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22 October 1993 In-situ measurement of reflectance and DC-resistivity of thin silver films in multilayer interference filters
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Abstract
Heat mirrors based on multilayers of silver and anti-reflective dielectrics can be used in solar process heat applications at elevated temperatures (approximately equals 250 degree(s)C). The optical properties of silver films depend on preparation conditions and differ from bulk material properties; especially in multilayer systems they are at present not well understood. An apparatus for simultaneous measurement of reflectance at one wavelength in the range 600 - 2000 nm and DC-resistivity during ion-beam sputtering of thin films is presented. The device is sensitive for changes in reflectance smaller than 0.001. Si3N4 / Ag / Si3N4 heat mirrors were produced on float glass. During growth of the silver film, reflectance initially decreases and then increases sharply. An interpretation with effective medium theories is presented. During deposition of the second dielectric layer, a sharp wavelength independent initial decrease in reflectance of approximately equals 2.5% is observed. After an increase of approximately equals 0.5% the reflectance decreases as predicted by Fresnel's equations. DC-resistivity closely follows this behavior. Different mechanisms for the observed effects are discussed.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Thomas Eisenhammer, F. Muggenthaler, and R. Sizmann "In-situ measurement of reflectance and DC-resistivity of thin silver films in multilayer interference filters", Proc. SPIE 2017, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XII, (22 October 1993); https://doi.org/10.1117/12.161981
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