title: A theoretical rationalization of a total inelastic electron tunneling spectrum: the comparative cases of formate and benzoate on Cu(111).
abstract: Inelastic electron tunneling spectroscopy (IETS) performed with the scanning tunneling microscope (STM) has been deemed as the ultimate tool for identifying chemicals at the atomic scale. However, direct IETS-based chemical analysis remains difficult due to the selection rules that await a definite understanding. We present IETS simulations of single formate and benzoate species adsorbed in the same upright bridge geometry on a (111)-cleaved Cu surface. In agreement with measurements on a related substrate, the simulated IET-spectra of formate/Cu(111) clearly resolve one intense C-H stretching mode whatever the tip position in the vicinity of the molecular fragment. At variance, benzoate/Cu(111) has no detectable IET signal. The dissimilar IETS responses of chemically related molecules--formate and benzoate adsorbates--permit us to unveil another factor that complements the selection rules, namely the degree of the vacuum extension of the tunneling active states perturbed by the vibrations. As a consequence, the lack of a topmost dangling bond orbital is entirely detrimental for STM-based inelastic spectroscopy but not for STM elastic imaging.
authors: Ecole Normale Supérieure de Lyon, Laboratoire de Chimie, CNRS UMR 5182, 46 Allée d'Italie, 69364 Lyon Cedex 07, France.
authors: S R
authors: SR
authors: Burema
authors: N
authors: N
authors: Lorente
authors: M-L
authors: ML
authors: Bocquet