The nucleation density of diamond films produced by microwave plasma enhanced chemical vapor deposition was enhanced up to four times using a cyclic methane flow modulation technique. In this technique, the plasma composition is alternated for short periods between a combination of methane and hydrogen and hydrogen only. This results in alternate periods of deposition and etching for the nucleation run. The highest nucleation density, 1.8×10(8) cm(-2), was obtained for the highest methane:hydrogen ratio of 8:200 sccm at a growing/etching time ratio of 180/30 s for 10.5 min over 3 h total time on the glass substrates. The grain size likewise increased up to 0.85 μm with a higher growing/etching time ratio. In contrast, the diamond quality, as measured by the relative intensity of Raman peaks corresponding to diamond and amorphous carbon was inversely related with the growing/etching time ratio.