Optical absorption spectroscopy by scanning force microscopy

Scanned-probe techniques are providing nanometer-resolution images of surface properties and surface features. In this contribution we suggest a technique identifying these features by locally recording their optical spectra. The technique is based on a simple modification to a scanning force microscope where an optical beam is focused onto the sample and the change in contact potential difference between tip and sample is measured as a function of laser wavelength. The change in contact potential difference can be due either to local heating or to a change in the surface dipole moment caused by optical excitation of sample and/or tip. Initial results of spectra and images of Au on mica and Cr are presented. © 1992.