Tuning the Electronic Structure of Graphite Moire with Chromium Deposition: a Scanning Tunneling Microscopy and Scanning Tunneling Spectroscopy Study

The growth of chromium (Cr) on moire patterns (MPs) on highly oriented pyrolytic graphite (HOPG) surface was studied by scanning tunneling microscopy/spectroscopy (STM/STS). At low coverage, Cr clusters can nucleate at top, bridge and hollow sites of the MP with no long-range or short-range orders. With increasing coverage, the size distribution of the Cr clusters remains constant and narrow, only the population increases. Compared to the situation before Cr deposition, the energy difference (Delta E-VHS) between the two van Hove singularities (VHSs) of the twisted HOPG surface layer is enlarged while remaining linearly proportional to the sine of the twisting angle. The distance-dependence of the Delta E-VHS enlargement, revealed by STS at extremely low Cr coverage, provides an estimate of each individual cluster's ability of modifying the graphite's electronic structure.