Spatial variation in local work function as an origin of moiré contrast in scanning tunneling microscopy images of Pb thin films/Si(111). (13th July 2016) - Kim, Howon
Abstract: By scanning tunneling microscopy (STM), we measured an evolution of electrical conductance from the tunneling to point contact regimes on Pb thin films formed on a Si(111) substrate. Immediately before the contact formation, the conductance evolution curves exhibit an onset of the conductance that is presumably due to a short-range chemical interaction between the tip apex atom and surface atom(s), and we found that the onset can be utilized as a reference of the tip–sample distance. By measuring the spatial variation in onset distance, we investigated surface atomic corrugation in moiré-corrugated areas and found that the geometrical corrugation is negligibly small (less than 2 pm) on the surfaces of 7-monolayer Pb thin films. We also observed a local variation in apparent barrier height depending on the moiré contrast in the tunneling regime, which leads us to conclude that the spatial variation in local work function is the origin of the moiré corrugation observed in STM images.