Thin diamond films have been grown by hot filament chemical vapor deposition (CVD) on untreated, diamond powder scratched and d.c.-bias pretreated Si(111), SiO2 and graphite substrates. The deposits were characterized using X-ray photoelectron spectroscopy, scanning Auger microprobe and scanning electron microscopy. The increased surface oxide thickness due to scratching has no influence on the nucelation of diamond films since SiO2 films of known thickness have been found to be reduced under growth conditions. Positive d.c.-bias pretreatment leads to an increased number density of nuclei which can be further increased by permanent biasing throughout the deposition. The pretreatment causes intermediate deposition of turbostratic carbon which promotes nucleation of diamond. The increased number density of nuclei is discussed in relation to deposition of diamond on various forms of graphite.