Magnesium doping for the promotion of rutile phase formation in the pulsed laser deposition of TiO2 thin films

Abstract

The preparation of a transparent and smooth rutile-type TiO2 thin film without the use of the crystallographical effect of the substrate is a challenge for the advanced utilization of TiO2 in the fields of optics and solid state ionics. Because acceptor doping leads to the formation of oxygen vacancies, this method has promise as a new approach to promote the formation of rutile-type TiO2. Mg2+-doped TiO2 thin films were prepared by pulsed laser deposition, and the effects of Mg2+ doping on the phases present, the microstructure, the optical properties, and the surface roughness of the films were investigated. Particular attention was paid to the Mg2+ distribution in the prepared films. The formation of the rutile phase was promoted by 2.7 mol% and 5.5 mol%Mg2+ doping. The negligible segregation of Mg2+ and absence of change in the extinction coefficient by Mg2+ doping indicate that Mg2+ worked as the acceptor and induced oxygen vacancies for charge compensation, which promoted the formation of the rutile phase. Given that Mg2+ is a doubly charged acceptor, Mg2+ doping is a more effective method for promoting the formation of the rutile phase than trivalence doping. Besides the excellent optical properties (n 3.03 and k < 0.02 at = 400 nm) of the 2.7%Mg2+-doped rutile-type TiO2 thin film deposited at 350°C, the films were smooth, with a roughness index of only approximately 0.8 nm. This method of preparing smooth rutile-type TiO2 thin films has potential for the further development of TiO2-based resistive memory devices.