倾斜黑硅：亚波长针状物的~0.45形双折射
Tilted black-Si: ~0.45 form-birefringence from sub-wavelength needles
摘要：
通过硅（Si）的等离子体蚀刻产生的自组织锥形针（称为黑硅（b-Si））在以$θ_i < 50 - 70^\circ$的角度（Si表面与垂直等离子体E场之间的角度）取向的Si的蚀刻时产生形状双折射表面纹理。在15分钟蚀刻之后，在形状双折射区域中的针的高度为$d\sim 200$ nm，并且具有100 $μ$ m宽度的光学延迟/双折射，使用偏光镜表征。对于可见光谱范围，b-Si针的高度与Si $\simλ/4$的趋肤深度密切对应。本文提出了一种带压控液晶延迟器的反射式偏振器，用于直接测量倾斜b-Si针状物区域的延迟量$Δn\times d/λ\approx 0.15$。得到了$Δn = - 0.45$在$λ= 400-700$ ~nm光谱窗口内双折射的定量形式。在可见光波长下如此高的$Δn$值只能在大多数双折射方解石或硼酸钡以及液晶中观察到。还证明了以高保真度将b-Si复制到Ni垫片中，并且可以用于将b-Si纳米图案压印到其他材料中。
英文摘要：
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 $θ_i < 50 - 70^\circ$ (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 $d\sim 200$ nm and had a 100 $μ$m width of the optical retardance/birefringence, characterised using polariscopy. The height of the b-Si needles corresponds closely to the skin-depth of Si $\simλ/4$ for the visible spectral range. Reflection-type polariscope with a voltage-controlled liquid-crystal retarder is proposed to directly measure the retardance $Δn\times d/λ\approx 0.15$ 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.
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