A monolithically sculpted van der Waals nano-opto-electro-mechanical coupler

The nano-opto-electro-mechanical systems (NOEMS) are a class of hybrid solid devices that hold promises in both classical and quantum manipulations of the inter...     

Many-Body Terms in van der Waals Cohesion Energy of Nanotubes

We have developed a model for the calculation of van der Waals force for layered systems with axial symmetry. Our result can be applied to compute the cohesion of a carbon nanotube to a substrate, the cohesion between nanotubes, and between shells of multiwall nanotubes. We have obtained unusal power laws for the distance dependence of the many-body van der Waals potential.     

MXene-GaN van der Waals metal-semiconductor junctions for high performance multiple quantum well photodetectors

A MXene-GaN-MXene based multiple quantum well photodetector was prepared on patterned sapphire substrate by facile drop casting. The use of MXene electrodes imp...     

Optimizing exciton transport in semiconductors

Excitons—charge-neutral quasiparticles comprised of bound electron hole pairs—can be formed within a wide range of semiconductors, including monolayer transitio...     

Optical Anisotropy in van der Waals materials:Impact on Direct Excitation of Plasmons and Photons by Quantum Tunneling

Inelastic quantum mechanical tunneling of electrons across plasmonic tunnel junctions can lead to surface plasmon polariton (SPP) and photon emission. So far, t...     

Inhomogeneous exciton broadening and mean free path in In1-xGaxAsyP1-y-InP heterostructures

Absorption and electroabsorption spectra are investigated at low temperature to derive broadening parameters of excitonic absorption edges in the alloy crystals. A strong increase of the inhomogeneous linewidth of excitons is observed for quaternary material which exceeds significantly the width expected from compositional fluctuations. The linewidth decreases again for phosphorous rich samples. Franz-Keldysh oscillations above the absorption edge contain information on the coherence length of band states. They show a corresponding decrease of the mean free path from 150 nm for ternary material to 70 nm for quaternary material     

Society news [including in memoriam: Heinz van der Broeck]

Includes: 1) Recent Prize Paper Announcements. 2) IEEE Joint IAS/PELS/IES German Chapter Meeting in Erlangen-Nuremberg. 3) IEEE Creates New Award. 4) Erratum and 5) The Lighter Side Needs Your Help.     

Quasi-bound levels,transmission and resonant tunneling in heterostructures with double and multi rectangular,trapezoidal, triangular barriers

In this work quasi-bound level energies, energy dependence of the transmission coefficients and negative differential resistance properties are studied in double and multi-barrier structures. Various barrier types such as rectangular, trapezoidal and triangular are chosen. In order to compare calculation results, maximum of the barrier height and base of the barrier width are kept constant. Only changes due to barrier shape and well region width are investigated. Mini-band formation in multi-barrier structures with different barrier shapes are compared for several well widths in energy scale. In addition, properties of the resonant tunneling peak shapes, I–V characteristics, peak-to-valley current ratios in negative differential resistance regions are compared for rectangular, trapezoidal, triangular barrier types for both double and multi-barrier structures.     

The role of exciton and charge carrier diffusion in photoenhancedcurrents

This work concerns the influence on photoenhanced currents of the diffusion of excitons as well as of charge carriers. It is shown that both kinds of diffusion are important for photoenhanced currents in the case of thin samples. Experimental results obtained on tetracene layers confirm this conclusion     

Dielectric relaxation in piezo-, pyro- and ferroelectric polyamide 11

Ferroelectric polyamide 11 films were prepared by melt-quenching, cold-drawing and electrical poling. Their ferroelectricity was studied by means of dielectric-hysteresis measurements. A remnant polarisation of up to 35 mC/m/sup 2/ and a coercive field of 75 MV/m were obtained. The piezoelectric d/sub 33/ coefficient and the pyroelectric coefficient of the films are reduced by annealing just below the melting region, but remain at about 3 pC/N and 8 /spl mu/C/(m/sup 2/K), respectively, during further heat treatment. Differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarisation (TSD) were applied for investigating the conformational changes induced by melt-quenching, cold-drawing and annealing. The results indicate that the cold-drawn film mainly consists of a rigid amorphous phase which exhibits considerably lower conductivity, no glass transition and consequently no dielectric /spl alpha/ relaxation. Instead, an /spl alpha//sub r/ relaxation is found, which is related to chain motions in regions of the rigid amorphous phase where the amide-group dipoles are not perfectly ordered. Annealing removes imperfectly ordered structures, but does not affect the ferroelectric polarisation. Therefore, it may be concluded that essentially the /spl alpha//sub r/ relaxation causes the thermally nonstable part of the piezo- and pyroelectricity in polyamide 11.     

Bias-induced destruction of ferromagnetism and disorder effects in GaMnAs heterostructures

The magneto-electric properties of resonant tunneling double barrier structures using GaMnAs for the quantum well is investigated within a self-consistent Green??s function approach and a tight-binding electronic structure model. The magnetic state of the well is determined self-consistently by the tunneling current which controls the hole spin density and, hence, the degree of exchange splitting of the subbands inside the well. Prompted by recent experiments we compare model systems of increasing defect concentration (substitutional disorder) regarding their I?CV curve, magnetic state, and spin polarization. We predict that, near resonance, the ferromagnetic order which may be present at zero bias in the GaMnAs well tends to be destroyed. Resonance peaks are found to be more sensitive to disorder than ferromagnetic ordering and spin polarization of the steady-state current.     

Ions,transport, and energetics in normal and diseased skeletal muscle

Magnetic resonance spectroscopy (MRS) has highlighted the relationship between intracellular ionic homeostasis and the control of muscle energetics. In skeletal muscle, the oxidative rate of ATP synthesis is largely controlled by ADP, the concentration of which is determined by the creatine kinase equilibrium that includes the concentration of H⁺. At the onset of aerobic dynamic exercise, ATP is maintained largely by glycolysis, producing lactic acid and PCr breakdown. Vasodilation follows and ATP synthesis becomes predominantly oxidative. During recovery, PCr resynthesis gives a measure of mitochondrial function, and pH recovery reflects the Na⁺:H⁺ antiport activity. Dynamic³¹P MRS measurements can be used to derive quantitative information about the processes (fluxes and concentrations) described above. In diseased muscle (e.g., mitochondrial myopathy, dystrophy, hypertension) specific changes are observed in some of the control functions, ionic fluxes, or mitochondrial oxidative rates.     

Molecular dynamics in homo, diblock and triblock polymers studiedby dielectric relaxation spectroscopy

The dynamics of poly(oxybutylene) chains was investigated in comparison to that of poly(oxybutylene) blocks in solid semicrystalline poly(oxyethylene)-poly(oxybutylene) (EB) diblock copolymers and poly(oxyethylene)-poly(oxybutylene)-poly(oxyethylene) (EBE) triblock copolymers, using broadband dielectric relaxation spectroscopy (10^-2 to 10⁹ Hz). The B homopolymers and the B blocks of the triblocks were dipole-inverted, whereas no dipole inversion occurred in the B blocks of the diblocks. For B blocks longer than a critical value B_cr, the main relaxation, which is related to the glass transition, exhibits similar characteristics in all three systems. The normal mode relaxation process due to chain motions of larger length scales than that of segmental motion, also was studied for the homopolymers and the copolymers. The results also imply that B blocks of triblock copolymers exhibit normal mode relaxation, where mainly normal eigenmodes of relatively high orders contribute. The mobility of the global chain motion is determined by the order of the normal eigenmodes with the highest intensities, whereas the whole chain conformations are mainly determined by the spatial confinement in the solid copolymers and the effects of fixed chain ends, irrespectively of the order of the most intensive eigenmodes. For very short B blocks, fixed chain end effects affect significantly the dynamics of both, main and normal mode relaxation     

Effect of temperature, electric and magnetic field on spin relaxation in bilayer graphene

In spintronics, spin degree of freedom of an electron is used to store and process information and thus can provide numerous advantages over conventional electronics by providing new functionalities. In this paper, we employ the semiclassical Monte Carlo approach to study the spin polarized transport in bilayer graphene. Due to lower spin orbit interaction (SOI) and higher spin relaxation lengths, graphene is considered as suitable material for spintronics application. Spin relaxation in bilayer graphene is caused by D’yakonov–Perel (DP) relaxation and Elliott–Yafet (EY) relaxation. The effect of temperature, magnetic field and driving electric field on spin relaxation length is studied. We have considered injection polarization along z-direction which is perpendicular to the plane of graphene and the magnitude of ensemble averaged spin variation is studied along the x-direction which is the transport direction.     

Telecommunications, matter, and the formation of value

An examination is presented of how basic aspects of telecommunications and information transfer require a new understanding of the concepts of commodity value and its relationship to public policy. The main focus is on the creation of value in an increasingly information-based economic environment. Determinants of economic value for information commodities are revealed in the analysis of communication channels. The investigation draws upon the general nature of telecommunications and information transfer for principles governing commodity-value formation in both broadcast media and telephone-type resources. These are contrasted with value formation for material commodities. This model has broader implications for the issue of creating information as a social value from a limited range of formats and conventions. it is shown how, at the level of social policy, the role of standard and individual choice are becoming dominant as the realities of an increasingly information-based society have their impact on the values of the culture     

Calculation of levitation,drag and lateral forces in EDS-MAGLEV transport systems

Contents The researches on magnetically levitated transport systems with electrodynamic suspension (EDS-MAGLEV systems) are today of great interest. The paper describes an analytical three-dimensional method which allows the determination of the levitation, drag and lateral forces acting on EDS-MAGLEV systems with superconducting and/or conventional coils, whatever their number, disposition and sizes may be. The application of the method to experimental prototypes shows a good concordance with the experimental data.

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Berechnung von Trag-Bewegungswiderstand- und Seitlichkräften in Magnetschwebefahrzeugen

Übersicht Untersuchungen über Magnetschwebeverkehrsysteme mit elektrodynamischer Abstoßung (EDS-MAGLEV) erregen heutzutage ein großes Interesse. Die vorliegende Abhandlung beschreibt ein analytisches dreidimensionales Verfahren für die Berechnung der Trag-Bewegungswiderstand-und Seitlichkräfte auf Magnetschwebefahrzeugen mit supraleitenden und/oder konventionellen Spulen, egal welche Anzahl, Anordnung und Ausdehnung sie haben. Die Anwendung dieses Verfahrens auf die Versuchsanlagen zeigt eine gute Übereinstimmung mit den Versuchsdaten.