Inelastic Electron Tunneling of C60 on Gold Surfaces from First-Principles Calculations

The simulation of IET spectra of a single C60 molecule placed between two gold electrodes has evidenced the high sensitivity of IET spectroscopy to the C60 orientation and also to the molecule-electrode distance. When considering a small molecule-electrode distance (d = 2.0 Å) the dominant peaks are associated with longitudinal displacements of the contact moieties. For d = 2.8 Å, depending on the adsorption configuration the dominant signatures are not associated with the same atomic motions, while for larger distances (d = 4.0 Å) the four configurations only exhibit peaks corresponding to C-C stretching modes. The best agreement between experimental measurements and our theoretical calculations has been found when considering a molecular junction characterized by two hexagons of the C60 molecule aligned parallel to the Au(111) surfaces and centered on a hcp site, with a distance between the center of the hexagon aligned parallel to the Au(111) surface and the hcp site of the source (drain) reservoir of 2.8 Å (3.4 Å). Our approach can therefore be of great help in understanding, beside the intrinsic vibrational behavior of one compound, the small structural variations induced by the proximity to the metal electrodes. © 2014 American Chemical Society.