Abstract
Surface diffusion on metal oxides is key in many areas of materials technology, yet it has been scarcely explored at the atomic scale. This work provides phenomenological insights from scanning tunneling microscopy on the link between surface diffusion, surface atomic structure, and oxygen chemical potential based on three model oxide surfaces: Fe2O3(11¯02), La1−xSrxMnO3(110), and In2O3(111). In all instances, changing the oxygen chemical potential used for annealing stabilizes reconstructions of different compositions while promoting the flattening of the surface morphology—a sign of enhanced surface diffusion. It is argued that thermodynamics, rather than kinetics, rules surface diffusion under these conditions: the composition change of the surface reconstructions formed at differently oxidizing conditions drives mass transport across the surface.
Highlights
Surface diffusion is central to numerous and technologically relevant areas
It is argued that thermodynamics, rather than kinetics, rules surface diffusion under these conditions: the composition change of the surface reconstructions formed at differently oxidizing conditions drives mass transport across the surface
Scanning tunneling microscopy was used to investigate the interplay between surface diffusion, atomic structure, and oxygen chemical potential, μO, on three model oxide surfaces, Fe2O3(1102), LSMO(110), and In2O3(111)
Summary
Surface diffusion is central to numerous and technologically relevant areas. In (heterogeneous) catalysis, the mobility of reactants on the catalyst’s surface determines the course and the rate of the reactions thereby occurring.[1,2] Surface diffusion plays an essential role in strong metal–support interactions[1,3,4] and catalyst deactivation due to sintering of supported metal nanoparticles.[5,6] In metallurgy, surface diffusion determines the sintering rates of metal powders.[7]. Metal oxides dominate many technological areas where the role of surface diffusion is vital, e.g., catalysis, thin-film devices, and fuel cells. The knowledge on surface diffusion on these materials is limited,[9,10] especially when compared to metals and semiconductors.[11–15] This work aims at shedding some light on the processes that govern diffusion on oxide surfaces by using scanning tunneling microscopy (STM) on three different systems: α-Fe2O3, the most stable iron oxide at ambient conditions,[16] interesting for its potential as a catalyst for photoelectrochemical water splitting;[17,18] Sr-doped LaMnO3 (LSMO), a perovskite oxide with uses and promises for catalytic,[19] energy-conversion,[20] and spintronics[21] applications; and In2O3, a transparent conductive oxide[22,23] used in various catalytic and gas-sensing applications.[24–26]. The surface of each sample was measured after two annealing treatments at different values of oxygen chemical potential (shortly μO), as determined by the chosen temperature and oxygen background pressure (for a definition of μO, see Sec. II C). The temperature was kept constant within each set of experiments (only the O2 pressure was changed), and bulk diffusion and cation evaporation were negligible at the chosen conditions
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