Ostwald Ripening in an Oxide‐on‐Metal System

Abstract

for performing fundamental studies on "inverse" catalysts, [3] as they resemble many structural features of real catalysts, such as oxide species of different size and stoichiometry, low-coordinated transition metal atoms (present at the perimeter of oxide islands and within internal defects), as well as exposed noble metal support regions.Depending on the application, it may be desirable to maximize the number of specific structural features within an oxide-on-metal system, such as certain crystal facets, edge sites, defects or exposed substrate regions. [4] This is usually done by optimizing the oxide's growth method. However, the structure of the system may also evolve under varying environmental conditions, for example, in response to high pressures of gases or elevated temperatures. In this respect, controlling the structure of metal-on-metal and metal-on-oxide systems, and predicting their behavior in different environments, is much more trivial, as the mechanisms governing the growth and structural evolution of metals under oxidizing and reducing conditions are wellunderstood. For example, thermal treatments under reducing conditions are known to lead to supported metal particles sintering and, thus, the change in the ratio between the facet and edge sites. The process usually proceeds through one of the two mechanisms: coalescence, [5] that is, Brownian-like motion of particles and their merging upon collision, or Ostwald Ostwald ripening is a well-known physicochemical phenomenon in which smaller particles, characterized by high surface energy, dissolve and feed the bigger ones that are thermodynamically more stable. The effect is commonly observed in solid and liquid solutions, as well as in systems consisting of supported metal clusters or liquid droplets. Here, evidence is provided for the occurrence of Ostwald ripening in an oxide-on-metal system which, in this case, consists of ultrathin iron monoxide (FeO) islands grown on Ru(0001) single-crystal support. The results reveal that the thermally-driven sintering of islands allows altering their fine structural characteristics, including size, perimeter length, defect density and stoichiometry, which are crucial, for example, from the point of view of heterogeneous catalysis.

Understanding palladium–tellurium cluster formation on WTe2: From a kinetically hindered distribution to thermodynamically controlled monodispersity

“…6 b and c). This is in contrast with expected ripening processes, generally induced by annealing ( 50 ). The cluster density decreases slightly, indicating relatively strong binding and stability of Pd-Te clusters on the surface.…”

Atomic Scale Insights into Reversible Oxygen Storage in Vanadium Oxide Thin Films

“…Moreover, the oxide islands are highly dispersed and interconnected by thin, elongated filaments. Such a behavior is incompatible with the commonly observed compactification of ad‐islands as a means to minimize their edge energy, [25] a concept that is clearly at work for the V 2 O 3 honeycomb islands in Figure 2a. In contrast, the disordered phase seems to maximize its boundary length at sub‐monolayer coverage.…”

A Platform for Addressing Individual Magnetite Islands Grown Epitaxially on Ru(0001) and Manipulating Their Magnetic Domains

“…Upon Fe deposition under an oxygen atmosphere, the Ru film is first covered by a FeO(111) wetting layer whose thickness is two atomic layers for the conditions we used, − followed by the growth of 3-dimensional magnetite islands with thicknesses ranging from a few nanometers to a hundred nanometers and a lateral extension of several micrometers . Depending on the particular details of the growth temperature and postprocessing of the samples (like further annealing steps), the magnetite islands either extend down to the Ru substrate or sit on top of the FeO wetting layer.…”