Nanopatterned silicon exhibiting partial polarization and chirality

In this paper, we report a study on Si nanopatterns, fabricated as a one-dimensional (1D) Si nanograting with a sub-wavelength (≈200 nm) period. Unpolarized light normally incident on the nanopatterned Si becomes partially polarized and chiral over the entire visible range of 380–740 nm. The degree and the state of polarization of light were measured using polarimetric and ellipsometric techniques. The analysis showed that the reflected light is partially linearly polarized and at the same time a slight chirality (Ŝ₃≠0) is observed. Although the polarization of the reflected light is related to the 1D nanograting anisotropy, the chiral transformation of the light could be related to a micrometer-scale chiral substructure on the Si nanopatterned surface. This structure results from the dynamic polarization rotation of the femtosecond laser pulses in their filaments in liquid carbon disulfide near the Si surface during the interferential plasmonic self-organization of the surface nanorelief. These results could underline a key enabling process for the fabrication of polarization-sensitive metasurface-based sensors or devices within the common complementary metal-oxide semiconductor (CMOS)-compatible technology.