Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 72: Oxide and Insulator Surfaces: Adsorption I
O 72.4: Vortrag
Mittwoch, 22. März 2017, 11:15–11:30, WIL C107
Diffusion barriers block defect occupation on reduced CeO2(111) — P. G. Lustemberg1, Y. Pan2, R. Pérez3, M. V. Ganduglia-Pirovano3, and •N. Nilius4 — 1Instituto de Física Rosario, 2000 Rosario, Argentina — 2Institute of Physics, Chinese Academy of Sciences, 100190 Beijing , China — 3Instituto de Catálisis y Petroleoquímica, 28049 Madrid, Spain — 4Institute of Physics, Carl von Ossietzky University, 26111 Oldenburg, Germany
Surface defects are believed to control the adsorption behavior of reducible oxides. We challenge this perception on the basis of a combined STM/DFT study that explores the mechanisms of Au adsorption on reduced CeO2(111). While theory predicts a clear binding preference to O-vacancies, Au atoms were found to populate mostly regular surface sites. Even at elevated temperature, no defect decoration is observed and gold rather aggregates at oxide step edges. Our findings are explained with the polaronic nature of the Au-ceria system, which results in a strongly diabatic diffusion of adatoms. The associated barriers are higher than in the adiabatic regime, in particular if the hopping step couples to an electron transfer between Ce3+ ions in the oxide and ad-gold. As population of O vacancies always requires such a charge exchange, adatom diffusion into the defect is kinetically hindered. Our study thus demonstrates that polaronic effects strongly govern the adsorption behavior, hence the chemistry of reducible oxides.