Advances in Physics Theories and Applications www.iiste.org ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol.34, 2014 1 Annealing Effect on the Structural and Optical Properties of Sol- Gel Deposited Nanocrystalline CdO Thin Films Adel H.Omran Alkhayatt 1* , Imad A. Disher Al-hussainy 2 , Oday A. Chichan Al-rikaby 1 1.Department of Physics, Faculty of Science, University of Kufa PO box.21 Najaf, Iraq 2.Ceramic Department , College of Material Engineering, University of Babylon , Iraq * E-mail: adilh.alkhayat@uokufa.edu.iq Abstract In this paper CdO thin films have been prepared by using SOL-GEL method with spin coating technique, by depoited four layers of mixtuer solution contians Cadmium acetate dehydrate, Triethylamine, glycerol and ethanol.The spin coated solution were dried at 100°C and annealied at (300,350 and 400 o C temperatures ). The x-ray diffraction techniques and UV-VIS spectrophotometer have confirmed the structural and the optical properties the prepared thin films. CdO thin films were found to have polycrystalline nature with cubic rock salt phase. The crystallinity being improved, the FWHM decreases and the grain size of the CdO thin films increased with increasing the annealing temperatures. The average grain size is observed in the range (23.97 - 30.47) nm which indicate that the prepared film have a nanocrystalline structure. From optical analysis, it can be seen that there are an increases in the absorbance and decreases in the trancemittance of the prepared films with the increasing of the annealing temperatures.The optical band gap decreases from 2.556, to 2.081 eV with increasing of annealing temperature fromm 300 to 400° C, this suggested that the optical band gap for CdO nanocrystalline thin films is strongly dependent on the annealing temperature. Keywords: CdO thin films, Sol–gel spin–coating, Structural and Optical properties, annealing temperature. 1. Introduction Transparent conducting oxides (TCOs) have long been a subject of various investigations due to its unique physical properties and applications in commercial devices [1, 2, 3]. (TCOs) are electrical conductive materials with a comparably low absorption of light and high optical transmittance in the visible region of the solar spectrum along with a moderate refractive index[2,3]. Among these TCOs, CdO is an important material for the fundamental studies. It is now well conceived that the CdO shows any excellent properties, which make it suitable as a TCO[4]. CdO is an n–type semiconductor with band gap of approximately 2.5 eV, CdO is cubic structure with each ion surrounded by six ions of opposite electric charge, octahedrally arranged [4,5].CdO films have been successfully used for many applications, including phototransistors [5], gas sensor [6], transparent electrodes, photovoltaic solar cells [7], liquid crystal displays, photodiodes, IR detectors and anti reflection coatings and optoelectronic devicess [7,8].CdO thin films have been prepared by different techniques such ultrasonic spray pyrolysis[9] , electrodeposition [10], chemical bath deposition [11], vacuum evaporation [12] , Pulse Laser Deposition [13] and Sol.Gel. deposition method[14] In this work, CdO film has been deposited by sol–gel method spin coating procress, which is a very simple and economical method. 2. Experimental work CdO films were deposited onto glass substrates by the sol–gel method using a spin coating method. In order to obtain acceptable results and measurable samples, Cadmium acetate dehydrate is used, which is white solid Sault Cd(CH 3 COC) 2 . 2 H 2 O supplied from FLUKA-GARANTIE co-England. With a molecular weight of 266.52 g/mol and a purity of 98% as a source for cadmium, Cubis® Analytical Balance MSU224S-0CE-DU, satoriues Gmbh- Germany with 0.1 mg readability is used, Cadmium acetate dehydrate was dissolved in methanol. Digital Hotplate stirrer, UK, Jenway co, model SD162 is used to insure complete dissolving. Glycerol is used to obtain gel from this solution. Triethylamine supplied from SIGMA-ALDRICH co-USA with Molecular Weight 101.19 was added to methanol, and then added to mixture. Then applying following procedure to obtain solution: 7 ml of methanol is added to 2 g (7.5 mmol) of cadmium acetate dehydrate. In order to obtain a transparent solution, continuous slow stirring is required. Adding 0.11 ml (1.5 mmol) of glycerol with continuous stirring, a solution of 0.52 triethylamine in 7 ml of methanol is prepared separately, and subsequently added with 1 hour stirring to cadmium acetate solution. Then storing the mixture of the two solutions for 24 hours at room temperature, the resulting solution is completely colorless and transparent during preparation and storing. The glass Substrates have been cleaned by distilled water in order to remove impurities and residuals from the surfaces, then they cleaned by dipping in methanol for 5 minutes, then dipping in acetone for 5 minutes, dipping in de-ionized water for 10 minutes, cleaning by Hcl for 10 minutes and finally dipping in de-ionized water for 10 minutes, For reaching best results. Samples exposed to ultrasonic cleaner inside de-ionized water for 15 minutes and dried