Transition from single to multi-walled carbon nanotubes grown by inductively coupled plasma enhanced chemical vapor deposition
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In this work a simple and up-scalable technique for creating arrays of high purity carbon nanotubes via plasma enhanced chemical vapor deposition is demonstrated. Inductively coupled plasma enhanced chemical vapor deposition was used with methane and argon mixtures to grow arrays in a repeatable and controllable way. Changing the growth conditions such as temperature and growth time led to a transition between single and multi-walled carbon nanotubes and was investigated. This transition from single to multi-walled carbon nanotubes is attributed to a decrease in catalytic activity with time due to amorphous carbon deposition combined with a higher susceptibility of single-walled nanotubes to plasma etching. Patterning of these arrays was achieved by physical masking during the iron catalyst deposition process. The low growth pressure of 100 mTorr and lack of reducing gas such as ammonia or hydrogen or alumina supporting layer further show this to be a simple yet versatile procedure. These arrays were then characterized using scanning electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy. It was also observed that at high temperature (550 °C) single-walled nanotube growth was preferential while lower temperatures (450 °C) produced mainly multi-walled arrays.