High resolution electron energy loss spectroscopy (HREELS) is employed to analyze reversible changes in the geometrical structure of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111), which are induced by UV-light and thermal activation. In the sub-monolayer regime TBA adsorbs in the planar (trans)-configuration. UV-light exposure at 3.5 eV leads to pronounced changes in the vibrational structure of the TBA molecules in direct contact with the Au(111) surface, which we assign to a trans to cis isomerization. The reverse process, i.e., the cis to trans isomerization can be stimulated by thermal activation. An intensity decrease of vibrational modes as a function of photon dose allows calculation of an effective cross section of σ eff ≈ 2x10-21 cm-2 for the trans to cis isomerization.
The publication is available at link DOI: 10.1021/jp075274o