Enhancement of optical and mechanical properties of Si nanopillars by ALD TiO2 coating

Abstract

The mechanical and optical properties of Si and TiO₂–Si nanopillars (NPl) were investigated. Mesoporous silicon NPl arrays were fabricated by metal-assisted chemical etching and nanosphere lithography, and then pillars were covered by TiO₂ using the atomic layer deposition technique. We performed scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, reflectance, photoluminescence (PL) spectroscopy and nanoindentation to characterize the as-prepared and annealed TiO₂–Si NPl. The main structural and mechanical parameters of TiO₂–Si NPl (grain size, strain, critical load, elastic recovery and Young's module) were calculated. Reflectance and PL spectroscopy were used to study the impact of morphology on optical properties of TiO₂–Si NPl before and after annealing. It was established that the nanostructures of TiO₂ penetrated inside the porous matrix of Si pillar improve the mechanical properties of TiO₂–Si NPl. The results of nanoindentation study have shown that Young's modulus of annealed TiO₂–Si NPl is about three times higher than for the pure Si NPl.