X-ray Photoelectron Spectroscopic Investigations of Cu−Ni, Au−Ag, Ni−Pd, and Cu−Pd Bimetallic Clusters

Abstract

Core-level binding energies of the component metals in bimetallic clusters of various compositions in the Ni-Cu, Au-Ag, Ni-Pd, and Cu-Pd systems have been measured as functions of coverage or cluster size, after having characterized the clusters with respect to sizes and compositions. The core-level binding energy shifts, relative to the bulk metals, at large coverages or cluster size, ∆E a , are found to be identical to those of bulk alloys. By substracting the ∆E a values from the observed binding energy shifts, ∆E, we obtain the shifts, ∆E c , due to cluster size. The ∆E c values in all the alloy systems increase with the decrease in cluster size. These results establish the additivity of the binding energy shifts due to alloying and cluster size effects in bimetallic clusters.

Charge transfer effects on the chemical reactivity of PdxCu1−xnanoalloys

“…The BE shift in core-level electrons is typically observed in Pd-Cu alloys, and corroborates the alloy formation in the carbon supported Pd x Cu 1−x NPs. It has been reported in both experimental and theoretical papers 13,[16][17][18][19] that, for bulk and thin-film Pd-Cu alloys, the magnitude of BE shifts (relative to the pure metallic Cu) observed for Cu 2p photoelectrons increase linearly with the Pd : Cu ratio. This effect has been explained in terms of charge transfer upon the alloying between Pd and Cu species.…”

“…The core-level binding energy shifts were explained in terms of charge transfer between Pd and Cu species, and have been described in many experimental and theoretical studies. 4,13,[16][17][18][19][20] However, there is still a lack of studies on PdCu nanoalloys produced by chemical reduction employing mild chemicals and conditions. Moreover, detailed investigations on the structural and electronic properties of PdCu nanoalloys with different compositions and similar sizes have not yet been reported to our knowledge.…”

Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

“…Earlier also shift in core level binding energies on decreasing the cluster size is reported in Pd-Cu and Pd-Ni clusters prepared by the physical evaporation techniques. 43,44 It must be noted that the values of DE S increase faster in Pd-alloy nanoparticles in comparison to Pd, Ag, and Cu metal nanoparticles. This indicates that size induced effects leading to bond length contraction which result in redistribution/hybridization of valence charges, are dominant in alloys in comparison to metal nanoparticles.…”

Charge transfer, lattice distortion, and quantum confinement effects in Pd, Cu, and Pd–Cu nanoparticles; size and alloying induced modifications in binding energy

“…4,5 In spite of its direct relevance in important technologies such as hydrogen sensing and storage, there are only limited reports on variation in core and valence levels in Pd and Pd-alloy nanoparticles. 4,6 The effect of size on valence and core levels in case of Pd, Pd-alloy islands and nanoparticulate thin films grown by vacuum evaporation technique was studied by controlling the thickness and coverage of the polycrystalline islands. 4,6 In the present letter, metal and alloy nanoparticles have been prepared by gas phase synthesis followed by in-flight sintering to reduce the chemical ligand and polycrystallinity induced effects.…”

“…4,6 The effect of size on valence and core levels in case of Pd, Pd-alloy islands and nanoparticulate thin films grown by vacuum evaporation technique was studied by controlling the thickness and coverage of the polycrystalline islands. 4,6 In the present letter, metal and alloy nanoparticles have been prepared by gas phase synthesis followed by in-flight sintering to reduce the chemical ligand and polycrystallinity induced effects. Structural and electronic properties of Pd-Cu alloy nanoparticles of different sizes have been studied and compared with those of Pd and Cu nanoparticles of similar sizes prepared under identical conditions.…”