Journal of Alloys and Compounds 478 (2009) 594–598 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Synthesis of cobalt oxide interconnected flacks and nano-worms structures using low temperature chemical bath deposition S.G. Kandalkar a , J.L. Gunjakar a , C.D. Lokhande b,∗ , Oh-Shim Joo b,∗ a Thin Film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur 416 004 (M. S.), India b Clean Energy Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea article info Article history: Received 27 September 2008 Received in revised form 18 November 2008 Accepted 21 November 2008 Available online 30 November 2008 Keywords: Cobalt oxide Thin films Chemical deposition Nanostructure abstract Interconnected flacks and nano-worms structures of cobalt oxide on glass and copper substrates have been deposited using chemical bath deposition method from aqueous alkaline cobalt chloride (CoCl 2 ·6H 2 O) solution. The cobalt oxide films were examined with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical absorption and electrical resistivity techniques. The structural analyses showed that as-deposited amorphous CoO(OH) films con- verted into crystalline Spinel Co 3 O 4 after annealing. Nanocrystalline grains with some overgrown clusters of cobalt oxide were revealed from surface morphological studies. TEM study showed the formation of nanocrystals with a diameter ranging from 5 to 10nm. From optical studies, band gap of 2.4eV was esti- mated for cobalt oxide thin film. The electrical resistivity exhibited semiconducting behavior of cobalt oxide thin film. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Oxide thin films are one of the most attracting areas of mate- rial research due to their fascinating domestic as well as industrial applications. Nanostructured oxides with different morphologies such as nanotubes, nanowires, nanorods, nanobelts, etc. have drawn considerable attention over the past few years due to their large surface area activated applications [1]. Cobalt oxide is a p-type antiferromagnetic oxide semiconductor with the highest Curie temperature, T c = 1396 K. Cobalt oxide thin films on conducting sub- strates are significant candidate for electrochemical capacitor [2–6]. Cobalt oxide occurs in two different modifications namely as CoO and Co 3 O 4 . The excess of oxygen in cobalt oxide yields a p-type semiconducting behaviour [7,8]. Various physical as well as chemical deposition techniques have been adopted for the deposition of cobalt oxide thin films [9–13]. However, physical deposition techniques suffer the dis- advantages like small area of deposition, extreme cleaning after each deposition, requirement of high deposition temperature, high working cost, etc. Owing to the disadvantages of the physical deposition techniques, the soft solution deposition techniques like chemical deposition (CBD), electrodeposition (ED), Successive ionic layer adsorption and reaction (SILAR), spray pyrolysis (SP), ∗ Corresponding authors. Tel.: +91 231 2609229; fax: +91 231 2600233. E-mail addresses: l chandrakant@yahoo.com (C.D. Lokhande), joocat@kist.re.kr (O.-S. Joo). etc. have received progressively growing attention in the recent years [14–17]. Soft solution chemical techniques allow bottom-up approach to tune morphology of nanocrystalline materials in thin film form with better control of particle size, shape, size distribu- tion, particle composition, degree of particle agglomeration, etc. Chemical bath deposition is one such technique, in which depo- sition of metal chalcogenide occurs due to substrates maintained in contact with dilute chemical bath containing a metal and chalco- gen ions. The film formation takes place when ionic product exceeds solubility product. CBD is simple, low cost and applicable for large- scale production [15]. In the present work, cobalt oxide thin films have been deposited using CBD from aqueous alkaline medium. The effect of different substrates on the surface morphology and structural properties has been investigated. The cobalt oxide thin films are annealed in air at 623 K to study the annealing effect on the structural, optical and electrical properties. 2. Experimental Deposition of cobalt oxide thin film was carried out onto previously cleaned glass and copper substrates. Before deposition, glass microslides were boiled in chromic acid for 30 min, washed with detergent, rinsed in acetone, and finally ultrasonically cleaned with double distilled water [18]. Similarly, copper substrates were mirror polished using zero grade polish paper and ultrasonically cleaned with double dis- tilled water. Preparation of cobalt oxide thin film by CBD method is based on the heating of alkaline bath of cobalt salt containing the substrates immersed in it. The 0.1 M cobalt (II) chloride (CoCl2·6H2O) was used as source of Co 2+ and to make it alkaline, 25% aqueous ammonia solution was added with constant stirring. Initially, solution becomes turbid due to precipitate formation of Co(OH)2. Further addition of excess ammonia dissolves precipitate of Co(OH)2 and makes clear and transparent 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.11.095