SEARCH · Searcharxiv

Results for “cond-mat.mtrl-sci”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources

arXiv2013

Crystals, magnetic and electronic properties of a new ThCr2Si2-type BaMn2Bi2 and K-doped compositions

This is a report on the new 122 ternary transition-metal pnictide of BaMn2Bi2, which is crystallized from bismuth flux. BaMn2Bi2 adopts ThCr2Si2-type structure (I4/mmm) with a = 4.4902(3) Å and c = 14.687(1) Å; it is antiferromagnetic with anisotropic magnetic susceptibility and semiconducting with a band gap of Eg = 6 meV. Heat capacity result confirms the insulating ground state in BaMn2Bi2 with the electronic residual Sommerfeld coefficient of γ ~ 0. The high temperature magnetization results show that magnetic ordering temperature is TN ~ 400 K. Hole-doping in BaMn2Bi2 via potassium in Ba1-xKxMn2Bi2 results in metallic behavior for x = 0.10(1), 0.32(1) and 0.36(1). With K-doping, more magnetically anisotropic behavior is observed. Although there is a downturn in electrical resistivity and low-field magnetization data below 4 K in > 30%-doped crystals, there is no sign of zero resistance or diamagnetism. This manuscript is a report on new materials of BaMn2Bi2 and Ba1-xKxMn2Bi2 (0 < x < 0.4). Results from powder X-ray diffraction, anisotropic temperature- and field-dependent magnetization, temperature-and field-dependent electrical resistivity, and heat capacity are presented.

cond-mat.supr-con↗

arXiv2013

Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue

Here we report on a novel chemical route to synthesize homogenous cobalt doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The influence of the synthesis temperature, autoclave dwell time and metal doping on the structural and microstructural as well as on the optical properties of the synthesized titanate nanotubes is studied and discussed. The optical band gaps of the CoTNT samples are red shifted in comparison with the values determined for the undoped samples, such red shifts bringing the absorption edge of the CoTNT samples into the visible region. CoTNT materials also demonstrate particular high adsorption ability for methylene blue, the amount of the adsorbed dye being higher than the one predictable for a monolayer formation. This suggests the possibility of intercalation of the dye molecule between the TiO6 layers of the TNT structure. It is also shown that the methylene blue sensitized Co-doped nanostructures are highly stable under UV radiation and present a strong and broad absorption in the visible region.

cond-mat.mtrl-sci↗

arXiv2013

Ordering and phonons in Ba$_3$CaNb$_{2}$O$_9$ complex perovskite

In this work we performed a detailed investigation about ordering in \bcn perovskite. The sintering temperature and time were changed to obtain samples with different ordering. The order parameters were probed by Raman spectroscopy based on a partial disordered model. To use the partial disordered model correctly we performed {\it ab initio} calculations in \bcn to assign the optical phonons. The results showed that sintering temperature improves order while sintering time is not so efficient to promote order.

cond-mat.mtrl-sci↗

arXiv2013

Massive production of graphene oxide from expanded graphite

In a deviation from the conventional Hummers method, a spontaneous expansion approach was introduced with expanded graphite as the precursors. The intercalating agent (H2SO4) was able to penetrate into the expanded graphite; this had further expanded the graphite and as a result, a foam-like intermediate was produced. The foam-like graphite was more easily oxidized in reaction with the oxidant (KMnO4) to form graphene oxide (GO). Fully exfoliated GO was obtained with expanded graphite having the median diameter ~ 15 μm as the precursors. This procedure was much safer and productive in scalable applications than the conventional Hummers methods.

cond-mat.mtrl-sci↗

arXiv2013

Spatial resolution of a μPIC-based neutron imaging detector

We present a detailed study of the spatial resolution of our time-resolved neutron imaging detector utilizing a new neutron position reconstruction method that improves both spatial resolution and event reconstruction efficiency. Our prototype detector system, employing a micro-pattern gaseous detector known as the micro-pixel chamber (μPIC) coupled with a field-programmable-gate-array-based data acquisition system, combines 100μm-level spatial and sub-μs time resolutions with excellent gamma rejection and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. From data taken at the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex (J-PARC), the spatial resolution was found to be approximately Gaussian with a sigma of 103.48 +/- 0.77 μm (after correcting for beam divergence). This is a significant improvement over that achievable with our previous reconstruction method (334 +/- 13 μm), and compares well with conventional neutron imaging detectors and with other high-rate detectors currently under development. Further, a detector simulation indicates that a spatial resolution of less than 60 μm may be possible with optimization of the gas characteristics and μPIC structure. We also present an example of imaging combined with neutron resonance absorption spectroscopy.

physics.ins-det↗

arXiv2013

Modelling surface restructuring by slow highly charged ions

We theoretically investigate surface modifications on alkaline earth halides due to highly charged ion impact, focusing on recent experimental evidence for both etch pit and nano-hillock formation on CaF2 [A. El-Said et al, PRL 109, 117602 (2012)]. We discuss mechanisms for converting the projectile potential and kinetic energies into thermal energy capable of changing the surface structure. A proof-of-principle classical molecular dynamics simulation suggests the existence of two thresholds which we associate with etch pit and nano-hillock formation in qualitative agreement with experiment.

cond-mat.mtrl-sci↗

arXiv2013

Optical reflectivity and magnetoelectric effects on resonant plasmon modes in composite metal-multiferroic systems

The rôle of the magnetoelectric effect upon optical reflectivity is studied by adapting an electrodynamic-based model for a system composed by a 2D metallic film in contact with an extended multiferroic material exhibiting weak ferromagnetism. The well-known \emph{Nakayama's} boundary condition is reformulated by taking into account the magnetoelectric coupling as well as an externally applied magnetic field $\mathbf{B}$ in an arbitrary direction. It is found that the reflectance shows strong fluctuations for incident radiation close to the characteristic antiferromagnetic resonance frequency associated with the multiferroic material in the THz regime. These results were verified for a 10 nm metallic foil by using a finite element method (FEM) and the Rouard's approach, for a wide range of wavelengths (0.1 - 5 mm), showing good agreement with respect to Nakayama's outcome, for the particular material BaMnF$_4$.

cond-mat.mtrl-sci↗

arXiv2013

Structure and magnetic properties of Heusler alloy Fe2NiZ (Z=Al, Ga, Si and Ge)

The Heusler alloys Fe2NiZ (Z=Al, Ga, Si and Ge) have been synthesized and investigated focusing on the phase stability and the magnetic properties. The experimental and theoretical results reveal the covalent bonding originated from p-d hybridization takes an important role in these alloys, which dominates the stability of ordered structure but leads to the decline of the band splitting. The electronic structure shows the IV group main group element (Si and Ge) provides stronger covalent effect than that of the III group element (Al and Ga). It has been found that the variations of the physical parameters, lattice constants, critical ordering temperature, magnetic moments and Curie temperature, precisely follow these covalent characters.

cond-mat.mtrl-sci↗

arXiv2013

Thermal treatment of superconductor thin film of the BSCCO system using domestic microwave oven

In this work, we report the preparation of a superconductor thin film of the BSCCO system using a good quality powder with nominal composition Bi_{1.8}Pb_{0.4}Sr_2CaCu_2O_x which was thermally treated using a domestic microwave oven (2.45 GHz, 800 W). This film was grew on a single crystal of LaAlO_3(100) substrate and exhibited a crystalline structure with the c-axis perpendicular to the plane of the substrate. An onset superconducting transition temperature was measured at 80 K.

cond-mat.mtrl-sci↗

arXiv2012

Synchronization of Josephson oscillations in mesa array of BSCCO single crystal through the Josephson plasma waves in base crystal

Using mesa array of $\rm{Bi_{2}Sr_{2}CaCu_{2}O_{8}}$ single crystal was demonstrated recently as a promising route to enhance the radiation power generated by Josephson oscillations in mesas. We study the synchronization in such an array via the plasma waves in the base crystal. First, we analyze plasma oscillations inside the base crystal generated by the synchronized mesa array and the associated dissipation. We then solve the dynamic equation for superconducting phase numerically to find conditions for synchronization and to check the stability of synchronized state. We find that mesas are synchronized when the cavity resonance of mesas matches with that of the base crystal. An optimal configuration of mesa arrays is also obtained.

cond-mat.supr-con↗

arXiv2013

Re-examining the electronic structure of germanium: A first-principle study

We report results from an efficient, robust, ab-initio method for self-consistent calculations of electronic and structural properties of Ge. Our non-relativistic calculations employed a generalized gradient approximation (GGA) potential and the linear combination of atomic orbitals (LCAO) formalism. The distinctive feature of our computations stem from the use of Bagayoko-Zhao-Williams-Ekuma-Franklin (BZW-EF) method. Our results are in agreement with experimental ones where the latter are available. In particular, our theoretical, indirect band gap of 0.65 eV, at the experimental lattice constant of 5.66 Å, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 5.63 Å, with a corresponding indirect band gap of 0.65 eV and a bulk modulus of 80 GPa. We also calculated the effective masses in various directions with respect to the $Γ$ point.

cond-mat.mtrl-sci↗

arXiv2013

The high strain-rate behaviour of three molecular weights of polyethylene examined with a magnesium alloy split-Hopkinson pressure bar

A traditional split-Hopkinson pressure bar system has been modified by the addition of ZK60A magnesium alloy pressure bars in order to increase the resolution of data when examining specimens of low-density, high-density and ultra-high molecular weight polyethylene. It was found that the low density of the ZK60A allowed a decent increase in transmitted pulse amplitude, whilst its relatively high yield strength afforded long-term reliability of the system. The accuracy of data obtained from the fitted strain gauges was verified with the use of a high-speed video camera, and was found to be an excellent match.

cond-mat.mtrl-sci↗

arXiv2013

Temperature induced inversion of oxygen response in CVD graphene on SiO2

We have synthesized single-layer graphene on Cu foils using chemical vapor deposition method and transferred the graphene to the top of a Si/SiO2 substrate with a pair of prefabricated Ti/Au electrodes. A resistive graphene-based gas sensor prepared in this way revealed n-type oxygen response at room temperature and we have successfully fitted the data obtained with varying oxygen levels using a two-site Langmuir model. P-type oxygen response of our sensor was observed after the temperature was raised to 100 oC, with a reversible transition to n-type behaviour when the temperature was lowered back to room temperature. Such inversion of the gas response type with temperature was interpreted as a result of interplay between the adsorbate-induced charge transfer and charge carrier scattering. The transduction function was derived, which relates the electrical response to surface coverage through both the induced mobility and charge density changes.

cond-mat.mtrl-sci↗

arXiv2013

Bandstructure and mobility variations in p-type Silicon nanowires under electrostatic gate field

The sp3d5s*-spin-orbit-coupled atomistic tight-binding (TB) model is used for the electronic structure calculation of Si nanowires (NWs), self consistently coupled to a 2D Poisson equation, solved in the cross section of the NW. Upon convergence, the linearized Boltzmann transport theory is employed for the mobility calculation, including carrier scattering by phonons and surface roughness. As the channel is driven into inversion, for [111] and [110] NW devices of diameters D>10nm the curvature of the bandstructure increases and the hole effective mass becomes lighter, resulting in a approx. 50% mobility increase. Such improvement is large enough to compensate for the detrimental effect of surface roughness scattering. The effect is very similar to the bandstructure variations and mobility improvement observed under geometric confinement, however, in this case confinement is caused by electrostatic gating. We provide explanations for this behavior based on features of the heavy-hole band. This effect could be exploited in the design of p-type NW devices. We note, finally, that the 'apparent' mobility of low dimensional short channel transistors is always lower than the intrinsic channel diffusive mobility due to the detrimental influence of the so called 'ballistic' mobility.

cond-mat.mtrl-sci↗

arXiv2013

To see or not to see: Imaging surfactant coated nano--particles using HIM and SEM

Nano--particles are of great interest in fundamental and applied research. However, their accurate visualization is often difficult and the interpretation of the obtained images can be complicated. We present a comparative scanning electron microscopy and helium ion microscopy study of cetyltrimethylammonium--bromide (CTAB) coated gold nano--rods. Using both methods we show how the gold core as well as the surrounding thin CTAB shell can selectively be visualized. This allows for a quantitative determination of the dimensions of the gold core or the CTAB shell. The obtained CTAB shell thickness of 1.0 nm--1.5 nm is in excellent agreement with earlier results using more demanding and reciprocal space techniques.

cond-mat.mtrl-sci↗

arXiv2013

Characterization of Al and Mg Alloys from Their X-Ray Emission Bands

The valence states of Mg-Al alloys are compared to those of reference materials (pure Mg and Al metals, and intermetallics). Two methods based on X-ray emission spectroscopy are proposed to determine the phases and their proportion: first, by analyzing the Al valence spectra of the Mg-rich alloys and the Mg valence spectra of the Al-rich alloys; second, by fitting with a linear combination of the reference spectra the Al spectra of the Al-rich alloys and the Mg spectra of the Mg-rich alloys. This enables us to determine that Al and Al3Mg2 are present in the 0-43.9 wt% Al composition range and Mg and Al12Mg17 are present in the 62.5-100 wt% Al composition range. In the 43.9-62.5% Al range, the alloy is single phase and an underestimation of the Al content of the alloy can be estimated from the comparison of the bandwidth of the alloy spectrum to the bandwidths of the reference spectra.

cond-mat.mtrl-sci↗

arXiv2022

High-Performance Mid-IR to Deep-UV van der Waals Photodetectors Capable of Local Spectroscopy at Room Temperature

The ability to perform broadband optical spectroscopy with sub-diffraction-limit resolution is highly sought-after for a wide range of critical applications. However, sophisticated tip-enhanced techniques are currently required to achieve this goal. We bypass this challenge by demonstrating an extremely broadband photodetector based on a two-dimensional (2D) van der Waals heterostructure that is sensitive to light across over a decade in energy from the mid-infrared (MIR) to deep-ultraviolet (DUV) at room temperature. The devices feature high detectivity (> 10^9 cm Hz^1/2 W^-1) together with high bandwidth (2.1 MHz). The active area can be further miniaturized to submicron dimensions, far below the diffraction limit for the longest detectable wavelength of 4.1 um, enabling such devices for facile measurements of local optical properties on atomic-layer-thickness samples placed in close proximity. This work can lead to the development of low-cost and high-throughput photosensors for hyperspectral imaging at the nanoscale.

physics.optics↗

arXiv2017

Surface zeta potential and diamond seeding on gallium nitride films

Measurement of zeta potential of Ga and N-face gallium nitride has been carried out as function of pH. Both the faces show negative zeta potential in the pH range 5.5-9. The Ga face has an isoelectric point at pH 5.5. The N-face shows higher negative zeta potential due to larger concentration of adsorbed oxygen. Zeta potential data clearly showed that H-terminated diamond seed solution at pH 8 will be optimal for the self assembly of a monolayer of diamond nanoparticles on the GaN surface. Subsequent growth of thin diamond films on GaN seeded with H-terminated diamond seeds produced fully coalesced films confirming a seeding density in excess of 10$^{12}$ cm$^{-2}$. This technique removes the requirement for a low thermal conduction seeding layer like silicon nitride on GaN.

cond-mat.mtrl-sci↗