Coloring with Focused Ion Beam
- Vivek Garg
- Mar 27, 2019
- 2 min read
It’s a beautiful and colorful world out there that we live in.
Colors are produced by absorption of light by molecules (pigments) or scattering of light by nanostructures (structural colors). Pigment based colors fades away with time and involves toxic metal oxides, hazardous for the environment. Interaction of visible light with subwavelength nanostructures leads to generation of unique structural colors.
Gold, silver and aluminium are most widely used metals for structural color generation, however, metals suffer significant optical losses, which results in loss of color purity. In addition, use of noble metals is uneconomical for industrial and large scale applications.
Silicon (Si), a widely adopted material in electronics, with a high index value and low loss in visible spectrum is the most suitable material for structural color printing. The low cost and compatibility of silicon with existing complementary metal oxide semiconductor (CMOS) techniques further makes it an ideal choice.
“A direct, mask-less approach for fabrication of subwavelength nanostructures using focused ion beam (FIB) for multicolor generation is developed, and 3D nanostructures having a unique geometry of tapered holes, were fabricated on Si, without requiring any pre- or post-processing in contrast to previously reported structural color filters."
The fabricated nanostructures exhibited generation of unique structural colors under a bright field optical microscope. The fabricated color filters exhibited high quality resonance over visible spectrum with a narrow bandwidth due to the unique 3D tapered nanohole geometry, leading to enhanced color purity.
With the developed technique, the color printing is possible beyond the diffraction limit of an optical microscope and colors can be printed at a resolution of ∼100,000 DPI. The proposed approach has the potential to be scaled up to assist future nanoscale color printing applications with the state of the art nanoimprinting methods.
The fabricated nanostructures exhibited generation of unique structural colors under a bright field optical microscope. The fabricated color filters exhibited high quality resonance over visible spectrum with a narrow bandwidth due to the unique 3D tapered nanohole geometry, leading to enhanced color purity.
Butterflies are a great example of structural color filtering present in the nature through the morphological features in their wings. It was fun demonstrating this approach for color printing applications via fabrication of striking multicolor butterflies, letters on Si. The novelty of FIB for coloring, in addition to its existing versatile applications in material science, is an important step forward towards the integration of FIB with structural color filtering applications.
The rapid and versatile nature of developed fabrication technique along with the robustness of fabricated color filters, will be inspiring for future research exploring applications, from high resolution color printing applications to optical security features such as anti-counterfeiting technology etc.
For more details, readers can refer to following references:
https://doi.org/10.1017/S1431927618004774
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