Effects of the pressure on growth of carbon nanotubes by plasma-enhanced hot filament CVD at low substrate temperature

Carbon nanotubes were prepared on silicon wafers deposited with NiFe catalyst films and Ta buffer films by plasma-enhanced hot filament chemical vapor deposition, and growth of the carbon nanotubes under different pressure were investigated by scanning electron microscopy. It is found that the average length of the carbon nanotubes grown at the pressure of 15 Torr is larger than that at the pressure of 30 Torr. But, it is difficult to grow the carbon nanotubes when the pressure is 5 Torr. These indicate that the pressure greatly influences on the growth of carbon nanotubes. Combined with theories related to thermodynamics of alloy and glow discharge, it is analyzed and discussed that the pressure affects the growth of the carbon nanotubes.