A vibronic resonance between Au{111} surface states and adsorbed CN vibrations has been predicted, which we target for study. We have formed stable monolayers of cyanide on Au{111} and observe a hexagonal close-packed lattice with a nearest neighbor distance of 3.8 ± 0.5 Å. Cyanide orients normal to the surface attached via a Au−C bond. We show that the substrate−molecule coupling is particularly strong, leading to ultrafast electron transfer from the cyanide molecules to the Au{111} substrate as measured by resonant Auger spectroscopy using the core−hole clock method. The CN/Au{111} system is a simple example of a strongly interacting adsorbate−substrate system and will be the subject of a number of further studies, as discussed.

We prepared titanyl phthalocyanine (TiOPc) monolayers on sapphire-prism supported Au{111} substrates through solution deposition and characterized their photo-responses using a custom-built laser-assisted scanning tunneling microscope under ambient conditions. Two types of lattice structures (hexagonal and rectangular) were observed and the distributions of photo-induced charges were measured under evanescently introduced 633 nm and 780 nm laser illumination. The distributions of photoelectrons in molecules in hexagonal lattices match theoretically calculated charge density changes in TiOPc molecules upon excitation. However, the photo-responses of TiOPc molecules in rectangular lattices are different than those predicted and TiOPc molecules in these arrangements may have lower excitation probabilities at 633 nm and 780 nm. Our results suggest that the photo carrier generation efficiency of TiOPc molecules is related to their packing arrangements in monolayers and local environments.

Cyanide monolayers on Au{111} restructure from a hexagonal close-packed lattice to a mixed-orientation "ribbon" structure through thermal annealing. The new surface structure loses most of the observed surface features characterizing the initial as-adsorbed system with "ribbon" domain boundaries isolating rotationally offset surface regions where the orientation is guided by the underlying gold lattice. A blue shift to higher frequencies of the CN vibration to 2235 cm with respect to the as-adsorbed CN/Au{111} vibration at 2146 cm is observed. In addition, a new low-frequency mode is observed at 145 cm, suggesting a chemical environment change similar to gold-cyanide crystallization. We discuss this new structure with respect to a mixed cyanide/isocyanide monolayer and propose a bonding scheme consisting of Au-CN and Au-NC bound molecules that are oriented normal to the Au{111} surface.