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Characterization of broadband complex refractive index of synthetic melanin coatings and their changes after ultraviolet irradiation

Weiyao Li, Anvay Patil, Xuhao Zhou, Zhao Wang, Ming Xiao, Matthew Shawkey (UGent) , Nathan C. Gianneschi and Ali Dhinojwala
(2020) APPLIED PHYSICS LETTERS. 117(20).
Author
Organization
Abstract
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.
Keywords
Physics and Astronomy (miscellaneous), STRUCTURAL PLUMAGE COLOR, OPTICAL-PROPERTIES, POLYDOPAMINE, MELANOSOMES, NANOPARTICLES, CONSTANTS, ANGLE, SKIN

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MLA
Li, Weiyao, et al. “Characterization of Broadband Complex Refractive Index of Synthetic Melanin Coatings and Their Changes after Ultraviolet Irradiation.” APPLIED PHYSICS LETTERS, vol. 117, no. 20, 2020, doi:10.1063/5.0024229.
APA
Li, W., Patil, A., Zhou, X., Wang, Z., Xiao, M., Shawkey, M., … Dhinojwala, A. (2020). Characterization of broadband complex refractive index of synthetic melanin coatings and their changes after ultraviolet irradiation. APPLIED PHYSICS LETTERS, 117(20). https://doi.org/10.1063/5.0024229
Chicago author-date
Li, Weiyao, Anvay Patil, Xuhao Zhou, Zhao Wang, Ming Xiao, Matthew Shawkey, Nathan C. Gianneschi, and Ali Dhinojwala. 2020. “Characterization of Broadband Complex Refractive Index of Synthetic Melanin Coatings and Their Changes after Ultraviolet Irradiation.” APPLIED PHYSICS LETTERS 117 (20). https://doi.org/10.1063/5.0024229.
Chicago author-date (all authors)
Li, Weiyao, Anvay Patil, Xuhao Zhou, Zhao Wang, Ming Xiao, Matthew Shawkey, Nathan C. Gianneschi, and Ali Dhinojwala. 2020. “Characterization of Broadband Complex Refractive Index of Synthetic Melanin Coatings and Their Changes after Ultraviolet Irradiation.” APPLIED PHYSICS LETTERS 117 (20). doi:10.1063/5.0024229.
Vancouver
1.
Li W, Patil A, Zhou X, Wang Z, Xiao M, Shawkey M, et al. Characterization of broadband complex refractive index of synthetic melanin coatings and their changes after ultraviolet irradiation. APPLIED PHYSICS LETTERS. 2020;117(20).
IEEE
[1]
W. Li et al., “Characterization of broadband complex refractive index of synthetic melanin coatings and their changes after ultraviolet irradiation,” APPLIED PHYSICS LETTERS, vol. 117, no. 20, 2020.
@article{8699329,
  abstract     = {{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.}},
  articleno    = {{203701}},
  author       = {{Li, Weiyao and Patil, Anvay and Zhou, Xuhao and Wang, Zhao and Xiao, Ming and Shawkey, Matthew and Gianneschi, Nathan C. and Dhinojwala, Ali}},
  issn         = {{0003-6951}},
  journal      = {{APPLIED PHYSICS LETTERS}},
  keywords     = {{Physics and Astronomy (miscellaneous),STRUCTURAL PLUMAGE COLOR,OPTICAL-PROPERTIES,POLYDOPAMINE,MELANOSOMES,NANOPARTICLES,CONSTANTS,ANGLE,SKIN}},
  language     = {{eng}},
  number       = {{20}},
  pages        = {{8}},
  title        = {{Characterization of broadband complex refractive index of synthetic melanin coatings and their changes after ultraviolet irradiation}},
  url          = {{http://dx.doi.org/10.1063/5.0024229}},
  volume       = {{117}},
  year         = {{2020}},
}
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