A combination study of conductivity and contact potential in low-field-emission carbon film by conductive scanning probe microscopy

Simultaneous measurements of surface topography of and nanoscale conductivity/potential distributions in low-field-emission carbon films were performed by conductive scanning probe microscopy (SPM). The films were produced by bias-enhanced nucleation (BEN) hot filament (HF) chemical vapor deposition (CVD). A turn-on field of as low as 1 V/mu m was obtained by field-emission measurements. Simultaneous topography-current maps were obtained by bias-applied conductive atomic force microscopy (AFM) in the contact mode and showed that highly conducting sites and dielectric regions of the micro- and/or nanometer order coexisted. Furthermore, in situ I-V characteristics of both regions showed that the conducting sites have a metallic ohmic property, whereas the dielectric regions have a degenerated Schottky property, which represents a semiconductor band structure. Contact potential differences (CPD) were measured as surface potential (V-CPD) images of one and the same area were obtained, which made it possible to evaluate the work function of the conducting sites. It is shown that the conducting sites have a work function of about 5.0 eV, which most likely indicates the graphite phase. It is revealed that randomly distributed conducting channels play an important role in the low-field-emission process. It is also suggested that simultaneous measurements of topography and conductivity/contact potential and the combination of the two are effective methods for investigating nanostructural surfaces.