Methylthiolate on Au(111): adsorption and desorption kinetics

Area of Science:

• Surface Science
• Materials Chemistry
• Chemical Physics

Background:

• Understanding the adsorption and desorption behavior of organosulfur compounds on metal surfaces is crucial for catalysis and materials science.
• Gold surfaces, particularly Au(111), are widely studied due to their inertness and relevance in nanotechnology and electronics.
• Dimethyldisulfide (DMDS) serves as a model compound for studying the surface chemistry of thiols and disulfides.

Purpose of the Study:

• To investigate the adsorption and desorption mechanisms of dimethyldisulfide (DMDS) on the Au(111) surface.
• To characterize the different adsorbed species (molecular DMDS, methylthiolate) and their surface structures.
• To determine the kinetic parameters (order of reaction, activation energy) for desorption processes.

Main Methods:

• Low Energy Electron Diffraction (LEED) for surface structure determination.
• Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) for surface composition analysis.
• Line of Sight Mass Spectrometry (LOSMS) coupled with Temperature Programmed Desorption (TPD) for studying desorption kinetics.

Main Results:

• At 300 K, DMDS adsorbs dissociatively, forming a methylthiolate adlayer with a (√3 × √3)R30° structure (1/3 ML).
• At 100 K, DMDS adsorbs molecularly, with dissociation to methylthiolate occurring between 138-160 K.
• A physisorbed DMDS layer forms on the methylthiolate surface below 180 K, with multilayers forming below 150 K.

Conclusions:

• The physisorbed DMDS layer acts as a precursor state, explaining adsorption kinetics and providing a mechanism for thiolate self-assembled monolayer mobility.
• Desorption kinetics reveal distinct pathways for multilayers, physisorbed, and chemisorbed species, influenced by lateral interactions.
• The study elucidates the complex surface chemistry of DMDS on Au(111), relevant for understanding organosulfur interactions on metal surfaces.