STM induced light from nontrivial metal structures: Local variations in emission efficiency

Scanning tunneling microscopy is performed on a gold surface which is structured on a length scale of 10-100 nm by colloidal lithography and the light emission induced by the tunneling electrons is investigated. The lithographically defined structure is reflected in a contrast in photon emission. It turns out that a major contrast mechanism depends only on the local geometry of the tunnel contact. Remarkable variations in photon images are observed, dark flat areas and bright slopes as well as the inverted case may be obtained upon imaging with different tips. A qualitative explanation for this behavior is proposed.