Formation of Zn-rich ZnO films with improved bulk and surface characteristics by approach of magnetron sputtering technique

Abstract

In this work Zn-rich ZnO films were formed by unconventional magnetron sputtering approach where oxygen flow cyclically varied between two different values during deposition process. Specifically, ZnO films were deposited using radio frequency power source with Zn target, while argon flow was set to keep total deposition pressure at constant and oxygen flow cyclically varied between stoichiometric ZnO and intermediate Zn/ZnO formation regimes. Such modification of physical vapor deposition method allowed to form complex structure ZnO films with altered bulk and surface characteristics. X-ray diffraction analysis of deposited films revealed highly expressed wurtzite structure with existence of small fraction of metallic Zn phase. In comparison to regular ZnO film surface morphology analysis of complex structure Zn-rich ZnO films showed significant increment of grain size and more than three times larger surface roughness. The reduction of optical transmittance as well as band gap value were observed by analysing optical properties of deposited films. Urbach energy analysis revealed that deposited Zn-rich ZnO films had higher level of disorder, dopants or defects comparing to the regular ZnO. Such combination of deposited films properties leads to the significant improvement of photocatalysis efficiency measured by the bleaching of methylene blue solution.