F 2-defect-based model for latent image formation and interactions of O, O– and O2– adsorbates at AgCl and AgBr (001) surfaces: DFT calculations

Abstract

In an attempt to look for defect-based models for latent image formation, we have examined the reduction and mobility of silver clusters over the F 2-defect-containing surfaces of AgBr and AgCl crystals as well as the interactions of O, O–and O2– external adsorbates using an embedded cluster model and density functional theory calculations with effective core potentials. The alkali halide clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. The most energetically preferred orientations of silver clusters were associated with the rotational angle θ=30° with an uncertainty of ±2°, 0.05 A above each surface, internuclear separations of ca. 2.72 and 2.77 A and activation energy barriers for rotational diffusion of ca. 0.36 and 0.364 eV for AgBr and AgCl, respectively. About 80–83% of the reduction of silver clusters was attributed to the internal structure of the lattice, leaving ca. 17–20% for reduction from external sources such as adsorbates, chemical reducing agents or developers. The contributions to adsorbate–substrate interactions were explainable in terms of surface electrostatic potentials. O, O– and O2– species adsorb chemically on the defect-containing surfaces. Charge transfer takes place from the surface to oxygen atoms and from the oxygen anions to the surface, confirming the donor–acceptor properties of the title adsorbates in the course of the adsorbate–substrate interactions.