A.P. Farkas

The growth and thermal properties of Au deposited on Rh(111): formation of an ordered surface alloy

Scanning tunnelling microscopy (STM), low energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) were applied for studying Au deposited on the Rh(111) surface. Both the deposition of Au at different substrate temperatures (400-800 K) and the effect of annealing Au deposited at 500 K were investigated. Gold deposition at 500 K, investigated by STM and LEIS methods, revealed that up to half monolayer Au the system exhibits clearly layer-by layer growth; however, above this coverage a slight deviation was identified, mainly due to kinetic and morphological effects. A continuous cover layer of Au was formed only above ∼2.5 monolayers (ML). Below this coverage, the pseudomorphic character of the Au overlayer was clearly proven by STM, but this feature disappears at 4 ML coverage. A moderate (5-10%) surface mixing of the two metals was observed only above 600 K, for both annealing the Au layer formed at lower temperatures and performing the deposition at elevated temperatures. Above 600 K a clear step-flow growth mechanism was verified. Depending on the Au coverage, a more extended mixing of the top layer and the sublayer was observed at even higher temperatures. In this case, nano-range ordering of the alloyed layer was detected by STM, where the lateral extension of the uniform commensurate (2 × 1) domains was around 4 × 4 nm2. In this case, the local intralayer mixing of Rh and Au can locally reach a value of 50%. The proposed structural model for the (2 × 1) alloy phase was also corroborated by HREELS investigations on CO adsorption.

The Adsorption of Oxygen and Coadsorption of CO and Oxygen on Structurally Well‐Defined PdAg Surface Alloys

The dissociative interaction of oxygen with structurally well-defined monolayer Pd(x)Ag(1-x)/Pd(111) surface alloys of different compositions, with well-known distributions of the respective surface atoms (A. K. Engstfeld et al., Phys. Chem. Chem. Phys. 2012, 14, 10754-10761), and the coadsorption of/reaction with CO on oxygen pre-covered surfaces were studied by high-resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption/reaction spectroscopy (TPD/TPR). The impact of geometric ensemble effects as well as electronic ligand and strain effects on the adsorption and reaction behaviour of the respective species on the bimetallic surfaces is elucidated and compared with related systems such as CO adsorption on similar surfaces and oxygen adsorption on a Pd(67)Ag(33)(111) bulk alloy surface. The data show a clear dominance of ensemble effects on the oxygen adsorption and CO coadsorption behaviour, with oxygen adsorption limited to threefold-hollow sites on Pd(3) sites, while the combined electronic effects, as evident from modifications in the adsorption and reaction characteristics on the Pd sites, are small.

Adsorption geometry of ethyl iodide on clean and oxygen covered Ru(001) surfaces: LEIS, XPS and TDS study

Ion scattering spectroscopy (LEIS) was used in conjunction with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) for the study of the adsorption of ethyl iodide on clean and oxygen covered Ru(001) surfaces. The data suggest that ethyl iodide forms chemisorbed, physisorbed second (bilayer) and condensed multilayer on clean surface. On oxygen-precovered Ru(001) ethyl iodide molecules bond preferentially to Ru sites but very close to oxygen adatoms holding together by Coulomb forces. # 2003 Elsevier Science B.V. All rights reserved.

Effect of Gold on the Adsorption Properties of Acetaldehyde on Clean and h-BN Covered Rh(111) Surface

Auger electron spectroscopy, high-resolution electron energy loss spectroscopy and temperature programmed desorption methods have been used in order to investigate the adsorption properties and reactions of acetaldehyde on gold decorated rhodium and BN/Rh(111) surfaces. Scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements were carried out to characterize the gold nanoparticles on clean and hexagonal boron nitride (h-BN) covered Rh(111). The adsorption of acetaldehyde was not completely hindered by gold atoms; however, depending on the structure of the outermost bimetallic layer (surface alloy) the dissociation of the parent molecule was suppressed, namely the production of carbon monoxide was inhibited by the gold domains. Our measurements with acetaldehyde on Au/h-BN/Rh(111) confirmed the observation that the lack of suitable adsorption sites eliminates the formation of CO. Nevertheless, increased coverage of gold enhanced the amount of adsorbed aldehyde at low temperature. We may predict that the low reactivity of acetaldehyde on Au/h-BN/Rh(111) significantly determine the ethanol decomposition mechanism on this surface.