SEXAFS STUDY OF AGBR(111) AND AGBR(100) SURFACES AND COMPARISON TO THEORETICAL-MODELS

[摘要] Silver halide surfaces play a central role in the photographic process and the development of an improved understanding of these surfaces at an atomic level is important to further progress in photographic science. Extensive fluorescence SEXAFS measurements, using the total reflection geometry, were made at both the Br and Ag edges for both the AgBr(111) and AgBr(100) surfaces. For the AgBr(111) case, contractions of 0.02 +/- 0.01, 0.03 +/- 0.01 and 0.02 +/- 0.01, 0.03 +/- 0.01 and 0.02 +/- 0.01 angstrom, relative to the bulk, were observed for the nearest-neighbor Ag-Br distance and the next-nearest-neighbor Ag-Ag and Br-Br distances, respectively. These contractions are consistent with a surface reconstruction predicted by theoretical models. Comparison of the SEXAFS data with the simulations of several models for this reconstruction suggests that the Ag+-top alternate-row model provides the best agreement. No corresponding contractions in the Ag-Br, Br-Br, and Ag-Ag distances were observed from the AgBr(100) SEXAFS data. The observed distances in the AgBr(100) show essentially no changes from the bulk values. The lack of contraction in the nearest-neighbor distances is consistent with the rumpling model, which predicts no (100) surface reconstruction but rather a rumpling of the top surface ions.

[发布日期] 1991-09-01