ELECTRON-MICROSCOPE CHARACTERIZATION OF AGBR HETEROJUNCTIONS WITH SILVER CARBOXYLATES AND THEIR INFLUENCE ON THE MORPHOLOGY OF DEVELOPED SILVER PARTICLES IN THERMALLY DEVELOPED PHOTOMATERIALS

Silver halide crystals formed during in situ treatment of silver stear ate crystals with various halidizing agents are observed by scanning a nd transmission electron microscopy to form on the lateral edges of th e silver carboxylate crystals. The location of the silver halide phase on the crystal edge is dictated by the anisotropic structure of the s ilver stearate crystal lattice, specifically, the layered structure in which silver ion layers are separated by long-chain hydrocarbon group s. The formation of AgBr on the lateral faces of these crystals is pro posed to be typical not only of the formation of silver halide on silv er stearate but also for all silver carboxylates of the general formul a [AgCnH2n-1O2](2) when the crystals of these silver carboxylates have anisotropic, layered structures. The silver bromide/silver carboxylat e heterojunction in an in situ system has been clearly observed by tra nsmission electron microscopy. The heterojunction is comprised of a di storted silver carboxylate lattice, which accommodates the misalignmen t between the AgBr and [Ag(O2CR)](2) crystal lattices. The nature of h eterojunction between the AgBr and the silver carboxylate when the AgB r is prepared separately from the preparation of the silver carboxylat e differs from the in situ heterojunction. In this case, a layered com pound, proposed to have a Ag(1-x)Na(x)St composition, forms between th e AgBr and the silver stearate which is a unique feature of this inter face. The differences in the structure of interfaces formed between th e silver halide and the silver fatty acid complex result in different silver particle morphologies during thermal development of exposed pho tothermographic films. The developed silver is generally filamentary w hen the photothermographic material contains silver halide prepared by the in situ exchange reaction between silver carboxylate and a bromin ating agent. If the photothermographic material is prepared from previ ously synthesized silver halide crystals, the preformed AgBr route, th e developed silver generally crystallizes as dendritic crystals. (C) 1 998 Wiley-Liss, Inc.