X-ray photoelectron spectroscopy study of the first stages of ZnO growth and nanostructure dependence of the effects of polarization at ZnO/SiO2 and ZnO/Al2O3 interfaces

Abstract

A critical characteristic of nanoparticles and, in general, of nanomaterials, is the overweighing importance of the surface and interface layers relative to the bulk because of the small size of the aggregates (in three dimensions) or thickness of the layers (in the case of two dimensions) that constitute the nanomaterial. This article reports the characterization of interface layers of ZnO/MOx (MOx: Al2O3 and SiO2) using x-ray photoelectron spectroscopy (XPS). Careful experiments consisting of the deposition of ZnO material on SiO2 and Al2O3 substrates have been performed. Several samples were produced and characterized in situ. The nanostructure of the first stages of growth of the ZnO deposited was determined by Tougaard peak-shape analysis of several photoelectron peaks in both the substrate and overlayer and the growth mechanisms determined were found to be consistent. Thus, the actual nanostructure of the growing ZnO films was carefully determined. In addition, the chemical interaction at the ZnO/MOx interface was monitored by following the variation of the Auger parameter of the Zn atoms as the amount of ZnO deposited was increased. Thus, changes of the Auger parameter of the Zn atoms were correlated with the actual nanostructures formed by the ZnO deposits. From this information, a model is presented that accounts for changes in the electronic parameters determined by XPS as a result of bonding and polarization interaction at the interface.