
their deposition processes to produce RF superconductors that yield nanoohms
surface resistances is a key metric for the wider adoption of SRF technology.
Here we report ZrNb(CO) RF superconducting films with high critical
temperatures (Tc) achieved for the first time under ambient pressure. The
attainment of a Tc near the theoretical limit for this material without applied
pressure is promising for its use in practical applications. A range of Tc,
likely arising from Zr doping variation, may allow a tunable superconducting
coherence length that lowers the sensitivity to material defects when an
ultra-low surface resistance is required. Our ZrNb(CO) films are synthesized
using a low-temperature (100 - 200 C) electrochemical recipe combined with
thermal annealing. The phase transformation as a function of annealing
temperature and time is optimized by the evaporated Zr-Nb diffusion couples.
Through phase control, we avoid hexagonal Zr phases that are equilibrium-stable
but degrade Tc. X-ray and electron diffraction combined with photoelectron
spectroscopy reveal a system containing cubic ZrNb mixed with rocksalt NbC and
low-dielectric-loss ZrO2. We demonstrate proof-of-concept RF performance of
ZrNb(CO) on an SRF sample test system. BCS resistance trends lower than
reference Nb, while quench fields occur at approximately 35 mT. Our results
demonstrate the potential of ZrNb(CO) thin films for particle accelerator and
other SRF applications. | 2302.14410v2 |
2020-01-07 | First principles evaluation of fcc ruthenium for use in advanced interconnects | As the semiconductor industry turns to alternate conductors to replace Cu for
future interconnect nodes, much attention as been focused on evaluating the
electrical performance of Ru. The typical hexagonal close-packed (hcp) phase
has been extensively studied, but relatively little attention has been paid to
the face-centered cubic (fcc) phase, which has been shown to nucleate in
confined structures and may be present in tight-pitch interconnects. Using
\emph{ab initio} techniques, we benchmark the performance of fcc Ru. We find
that the phonon-limited bulk resistivity of the fcc Ru is less than half of
that of hcp Ru, a feature we trace back to the stronger electron-phonon
coupling elements that are geometrically inherited from the modified Fermi
surface shape of the fcc crystal. Despite this benefit of the fcc phase, high
grain boundary scattering results in increased resistivity compared to Cu-based
interconnects with similar average grain size. We find, however, that the line
resistance of fcc Ru is lower than that of Cu below 21 nm line width due to the
conductor volume lost to adhesion and wetting liners. In addition to studying
bulk transport properties, we evaluate the performance of adhesion liners for
fcc Ru. We find that it is energetically more favorable for fcc Ru to bind
directly to silicon dioxide than through conventional adhesion liners such as
TaN and TiN. In the case that a thin liner is necessary for the Ru deposition
technique, we find that the vertical resistance penalty of a liner for fcc Ru
can be up to eight times lower than that calculated for conventional liners
used for Cu interconnects. Our calculations, therefore, suggest that the
formation of the fcc phase of Ru may be a beneficial for advanced,
low-resistance interconnects. | 2001.02216v3 |
2021-12-12 | Electric-field-driven resistive transition in multiferroic SrCo$_2$Fe$_{16}$O$_{27}$/Sr$_3$Co$_2$Fe$_{24}$O$_{41}$composite | We report observation of electric-field-driven resistive transition at a
characteristic threshold field $E_{th}(T)$ across a temperature range 10-200 K
in an off-stoichiometric composite of (~80 vol%) W- and (~20 vol%) Z-type
hexaferrites. The dielectric constant $\epsilon$ and the relaxation time
constant $\tau$ too exhibit anomalous jump at $E_{th}(T)$. The $E_{th}(T)$, the
extent of jump in resistivity ($\Delta\rho$), and the hysteresis associated
with the jump [$\Delta E_{th}(T)$] are found to decrease systematically with
the increase in temperature ($T$). Several temperature-driven phase transitions
have also been noticed in low and high resistive states (LRS and HRS). The
temperature-driven conduction turns out to be governed by activated hopping of
small polarons at all the phases with electric ($E$) and magnetic ($H$) field
dependent activation energy $U(E,H)$. Interestingly, as the temperature is
raised, the $E$-driven conduction at a fixed temperature evolves from
$\textit{Ohmic}$ to $\textit{non-Ohmic}$ across 10-200 K and within 110-200 K,
$\rho$ follows three-dimensional variable range hopping (3D-VRH) with stretched
exponential $\sim$ $exp[(E_0/E)^4]$ or power law $\sim$ $(E_0/E)^m$ ($m$ varies
within $\sim$0.6-0.7 and $\sim$0.6-0.8 at LRS and HRS, respectively) dependence
depending on the localization length ($\zeta_E$) to diffusion length ($d_E$)
ratio associated with $E$-driven conduction. The $\rho(E,T)$ follows universal
scaling only at LRS within 10-110 K but not at higher temperature or at HRS.
The entire set of observations has been discussed within the framework of
structural evolution of the point-defect (cation vacancies or oxygen excess)
network. This comprehensive map of esoteric $\rho-E-T-H$ and $\epsilon-E-T-H$
patterns provides insights on defect driven effects in a composite useful for
tuning both the resistive transition and multiferroicity. | 2112.06246v1 |
2023-02-20 | Observation of near room temperature thin film superconductivity of atmospherically stable Ag-Au mesoscopic thin film | An environmentally stable mesoscopic thin film of Au of certain thickness has
been deposited thermally on top of a Ag+ implanted oxide substrate to develop a
close to room temperature superconductor. This thin film has been deposited in
two different stages. Initially, a sol-gel derived ion conducting metal oxide
(ICMO) thin film has been deposited by spin coating. Afterward, Ag+ has been
introduced inside ICMO thin film by a chemical method. Following this, a thin
layer of Au has been deposited on top of that Ag ion-implanted oxide via
thermal evaporation. The temperature dependent resistivity (R-T) has been
studied by four probe method. During high-to-low temperature sweep, around 240
K this thin film sample shows a sudden drop of resistance from 0.7 Ohm to 0.1
micro-Ohm. This 6-7 orders drop of resistance has been observed instantly
within <0.1 K temperature variation of the sample. This transition temperature
(TC) has been shifted toward the higher temperature by 5-6 degrees when
temperature has been increased from low to the higher side. During 2nd and 3rd
temperature cycling, both these transitions have been shifted by ~10 K towards
room temperature w.r.t the earlier. However, after three successive temperature
cycles, TC becomes stable and transitions occur close to 0 oC repeatedly. At
the low resistance phase, current level has been varied from +100 mA to -100 mA
which shows a random fluctuation of voltage drop within 10 nV range, indicating
resistance under such circumstance is too low to measure by Delta mode
electrical measurement (0.1 micro-Ohm). Besides, transition temperature reduces
to lower temperature by 4 K, after applying 1 tesla magnetic field
perpendicular to the thin film. Few YouTube video links of temperature
dependent electrical characterization of such a thin film is given next to the
acknowledgement section. | 2302.09974v3 |
2023-10-11 | Absence of topological Hall effect in Fe$_x$Rh$_{100-x}$ epitaxial films: revisiting their phase diagram | A series of Fe$_x$Rh$_{100-x}$ ($30 \leq x \leq 57$) films were epitaxially
grown using magnetron sputtering, and were systematically studied by
magnetization-, electrical resistivity-, and Hall resistivity measurements.
After optimizing the growth conditions, phase-pure Fe$_{x}$Rh$_{100-x}$ films
were obtained, and their magnetic phase diagram was revisited. The
ferromagnetic (FM) to antiferromagnetic (AFM) transition is limited at narrow
Fe-contents with $48 \leq x \leq 54$ in the bulk Fe$_x$Rh$_{100-x}$ alloys. By
contrast, the FM-AFM transition in the Fe$_x$Rh$_{100-x}$ films is extended to
cover a much wider $x$ range between 33 % and 53 %, whose critical temperature
slightly decreases as increasing the Fe-content. The resistivity jump and
magnetization drop at the FM-AFM transition are much more significant in the
Fe$_x$Rh$_{100-x}$ films with $\sim$50 % Fe-content than in the Fe-deficient
films, the latter have a large amount of paramagnetic phase. The
magnetoresistivity (MR) is rather weak and positive in the AFM state, while it
becomes negative when the FM phase shows up, and a giant MR appears in the
mixed FM- and AFM states. The Hall resistivity is dominated by the ordinary
Hall effect in the AFM state, while in the mixed state or high-temperature FM
state, the anomalous Hall effect takes over. The absence of topological Hall
resistivity in Fe$_{x}$Rh$_{100-x}$ films with various Fe-contents implies that
the previously observed topological Hall effect is most likely extrinsic. We
propose that the anomalous Hall effect caused by the FM iron moments at the
interfaces nicely explains the hump-like anomaly in the Hall resistivity. Our
systematic investigations may offer valuable insights into the spintronics
based on iron-rhodium alloys. | 2310.07140v1 |
2022-06-22 | Thermoelectric properties of high-entropy rare-earth cobaltates | High-entropy concept introduced with a promising paradigm to obtain exotic
physical properties has motivated us to explore the thermoelectric properties
of Sr-substituted high-entropy rare-earth cobaltates i.e.,
(LaNdPrSmEu)$_{1-x}$Sr$_x$CoO3 (0 \leq x \leq 0.10). The structural analysis of
the samples synthesized using the standard solid-state route, confirms the
orthorhombic structure with the Pbnm space group. The Seebeck coefficient and
electrical resistivity decrease with rising Sr concentration as well as with an
increase in temperature. The multiple A-site ions in high-entropy rare-earth
cobaltates result in an improved Seebeck coefficient ({\alpha}) compared to
La$_{0.95}$Sr$_{0.05}$CoO$_3$, associated with a decrease in the Co-O-Co bond
angle, which further enhances the power factor. The random distribution of
cations at the rare-earth site results in a significant lowering of phonon
thermal conductivity. As a result, a maximum figure of merit (zT) of 0.23 is
obtained at 350K for (LaNdPrSmEu)$_{0.95}$Sr$_{0.05}$CoO$_3$, which is one of
the highest values of zT reported at this temperature for oxide materials. This
study shows promise to decouple thermoelectric parameters using the
high-entropy concept in several materials. | 2206.11106v1 |
2005-12-15 | The WHO surveillance threshold and the emergence of drug-resistant HIV strains in Botswana | Background: Approximately 40% of adults in Botswana are HIV-infected. The
Botswana antiretroviral program began in 2002 and currently treats 34,000
patients with a goal of treating 85,000 patients (~30% of HIV-infected adults)
by 2009. We predict the evolution of drug-resistant strains of HIV that may
emerge as a consequence of this treatment program. We discuss the implications
of our results for the World Health Organization's (WHO's) proposed
surveillance system for detecting drug-resistant strains of HIV in Africa.
Methods: We use a mathematical model of the emergence of drug resistance. We
incorporate demographic and treatment data to make specific predictions as to
when the WHO surveillance threshold is likely to be exceeded. Results: Our
results show - even if rates of acquired resistance are high, but the
drug-resistant strains that evolve are only half as transmissible as wild-type
strains - that transmission of drug-resistant strains will remain low (< 5% by
2009) and are unlikely to exceed the WHO's surveillance threshold. However,our
results show that transmission of drug-resistant strains in Botswana could
increase to ~15% by 2009 if resistant strains are as transmissible as wild-type
strains. Conclusion: The WHO's surveillance system is designed to detect
transmitted resistance that exceeds a threshold level of 5%. Whether this
system will detect drug-resistant strains in Botswana by 2009 will depend upon
the transmissibility of the strains that emerge. Our results imply that it
could be many years before the WHO detects transmitted resistance in other
sub-Saharan African countries with less ambitious treatment programs than
Botswana. | 0512032v1 |
2020-04-10 | Strain-engineering the Schottky barrier and electrical transport on MoS2 | Strain provides an effective means to tune the electrical properties while
retaining the native chemical composition of the material. Unlike
three-dimensional solids, two-dimensional materials withstand higher levels of
elastic strain making it easier to tune various electrical properties to suit
the technology needs. In this work we explore the effect of uniaxial
tensile-strain on the electrical transport properties of bi- and few-layered
MoS2, a promising 2D semiconductor. Raman shifts corresponding to the in-plane
vibrational modes show a redshift with strain indicating a softening of the
in-plane phonon modes. Photo luminescence measurements reveal a redshift in the
direct and the indirect emission peaks signalling a reduction in the material
bandgap. Transport measurements show a substantial enhancement in the
electrical conductivity with a high piezoresistive gauge factor of ~ 321
superior to that for Silicon for our bi-layered device. The simulations
conducted over the experimental findings reveal a substantial reduction of the
Schottky barrier height at the electrical contacts in addition to the
resistance of MoS2. Our studies reveal that strain is an important and
versatile ingredient to tune the electrical properties of 2D materials and also
can be used to engineer high-efficiency electrical contacts for future device
engineering. | 2004.05061v1 |
2011-08-25 | Synthesis, Crystal Growth and Epitaxial Layer Deposition of FeSe0.88 Superconductor and Other Poison Materials by Use of High Gas Pressure Trap System | The FeSe samples in the form of polycrystals, single crystals and thin films
have been prepared and characterized. The synthesized material has been hot
isostatically pressed under pressure of 0.45 GPa of 5N purity argon with the
use of the high gas pressure trap system (HGPTS). Thin films have been
fabricated by the mixed procedures with the use of DC sputtering from various
types of targets and processed employing the HGPTS. The used HGPTS assures a
full separation of the active volume for synthesis or crystal growth of
material and the inert gas medium. The obtained FeSe0.88 samples have Tc
between 8 and 12 K. The samples have been characterized by SEM, EDX, XRD,
magnetic susceptibility and resistivity measurements. | 1108.5069v1 |
2021-07-19 | Making high-quality quantum microwave devices with van der Waals superconductors | Ultra low-loss microwave materials are crucial for enhancing quantum
coherence and scalability of superconducting qubits. Van der Waals (vdW)
heterostructure is an attractive platform for quantum devices due to the
single-crystal structure of the constituent two-dimensional (2D) layered
materials and the lack of dangling bonds at their atomically sharp interfaces.
However, new fabrication and characterization techniques are required to
determine whether these structures can achieve low loss in the microwave
regime. Here we report the fabrication of superconducting microwave resonators
using NbSe$_2$ that achieve a quality factor $Q > 10^5$. This value sets an
upper bound that corresponds to a resistance of $\leq 192 \mu\Omega$ when
considering the additional loss introduced by integrating NbSe$_2$ into a
standard transmon circuit. This work demonstrates the compatibility of 2D
layered materials with high-quality microwave quantum devices. | 2107.09147v3 |
2021-10-21 | Phonon anharmonicity: a pertinent review of recent progress and perspective | Anharmonic lattice vibrations govern the thermal dynamics in materials and
present how the atoms interact and how they conduct heat. An indepth
understanding of the microscopic mechanism of phonon anharmonicity in condensed
systems is critical for developing better functional and energy materials. In
recent years, a variety of novel behaviors in condense matters are driven by
phonon anharmonic effects in some way or another, such as soft mode phase
transition, negative thermal expansion, multiferroicity, ultralow thermal
conductivity or high thermal resistance, and high-temperature
superconductivity, etc. All these properties have endowed anharmonicity with
many promising applications and provided remarkable opportunities for
developing anharmonicity engineering, regulating heat transport towards
excellent performance in materials. In this work, we review the recent
development of the study on phonon anharmonic effect and summarize its
origination, influence and mechanism, research methods, and applications.
Besides, the remaining challenges, future trends, and prospects of phonon
anharmonicity are also put forward. | 2110.11094v1 |
2023-01-16 | Nonlinear transport in a photo-induced superconductor | Optically driven quantum materials exhibit a variety of non-equilibrium
functional phenomena [1-11], which are potentially associated with unique
transport properties. However, these transient electrical responses have
remained largely unexplored, primarily because of the challenges associated
with integrating quantum materials into ultrafast electrical devices. Here,
thin films of K3C60 grown by Molecular Beam Epitaxy were connected by coplanar
terahertz waveguides to a series of photo-conductive switches. This geometry
enabled ultrafast transport measurements at high current densities, providing
new information on the photo-induced phase created in the high temperature
metal by mid-infrared excitation [12-16]. Nonlinearities in the current-voltage
charactersitics of the transient state validate the assignment of transient
superconductivity, and point to an inhomogeneous phase in which superconducting
regions of the sample are connected by resistive weak links [17-23]. This work
opens up the possibility of systematic transport measurements in driven quantum
materials, both to probe their properties and to integrate them into ultrafast
optoelectronic platforms. | 2301.06425v1 |
2015-09-03 | On the Concept of Cryptographic Quantum Hashing | In the paper we define a notion of quantum resistant
($(\epsilon,\delta)$-resistant) hash function which combine together a notion
of pre-image (one-way) resistance ($\epsilon$-resistance) property we define in
the paper and the notion of collision resistance ($\delta$-resistance)
properties.
We show that in the quantum setting a one-way resistance property and
collision resistance property are correlated: the "more" a quantum function is
one-way resistant the "less" it collision resistant and vice versa. We present
an explicit quantum hash function which is "balanced" one-way resistant and
collision resistant and demonstrate how to build a large family quantum hash
functions. Balanced quantum hash functions need a high degree of entanglement
between the qubits. We use a "phase constructions" technique to express quantum
hashing constructions, which is good to map hash states to coherent states in a
superposition of time-bin modes. The later is ready to be implemented with
current optical technology. | 1509.01268v2 |
2019-12-11 | Observation of excess resistance anomaly at resistive transitions in Ag/Au nanostructures | The resistive transition in nanocomposite films of silver (Ag) nanoclusters
of ~ 1 nm diameter embedded in gold (Au) matrix exhibits an anomalous
resistance peak at the onset of the transition, even for transition
temperatures as high as 260 K. The maximum value of the resistance ranges
between ~ 30% - 300% above that of the normal state depending on devices as
well as lead configuration within a single device. The excess resistance regime
was observed in about 10% of the devices, and extends from ~ 10 - 100 K.
Application of magnetic field of 9 T was found to partially suppress the excess
resistance. From the critical current behavior, as well as negative
differential resistance in the current-voltage characteristics, we discuss the
possibility of interacting phase slip centers and alternate physical scenarios
that may cause the excess resistance in our system. | 1912.05428v1 |
2020-08-13 | Properties of materials considered for improvised masks | During a pandemic in which aerosol and droplet transmission is possible, the
demand for masks that meet medical or workplace standards can prevent most
individuals or organizations from obtaining suitable protection. Cloth masks
are widely believed to impede droplet and aerosol transmission but most are
constructed from materials with unknown filtration efficiency, airflow
resistance and water resistance. Further, there has been no clear guidance on
the most important performance metrics for the materials used by the general
public (as opposed to high-risk healthcare settings). Here we provide data on a
range of common fabrics that might be used to construct masks. None of the
materials were suitable for masks meeting the N95 NIOSH standard, but many
could provide useful filtration (>90%) of 3 micron particles (a plausible
challenge size for human generated aerosols), with low pressure drop. These
were: nonwoven sterile wraps, dried baby wipes and some double-knit cotton
materials. Decontamination of N95 masks using isopropyl alcohol produces the
expected increase in particle penetration, but for 3 micron particles,
filtration efficiency is still well above 95%. Tightly woven thin fabrics,
despite having the visual appearance of a good particle barrier, had remarkably
low filtration efficiency and high pressure drop. These differences in
filtration performance can be partly explained by the material structure; the
better structures expose individual fibers to the flow while the poor materials
may have small fundamental fibers but these are in tightly bundled yarns. The
fit and use of the whole mask are critical factors not addressed in this work.
Despite the complexity of the design of a very good mask, it is clear that for
the larger aerosol particles, any mask will provide substantial protection to
the wearer and those around them. | 2008.06001v1 |
2022-06-01 | A Pseudo-Two-Dimensional (P2D) Model for FeS2 Conversion Cathode Batteries | Conversion cathode materials are gaining interest for secondary batteries due
to their high theoretical energy and power density. However, practical
application as a secondary battery material is currently limited by practical
issues such as poor cyclability. To better understand these materials, we have
developed a pseudo-two-dimensional model for conversion cathodes. We apply this
model to FeS2 - a material that undergoes intercalation followed by conversion
during discharge. The model is derived from the half-cell Doyle-Fuller-Newman
model with additional loss terms added to reflect the converted shell
resistance as the reaction progresses. We also account for polydisperse active
material particles by incorporating a variable active surface area and
effective particle radius. Using the model, we show that the leading loss
mechanisms for FeS2 are associated with solid-state diffusion and electrical
transport limitations through the converted shell material. The polydisperse
simulations are also compared to a monodisperse system, and we show that
polydispersity has very little effect on the intercalation behavior yet leads
to capacity loss during the conversion reaction. We provide the code as an
open-source Python Battery Mathematical Modelling (PyBaMM) model that can be
used to identify performance limitations for other conversion cathode
materials. | 2206.00647v2 |
2024-03-12 | Physics-Transfer Learning for Material Strength Screening | The strength of materials, like many problems in the natural sciences, spans
multiple length and time scales, and the solution has to balance accuracy and
performance. Peierls stress is one of the central concepts in crystal
plasticity that measures the strength through the resistance of a dislocation
to plastic flow. The determination of Peierls stress involves a multiscale
nature depending on both elastic lattice responses and the energy landscape of
crystal slips. Material screening by strength via the Peierls stress from
first-principles calculations is computationally intractable for the nonlocal
characteristics of dislocations, and not included in the state-of-the-art
computational material databases. In this work, we propose a physics-transfer
framework to learn the physics of crystal plasticity from empirical atomistic
simulations and then predict the Peierls stress from chemically accurate
density functional theory-based calculations of material parameters. Notably,
the strengths of single-crystalline metals can be predicted from a few
single-point calculations for the deformed lattice and on the {\gamma} surface,
allowing efficient, high-throughput screening for material discovery.
Uncertainty quantification is carried out to assess the accuracy of models and
sources of errors, showing reduced physical and system uncertainties in the
predictions by elevating the fidelity of training models. This physics-transfer
framework can be generalized to other problems facing the accuracy-performance
dilemma, by harnessing the hierarchy of physics in the multiscale models of
materials science. | 2403.07526v1 |
2016-06-25 | Observation of Optical and Electrical In-plane Anisotropy in High-mobility Few-layer ZrTe5 | Transition metal pentatelluride ZrTe5 is a versatile material in
condensed-matter physics and has been intensively studied since the 1980s. The
most fascinating feature of ZrTe5 is that it is a 3D Dirac semimetal which has
linear energy dispersion in all three dimensions in momentum space.
Structure-wise, ZrTe5 is a layered material held together by weak interlayer
van der Waals force. The combination of its unique band structure and 2D atomic
structure provides a fertile ground for more potential exotic physical
phenomena in ZrTe5 related to 3D Dirac semimentals. However the physical
properties of its few-layer form have yet to be thoroughly explored. Here we
report strong optical and electrical in-plane anisotropy of mechanically
exfoliated few-layer ZrTe5. Raman spectroscopy shows significant intensity
change with sample orientations, and the behavior of angle-resolved phonon
modes at the gamma point is explained by theoretical calculation. DC
conductance measurement indicates a 50% of difference along different in-plane
directions. The diminishing of resistivity anomaly in few-layer samples
indicates the evolution of band structure with reduced thickness.
Low-temperature Hall experiment sheds lights on more intrinsic anisotropic
electrical transport, with hole mobility of 3,000 and 1,500 cm2/Vs along a-axis
and c-axis respectively. Pronounced quantum oscillations in magneto-resistance
are observed at low temperatures with highest electron mobility up to 44,000
cm2/Vs. | 1606.07960v2 |
2018-09-25 | Intrinsic Insulating Ground State in Transition Metal Dichalcogenide TiSe2 | The transition metal dichalcogenide TiSe$_2$ has received significant
research attention over the past four decades. Different studies have presented
ways to suppress the 200~K charge density wave transition, vary low temperature
resistivity by several orders of magnitude, and stabilize magnetism or
superconductivity. Here we give the results of a new synthesis technique
whereby samples were grown in a high pressure environment with up to 180~bar of
argon gas. Above 100~K, properties are nearly unchanged from previous reports,
but a hysteretic resistance region that begins around 80~K, accompanied by
insulating low temperature behavior, is distinct from anything previously
observed. An accompanying decrease in carrier concentration is seen in Hall
effect measurements, and photoemission data show a removal of an electron
pocket from the Fermi surface in an insulating sample. We conclude that high
inert gas pressure synthesis accesses an underlying nonmetallic ground state in
a material long speculated to be an excitonic insulator. | 1809.09467v2 |
2018-08-24 | Data-driven Exploration of New Pressure-induced Superconductivity in PbBi$_2$Te$_4$ with Two Transition Temperatures | Candidates compounds for new thermoelectric and superconducting materials,
which have narrow band gap and flat bands near band edges, were exhaustively
searched by the high-throughput first-principles calculation from an inorganic
materials database named AtomWork. We focused on PbBi$_2$Te$_4$ which has the
similar electronic band structure and the same crystal structure with those of
a pressure-induced superconductor SnBi2Se4 explored by the same data-driven
approach. The PbBi$_2$Te$_4$ was successfully synthesized as single crystals
using a melt and slow cooling method. The core level X-ray photoelectron
spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in
PbBi$_2$Te$_4$. The thermoelectric properties of the PbBi$_2$Te$_4$ sample were
measured at ambient pressure and the electrical resistivity was also evaluated
under high pressure using a diamond anvil cell with boron-doped diamond
electrodes. The resistivity decreased with increase of the pressure, and two
pressure-induced superconducting transitions were discovered at 3.4 K under
13.3 GPa and at 8.4 K under 21.7 GPa. The data-driven approach shows promising
power to accelerate the discovery of new thermoelectric and superconducting
materials. | 1808.07973v1 |
2021-03-17 | Multi-level resistance switching and random telegraph noise analysis of nitride based memristors | Resistance switching devices are of special importance because of their
application in resistive memories (RRAM) which are promising candidates for
replacing current nonvolatile memories and realize storage class memories.
These devices exhibit usually memristive properties with many discrete
resistance levels and implement artificial synapses. The last years,
researchers have demonstrated memristive chips as accelerators in computing,
following new in-memory and neuromorphic computational approaches. Many
different metal oxides have been used as resistance switching materials in MIM
or MIS structures. Understanding of the mechanism and the dynamics of
resistance switching is very critical for the modeling and use of memristors in
different applications. Here, we demonstrate the bipolar resistance switching
of silicon nitride thin films using heavily doped Si and Cu as bottom and
top-electrodes, respectively. Analysis of the current-voltage characteristics
reveal that under space-charge limited conditions and appropriate current
compliance setting, multi-level resistance operation can be achieved.
Furthermore, a flexible tuning protocol for multi-level resistance switching
was developed applying appropriate SET/RESET pulse sequences. Retention and
random telegraph noise measurements performed at different resistance levels.
The present results reveal the attractive properties of the examined devices. | 2103.09931v1 |
2021-10-28 | Spread and erase -- How electron hydrodynamics can eliminate the Landauer-Sharvin resistance | It has long been realized that even a perfectly clean electronic system
harbors a Landauer-Sharvin resistance, inversely proportional to the number of
its conduction channels. This resistance is usually associated with voltage
drops on the system's contacts to an external circuit. Recent theories have
shown that hydrodynamic effects can reduce this resistance, raising the
question of the lower bound of resistance of hydrodynamic electrons. Here we
show that by a proper choice of device geometry, it is possible to spread the
Landauer-Sharvin resistance throughout the bulk of the system, allowing its
complete elimination by electron hydrodynamics. We trace the effect to the
dynamics of electrons flowing in channels that terminate within the sample. For
ballistic systems this termination leads to back-reflection of the electrons
and creates resistance. Hydrodynamically, the scattering of these electrons off
other electrons allows them to transfer to transmitted channels and avoid the
resistance. Counter-intuitively, we find that in contrast to the ohmic regime,
for hydrodynamic electrons the resistance of a device with a given width can
decrease with its length, suggesting that a long enough device may have an
arbitrarily small total resistance. | 2110.15369v2 |
2005-08-04 | Subharmonic gap structures and Josephson effect in MgB2/Nb micro-constrictions | Superconducting micro-constrictions between Nb tips and high quality
MgB$_{2}$ pellets have been realized by means of a point-contact inset, driven
by a micrometric screw. Measurements of the current-voltage characteristics and
of the dynamical conductance versus bias have been performed in the temperature
range between 4.2 K and 500 K. Above the Nb critical temperature T$_{C}^{Nb}$,
the conductance of the MgB$_2$/normal-metal constrictions behaves as predicted
by the BTK model for low resistance contacts while high resistance junctions
show quasiparticle tunneling characteristics. Consistently, from the whole set
of data we infer the value $\Delta_{\pi} = 2.5 \pm 0.2$ meV for the
three-dimensional gap of MgB$_2$. Below T$_{C}^{Nb}$, low resistance contacts
show Josephson current and subharmonic gap structures (SGS), due to multiple
Andreev reflections. Simultaneous observations of both features, unambiguously
indicate coupling of the 3D band of MgB$_2$ with the Nb superconducting order
parameter. We found that the temperature dependence of the Josephson critical
current follows the classical Ambegaokar-Baratoff behavior with a value
$I_CR_N=(2.1 \pm 0.1)$ meV at low temperatures. | 0508137v2 |
2007-02-02 | Dependence of electronic structure of SrRuO3 and the degree of correlation on cation off-stoichiometry | We have grown and studied high quality SrRuO3 films grown by MBE as well as
PLD. By changing the oxygen activity during deposition we were able to make
SrRuO3 samples that were stoichiometric (low oxygen activity) or with ruthenium
vacancies (high oxygen activity). Samples with strontium vacancies were found
impossible to produce since the ruthenium would precipitate out as RuO2. The
volume of the unit cell of SrRuO3 becomes larger as more ruthenium vacancies
are introduced. The residual resistivity ratio (RRR) and room temperature
resistivity were found to systematically depend on the volume of the unit cell
and therefore on the amount of ruthenium vacancies. The RRR varied from ~30 for
stoichiometric samples to less than two for samples that were very ruthenium
poor. The room temperature resistivity varied from 190 microOhm cm for
stoichoimetric samples to over 300 microOhm cm for very ruthenium poor samples.
UPS spectra show a shift of weight from the coherent peak to the incoherent
peak around the Fermi level when samples have more ruthenium vacancies. Core
level XPS spectra of the ruthenium 3d lines show a strong screened part in the
case of stoichiometric samples. This screened part disappears when ruthenium
vacancies are introduced. Both the UPS and the XPS results are consistent with
the view that correlation increases as the amount of ruthenium vacancies
increase. | 0702050v1 |
2007-11-17 | Development of New Hole-Type Avalanche Detectors and the First Results of their Applications | We have developed a new detector of photons and charged particles- a
hole-type structure with electrodes made of a double layered resistive
material: a thin low resistive layer coated with a layer having a much higher
resistivity. One of the unique features of this detector is its capability to
operate at high gas gains (up to 10E4) in air or in gas mixtures with air. They
can also operate in a cascaded mode or be combined with other detectors, for
example with GEM. This opens new avenues in their applications. Several
prototypes of these devices based on new detectors and oriented on practical
applications were developed and successfully tested: a detector of soft X-rays
and alpha particles, a flame sensor, a detector of dangerous gases. All of
these detectors could operate stably even in humid air and/or in dusty
conditions. The main advantages of these detectors are their simplicity, low
cost and high sensitivity. For example, due to the avalanche multiplication,
the detectors of flames and dangerous gases have a sensitivity of 10-100 times
higher than commercial devices. We therefore believe that new detectors will
have a great future. | 0711.2747v1 |
2010-10-29 | Analytical method for parameterizing the random profile components of nanosurfaces imaged by atomic force microscopy | The functional properties of many technological surfaces in biotechnology,
electronics, and mechanical engineering depend to a large degree on the
individual features of their nanoscale surface texture, which in turn are a
function of the surface manufacturing process. Among these features, the
surface irregularities and self-similarity structures at different spatial
scales, especially in the range of 1 to 100 nm, are of high importance because
they greatly affect the surface interaction forces acting at a nanoscale
distance. An analytical method for parameterizing the surface irregularities
and their correlations in nanosurfaces imaged by atomic force microscopy (AFM)
is proposed. In this method, flicker noise spectroscopy - a statistical physics
approach - is used to develop six nanometrological parameters characterizing
the high-frequency contributions of jump- and spike-like irregularities into
the surface texture. These contributions reflect the stochastic processes of
anomalous diffusion and inertial effects, respectively, in the process of
surface manufacturing. The AFM images of the texture of corrosion-resistant
magnetite coatings formed on low-carbon steel in hot nitrate solutions with
coating growth promoters at different temperatures are analyzed. It is shown
that the parameters characterizing surface spikiness are able to quantify the
effect of process temperature on the corrosion resistance of the coatings. It
is suggested that these parameters can be used for predicting and
characterizing the corrosion-resistant properties of magnetite coatings. | 1010.6232v1 |
2013-04-04 | Non-contact method for measurement of the microwave conductivity of graphene | We report a non-contact method for conductivity and sheet resistance
measurements of graphene samples using a high Q microwave dielectric resonator
perturbation technique, with the aim of fast and accurate measurement of
microwave conductivity and sheet resistance of monolayer and few layers
graphene samples. The dynamic range of the microwave conductivity measurements
makes this technique sensitive to a wide variety of imperfections and
impurities and can provide a rapid non-contacting characterisation method.
Typically the graphene samples are supported on a low-loss dielectric
substrate, such as quartz, sapphire or SiC. This substrate is suspended in the
near-field region of a small high Q sapphire puck microwave resonator. The
presence of the graphene perturbs both centre frequency and Q value of the
microwave resonator. The measured data may be interpreted in terms of the real
and imaginary components of the permittivity, and by calculation, the
conductivity and sheet resistance of the graphene. The method has great
sensitivity and dynamic range. Results are reported for graphene samples grown
by three different methods: reduced graphene oxide (GO), chemical vapour
deposition (CVD) and graphene grown epitaxially on SiC. The latter method
produces much higher conductivity values than the others. | 1304.1304v1 |
2016-02-03 | Robust tunability of magnetorestance in Half-Heusler RPtBi (R = Gd, Dy, Tm, and Lu) compounds | We present the magnetic field dependencies of transport properties for
$R$PtBi ($R$ = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature and
field dependent resistivity measurements of high quality $R$PtBi single
crystals reveal an unusually large, non-saturating magnetoresistance (MR) up to
300 K under a moderate magnetic field of $H$ = 140 kOe. At 300 K, the large MR
effect decreases as the rare-earth is traversed from Gd to Lu and the magnetic
field dependence of MR shows a deviation from the conventional $H^{2}$
behavior. The Hall coefficient ($R_{H}$) for $R$ = Gd indicates a sign change
around 120 K, whereas $R_{H}$ curves for $R$ = Dy, Tm, and Lu remain positive
for all measured temperatures. At 300 K, the Hall resistivity reveals a
deviation from the linear field dependence for all compounds. Thermoelectric
power measurements on this family show strong temperature and magnetic field
dependencies which are consistent with resistivity measurements. A highly
enhanced thermoelectric power under applied magnetic field is observed as high
as $\sim$100 $\mu$V/K at 140 kOe. Analysis of the transport data in this series
reveals that the rare-earth-based Half-Husler compounds provide opportunities
to tune MR effect through lanthanide contraction and to elucidate the mechanism
of non-trivial MR. | 1602.01194v1 |
2018-06-07 | A Timing RPC with low resistive ceramic electrodes | For precise start time determination a Beam Fragmentation T$_0$ Counter
(BFTC) is under development for the Time-of-Flight Wall of the Compressed
Baryonic Matter Spectrometer (CBM) at the Facility for Antiproton and Ion
Research (FAIR) at Darmstadt/Germany. This detector will be located around the
beam pipe, covering the front area of the Projectile Spectator Detector. The
fluxes at this region are expected to exceed 10$^5$cm$^{-2}$s$^{-1}$. Resistive
plate chambers (RPC) with ceramic composite electrodes could be use because of
their high rate capabilities and radiation hardness of material. Efficiency
$\ge$ 97\%, time resolution $\le$ 90 ps and rate capability $\ge$
10$^5$cm$^{-2}$s$^{-1}$ were confirmed during many tests with high beam fluxes
of relativistic electrons. We confirm the stability of these characteristics
with low resistive Si$_3$N$_4$/SiC floating electrodes for a prototype of eight
small RPCs, where each of them contains six gas gaps. The active RPC size
amounts 20$\times$20 mm$^2$ produced on basis of Al$_3$O$_2$ and
Si$_3$N$_4$/SiC ceramics. Recent test results obtained with relativistic
electrons at the linear accelerator ELBE of the Helmholtz-Zentrum
Dresden-Rossendorf with new PADI-10 Front-end electronic will be presented. | 1806.02629v2 |
2019-05-07 | Single-parameter scaling in the magnetoresistance of optimally doped La$_{2-x}$Sr$_{x}$CuO$_4$ | We show that the recent magnetoresistance data on thin-film
La$_{2-x}$Sr$_{x}$CuO$_4$ (LSCO) in strong magnetic fields ($B$) obeys a
single-parameter scaling of the form MR$(B,T)=f(\mu_H(T)B)$, where
$\mu_H^{-1}(T)\sim T^{\alpha}$ ($1\le\alpha\le2$), from $T=180$K until
$T\sim20$K, at which point the single-parameter scaling breaks down. The
functional form of the MR is distinct from the simple quadratic-to-linear
quadrature combination of temperature and magnetic field found in the optimally
doped iron superconductor BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$. Further,
low-temperature departure of the MR in LSCO from its high-temperature scaling
law leads us to conclude that the MR curve collapse is not the result of
quantum critical scaling. We examine the classical effective medium theory
(EMT) previously used to obtain the quadrature resistivity dependence on field
and temperature for metals with a $T$-linear zero-field resistivity. It appears
that this scaling form results only for a binary, random distribution of
metallic components. More generally, we find a low-temperature, high-field
region where the resistivity is simultaneously $T$ and $B$ linear when multiple
metallic components are present. Our findings indicate that if mesoscopic
disorder is relevant to the magnetoresistance in strange metal materials, the
binary-distribution model which seems to be relevant to the iron pnictides is
distinct from the more broad-continuous distributions relevant to the cuprates.
Using the latter, we examine the applicability of classical effective medium
theory to the MR in LSCO and compare calculated MR curves with the experimental
data. | 1905.02737v1 |
2021-01-18 | Intrinsic hysteresis in the presumed superconducting transition of hydrides under high pressure | Superconducting transitions in the absence of magnetic field should be
non-hysteretic. Here we address the fact that the drops in electrical
resistance that have been interpreted as evidence of superconductivity in
several hydrides under high pressure (so-called "superhydrides") show
hysteresis. We argue that the experimental evidence shows that the observed
hysteresis cannot be attributed to experimental artifacts but is intrinsic to
the samples. Assuming that the drops in resistance signal a thermodynamic phase
transition, we argue that the presence of intrinsic thermal hysteresis
indicates that these are first order transitions, whereas for standard
superconductors the transition in the absence of applied magnetic field is
always second order. We conclude that this is another feature that
qualitatively distinguishes superhydrides from standard superconductors, in
addition to the ones that have been pointed out earlier [1,2], $assuming$ these
materials are superconductors. Alternatively and more likely, whether or not
the drops in resistance signal a thermodynamic phase transition, our analysis
indicates that superhydrides are not superconductors. | 2101.07208v4 |
2021-03-27 | Tesla's fluidic diode and the electronic-hydraulic analogy | Reasoning by analogy is powerful in physics for students and researchers
alike, a case in point being electronics and hydraulics as analogous studies of
electric currents and fluid flows. Around 100 years ago, Nikola Tesla proposed
a flow control device intended to operate similarly to an electronic diode,
allowing fluid to pass easily in one direction but providing high resistance in
reverse. Here we use experimental tests of Tesla's diode to illustrate
principles of the electronic-hydraulic analogy. We design and construct a
differential pressure chamber (akin to a battery) that is used to measure flow
rate (current) and thus resistance of a given pipe or channel (circuit
element). Our results prove the validity of Tesla's device, whose anisotropic
resistance derives from its asymmetric internal geometry interacting with
high-inertia flows, as quantified by the Reynolds number (here, Re ~ 1e3).
Through the design and testing of new fluidic diodes, we explore the
limitations of the analogy and the challenges of shape optimization in fluid
mechanics. We also provide materials that may be incorporated into lesson plans
for fluid dynamics courses, laboratory modules and further research projects. | 2103.14813v1 |
2021-08-19 | Measurement of the Low-temperature Loss Tangent of High-resistivity Silicon with a High Q-factor Superconducting Resonator | In this letter, we present the direct loss tangent measurement of a
high-resistivity intrinsic (100) silicon wafer in the temperature range from ~
70 mK to 1 K, approaching the quantum regime. The measurement was performed
using a technique that takes advantage of a high quality factor superconducting
niobium resonator and allows to directly measure the loss tangent of insulating
materials with high level of accuracy and precision. We report silicon loss
tangent values at the lowest temperature and for electric field amplitudes
comparable to those found in planar transmon devices one order of magnitude
larger than what was previously estimated. In addition, we discover a
non-monotonic trend of the loss tangent as a function of temperature that we
describe by means of a phenomenological model based on variable range hopping
conduction between localized states around the Fermi energy. We also observe
that the dissipation increases as a function of the electric field and that
this behavior can be qualitatively described by the variable range hopping
conduction mechanism as well. This study lays the foundations for a novel
approach to investigate the loss mechanisms and accurately estimate the loss
tangent in insulating materials in the quantum regime, leading to a better
understanding of coherence in quantum devices. | 2108.08894v5 |
2007-06-01 | High-Tc superconductivity originated from strong spin-charge correlation: indication from linear temperature dependence of resistivity | Both the highest- and the linear temperature dependence of the resistivity in
wide temperature range appear at the optimally doped regions of Cu-based
superconductors1,2,3,4,5, and the highest- of Fe-based superconductors6,7 are
also associated with the linear temperature dependence of the resistivity in
normal states near superconducting states. This means that the high temperature
superconductivity and the linear temperature dependence of the resistivity
should be dominated by the same mechanism. This letter on theoretic calculation
clearly shows that strong spin-charge correlation dominated resistivity behaves
the linear temperature dependence, thus high-temperature superconductivity
should be induced by strong spin-charge correlation. | 0706.0059v2 |
2023-08-30 | Investigation of W-SiC compositionally graded films as a divertor material | W-SiC composite material is a promising plasma-facing material candidate
alternative to pure W due to the low neutron activation, low impurity
radiation, and low tritium diffusivity of SiC while leveraging the high erosion
resistance of the W armor. Additionally, W and SiC have high thermomechanical
compatibility given their similar thermal expansion rates. The present study
addresses the synthesis and performance of compositionally graded W-SiC films
fabricated by pulsed-DC magnetron sputtering. Compositional gradients were
characterized using transmission electron microscopy (TEM) and
energy-dispersive X-ray spectroscopy (EDS), and crystallographic information
was obtained using electron diffraction and X-ray diffraction (XRD). Samples
were exposed to L-mode deuterium plasma discharges in the DIII-D tokamak using
the Divertor Material Evaluation System (DiMES). Post-mortem characterizations
were performed using scanning electron microscopy (SEM) and XRD. Electron
diffraction and XRD showed that the compositionally graded W-SiC films were
composed of polycrystalline W and amorphous SiC with amorphous W+SiC
interlayers. No macroscopic delamination or microstructural changes were
observed under mild exposure conditions. This study serves as a preliminary
examination of W-SiC compositionally graded composites as a potential candidate
divertor material in future tokamak devices. | 2308.16358v2 |
1999-09-28 | Magnetotransport properties of (Ga,Mn)As investigated at low temperature and high magnetic field | Magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As have
been investigated. Measurements at low temperature (50 mK) and high magnetic
field (<= 27 T) have been employed in order to determine the hole concentration
p = 3.5x10^20 cm ^-3 of a metallic (Ga0.947Mn0.053)As layer. The analysis of
the temperature and magnetic field dependencies of the resistivity in the
paramagnetic region was performed with the use of the above value of p, which
gave the magnitude of p-d exchange energy |N0beta | ~ 1.5 eV. | 9909393v1 |
2003-09-28 | Electron-Phonon Scattering in Metallic Single-Walled Carbon Nanotubes | Electron scattering rates in metallic single-walled carbon nanotubes are
studied using an atomic force microscope as an electrical probe. From the
scaling of the resistance of the same nanotube with length in the low and high
bias regimes, the mean free paths for both regimes are inferred. The observed
scattering rates are consistent with calculations for acoustic phonon
scattering at low biases and zone boundary/optical phonon scattering at high
biases. | 0309641v1 |
1998-10-26 | High frequency magneto-impedance of double perovskite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$: secondary transitions at high temperatures | Radio frequency magneto-impedance measurements clearly reveal a pronounced
anomaly at 260K besides the main MI transition at 125K in the double perovskite
material $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$. This feature is not seen clearly in
static resistivity and magnetization measurements. We suggest that this anomaly
represents short range magnetic correlations enhanced at radio frequencies,
with the easy axis along the c-axis . | 9810351v2 |
1999-04-29 | Consilience of High-Tc Theories | Improvements both in the quality and in the variety of experiments on
high-temperature superconductors have yielded new insights into the microscopic
origins of pairing. A number of competing theories have already been ruled out.
Some of the more promising descriptions -- gauge theories, coupled-chains,
nesting instabilities, nodal liquids, and stripes -- share features in common.
A unified picture of the cuprates is beginning to emerge. | 9904437v1 |
1999-09-03 | A thermostable trilayer resist for niobium lift-off | We have developped a novel lift-off process for fabrication of high quality
superconducting submicron niobium structures. The process makes use of a
thermostable polymer with a high transition temperature T_{g}= 235 C and an
excellent chemical stability. The superconducting critical temperature of 100
nm wide niobium lines is above 7 K. An example of shadow evaporation of a Nb-Cu
submicron hybrid structure is given. A potential application of this process is
the fabrication of very small single electron devices using refratory metals. | 9909053v1 |
2003-10-29 | Ultrasonic Defect Modification in Irradiated Silicon | It is shown for the first time, that room temperature Ultrasonic Defect
Manipulation (UDM) can significantly reduce the concentration of radiation
defects in high resistivity silicon. Secondary Ion Mass Spectroscopy revealed
that oxygen- and hydrogen- related chemical reactions in silicon are likely to
occur under UDM at room temperature. Ultrasonically stimulated chemical
reactions in solids can be an important source of energy, which is required for
UDM. | 0310675v1 |
2004-08-24 | Barrier layer formation and PTCR effect in (1-x) Pb(Fe1/2Nb1/2)O3]-xPbTiO3 (x = 0.13) ceramics | (1-x)Pb(Fe1/2Nb1/2)O3-PbTiO3(PFN-xPT)Ceramics with x = 0.13 sintered at 1473K
show diffuse phase transition and very high dielectric constant at lower
frequencies.The high value of dielectric constant at lower frequencies is shown
to be due to the barrier layer formation.The resistivity of the PFN-xPT
ceramics, obtained by complex impedance analysis, initially decreases with
temperature and then shows an upward trend beyond the ferroelectric Curie point
reminiscent of BaTiO3 based thermistors with PTCR effect. | 0408509v1 |
2005-02-06 | Model for a Macroscopically Disordered Conductor with an Exactly Linear High-Field Magnetoresistance | We calculate the effective resistivity of a macroscopically disordered two
dimensional conductor consisting of two components in a perpendicular magnetic
field. When two components have equal area fractions, we use a duality theorem
to show that the magnetoresistance is non-saturating and at high fields varies
exactly linearly with magnetic field. At other compositions, an effective
medium calculation leads to a saturating magnetoresistance. We briefly discuss
possible connections between these results and magnetoresistance measurements
on heavily disordered chalconide semiconductors. | 0502162v2 |
2007-07-28 | Performances of a Newly High Sensitive Trilayer F/Cu/F GMI Sensor | We have selected stress-annealed nanocrystalline Fe-based ribbons for
ferromagnetic/copper/ferromagnetic sensors exhibiting high magneto-impedance
ratio. Longitudinal magneto-impedance reaches 400% at 60 kHz and longitudinal
magneto-resistance increases up to 1300% around 200 kHz. | 0707.4232v2 |
2009-09-25 | Spin Injection Enhancement Through Schottky Barrier Superlattice Design | We predict it is possible to achieve high-efficiency room-temperature spin
injection from a mag- netic metal into InAs-based semiconductors using an
engineered Schottky barrier based on an InAs/AlSb superlattice. The Schottky
barrier with most metals is negative for InAs and positive for AlSb. For such
metals there exist InAs/AlSb superlattices with a conduction band edge
perfectly aligned with the metal's Fermi energy. The initial AlSb layer can be
grown to the thickness required to produce a desired interface resistance. We
show that the conductivity and spin lifetimes of such superlattices are
sufficiently high to permit efficient spin injection from ferromagnetic metals. | 0909.4594v1 |
2009-11-29 | Current driven discontinuous insulator-metal transition and colossal low-field magnetoresistance in Sm0.6Sr0.4MnO3 | It is shown that with increasing magnitude of current (I), resistivity of
Sm0.6Sr0.4MnO3 transforms from a smooth to a discontinuous insulator-metal
transition which is also accompanied by an abrupt decrease in temperature of
the sample. We report colossal low-field magnetoresistance under a high current
bias (-99% at H = 0.5 T and 70 K) and electroresistance (-8000 % at H = 0 T and
60 K) for I = 11 mA. We interpret our observations in terms of current induced
supercooling of the high temperature paramagnetic phase and enlargement of
volume fraction of the ferromagnetic phase under a magnetic field. | 0911.5491v1 |
2010-03-26 | Superconductor terahertz metamaterial | We characterize the behaviour of split ring resonators made up of
high-transition temperature YBCO superconductor using terahertz time domain
spectroscopy. The superconductor metamaterial shows sharp change in the
transmission spectrum at the fundamental inductive-capacitive resonance and the
dipole resonance as the temperature dips below the transition temperature. Our
results reveal that the high performance of such a metamaterial is limited by
material imperfections and defects such as cracks, voids and secondary phases
which play dominant role in partially impeding the flow of current causing
dissipation of energy and electrical resistance to appear in the superconductor
film. | 1003.5169v1 |
2013-08-15 | Low Temperature Nanoscale Electronic Transport on the MoS_2 surface | Two-probe electronic transport measurements on a Molybdenum Disulphide
(MoS_2) surface were performed at low temperature (30K) under ultra-high vacuum
conditions. Two scanning tunneling microscope tips were precisely positioned in
tunneling contact to measure the surface current-voltage characteristics. The
separation between the tips is controllably varied and measured using a high
resolution scanning electron microscope. The MoS_2 surface shows a surface
electronic gap (E_S) of 1.4eV measured at a probe separation of 50nm.
Furthermore, the two- probe resistance measured outside the electronic gap
shows 2D-like behavior with the two-probe separation. | 1308.3299v1 |
2014-02-27 | Nonlinear conductivity in CaRuO3 thin films measured by short current pulses | Metals near quantum critical points have been predicted to display universal
out-of equilibrium behavior in the steady current-carrying state. We have
studied the non-linear conductivity of high-quality CaRuO$_3$ thin films with
residual resistivity ratio up to 57 using micro-second short, high-field
current pulses at low temperatures. Even for the shortest pulses of $5\mu$s,
Joule heating persists, making it impossible to observe a possible universal
non-linearity. Much shorter pulses are needed for the investigation of
universal non-linear conductivity. | 1402.6845v1 |
2015-02-02 | Electrical and magnetic properties of La$_{0.5}$Rh$_4$Sb$_{12}$ filled skutterudite synthesized at high pressure | A filled skutterudite, La$_{0.5}$Rh$_4$Sb$_{12}$, with a lattice constant of
9.284(2) {\AA} was synthesized using a high-pressure technique. The electrical
resistivity showed semiconducting behavior and the energy gap was estimated to
be more than 0.08 eV. Magnetic susceptibility measurements indicated
temperature-independent diamagnetism, which originates from Larmor
diamagnetism. The electrical properties of this compound are more similar to
those of the La$_{0.5}$Rh$_4$As$_{12}$ semiconductor with an energy gap of 0.03
eV than to those of the La$_{0.6}$Rh$_4$P$_{12}$ superconductor. | 1502.00337v2 |
2016-01-12 | Melting of B12P2 boron subphosphide under pressure | Melting of boron subphosphide (B12P2) to 26 GPa has been studied by in situ
synchrotron X-ray powder diffraction in a laser-heated diamond anvil cell, and
by quenching and electrical resistance measurements in a toroid-type
high-pressure apparatus. B12P2 melts congruently, and the melting curve has a
positive slope of 23(6) K/GPa. No solid-state phase transition was observed up
to the melting in the whole pressure range under study. | 1601.02930v1 |
2016-02-23 | Preparation of Silver and Silver-backing self-supported thin targets by high vacuum evaporation | We have produced in the Nuclear Physics Center in Lisbon thin film
self-supported targets of Ag, LiF/Ag and CaF$_2$/Ag by a high vacuum resistance
evaporation method. The production setup, materials, methods, characterization
and results are described. | 1602.07172v2 |
2016-05-09 | Highly Non-linear and Reliable Amorphous Silicon Based Back-to-Back Schottky Diode as Selector Device for Large Scale RRAM Arrays | In this work we present silicon process compatible, stable and reliable
($>10^{8}$cycles), high non-linearity ratio at half-read voltage ($>5\times
10^{5}$), high speed ($<60ns$) low operating voltage ($<2V$) back-to-back
Schottky diodes. Materials choice of electrode, thickness of semiconductor
layer and doping level are investigated by numerical simulation, experiments
and current-voltage equations to give a general design consideration when
back-to-back Schottky diodes are used as selector device for Resistive Random
Access Memory(RRAM) arrays. | 1605.02757v1 |
2016-07-19 | Performance Enhancement of Black Phosphorus Field-Effect Transistors by Chemical Doping | In this letter, a new approach to chemically dope black phosphorus (BP) is
presented, which significantly enhances the device performance of BP
field-effect transistors for an initial period of 18 h, before degrading to
previously reported levels. By applying
2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), low ON-state
resistance of 3.2 ohm.mm and high field-effect mobility of 229 cm2/Vs are
achieved with a record high drain current of 532 mA/mm at a moderate channel
length of 1.5 {\mu}m. | 1607.05760v1 |
2018-04-04 | Ultra-high Vacuum Deposition of Higher Manganese Silicide Mn4Si7 Thin Films | We have successfully grown one of the higher manganese silicides, Mn4Si7 thin
films on silicon (100) substrates using an ultra-high vacuum deposition with a
base pressure of 1x10-9 torr. The thickness of the film was varied from 65-100
nm. These films exhibit a tetragonal crystal structure and display paramagnetic
behavior as predicted for the stoichiometric Mn4Si7 system. They have a
resistivity of 3.321 x 10-5 ohm-m at room temperature and show a semi-metallic
nature. | 1804.01604v1 |
2018-04-09 | Superconductivity in REO0.5F0.5BiS2 with high-entropy-alloy-type blocking layers | We synthesized new REO0.5F0.5BiS2 (RE: rare earth) superconductors with the
high-entropy-alloy-type (HEA-type) REO blocking layers. According to the RE
concentration and the RE ionic radius, the lattice constant of a systematically
changed in the HEA-type samples. A sharp superconducting transition was
observed in the resistivity measurements for all the HEA-type samples, and the
transition temperature of the HEA-type samples was higher than that of typical
REO0.5F0.5BiS2. The sharp superconducting transition and the enhanced
superconducting properties of the HEA-type samples may indicate the
effectiveness of the HEA states of the REO blocking layers in the
REO0.5F0.5BiS2 system. | 1804.02880v2 |
2020-09-01 | Solute softening and vacancy generation by diffusion-less climb in magnesium alloys | Active room temperature diffusion-less climb of the <a> edge dislocations in
model Mg-Al alloys was observed using molecular dynamics simulations.
Dislocations on prismatic and pyramidal I planes climb through the basal plane
to overcome solute obstacles. This out-of-plane dislocation motion softens the
high resistance pyramidal I glide and significantly reduces the anisotropy of
dislocation mobility, and could help improve the ductility of Mg. The flow
stress scales linearly with solute concentration, cAl. Dislocations climb
predominantly in the negative direction, with climb angle on the order of
0.01cAl, producing very high vacancy concentration on the order of 10-4. | 2009.00656v1 |
2020-06-20 | Can an amorphous crystallize into a high entropy alloy? | On the premise that amorphous-HEA composites could demonstrate high toughness
and resistance to embrittlement akin to the phase separating glassy-solid
solution composites, we develop a thermodynamics based approach to identify
chemical compositions capable of undergoing the amorphous to HEA
transformation. We introduce two new parameters called phase selection value
(PSV) and molar volume dispersity parameter. Using this thermodynamic approach
seven multi-component compositions were proposed and the general guidelines for
identifying such compositions was established. The approach also reveals that
BMGs may not be as such amenable to undergo an amorphous to HEA transformation. | 2006.11579v1 |
2015-03-20 | Bottom-up assembly of metallic germanium | Extending chip performance beyond current limits of miniaturisation requires
new materials and functionalities that integrate well with the silicon
platform. Germanium fits these requirements and has been proposed as a
high-mobility channel material,[1] a light emitting medium in
silicon-integrated lasers,[2,3] and a plasmonic conductor for bio-sensing.[4,5]
Common to these diverse applications is the need for homogeneous, high electron
densities in three-dimensions (3D). Here we use a bottom-up approach to
demonstrate the 3D assembly of atomically sharp doping profiles in germanium by
a repeated stacking of two-dimensional (2D) high-density phosphorus layers.
This produces high-density (10^19 to 10^20 cm-3) low-resistivity (10^-4 Ohmcm)
metallic germanium of precisely defined thickness, beyond the capabilities of
diffusion-based doping technologies.[6] We demonstrate that free electrons from
distinct 2D dopant layers coalesce into a homogeneous 3D conductor using
anisotropic quantum interference measurements, atom probe tomography, and
density functional theory. | 1503.05994v1 |
2014-08-06 | Permanent magnet with MgB2 bulk superconductor | Superconductors with persistent zero-resistance currents serve as permanent
magnets for high-field applications requiring a strong and stable magnetic
field, such as magnetic resonance imaging (MRI). The recent global helium
shortage has quickened research into high-temperature superconductors (HTSs)
materials that can be used without conventional liquid-helium cooling to 4.2 K.
Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB2)
makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week
with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in
this magnet is uniformly distributed, as for single-crystalline
neodymium-iron-boron. Magnetic hysteresis loop of the MgB2 permanent bulk
magnet was detrmined. Because MgB2 is a simple-binary-line compound that does
not contain rare-earth metals, polycrystalline bulk material can be
industrially fabricated at low cost and with high yield to serve as strong
magnets that are compatible with conventional compact cryocoolers, making MgB2
bulks promising for the next generation of Tesla-class permanent-magnet
applications. | 1408.1277v1 |
2014-08-20 | In-situ hydrogen charging of zirconium powder to study isothermal percipitation of hydrides and determination of Zr-hydride crystal structure | Zirconium alloys are widely used in the nuclear industry because of their
high strength, good corrosion resistance and low neutron absorption
cross-section. However, zirconium has strong affinity for hydrogen which leads
to hydrogen concentration build-up over time. It is well known that the
formation of hydrides will degrade the material and leads to, for example,
delayed hydride cracking during high burn up. Even though zirconium hydrides
have been studied for several decades, there still remain some controversies
regarding the formation mechanisms, exact crystal structure, and stability of
various hydride phases. This study uses high resolution synchrotron radiation
as a probing tool to observe the precipitation and dissolution of hydrides in
highly pure zirconium powder during in-situ hydrogen charging. The experiment
enabled the direct observation of the hydride formation and phase
transformations. It, also, provided high quality data for crystal structure
determination. | 1408.4665v1 |
2022-12-02 | Ablation threshold and temperature dependent thermal conductivity of high entropy carbide thin films | High entropy carbides (HECs) are a promising new class of ultra-high
temperature ceramics that could provide novel material solutions for leading
edges of hypersonic vehicles, which can reach temperatures above 3500C and
experience extreme thermal gradients. Although the mechanical and thermal
properties of HECs have been studied extensively at room temperature, few works
have examined HEC properties at high temperatures or considered these
materials' responses to thermal shock. In this work, we measure the thermal
conductivity of a five-cation HEC up to 1200C. We find that thermal
conductivity increases with temperature, consistent with trends demonstrated in
single-metal carbides. We also measure thermal conductivity of an HEC deposited
with varying CH4 flow rate, and find that although thermal conductivity is
reduced when carbon content surpasses stoichiometric concentrations, the films
all exhibited the same temperature dependent trends regardless of carbon
content. To compare the thermal shock resistance of HECs with a refractory
carbide, we conduct pulsed laser ablation measurements to determine the fluence
threshold the HECs can withstand before damaging. We find that this metric for
the average bond strength trends with the theoretical hardness of the HECs as
expected. | 2212.01238v1 |
2023-10-18 | A New Class of Materials Based on Nanoporous High Entropy Alloys with Outstanding Properties | Nanoporous metals with a random, bicontinuous structure of both pores and
ligaments exhibit many unique mechanical properties, but their technical
applications are often limited by their intrinsic brittleness under tensile
strain triggered by fracture of the weakest ligaments. Here, we use molecular
dynamics simulations to study the mechanical behavior and thermal stability of
two different bicontinuous nanoporous high entropy alloys, Al0.1CoCrFeNi and
NbMoTaW. To isolate the properties related to the nanoporous nature of our
samples, we also studied the corresponding bulk and nanocrystalline systems.
The results demonstrate that the specific modulus of nanoporous HEAs are 2 to 3
times greater than that of single element nanoporous materials with specific
strength reaching values 5 to 10 times higher, comparable to bulk metals with
the highest specific strength. Bicontinuous HEAs also displayed excellent
resistance to thermal degradation as evidenced by the absence of coarsening
ligaments up to temperatures of 1273 K which ensures the durability and
reliability in high-temperature applications. The findings uncover
unprecedented mechanical and thermal properties of bicontinuous nanoporous high
entropy alloys, paving the way for their promising utilization in advanced
engineering and structural applications. | 2310.11937v1 |
1996-09-20 | High Temperature Thermopower in La_{2/3}Ca_{1/3}MnO_3 Films: Evidence for Polaronic Transport | Thermoelectric power, electrical resistivity and magnetization experiments,
performed in the paramagnetic phase of La_{2/3}Ca_{1/3}MnO_3, provide evidence
for polaron-dominated conduction in CMR materials. At high temperatures, a
large, nearly field-independent difference between the activation energies for
resistivity (rho) and thermopower (S), a characteristic of Holstein Polarons,
is observed, and ln(rho) ceases to scale with the magnetization. On approaching
T_c, both energies become field-dependent, indicating that the polarons are
magnetically polarized. Below T_c, the thermopower follows a law S(H) prop.
1/rho (H) as in non saturated ferromagnetic metals. | 9609212v1 |
2000-01-25 | Influence of high-energy electron irradiation on the transport properties of La_{1-x}Ca_{x}MnO_{3} films (x \approx 1/3) | The effect of crystal lattice disorder on the conductivity and colossal
magnetoresistance in La_{1-x}Ca_{x}MnO_{3} (x \approx 0.33) films has been
examined. The lattice defects are introduced by irradiating the film with
high-energy (\simeq 6 MeV) electrons with a maximal fluence of about 2\times
10^{17} cm^{-2}. This comparatively low dose of irradiation produces rather
small radiation damage in the films. The number of displacements per atom (dpa)
in the irradiated sample is about 10^{-5}. Nethertheless, this results in an
appreciable increase in the film resistivity. The percentage of resistivity
increase in the ferromagnetic metallic state (below the Curie tempetature
T_{c}) was much greater than that observed in the insulating state (above
T_{c}). At the same time irradiation has much less effect on T_{c} or on the
magnitude of the colossal magnetoresistance. A possible explanation of such
behavior is proposed. | 0001372v1 |
2001-07-27 | Lattice coupled first order magnetoresistance transition in an A-type antiferromagnet: Pr$_{0.46}$Sr$_{0.54}$MnO$_3$ | We investigated magnetic, magnetotransport and magnetostriction properties of
the A-type antiferromagnet Pr$_{0.46}$Sr$_{0.54}$MnO$_3$ which undergoes a
first order paramagnetic-antiferromagnetic transition below T$_N$ = 210 K while
cooling and T$_N$ = 215 K while warming. The zero field ($\mu_0$H = 0 T)
resistivity shows a sudden jump at T$_N$ and a small bump around T$_{max}$ =
220 K (\TEXTsymbol{>} T$_N$). T$_N$ shifts down and T$_{max}$ shifts up with
increasing $\mu_0$H. Magnetoresistance as high as -45-57 % at 7 T is found in
the temperature range 180 K-230 K. Isothermal measurements indicate that the
field induced antiferromagnetic to ferromagnetic transition below T$_N$ is
accompanied by a rapid decrease of the resistivity but increase of volume
($\Delta $V/V = +0.25 % at 180 K and 13.7 T). This lattice coupled
magnetoresistance transition is suggested due to the field induced structural
transition from the low volume orthorhombic to the high volume tetragonal
structure. | 0107560v1 |
2001-09-04 | Magnetotransport in a bi-crystal film of La_0.7Sr_0.3MnO_3 | Transport properties of an epitaxial film of La_0.7Sr_0.3MnO_3 (LSMO),
deposited epitaxially on a LaAlO_3 bi-crystal substrate having a misorientation
angle of 9.2 deg., have been studied.
The film was patterned into a meander containing 100 grain boundaries. The
resistivity of the sample exhibits two components; one originating from the
grain boundary regions, and one from the LSMO elements in the meander; the
latter contribution is similar to the resistivity of a reference epitaxial LSMO
film. The low (<0.5 T) and high (up to 6 T) field magnetoresistance was also
studied. The meander show a large low field magnetoresistance, increasing with
decreasing temperature, and a constant high field slope of the
magnetoconductance, results that are well explained by a two-step spin
polarized tunneling model. | 0109052v1 |
2002-08-20 | Fabrication and properties of gallium metallic photonic crystals | Gallium metallic photonic crystals with 100% filling factor have been
fabricated via infiltration of liquid gallium into opals of 300-nm silica
spheres using a novel high pressure-high temperature technique. The electrical
resistance of the Ga-opal crystals was measured at temperatures from 10 to 280
K. The data obtained show that Ga-opal crystals are metallic network with
slightly smaller temperature coefficient of resistivity than that for bulk
gallium. Optical reflectivity of bulk gallium, plain opal and several Ga-opal
crystals were measured at photon energies from 0.3 to 6 eV. A pronounced
photonic stop band in the visible spectral range was found in both the plain
and Ga infiltrated opals. The reflectivity spectra also show increase in
reflectivity below 0.6 eV; which we interpret as a significantly lower
effective plasma frequency of the metallic mesh in the infiltrated opal compare
to the plasma frequency in the pure metal. | 0208392v1 |
2002-09-24 | High Curie temperature GaMnAs obtained by resistance-monitored annealing | We show that by annealing Ga1-xMnxAs thin films at temperatures significantly
lower than in previous studies, and monitoring the resistivity during growth,
an unprecedented high Curie temperature Tc and conductivity can be obtained. Tc
is unambiguously determined to be 118 K for Mn concentration x=0.05, 140 K for
x=0.06, and 120 K for x=0.08. We also identify a clear correlation between Tc
and the room temperature conductivity. The results indicate that Curie
temperatures significantly in excess of the current values are achievable with
improvements in growth and post-growth annealing conditions. | 0209554v1 |
2003-10-09 | RF Surface Resistance of a HIPped MgB2 Sample at 21 GHz | Magnesium diboride (MgB2) is attractive for RF cavity application for
particle accelerators because it might not show an increase of RF surface
losses at high magnetic surface fields, a phenomenon that has prevented high-Tc
superconducting materials such as YBCO from being used for this application. We
have measured the RF surface resistance (Rs) at 21 GHz of a MgB2 sample
fabricated using Hot Isostatic Press (HIP) at 200 MPa and 1000 C. The results
show that polishing with 0.1-micron diamond lapping film followed by a 1500-psi
DI water rinse in a clean room reduced the Rs by a factor of 6.2 at 15 K and it
is the lowest compared to other published data. The Rs data near the lowest
temperature (~13 K) scatter between 0.6 and 1.3 mOhm. The penetration depth and
energy gap were estimated to be 263 nm and 1.9-2.7, respectively, for the
polished surface. | 0310213v1 |
2004-08-31 | Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta | By lithographically fabricating an optimised Wheatstone bridge geometry, we
have been able to make accurate measurements of the resistance of grain
boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition
temperature, Tc, and room temperature. Below Tc the normal state properties
were assessed by applying sufficiently high currents. The behaviour of the
grain boundary resistance versus temperature and of the conductance versus
voltage are discussed in the framework charge transport through a tunnel
barrier. The influence of misorientation angle, oxygen content, and calcium
doping on the normal state properties is related to changes of the height and
shape of the grain boundary potential barrier. | 0409004v1 |
2005-07-06 | Oxidation Resistant Germanium Nanowires: Bulk Synthesis, Long Chain Alkanethiol Functionalization and Langmuir-Blodgett Assembly | A simple method is developed to synthesize gram quantities of uniform Ge
nanowires (GeNWs) by chemical vapor deposition on preformed, monodispersed
seed-particles loaded onto high surface area silica support. Various chemical
functionalization schemes are investigated to passivate the GeNW surfaces using
alkanethiols and alkyl Grignard reactions. The stability of functionalization
against oxidation of germanium for various alkyl chain lengths is elucidated by
X-ray photoelectron spectroscopy. Among all schemes tested, long chain
alkanethiols (>=C12) are found to impart the most stable GeNW passivation
against oxidation upon extended exposure to ambient air. Further, the
chemically functionalized oxidation-resistant nanowires are soluble in organic
solvents and can be readily assembled into close-packed Langmuir-Blodgett films
potentially useful for future high performance electronic devices. | 0507145v2 |
2006-03-08 | Nanoscopic processes of Current Induced Switching in thin tunnel junctions | In magnetic nanostructures one usually uses a magnetic field to commute
between two resistance (R) states. A less common but technologically more
interesting alternative to achieve R-switching is to use an electrical current,
preferably of low intensity. Such Current Induced Switching (CIS) was recently
observed in thin magnetic tunnel junctions, and attributed to electromigration
of atoms into/out of the insulator. Here we study the Current Induced
Switching, electrical resistance, and magnetoresistance of thin
MnIr/CoFe/AlO$_x$/CoFe tunnel junctions. The CIS effect at room temperature
amounts to 6.9% R-change between the high and low states and is attributed to
nanostructural rearrangements of metallic ions in the electrode/barrier
interfaces. After switching to the low R-state some electro-migrated ions
return to their initial sites through two different energy channels. A low
(high) energy barrier of $\sim$0.13 eV ($\sim$0.85 eV) was estimated. Ionic
electromigration then occurs through two microscopic processes associated with
different types of ions sites/defects. Measurements under an external magnetic
field showed an additional intermediate R-state due to the simultaneous
conjugation of the MR (magnetic) and CIS (structural) effects. | 0603208v1 |
2007-04-13 | Counting and manipulating single electrons using a carbon nanotube transistor | We report on the electric measurements of an individual Au nanoparticle with
an ultra-high contact resistance of about $10^{19} \Omega$. The high-impedance
measurements have been carried out by counting the electrons that are
transferred onto the particle. In order to do this, a carbon nanotube is used
as the electrode for the supply of electrons but also as the detector of the
charge transfer. Measurements using single-electron detection allow us to
determine the separation between the electron states in the Au nanoparticle,
which is about 4 meV, consistent with the charging energy of the particle.
Single-electron detection with nanotubes offers great promise for the study of
electron transfer in highly resistive molecular systems. | 0704.1794v1 |
2007-07-17 | Positive and negative pressure effects on the magnetic ordering and the Kondo effect in the compound Ce2RhSi3 | The competition between magnetic ordering and the Kondo effect in Ce2RhSi3,
ordering antiferromagnetically at 7 K, is investigated by the measurements of
magnetization, heat capacity and electrical resistivity on the solid solutions,
Ce(2-x)La(x)RhSi3, Ce(2-y)Y(y)RhSi3, and Ce2RhSi(3-z)Ge(z), as well as by high
pressure studies on this compound. The trends in the Kondo and Neel temperature
variations among these alloys are compared to infer the roles of unit-cell
volume and electronic structure changes. On the basis of the results, we infer
that this compound lies at the peak of Doniach-magnetic-phase-diagram. The high
pressure electrical resistivity data indicate that the quantum critical point
for this compound is in the vicinity of 4 GPa. | 0707.2518v1 |
2007-09-05 | Thickness-dependence of the electronic properties in V2O3 thin films | High quality vanadium sesquioxide V2O3 films (170-1100 {\AA}) were grown
using the pulsed laser deposition technique on (0001)-oriented sapphire
substrates, and the effects of film thickness on the lattice strain and
electronic properties were examined. X-ray diffraction indicates that there is
an in-plane compressive lattice parameter (a), close to -3.5% with respect to
the substrate and an out-of-plane tensile lattice parameter (c) . The thin film
samples display metallic character between 2-300 K, and no metal-to-insulator
transition is observed. At low temperature, the V2O3 films behave as a strongly
correlated metal, and the resistivity (\rho) follows the equation \rho =\rho_0
+ A T^2, where A is the transport coefficient in a Fermi liquid. Typical values
of A have been calculated to be 0.14 \mu\Omega cm K^{-2}, which is in agreement
with the coefficient reported for V2O3 single crystals under high pressure.
Moreover, a strong temperature-dependence of the Hall resistance confirms the
electronic correlations of these V2O3 thin films samples. | 0709.0692v1 |
2008-06-09 | Superconductivity in single crystals of LaFePO | Single crystals of the compound LaFePO were prepared using a flux growth
technique at high temperatures. Electrical resistivity measurements reveal
metallic behavior and a resistive transition to the superconducting state at a
critical temperature T_c ~ 6.6 K. Magnetization measurements also show the
onset of superconductivity near 6 K. In contrast, specific heat measurements
manifest no discontinuity at T_c. These results lend support to the conclusion
that the superconductivity is associated with oxygen vacancies that alter the
carrier concentration in a small fraction of the sample, although
superconductivity characterized by an unusually small gap value can not be
ruled-out. Under applied magnetic fields, T_c is suppressed anisotropically for
fields perpendicular and parallel to the ab-plane, suggesting that the
crystalline anisotropy strongly influences the superconducting state.
Preliminary high-pressure measurements show that T_c passes through a maximum
of nearly 14 K at ~ 110 kbar, demonstrating that significantly higher T_c
values may be achieved in the phosphorus-based oxypnictides. | 0806.1265v2 |
2009-08-23 | Superconductivity at high Tc in neodymium-doped 1111-SrFeAsF system | Polycrystalline Sr1-xNdxFeAsF samples were prepared at various Nd-doping
levels using both a stoichiometric mixture of the starting materials and in
slight excess amounts of FeAs. Susceptibility and resistivity of the samples
were studied down to 4 K revealing a probable coexistence of superconductivity
and a magnetic ordering. Temperature dependence of resistivity for all the
Nd-doped samples shows the presence of a transition below 15 K most likely
originating from the magnetic ordering of Nd moments, while the
spin-density-wave anomaly at 175 K survives up to 0.35 Nd-doping.
Superconductivity only occurs above 0.40 Nd-doping with onset maximum Tc
reaching as high as 52 K. | 0908.3285v3 |
2011-06-29 | Hysteretic magnetoresistance and thermal bistability in a magnetic two-dimensional hole system | Colossal negative magnetoresistance and the associated field-induced
insulator-to-metal transition, the most characteristic features of magnetic
semiconductors, are observed in n-type rare earth oxides and chalcogenides,
p-type manganites, n-type and p-type diluted magnetic semiconductors (DMS) as
well as in quantum wells of n-type DMS. Here, we report on magnetostransport
studies of Mn modulation-doped InAs quantum wells, which reveal a magnetic
field driven and bias voltage dependent insulator-to-metal transition with
abrupt and hysteretic changes of resistance over several orders of magnitude.
These phenomena coexist with the quantised Hall effect in high magnetic fields.
We show that the exchange coupling between a hole and the parent Mn acceptor
produces a magnetic anisotropy barrier that shifts the spin relaxation time of
the bound hole to a 100 s range in compressively strained quantum wells. This
bistability of the individual Mn acceptors explains the hysteretic behaviour
while opening prospects for information storing and processing. At high bias
voltage another bistability, caused by the overheating of electrons10, gives
rise to abrupt resistance jumps. | 1106.5832v1 |
2011-09-06 | Evolution of transport properties of BaFe2-xRuxAs2 in a wide range of isovalent Ru substitution | The effects of isovalent Ru substitution at the Fe sites of BaFe2-xRuxAs2 are
investigated by measuring resistivity and Hall coefficient on high-quality
single crystals in a wide range of doping (0 < x < 1.4). Ru substitution
weakens the antiferromagnetic (AFM) order, inducing superconductivity for
relatively high doping level of 0.4 < x < 0.9. Near the AFM phase boundary, the
transport properties show non-Fermi-liquid-like behaviors with a
linear-temperature dependence of resistivity and a strong temperature
dependence of Hall coefficient with a sign change. Upon higher doping, however,
both of them recover conventional Fermi-liquid behaviors. Strong doping
dependence of Hall coefficient together with a small magnetoresistance suggest
that the anomalous transport properties can be explained in terms of
anisotropic charge carrier scattering due to interband AFM fluctuations rather
than a conventional multi-band scenario. | 1109.1083v1 |
2012-09-06 | High-temperature thermoelectric properties of the double-perovskite ruthenium oxide (Sr$_{1-x}$La$_x$)$_2$ErRuO$_6$ | We have prepared polycrystalline samples of (Sr$_{1-x}$La$_x$)$_2$ErRuO$_6$
and (Sr$_{1-x}$La$_x$)$_2$YRuO$_6$, and have measured the resistivity, Seebeck
coefficient, thermal conductivity, susceptibility and x-ray absorption in order
to evaluate the electronic states and thermoelectric properties of the doped
double-perovskite ruthenates. We have observed a large Seebeck coefficient of
-160 $\mu$V/K and a low thermal conductivity of 7 mW/cmK for $x$=0.1 at 800 K
in air. These two values are suitable for efficient oxide thermoelectrics,
although the resistivity is still as high as 1 $\Omega$cm. From the
susceptibility and x-ray absorption measurements, we find that the doped
electrons exist as Ru$^{4+}$ in the low spin state. On the basis of the
measured results, the electronic states and the conduction mechanism are
discussed. | 1209.1250v1 |
2012-10-12 | Simultaneous measurement of pressure evolution of crystal structure and superconductivity in FeSe0.92 using designer diamonds | Simultaneous high pressure x-ray diffraction and electrical resistance
measurements have been carried out on a PbO type {\alpha}-FeSe0.92 compound to
a pressure of 44 GPa and temperatures down to 4 K using designer diamond anvils
at synchrotron source. At ambient temperature, a structural phase transition
from a tetragonal (P4/nmm) phase to an orthorhombic (Pbnm) phase is observed at
11 GPa and the Pbnm phase persists up to 74 GPa. The superconducting transition
temperature (TC) increases rapidly with pressure reaching a maximum of ~28 K at
~ 6 GPa and decreases at higher pressures, disappearing completely at 14.6 GPa.
Simultaneous pressure-dependent x-ray diffraction and resistance measurements
at low temperatures show superconductivity only in a low pressure orthorhombic
(Cmma) phase of the {\alpha}-FeSe0.92. Upon increasing pressure at 10 K near
TC, crystalline phases change from a mixture of orthorhombic (Cmma) and
hexagonal (P63/mmc) to a high pressure orthorhombic (Pbnm) phase near 6.4 GPa
where TC is maximum. | 1210.3645v1 |
2012-11-20 | Optically excited multi-band conduction in LaAlO3/SrTiO3 heterostructures | The low-temperature resistance of a conducting LaAlO3/SrTiO3 interface with a
10 nm thick LaAlO3 film decreases by more than 50% after illumination with
light of energy higher than the SrTiO3 band-gap. We explain our observations by
optical excitation of an additional high mobility electron channel, which is
spatially separated from the photo-excited holes. After illumination, we
measure a strongly non-linear Hall resistance which is governed by the
concentration and mobility of the photo-excited carriers. This can be explained
within a two-carrier model where illumination creates a high-mobility electron
channel in addition to a low-mobility electron channel which exists before
illumination. | 1211.4778v1 |
2013-12-04 | Physical characteristics and cation distribution of NiFe2O4 thin films with high resistivity prepared by reactive co-sputtering | We fabricated NiFe2O thin films on MgAl2O4 (001) substrates by reactive dc
magnetron co-sputtering in a pure oxygen atmosphere at different substrate
temperatures. The film properties were investigated by various techniques with
a focus on their structure, surface topography, magnetic characteristics, and
transport properties. Structural analysis revealed a good crystallization with
epitaxial growth and low roughness and a similar quality as in films grown by
pulsed laser deposition. Electrical conductivity measurements showed high room
temperature resistivity (12 Ohmm), but low activation energy, indicating an
extrinsic transport mechanism. A band gap of about 1.55 eV was found by optical
spectroscopy. Detailed x-ray spectroscopy studies confirmed the samples to be
ferrimagnetic with fully compensated Fe moments. By comparison with multiplet
calculations of the spectra we found that the cation valencies are to a large
extent Ni2+ and Fe3+. | 1312.1086v1 |
2013-12-13 | Low-energy electronic properties of clean CaRuO$_3$: elusive Landau quasiparticles | We have prepared high-quality epitaxial thin films of CaRuO$_3$ with residual
resistivity ratios up to 55. Shubnikov-de Haas oscillations in the
magnetoresistance and a $T^2$ temperature dependence in the electrical
resistivity only below 1.5 K, whose coefficient is substantially suppressed in
large magnetic fields, establish CaRuO$_3$ as a Fermi liquid (FL) with
anomalously low coherence scale. Non-Fermi liquid (NFL) $T^{3/2}$ dependence is
found between 2 and 25 K. The high sample quality allows access to the
intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6
THz, the conductivity is Drude-like and can be modeled by FL concepts, while
for higher frequencies non-Drude behavior, inconsistent with FL predictions, is
found. This establishes CaRuO$_3$ as a prime example of optical NFL behavior in
the THz range. | 1312.3809v1 |
2017-10-18 | Near-thermal limit gating in heavily-doped III-V semiconductor nanowires using polymer electrolytes | Doping is a common route to reducing nanowire transistor on-resistance but
has limits. High doping level gives significant loss in gate performance and
ultimately complete gate failure. We show that electrolyte gating remains
effective even when the Be doping in our GaAs nanowires is so high that
traditional metal-oxide gates fail. In this regime we obtain a combination of
sub-threshold swing and contact resistance that surpasses the best existing
p-type nanowire MOSFETs. Our sub-threshold swing of 75 mV/dec is within 25% of
the room-temperature thermal limit and comparable with n-InP and n-GaAs
nanowire MOSFETs. Our results open a new path to extending the performance and
application of nanowire transistors, and motivate further work on improved
solid electrolytes for nanoscale device applications. | 1710.06950v2 |
2018-02-02 | Magneto-transport properties of proposed triply degenerate topological semimetal Pd$_{3}$Bi$_{2}$S$_{2}$ | We report transport properties of single-crystalline Pd$_{3}$Bi$_{2}$S$_{2}$,
which has been predicted to host an unconventional electronic phase of matter
beyond three-dimensional Dirac and Weyl semimetals. Similar to several
topological systems, the resistivity shows field induced
metal-semiconductor-like crossover at low temperature. Large, anisotropic and
non-saturating magnetoresistance (MR) has been observed in transverse
experimental configuration. At 2 K and 9 T, the MR value reaches as high as
$\sim$1.1$\times$10$^{3}$ \%. Hall resistivity reveals the presence of two
types of charge carriers and has been analyzed using two-band model. In spite
of the large density ($>$ 10$^{21}$ cm$^{-3}$), the mobility of charge carriers
is found to be quite high ($\sim$ 0.75$\times$10$^{4}$ cm$^{2}$ V$^{-1}$
s$^{-1}$ for hole and $\sim$ 0.3$\times$10$^{4}$ cm$^{2}$ V$^{-1}$ s$^{-1}$ for
electron). The observed magneto-electrical properties indicate that
Pd$_{3}$Bi$_{2}$S$_{2}$ may be a new member of the topological semimetal
family, which can have a significant impact in technological applications. | 1802.00712v2 |
2019-09-17 | Spin-Orbit-Torque Field-Effect Transistor (SOTFET): Proposal for a New Magnetoelectric Memory | Spin-based memories are attractive for their non-volatility and high
durability but provide modest resistance changes, whereas semiconductor logic
transistors are capable of large resistance changes, but lack memory function
with high durability. The recent availability of multiferroic materials
provides an opportunity to directly couple the change in spin states of a
magnetic memory to a charge change in a semiconductor transistor. In this work,
we propose and analyze the spin-orbit torque field-effect transistor (SOTFET),
a device with the potential to significantly boost the energy efficiency of
spin-based memories, and to simultaneously offer a palette of new
functionalities. | 1909.08133v3 |
2017-03-09 | Transport properties of iron at the Earth's core conditions: the effect of spin disorder | The electronic and thermal transport properties of the Earth's core are
crucial for many geophysical models such as the geodynamo model of the Earth's
magnetic field and of its reversals. Here we show, by considering bcc-iron and
iron-rich iron-silicon alloy as a representative of the Earth's core
composition and applying the first-principles modeling that the spin disorder
at the Earth's core conditions provides an essential contribution, of order
20~$\mu\Omega$\,cm, to the electrical resistivity. This value is comparable in
magnitude with the electron-phonon and with the recently estimated
electron-electron scattering contributions. The origin of the spin-disorder
resistivity (SDR) consists in the existence of fluctuating local moments that
are stabilized at high temperatures by the magnetic entropy even at pressures
at which the ground state of iron is non-magnetic. We find that electron-phonon
and SDR contributions are not additive at high temperatures. We thus observe a
large violation of the Matthiessen rule, not common in conventional metallic
alloys at ambient conditions. | 1703.03205v3 |
2020-04-07 | Large-scalable fabrication of improved Bi-Te-based flexible thermoelectric modules using a semiconductor manufacturing process | Among the several flexible thermoelectric modules in existence, sintered
Bi-Te-based modules represent a viable option because of their high output
power density and flexibility, which enables the use of arbitrary heat sources.
We have fabricated Bi-Te-based modules with a large-scalable fabrication
process and improved their output performance. The reduction in the
interconnection resistance, using thick electrodes of the flexible printed
circuit, significantly improves the module's output power to 87 mW/cm$^{2}$ at
$\Delta T$ = 70 K, which is 1.3-fold higher than a previous prototype module.
Furthermore, the establishment of the fabrication for the top electrodes by
using the surface mount technology makes it possible to realize a
high-throughput manufacturing of the module. Our durability tests reveal that
there is no significant change in the internal resistance of the module during
10000 cycles of mechanical bending test and 1000 cycles of thermal stress test. | 2004.03068v1 |
2020-09-24 | Pressure-Temperature Phase Diagram of $α$-Mn | Electrical resistivity and ac-susceptibility measurements under high pressure
were carried out in high-quality single crystals of $\alpha$-Mn. The
pressure-temperature phase diagram consists of an antiferromagnetic ordered
phase (0<$P$<1.4 GPa, $T<T_{\rm N}$), a pressure-induced ordered phase
(1.4<$P$<4.2-4.4 GPa, $T<T_{\rm A}$), and a paramagnetic phase. A significant
increase was observed in the temperature dependence of ac-susceptibility at
$T_{\rm A}$, indicating that the pressure-induced ordered phase has a
spontaneous magnetic moment. Ferrimagnetic order and parasitic ferromagnetism
are proposed as candidates for a possible magnetic structure. At the critical
pressure, where the pressure-induced ordered phase disappears, the temperature
dependence of the resistivity below 10 K is proportional to $T^{5/3}$. This
non-Fermi liquid behavior suggests the presence of pronounced magnetic
fluctuation. | 2009.11488v1 |
2012-01-09 | Physical properties of $A_x$Fe$_{2-y}$S$_2$ ($A$=K, Rb and Cs) single crystals | We successfully synthesized two new compounds Rb$_x$Fe$_{2-y}$S$_2$ and
Cs$_x$Fe$_{2-y}$S$_2$ which were isostructural with K$_x$Fe$_{2-y}$Se$_2$
superconductor. We systematically investigated the resistivity, magnetism and
thermoelectric power of $A_x$Fe$_{2-y}$S$_2$ ($A$=K, Rb and Cs) single
crystals. High temperature resistivity and magnetic measurements show anomalies
above 500 K depending on $A$ which are similar to $A_x$Fe$_{2-y}$Se$_2$.
Discrepancy between ZFC and FC curves was observed in K$_x$Fe$_{2-y}$S$_2$ and
Rb$_x$Fe$_{2-y}$S$_2$, while it disappears in Cs$_x$Fe$_{2-y}$S$_2$. Our
results indicate the similar magnetism between $A_x$Fe$_{2-y}$S$_2$ and
$A_x$Fe$_{2-y}$Se$_2$ at high temperature. | 1201.1709v1 |
2019-03-12 | Single-crystal growth and extremely high H_c2 of 12442-type Fe-based superconductor KCa_2Fe_4As_4F_2 | Millimeter sized single crystals of KCa_2Fe_4As_4F_2 were grown using a
self-flux method. The chemical compositions and crystal structure were
characterized carefully. Superconductivity with the critical transition T_c =
33.5 K was confirmed by both the resistivity and magnetic susceptibility
measurements. Moreover, the upper critical field H_c2 was studied by the
resistivity measurements under different magnetic fields. A rather steep
increase for the in-plane H_c2^ab with cooling, d\mu_0H_c2^a/dT|T_c = -50.9
T/K, was observed, indicating an extremely high upper critical field. Possible
origins for this behavior were discussed. The findings in our work is a great
promotion both for understanding the physical properties and applications of
12442-type Fe-based superconductors. | 1903.04822v1 |