Room-temperature growth of carbon nanofibers induced by Ar⁺-ion bombardment

Glassy carbon plates, a Ni mesh coated with a carbon film and mechanically polished graphite plates were Ar⁺ ion-bombarded with and without a simultaneous Mo supply at room temperature. Conical protrusions were formed on the sputtered surfaces, and in some cases carbon nanofibers (CNFs) 0.2-10 μm in length and 10-50 nm in diameter grew on the tips. The growth of CNF-tipped-cones was optimized in terms of the ion-incidence angle and the rate-ratio of sputtering and seeding. Oblique sputtering was proved to be quite effective to grow the CNF-tipped-cones. Thus, the redeposited massive carbon atoms onto cones were thought to diffuse toward the cone tips, resulting in CNF formation. This growth mechanism was confirmed by transmission electron microscope (TEM) observation disclosing the boundary-less structure between conical bases and CNFs. TEM observation of CNF-tipped-cones also revealed no-hollow structure and an amorphous nature of CNFs. Since this sputtering method is a room-temperature process and quite straightforward, ion-induced CNFs promise to have myriad applications, such as field emission sources for flat panel displays.