Nanometer-scale mapping of local work function with a photon-assisted STM technique

Local work-function mapping has been performed using scanning tunneling microscopy (STM) combined with visible laser light. Spatial distribution of the work function was visualized for inhomogeneous alkali-metal overlayers on a patterned Cu surface in a nanometer scale formed by nitrogen ion implantation. The spatial resolution of this technique is estimated to be in a sub-nanometer range.