Diamond particles have been synthesized on an abraded silicon substrate from a gas mixture of methane and hydrogen by hot filament chemical vapour deposition. The nucleation and growth process of the diamond particles have been studied by varying the deposition time. The intermediate layer between the diamond particle clusters and the substrate was observed by scanning electron microscopy of the films deposited for 60 and 120 min. By micro-IR absorption measurements, absorptions were detected between 2800 cm(-1) and 3000 cm(-1) for the intermediate layer, while for the diamond particle clusters little absorption was observed in the same region. Raman spectra from the intermediate layer displayed the broad peak lying between 1300 cm(-1) and 1600 cm(-1), indicating amorphous carbon. The intermediate layer was found to be a hydrogenated amorphous carbon (a-C:H) film. Atomic force microscopy (AFM) studies have been performed on the surfaces of films deposited for 30, 60, and 120 min. AFM observations revealed that the surface of the intermediate a-C:H layer in the films deposited for 60 min was covered with numerous protrusions and in the films deposited for 120 min these protrusions were developed to layered triangular pyramids. Several aggregates of triangular pyramids were found in the a-C:H layer, suggesting a precursor to the diamond particles. However, the surfaces of the films deposited for only 30 min were not covered with the protrusions, but were covered with particle-like features. It is proposed that a-C:H films are initially formed on the substrate and that diamond nuclei are created in the a-C:H films and grow to be diamond particles.