An interpretation of the temperature-dependent growth mode of copper on the Cu(001)(2 root 2 x root 2)R45 degrees-O surface

The growth mode of copper during homoepitaxial growth on the Cu(001)(2 root 2 x root 2)R45 degrees-0 surface has been discussed on the basis of a phen omenological (a simple statistical thermodynamic) treatment of the order-di sorder arrangement of the missing-row structure. In this treatment the oxyg en surface coverage, theta, is fixed at 0.5 ML (monolayer), and the surface free energy is calculated as a function of the concentration of copper vac ancies on the first surface layer. Based on the fact that the missing-row s tructure, in which every fourth topmost copper row is deficient, is the mos t stable structure thermodynamically, the surface free energy is expressed as a function of copper vacancies. According this treatment, it is shown th at only 1/4 ML copper deposition is sufficient to lose the Cu(001)(2 root 2 x root 2)R45 degrees-O reconstruction structure provided that impinging co pper atoms predominantly occupy missing-row copper sites. This is compatibl e with the disappearance of (1/2,1/2) and (3/4,3/4) reflective high-energy electron diffraction superlattice reflections at low substrate temperatures and/or at high deposition rate. At higher substrate temperature (>510 K), the reaction proceeds to keep the surface free energy a minimum; i.e., to k eep the (2 root 2 x root 2)R45 degrees-O surface structure of one step heig ht difference. Consequently, the growth mode becomes step-dow growth or lay er-by-layer growth depending on the temperature and deposition rate. In thi s step how or layer-by-layer growth, the assumption of different copper cap ture probabilities on each row, e.g., 1/2 for a normal row, 1 for missing a row, 0 or 1/2 on an oxygen-adsorbed row, is essential. (C) 1998 Elsevier S cience B.V. All rights reserved.