Droop-free amplified red emission from Eu ions in GaN

Eu-doped GaN (GaN:Eu) are novel candidates for red light-emitting diodes (LEDs). To further improve the luminescent efficiency of the GaN:Eu-based LED, the efficiency-droop under strong excitation conditions should be suppressed. In this paper, we demonstrate droop-free luminescence of GaN:Eu emitted from a sample-edge using a stripe excitation configuration. The Eu emission intensity clearly increases compared to the conventional surface-emission, and the enhancement is more pronounced for stronger excitation conditions. We clarify that the wavelength dependence of the enhancement agrees well with the optical gain spectrum of the GaN:Eu and is attributed to amplified spontaneous emission.

Bi-reflection of spin waves

When a light wave is refracted at a boundary between two different media, it may split into two rays due to optical anisotropy, a phenomenon called birefringence. On the other hand, for a reflected light wave in an ordinary medium, the angle of reflection is always the same as the incident angle as expected from the law of reflection. Here, we report the observation of a split of reflected spin-waves, or bi-reflection of spin-waves, where a spin-wave refers to a wavy motion of electron spins in a magnetic material. We measured the spin-wave propagation in a magnetic garnet Lu2Bi1Fe3.4Ga1.6O12 by using time-resolved magneto-optical microscopy and found that the spin-wave splits in two as a result of reflection at the sample edge of an out-of-plane magnetized film. Systematic measurements combined with calculations unveiled that the bi-reflection is due to the hybridization with elastic waves.

Structure and Tensile Strength of Pure Cu after High Pressure Torsion Extrusion

The microstructure and mechanical properties of rod-shaped samples (measuring 11.8 mm in diameter and 35 mm in length) of commercially pure (CP) copper were characterized after they were processed by high pressure torsion extrusion (HPTE). During HPTE, CP copper was subjected to extremely high strains, ranging from 5.2 at central area of the sample to 22.4 at its edge. This high but varying strain across the sample section resulted in HPTE copper displaying a gradient structure, consisting of fine grains in the central area and of ultrafine grains both in the middle-radius area and at the sample edge. A detailed analysis of the tensile characteristics showed that the strength of HPTE copper with its gradient structure is similar to that of copper after severe plastic deformation (SPD) techniques, typically displaying a homogeneous structure. Detailed analysis of the contributions of various strengthening mechanisms to the overall strength of HPTE coper revealed the following: The main contribution comes from Hall–Petch strengthening due to the presence of high and low angle grain boundaries in gradient structure, which act as effective obstacles to dislocation motion. Therefore, both types of boundaries should be taken into account in the Hall–Petch equation. This study on CP copper demonstrated the potential of using the HPTE method for producing high-strength metallic materials in bulk form for industrial use.

Study of anisotropic electrical resistance of knitted fabrics

Knitted fabrics, due to their multifunctional characteristics in terms of flexibility, elasticity and pliancy, are suitable to be used in electro-thermal garments as monitoring sensors for body movement. The arrangement of fibers and yarns in textiles makes them, in the majority of cases, inhomogeneous and anisotropic materials. Five highly conductive plain weft knitted fabrics in which anisotropy of electro-conductive properties occurred were chosen. In order to assess the global degree of planar anisotropy of the knitted fabrics, a new measurement procedure was designed. The Van der Pauw electrode configuration was used. The determination of resistance at selected points on the sample surface allowed us to find the surface response for each sample. Based on the results, the assessment of the global degree of planar anisotropy of electro-conductive properties of knitted fabrics was possible. Moreover, the experiment was designed to simultaneously solve the problem of measuring the resistance at the sample edge. The quotients ratio used as a measure representing the degree of global anisotropy was found to range from 2.5 to 11.1. This quotient was higher compared to that determined on the basis of measurements conducted in multi-directions lying in the sample plane and at a constant distance from the electrodes and from the sample edge. The relatively wide range of resistance values obtained for three samples makes it possible to use them as strain sensors, for example. The narrow resistance range observed in two samples is suited for the development of medical sensors, such as electrocardiogram electrodes.

Эффективная скорость движения доменной границы в квазиодномерной наносистеме при множественном рождении доменов новой фазы

The process of switching a metastable state into an energetically preferable state in extended quasione- dimensional systems often occurs through the motion of domains walls of new phase. Usually considered limit cases are the propagation of the edge domains over the whole system or multiple nucleation and coalescence of domains in the volume of the material. This paper deals with the more general situation of front propagation of the switching state from the sample edge at a multiple nucleation of domains of a new phase on randomly located defects in the volume. The corresponding statistically-kinetic problem is solved with the calculation of the average magnitude and dispersion of path lengths, as well as the full generating function for finding higher moments of distribution of “the relay” run lengths of the boundary of the edge domain.

Direct tomography imaging for inelastic X-ray scattering experiments at high pressure

A method to separate the non-resonant inelastic X-ray scattering signal of a micro-metric sample contained inside a diamond anvil cell (DAC) from the signal originating from the high-pressure sample environment is described. Especially for high-pressure experiments, the parasitic signal originating from the diamond anvils, the gasket and/or the pressure medium can easily obscure the sample signal or even render the experiment impossible. Another severe complication for high-pressure non-resonant inelastic X-ray measurements, such as X-ray Raman scattering spectroscopy, can be the proximity of the desired sample edge energy to an absorption edge energy of elements constituting the DAC. It is shown that recording the scattered signal in a spatially resolved manner allows these problems to be overcome by separating the sample signal from the spurious scattering of the DAC without constraints on the solid angle of detection. Furthermore, simple machine learning algorithms facilitate finding the corresponding detector pixels that record the sample signal. The outlined experimental technique and data analysis approach are demonstrated by presenting spectra of the SiL2,3-edge and OK-edge of compressed α-quartz. The spectra are of unprecedented quality and both the OK-edge and the SiL2,3-edge clearly show the existence of a pressure-induced phase transition between 10 and 24 GPa.

Dirac spin-gapless semiconductors: promising platforms for massless and dissipationless spintronics and new (quantum) anomalous spin Hall effects

It is proposed that the new generation of spintronics should be ideally massless and dissipationless for the realization of ultra-fast and ultra-low-power spintronic devices. We demonstrate that the spin-gapless materials with linear energy dispersion are unique materials that can realize these massless and dissipationless states. Furthermore, we propose four new types of spin Hall effects that consist of spin accumulation of equal numbers of electrons and holes having the same or opposite spin polarization at the sample edge in Hall effect measurements, but with vanishing Hall voltage. These new Hall effects can be classified as (quantum) anomalous spin Hall effects. The physics for massless and dissipationless spintronics and the new spin Hall effects are presented for spin-gapless semiconductors with either linear or parabolic dispersion. New possible candidates for Dirac-type or parabolic-type spin-gapless semiconductors are proposed in ferromagnetic monolayers of simple oxides with either honeycomb or square lattices.