Charge competition with oxygen molecules determines the growth of gold particles on doped CaO films

Yi Cui, Kai Huang, Niklas Nilius*, Hans Joachim Freund

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

7 Scopus citations

Abstract

The influence of gas-phase oxygen on the growth of Au nanoparticles on Mo-doped CaO films has been investigated by means of low temperature scanning tunnelling microscopy and X-ray photoelectron spectroscopy. Whereas at ideal vacuum conditions, only 2D Au islands develop on the oxide surface, the fraction of 3D deposits increases with increasing O2 pressure until they become the dominant species in 10-6 mbar oxygen. The morphology crossover arises from changes in the interfacial electron flow between Mo donors in the CaO lattice and different ad-species on the oxide surface. In the absence of O2 molecules, the donor electrons are predominately transferred to the Au ad-atoms, which consequently experience enhanced binding to the oxide surface and agglomerate into 2D islands. In an oxygen atmosphere, on the other hand, a substantial fraction of the excess electrons is trapped by adsorbed O2 molecules, while the Au atoms remain neutral and assemble into tall 3D particles that are typical for non-doped oxides. Our experiments demonstrate how the competition for charge between different adsorbates governs the physical and chemical properties of doped oxides, so widely used in heterogeneous catalysis.

Original languageEnglish
Pages (from-to)153-163
Number of pages11
JournalFaraday Discussions
Volume162
DOIs
StatePublished - 11 Jul 2013
Externally publishedYes

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