ATOMIC-FORCE MICROSCOPE STUDY OF THE EARLY STAGES OF NIO DEPOSITION ON GRAPHITE AND MICA

An atomic force microscope (AFM) operating in air has been used to stu dy the growth of evaporated nickel oxide on highly oriented pyrolytic graphite (HOPG) and mica. These substrates show atomically flat surfac es which can be imaged by the AFM with atomic resolution enabling, the refore, a clear identification of the deposit. On HOPG, spherical NiO structures (diameter similar to 100 nm, height similar to 10 nm) are o bserved to coalesce along the steps. Increasing the evaporation time a nd once the steps are occupied, a 'dendritic' growth on the terraces i s observed. On mica, a more homogeneous distribution of smaller NiO is lands is obtained over the whole surface. Nevertheless, a weak adhesio n to the substrate is found. The friction AFM images have allowed to e stablish the relative friction of the materials, which follow the decr easing sequence: graphite, NiO and mica. (C) 1998 Elsevier Science S.A .