Kinetic Monte Carlo simulations of Pd deposition and island growth on MgO(1 0 0)

• Published in: Surface science Vol. 601; no. 14; pp. 3133 - 3142
• Main Authors: Xu, Lijun, Campbell, Charles T., Jónsson, Hannes, Henkelman, Graeme
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.07.2007; Amsterdam Elsevier Science; New York, NY
• Subjects: BINDING ENERGY; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Density functional calculations; DENSITY FUNCTIONAL METHOD; DEPOSITION; Deposition, island formation, and ripening; Environmental Molecular Sciences Laboratory; Exact sciences and technology; KINETIC EQUATIONS; Kinetic Monte Carlo; MAGNESIUM OXIDES; MATERIALS SCIENCE; MONTE CARLO METHOD; PALLADIUM; Pd on MgO; Physics; SUBSTRATES; VACANCIES; Deposition, island formation, and ripening; Density functional calculations; Kinetic Monte Carlo; Pd on MgO; Monte Carlo methods; Inorganic compounds; Digital simulation; and ripening; Pd on MgO; Density functional calculations; Magnesium oxides; Density functional method; island formation; Kinetic Monte Carlo; Deposition; Kinetics; Island structure; Surface structure
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2007.05.027

The deposition and ripening of Pd atoms on the MgO(1 0 0) surface are modeled using kinetic Monte Carlo simulations. The density of Pd islands is obtained by simulating the deposition of 0.1 ML in 3 min. Two sets of kinetic parameters are tested and compared with experiment over a 200–800 K temperature range. One model is based upon parameters obtained by fitting rate equations to experimental data and assuming the Pd monomer is the only diffusing species. The other is based upon transition rates obtained from density functional theory calculations which show that small Pd clusters are also mobile. In both models, oxygen vacancy defects on the MgO surface provide strong traps for Pd monomers and serve as nucleation sites for islands. Kinetic Monte Carlo simulations show that both models reproduce the experimentally observed island density versus temperature, despite large differences in the energetics and different diffusion mechanisms. The low temperature Pd island formation at defects is attributed to fast monomer diffusion to defects in the rate-equation-based model, whereas in the DFT-based model, small clusters form already on terraces and diffuse to defects. In the DFT-based model, the strong dimer and trimer binding energies at charged oxygen vacancy defects prevent island ripening below the experimentally observed onset temperature of 600 K.