Crossed-beam pulsed laser deposition in a moderate He background gas pressure was used to prepare PtAu thin films. The Pt bulk content was determined by neutron activation analysis, whereas X-ray diffraction and X-ray photoelectron spectroscopy were used to assess the bulk and the surface structure of the films, respectively. It is shown that metastable PtAu alloys with a unique fcc structure are formed over the whole composition range. The surface composition of the films closely follows the bulk content, and X-ray photoelectron spectroscopy reveals that the surface of the films is also made of a PtAu alloy. These films are stable under ambient conditions. The electrochemical properties of these films were determined by cyclic voltammetry in H 2 SO 4 electrolyte, and their reactivity toward the electrooxidation of CO and the electroreduction of O 2 was assessed. The CO stripping peak potential value increases with the Au content, indicating an increased binding energy in comparison with polycrystalline Pt. Similarly, there is a cathodic shift of the Pt oxide reduction peak for the Au-rich alloy that indicates stronger Pt-O binding energies as compared with Pt-rich alloy electrodes. At the surface, the presence of Au in close proximity to Pt atoms induces a shift of the d-band center of the Pt atoms that translates into stronger bonds with CO-and O-containing species at the surface of the samples. As far as we can tell, the surface composition and structure of the deposits are not modified following the electrochemical measurements.

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The expansion dynamics of plasma produced by excimer laser ablation of a gold target was measured by means of spatially resolved real time emission spectroscopy. The emission line of the Au(I) neutral gold species at 267.65 nm was used to monitor the expansion dynamics of the plasma in several background gases (He, N2, O2, and Ar). The measurements were performed as a function of the gas pressure (from 4×10−5 to 4 Torr) and target-to-substrate distance (from 1.5 to 11 cm). Gold thin films were prepared in the same conditions and their structure was analyzed by x-ray diffraction. All films prepared fall into one of three categories: highly (111) oriented, mixed, or polycrystalline. All the films prepared herein show a transition from highly (111) oriented to mixed and then to polycrystalline as the velocity of the Au(I) neutral gold species decreases. In the case of inert background gases (He, N2, and Ar), the velocity at which the transition between the various types of structure occurs is remarkably constant. Highly (111) oriented films are obtained for Au(I) neutral gold species exceeding v1=2.4 km s−1 (5.8 eV), while a polycrystalline (nanocrystalline) film is formed when the velocity falls below v2=0.8 km s−1 (0.6 eV). The conditions of distance and pressure at which these velocities are attained differ greatly from one atmosphere to the other, reflecting the fact that the interaction between the expanding plasma and the background gases varies with the molar mass of the gas. In the case of O2, the transition velocities between the different structures are higher than those observed in He, N2, and Ar [v1=8.3 km s−1 (70.4 eV) and v2=3.4 km s−1 (11.8 eV)]. This reflects a significant difference in the growth mechanism of these films compared to those prepared in an inert atmosphere.

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