Defect-pinned nucleation, growth, and dynamic coalescence of Ag islands on MgO(001): An<i>in situ</i>grazing-incidence small-angle x-ray scattering study

Abstract

The growth of Ag/MgO(001) was investigated at three temperatures, 300, 540, and 640 K, in situ, in ultrahigh vacuum, by grazing incidence small angle x-ray scattering (GISAXS). The samples prepared at 300 and 540 K were also examined ex situ by transmission electron microscopy (TEM). Nucleation, growth, and coalescence are studied via the evolution of the average particle diameter, height, interparticle distance, and size distributions. Power laws are given. Size-spacing correlations are evidenced by TEM and GISAXS. A heterogeneous nucleation of silver on the defects $[(7.5\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{defects}\text{ }{\text{cm}}^{\ensuremath{-}2}]$ of the MgO surface is evidenced. Above a silver coverage of approximately 2 nm, a dynamic coalescence regime takes place involving diffusion of the islands. A value of $0.76\ifmmode\pm\else\textpm\fi{}0.1\text{ }\text{J}\text{ }{\text{m}}^{\ensuremath{-}2}$ for the Ag/MgO(001) adhesion energy is derived by using a Wulff-Kaishew construction from the particle shape obtained by GISAXS. The diffusion energy of Ag on MgO(001) is estimated to be $0.05\ifmmode\pm\else\textpm\fi{}0.02\text{ }\text{eV}/\text{atom}$ via kinetic Monte Carlo simulations of the growth stage.