X-ray Diffraction Study of the Structure and Defect System of Yb-Activated (Na0.5Gd0.5)WO4 Crystals

Nominally pure and Yb-activated Czochralski-grown (Na_0.5Gd_0.5)WO₄ crystals (scheelite type) were studied by x-ray diffraction (phase analysis, unit-cell parameters, and structure refinement by the Rietveld method and single-crystal techniques). A pseudotetragonal (orthorhombic) superstructure was revealed, which was shown to have doubled unit-cell parameters compared to the scheelite cell. Some of the crystals were found to contain tungsten and oxygen vacancies, which give rise to additional optical absorption. The effects of the growth and heat-treatment conditions and Yb activation on the structure, defect system, and additional absorption spectrum of (Na_0.5Gd_0.5)WO₄ are analyzed.     

A Comparison of Extinction Efficiencies in the Eikonal and the Anomalous Diffraction Approximations for Spheres

Abstract

Extinction curves in the eikonal approximation and the anomalous diffraction approximation have been compared with exact extinction curves for homogeneous spheres of various refractive indices. Our results show the anomalous diffraction approximation to be more suitable for extinction calculations.     

Two in One: Light as a Tool for 3D Printing and Erasing at the Microscale

The ability to selectively remove sections from 3D‐printed structures with high resolution remains a current challenge in 3D laser lithography. A novel photoresist is introduced to enable the additive fabrication of 3D microstructures at one wavelength and subsequent spatially controlled cleavage of the printed resist at another wavelength. The photoresist is composed of a difunctional acrylate cross‐linker containing a photolabile o‐nitrobenzyl ether moiety. 3D microstructures are written by photoinduced radical polymerization of acrylates using Ivocerin as photoinitiator upon exposure to 900 nm laser light. Subsequent scanning using a laser at 700 nm wavelength allows for the selective removal of the resist by photocleaving the o‐nitrobenzyl group. Both steps rely on two‐photon absorption. The fabricated and erased features are imaged using scanning electron microscopy (SEM) and laser scanning microscopy (LSM). In addition, a single wire bond is successfully eliminated from an array, proving the possibility of complete or partial removal of structures on demand.     

Solid State Properties and Photographic Activity of Crystalline Ag2S- and (Ag,AU)2S-Specks at the Surface of Silver Halide Crystals

In the present paper a model is proposed according to which the photographic activity of silver sulphide specks is explained on behalfof the solid state properties of crystalline cubic silver sulphide, Epitaxial deposit ion of the laller is cia imed to occur at least partly at the (III) faces of AgBr during chemical sensitization, The disorder of the cation sublallice in cubic silver sulphide is con idered to be the physical base of highly efficient electron trapping, whereas the high electronic conductivity is rcsponsible for its catalytic activity towards developmcnt (fog). Excess silvcr in non stoichiometric cubic silver sulphide plays a very important role in its photographic behaviour inclUding development kinetics, The model provides a coherent explanation of a great number of experimental facts including the effects introduced by gold ions during sulphur sensitization.     

Breakdown of Zero-Energy Quantum Hall State in Graphene in the Light of Current Fluctuations and Shot Noise

We have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find an avalanche type of transport that sets in at a smaller current the larger the magnetic field is. The low-frequency noise indicates strong bunching of the electrons in the avalanches. On the basis of the measured low-frequency switching noise power, we deduce the characteristic switching rates of the avalanche sequence. The simultaneous microwave shot noise measurement also reveals intrinsic correlations within the avalanche pulses and indicate a decrease in correlations with increasing bias.     

Vapor Agglomerates and Dry Spots as Precursors of the Subcooled Liquid Boiling Crisis in a Channel

High Temperature - The mechanism of the formation of large vapor agglomerates was experimentally studied in a subcooled water flow boiling in a channel at a heat flux that approaches the critical...     

PAN基原丝预氧丝炭纤维微结构的几种新的X射线衍射散射定量表征技术

介绍几种新近开发的针对PAN基原丝、预氧丝和炭丝微结构和结构缺陷的X射线衍射与散射定量表征技术,它们是:纤维材料中柱状(椭球状)纳米取向微孔体积分数X射线小角散射定量表征方法;纤维材料中柱状(椭球状)纳米取向微孔取向角的小角散射定量表征方法;预氧丝中链状相与环化相体积分数的小角衍射定量表征方法以及炭纤维中乱层石墨相与单层石墨相的X射线广角衍射定量表征方法等。     

Asymmetry of the Forward and Backward Raman Gain Coefficient at 1.54 mum in Methane

The threshold pump energies at 1.06 mum and Raman gain coefficients of stimulated Raman scattering (SRS) at 1.54 mum have been measured in both single-pass and half-resonator configurations at various methane pressures. In the single-pass configuration, the Raman gain coefficients of the backward and forward SRS are 0.32 and 0.23 cm/GW at 95 atm, respectively. The backward Raman gain coefficient is higher than the forward Raman gain coefficient. This gain reduction is caused by the depletion of local pump intensity, the phase-matching conditions, and the transient effect of the high amplification rate in the forward SRS process. In the half-resonator configuration, the Raman gain coefficient was 0.46 cm/GW at 75 atm of methane.     

Tunneling in rf-SQUIDs and Tests of Quantum Mechanics at the Macroscopic Level

Superconducting devices such as rf-SQUIDs have been proposed to test the validity of quantum mechanics by means of Bell-like inequalities involving different-time correlation probabilities for measurements of magnetic flux. We calculate the quantum mechanical violations to such temporal Bell inequalities taking into account the effect of the measurement process on the probability distribution for the outcomes. We define a general criterion quantifying the observability of the violations and show that it is not fulfilled for the various experimental configurations proposed so far.     

Comparison of Electronic Speckle Laser Interferometry Hole-Drilling and X-ray Diffraction Techniques for Determination of Residual Stresses in the Heat Treated Steels

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 \(^{\circ }\)C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.     

Enhancement of the Magnetic Coupling in Exfoliated CrCl3 Crystals Observed by Low-Temperature Magnetic Force Microscopy and X-ray Magnetic Circular Dichroism

Magnetic crystals formed by 2D layers interacting by weak van der Waals forces are currently a hot research topic. When these crystals are thinned to nanometric size, they can manifest strikingly different magnetic behavior compared to the bulk form. This can be the result of, for example, quantum electronic confinement effects, the presence of defects, or pinning of the crystallographic structure in metastable phases induced by the exfoliation process. In this work, an investigation of the magnetism of micromechanically cleaved CrCl₃ flakes with thickness >10 nm is performed. These flakes are characterized by superconducting quantum interference device magnetometry, surface-sensitive X-ray magnetic circular dichroism, and spatially resolved magnetic force microscopy. The results highlight an enhancement of the CrCl₃ antiferromagnetic interlayer interaction that appears to be independent of the flake size when the thickness is tens of nanometers. The estimated exchange field is 9 kOe, representing an increase of ≈900% compared to the one of the bulk crystals. This effect can be attributed to the pinning of the high-temperature monoclinic structure, as recently suggested by polarized Raman spectroscopy investigations in thin (8–35 nm) CrCl₃ flakes.     

The Effect of the Polarization Characteristics of Probe Light on the Signal of Optically Detected Magnetic Resonance in Magnetometric and Gyroscopic Quantum Sensors

Technical Physics Letters - We consider the effect of the polarization characteristics of probe light on the signal of optically detected magnetic resonance in quantum sensors, including quantum...     

On the Phase Distributions in Images and Fraunhofer Diffraction Patterns Produced by a Thin,Non-aberrant Lens Illuminated by a Monochromatic Point Source of Light

The paraxial approximation is used to show that the phase distribution in the image plane for an object which itself introduces no phase distortions is that which would be obtained from a monochromatic point source placed in the Fraunhofer diffraction plane and vice versa. The idea of image formation as amplitude modulation of a carrier is suggested.     

Thermalization of X-rays in evaporated tin and bismuth films used as the absorbing materials in X-ray calorimeters

We have investigated the use of evaporated tin and bismuth films as the absorbing materials in X-ray calorimeters. When the films were deposited directly on monolithic silicon calorimeters, the output signal from both Sn and Bi devices was strongly dependent on the location of the absorption event relative to the ion-implanted thermistors, presumably indicating thermistor sensitivity to a non-thermal spectrum of phonons. With Sn films we also observed that a component of the thermalization proceeded slowly, relative to a complete thermalization reference. The thermalization function could be modified by trapping magnetic flux within the film. In order to distinguish thermalization effects in the films from the thermistor sensitivity to energetic phonons, we deposited Sn and Bi films on thin Si substrates which we then affixed to calorimeters using epoxy. With glued Sn films, we were able to attain as good as 13.6 eV resolution of 6 keV X-rays with no excess broadening of the line beyond the width of the baseline, while similarly made Bi devices showed excess broadening.     

Near-Infrared Spectral Emissivity of Cu, Ag, and Au in the Liquid and Solid States at Their Melting Points

Normal spectral emissivities of liquid and solid Cu, Ag, and Au have been determined at their melting points over a wavelength range 1000 to 2500 nm using an apparatus that consists of a cold crucible and a diffraction grating spectrometer. For the noble metals, the emissivities of liquid phases are systematically larger than those of solid phases over the measured wavelength range, and the wavelength dependence of the liquid is similar to that of the solid. The measured emissivities for the liquid metals are compared with those deduced from the optical constants measured by Miller and Krishnan et al. The present results for liquid Cu and Au are in good agreement with the data of Krishnan et al., but not with those of Miller for Cu, which suggests that the optical constants measured by Krishnan et al. for liquid Cu are more accurate than those of Miller. The present data for liquid Ag and Au are in excellent agreement with all previously reported data. For the solid metals at their melting point, a semi-empirical estimation of the emissivity was carried out based upon the Drude model incorporating the effects of interband absorption and a frequency-dependent scattering rate, ^–1()= ^–1 ₀+b ². The values of ^–1 ₀ and b at the melting point are obtained by fitting the modified Drude model to the measurement results for the solid noble metals.     

Detectors of the Cryogenic Dark Matter Search: Charge Transport and Phonon Emission in Ge 〈100〉 Crystals at 40 mK

The Cryogenic Dark Matter Search (CDMS) measures both the ionized charge and the energy in athermal phonons created by particle interactions in ultrapure germanium and silicon crystals at a temperature of 40 mK. Charge collection potentials must remain at only a few volts, else emitted phonons from drifted carriers will dominate the phonons of the original interaction. At these drift fields, there are practically no thermal phonons and carrier transport is determined by phonon emission. We present results for drift-limited carrier dynamics and rates of phonon emission in 〈100〉 germanium. As these transport conditions represent an extreme limit, a Monte Carlo technique was used to bypass analytical assumptions commonly used in solving the Boltzmann transport equation. This work will assist us in understanding phenomena found in our detectors.      

The nature of the lamellar overgrowth in polyethylene shish-kebab fibres as revealed by small-angle X-ray scattering and electron microscopy

The melting, dissolution and crystallization behaviour of the lamellar overgrowth in polyethylene shish-kebab fibres have been studied by small-angle X-ray scattering and electron microscopy. SAXS experiments in which fibres were heatedin situ demonstrated the irreversible reorganization of the lamellar overgrowth already at 60° C. Reorganization continued in an inhomogeneous manner until the fibre lost its porosity around 140° C. The morphology that developed upon cooling depended on the crystallization temperature as well as on the maximum temperature attained before crystallization. Transmission electron microscopy observations showed the influence of molecular weight on aggregation. The SAXS patterns obtained duringin situ dissolution experiments disclosed that the lamellae dissolved in dodecane above 115° C. Recrystallization of the lamellae on to the backbones was almost complete within 10 min at 110° C. These high temperatures, as compared with single-crystal behaviour, indicate that the cilia nucleated with exceptionally high stem lengths on to the backbones. SAXS of fibres elongated to a maximum ratio of 1.5 at 90° C demonstrated the role of the lamellar overgrowth as a matrix between the elementary fibrils. The shish-kebab morphology could be restored after elongation by selective dissolution of the lamellae and recrystallization.     

Effects of the Non Equilibrium Phonons and the Band Non Parabolicity on the Small Signal High Frequency ac Mobility in Narrow Gap Semiconductors in the Extreme Quantum Limit at Low Temperatures

The small signal high frequency ac mobility of the hot electrons in n-HgCdTe and n-InSb has been calculated in the extreme quantum limit at low temperatures considering the non equilibrium phonon distribution as well as the thermal phonon distribution. The energy and the momentum losses of the carriers have been considered due to acoustic phonon scattering via deformation potential and piezoelectric coupling. The ac mobility is found to remain constant up to about 110 GHz for n-HgCdTe and up to about 100 GHz for n-InSb and then it decreases at higher frequencies. The ac mobility for the non equilibrium phonon distribution at lower frequency is found to be higher compared to the thermal phonon distribution and the variation at higher frequency is faster for the thermal phonons. The inclusion of the non equilibrium phonons increases the cut off frequency i.e. the cut off frequency is higher for the non equilibrium phonon distribution. The phase lag of drift velocity is found to increase with the frequency both for the nonequilibrium and the thermal phonon distribution respectively. The influence of the band non parabolicity based on simplified Kane’s model for the extreme quantum limit has also been investigated on the ac mobility of hot electrons and the phase angle. It is observed that at lower frequencies the normalized ac mobility is same both for the parabolic and the non parabolic band but at higher frequencies it is higher for the non parabolic than that of the parabolic band structure. The phase angle increases with frequency and is found to be higher for the parabolic band compared to the non parabolic band. These results can be explained by the Drude theory for ac conductivity.