Photon Emission from the Scanning Tunneling Microscope

Abstract

Much of the fascination of Scanning Tunneling Microscopy (STM) results from its ability to directly image atomic and molecular structures of a wide variety of materials. Since its inception, one purpose of STM has been to go beyond imaging by performing local experiments with individual nanoscopic objects addressed by the STM tip [5.1]. The concept of the technique to be presented in this chapter is to use the tip of a STM as a source of low-energy electrons or holes to locally excite photon emission and thus study luminescence1 phenomena on nanometer-sized structures of metals, semiconductors and molecules [5.2]. This combination of STM with optical methods offers several attractive features. First, photons represent a particularly versatile channel of information in addition to the tunneling current. Their intensity, spectral distribution, angular emission pattern, polarization status, and time correlation are accessible by sensitive optical methods and represent unique probes of the tunneling region. Spatial mapping of these physical quantities permits the addition of “true color” to STM images. Second, the emission of visible or infrared light is a chemically specific characteristic of many excitations of solids and molecules.