Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructures

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Abstract

Nature routinely produces nanostructured surfaces with useful properties1,2,3,4, such as the self-cleaning lotus leaf5, the colour of the butterfly wing6, the photoreceptor in brittlestar7 and the anti-reflection observed in the moth eye8. Scientists and engineers have been able to mimic some of these natural structures in the laboratory and in real-world applications9,10,11,12. Here, we report a simple aperiodic array of silicon nanotips on a 6-inch wafer with a sub-wavelength structure that can suppress the reflection of light at a range of wavelengths from the ultraviolet, through the visible part of the spectrum, to the terahertz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the silicon result from changes in the refractive index caused by variations in the height of the silicon nanotips, and can be simulated with models that have been used to explain the low reflection from moth eyes8,13,14. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electro-optical devices for the military.

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Figure 1: Photographic and scanning electron microscopy (SEM) images of a 6-inch silicon nanotips (SiNTs) wafer.
Figure 2: Broadband anti-reflection properties of silicon nanotips (SiNTs).
Figure 3: Angle of incidence and polarization-dependent anti-reflection properties of silicon nanotips (SiNTs).
Figure 4: Gradient refractive-index profile simulation of the surface of the SiNTs.

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Acknowledgements

We acknowledge financial support from the Ministry of Education under the ATU plan and the National Science Council in Taiwan, the Air Force Office of Scientific Research, the Asian Office of Aerospace Research and Development and the US Army Research Office in the Far East.

Author information

Y.F.H. conceived and performed the UV-VIS, IR and angle-dependent experiments; H.C.L. and C.H.H. synthesized the SiNTs; Y.H.C. and C.S.L. performed the far IR measurements; T.A.L. Y.K.H. and C.L.P. performed the THz measurements; Y.J.J. and C.Y.P. carried out the theoretical analyses; Y.F.H., S.C., K.H.C. and L.C.C. discussed and interpreted the result; and S.C., K.H.C. and L.C.C. co-wrote the paper.

Correspondence to Surojit Chattopadhyay or Li-Chyong Chen.

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Huang, Y., Chattopadhyay, S., Jen, Y. et al. Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructures. Nature Nanotech 2, 770–774 (2007) doi:10.1038/nnano.2007.389

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