Tilted black-Si: ~0.45 form-birefringence from sub-wavelength needles
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 ¿i¿<¿50¿-¿70° (angle between the Si surface and vertical plasma E-field). The height of the needles i...
| Autores: | , , |
|---|---|
| Tipo de recurso: | artículo |
| Fecha de publicación: | 2020 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/328014 |
| Acceso en línea: | https://hdl.handle.net/2117/328014 https://dx.doi.org/10.1364/OE.392646 |
| Access Level: | acceso abierto |
| Palabra clave: | Raman spectroscopy Form birefringence Nonlinear effects Espectroscòpia Raman Àrees temàtiques de la UPC::Física |
| Sumario: | 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 ¿i¿<¿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 ~¿/4 for the visible spectral range. Reflection-type polariscope with a voltage-controlled liquid-crystal retarder is proposed to directly measure the retardance ¿n¿×¿d/¿¿˜¿0.15 of the region with tilted b-Si needles. The quantified form birefringence of ¿n¿=¿-0.45 over ¿¿=¿400¿-¿700 nm spectral window was obtained. Such high values of ¿n 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. |
|---|