Characterization of surface nanostructures by STM light emission spectroscopy

Abstract

Visible light is emitted when electrons (holes) are injected into a sample from the tip of a scanning tunneling microscope (STM). Since the emission spectrum reflects the materials properties of the sample immediately below the STM tip, one can not only determine the surface topography by the usual STM imaging, but also, by simultaneously measuring the emission spectra, characterize the materials that make up nanostructures on a surface. The unique advantage of STM light emission (STM-LE) spectroscopy lies in the fact that it combines the atomic scale spatial resolution with a high energy resolution of the electronic states involved in the tunneling process. We have investigated the elementary processes that contribute to the STM light emission, and at the same time applied the technique to problems that can be uniquely addressed by this novel spectroscopic method. Two examples are discussed in this paper: (1) the measurement of the emission spectra from isolated individual nanostructures on the porous Si surface, and (2) the observation of the single-electron charging effect (Coulomb blockade) in small particles of Au.