Mechanical behavior of surface-patterned and coated Si or Ge wafers for superhydrophobic and antireflective light transmitting windows

Abstract

The compressive resistance of truncated nanocone lattices produced by lithography and etching steps on Si or Ge wafers to get superhydrophobic and antireflective light transmitting windows, as well as the protection efficiency of alumina or diamond coatings are investigated by numerical simulations of elastic buckling, and nano-compression tests. The latter reveal the limits of an elastic analysis, since the stress at the top of the cones is high enough to trigger plastic flow, or phase changes. Ge nano-cones exhibit a large ductility in compression, and even seem to creep at room temperature. Thin alumina or diamond coatings are however shown to provide an effective protection against both buckling and plastic flow.Surface patterning is shown to induce stress concentrations at the foot of the cones, which reduces the fracture resistance of the substrate in biaxial bending.

A Review on Potential Mechanically Resistant Materials for Optical Multifunctional Surfaces: Bioinspired Surfaces with Advanced Properties

“…Nanoindentation has been used in a few studies to investigate the mechanical behavior of sub-wavelength scale structured surfaces with high transmission and a high aspect ratio. One recent study by Doquet et al [89] focused on the mechanical properties of nanopatterned silicon (Si) and germanium (Ge) surfaces with a high aspect ratio using the nanoindentation technique. The aim was to test the compression resistance of nanocones patterned optical surfaces.…”

“…These methods include the sandpaper abrasion test, [93] the tape-peel test, [94] the wiping test, [17] the abrasive pad test, [95] and the bending test. [89] The sandpaper abrasion test performed on the transparent superhydrophobic polydimethylsiloxane (PDMS) film with microprotrusions structured between microwalls showed promising results in terms of abrasion resistance and surface robustness. [93] The femtosecond laser-ablated template allowed for precise structuring of the microprotrusions.…”

“…While many studies have reported on the mechanical properties of hard coatings on flat surfaces, only a few have investigated the efficiency of this method in protecting patterned surfaces from damage and fracture. [73,74,89] The main goal is to preserve the shape of the pattern and maintain the durability of the surface by depositing a thin layer of a hard and transparent material without altering the optical properties obtained after structuring. This problem involves considering various parameters, and one critical aspect is the selection of the coating material.…”

“…One recent study by Doquet et al. [ 89 ] focused on the mechanical properties of nanopatterned silicon (Si) and germanium (Ge) surfaces with a high aspect ratio using the nanoindentation technique. The aim was to test the compression resistance of nanocones patterned optical surfaces.…”

“…The dimensions of the structures submitted to the nanocompression test investigated by Doquet et al[89] Structures submitted to nano-compression test…”