Spatial Variations in Submolecular Vibronic Spectroscopy on a Thin Insulating Film

Abstract

Scanning tunneling spectroscopy on single naphthalocyanine molecules adsorbed on an ultrathin aluminum oxide film exhibits electron-vibronic coupling that varies with the position of tunneling over the molecule. The spectra at different positions are composed of several series of equally spaced peaks, which are interpreted as progression of progressions of molecular vibrational modes. The spatial variations correlate with the molecular orbital structure, revealing spatially dependent electron-vibronic coupling and selective vibrational excitation.