Impact of the etching gas on vertically oriented single wall and few walled carbon nanotubes by plasma enhanced chemical vapor deposition

Vertically oriented single wall nanotubes (SWNTs) and few walled nanotubes (FWNTs) have been grown by electronic cyclotron resonance plasma enhanced chemical vapor deposition (PECVD) on silica flat substrates. The impact of the plasma parameters on SWNT and FWNT growth has been investigated using two different etching gas mixtures, namely, C2H2/NH3 and C2H2/H-2 with various ratios and applied bias voltages. Kinetic studies are also proposed in order to describe the FWNT growth mechanism by plasma techniques. A key role played by the reactive gas (NH3 and H-2) is observed in the PECVD process, contrary to multiwalled nanotube growth. It is demonstrated that the balance between FWNT growth versus FWNT etching can be widely modulated by varying the gas mixture and bias voltage. It is shown that the use of hydrogen for hydrocarbon gas dilution restricts the destruction of SWNT and FWNT by the plasma species (ions and radicals). (c) 2007 American Institute of Physics.