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While titania and carbon are conventionally perceived as white and black materials, here we show that their combination in the form of composite hollow nanoshells can display striking colors with considerably high contrast through resonant Mie scattering. Our unique design utilizes hollow nanostructures to produce the color by minimizing random multiple scattering and the incorporated carbon species to act as an internal black background to suppress multiple scattering and enhance the color contrast. Synthesized through a simple sol–gel process followed by high-temperature carbonization, these hollow carbon-containing titania (C-TiO 2 ) nanoshells can exhibit variable bright colors from purple to blue and green by controlling their diameter. They can be conveniently used as alternative pigments in many color-related applications, with the advantages of high chemical and optical stability and low toxicity that are associated with titania and carbon materials and the structural coloration mechanism. In addition, as the visible Mie scattering responds rapidly and reversibly to changes in the surrounding medium, these nanoshells may also serve as active color components for many applications that require dynamic color switching, such as signage and displays, colorimetric sensors and detectors, and anti-counterfeiting devices.
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This content will become publicly available on May 12, 2026
Optical identification and anti-counterfeiting based on plasmonic core–shell nanoparticles with Fano resonance
Fano resonance with an asymmetric and ultrasharp resonant line shape has been extensively studied in various light scattering scenes, unlocking several applications for sensing, information processing, and optical identification. Fano resonance appearing in multilayered nanoparticles (NPs) is particularly intriguing as its sharp and comb-like resonant line shape may enable optical identification at the nanoscale. We herein propose the concept of the optical physical unclonable function (PUF) based on the scattering responses of core–shell (plasmonic-dielectric) NPs. Specifically, the sharp, asymmetric spectral responses near the Fano resonance frequency, which are highly sensitive to perturbations (e.g., nanomanufacturing imperfections), can be exploited as a unique electromagnetic fingerprint for PUF-based identification and anti-counterfeiting applications. Here, we theoretically and statistically demonstrate that scattering from Fano-resonant multilayered NPs can be regarded as a perfect entropy source for the generation of PUF encryption keys, with outstanding performance in terms of uniqueness, randomness, encoding capacity, and NIST randomness test results. The proposed optical PUF opens pathways to implement nano-tags for optical identification, authentication, and anti-counterfeiting applications.
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- Award ID(s):
- 2210977
- PAR ID:
- 10633024
- Publisher / Repository:
- AIP (American Institute of Physics)
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 126
- Issue:
- 19
- ISSN:
- 0003-6951
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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