Effect of post-annealing temperature on nano-structure and energy band gap of indium tin oxide (ITO) nano-particles synthesized by polymerizing-complexing sol-gel method

In this paper, we report on the structural, microstructural and optical properties of nano-crystalline indium tin oxide (ITO) particle, which has been synthesized by sol-gel process using a simple starting hydro-alcoholic solution consisting of In(NO3)(3 center dot)5H(2)O, SnCl(4 center dot)5H(2)O, citric acid as complexing and ethylene glycol as polymerization agents. The structural properties of indium tin oxide nano-powders annealed at different temperatures (T=350-650 degrees C) have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The XRD patterns show In2O3-cubic phase in nano-powders without any indication of crystalline SnOx as an additional phase. The TEM images show the nano-particles as nearly spherical shaped with size in the range of 10-45 nm as the size of grains increases by increasing the annealing temperatures. The optical direct band gap of ITO nano-particles was calculated to be about 3.39-4.02 eV in the temperature range 350-650 degrees C by optical absorption measurements. The optical band gap shifts to a higher energy with increasing annealing temperature is due to the improvement of the crystallinity, thereby increasing the carrier concentration as determined from the Burstein-Moss effect. (C) 2010 Elsevier B.V. All rights reserved.