Model bimetallic catalysts: The preparation and characterisation of Au/Ru(0001) surfaces and the adsorption of carbon monoxide
1986; Elsevier BV; Volume: 165; Issue: 2-3 Linguagem: Inglês
10.1016/0039-6028(86)90817-4
ISSN1879-2758
AutoresC. Harendt, K. Christmann, W. Hirschwald, J. C. Vickerman,
Tópico(s)Advanced Chemical Physics Studies
ResumoWe have studied the growth and structure of gold films deposited onto a Ru(0001) single-crystal substrate in UHV using LEED, Auger electron spectroscopy (AES) and thermal desorption mass spectroscopy (TDS). The gold concentrations (θAu) varied from fractions of a monolayer up to several monolayers with the Ru substrate held at either 540 K (low-temperature series) or at 1110 K (high-temperature series) during deposition. A correlation between the AES signal heights of Ru and Au in conjunction with TDS peak areas revealed a layer-by-layer growth of Au, particularly for the high-T series. TDS revealed three different Au binding states which are subsequently populated, viz., a β3 state around 1320 K desorbing in a first-order kinetics and associated with the first Au monolayer, followed by a β2 state (Tdes around 1180–1280 K, fractional-order desorption) reflecting the second monolayer and a β1 state (Tdes around 1160–1260 K, zero-order desorption) corresponding to the third and all following Au layers. The activation energy of desorption. ΔEdes, increases with increasing coverage in the submonolayer regime; it rises from 330 J mol−1 at θAu = 0.1 to about 400 J mol−1 at θ = 0.6 ML. As a general tendency, the lower substrate temperatures favour an island growth of the Au whereas higher Ru temperatures lead to a more pronounced spreading and dispersion of the Au atoms. Epitaxial growth of Au can be observed at higher coverages (θAu ≲ 3 ML) as indicated by double-scattering LEED features. The CO adsorption data support the conclusions about the lateral dispersion of the Au on the Ru substrate in that the high-T Au films suppress the CO uptake more effectively than the low-T films.
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