Evidence of Mixed Oxide Formation on the Cu/SiO₂ Interface

Abstract

The deposition of Cu onto SiO2 has been carried out by electron beam evaporation in order to study the interface formation by X-ray photoelectron spectroscopy and angle resolved X-ray photoelectron spectroscopy. Shifts in the binding energy of Cu 2p3/2 and Si 2p bands, as well as in the Cu LMM kinetic energy, have been observed during the growth. These changes are indicative of a modification in the coordination number of Cu or the formation of M–O–M′ cross-linking bonds at the interface. Moreover, different coordination states of Cu+ and Cu2+ (tetrahedral and octahedral) have been detected. Apart from different coordination numbers, a new chemical state appears during the Cu/SiO2 interface formation. This new contribution, Cux+, is attributed to the formation of a mixed oxide Cu-O-Si. Additionally, two different stages of growth of the Cu/SiO2 interface have been observed: The first one, where no metallic Cu is detected and a mixture of copper oxides is measured onto the SiO2 substrate, and the second one, in which metallic Cu appears on the surface and a multilayer Cu0/Cux+/Cu oxides/SiO2 can be inferred.