Structural, optical and electrical properties of sputtered NiO thin films for gas detection

Abstract

This study systematically investigates the nanostructural evolution, optical and electrical properties of sputtered nickel oxide films prepared at room temperature. The films with 50 and 100nm thicknesses were deposited by DC reactive magnetron sputtering. After annealing at 500°C, the films had a polycrystalline (fcc) NiO phase structure. The size of crystallites was from 8 to 28nm for NiO films with 50nm thickness and from 7 to 26nm for those with 100nm thickness. The grains in both of the annealed NiO thin films exhibited polyhedral morphology with regular and flat edges. It was observed that annealed NiO films were highly transparent, about 70–90% in the spectral range from 500 to 900nm. A double Schottky barrier was found between two adjacent grains which affects the conductivity of NiO thin films on exposing to different gas atmospheres. NiO thin films with 50nm thickness exhibit bigger differences of the conductivity to hydrogen in comparison with NiO films with 100nm thickness in the temperature range from 100 to 250°C.