Capture numbers in the presence of repulsive adsorbate
J. A. Venables and H. Brune, submitted to Phys. Rev. B, March 2002.
Capture numbers are used in models of nucleation and growth on surfaces, and have
been widely applied to predict nucleation densities and other quantities via rate
equations. In conventional nucleation theory, much effort has historically been
expended on obtaining good expressions for capture numbers in the diffusion-limited case.
However, recent experiments and calculations have shown that weak repulsive interactions
between adsorbate atoms on relatively smooth (e.g. close-packed metal) surfaces may shift
nucleation kinetics towards the attachment-limited case. This paper clarifies the
distinctions between diffusion- and attachment-limited kinetics, and emphasizes the
increased importance of the transient nucleation regime in the latter case, which is due
to a combination of delayed nucleation and reduced capture. The consequences of long-range
repulsive adsorbate interactions for the form and values of the capture numbers are explored,
and the effects of attachment-limited kinetics in relation to low temperature deposition
and annealing experiments are demonstrated. An approximate interpolation scheme between
attachment- and diffusion-limited kinetics is proposed, and tested against Kinetic Monte
Carlo (KMC) simulations. Using this scheme to interpret recent scanning tunneling
microscopy (STM) results on Cu/Cu(111), lower and upper bounds on the maximum
adatom-adatom potential repulsive energy of 10 and 14 meV are deduced.
Latest version of this document: 13th July 2002.