Ultrathin crytalline solid films are found to dewet with a faceted rim. In the case of heterogeneous dewetting initiated from a linear trench or from periodically arranged holes, the dewetted area expands either with a faceted multilayer rim or in a layer-by-layer fashion. In the case of homogeneous dewetting, holes are accompanied with multilayer rims and the uncoverage increases as a power law of time. Results of kinetic Monte Carlo simulations are elucidated within the frame of nucleation theory and surface diffusion limited dynamics.

We simulated a growth model in (1+1) dimensions in which particles are aggregated according to the rules of ballistic deposition with probability p or according to the rules of random deposition with surface relaxation (Family model) with probability 1-p. For any p>0, this system is in the Kardar-Parisi-Zhang (KPZ) universality class, but it presents a slow crossover from the Edwards-Wilkinson class (EW) for small p. From the scaling of the growth velocity, the parameter p is connected to the coefficient lambda of the nonlinear term of the KPZ equation, giving lambda approximately p(gamma), with gamma=2.1+/-0.2. Our numerical results confirm the interface width scaling in the growth regime as W approximately lambda(beta)t(beta) and the scaling of the saturation time as tau approximately lambda(-1)L(z), with the expected exponents beta=1/3 and z=3/2, and strong corrections to scaling for small lambda. This picture is consistent with a crossover time from EW to KPZ growth in the form t(c) approximately lambda(-4) approximately p(-8), in agreement with scaling theories and renormalization group analysis. Some consequences of the slow crossover in this problem are discussed and may help investigations of more complex models.

We report on the dewetting of a monolayer on a solid substrate, where mass transport occurs via surface diffusion. For a wide range of parameters, a labyrinthine pattern of bilayer islands is formed. An irreversible regime and a thermodynamic regime are identified. In both regimes, the velocity of a dewetting front, the wavelength of the bilayer island pattern, and the rate of nucleation of dewetted zones are obtained. We also point out the existence of a scaling behavior, which is analyzed by means of a geometrical model.Liquid films, once spread on a substrate, may breakup into droplets to lower the surface energy. Such a process is called dewetting. As for liquids, thin solid films may break-up into droplets. However two main differences may be pointed out. Firstly, solids exhibit strong surface anisotropy whereas liquids are usually isotropic. Secondly, mass transport mainly occurs via surface diffusion on solids at small scales, while it is mediated by hydrodynamics in liquids.Dewetting of solid layers with sub-micron thicknesses was observed in recent experimental studies [1,2,3]. Spontaneous breakup of the film into dots can be analyzed within the frame of continuum models including an effective wetting potential, with surface energy [4], and elastic effects [5]. Moreover, the nonlinear dynamics of the edges of these layers [2,6,7] may also lead to the periodic formation of holes behind the dewetting rim.For even thinner films, such as 1nm thick Ag on Si[8], one expects the discreteness of the underlying crystalline lattice to come to the fore. In order to investigate these effects, we study the dewetting of the thinnest possible layer: a monolayer. In order to focus on the basic processes, we discard effects related to substrate roughness, elastic interactions, or alloying. We focus on the case where dewetting occurs via the nucleation of holes, subsequently invading the whole film. This occurs in a well defined temperature window: if the temperature were too low the surface would be frozen; if it were too high -above the roughening transition-the film would be unstable and would break up into a microscopically disordered pattern.We show that monolayer dewetting proceeds differently from thicker layers dewetting. As shown on Fig.1, monolayers initially lead to a labyrinthine pattern of bilayer islands, which then slowly thicken into 3-layer, and then 4-layers islands, etc. Two different regimes for monolayer dewetting, henceforth denoted as regimes I and II, are analyzed. While both regimes exhibit the same temporal scaling behavior, their microscopic dynamics is qualitatively different.We employ Kinetic Monte Carlo (KMC) simulations in order to mimic experiments with a minimum number of ingredients. We use a Solid on Solid model on a 2D square lattice, with lattice unit a, and local height h ≥ 0. The substrate surface, at h = 0, is perfectly flat and frozen. Epilayer atoms hop to nearest neighbor sites with the rates r n when h = 1, and ν n when h > 1, withwhere ν 0 is a constant frequency, T is the tem...

We discuss the methods to calculate the roughness exponent alpha and the dynamic exponent z from the scaling properties of the local roughness, which is frequently used in the analysis of experimental data. Through numerical simulations, we studied the Family, the restricted solid-on-solid (RSOS), the Das Sarma-Tamborenea (DT) and the Wolf-Villain (WV) models in one- and two dimensional substrates, in order to compare different methods to obtain those exponents. The scaling at small length scales do not give reliable estimates of alpha, suggesting that the usual methods to estimate that exponent from experimental data may provide misleading conclusions concerning the universality classes of the growth processes. On the other hand, we propose a more efficient method to calculate the dynamic exponent z, based on the scaling of characteristic correlation lengths, which gives estimates in good agreement with the expected universality classes and indicates expected crossover behavior. Our results also provide evidence of Edwards-Wilkinson asymptotic behavior for the DT and the WV models in two-dimensional substrates.Comment: To appear in Surface Scienc

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