PHOTON-EMISSION SCANNING-TUNNELING-MICROSCOPY OF SILVER FILMS IN ULTRAHIGH-VACUUM - A SPECTROSCOPIC METHOD

We describe photon-emission scanning-tunneling-microscopy experiments on polycrystalline silver surfaces. By performing a method of simultan eous photon emission and tunneling spectroscopy measurements, we are a ble to show that the photon emission process and, in particular, the i ntergranular contrast in the photon maps depend upon interactions betw een individual grains in the silver film. Factors known to affect phot on emission, such as grain shape and surface morphology, are shown to be inconsistent with the detailed structure of the photon maps. We obs erve that certain grains behave as isolated entities while others radi ate in a more collective manner. This is indicative that for these mat erials the photon emission behavior is strongly affected by grain-boun dary effects and we discuss a recent model which takes these into acco unt.