Noise in Scanning Tunneling Microscopy and Surface Phonons

Abstract

The spatial distribution of the fluctuations of the tunneling current occurring in a Scanning Tunneling Microscope are investigated. Experiments performed in ultra high vacuum on a cleaved (110) surface of GaAs reveal a noise pattern with a commensurate structure of atomic dimensions. The maxima in the noise distribution are located near the Ga-atoms while the maxima in the topography are located either near the Ga- or the As-atoms depending on the polarity of the applied bias. Due to the buckling relaxation of the surface the Ga-atoms have an almost planar coordination resulting in a large vibrational amplitude. The enhanced current noise at the position of the Ga-atoms appears to be associated to fluctuations of the occupation number of a specific librational surface phonon.