Photon-emission scanning tunneling microscopy of silver films in ultrahigh vacuum: A spectroscopic method

Abstract

We describe photon-emission scanning-tunneling-microscopy experiments on polycrystalline silver surfaces. By performing a method of simultaneous photon emission and tunneling spectroscopy measurements, we are able to show that the photon emission process and, in particular, the intergranular contrast in the photon maps depend upon interactions between individual grains in the silver film. Factors known to affect photon emission, such as grain shape and surface morphology, are shown to be inconsistent with the detailed structure of the photon maps. We observe that certain grains behave as isolated entities while others radiate in a more collective manner. This is indicative that for these materials the photon emission behavior is strongly affected by grain-boundary effects and we discuss a recent model which takes these into account. © 1993 The American Physical Society.