Alison Crossley

Ultra-low friction for a layered carbide-derived ceramic, , investigated by lateral force microscopy (LFM)

The carbide-derived ceramic has a layered structure with double TiC-like blocks separated by planes of Si in six-fold coordination. It also has an unusual combination of electrical, thermal and mechanical properties. The polycrystalline ceramic exhibits a preferred plane of easy cleavage. Fracture/cleavage faces have been investigated by lateral and atomic force microscopy, scanning electron microscopy and other techniques. The results show that the ceramic is an exceptional solid lubricant. Freshly prepared (by fracture, abrasion or scraping) cleavage faces exhibit coefficients of friction at or below the limit of resolution, about , which are comparable to the lowest values measured for the best solid lubricants ( and graphite). Exposure to air leads to slight degradation, but values below were obtained after exposures of several months. Analysis of other faces leads to outcomes in the range 0.1-0.3, which are consistent with the outcome of macroscopic analysis. The favourable mechanical and electrical properties, in combination with ultra-low solid friction, may have important technical implications.

Surface modification of MgO substrates from aqueous exposure: an atomic force microscopy study

Abstract Cleaved MgO was subjected to fluid and gaseous chemical attack by water at or near ambient temperature. The exposure experiments were designed to mimic the variety of conditions that MgO may encounter as a substrate material in thin film technology. The resultant surface alterations were monitored with contact mode atomic force microscopy. It was found that MgO was relatively inert, at the near-atomic scale of detail, when the relative humidity of the gaseous phase was below 30%. When the humidity exceeded 30%, degradation was initiated at sites of low coordination (corners and steps). These results would indicate that, when handling MgO as a substrate for thin film technology, the processing environment must be carefully controlled to exclude bulk water and maintain humidity below 30%.

High temperature Raman studies of diamond thin films

Raman spectroscopy has become the definitive technique for assessing the quality of diamond thin films. Not only can the diamond/graphite contents be determined, but more detailed information, for example, about the domain size and the stress associated with a coating can be gleaned. The results of a Raman microprobe study of synthetic diamond coatings on silicon and alumina substrates, at elevated temperatures (up to 750°C) in controlled atmospheres of hydrogen, argon and oxygen are presented. The position of the Raman band associated with crystalline diamond (1332 cm−1) was monitored as a function of temperature. From the shift of the Raman band from its natural position, an associated stress value can be obtained.

Surface treatment for 'galling' protection of titanium alloys - characterization by surface-specific electron and Raman spectroscopies

Abstract It has been shown that the surface properties of titanium and its alloys, in particular the resistance to ‘galling’ and wear, can be enhanced by surface treatment/coating based on chemical/physical vapour deposition or ion implantation processes. Surface alteration of Ti arising from two processing routes, IonSlip™ and diamond-like carbon deposition, have been characterized by Raman and surface-specific electron spectroscopies, and then correlated with surface-mechanical properties.

Raman and reflection anisotropy spectroscopic studies of GaN and AlN growth on GaAs(100)

Abstract Initial nitridation of gallium arsenide to promote the nucleation and epitaxy of gallium nitride (GaN) is prone to interface roughening and defect generation. This paper reports the deposition of gallium nitride (GaN) onto GaAs(100) substrates using two alternative approaches: either a low temperature aluminium nitride (AlN) buffer layer or a graded transition from gallium arsenide to gallium nitride growth. The interaction of nitrogen atoms with the GaAs(100) — c(4 × 4)As stabilized surface and the recrystallization of A1N buffer layers deposited at 400 °C were observed by reflection anisotropy spectroscopy and dynamic optical reflectivity. Raman spectra of the resulting films suggest the presence of mixed cubic and hexagonal GaN phases.