Deposition of NiO_x thin films by sol–gel technique

Abstract

High quality NiO_x thin films have been prepared by the sol–gel technique following alternative routes to the classic metal alkoxide route. Using nickel (II) diacetate as precursor reagent, a nickel complex was deposited on glass substrates. The nickel complex transforms to NiO_x after a heat treatment in air above 250°C. X-ray diffraction analysis confirmed the crystalline → amorphous phase transition during annealing of the films. The NiO_x thin films prepared in this way are very homogeneous and mostly amorphous. Compared with intrinsic single crystals, they have relatively high electrical conductivity and low optical transmittance in the visible and infrared regions. An optical band gap narrowing from 3·90 to 3·80 eV with increasing film thickness was measured in the films. Sol–gel prepared NiO_x thin films are well suited for use as electrochromic films.