Growth Rate Effects during Indium-Antimony Crystal Growth

Local interface velocities are tracked radioscopically in the III-V semiconductor compound indium-antimony grown in a vertical Bridgman-Stockbarger furnace. Comparisons are made of interface velocities from five different compositions (40, 49, 50, 55, and 60 at.% Sb). Under specific growth conditions, the growth velocity for stoichiometric melts was comparatively constant and very close to the translation velocity. Measured chemical homogeneity was excellent, though polycrystallinity could occur when concentration boundary layers formed ahead of the interface. Off-stoichiometric melts exhibited initial supercooling, resulting in transient interface velocities and polycrystallinity. The observed supercooling is governed by chemical segregation in the melt. Thus, local growth velocity fluctuations are unambiguously attributed to a coupling of ompositional effects in the melt and crystal facetting kinetics.     

Depletion kinetics of low-lying states of tungsten in the presence of NO,N2O,and SO2

The gas-phase reactivities of W(a⁵D_J, a⁷S₃) with N₂O, SO₂, and NO in the temperature range of 295–573 K are reported. Tungsten atoms produced by the photodissociation of W(CO)₆. The tungsten atoms were detected by a laser-induced fluorescence technique. The removal rate constants for the 6s²5d⁴ a⁵D_l states were found to be pressure dependent for all of the reactants. Removal rate constants for the 6s¹5d⁵ a⁷S₃ state were found to be fast compared to the a⁵D_J states and often approached the gas kinetic rate constant. The reaction rates for all the states were found to be pressure independent with respect to the total pressure. Results are discussed in terms of the different electronic configurations of the states of tungsten © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 367–375 1997     

Metal point contacts and metal-oxide tunnel barriers fabricated with an AFM

We report the fabrication of atomic point contacts and lateral tunnel junctions by using anodic oxidation of thin metal films with an atomic force microscope.In situelectrical measurements were used as feedback to control the fabrication of metal nanowires that were subsequently anodized through their cross section to form point contacts and tunnel junctions. When the conductance of an Al device is reduced below 5×10⁻⁴S it starts to decrease in discrete steps of 2e²/h. In some devices we are able to stabilize the conductance at a value near 2e²/hwhich corresponds to a single, atomic-sized conducting channel. Similar experiments on Ti devices result in a continuous decrease of the conductance and the formation of stable tunnel junctions. This continuous behavior is a result of the large series resistance and the small oxide barrier height of the Ti/TiO_xsystem.     

An Investigation of the Dynamic Structures of Ferrocene,Ruthenocene and Dibenzenechromium in the Solid State and in Solution

Pulse nuclear magnetic resonance measurements have been used to determine the activation enthalpies for the reorientation of the organic rings in ferrocene, ruthenocene and dibenzenechromium. The contribution from non-bonded interactions to the total potential for reorientation of the rings has been calculated and is compared to the experimental activation enthalpies. The results indicate that there is no contribution to the potential from the non-bonded interactions between the two rings on a single molecule and that the observed potential barrier is due to a combination of crystal packing forces and bonding forces within the molecule.

The crystal structure of ferrocene is thought to be disordered above 135[ddot]K, and a model is proposed for the order-disorder transition in the solid state. On this basis, dynamic models are proposed for the structures of the three metallocenes in solution.     

Review of LDA and PIV applied to the measurement of sound and acoustic streaming

A review of laser Doppler anemometry (LDA) and particle image velocimetry (PIV) with their application to the measurement of sound is presented. The fundamental principles behind LDA and PIV are discussed and extended to the application of sound measurement. Special attention is paid to analysis of LDA signals including the Hilbert transform, which enables amplitude information to be obtained about various frequency components of a signal and wavelet analysis, which allows non-stationary signals to be accurately analysed. The influence of the refractive index variations in a medium due to a sound wave on the laser beams of an LDA signal is discussed. Attention is also paid to acoustic streaming which arises due to high-intensity sound, and PIV results are presented to demonstrate the effect.