Scanning tunneling microscopy and atomic force microscopy of chemical-vapor-deposition diamond and diamond-like carbon thin films

Insulating polycrystalline diamond films grown by chemical vapor deposition (CVD) and semiconducting diamond-like carbon (DLC) films grown by laser-ablation have been studied using STM and AFM as well as other complementary techniques. Issues relating to the STM technique as well as the materials properties of these films have been explored. In a novel approach, photo-induced bulk carrier transport using a xenon are lamp providing broadband radiation (lambda = 189-700 nm) was used successfully to establish bulk conduction for STM imaging of the insulating films. Comparisons of topographic STM images with AFM images acquired on the same samples demonstrated the ability to correlate sub-micrometer structures observed in the images. This capability opens up the possibility that local electronic surface structure can be measured with STS. Preliminary tunneling spectra acquired on semiconducting DLC films demonstrated that illumination promotes the occupation of new electronic states resulting in a reduction of the observed energy gap at the surface. Images of DLC samples grown under a variety of conditions are providing new information into the preparation and growth parameters required to obtain the best quality films and their integrity after thermal cycling and other postfabrication treatments.