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The optical properties of sputtered composite of Al-AlN
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2006 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 90, no 13, 1861-1874 p.Article in journal (Refereed) Published
Abstract [en]

Optical constants n and k have been determined for aluminum-aluminum nitride composite in a reactive gas flow from zero to a flow giving stoichiometric nitride. A method using a dielectric function model was applied for each component in the Bruggeman equation to fit the experimental reflectance and transmittance spectra in the wavelength range of 0.3-2.5 mu m. The refractive index of aluminum-aluminum nitride showed a maximum as the reactive gas increased. The extinction coefficient, on the other hand, decreased with increased reactive gas flow. The determined optical properties were then used to design a multilayer selective surface for solar thermal applications. Two absorbing layers with a graded feature plus an anti-reflection layer resulted in a high calculated solar absorptance of 0.97. The optimized metal content corresponds to the composite around the maximum refractive index. A solar absorptance of 0.96 was reached for experimentally prepared surfaces according to the theoretical prediction.

Place, publisher, year, edition, pages
2006. Vol. 90, no 13, 1861-1874 p.
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-95474DOI: 10.1016/j.solmat.2005.11.006ISI: 000238594000001OAI: oai:DiVA.org:uu-95474DiVA: diva2:169698
Available from: 2007-02-22 Created: 2007-02-22 Last updated: 2016-10-13Bibliographically approved
In thesis
1. Spectrally Selective Solar Absorbing Coatings Prepared by dc Magnetron Sputtering
Open this publication in new window or tab >>Spectrally Selective Solar Absorbing Coatings Prepared by dc Magnetron Sputtering
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spectrally selective solar absorber using composite Ni-NiO as coating materials was studied. Samples were prepared by dc magnetron sputtering unit named Rulle, which is a miniature copy of an industrial roll-coater unit. Using asymmetric location of the oxygen nozzele, it is possible to form the desired metallic concentration distribution along the sputtering zone under optimized conditions. This distribution can be transferred into a graded film profile by moving the substrate, obtaining good spectral selectivity. For specified mechanical settings (such as locations of gas sprays, target and pump positions etc.), the ratio of used oxygen flow to the corresponding critical oxygen flow, RO, is a dimensionless parameter to control the zone specification. The optimal value is around 0.80 for the Rulle. Optimized zone shows properties with two main parts: the metallic composite part of varied nickel volume fraction and the dielectric part. Two parts of the sputtering zone can form a graded absorbing layer with the right ratio of base and middle layer by the moving substrate technique. Distribution of normalized conductivity, NC, along the absorbing sputtering zone is a simple and good specification of zone property. Profile of graded film prepared by the moving substrate technique can be tailored according to NC distribution. XRD and XPS study confirms the NC results. Simulation reveals that absorption should mainly rely on the intrinsic, but less on the interference mechanism. Used metallic volume fraction of Ni-NiO is 0.3 for main absorbing layer. The front surface reflection loss due to high refractive index can be reduced by adding a layer with low refractive index on the top. Simulation shows that three-layer coatings are a good and simple coating structure. High solar absorptance of 0.97 has been achieved with low thermal emittance of 0.05 by theoretical simulation as well as experimentally prepared samples.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 85 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 273
Materials science, spectrally selective surface, solar energy, magnetron sputtering, thin film, Materialvetenskap
urn:nbn:se:uu:diva-7530 (URN)978-91-554-6803-3 (ISBN)
Public defence
2007-03-16, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Available from: 2007-02-22 Created: 2007-02-22Bibliographically approved

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Wäckelgård, Ewa
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