Abstract

This thesis investigates the structures formed by neat dimethyl sulfoxide (DMSO) on Au surfaces at ambient conditions and what happen to the neat DMSO structures when simple ions are added to it. The structure of solvent and electrolyte solutions at metal surface is of fundamental importance in electrochemistry and surface science.

In situ scanning tunneling microscopy (STM) reveals that DMSO forms ordered arrays of chains on Au(111) lattices, but is substantively disordered on the other low Miller index faces of Au. The chain structures are interpreted in terms of a head-to-tail association of DMSO with itself and the interchain repulsions also observed are interpreted in terms of dipolar misfit between the chain. While the neat DMSO structure shows a low and nearly charge independent interfacial capacity, the capacity with added nitric acid is an order of magnitude higher and exhibits considerable structure over the potential range studies.

In situ STM, uv-vis spectroscopy, and differential capacitance are then used to examine the solvent structure of DMSO and tetramethylene sulfoxide (TMSO) containing either KI or KBr on Au(111) and Ag(111) surfaces. STM measurements initially reveal the formation of the expected I or Br adlattice, but later show the formation of an additional surface species, the growth of which is dependent on the exact nature of the surface, solvent, and anion. The results are interpreted in terms of formation of a 1:1 charge transfer complex between the solvent and I₂ or Br₂.

Finally, tetrabutylammonium perchlorate (TBAP) is added to DMSO. Under potential control, positive of the potential of zero charge (PZC), STM reveals the DMSO solvent structure together with the perchlorate anion. The tetrabutylammoniurn cation can not be seen due to the presence of water in the DMSO solution. With appropriate choice of electrolyte, it may now be possible, by means of in situ STM, to examine the interplay of solvent, anion, and cation at the solid/liquid interface.