ELECTRONIC-STRUCTURE OF MONOLAYER GRAPHITE ON A TIC(111) SURFACE

The electronic structure of monolayer graphite on a TiC(111) surface is investigated by first-principles band calculations. Occupied pi bands of the graphite layer are similar to those of bulk graphite with a constant shift to a lower-energy region. Unoccupied pi* bands are drastically deformed by hybridization with the substrate. The calculated band structure reproduces well an experimental band dispersion. Calculated electronic charges show no charge transfer from the substrate to the graphite layer. The lowering of the pi bands is explained by a change of electronic occupation in the graphite layer from the occupied sigma and pi states to the unoccupied pi* states due to hybridization with the substrate. The calculated results are consistent with the observed anomalous expansion of the lattice constant of monolayer graphite on metal substrates. The calculated band dispersion and electronic charges do not depend on the lateral position of the monolayer graphite relative to the substrate, which is explained by an averaging effect in incommensurate systems. Scanning-tunneling-microscopy (STM) images calculated from the results of the band calculation do not show the atomic structure of the graphite but show superstructures, which explain the experimental STM images.