Inelastic and Elastic Multiple Scattering of Fast Electrons Described by the Transport Equation

A method for solving the transport equation for the propagation of electrons in the primary energy range of interest in electron beam technology has been developed which is based on discretizing the related integral equation. The integral equation is solved by a collocation procedure yielding a system of linear equations. The elementary scattering processes were described for elastic scattering by quantum mechanical differential cross sections and for inelastic scattering by Gryzinski type semi-empirical excitation functions for core and outer electrons separately. From the electron flux density calculated, angular and energy distributions of transmitted and backscattered electrons were derived for various elements (Al, Cu, Ag, Au) and film thicknesses. The results agree with experimental data, including finer details as e.g. the dependence of the elastic backscattering peak on scattering angle and atomic number

Vibrating quartz crystal as a tool for studying the flow of cryogenic fluids

Department of Condensed Matter PhysicsKatedra fyziky kondenzovaných látekFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Cryogenic broadband vibration measurement on a cryogen-free dilution refrigerator

This manuscript reports a set of acceleration measurements in the frequency range from 0 to 50 kHz performed at the mixing chamber plate (2 axes) and the top flange (3 axes) of a cryogen-free dilution refrigerator. Various configurations of the support frame and coupling to the pulse tube compressor and motor have been tested, and the dominant contribution in the spectrum of vibrations is located, surprisingly, near 20 kHz. Finally, the efficiency of various precautions in suppressing the observed vibration levels is illustrated

Crossover from hydrodynamic to acoustic drag on quartz tuning forks in normal and superfluid 4He

We present measurements of the drag forces on quartz tuning forks oscillating at low velocities in normal and superfluid 4He. We have investigated the dissipative drag over a wide range of frequencies, from 6.5 to 600 kHz, by using arrays of forks with varying prong lengths and by exciting the forks in their fundamental and first overtone modes. At low frequencies the behavior is dominated by laminar hydrodynamic drag, governed by the fluid viscosity. At higher frequencies acoustic drag is dominant and is described well by a three-dimensional model of sound emission

Utilization of an Electron-Beam Tester for Determining Internal Electric Field Profiles in Micro-Structured Thin-Film Semiconductor Devices

An electron-beam tester was used to determine the depth profile of the internal potential distribution in an a-Si:H solar cell and hence the internal electric field profile. The a-Si:H solar cells were prepared for the measurements with the electron-beam tester by low-energy chemical plasma beam etching through a plasma-resistant mask structured by electron-beam lithography. In contrast to an earlier work, the solar cells were in situ illuminated and the electric field profiles were determined for new, degraded and in situ annealed solar cells at various cell temperatures. The measuring results demonstrate that the electron-beam testing technique in combination with a suitable micro-structure preparation method is appropriate to measure internal electric field profiles in semiconductor devices as, e.g., solar cells for arbitrarily chosen bias and illumination states

Rotational Effects In The Continuous Vacuum-ultraviolet Fluorescence Spectrum Of H2 Associated With Spontaneous Dissociation

The effects of rotational-vibrational interaction, and of rotational coupling between the B 2p u+1 and C 2p u1 electronic states, on the B X fluorescence continuum of H2 associated with spontaneous dissociation were investigated spectroscopically using monochromatized synchrotron radiation for selective excitation of rovibronic states. The rotational shifts and perturbations in the modulated continua intensities observed agree well with close-coupling and Jeffreys-Wentzel-Kromers-Brillouin (JWKB) calculations also performed and are explained in terms of nonadiabatic coupling effects and rainbow-interference structures. A straightforward experimental technique is described to detect mixed electronic states. © 1990 The American Physical Society

Multiple critical velocities in oscillatory flow of superfluid 4He due to quartz tuning forks

We report recent investigations into the transition to turbulence in superfluid $^4$He, realized experimentally by measuring the drag forces acting on two custom-made quartz tuning forks with fundamental resonances at 6.5 kHz and 55.5 kHz, in the temperature range 10 mK to 2.17 K. In pure superfluid in the zero temperature limit, three distinct critical velocities were observed with both tuning forks. We discuss the signicance of all critical velocities and associate the third critical velocity reported here for the first time with the development of large vortical structures in the flow, which thus starts to mimic turbulence in classical fluids. The interpretation of our results is directly linked to previous experimental work with oscillators such as tuning forks, grids and vibrating wires, focusing on the behavior of purely superfluid $^4$He at very low temperature

Rotational Effects In The VUV Continuum Of H2

The effects of rotation-vibration interaction and of rotational coupling between the B 2p 1Σu+ and C 2p 1Πu electronic states on the B-X continuum of H2 were investigated spectroscopically using monochromatized synchrotron radiation for selective excitation of rovibronic states. The perturbed continuum intensities observed for the first time agree well with close-coupling calculations also performed. © 1990 IOP Publishing Ltd