Structure and Photocatalytic Activity of Copper and Carbon-Doped Metallic Zn Phase-Rich ZnO Oxide Films

ZnO is one of the most important industrial metal oxide semiconductors. However, in order to fully realise its potential, the electronic structure of ZnO has to be modified to better fit the needs of specific fields. Recent studies demonstrated that reactive magnetron sputtering under Zn-rich conditions promotes the formation of intrinsic ZnO defects and allows the deposition of metallic Zn phase-rich ZnO films. In photocatalytic efficiency tests these films were superior to traditional ZnO oxide, therefore, the purposeful formation of intrinsic ZnO defects, namely Zn interstitials and oxygen vacancies, can be considered as advantageous self-doping. Considering that such self-doped ZnO remains a semiconductor, the natural question is if it is possible to further improve its properties by adding extrinsic dopants. Accordingly, in the current study, the metallic Zn phase-rich ZnO oxide film formation process (reactive magnetron sputtering) was supplemented by simultaneous sputtering of copper or carbon. Effects of the selected dopants on the structure of self-doped ZnO were investigated by X-ray diffractometer, scanning electron microscope, X-ray photoelectron spectroscope and photoluminescence techniques. Meanwhile, its effect on photocatalytic activity was estimated by visible light activated bleaching of Methylene Blue. It was observed that both dopants modify the microstructure of the films, but only carbon has a positive effect on photocatalytic efficiency.

Photoluminescence and structural defects of ZnO films deposited by reactive magnetron sputtering with unconventional Ar-O2 gas mixture formation

ZnO is a well-known traditional industrial material which has high potential to become one of the key components for the next generation of future electronics, LED emitters, visible light photocatalysis and others. In its pristine form ZnO has relatively wide band gap of approximately 3.4 eV, but a lot of emerging applications requires some level of electronic structure engineering and structure optimisation. Studies show that ZnO properties strongly depend on the intrinsic defects type and concentrations. Both characteristics usually are depending on the synthesis method. Accordingly, there is great interest to develop new methods which would allow to obtain ZnO with optimised band gap and other properties. In current, study ZnO films were deposited using reactive magnetron sputtering with unconventional Ar-O2 gas mixture supply control: Ar flow was controlled to maintain total gas pressure at 1x10-2 mbar, whereas O2 flow rate was actively adjusted to maintain the selected intensity of optical zinc emission from the working cathode zone. Applying such ZnO formation method it was possible to stabilise reactive magnetron sputtering process over wide range of conditions. Elemental composition analysis by XPS revealed that despite large variations in Zn emission peak intensity within tested experimental conditions all films had nearly identical Zn:O ratios but at the same time their structural and optical properties differed significantly. The colour of the films varied from highly transparent yellowish-greenish, to intense orange, to opaque black. XRD analysis showed that films consisted of single polycrystalline wurtzite phase with varying orientations. PL spectroscopy analysis revealed that films had a lot of various defects including oxygen and zinc vacancies, interstitials and surface defects. Wide variation of ZnO properties obtained by different reactive sputtering conditions demonstrates the potential of the proposed method to control the formation of various intrinsic defects and to tailor their concentration.

Magnetron sputtered TiO2 with metal NPs for plasmonic applications

This work is aimed at finding the optimal technological modes for the deposition of TiO2 films by reactive magnetron sputtering for use as a photoactive material in plasmonic applications. The structural and optical parameters of films obtained at different ratios of oxygen in a mixture of working gases were studied. On the basis of the obtained experimental results, a numerical simulation of the spectral characteristics of the TiO2 / NP structure of the metals silver and gold was carried out.