Structural, optical and electrical properties of CuO nanostructures prepared by reactive DC magnetron sputtering

Abstract

An attempt is made to explore the CuO nanostructures and their attributes in this work. CuO nanostructures are deposited on glass substrates using DC reactive magnetron sputtering using Cu target in argon (84%) and oxygen (16%) environment. These nanostructures are deposited at sputtering power of 70 W, different sputtering pressures in the range 1.0–8.0 Pa and deposition time of 10–60 min. X-ray diffraction (XRD) technique is used to determine the oxide phase of the deposited nanostructures. The XRD pattern matches CuO standard diffraction data (ICDD file 00-005-0661), confirming that no additional oxide phases appeared in the nanostructure coated for different deposition time at higher pressure. Due to the very low content of CuO, no peaks attributable to CuO are observed in the nanostructures deposited for 10 min at sputtering pressure of 3.0–8.0 Pa. In the nanostructure deposited at 1.0 Pa, a new phase Cu2O has evolved. The nanostructure deposited for 60 min has a crystallite size of 26 nm. Field emission scanning electron microscopy (FESEM) is used to analyse the morphologies of the nanostructures. Isolated nanograins of CuO are observed in nanostructures that have been deposited for 10 min, when the deposition time is extended to 40 and 60 min, an almost film-like structure is formed. Sputtering pressure of 8.0 Pa produces highly isolated nanograins; lowering the pressure results in less isolated nanograins. UV–Visible absorption spectroscopy is utilized for optical studies. Transmittance and absorbance spectra are recorded in the 200–1100 nm wavelength range. The nanostructures absorb light strongly in the 280–400 nm region and it is observed that decrease in the sputtering pressure (from 8.0 Pa to 1.0 Pa) and higher deposition time enhance the absorption capacity in this range (280–400 nm) as well as in the visible range. The nanostructures have transmittance of more than 80% in the wavelength range 780–1100 nm. The sheet resistance of the nanostructures is estimated to be between 10.3 and 25.0 kΩ/sq. Hall measurement confirms p-type conductivity of CuO nanostructures and carrier concentration reaches the order of 1018 cm−3.