Nucleation, growth and acoustic properties of thin film diamond

The unusual combination of extreme properties possessed by diamond could benefit a wide range of applications. Thus far practical utilisation of this material has remained difficult and consequently limited; natural and synthetic crystals are unsuitable forms for many uses; particularly electronic applications which ideally require large area, single crystal substrates. Emerging CVD methods for the growth of thin film diamond offer a practical alternative; although nucleation on non-diamond substrates during CVD growth is in general poor, recently introduced negative substrate biasing has shown that very high nucleation densities and limited forms of heteroepitaxy can be achieved. However, although development has been rapid many problems remain; in particular, the underlying mechanisms of biased nucleation and growth on non-diamond substrates are not well understood. Furthermore, the successful development of a new material such as CVD diamond relies on a balance between fundamental research and exploitation of its benefits in the form of applications; at present there are only a few such examples for CVD diamond. This thesis addresses these issues by considering the bias enhanced nucleation of CVD diamond on silicon and tungsten substrates together with a study of the acoustic properties of the material. Bias enhanced nucleation and growth of (100) diamond on tungsten substrates has been characterised using secondary electron microscopy and Raman spectroscopy. Optical emission spectroscopy has been used to study the influence of substrate bias on the microwave plasma during diamond nucleation. Surface acoustic wave (SAW) devices have recently emerged as promising near term applications for currently available CVD diamond however little is known about the propagation of acoustic waves in this material; a detailed study of the influence of film characteristics on acoustic propagation in free standing CVD diamond films has been undertaken using the techniques of laser ultrasonic analysis. (author)