Electrochemical NanoScience Group
‹— Electrochemical Double Layer | ‹— Research topics

Electrode as Reactant: Single Crystals, Nanoelectrodes, Films

The specific control and local tailoring of the morphological and electronic properties of electrode surfaces at the nanoscale level provide access to tune reaction sites and pathways. We focus on several strategies:
Figure shows a typical current vs. potential curve of a nearly ideal Au(111) electrode in sulphuric acid, the terrace width amounts to 200 to 400 nm. The experiment started with a flame-annealed reconstructed surface. Around 0.30 V, the reconstruction is lifted, and during a slow positive potential scan an ideal (1 x 1) terminated surface is created, on which at around 0.80 V the ordered (√3 x √7) sulphate structure is formed. Oxidation starts with a small shoulder OA1 followed by the main peak OA2, which consumes up to 620 μC·cm-2. The STM-contrast pattern of the surface changes in this potential region into an array of irregularly distributed small clusters of 1 to 3 nm size, and approximately monatomic height. This pattern disappears after passing the main reduction peak giving rise to the well known hole pattern after returning into the double layer region.

Calibration experiments with two series of stepped Au(111)-electrodes having either (110) or (100) steps indicate that OA1 grows with increasing step density, rather independent of step direction, while OA2 decreases and broadens. Consequently, and in agreement with previous studies of Adzic and Kolb, OA1 is assigned to an oxidation process involving steps, and OA2 represents mostly contributions from terrace sites. The energetic separation of OA1 and OA2 is approximately 0.2 V, and OA2 shifts with increasing step density towards more negative potentials, independent of the nature of the steps.

Depending on the number of oxidation cycles and the chosen return potential in the oxidised region one can create template structures composed of cascade islands, monatomic deep holes, larger holes in multiple layers as well as channels. The shape and size of these features depend strongly on the proximity and on the field of the STM tip.
Revised: 08.12.2007     ©: 2005-2007