Formation and Valence Band Density of States of Nonspherical Cu Nanoparticles Deposited on Si(100) Substrate

Abstract

Copper thin films consisting of nanosized particles were deposited on a Si(100) single-crystal substrate by laser ablation in an argon atmosphere. In order to obtain isolated particles with nanometer sizes, the film was sputtered by low-energy Ar+ ions. The valence band density of states of the film was in situ investigated by X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) during the Ar+ ion sputtering. The size of the particles formed after sputtering was in the range between 3 and 6 nm in lateral dimension and 2−3 nm in height, as measured by transmission electron microscopy. In the as-deposited state the photoelectron spectrum of the thin layer was identical to what was observed in the bulk. At the end of thinning by Ar+ ion sputtering the 3d valence states were rehybridized with respect to the bulk states, which indicates that the lower binding energy part of the d band (around 2.5 eV) is the most sensitive for size reduction. The Fermi edge became undetectable by photoemission. Thes...