(Invited) In-Situ Observation of Electrodeposition Processes By High Speed Scanning Probe Microscope

Abstract

Electrodeposition is important technology for developing the novel functional materials such as MEMS. In nanotechnology term, the metal deposition is one of the hot topics since it can control the surface structure precisely and easily. Generally, in metal electrodeposition, an adatom deposited on the electrode diffuses and reaches a step or kink before forming a crystal. In the process, the solvents and additives adsorbed on the surface are often incorporated into the deposits. Since they works as an impurity in the film, they induce the crystal defects and surface defects, which may cause the performance degradation of the produces. Because each processes occur at high speeds and on the atomic scale, the deposition mechanism is difficult to understand. The methods for observing the nucleation have been developed in various ways. With the invention of the scanning probe microscope (SPM) in the 1980’s, we could directly observe the nanostructure. It has been applied to the electrodeposition in aqueous solution. However, since SPM usually takes some time to observe the surface, it is very difficult to catch the dynamic process such as the nucleation and growth of the deposits. Therefore, I believe that the high-speed SPM is the promising solution of both temporal and special problems. There are two types of SPM: scanning tunneling microscope (STM) and atomic force microscope (AFM). In the former type, there is a video rate STM (Video STM) that can capture up to 30 frames per second. Furthermore, the spatial resolution can reach the atomic scale. For example, the Bi kink growth along the step is reported and Pb surface diffusion on the Cu surface is clarified [1-3]. However, since the tunneling current flows continuously between the probe and the substrate during the measurement, it is necessary to sufficiently consider the effects on electrochemical reactions. Although the resolution of the high-speed scanning AFM (HS-AFM) is inferior to that of the STM, the influence of the probe can be less. Therefore, in addition to the nucleation phenomenon during Cu electrodeposition (Fig. 1-A) [4], we have observed the weak adsorption of PEG polymer that is known as the major additives during the electrodeposition (Fig.1-B). By taking the advantage of the low contact pressure of the probe, the transient behavior of nucleation and growth of electrolytic nanobubbles can be observed. In this presentation, the dynamic variations of the electrolytic nucleation & growth by using a high-speed SPM will be presented. References H. Matsushima et al., Faraday Discuss., 193 (2016) 171.A. Taranovskyy et al., Phys. Chem. Chem. Phys., 14 (2012) 10579.S. Guezo et al., J. Phys. Chem. C, 115 (2011) 19336.T. Yoshioka et al., Electrochim. Acta, 302 (2019) 422. Figure 1