Characterizing the CH₃SSCH₃–Au(111) System From Single Molecules To Full Surface Coverage: A Scanning Tunneling Microscopy Study

Abstract

The adsorption process of dimethyl disulfide onto the Au(111) surface was resolved with subnanometer resolution at temperatures below 130 K. We report two temperature dependent adsorption studies to reach totally different surface morphologies for this CH 3 SSCH 3 −Au(111) system. Starting with a coldsynthesis approach at low-temperature and low coverage, the STM images reveal preferential adsorption at specific regions on the Au(111) herringbone reconstructed surface. However, at saturated surface coverage, annealing at 80 K leads to self-assembly of an epitaxial monolayer of CH 3 SSCH 3 that is influenced by the anisotropic nature of the herringbone reconstruction. In contrast, depositing CH 3 SSCH 3 at 80 K and above leads to simultaneous adsorption of CH 3 SSCH 3 and dissociated SCH 3 fragments on the surface. Saturation coverage of CH 3 SSCH 3 deposited on an 80 K Au surfaces produces no self-assembled monolayer. DFT calculations are used to provide insights into these two synthesis methods that lead to a discrepancy in surface morphology in the CH 3 SSCH 3 −Au(111) system. We also demonstrate both tip induced and UV induced dissociation of CH 3 SSCH 3 at cryogenic temperatures. We find that the spatial distribution of the UV produced fragments is significantly greater than that of those produced by tip electrons indicating differing mechanisms for the two processes.

Computational Study of Solvent Incorporation into a Porphyrin Monolayer

“…All the geometries were fully optimized to less than 0.5 meV energy convergence and less than 0.02 eV/Å forces. The choice of our DFT methodology, plane wave cutoff energies, and k-point was based on previous periodic DFT simulations of similar systems of type ,,,− and size . VASP calculations were performed on species adsorbed to three-layer unreconstructed Au and on the same species in the gas phase.…”

Selectivity of Laser-Induced versus IET-Induced Carbene Formation from Methoxydiazofluorene on Ag(111)

“…17 A first direct comparison between products of IET manipulation and photoexcitation revealed that the distance between the two products upon dimethyl disulfide dissociation on Au(111) is on average slightly shorter for 1.4 V excitation by electrons from the tip than for 254 nm (4.9 eV) excitation by an UV lamp. 18 It has been assigned to an excitation of higher electronic states by the photons, and thus an excess energy that leads to a motion of the photolytically dissociated molecules.…”