Evolution of metallic screening in small metal clusters probed by PCI-Auger spectroscopy

Abstract

Excitation-energy dependent Auger spectra of small copper clusters supported by a thin silica layer have been measured as function of cluster size. The Auger kinetic energy of the clusters clearly changes with the excess energy of the emitted photoelectron while not for the bulk. The kinetic energy shift is attributed to post-collision interaction (PCI) and exhibits a reduced metallic screening ability of small Cu-clusters. The spectroscopic data reveal an evolution from a long-range Coulomb-like interaction to a short-range "screened" electrostatic interaction within the sub-nm range. The data show that core electron spectroscopy such as PCI-Auger measurements can be used as a general tool to follow the metallic character of supported clusters.

Size-dependent Auger spectra and two-hole Coulomb interaction of small supported Cu-clusters

“…This also explains the attenuated electrostatic screening properties of deposited Cu N -clusters as previously shown by us using PCI-Auger spectroscopy. 18 …”

“…Core-level photoelectron spectroscopy is a surface sensitive and element specific tool which can be applied to study highly diluted samples such as free and deposited clusters by X-ray photoelectron spectroscopy (XPS), [1][2][3][4][5][6][7][8][9] X-ray absorption spectroscopy (XAS) [10][11][12] , extended X-ray absorption fine structure analysis (EXAFS), 13 grazing-incidence small-angle X-ray scattering (GISAXS), 14 X-ray magnetic circular dichroism (XMCD) [15][16][17] and Auger electron spectroscopy (AES). 18 In particular AES and XPS provide information on the initial and final states such as chemical effects, charge transfer, core-hole screening, core-hole binding energies, and electron correlation including final-state term splitting and on-site electron-electron interaction. Regarding electron correlation Auger spectra have been used to obtain valuable information on the effective Coulomb interaction of two 3d holes in transition metals and their compounds such as oxides and cuprates.…”

“…18 In particular AES and XPS provide information on the initial and final states such as chemical effects, charge transfer, core-hole screening, core-hole binding energies, and electron correlation including final-state term splitting and on-site electron-electron interaction. Regarding electron correlation Auger spectra have been used to obtain valuable information on the effective Coulomb interaction of two 3d holes in transition metals and their compounds such as oxides and cuprates.…”

Pb 4f photoelectron spectroscopy on mass-selected anionic lead clusters at FLASH

“…The most direct method to investigate the electronic level structure is photoelectron spectroscopy (PES). PES on clusters has a long history, comprising systems grown at surfaces [2,3], deposited from beams [4][5][6][7] and in gas phase. The latter yielded a fundamental understanding of how the electronic structure develops when the number of atoms N changes.…”