Time-correlations as a contrast mechanism in scanning-tunneling-microscopy-induced photon emission

We have developed an experimental technique based on scanning-tunneling microscope (STM) which permits to record simultaneously topography, STM-induced photon emission and a map of two-photon auto-correlations for time resolutions down to the sub-nanosecond range. In the case of a gold surface at air, we show that the tip-induced luminescence exhibits a photon-bunching phenomenon at a 10-ns time scale which depends both on bias and on local topography. The photon bunching was exclusively observed at specific bumps of the surface.