Properties of Silver Clusters Adsorbed to Silver Bromide

Abstract

Density functional calculations of the structure and electronic properties of silver clusters interacting with a fragment of silver bromide that is embedded within a polarizable representation of the AgBr crystal are presented. Flat (001) surfaces and kinked surfaces are considered. The optimized geometry of the silver clusters is nearly planar for the clusters up to four atoms that are considered. We examined the degree to which different surface defect sites could modulate the properties of the adsorbed silver cluster. The positive kink site is unique in providing a location where the neutral cluster can capture photoelectrons. This effect can be rationalized by electrostatic arguments and is consistent with this site functioning as a location for photolytic silver formation. Other kink sites of neutral or partial negative charge do not permit electron trapping at neutral silver clusters. These sites could act as locations for chemically produced silver clusters. Calculations are presented showing that some geometries of Ag3 + adsorbed at the negative kink can trap electrons in accord with a proposal by Tani. The calculations are used to compare different mechanisms for photolytic formation of silver clusters. They can be compared to gas-phase calculations adjusted for the interaction with a polarizable surface to show that both calculations agree that cationic silver clusters are unstable with respect to dissociation except on the negative kink. The calculations show a deep electron trap depth for the silver atom consistent with its participation in the nucleation phase of silver cluster growth during photolysis. A sulfide ion substituted for bromide at a positive kink is shown to provide a means of coupling the electron to the crystal ions.

Atomistic Modeling of Silver Clusters Formed on the Surface of AgBr

“…We employed the LANL2DZ basis and associated pseudopotentials 35 on the Ag + and Br -ions and the full core pseudopotential 32 on neighboring Ag + ions, as in earlier work. 1 Comparisons to the Stuttgart quasi-relativistic pseudopotentials and basis sets 36 denoted SDD were made to evaluate the effects of basis and pseudopotentials. The interatomic potential and shell model parameters of Catlow et al 31 were employed for AgBr crystal ions.…”

“…In earlier work, 1 we used density functional theory to compute the electronic properties of silver clusters adsorbed to particular sites upon a crude representation of the surface of silver bromide. That study, within a photographic context, focused on the mechanism of forming small clusters of silver from the absorption of light for which much information is known.…”

The band structures of the silver halides AgF, AgCl, and AgBr: A comparative study

“…23 We also note the increase in covalency. It affects the surface properties of the materials which was investigated in some detail for AgCl 20 and AgBr 24, 25 but not for AgF. The energy separation of the 2p(F) and the 4d(Ag) band in AgF was calculated to be larger than the corresponding separation in AgCl and AgBr.…”

Review of mechanisms of photographic sensitivity

“…Baetzold supported the formation of P centres by reduction sensitization, and proposed the possibility that reduction sensitization P centres were different from photolytically formed P centres. 95 Kuge et al also supported the formation of reduction sensitization P centres by observing their enhancement of the dispersion of latent image centres. 96 By means of diffuse reflection spectra of reductionsensitized emulsions, Tani and Murofushi 90 observed not only plasmon absorption spectra of silver nanoclusters acting as fog centres, but also absorption spectrum of reduction sensitization centres for the first time, providing photographic scientists with a new method of studying silver clusters in photographic materials.…”