Real-space structural characterization of benzene monolayer on graphite (0001) surface investigated by low-temperature scanning tunneling microscopy

Real-space structural characterization of benzene (C6H6) adsorbed on the graphite (0001) surface was investigated at the nanoscale. Scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) were used to assign a well-ordered (root 7 x root 7) R19.1 degrees structure at around monolayer coverages. The STM image clarified the flat-lying adsorption of benzene with its molecular plane parallel to the surface. At a sample bias around the adsorption-induced highest occupied molecular orbital (HOMO) level, the STM image showed an elongated protrusion separated by a single nodal depression; this is because the degeneracy of the HOMO is lifted by the interaction with the substrate.