Self-Limited Growth of a Thin Oxide Layer on Rh(111)

Abstract

The oxidation of the Rh(111) surface at oxygen pressures from 10(-10) mbar to 0.5 bar and temperatures between 300 and 900 K has been studied on the atomic scale using a multimethod approach of experimental and theoretical techniques. Oxidation starts at the steps, resulting in a trilayer O-Rh-O surface oxide which, although not thermodynamically stable, prevents further oxidation at intermediate pressures. A thick corundum like Rh2O3 bulk oxide is formed only at significantly higher pressures and temperatures.

Nanometer and Subnanometer Thin Oxide Films at Surfaces of Late Transition Metals

“…A qualitatively similar picture has recently been reported for Rh(111) 32 , where after adsorbate phases with O in fcc sites, bulk Rh 2 O 3 becomes most stable at higher oxygen chemical potentials. Due to the already decreased heat of formation per O atom of Rh 2 O 3 compared to RuO 2 , the stability range of the bulk oxide is smaller, but starts in contrast to the situation at Ru(0001) nevertheless before higher coverage adsorbate phases corresponding to Θ > ∼ 0.5 ML could become favorable.…”

“…Although a O-Rh-O trilayer structure equivalent to the one discussed for Ru(0001) above results similarly as only a kinetic precursor in DFT-GGA, it is interesting to note that at Rh(111) this structure could recently be experimentally prepared and characterized close to step edges. 32 Proceeding to Pd(111) one observes in most aspects a continuation of the identified trends. As apparent in Fig.…”

“…Recent experimental studies seem to support this view, i.e., they indicate that thin oxidic structures, now mostly coined surface oxides, start to form roughly at coverages Θ c . 30,31,32,33,34 For the "true" bulk oxide a higher oxygen concentra- tion might be required, but for oxide nucleation and for the formation of oxidic islands such increased oxygen content is only needed locally. In this respect it is remarkable that although for the on-surface adsorption at the late 4d TM basal surface the adatom-adatom interaction is repulsive (see the discussion of Fig.…”

“…This may result in commensurable or incommensurable overlayers, and both types have already been observed experimentally on the late 4d basal surfaces. 31,32,33,34 In addition, strain may be easier relaxed at more open sites like steps, pointing again at the relevance of the latter for the oxidation process. Apart from the strain energy, another influential factor is the thermodynamic driving force to form an oxide.…”

Major Successes of Theory-and-Experiment-Combined Studies in Surface Chemistry and Heterogeneous Catalysis

“…These two techniques give a good approximation of the symmetry of surface structure and in-plane lattice distances. Figure 10a and b shows the LEED pattern and the STM image of a surface oxide on Rh(111) formed under conditions: 1 9 10 -3 mbar of O 2 and 700 K [52]. These experimental results suggest the formation moiré pattern consisting of a hexagonal layer with a larger in-plane lattice distance being on top of hexagonal Rh(111) substrate.…”