Single phase CuO thin films prepared by thermal oxidation in air with water vapor JianBo Liang a , XuYang Li b , Naoki Kishi c , Tetsuo Soga d Department of Frontier Materials,Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan. a liangjienbo1980@yahoo.co.jp, b lxy_104@hotmail.com, c kishi.naoki@nitech.ac.jp, d soga@nitech.ac.jp Keywords: CuO; Semiconducting materials; Water vapor; Surfaces Abstract. Single phase CuO films have been successfully synthesized by thermal oxidation of cupper foil in air with water vapor. The structural and optical properties of CuO films were investigated. It is observed that the grain size increases with increasing the oxidation temperature. The optical band gap of CuO film is determined by the transmittance and reflectance spectra. Introduction In recent years, cupric oxide (CuO) thin films have attracted much interest due to their potential applications in optical and electronic devices. CuO has been known as a p-type semiconductor that exhibits a narrow band gap (1.2 eV) and a number of other interesting properties [1, 2]. CuO has also an interesting monoclinic crystal structure belonging to the Mott insulator material class whose electronic structure cannot be described by conventional band theory [3]. During the past years, in order to obtain high quality cupric oxide films, it has been prepared by various techniques such as thermal oxidation [4]; electro deposition [5]; chemical conversion [6]; chemical brightening [7]; spraying [8]; plasma evaporation [9]; reactive sputtering [10]; and molecular beam epitaxy [11]. Among various methods employed for the preparation of CuO films, CuO thin films by thermal oxidation at higher temperature are an inexpensive and convenient method. However, in most of these studies, a mixture of phases, like Cu, CuO and Cu 2 O is generally obtained [12]. A copper foil is oxidized in air at 400 and 500 °C, the majority of copper foil converted into Cu 2 O with only a small amount of CuO on the surface in the form of nanowires [13]. Huang et al reported CuO nanowires formed at 300 °C in oxygen by thermal oxidation of copper foils [14]. Hence it is the essential problem to find out the specific reaction parameters for producing pure CuO phase. Here, we report the synthesis CuO films on quartz substrates by thermal oxidation in air with water vapor and conduct a detailed structural and optical investigation of CuO films. Experimental Thin CuO films have been synthesized by thermal oxidation of copper films on quartz substrates in cylinder air with water vapor and in atmospheric air. Experimental detail of oxidation in atmospheric air as reported in [13]. 300 - 600 nm thick copper films were deposited on quartz substrates by using a thermal vacuum evaporator. The substrates were cleaned in acetone, methanol and deionized water under an ultrasonic bath for 5 min followed by drying with N 2 flow. The cleaned Cu on quartz substrate was placed onto a quartz boat. The quartz boat was positioned in the center of a quartz tube that was mounted in the middle of a horizontal tube furnace. One end of the quartz tube was attached to a nebulizer and other to the gas bubble. The tube furnace was heated to the set-point temperature and gas flow of air was kept at a rate of 0.5 L/min. The system was allowed to cool naturally to room temperature to prevent the thin film from cracking, caused by thermal stress and further oxidized in air if the film was directly taken out of the high temperature furnace. The substrate is pulled out of the furnace for further analysis. The crystal structure and phase composition were identified by X-ray diffraction (XRD, Rigaku RINT-2100) using a 40 kV, 30 mA, Cu-Kα X-ray. A scanning step of degree of 0.02° was applied to record the XRD patterns in the 2θ range of degree of Advanced Materials Research Vol. 1109 (2015) pp 544-548 Submitted: 2015-01-05 © (2015) Trans Tech Publications, Switzerland Accepted: 2015-01-05 doi:10.4028/www.scientific.net/AMR.1109.544 Online: 2015-06-10 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 132.239.1.230, University of California, San Diego, La Jolla, USA-03/09/15,02:20:58)