A. Bzowski

Adsorption of Au on Ru(001): electronic perturbations and the nature of the bimetallic bond

Abstract The electronic properties of Au Ru (001) surfaces have been investigated using high-resolution photoemission spectroscopy with synchrotron radiation, and ab initio self-consistent-field calculations. For submonolayer coverages of Au, the interaction between the Au 5d and Ru 4d bands produces an interface state that appears at ∼ 1.5 eV. A monolayer of Au in contact with Ru(001) has a Au 4 f 7 2 binding energy of ∼ 0.25 eV higher than that of the surface atoms of Au(111). The AuRu bond is complex with Au losing 5d electrons and gaining 6s and 6p electrons. This redistribution of charge affects the stability of the bimetallic bond.

Study of the electronic structure of Au-V bimetallics using X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES)

Abstract Core-level binding energy shifts and valence band behaviour for Au–V intermetallic compounds have been studied with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES). It is found that both the Au 4f and V 2p core levels exhibit a positive binding energy shift, relative to the pure metals. These results can be explained with the charge compensation model (Watson et al., Phys. Rev. B4 (1971) 4139): there is an increase in the number of sp-like conduction electrons accompanied by a decrease in the d-electron count at the Au site resulting in a small net charge flow onto the Au site in accord with electronegativity and electroneutrality considerations. Au L-edge X-ray absorption near-edge structures (XANES) provide direct evidence for d-charge depletion at the gold site confirming the XPS results. V K-edge XANES indicate d-charge depletion at the V site, as well. These results are compared with those for Au–Ti and Au–Ta alloys.

Observations on the d-band width of AuAg and AuCu alloys

Abstract The d-band widths of a series of AuAg and AuCu alloys have been studied with photoemission spectroscopy. The main concern is whether or not the Au d band width is maintained in these alloys. It is found that in concentrate alloys (>50% atomic Au), the alloy d-band width narrows little in both Ag and Cu alloys relative to that of pure Au. At 25% (and less) atomic Au concentration however, the d band widths of the Au alloys in the two hosts are significantly different. While the d-band width of Cu 3 Au (ordered and disordered) remains the same as that of the pure Au, the d-band width of Ag 3 Au (disordered) narrows by sim 1eV. The implication of this observation is discussed in terms of dilution and chemical effects.

Ru-promoted alloying of Au and Cu ultrathin films: photoemission studies

Abstract For the co-adsorption of Au and Cu on Ru(001), the Ru substrate promotes the alloying of the noble metals by lowering the activation energy required for the process. High-resolution photoemission spectroscopy with synchrotron radiation and X-ray photoelectron spectroscopy have been used to investigate the core-level binding energy shifts and the valence-band behaviour in a series of Au and Cu overlayers on Ru(001): 1 ML Au, 1 ML Cu, 1 ML Au and 1 ML Cu, 3 ML Au and 1 ML Cu, as well as 1 ML Au and 3 ML Cu. A monolayer of Au in contact with Ru(001) has a Au 4 f 7 2 binding energy ∼0.23 eV higher than that of Au surface atoms on pure Au but still ∼0.1 eV smaller than that of the bulk Au. In contrast a monolayer of Cu bonded to Ru(001) exhibits a Cu 2 p 3 2 binding energy ∼0.1 eV lower than that of a Cu surface atom on pure Cu. Most of the co-deposited AuCu systems formed ultrathin alloys on top of the Ru(001) surface. The strain and electronic perturbations induced by the Ru substrate on the Au and Cu overlayers favour the formation of AuCu alloys. Binding energy shifts of the Au 5d band components and the accompanying change to the overall d-band width were found to be very sensitive to the alloying process, as has been observed in bulk AuCu alloys. The order of deposition, annealing, and the temperature of the substrate were all found to have an effect on the formation of AuCu ultrathin alloys. These ultrathin alloys exhibit Au 4 f 7 2 and Cu 2 p 3 2 binding energies that are significantly different from those of bulk AuCu alloys as a consequence of the interactions with the Ru(001) substrate.

Au-197 Mössbauer isomer shift in Au-Cu and Au-Ag alloys: The role of the Au 5d electrons

The Au-197 Mössbauer isomer shift (IS) for a series of Au-Cu and Au-Ag alloys is correlated with the change in the 5d electron population (5d hole count) at the Au site upon alloying. The Au 5d hole counts have been derived from the area under the whiteline of the Au L3,2 edge X-ray absorption near edge structures (XANES) of the alloys. It is found that there exists a linear corelation betweenIS and Au 5d hole counts, indicating that the redistribution of 5d electrons has a significant effect on the isomer shift. From theIS-5d hole correlation, the ratio of 5d loss to 6s gain (Δnd/Δns) is determined to be −0.62.