AVS 47th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM1
Optical Thin Film Multilayer Systems for Thermal Emittance Modulation in the 300K Blackbody Spectral Region

Thursday, October 5, 2000, 8:20 am, Room 203

Session: Optical Films
Presenter: J.A. Woollam, University of Nebraska, Lincoln
Authors: C.L. Trimble, University of Nebraska, Lincoln
E.B. Franke, University of Nebraska, Lincoln
J.S. Hale, J.A. Woollam Company, Lincoln
M. Schubert, University of Nebraska, Lincoln
J.A. Woollam, University of Nebraska, Lincoln
Correspondent: Click to Email
We report on all-solid state electrochromic multilayer systems for thermal emittance modulation in the 300 K blackbody spectral region (2 to 40 microns). Amorphous and polycrystalline WO@sub 3@ thin films were used as ion storage and electrochromic layers, respectively. Tantalum oxide thin films were used as ion-conductor layers. All films were grown by magnetron sputtering. The multilayer system was switched between low and high emittance states by application of small voltages between two electrodes enclosing the stack, thereby moving previously electrochemically inserted Li@super +@ from the electrochromic to the storage layer and back. Two electrode designs were tested. One was built with an aluminum bottom layer electrode and an aluminum grid top electrode, and a second was made with aluminum grid electrodes on top and bottom. The optical constants of Li@super +@ intercalated and deintercalated tantalum oxide and WO@sub 3@ thin films were measured by ellipsometry from 2 to 35 microns. Prior to experimental layer stack formation, the thin film layer structure was optimized by calculations of emittance modulation based on the single layer optical constants and thicknesses. Performance of the layer stack was obtained by reflectance modulation @DELTA@R from 2 to 40 microns, and related to spectral emittance. Reflectance spectra were further used to calculate the emissivity modulation @DELTA@@epsilon@ integrated over a 300 K blackbody spectrum. Calculations also suggest application of thermal emittance modulating multilayers for temperatures up to 900 K. Additional simulations were performed assuming the layer stack covered by either a ZnS or a MgF@sub 2@ layer. Cover layers should protect the WO@sub 3@ layer, prevent Li@super +@ chemical reactions and moisture incorporation, and act as optical impedance match to improve switching performance. Supported by BMDO # DSAG60-98-C-0054, NASA Glenn Research Center grant # NAG3-2219, and NASA Epscor grant # NCC5-169.