The　catalyst-free　growth　of　carbon　nanotips　and　nanotubes　on　silicon　substrate　pre-deposited　with　carbon　film　was　realized　under　different　temperatures　in　plasma-enhanced　hot　filament　chemical　vapor　deposition　system,　in　which　methane,　nitrogen　and　hydrogen　were　used　as　the　reactive　gases.　The　structure　and　composition　of　synthesized　carbon　nanotips　and　nanotubes　were　investigated　using　field　emission　scanning　electron　microscope,　transmission　electron　microscope　and　micro-Raman　spectroscopy,　respectively.　The　results　indicate　that　the　carbon　nanotips　are　formed　at　about　800　degrees　C　while　the　carbon　nanotubes　are　formed　about　900　degrees　C.　According　to　the　ion　bombardment　effect　and　the　diffusion　at　different　temperatures,　the　catalyst-free　formation　of　carbon　nanotips　and　nanotubes　was　comparatively　studied.　The　transformation　from　carbon　film　to　spherical　carbon　particles　at　a　high　temperature　results　in　the　formation　of　carbon　nanotubes　depending　on　the　diffusion　of　carbon.　At　a　low　temperature,　the　carbon　film　still　locates　at　the　substrate　and　leads　to　the　formation　of　carbon　nanotips　relying　on　the　sputtering-etching　of　etching　ions　and　the　deposition　of　carbonaceous　ions.　In　addition,　the　electron　field　emission　characteristics　of　carbon　nanotips　and　nanotubes　were　investigated.　The　results　indicate　that　there　is　much　difference　in　the　electron　field　emission　properties　for　the　carbon　nanotips　and　nanotubes.　According　to　the　thermal　effect　produced　by　Joule　heat　during　electron　emission,　the　difference　was　interpreted.　(C)　2013　Elsevier　B.V.　All　rights　reserved.