EFFECT OF ATOMIC HYDROGEN SORPTION AND DESORPTION ON TOPOGRAPHY AND ELECTRONIC PROPERTIES OF PYROLYTIC GRAPHITE

摘要

Interaction of hydrogen atoms with the (0001) basal plane of highly oriented pyrolytic graphite surface has been studied by atomic force microscopy (AFM), scanning tunneling microscopy and spectroscopy (STM/STS) and thermal desorption (TD) spectroscopy methods. The AFM and STM studies have shown that this interaction drastically changes the initially atomically flat graphite surface into a very rough surface. Sorption of hydrogen atoms takes place, causing bumps on the surface with heights up to 5 nm. The TD of sorbed hydrogen atoms results in smoothing the surface, leaving no bumps, however creating monolayer deep etch-pits. The TD spectra show two maxima, at 850℃ and 1250℃, indicating that there are at least two activation processes. The cycles of hydrogen atoms sorption with subsequent TD result in the lateral growth of the etch-pits, formation of new etch-pits on the bottom of the former ones and finally in the layer by layer removal of the graphite monolayers. STS studies have revealed formation of distinct electronic states at the edges of the etch-pits. These surface states appear as maximums of the local density of states in the energy range of 90-200 meV above the Fermi level, the localized state energy being dependent on the position along the edge of pit. This observation manifests dependence of the localized state energy on local conditions at the pit edges.