Photon emission from STM of granular gold in UHV: comparison with air and study of spectra shifting with tip position

This paper presents an experimental study using photon emission derived from scanning tunnelling microscopy (STM) of a granular gold surface in Ultra High Vacuum (UHV). The aim is to make a comparison with previous results obtained in air or in UHV. The photon emission spectrum also evidences a significant energy shift as the tip moves on a surface grain. This shift is attributed to the local geometry of the junction and to peculiar crystallographic properties of the surface