Hierarchical structures of AlOOH nanoflakes nested on Si nanopillars with anti-reflectance and superhydrophobicity

Abstract

A novel method to fabricate ultra-low reflective Si surfaces with nanoscale hierarchical structures is developed by the combination of AlOOH or boehmite nanoflakes nested on plasma-etched Si nanopillars. Using CF4 plasma etching, Si surfaces are nanostructured with pillar-like structures by selective etching with self-masking by fluorocarbon residues. AlOOH nanoflakes are formed by Al thin film coating with various thicknesses and subsequent immersion in boiling water, which induces the formation of nanoscale flakes through the hydrolysis reaction. AlOOH nanoflakes are formed on Si nanopillared surfaces for hierarchical structures, which are coated with a low-surface-energy material, resulting in a higher water wetting angle of over 150° and a very low contact angle hysteresis of less than 5°, and implying a self-cleaning surface. Reflectance reduced to 5.18% on average on hierarchical nanostructures in comparison to 9.63% on the Si nanopillar surfaces only. We found that Si nanopillars reduced reflection for wavelengths ranging from 200 to 1200 nm while AlOOH nanoflakes reduced reflection for wavelengths longer than 600 nm.

Highly Selective Solar Thermal Sprayable Coating Based on Carbon Nanotubes

“…Radiation above 1.1 μm is reflected by the ITO (Scheme b) thus making the coating spectrally selective. The antireflective AlOOH layer on top of the ITO, increases the absorptance of the CNT/ITO/AlOOH coating by decreasing the reflectance at 0.3–1.5 μm because of its low‐refractive index (Scheme c) …”

“…To further increase the absorptance, an anti‐reflecting layer on top of the coating can be added. It has been reported that Boehmite (AlOOH) layer exhibits anti‐reflecting property on various substrates such as Si, glass, and polymer because of its low refractive index . Recently, we have demonstrated that the coating of anti‐reflecting AlOOH layer on CNT coating significantly increases its absorptance …”

A facile method for in situ growing nano-flaky γ-Al2O3 on the surface of Al–Si alloy sphere

“…References indicated that Si-eutectic in Al-Si alloy is radial distributed across the bulk Al dendrites to form flakes or sheets [26][27][28]. As for AlOOH species, it is easy to form rectangular nanocrystalline boehmite via hydrolytic reaction [29][30][31][32][33]. As a result, the AlOOH species nucleated and grew into nano-flakes under the induction of flaky Si-eutectic substrate.…”

Plasma-Based Nanostructuring of Polymers: A Review

“…Yu et al [88] have reported a Si surface with ultra-low reflective nanoscale hierarchical structure fabricated nanograss-like structures, by adopting CF 4 plasma etching, and the hydrolysis effect of Al coating. This surface not only has the potential to capture photons to increase the efficiency of solar energy devices, but also the roughness to improve self-cleaning properties.…”