The effect of the reaction pressure has been studied on the nucleation behavior of the diamond synthesised by the hot-filament assisted chemical vapor deposition (HFCVD). Reaction pressure as a experimental variable was changed from 2 torr to 50 torr under the condition of filament temperature 2200℃, substrate temperature 850℃, total flow rate 200sccm and methane concentration 0.8%. Diamond deposites on the Si wafer and the polycrystalline $Al_{2}O_{3}$ substrate were characterizied by the micro-Raman spectroscopy, the scanning electron microscopy and the optical microscopy.
The maximum nucleation density of the diamond particles is observed on the Si substrate at the reaction pressure of 5torr. But this behavior is not seen on the $Al_{2}O_{3}$ substrate. These phenomena can be explained by the competition between the etching effect of atomic hydrogen and the formation of the β-SiC which favors the nucleation of diamond.
With the introduction of low pressure (5torr) nucleation and high pressure (30torr) growth process, the formation of diamond film is demonstrated on the Si substrate without any surface pretreatment by the HFCVD method.
