Film and Interface Atomic Structures of Electrodeposited Co/Au(111) Layers: An in Situ X-ray Scattering Study as a Function of the Surface Chemistry and the Electrochemical Potential

The growth and atomic structure of thin Co films electrodeposited onto Au(111) have been studied using in situ surface X-ray diffraction (SXRD) and scanning tunneling microscopy (STM). SXRD is used to monitor the growth in real-time and, following Co deposition, the strain of the Co film is characterized as a function of the Co thickness. In-plane SXRD measurements show that Co deposition leads to the formation of a reconstructed Au layer at the Au-Co interface that is composed of an unfaulted, single Au monolayer uniformly compressed with respect to the underlying bulk Au lattice. The surface normal structure of the Au-Co interface and Co films are examined by measurement of the extended X-ray reflectivity (or specular crystal truncation rod (CTR)) for a nominally two monolayer thick (2 ML) Co deposit. In situ STM has also been used to obtain the morphology of the Co films and the Au(111) reconstruction pattern both before and after Co dissolution. The STM data give complementary information to the SXRD results. The influence on the Co structure of the adsorption of carbon monoxide is also investigated in detail for a 2-3 ML thick Co film. It is shown that CO adsorption induces small vertical relaxations in the Co layers. In contrast, varying the electrochemical potential has negligible influence on the Co structure and affects only the electrolyte layering in the electrochemical double layer. The results are discussed in relation to the magnetic properties of the Co films.