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Nanostructure effects and the performance of optical interference coatings

: Stenzel, O.; Schulz, U.; Kaiser, N.


Martin-Palma, R.J. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Nanostructured Thin Films IV : 21.-25.8.2011, San Diego, California, USA
Bellingham, WA: SPIE, 2011 (Proceedings of SPIE 8104)
ISBN: 978-0-8194-8714-8
Paper 810409
Conference "Nanostructured Thin Films <4, 2011, San Diego/Calif.>
Conference Paper
Fraunhofer IOF ()
interference coatings; nanostructure; optical constants; absorption; antireflection

The theory of "classical" optical interference coatings is based on assumptions like ideal homogeneity and isotropy of the materials, as well as absolutely smooth and infinitesimally thin interfaces between the individual coating materials. Within the framework of these assumptions, there exists an elaborated theoretical apparatus for solving design and characterization tasks for optical coatings. At the same time, coating deposition techniques have been perfected in order to match with the requirements of homogeneity and smoothness of these coatings in practice. Remaining discrepancies between the theoretically predicted and practically achieved coating performance can - at least partially - be attributed to the violation of the above-mentioned ideal assumptions. But a closer look on this matter reveals a more differentiated picture: Nanostructure effects can be tackled as additional degrees of freedom for coating design, and can lead to useful property combinations that are inaccessible to "classical" coatings prepared on the basis of the traditionally available coating materials. This presentation deals with practical examples, where explicit violations of the usually assumed perfect homogeneity and smoothness of the coatings have resulted in novel and innovative coating material properties or coating designs. Examples include: - Effects of noble metal islands embedded in semiconductor films: applications in photovoltaics - Antireflection effects of nanostructured surfaces: motheye-structures - Effects of nanoporosity in oxide films on refractive index, thermal shift and mechanical stress: balanced coating properties The examples demonstrate the possible benefits of the exploitation of nanostructure-caused effects in interference coating science and technology.