In Situ Observation of the Surface Processes Involved in Dissolution from the (010) Surface of Potassium Ferrocyanide Trihydrate in Aqueous Solution Using an Integrated Electrochemical−Atomic Force Microscope

• Published in: The journal of physical chemistry. B 2000-03, Vol.104 (10), p.2351-2359
• Main Authors: Jones, Claire E, Macpherson, Julie V, Unwin, Patrick R
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp993532e

The surface processes accompanying dissolution from the (010) surface of potassium ferrocyanide trihydrate in aqueous solution have been determined using an integrated electrochemical−atomic force microscope (IE-AFM). This instrument employs a Pt-coated AFM tip that functions as an electrode, as well as a conventional topographical imaging device. The dissolution process was induced by oxidizing ferrocyanide at the tip, from an initially saturated solution, thereby creating a local undersaturation at the crystal−solution interface. The subsequent dissolution behavior was imaged in real time as a function of the diffusional driving force. At low driving force, the dissolution process proceeds mainly by the retreat of preexisiting steps aligned in the dominant [102] direction. With increasing driving force, dissolution occurs via the unwinding of steps from screw dislocation sites, leading to the formation of macroscopic etch pits, with an outline morphology determined by the [102] and [201] directions. At the highest driving forces the density of etch pits corresponds closely with the observed density of growth hillocks on the crystal surface, prior to dissolution. The surface dynamics observed under diffusion-controlled conditions are consistent with earlier scanning electrochemical microscopy kinetic studies (Macpherson, J. V.; Unwin, P. R. J. Phys. Chem. 1995, 99, 3338) which interpreted the process in terms of the classical Burton, Cabrera, and Frank dissolution model.