Dynamic Properties of Spectrally Selective Reactively Sputtered Metal Oxides
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Dynamic Properties of Spectrally Selective Reactively Sputtered Metal Oxides A.V. Adedeji*1, S.D. Worsley1, T.L. Baker1, R. Mundle2, A.K. Pradhan2, A.C. Ahyi3 and T. Isaacs-Smith3 1
Department of Chemistry, Geology & Physics, Elizabeth City State University, 1704 Weeksville Road, Elizabeth City, NC 27909, USA 2 Center for Materials Research, Norfolk State University, 700 Park Avenue, Norfolk, VA 23504, USA 3 Department of Physics, Auburn University, Auburn, AL 36849, USA
ABSTRACT Thin films of Transition Metal Oxides (TMOs) were deposited by reactive sputtering of pure transition metal targets in Argon-Oxygen gas mixture at elevated substrate temperature for efficient energy consumption. The atomic composition and thickness of the TMO films was determined by Rutherford Backscattering Spectroscopy (RBS). Optical transmittance and reflectance spectrum of the films on quartz substrate was measured with thin film measuring system at room temperature and slightly elevated temperature. The surface morphology and structure of the TMO films was determined with Atomic Force Microscope (AFM). INTRODUCTION In the 21st century, energy conservation and efficient energy consumption are extremely important in order to prevent looming energy crisis. Smart window technology that uses chromogenic materials to vary the throughput of solar radiation in buildings and automobile and similar applications may become essential part of the energy conservation model of the near future. Most of the known chromogenic materials are based on Transition Metal Oxides (TMOs) and their alloys [1]. Transition metal oxides are complex oxides with very rich physics and many potential applications. The complexity of TMOs arises from competing interactions and coupling between charge, spin and orbital wave functions of electrons [2,3]. Couplings and interactions lead to important changes that drive the system into new states with very different properties when external stimuli are applied. For example, temperature can induce metalinsulator, charge and magnetic ordering, or superconducting transitions [3]. Chemical substitution is another method used to tune materials properties. Apart from advancing the fundamental understanding of low-dimensional TMO, basic research on the optical properties can lead to practical applications, especially in energy-related technology [2,4,5]. Many TMOs are known to be chromogenic materials. They allow the transmittance of visible light and solar energy to be varied under the action of an external stimulus [6]. In warm climate, windows can be coated with spectrally selective thin films that will allow the transmittance of visible light and reflect the infrared. In climates where the ambient temperature is not constant, thin films with dynamic optical properties will be the solution solar energy control [7,8]. Thin films that respond to light stimulus are called photochromic (e.g TiO2 and
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MoO3 based films) [9]; thin films that respond to temperature are called thermochromic (e.g. VO2 and VO2 doped with other transi
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