期刊
APPLIED PHYSICS LETTERS
卷 117, 期 20, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/5.0024229
关键词
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资金
- Air Force Office of Scientific Research (AFOSR) under the Multi-University Research Initiative (MURI) Grant [FA9550-18-1-0142]
- AFOSR Grant [FA9550-18-1-0477]
- FWO Grant [G007117N]
- HFSP Grant [RGP 0047]
Melanin, with its high refractive index (RI) and broadband absorption, is an important biomaterial responsible for many of the vibrant structural colors observed in nature and for UV protection. Even though the RI plays an important role in the function of melanin, there is an ambiguity in its reported complex RI and a lack of understanding of whether and how the UV radiation, these materials are likely to experience under normal use, will affect the complex RI. Here, we measured the wavelength-dependent (360-1700nm) complex RI of synthetic melanin films before and after in situ UV treatment using ellipsometry. We modeled the ellipsometric data using a modified Tauc-Lorentz dispersion model and measured the thickness independently using atomic force microscopy. The UV radiation reduces the film thickness. Interestingly, we find that both the real and imaginary terms of the RI increase upon UV radiation. These experiments provide accurate measurements of the optical properties of melanin and a surprising result that synthetic melanin absorbs more light (similar to 25% increase in extinction coefficient) below 600nm after UV exposure.
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