Nucleation and growth on defect sites: experiment–theory comparison for Pd/MgO(001)

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 F s + 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.

Site-specific growth of ZnO nanowires from patterned Zn via compatible semiconductor processing

“…Zn can also be deposited directly onto the nitride surface without the intervening Au layer. It is a well-known fact that plasma sputtering roughens surfaces, and a rough surface is known to act as a preferred nucleation site for Zn metal vapor deposition [21,22]. It is noted that our two proposed methods for Zn deposition produce similar Zn grains and ZnO nanowires in terms of morphology and orientation from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations.…”

Kinetic Monte Carlo simulations of Pd deposition and island growth on MgO(100)

“…A significant step forward in the understanding of Pd ripening dynamics on MgO(1 0 0) was made in the experimental work of Brune and coworkers [24,25], who used atomic force microscopy (AFM) to measure the Pd island density as a function of temperature, and the theoretical work of Venables and coworkers, who developed a microscopic model with only a few adjustable parameters which reproduces the experimental measurements [14,17,[25][26][27]. The experiments start with an Ar-cleaved MgO(1 0 0) surface, upon which 0.1 ML of Pd atoms are deposited in the course of 3 min.…”

“…Furthermore, it was shown that threedimensional clusters are energetically favorable at these defects. Since these calculations were done, Venables et al have been able to adjust the mean field model to accommodate the DFT binding energetics of three-dimensional clusters at defects without substantially altering the assumptions or fitting parameters [27].…”

Hot-wire CVD of Ge nanoparticles on Si-etched silicon dioxide

“…1. Surface defects can serve as traps for adatoms and lead to nucleation in a variety of systems [25][26][27][28], including Ge [29]. Si-etching of SiO 2 has been shown to create defects through the reaction Si(ad)+ SiO 2 (s)-2SiO(g) [30,31], and these defects can trap GeH x adatoms [32].…”

“…Mean-field rate equations incorporating a critical cluster size can be used to model particle nucleation and growth [27,[34][35][36]. A critical cluster size is defined as the cluster size such that the addition of one adatom results in stable nuclei [35,36].…”