Characteristics of low field-emission diamond films by scanning probe microscopy (SPM)

Field emission from the polycrystalline diamond film prepared by a two-step hot filament (HF) CVD method showed a turn-on held of 1.7 V mum(-1). To understand the low field-emission mechanism, nanoscale characteristics of both step films, the bias enhanced nucleation (BEN) film, and the subsequent poly-diamond film, were investigated by SPM. Simultaneous measurement of the topography and conductivity was carried out on both step samples. The topography image of the BEN him showed globe-shaped particles, whereas the poly-diamond him showed textured structures. Current images of both samples were found to be similar, however, which showed that highly conducting and non-conducting regions coexisted on a micro- and/or nanoscale. A comparison between the current images and the topography images revealed no obvious relationship between the morphology and the local conductivity. Further in situ I-V characteristics demonstrated that the conducting sites have an ohmic property, indicating the existence of metallic carbon phases, whereas non-conducting regions are not simply insulating, but show a characteristic of the Schottky property of a semiconductor in both samples. It is suggested that the conducting graphite channels were distributed in the semiconductor matrix on a nanoscale in both samples, despite the topography difference. It is revealed that the field enhancement on the conducting channels plays an important role in the low field emission. It is suggested that conductive SPM, capable of multiple operation modes, has tremendous potential for the elucidation of the microscopic properties of complex-phase materials. (C) 2001 Elsevier Science B.V. All rights reserved.