STM-INDUCED PHOTON-EMISSION SPECTROSCOPY OF GRANULAR GOLD SURFACES INAIR

Light emission has been detected under ambient conditions in the tip-s ample region of a scanning tunneling microscope (STM) consisting of an etched gold tip and a granular gold film. The photon yield as a Funct ion of surface geometry (photon mapping) has been studied. BS' means o f STM, it was possible to measure photon emission spectra locally. We have studied the effect of grain size and applied bias voltage on the spectrum. We found that the peak position in the photon emission spect rum shifts to a shorter wavelength when increasing the bias voltage an d shifts to a longer wavelength when tunneling to larger grains. These effects can be understood in a simple model which considers tunneling electrons exciting localized surface plasmons which decay bq emitting photons. (C) 1998 Elsevier Science B.V.