In addition, the FDTD simulation result

also shows that a PDMS buffer layer further reduces the reflectance: the reflectance was reduced by approximately 5% over all the wavelength regions. These simulation results correspond well with the experimental results shown in Figure 7. In addition, although a buffer layer is deposited on the Si nanostructure, a reflection occurs at the surface of the buffer layer because of the difference in n between air and the PDMS buffer layer (see the small step in Figure 5c). QNZ price However, we observed that surface of a PDMS layer was not perfectly flat. As shown in the AFM image (Figure 6b), the PDMS layer has a rough surface with the roughness of approximately 20 nm. This rough surface was naturally formed when the PDMS layer was coated on the Si nanostructures through the doctor blade technique. This rough surface of the PDMS layer induces a diffused reflection like the Si nanostructures on a Si plate and thus, the reflectance at the interface between air and PDMS layer is decreased [28]. The Idasanutlin FDTD simulation result clearly demonstrates this fact (Figure 6d): relatively uniform low reflectance was obtained by the rough surface of the

PDMS layer on the fabricated Si nanostructures (black line in Figure 6d). However, a flat surface of the PDMS layer with the thickness of 1 μm could induce the fluctuated and slightly high reflectance (blue line in Figure 6d) compared to that PRKACG of the rough PDMS surface.

These are because constructive and destructive interferences between reflections from the flat PDMS surface and the Si nanostructures are alternately occurred due to the flat surface of the PDMS layer (inset of Figure 6d). On the other hand, the rough surface of the PDMS layer could randomly scatter the reflections from the PDMS surface and the Si nanostructures, and thus, these arbitrarily scattered reflections by the rough PDMS surface could be dissipated through the destructive inference of themselves. Therefore, Si nanostructures and a PDMS buffer layer with a rough surface can dramatically improve the AR properties of a Si surface (Figure 7). Conclusions Pyramid-shaped Si nanostructures were fabricated on a Si plate using a hydrogen etching process. Due to the nanopyramid structure, the Si surface exhibited a significantly low reflectance at UV and Sapanisertib clinical trial visible light regions. Furthermore, the discontinuity of n eff at the air-Si interface could be reduced through the deposition of a Si-based polymer with a rough surface. Consequently, the AR properties of the Si nanostructures were further enhanced. The hydrogen etching method combined with a polymer coating can be easily scalable to a large surface and is a cheap process.