We present a systematic study of the mechanical properties of bulk Si, GaP, GaAs and ZnSe semiconducting materials. Nanoindentation tests have been performed on the (001) surface of single crystals and their interpretation has been supported by AFM imaging of the indented surface. For all four materials, hardness and Young's modulus appear to be independent of the orientation of the Berkovich nanoindenter tip relative to the [100] direction. In contrast, hardness varies significantly with the applied load for ZnSe, which is the only material exhibiting large creep. All mechanical properties—plasticity, hardness, Young's modulus—depend on both the interatomic distance and the ionicity of the materials. Si and ZnSe are, respectively, the hardest and the softest materials of the series, the hardness of ZnSe being comparable to that of soft metals.

Experiments on the analysis of the wear debris produced during the polishing of diamond and the rapid sliding of diamond upon diamond using a high-speed sliding machine are presented. The debris was studied by electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) and by transmission electron microscopy (TEM). The aim of the work was to improve understanding of the polishing process. It was found that the debris produced when polishing diamond in a direction on a plane consisted of less dense forms of carbon. Diamond debris was instead found in the experiment with the high-speed sliding machine, but the wear track showed markedly different features from those observed on a surface after conventional polishing. The results suggest that the polishing of diamond in the soft directions occurs by a process in which diamond transforms to less dense forms of carbon, after which the transformed material detaches.

Results are presented of friction and wear measurements during diamond polishing using new instrumentation designed and built in our laboratory. The wear rates are found to be highly anisotropic, depending both on the crystallographic plane and on the direction along which sliding occurs. Friction measurements performed during polishing on a {100} plane in the 100 direction (the direction of the highest wear rate on the plane) and the 110 direction (the direction of the lowest wear rate) exhibit similar trends to those occurring in friction at low speed on the {100} face, with the 100 direction having a higher friction coefficient than the 110 direction. It was further found that the variation of friction with pressure in the 100 and the 110 directions are different, pointing to the fact that two wear mechanisms operate in the two principal directions. The results are consistent with, and provide macroscopic evidence in support of, a model of mechanically induced transformation of diamond to sp 2 hybridized carbon occurring on the diamond surface during polishing along the direction in which the wear rate is high. In contrast to this, the wear process proposed for the 110 direction is one of micro-fracture, in agreement with earlier studies of the polished surface and the wear debris. By explaining the wear mechanism in terms of two different types of processes operating in the two directions, we are able to understand the high anisotropy observed.

Results are presented from studies of the relationship between the friction coefficient and environment, load and sliding velocity for a natural diamond stylus performing reciprocating sliding over a CVD diamond sample. The properties of CVD diamond are not necessarily similar to those of natural diamond. It is thus important to study the tribological properties of the former, both to attempt to understand the friction mechanism and because of its increasing potential applications as a coating material. Traditionally, friction for diamond sliding against diamond has been interpreted principally in terms of the adhesion and surface roughness theories. We put forward, here, a hypothesis based on a chemical transformation occurring during sliding, resulting in the production of graphitic material. The very low friction coefficients that have been measured under certain conditions of load and sliding velocity may thus be partly explained by the lubricating effect of graphite.

The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N2 discharge, was studied for postdeposition annealing temperatures TA up to 1000 °C. Films were grown at temperatures of 100 °C (amorphous structure) and 350 and 550 °C (fullerenelike structure) and were analyzed with respect to thickness, composition, microstructure, bonding structure, and mechanical properties as a function of TA and annealing time. All properties investigated were found to be stable for annealing up to 300 °C for long times (>48 h). For higher TA, nitrogen is lost from the films and graphitization takes place. At TA = 500 °C the graphitization process takes up to 48 h while at TA = 900 °C it takes less than 2 min. A comparison on the evolution of x-ray photoelectron spectroscopy, electron energy loss spectroscopy and Raman spectra during annealing shows that for TA > 800 °C, preferentially pyridinelike N and –C≡N is lost from the films, mainly in the form of molecular N2 and C2N2, while N substituted in graphite is preserved the longest in the structure. Films deposited at the higher temperature exhibit better thermal stability, but annealing at temperatures a few hundred degrees Celsius above the deposition temperature for long times is always detrimental for the mechanical properties of the films.