Journal of Science: Advanced Materials and Devices (2017) 225e232 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Electrochromic behavior of NiO film prepared by e-beam evaporation D.R Sahu a, b, *, Tzu-Jung Wu b, Sheng-Chang Wang c, Jow-Lay Huang b, d, ** a Department of Natural and Applied Sciences, Namibia University of Science and Technology, Private Bag 13388, Windhoek, Namibia Department of Materials Science and Engineering, National Cheng-Kung University, Tainan 701, Taiwan, ROC c Department of Mechanical Engineering, Southern Taiwan University of Science and Technology, Tainan 710, Taiwan, ROC d Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 701, Taiwan, ROC b a r t i c l e i n f o a b s t r a c t Article history: Received December 2016 Received in revised form May 2017 Accepted May 2017 Available online 12 May 2017 The NiO thin films were prepared by the electron beam evaporation method using synthesized sintered targets As-prepared films were characterized using X-ray diffraction, scanning electron microscopy, UVeVIS spectroscopy and cyclic voltammetry The thicker films were found to exhibit a well-defined structure and a well-developed crystallite size with greater transmittance modulation and durability The as-deposited thinner films of 170 nm showed a faster response time during electrochromic cycles with a coloration efficiency of 53.1 C/cm2 than the thicker ones However, the thicker films showed no enhanced electrochromic properties such as a larger intercalated charge than the thinner ones The electrochromic properties of the thinner films became deteriorated after 800 cycling tests © 2017 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: E-beam evaporation Nickel oxide Electrochromic properties Introduction Nickel oxide (NiO) is used as an efficient electrochromic (EC) material in EC devices It is an anodic coloring material, which is optically and electrochemically compatible with the well-known tungsten trioxides [1e3] The electrochromics is a special property of a material to change its color reversibly by the application of a voltage The electrochromic process is unique and it strongly depends on the method of preparation of the materials [4e6] To ensure the sustainable development of its functional properties in devices, high quality thin films can be produced as a coating on the surface of the devices The properties of the thin films are thickness dependent [6e8] and this makes the film thickness a more important parameter not only as a geometrical but also as a functional one in the design of materials and devices Efforts have been explored to understand the thickness dependence of optical properties in nanocrystalline oxide films [6e9] and demonstrated that the optical constants of very thin oxide films may deviate considerably from those of the bulk materials This means *Corresponding author Department of Natural and Applied Sciences, Namibia University of Science and Technology, Private Bag 13388, Windhoek, Namibia ** Corresponding author Department of Materials Science and Engineering, National Cheng-Kung University, Tainan 701, Taiwan, ROC Fax: ỵ886 276 3586 E-mail addresses: dsahu@nust.na (D.R Sahu), scwang@mail.stust.edu.tw (S.-C Wang), jlh888@mail.ncku.edu.tw (J.-L Huang) Peer review under responsibility of Vietnam National University, Hanoi that the respective materials constant is sometimes no longer constant in thin films As a matter of fact, systematic investigations of thickness-dependent film properties are necessary for device application NiO films have been prepared by chemical, electrochemical techniques and by vacuum technologies, such as e-beam evaporation and sputtering [1,4,5,10e12] Among these methods, those which employ vacuum technologies provide highly stable EC NiO films with good electrochemical efficiency The electrochromic property is also affected by the structure, binding conditions, water contents, stoichiometry and thickness of the films [13,14] In this work, nickel oxide films with different thickness were prepared by e-beam evaporation methods and investigated Their EC properties have been compared with those of different films with respect to structure, surface morphology and electrochemical behavior for possible device applications Experimental The NiO thin films were deposited on Indium tin oxide (ITO) glass substrates in an e-beam evaporation system with electron energy in the order of keV using a NiO sintered target The target was prepared by pressing high purity NiO powder (OSAKA, purity 99.99%,