Degradation Studies of Multilayer Coatings Exhibiting Angular Dependent Transmittance
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Date
2002Author
Musembi, Robinson J
Type
ThesisLanguage
enMetadata
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Multilayer coatings exhibiting angular dependent transmittance were prepared by evaporation method. Different multilayer combinations have been studied, which included MgF2/Ag/MgF2, MgF2/Al/MgF2, Ti02/Ag/Ti02 and Ti02/Al/Ti02. Among these combinations, MgF2/Ag/MgF2 multilayer has been found to display the best optical properties, that is, high transmittance in the visible region and low transmittance in the near infrared region and substantial angular dependency (i.e. tendency of optical transmittance and reflectance to depend on variation of angle of incidence beam).
MgF2/Ag based multilayer coating was adopted for degradation study due to their superior optical properties. Transmittance and reflectance were measured before and after the samples were exposed to degradation environment. The environment could be extreme temperature, inflated humidity, saline solution, organic solvents or aquatic condition for the case of accelerated degradation study. For non-accelerated degradation studies, the samples were left to age naturally in the normal atmosphere for predetermined duration.
The samples’ spectral properties were found to insignificantly degrade after they were subjected to various degradation environments. The highest change in transmittance and reflectance was registered for samples soaked in saline solution while no change was noted for samples kept in room environment (i.e. normal atmosphere). The changes observed can be attributed to changes in crystallographic structure (amount of defects and dislocations), packing density and surface roughness of the multilayer films. It is concluded that the optical properties of MgF2/Ag/MgF2 multilayer coatings are virtually unaffected by most of the adverse weather conditions considered in this study.
VI
Publisher
University of Nairobi
Rights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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