In situ growth rate measurements during plasma-enhanced chemical vapour deposition of vertically aligned multiwall carbon nanotube films

In situ laser reflectivity measurements are used to monitor the growth of multiwalled carbon nanotube (MWCNT) films grown by DC plasma- enhanced chemical vapour deposition (PECVD) from an iron catalyst film deposited on a silicon wafer. In contrast to thermal CVD growth, there is no initial increase in the growth rate; instead, the initial growth rate is high (as much as 10 mu m min(-1)) and then drops off rapidly to reach a steady level (2 mu m min-1) for times beyond 1 min. We show that a limiting factor for growing thick films of multiwalled nanotubes (MWNTs) using PECVD can be the formation of an amorphous carbon layer at the top of the growing nanotubes. In situ reflectivity measurements provide a convenient technique for detecting the onset of the growth of this layer.