Transient Mobility Mechanisms of Deposited Metal Atoms on Insulating Surfaces: Pd on MgO (100)

• Published in: Journal of physical chemistry. C Vol. 116; no. 27; pp. 14471 - 14479
• Main Authors: Gao, David Z, Watkins, Matthew B, Shluger, Alexander L
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 12.07.2012
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Theory and models of film growth; Thermal diffusion; Nanocluster; Growth rate; Digital simulation; Molecular dynamics method; Theoretical study; Surface temperature; Palladium; Surface diffusion; High temperature; Transients; Solid clusters; Surface defect; Growth mechanism; Diffusion process; Incidence angle; Kinetic energy; Surface layers; Activation energy
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp303951y

The importance and mechanisms of transient mobility of atoms and molecules adsorbing at surfaces have been a subject of controversy for many years. We used classical molecular dynamics simulations to examine transient mobility of Pd atoms adsorbing on the MgO (100) surface with incident kinetic energies not exceeding 0.4 eV. The calculations show that deposited Pd atoms exhibit high mobility at temperatures below 80 K where the contribution from thermal diffusion processes should be negligible. For our selected deposition conditions, aimed at simulation of Pd cluster growth experiments, an estimated 76% of the impinging Pd atoms are expected to travel up to 20 Å away from the collision site before capture on a 5 K surface. We find that mobility of metal atoms on oxide surfaces is expected to decrease with decreasing incident energy and increase with decreasing incident angle. Comparison with prior studies highlights similarities and differences with other surface diffusion processes, such as long jumps. At higher surface temperatures, the observed mobility will mainly be due to thermally activated processes rather than transient mobility mechanisms. Atoms that exhibit transient mobility upon deposition may quickly migrate to surface features and defects affecting kinetics of growth and structures of nanoclusters and surface layers.