Dresden 2011 – scientific programme
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O: Fachverband Oberflächenphysik
O 53: Solid / liquid interfaces III
O 53.4: Talk
Wednesday, March 16, 2011, 15:45–16:00, WIL C107
Competing Phase Transition in Binary Viologen Layers on Cl/Cu(001) — •Martino Saracino1, Nguyen Thi Minh Hai2, Peter Broekmann2, and Klaus Wandelt1 — 1Institute of Physical and Theoretical Chemistry, Bonn University, Wegelerstr. 12, D-53115 Bonn — 2Interfacial Electrochemistry Group, Department of Chemistry and Biochemistry, Bern University, Freiestr. 3, CH-3012 Berne
In-situ STM and cyclic voltammetry are employed to analyze the competing adsorption of Diphenyl- (DPV) and Dibenzylviologen (DBV) on a chloride precovered Cu(001) surface. This model system for similar N-containing aromatic molecules is studied for the significant role of this type of organic and inorganic additives in metal plating processes. DPV2+ is reduced even at most anodic potentials to the mono-cationic radical DPV+• and forms a full monolayer of a hydrophobic π-stacked stripe-phase, preventing the post-adsorption of the di-cationic DBV2+. Lowering the concentration of DPV in solution till only a sub-monolayer coverage with mono-cationic π-stacked DPV+• stripes is obtained permits the co-adsorption of the less stable di-cationic DBV2+ in its characteristic quadratic cavitand structure next to the DPV+• stripe-phase. Lowering the electrode potential to the DBV2+ reduction potential at -250mVRHE leads first to a complete replacement of the more stable DPV+• stripe-phase by a π-stacked stripe-phase of mono-cationic DBV+•. The resulting proximity of DBV+• stripes and DBV2+ cavitands now permits the decay of the cavitand-phase starting at the domain boundaries to the mono-cationic DBV+• stripe-phase, which finally fully covers the whole surface.