(Invited) In-Situ Observation of Dynamic Electrochemical Interfacial Phenomena

Abstract

Electrochemical interfacial phenomena play important roles for developing advanced nano-materials such as actuators, MEMS and catalyst. For advanced control, metal nucleation by electrodeposition is one of key technology, while the research for high durability of the nanomaterials will be an important issue in the future. It is necessary to understand the corrosion in the fine region. These processes are electrochemical-deposition and dissolution reactions of metals. Thus, the reaction is too fast to observe in real time. In this presentation, I would like to introduce some recent research on dynamic electrochemical interface phenomena using a high-speed probe microscope [1, 2] and a holographic interferometric microscopy [3, 4].The Cu dissolution was investigated by HS-AFM (High-Speed Atomic Force Microscopy). The in-situ observation was conducted using an Au(111) single in 3 mM copper sulfate solution with 50 mM sulfuric acid. The HS-AFM operating in a dynamic mode can measure surfaces at frame rates up to 10 frame s−1. In the present experiment, the scan area range was in the range of 375–1000 nm2 and the scanning speed was 1 frame s−1. The dissolution process was observed at 0.05 V vs. Cu reference. The dissolution could be occurred as soon as the electrolysis was started. The dissolution rate was independent of the edge type. At 3 s, the effects of dissolution became clear and the step lines of the nuclei became uneven. Interestingly, as dissolution progressed beyond 5 s, some clusters [indicated by arrows in Fig.1] remained on the substrate briefly. This behavior had the appearance of small water droplets drying on a flat surface. The average size of the clusters was approximately 8 nm. After the large nuclei dissolved, these small clusters gradually dissolved. In the interferometric microscopy, the ionic mass transfer phenomenon of Al3+ in a sulfuric acid (pH 1) was investigated. The investigation revealed the refractive index profile corresponding to the Al3+ concentration profile in the electrolyte. The thickness of the diffusion layer was proportional to the square root of time, which supported the reaction dominated by the mass transportation. The Al3+ surface concentration started to decrease at 20 s after starting electrolysis, probably because the Al dissolution reaction was hindered and the Al oxide layer formation progressed. This in-situ research might be a steppingstone in order to understand the mechanism of anodization of Al.