The kinetic MC modelling of reversible pattern formation in initial stages of thin metallic film growth on crystalline substrates

The results of kinetic MC simulations of the reversible pattern formation during the adsorption of mobile metal atoms on crystalline substrates are discussed. Pattern formation, simulated for submonolayer metal coverage, is characterized in terms of the joint correlation functions for a spatial distribution of adsorbed atoms. A wide range of situations, from the almost irreversible to strongly reversible regimes, is simulated. We demonstrate that the patterns obtained are defined by a key dimensionless parameter: the ratio of the mutual attraction energy between atoms to the substrate temperature. Our ab initio calculations for the nearest Ag-Ag adsorbate atom interaction on an MgO substrate give an attraction energy as large as 1.6 eV, close to that in a free molecule. This is in contrast to the small Ag adhesion and migration energies (0.23 and 0.05 eV, respectively) on a defect-free MgO substrate. (C) 2003 Elsevier Science Ltd. All rights reserved

Atomic and electronic structure of both perfect and nanostructured Ni(111) surfaces: First-principles calculations

article i nfo In this study, we perform first principles simulations on both atomically smooth and nanostructured Ni(111) slabs. The latter contains periodically distributed nickel nanoclusters atop a thin metal film gradually growing from adatoms and serving as a promising catalyst. Applying the generalized gradient approximation within the formalism of the density functional theory we compare the atomic and electronic structures of Ni bulk, as well as both perfect and nanostructured (111) surfaces obtained using two different ab initio approaches: (i) the linear combination of atomic orbitals and (ii) the projector augmented plane waves. The most essential inter-atomic forces between the Ni adatoms upon the substrate have been found to be formed via: (i) attractive pair-wise interactions, (ii) repulsive triple-wise interactions within a triangle and (iii) attractive triple-wise interactions within a line between the nearest adatoms. The attractive interactions surmount the repulsive forces, hence resulting in the formation of stable clusters from Ni adatoms. The magnetic moment and the effective charge (within both Mulliken and Bader approaches) of the outer atoms in Ni nanoparticles increase as compared to those for the smooth Ni(111) surface. The calculated electronic charge redistribution in the Ni nanoclusters features them as possible adsorption centers with increasing catalytic activity, e.g., for further synthesis of carbon nanotubes

Simulation of Reaction-Induced Phase Separation in Surface Alloy

Using kinetic Monte Carlo method we simulate the dynamics of biatomic $Au_{0.3}Ni_{0.7}$ surface alloy separation on Ni(111) due to $Ni(CO)_4$ out-reaction. The experiment of Vestergaard et al. is modeled by counterbalancing dynamical processes and interactions between reactants. The simulations demonstrate step flow rate increase with CO coverage, $c_{CO},$ in qualitative agreement with the experiment only for $c_{CO}$ ≲ 0.45 monolayer. Moreover, we demonstrate both CO influence on reaction process and Au domain formation

Autoregressive moving average model for analyzing edge localized mode time series on Axially Symmetric Divertor Experiment (ASDEX) Upgrade tokamak

An approach to analysis of time series of edge localized modes (ELMs) is proposed. It is based on the use of the autoregressive moving average model, which decomposes time series into deterministic and noise components. Despite the inclusion of nonlinearity in the model, the resulting deterministic equations for the ELM time series measured on Axially Symmetric Divertor Experiment Upgrade tokamak turn out to be linear. This contrasts with the findings on JAERI tokamak (JT-60U) and tokamak a configuration variable that ELMs exhibit features of chaotic dynamics, namely, the presence of unstable periodic orbits. This methodology for distinguishing chaotic behavior is examined, and found to be susceptible to misinterpretation. (C) 2004 American Institute of Physics