BARRIER HEIGHT IMAGING INVESTIGATION OF LIQUID-CRYSTAL MOLECULES ADSORBED ON GRAPHITE

The barrier height imaging technique was applied to a graphite surface covered with liquid crystal molecules, Barrier height images of the molecules were found to exhibit better image quality than the scanning tunneling microscope (STM) images. Under different conditions, images of underlying graphite were obtained instead of molecular images, in both STM and barrier height images. It was also found that the barrier height image and the simultaneously obtained STM image of adsorbed molecules were reversed in contrast while those of the underlying substrate graphite were similar. The reason for this difference was discussed in relation to the mechanism of molecular image formation.