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