Abstract
Growth of Zn on Cu(110) with and without the influence of oxygen was investigated by a combination of scanning tunneling microscopy, low-energy ion scattering, and low-energy electron diffraction in analogy to previous studies on growth and oxidation of Zn on Cu(111). Upon room-temperature deposition of submonolayer Zn films on Cu(110), a step-flow growth mode is observed—possibly accompanied by some intermixing—with Zn atoms adopting the fcc(110) structure of the copper substrate. Upon oxidation of submonolayer Zn films at temperatures around 400–500 K, ill-ordered clusters of oxidized zinc are formed, but the Cu(110) substrate becomes oxidized too. Room-temperature deposition of submonolayer amounts of Zn onto a partly oxidized “striped” Cu(110) surface results in partial destruction of the CuO stripes, formation of ZnOx clusters, and in addition growth of Zn “nanowires” with an fcc(110) structure on the clean copper stripes. On the fully developed (2 × 1)O template, zinc atoms adopt a geometry reminiscent of the (2 × 1) reconstructed CuO surface.
Highlights
The Cu/ZnO system is widely used as an active catalyst for several industrially relevant reactions such as methanol synthesis,[1−3] methanol steam reforming,[4,5] and water gas shift reaction.[6]
It has been characterized with respect to CO oxidation.[7−9] In a recent publication, we showed that on an inverse model catalyst with polycrystalline copper serving as a substrate, CO oxidation is temporarily promoted by the transient presence of a ZnO−Cu interface.[9]
We investigated the structure resulting from the various preparations by low-energy ion scattering (LEIS) in the impact collision ion-scattering spectroscopy (ICISS) mode
Summary
The Cu/ZnO system is widely used as an active catalyst for several industrially relevant reactions such as methanol synthesis,[1−3] methanol steam reforming,[4,5] and water gas shift reaction.[6]. Zinc oxide growth on Cu(110) was already investigated using TPD, LEED, and Auger electron spectroscopy (AES) by Fu and Somorjai.[19] In contrast to the present preparation method, which applies sequential exposure to Zn and oxygen (or the other way round), these authors mostly used a different preparation scheme where zinc was deposited in oxygen ambient of 1 × 10−7 torr onto a fully (2 × 1)O reconstructed Cu(110) surface. From CO and CO2 titration experiments, they concluded that heating a twodimensional ZnOx monolayer above 300 K leads to threedimensional cluster formation. They observed that in the presence of oxygen, zinc is stabilized on the surface. Temperature from ≈680 K on clean Cu(110) up ≈1000 K, depending on the amount of oxygen offered
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