Thin polycrystalline diamond films have been deposited using both conventional chemical vapour deposition (CVD) and time-modulated CVD (TMCVD) processes. Films deposited using conventional CVD methods were found to be rough and exhibited columnar growth characteristics. The average crystallite size and the surface roughness of the as-grown films increased with film thickness. It was found that with increasing methane concentration the overall nucleation density increased. However, increasing the methane concentration deteriorated the quality of the films, in terms of diamond carbon phase purity, as evident from the Raman spectra. The TMCVD process involved pulsing methane gas initially at higher concentration, into the CVD reactor during the nucleation stage of the diamond CVD process followed by the extended growth duration at a lower methane concentration. The TMCVD process produced films that displayed smoother surfaces. In addition, the films were grown at higher growth rates compared to the conventional CVD films. A preliminary model explaining the mechanism of the TMCVD process is presented.