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Abstract Drop‐casting manganese oxide (MnO2) hollow nanospheres synthesized via a simple surface‐initiated redox route produces thin films exhibiting angle‐independent structural colors. The colors can rapidly change in response to high‐humidity dynamic water vapor (relative humidity > 90%) with excellent reversibility. When the film is triggered by dynamic water vapor with a relative humidity of ≈100%, the color changes with an optimal wavelength redshift of ≈60 nm at ≈600 ms while there is no shift under static water vapor. The unique selective response originates from the nanoscale porosity formed in the shells by randomly stacked MnO2nanosheets, which enhances the capillary condensation of dynamic water vapor and promotes the change of their effective refractive index for rapid color switching. The repeated color‐switching tests over 100 times confirm the durability and reversibility of the MnO2film. The potential of these films for applications in anti‐counterfeiting and information encryption is further demonstrated by reversible encoding and decoding initiated exclusively by exposure to human breath.
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Iridescent structural color by using ultra-low refractive index aerogel as optical cavity dielectric
Abstract Iridescent color-shift pigments have been used in some industrial applications, e.g., for cosmetics and packaging. To achieve environmental-friendly and lasting color, thin-film interference is used to generate structural color. By maximizing the refractive index (RI) difference between the thin films (i.e., using an ultralow RI film), super-iridescent structural color can be produced. While the lowest refractive index of a naturally occurring solid dielectric is close to 1.37 (i.e., MgF2), we synthesized highly porous dielectric SiO2aerogel to achieve ultralow-RI (n ~ 1.06) and demonstrated a high-refractive index/low-refractive index/absorber (HLA) trilayer structural color. The achieved structural color is highly iridescent and capable of tracing a near-closed loop in CIE color space. By tuning the refractive index, thickness, and geometry of the aerogel layer, we control the reflection dip’s shape, therefore producing a wide range of vivid and iridescent colors.
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- PAR ID:
- 10559848
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Micro & Nano Manufacturing
- Volume:
- 1
- Issue:
- 1
- ISSN:
- 3005-1495
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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