Surface Structure and Electron Transfer Dynamics of the Self-Assembly of Cyanide on Au{111}

Abstract

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.

Hexagons to Ribbons: Flipping Cyanide on Au{111}

“…Cyanide molecules deposited on Au{111} from exposure to HCN(g) under atmospheric conditions order in a hcp lattice at room temperature. 38 Figure 1A shows the structural details of cyanide monolayers, obtained under ambient conditions by scanning tunneling microscopy (STM), which include surface features such as vacancy islands, protruding islands, and multiple highly ordered domains. In this cyanide-on-Au{111} structure, the measured nearest-neighbor spacing is 3.8 ± 0.5 Å.…”

“…Cyanide molecules initially adsorbed on Au{111} at room temperature exhibit a peak at 2146 cm −1 as shown by attenuated total reflection infrared (ATR-IR) spectroscopy, which is in good agreement with the typical blue shift expected from the free cyanide ion in solution. 38,40,55 The Au−CN bond is typically considered to be of partially covalent character in gold−cyanide coordination complexes, with the bond strength exceeding that of Au−S. 7,13,56,57 Alkanethiol SAMs exhibit mobility on the surface, 7,58 and the same can be suggested for cyanide monolayers.…”

“…The new peak is within the expected range for covalently bound CN on Au. 38,50,59 Additional heating, typically for 18 h, generates a monolayer with the spectrum shown in Figure 6B, where the original peak has disappeared. Surprisingly, the IR spectra did not contain a separate measurable peak for the weaker Au-NC bound molecules, and no other peaks were observed in regions indicating new bond formation.…”

“…24,36,37 To this end, we have fabricated and probed the vibrational spectra and structures of monolayers of cyanide molecules on Au{111}. 7,38 In this work, we report the structure and orientation for annealed cyanide monolayers on Au{111}, report changes in the vibrational spectra, and propose mixed bonding schemes to explain the appearance of "ribbons" consisting of rows of cyanide molecules.…”

“…Initially, cyanide molecules deposited at room temperature assemble on Au{111} in a hexagonal close-packed (hcp) lattice attached through the carbon atom, oriented primarily normal to the surface. 38 Cyanide has a strong dipole moment, 2.8 D, that makes it ideal as a small-molecule probe. 39,40 In our previous work we adsorbed cyanogen (C 2 N 2 ) on Au{111}, but it did not dissociate under the conditions used.…”