Influence of self-ordered Au nanoparticles on chemically textured Si surfaces with improved antireflection and hydrophobicity.

A facile approach to improve hydrophobicity of chemically etched Si pyramids is presented by introducing Au nanoparticles (NPs). Initially, a clear transformation of pristine Si from hydrophilic to hydrophobic is established by chemical texturing, and manifested by observing an increase in contact angle (CA) from 58$^{\mathrm{0\thinspace }}$to 98$^{\mathrm{0}}$. X-ray diffraction studies reveal the evolution of a tensile strain in microscale Si pyramids followed by the formation of conformal Au layers without showing any significant change in CA (96$^{\mathrm{0}})$. However, the development of Au NPs with additional self-ordered structures at the pyramid edges at 400 $^{\mathrm{0}}$C gives a sharp rise in CA up to 118$^{\mathrm{0}}$, while the underlying phenomenon has been discussed in the light of a decrease in solid fractional surface area according to the Wenzel model. Detailed transmission electron microscopy investigations, however, suggest that Au and Si are immiscible at the Au/Si interfaces. Moreover, a sharp reduction of specular reflectance, especially in the ultraviolet region up to 0.4 {\%} has been manifested from ultraviolet-visible spectroscopy and discussed in details.