Investigation of photoinduced tunneling current and local surface photovoltage by STM

Photoassisted scanning tunneling microscopy was used to simultaneously image topography, photoinduced tunneling current and local surface photovoltage on an nm-scale. A novel interrupted z-feedback technique is presented which overcomes the limitations of previously reported techniques, that were restricted to semiconductor surfaces with a high density of surface states. As an example, measurements on the van der Waals surface of WS2 are shown. This semiconductor surface is known to be free of intrinsic surface states. In the vicinity of monolayer steps an enhanced minority charge carrier recombination and a reduced photovoltage was observed.