Nucleation and growth on defect sites:
experiment-theory comparison for Pd/MgO(001)
J.A. Venables, L. Giordano and J.H. Harding
J. Phys. Condensed Matter 18 (2006) S411-S427
Abstract
It is well established that nucleation of metal clusters on oxide and
halide surfaces is typically dominated by defect sites. Rate equation
models of defect nucleation have been developed and applied to these
systems. By comparing the models with nucleation density experiments,
energies for defect trapping, adsorption, surface diffusion and pair
binding have been deduced in favourable cases, notably for Pd deposited
on Ar-cleaved MgO(001). However, the defects responsible remain largely
unknown. More recently, several types of ab-initio calculation have been
presented of these energies for Pd and related metals on MgO(001)
containing several types of surface defects; these calculated values
are surveyed, and some are widely divergent. New rate equation nucleation
density predictions are presented using the calculated values. Some
calculations, for some defect types, are much closer to experiment than
others; the singly charged Fs+ centre and the neutral
divacancy emerge as candidate defects. In these two cases, the
Pd/MgO(001) nucleation density predictions agree well with experiment,
and the corresponding surface defects deserve to be taken seriously.
Energy and entropy values are discussed in the light of differences
in calculated charge redistribution between the metal atoms, clusters
and (charged) surface defects, and (assumed or calculated) cluster
geometries.
Latest version of this document: 15th August 2006.