An In-Situ Oblique-Incidence Optical Reflectance Difference Study of Co Electrodeposition on a Polycrystalline Au(111) S
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An in-situ oblique-incidence optical reflectance difference study of Co electrodeposition on a polycrystalline Au(111) surface J. Gray1, W. Schwarzacher2, X.D. Zhu1 1 University of California, Davis Davis, CA 95616, U.S.A. 2 H.H. Wills Physics Laboratory, Tyndall Avenue Bristol BS8 1TL, U.K. ABSTRACT We studied submonolayer and multilayer deposition of Co on Au(111) using in-situ obliqueincidence optical reflectance difference (OI-RD). We show that the optical technique is highly sensitive and accurate in determining the electrodeposited film thickness and growth mode. We found that the optically determined thickness of the ultrathin Co film is in very good agreement with that deduced from the integration of the anodic current during cyclic voltammetry (CV). From a weak oscillatory behavior of the optical reflectance difference signal, it seems that the growth of electrodeposited Co on Au(111) under pulsed deposition condition proceeds by a combination of three dimensional island and quasi layer-by-layer growth modes. INTRODUCTION Electrochemically deposited Co layers on non-magnetic metal substrates are known to display perpendicular magnetic anisotropy [1]. This property, together with inherently high throughput of electrodeposition for film fabrication, has sparked a wealth of research to further understand the initial stage of Co electrodeposition on non-ferromagnetic systems [2-10]. Most of the emphasis has been placed on Co electrodeposition on single crystal Au [2-8]. Structural information during nucleation and the initial growth has been obtained by scanning tunneling microscopy (STM). The thickness of the electrodeposited Co films as a result of subsequent growth is usually determined ex-situ by Rutherford-Back-Scattering (RBS). Both the film structure (governed by the growth mode) and thickness govern the resulting magnetic anisotropy of an electrodeposited Co film. It is thus desirable that one monitors the electrodeposition in-situ so that the kinetics, such as growth mode and film thickness can be determined and controlled during growth. We demonstrate that an oblique-incidence optical reflectance difference (OI-RD) technique can be used for such a purpose. This OI-RD technique is a special form of ellipsometry that is optimized to probe the change that takes place on a substrate surface or the interface between two condensed media. It has been used to characterize both growth mode and film thickness in vapor-phase epitaxy under ultra high vacuum (UHV) conditions [11-14]. In the present study we use this technique to follow and characterize the electrodeposition of Co on Au(111). EXPERIMENT Gold substrates were prepared by vacuum evaporation of 100nm thick gold films onto microscope slides. The polycrystalline gold exposes primarily (111) facets. Electrodeposition experiments were conducted in a conventional three-electrode cell with the gold film on the glass J1.4.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 27 Aug 2017 at 02:22:01, subject to the Cambridge Core
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