We have theoretically investigated the intersubband transition for different doping concentrations and thickness in Si δ-doped GaAs with an applied electric field. The electronic properties such as the δ-potential profile and the subband energy have been calculated by solving the Schrödinger and Poisson equations self-consistently. We show an abrupt drop of the energy differences and the absorption peaks whenever the external electric field reaches a certain value. We can say that the appearance of a second quantum well in the effective potential dependent on the applied electric field creates a rapid change in the subband energies. This critical electric field value changes as dependent on the donor concentration and thickness. Thus, we conclude that the intersubband optical absorption is very sensitive to the donor distribution and thickness as dependent on the applied electric field. This changing in the intersubband transition gives a new degree of freedom in regions of interest semiconductor device applications.

This paper investigates the self-heating effect in SiGe heterojunction bipolar transistors. A physical study leads to a nonlinear physical model describing static and dynamic self-heating mechanism. The implementation of this model using an electrical equivalent circuit is presented. Our approach is validated using measurements on devices from different technologies. System configuration, measurement, and calibration issues are presented.

Neodymium nickelate thin films have been prepared on NdGaO3 substrates by RF magnetron sputtering and post-annealing treatment under oxygen pressure. Transport properties are found to depend strongly on film thickness. Thick films show transport properties close to bulk ceramics, while very thin films exhibit a large transition from metal to insulator which occurs over a wide temperature range with high resistivity. Structure and surface morphology of the films have been investigated by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). Thin films (≈17 nm) grow heteroepitaxially, while thicker films (≈73 nm) show a granular structure. The thinnest sample suggests a symmetry change induced by the epitaxial strain of the substrate. This paper discusses the relationship between microstructure and transport properties.

The ablation rate of sintered polytetrafluoroethylene (PTFE) targets has been investigated as a function of wavelength within the range $193 \le \lambda \le 1064$ nm and pulse durations $5 \le \tau _{l} \le 25$ ns by means of various different lasers. In this parameter range, the apparent optical properties of targets and the depth of energy deposition are determined mainly by the scattering of the laser light. Therefore, measurements of the scattered light were performed for samples of various thicknesses by means of a modified UV-VIS spectrometer. For selected wavelengths, the angular distribution of the reflected and transmitted light intensity was determined. From these measurements, the coefficients for linear absorption, linear scattering and the scattering anisotropy were calculated using the inverse adding doubling algorithm. The results were tested by Monte Carlo simulation. With these coefficients the apparent optical penetration depths were estimated. These are about one order of magnitude larger than the ablation depths per pulse, which were determined from the weight loss of the targets. Laser deposition

Low concentration of toxic radioactive metals in environmental samples often limits the interpretation of results of infrared studies investigating the interaction processes between the metal ions and environmental compartments. For the first time, we could show that photothermal infrared spectroscopy performed with a pulsed free electron laser can provide reliable infrared spectra throughout a distinct spectral range of interest. In this model investigation, we provide vibrational absorption spectra of a rare earth metal salt dissolved in a KBr matrix and a natural calcite sample obtained by photothermal beam deflection (PTBD) technique and FT-IR spectroscopy, respectively. General agreement was found between all spectra of the different recording techniques. Spectral deviations were observed with samples containing low concentration of the rare earth metal salt indicating a lower detection limit of the photothermal method as compared to conventional FT-IR spectroscopy.

The spatial transition behaviour of the electron gas on its way from a uniform active plasma through an adjacent region of field decay and reversal into a field-free remote plasma is studied in neon on a nonlocal kinetic basis by solving the appropriate electron Boltzmann equation and by performing complementary Monte Carlo simulations. The main objective of the analysis concerns the complex features of the electron gas in its transition process from a field-driven active plasma, through a range of partial electron trapping in a potential energy valley to a diffusion-driven remote plasma. In this context especially the influence of the electron trapping and of the extent and depth of the potential valley is elaborated. In addition to the macroscopic characterization by means of the important transport and dissipation properties of the electrons their energy space resolved behaviour is derived and interpreted. A distinct decoupling between the spatial evolution of the isotropic and anisotropic part of the velocity distribution function and complex structures in the anisotropic part have been found. These findings could be clearly confirmed by the almost perfect coincidence with corresponding results obtained by the MC simulations. Glow; corona

This article deals with the analytical modelling of piezoelectric cylindrical micromotors [Morita et al., Jpn J. Appl. Phys. 35, 3251 (1996) and IEEE Trans. Ultrason. Ferroelectr. and Frequency Control 45, 1178 (1998)] and supplements the kinematics analysis of Pin Lu et al. [Sens. and Actuators A 87, 194 (2001)]. The modelling, based on an equivalent electric circuit, is established using geometrical and electromechanical parameters for the different parts of the motor. It gives electromechanical characteristics and other useful values for motor design.

This study is to look at the distribution of current densities in proton exchange membrane fuel cells (PEMFC) to enable optimisation of fuel cell performance. The feasibility of using a new measurement technique of the local magnetic field, in the conductive plates of the cell was studied. The magnetic field is measured throughout the cell using the Maxwell equations and the current densities calculated. The measurement system and its validation are outlined in the first section. The next section outlines the experimental current density distribution within the cell, operating under standard conditions and special configurations, such as the partially active membrane electrodes assembly (MEA). Using a Matlab or Femlab model of the cell, (which is briefly outlined) our experiments are compared and an attempt made to explain the distribution of the current densities. Finally recent developments of the device are described, which will be used in several tests of PEMFC small stacks.