Electrochromic reaction of InN thin films

Electrochromic (EC) reaction of indium nitride (InN) films prepared by radio frequency (rf) ion plating was studied through their chemical bonding states and crystalline structures as measured by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. In addition, the pH dependence of the EC reaction was characterized Color of the InN films became darker or lighter when the InN films were polarized anodically or cathodically, respectively, in a Na2SO4 solution. Similar color changes were observed when pH of the Na2SO4 solution was changed from 4.0 to 11.6. The color change at one unit of pH difference corresponded to the EC color change at a potential difference of 59 mV. From these results, H+ and OH- were confirmed to be active reactants in the EC reaction of the InN films. On the other hand, it was revealed from XPS and XRD results that the amount of hydroxides formed at the rain boundaries and the surface of the anodically polarized InN films was seater than that of the film polarized cathodically. Therefore, the electrochromism of the InN films was concluded to be governed by chemisorption of H+ and OH- at grain boundaries. (C) 1999 The Electrochemical Society. S0013-4651(98)08-049-5. All rights reserved.