Direct observation of the water dimer adsorbed on graphite

Abstract Water/solid interfaces are closely related to our daily lives and play an important role in nature and technology. In this paper, we investigate the water molecules adsorbed on highly oriented pyrolytic graphite (HOPG) surface. The frontier molecular orbitals of adsorbed water dimer are directly observed by means of the low-temperature scanning tunneling microscopy (LT-STM). Furthermore, we find there are many water dimers and few small water clusters on HOPG, since the average adsorption energy per molecule of water dimer are higher than that of others. These results shed important light on the water/graphite interactions.