• DOI:10.1364/oe.392646
• Corpus ID: 214743301

Tilted black-Si: ∼0.45 form-birefringence from sub-wavelength needles.

@article{Gaileviius2020TiltedB,
  title={Tilted black-Si: ∼0.45 form-birefringence from sub-wavelength needles.},
  author={Darius Gailevi{\vc}ius and Meguya Ryu and Reo Honda and Stefan Lundgaard and Tai Suzuki and Jovan Maksimovic and Jingwen Hu and Denver P. Linklater and Elena P. Ivanova and Tomas Katkus and Vijayakumar Anand and Mangirdas Malinauskas and Yoshiaki Nishijima and Soon Hock Ng and Kȩstutis Staliūnas and Junko Morikawa and Saulius Juodkazis},
  journal={Optics express},
  year={2020},
  volume={28 11},
  pages={
          16012-16026
        }
}

• D. Gailevičius, M. Ryu, +14 authors S. Juodkazis
• Published 31 March 2020
• Physics
• Optics express

The self-organised conical needles produced by plasma etching of silicon (Si), known as black silicon (b-Si), create a form-birefringent surface texture when etching of Si orientated at angles of θi < 50 - 70° (angle between the Si surface and vertical plasma E-field). The height of the needles in the form-birefringent region following 15 min etching was d ∼ 200 nm and had a 100 μm width of the optical retardance/birefringence, characterised using polariscopy. The height of the b-Si needles corresponds closely to the skin-depth of Si ∼λ/4 for the visible spectral range. Reflection-type polariscope with a voltage-controlled liquid-crystal retarder is proposed to directly measure the retardance Δn × d/λ ≈ 0.15 of the region with tilted b-Si needles. The quantified form birefringence of Δn = -0.45 over λ = 400 - 700 nm spectral window was obtained. Such high values of Δn at visible wavelengths can only be observed in the most birefringence calcite or barium borate as well as in liquid crystals. The replication of b-Si into Ni-shim with high fidelity was also demonstrated and can be used for imprinting of the b-Si nanopattern into other materials.