Field electron emission from sputter-induced carbon nanofibers grown at room temperature

Graphite, carbon-coated silicon, and carbon-coated nickel surfaces were bombarded with obliquely incident Ar⁺ ions at room temperature. The sputtered surfaces were covered with conical protrusions, ∼2.5 × 10⁵ mm^-2 or higher in numerical density, and partially aligned single carbon nanofibers (CNFs), ∼20 nm in diameter and 0.3-2 μm in length, grew on the tips. They were characterized by the amorphous nature and the boundaryless structure between the CNF and the conical base. The field electron emission measurements for the CNFs thus grown on the carbon-coated silicon substrate showed the threshold field of 1.8 V/μm with a current density of 1 μA/cm², and the field enhancement factor was estimated to be 1951 from the Fowler-Nordheim plot assuming the work function of 4.6 eV for graphite. The morphological structure of CNFs grown on conical bases was thought to be effective to reduce the screening effect due to sufficient distance between adjacent CNFs. Thus, the sputter-induced CNFs were concluded to be quite promising as a field electron emission source.