Influence of sputtering conditions and annealing parameters on structure and morphology of NiTiO3 ilmenite thin films

Abstract

Nickel titanate (NiTiO3) is well known for its interesting functional properties such as photocatalysis, high-K materials or magnetoelectric coupling. Some of these properties are strongly dependent on crystallographic orientation and morphological characteristics. Deposition as thin films through adapted processes enables to control such feature during NiTiO3 growth. In this context, NiTiO3 thin films were obtained by a two-step process: i) room temperature radio-Frequency co-sputtering of metallic Ni and Ti targets, ii) ex situ annealing in air. Influences of the deposition and annealing parameters on the morphological and structural features of NiTiO3 thin films were systematically studied. First, in situ X-ray diffraction as a function of temperature (from 30°C to 1200°C) was carried out in air on a NiTi thin film to identify suitable annealing temperatures for NiTiO3 oxide formation. Then, effects of annealing duration and temperature on morphology and orientation were investigated. Annealing temperature was found to influence grain size, while increasing the annealing time was found to bring (006) crystallographic orientation. Finally, an increase of the deposition pressure from 0.5 Pa to 5 Pa promoted the growth of (104) oriented films with a Lotgering factor LF104=0.44. This approach enables to independently tune preferential orientation and grain size of NiTiO3 thin films, by tailored deposition and annealing conditions.