Nickel oxide thin films were prepared using chemical bath deposition and reactive magnetron dc-sputtering. Through the chemical route, Ni(OH)(2) films were deposited with a nano-porous structure providing large specific surface area. Subsequent annealing at 300 degrees C transformed the films into NiO. These films showed high absorption in the visible range and low crystallinity due to Ni vacancies. Annealing at higher temperatures removes Ni vacancies improving transmittance and crystallinity. Sputtered films were obtained in Ar+O(2) and Ar+H(2)+O(2) atmospheres at different flux ratios. During deposition in the former atmosphere, substrate temperature was 300 degrees C producing dense polycrystalline films with excellent optical properties. In the hydrogen containing atmosphere, the substrate was at room temperature and polycrystalline films with a dark-yellowish color and expanded lattice were obtained. (C) 2008 Elsevier B.V. All rights reserved.