Characterization of Bimetallic Au/Pd(110) Surfaces

Abstract

The growth as well as the compositional, electronic and structural properties of thin Au films deposited on a Pd(110) single crystal have been studied by means of ultraviolet photoelectron spectroscopy (UPS), photoemission of adsorbed xenon (PAX) and scanning tunneling microscopy (STM) as a function of film thickness (ranging from submonolayer amounts up to multilayers) and temperature. Our investigations indicate a Volmer-Weber growth mode of Au on Pd(110) at a deposition temperature of 300 K and below. As former studies already have shown, depositing Au amounts of less than 1 ML results in the formation of unreconstructed pseudomorphic Au islands. Above a critical thickness of 2 ML the formation of a (1 × 2) missing-row reconstruction typical for Au can be observed. This reconstructed Au bilayer is still in registry with Pd(110) and, thus, strained. Furthermore, our experiments show a strong temperature dependence of the surface morphology. Au multilayers prepared at 150 K, which are already quite flat, undergo a weak smoothening of the topmost atomic layer by annealing the sample up to 350 K. At a surface temperature of ∼ 450 K the diffusion of Au atoms into the bulk is initiated at the Au-Pd interface. Annealing a 3 ML thick Au film to 600 K finally results in the formation of an Au-Pd surface alloy, which is stable up to 900 K. A complete loss of Au from the surface can be detected at around 1050 K. Adsorption of CO as a probe molecule on the Au containing surfaces is only possible at low temperatures.

Acceleration of hydrogen absorption by palladium through surface alloying with gold

“…There is also intensity around 6–7 eV. These bands around 2–5 and 6–7 eV correspond to the Au d bands and the flat region with a low intensity from E F to 2 eV corresponds to the Au s-p band as observed on Au surfaces and Au-rich Pd–Au surface alloys ( 24 – 26 ), indicating that the as-grown 2.4-ML Au/Pd(110) surface is similar to the Au surface. Therefore, the band around 2–3 eV near k y = 0 observed in Fig.…”

“…The amount of deposited Au atoms was monitored by a quartz oscillator placed near the sample. In the ARPES measurement, the amount of deposited Au was determined from the ARPES spectra on the basis of a previous study where the Au-derived band almost saturates in intensity at 1-ML Au ( 24 ). In the TDS experiments shown in Fig.…”

Characterization of Bimetallic Systems with UPS and PAX: Gold on Platinum and Palladium Surfaces

“…In the further discussion we will mainly concentrate on the most intense peak at 6.0 eV (peak A). Former studies by Salmeron et al [19] and Kobiela et al [20] on different Pt surfaces, by Moors et al [21] on Pd(110) and by Citrin and Wertheim [22] on a glass substrate showed that, independent of the used substrate, the position of this peak (stemming from the Au 5d 3/2 -derived subband) is stable at mono-and multilayer coverage. However, a characteristic shift to lower binding energy has been found for submonolayer coverages.…”