K. Nakamura et M. Yata, An interpretation of the temperature-dependent growth mode of copper on the Cu(001)(2 root 2 x root 2)R45 degrees-O surface, SURF SCI, 417(2-3), 1998, pp. 268-280
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.