Abstract
NiO films were deposited by DC magnetron sputtering under various pressures from 0.12 to 12 Pa. The structure of the films was investigated using X-ray diffraction, scanning electron microscopy, and measurement of density and surface area. The films generally consisted of columnar grains. In the as-deposited films, as the pressure increased, voids developed between columnar grains and the density decreased with an abrupt increase in surface area. The surface area of a film with a low density considerably decreased after annealing at 400°C. The sensitivity of annealed films to NO2 at a concentration of 1 ppm in dry air was also investigated. The highest sensitivity, 3.0, was obtained at 200°C for the sensor made of a film with the lowest density deposited at 12 Pa.
