Electronic structure of Au-Ag bimetallics: Surface alloying on Ru(001)

Bzowski, A.; Kühn, M.; Sham, Tsun‐Kong; Rodriguez, JoséA.

doi:10.1103/physrevb.59.13379

Cited by 29 publications

(23 citation statements)

References 27 publications

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“…Similar Au 5d narrowing has been observed in other small clusters 58,61−63 coupling between neighboring Au atoms and a disruption in long-range periodicity. 6,7 This interpretation is reasonable because the clusters contain a maximum of 25 Au atoms, whereas the bulk Au sample contains an extended network of Au−Au neighbors. The Au 5d doublet of Au 25−x Ag x appeared "filled in", and the apparent Au 5d peak separation was equivalent to isolated Au atoms (1.5 eV).…”

Section: Resultsmentioning

confidence: 96%

A Quantum Alloy: The Ligand-Protected Au_25–xAg_x(SR)₁₈ Cluster

et al. 2013

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Recent synthetic advances have produced very small (sub-2 nm), ligand-protected mixed-metal clusters. Realization of such clusters allows the investigation of fundamental questions: (1) Will heteroatoms occupy specific sites within the cluster? (2) How will the inclusion of heteroatoms affect the electronic structure and chemical properties of the cluster? (3) How will these very small mixed-metal systems differ from larger, more traditional alloy materials? In this report we provide experimental and computational characterization of the ligand-protected mixed-metal Au 25−x Ag x (SC 2 H 4 Ph) 18 cluster (abbreviated as Au 25−x Ag x , where x = 0−5 Ag atoms) compared with the unsubstituted Au 25 (SC 2 H 4 Ph) 18 cluster (abbreviated as Au 25 ). Density functional theory analysis has predicted that Ag heteroatoms will preferentially occupy sites on the surface of the cluster core. X-ray photoelectron spectroscopy revealed Au−Ag state mixing and charge redistribution within the Au 25−x Ag x cluster. Optical spectroscopy and nonaqueous electrochemistry indicate that Ag heteroatoms increased the cluster lowest unoccupied molecular orbital (LUMO) energy, introduced new features in the Au 25−x Ag x absorbance spectrum, and rendered some optical transitions forbidden. In situ spectroelectrochemical experiments revealed charge-dependent Au 25−x Ag x optical properties and oxidative photoluminescence quenching. Finally, O 2 adsorption studies have shown Au 25−x Ag x clusters can participate in photomediated charge-transfer events. These results illustrate that traditional alloy concepts like metal-centered state mixing and internal charge redistribution also occur in very small mixed-metal clusters. However, resolution of specific heteroatom locations and their impact on the cluster's quantized electronic structure will require a combination of computational modeling, optical spectroscopy, and nonaqueous electrochemistry.

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Section: Resultsmentioning

confidence: 96%

A Quantum Alloy: The Ligand-Protected Au_25–xAg_x(SR)₁₈ Cluster

et al. 2013

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“…A similar narrowing has been observed for other valence and conduction band peaks upon dilution of metals in a host matrix, e.g., for U diluted in the weakly interacting Ag matrix, 43 of Au diluted in Ag. 44 Conversely, the O-2p line width of oxygen chemisorbed on metal surfaces increases with surface oxygen concentration. In all these case decrease of the spectral line width seems to reflect the narrowing of the bandwidth, due to spatial restriction or atomic isolation.…”

Section: Resultsmentioning

confidence: 99%

An XPS and UPS Study on the Electronic Structure of ThO_x (x ≤ 2) Thin Films

et al. 2014

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Model systems are needed for surface corrosion studies of spent nuclear oxide fuels. For this purpose ThO 2 films have been prepared in situ by adsorption of molecular and atomic oxygen on Th metal films and by sputter deposition of Th metal in an Ar/O 2 gas mixture. Surface compositions and electronic structure were compared to the bulk oxide and oxygen substoichiometry effects investigated. X-ray and ultraviolet photoemission spectroscopy (XPS and UPS, respectively) were used to measure to Th-4f, O-1s core levels and the valence band region. The Th-4f line was analyzed in terms of the final-state screening model. The evolution of the binding energies with oxygen concentration has been studied. On Th metal, adsorption of molecular oxygen ceased after the formation of a ThO 2 surface layer. In the presence of atomic oxygen, the oxidation proceeded into the underlying bulk. The formation of oxygen interstitials was shown by the broadening of the O-2p and O-1s lines and by the increase of the O-1s/Th-4f ratio. Once ThO 2 is formed, all photoemission peaks from Th and O undergo a rigid shift to low binding energy.

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“…% Au) is intermediate (83.44 eV) between those of the most dilute (83.21 eV) and the more Au-rich alloys (83.66 and 83.69 eV), suggesting that high activity is associated with achieving the right balance between the influence of small particle and bulk electronic structure effects. The Ag 3d binding energies detected by XPS vary only slightly and are in the range expected for metallic Ag and its alloys with Au. − …”

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confidence: 84%

Correlating Catalytic Activity of Ag–Au Nanoparticles with 3D Compositional Variations

et al. 2014

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Significant elemental segregation is shown to exist within individual hollow silver-gold (Ag-Au) bimetallic nanoparticles obtained from the galvanic reaction between Ag particles and AuCl4(-). Three-dimensional compositional mapping using energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope (STEM) reveals that nanoparticle surface segregation inverts from Au-rich to Ag-rich as Au content increases. Maximum Au surface coverage was observed for nanoparticles with approximately 25 atom % Au, which correlates to the optimal catalytic performance in a three-component coupling reaction among cyclohexane carboxyaldehyde, piperidine, and phenylacetylene.

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Electronic structure of Au-Ag bimetallics: Surface alloying on Ru(001)

Cited by 29 publications

References 27 publications

A Quantum Alloy: The Ligand-Protected Au_25–xAg_x(SR)₁₈ Cluster

A Quantum Alloy: The Ligand-Protected Au_25–xAg_x(SR)₁₈ Cluster

An XPS and UPS Study on the Electronic Structure of ThO_x (x ≤ 2) Thin Films

Correlating Catalytic Activity of Ag–Au Nanoparticles with 3D Compositional Variations

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Electronic structure of Au-Ag bimetallics: Surface alloying on Ru(001)

Cited by 29 publications

References 27 publications

A Quantum Alloy: The Ligand-Protected Au25–xAgx(SR)18 Cluster

A Quantum Alloy: The Ligand-Protected Au25–xAgx(SR)18 Cluster

An XPS and UPS Study on the Electronic Structure of ThOx (x ≤ 2) Thin Films

Correlating Catalytic Activity of Ag–Au Nanoparticles with 3D Compositional Variations

Contact Info

Product

Resources

About

A Quantum Alloy: The Ligand-Protected Au_25–xAg_x(SR)₁₈ Cluster

A Quantum Alloy: The Ligand-Protected Au_25–xAg_x(SR)₁₈ Cluster

An XPS and UPS Study on the Electronic Structure of ThO_x (x ≤ 2) Thin Films