Evidence of Anisotropic Diffusion of Indium Atoms on a Surface of Perylene-3,4,9,10-tetracarboxilic dianhydride/MoS2 System Observed by Photoelectron Emission Microscopy (PEEM)

An unusual triangular image was observed by photoelectron emission microscopy (PEEM) when a square-shaped microstructure of In metal was deposited on a thin film of perylene-3,4,9,10-tetracarboxilic dianhydride (PTCDA) grown semiepitaxially on a cleaved MoS2 surface. The formation of the triangular pattern demonstrates the anisotropic surface diffusion of In atoms on the PTCDA/MoS2 system. The threefold diffusion directions, which form the triangular structure, correspond excellently with the three equivalent surface crystal axes of the MoS2 substrate. When In atoms were directly deposited on MoS2, such diffusion was not observed, suggesting that the phenomenon is related to the strong chemical interaction between In atoms and oriented PTCDA molecules.