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We examine the influence of dimer mobility on the size distribution of two-dimensional islands formed by irreversible nucleation and growth during deposition. We first characterize the transition in scaling of the mean island density with increasing dimer mobility, from the classic form described by Venables [Philos. Mag. 27, 697 (1973)] to the modified form for "rapid" mobility described by Villain et al. [ J. Phys. (France)

We present results of a comprehensive scanning tunneling microscopy study of the nucleation and growth of Au islands on Au(100). It is shown that the reconstruction of the substrate produces strong anisotropic effects. Rate equation analysis of the experimental flux and temperature dependence of the island density suggests: (i) a critical size of i = 3 for T = 315 -380 K, but i ) 3 above 400 K; and (ii) strongly anisotropic diffusion, preferentially parallel to the reconstruction rows (activation energy -0.2 eV). We comment on energetic and kinetic aspects of the observed island shape anisotropy. PACS numbers: 61.16.Ch, 68.55.a Nucleation and growth of islands during thin film deposition has been studied for decades. Traditional analyses, using mainly scanning and transmission electron microscopy, concentrated on systems where three-dimensional islands form [1]. The results were generally interpreted via rate equations. Recent revival of interest is associated with the availability of scanning tunneling microscopy (STM) [2 -7] and high resolution surface sensitive diffraction techniques [8 -11],which are especially suited for analyses of nucleation and growth of two-dimensional (2D) islands on atomic length scales.Here we provide results of the first comprehensive study of anisotropic nucleation and growth in a metalon-metal system. STM observations on the homoepitaxial growth on the reconstructed Au(100) surface at temperatures between 31S and 43S K are analyzed quantitatively in a rate equation approach. A key component of our analysis is the demonstration that diffusion is actually strongly anisotropic for Au on Au(100). This is a consequence of the reduced symmetry of the reconstructed Au(100) surface. To this end, we must extend the traditional mean-field rate equations [1] to treat strongly anisotropic diffusion. Comparison with "exact" Monte Carlo simulation results is also used. In this system, we observe noticeable denuded zones at steps orthogonal, but not parallel, to the reconstruction rows. Analogous behavior for Si/Si(100) homoepitaxy was attributed to strongly anisotropic diffusion [2]. In our analysis we do not preclude a priori the possibility that the observed anisotropy is caused by different sticking coefficients (anisotropic bonding) at differently oriented step edges. Instead we examine data for the dependence of the average density of islands N, on the deposition flux R and substrate temperature T at fixed submonolayer coverages, thereby deducing diffusion anisotropy, the probable values of the critical island size i, at and above room temperature, as well as estimates of the binding energy of critical islands and the energy barrier for isolated adatom diffusion.The experiments were performed in a UHV system with standard facilities for sample preparation and characterization and a pocket-size STM (base pressure 6 x 10 9 Pa).

The nucleation and growth of several metal/metal thin film systems have been studied and compared using scanning tunneling microscopy (STM). Homogeneous and heterogeneous nucleation have been observed and the effect of surface inhomogeneities on the nucleation behavior has been studied. Systematic measurements of the film morphology as a function of coverage and annealing temperature have allowed different two- and three-dimensional growth mechanisms to be studied. Both kinetic and thermodynamic factors are found to determine these growth processes and in some cases could be separately identified. In addition, the effect of chemically modifying the substrate by oxygen preadsorption has been studied and compared to the clean substrate systems. A variety of changes in the growth behavior were found to occur, which can be understood in terms of changes in both the kinetics and thermodynamics due to the oxygen adlayer.