title: Converting carbon nanofibers to carbon nanoneedles: catalyst splitting and reverse motion.
abstract: Carbon nanoneedles (CNNs) were grown using a plasma-enhanced chemical vapor deposition process in which the source gas (C(2)H(2)) was turned off 10 min before the NH(3) flow and plasma were turned off. It is demonstrated that tubular carbon nanofibers (CNFs) grow while the source gas is on. However, once the source gas is turned off, the Ni catalyst at the top of each CNF splits to form a small catalyst that remains at the top of the tube and a larger catalyst that travels down the interior of the tube. We postulate that the motion of the bottom (larger) catalyst is driven by etching of the graphitic walls and 'cups' inside the CNF. This process, combined with slowing growth of the CNFs and etching of the material above the bottom catalyst, converts the carbon nanofibers to the final nanoneedle shape.
authors.affiliation: Advanced Materials for Micro- and Nano-Systems Programme, Singapore-MIT Alliance, Singapore.
authors.forename: Jia
authors.initials: J
authors.lastname: Yun
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: M H
authors.initials: MH
authors.lastname: Hong
authors.forename: J T L
authors.initials: JT
authors.lastname: Thong
authors.forename: Y L
authors.initials: YL
authors.lastname: Foo
authors.forename: C V
authors.initials: CV
authors.lastname: Thompson
authors.forename: W K
authors.initials: WK
authors.lastname: Choi
mesh_terms: D015374:Biosensing Techniques; D002384:Catalysis; D004581:Electronics; D005740:Gases; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning / Q000379:methods; D046529:Microscopy, Electron, Transmission / Q000379:methods; D049329:Nanostructures; D036103:Nanotechnology / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry; D010777:Photochemistry / Q000379:methods; D012825:Silicon / Q000737:chemistry
chemical_list: D005740:Gases; D037742:Nanotubes, Carbon; D009532:Nickel; D012825:Silicon