Growth of aligned carbon nanotubes by plasma-enhanced chemical vapor deposition: Optimization of growth parameters

Direct-current plasma-enhanced chemical vapor deposition (CVD) with mixture s of acetylene and ammonia was optimized to synthesize aligned carbon nanot ubes (CNTs) on Co- or Ni-covered W wires with regard to wire temperature, w ire diameter, gas pressure, and sample bias. A phase diagram of CNT growth was established experimentally in this optimization process. It was reveale d by transmission electron microscopy that Co-catalyzed CNTs encapsulated a Co carbide nanoparticle at their tip, disagreeing with a previous report t hat Co particles were located at the base of CNTs CVD grown on Co-covered S i substrates [C. Bower , Appl. Phys. Lett. 77, 2767 (2000)]. This leads to the conclusion that the formation mechanism of aligned CNTs depends signifi cantly on the catalyst support material as well as the catalyst material it self. Since the sample bias strongly affected the morphology of CNTs, the s elective supply of positive ions to CNT tips was possibly responsible for t he alignment of growing CNTs. (C) 2001 American Institute of Physics.