Journal
NANO RESEARCH
Volume 9, Issue 8, Pages 2354-2363Publisher
TSINGHUA UNIV PRESS
DOI: 10.1007/s12274-016-1122-x
Keywords
ultrathin planar film; broadband absorber; effective medium design; solar energy
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Funding
- National Natural Science Foundation of China [51236004, 51321002]
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Ultrathin planar absorbers hold promise in solar energy systems because they can reduce the material, fabrication, and system cost. Here, we present a general strategy of effective medium design to realize ultrathin planar broadband absorbers. The absorber consists of two ultrathin absorbing dielectrics to design an effective absorbing medium, a transparent layer, and metallic substrate. Compared with previous studies, this strategy provides another dimension of freedom to enhance optical absorption; therefore, destructive interference can be realized over a broad spectrum. To demonstrate the power and simplicity of this strategy, we both experimentally and theoretically characterized an absorber with 5-nm-thick Ge, 10-nm-thick Ti, and 50-nm-thick SiO2 films coated on an Ag substrate fabricated using simple deposition methods. Absorptivity higher than 80% was achieved in 15-nm-thick (1/50 of the center wavelength) Ge and Ti films from 400 nm to near 1 mu m. As an application example, we experimentally demonstrated that the absorber exhibited a normal solar absorptivity of 0.8 with a normal emittance of 0.1 at 500 A degrees C, thus demonstrating its potential in solar thermal systems. The effective medium design strategy is general and allows material versatility, suggesting possible applications in real-time optical manipulation using dynamic materials.
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