Abstract EN:

The present work is concentrated on the study of two isomers of an organic molecule -methylterrylene- adsorbed on a thin insulating _lm (a NaCl bi or tri-layer) deposited on a metallic substrate -Cu(111)-, by Scanning Tunneling Microscopy and Spectroscopy (STM and STS). Most STM studies of adsorbed atoms and molecules up to now have been performed on metallic or semiconducting surfaces. In this situation, the object is strongly electronically coupled to the substrate. The atomic or molecular levels are then shifted and broadened in energy, with the consequence that some of the intrinsic properties of the object are lost, to a more or less large extend. It has been shown recently that interposing between this object and the substrate an insulating leads to an efficient decoupling which allows to recover some of these properties. This decoupling effect of the insulating layer is at the center of the work reported here. Experiments where the molecules are directly adsorbed on the metal are compared with experiments where the molecule is decoupled from the Cu(111) surface by a NaCl bi-layer. The interpretation of these experimental results is supported and extended by current and image calculations with the Elastic Scattering Quantum Chemistry method where the structure of the Metal-insulating layer-molecule-metal junction is described at the atomic level. In the framework of molecular electronics, where the objective is to design and use molecules as electronic devices, understanding and controlling the coupling of a molecule to its environment is a central issue.