MICROSTRUCTURE AND PHASE CHARACTERIZATION OF DIAMOND-LIKE AMORPHOUS HYDROGENATED CARBON-FILMS USING STM STS/

Scanning tunneling microscopy and spectroscopy (STM/STS) are used to o btain nanoscale information on morphological and electronic properties of the surface of diamond-like amorphous hydrogenated carbon (a-C:H) films. The films are prepared by r.f. plasma decomposition of methane CH4. A two phase model of a-C:H involving sp(2) clusters, embedded in a sp(3)-bonded matrix, is suggested. A new approach to a detection of graphite-like clusters at the surface of a-C:H films is proposed. An o verlayer of indium tin oxide (ITO) which helps to detect graphite-like clusters is used. The ITO deposition is performed in the conditions w hich routinely cause ITO to grow as a good conductor with high electro n density. The shape of current-voltage (I-V) characteristics obtained on the ITO/a-C:H, however, indicates nanoclusters of insulator within the matrix of the conductor. To explain the observed phenomenon the f ollowing results are considered. First, I-V characterization hints tha t thin films of ITO grown on weakly textured graphite normally have re duced electron density. Second, X-ray photoelectron spectroscopy measu rements show that weakly textured graphite adsorbs oxygen much stronge r than a-C:H. It is suggested, therefore, that it is oxygen, adsorbed by graphite-like clusters at the surface of a-C:H, which causes local drop of electron density in the ITO. As a consequence, I-V characteriz ation of ITO/a-C:H can be used for obtaining a high resolution map of the location of graphite-like clusters over the a-C:H surface.