Sensors and Actuators B 206 (2015) 671–678 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo ur nal home page: www.elsevier.com/locate/snb General Synthesis, characterization and gas-sensing properties of SILAR deposited ZnO-CdO nano-composite thin film Assumpta C. Nwanya a,b , P.R. Deshmukh c , Rose U. Osuji b,d,e , Malik Maaza c,d , C.D. Lokhande c , Fabian I. Ezema b,d,e,∗ a National Centre for Energy Research and Development, University of Nigeria, Nsukka, Nigeria b Department of Physics, and Astronomy, University of Nigeria, Nsukka c Thin film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur, 416 004, (M.S), India d Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, South Africa e UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk ridge, P.O.Box 392, Pretoria South Africa a r t i c l e i n f o Article history: Received 29 July 2014 Received in revised form 28 September 2014 Accepted 30 September 2014 Available online 8 October 2014 Keywords: ZnO-CdO Nano-composite film SILAR Gas sensor Activation energy a b s t r a c t The deposition of ZnO-CdO thin films are carried out using successive ionic layer adsorption and reaction (SILAR) method at room temperature. The deposited ZnO-CdO thin films have been characterized using FT-Raman spectroscopy, scanning electron microscopy, UV-vis spectrophotometer, two point probe resis- tivity method, and contact angle mode. Raman spectroscopy show various peaks from the as deposited films which disappeared after annealing. The SEM reveals the morphology of the films nanosized smooth interlocked sheets all over the surface. The bandgap value of 3.8 eV is observed for as deposited but decreased to 2.9 eV after annealing. Activation energies of 0.43 and 0.11 eV are estimated for the as deposited film and annealed film, respectively. The Gas response of the ZnO-CdO composite film shows maximum (about 50%) at 623 K upon exposure to 780 ppm of LPG. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Both ZnO and CdO have been reported to show n-type con- ductivity [1,2]. This type of conductivity is mainly due to oxygen vacancies. With bandgap ranging from 2.2 to 2.7 eV [1–4], CdO has the advantage of a low resistivity while ZnO has high bandgap of approximately 3.2–3.4 eV [4–6], but exhibits a higher transparency. ZnO has received considerable attention in the past few years due to its application potential in many technological areas such as window layer, electrodes in solar cells, varistor, gas sensor, solar cells, photo-catalysis, transparent contact fabrication [7–14]. CdO properties like large bandgap, low electrical resistivity and high transmittance in the visible region make it useful for a wide range of applications such as photodiodes, phototransistors, photovoltaic cells, transparent electrodes, liquid crystal displays, IR detectors, anti reflection coatings, gas sensing, etc. [15–19]. The nanocomposites of ZnO-CdO have been developed in order to enhance the advantages and reduce the shortcomings of the ∗ Corresponding author. Tel.: +234 8036239214. E-mail address: fiezema@yahoo.com (F.I. Ezema). individual oxide films for a particular application. Such composites developed have been applied as optical switches and conducting optical layer for optoelectronic devices [13,20,21] due to its better transmittance and low resistivity compared to the individual oxide films. ZnO-CdO composite films have been prepared by various techniques such as electrochemical method [13,22], spray pyrolysis [23], molecular-beam epitaxy [24], thermal decomposition method [20,25], pulse laser deposition (PLD) [26], sol gel [27], etc. Most of these techniques require high temperature and pressure hence, limits the kind of substrate that can be used for the deposition. We deposited ZnO-CdO nano-composite films on steel and glass substrates using the SILAR method. Successive ionic layer adsorp- tion and reaction (SILAR) is a simple chemical method in which deposition takes place by successive adsorption of metallic ions and reaction with chalcogenide ions takes place. It is one of the suitable chemical methods used for large area formation of metal oxides in which the thin films are obtained by immersing a substrate into separately placed cationic and anionic precursor solutions [28]. The method is capable of producing metal oxide films at relatively low temperature, is relatively simple, does not require expensive equip- ment, and there is minimal waste of chemicals as compared with other methods. The deposition rate and thickness of the film can http://dx.doi.org/10.1016/j.snb.2014.09.111 0925-4005/© 2014 Elsevier B.V. All rights reserved.