The effect of stoichiometric ratio of Mg/SiO2 and annealing on physical properties of silicon nanoparticles by magnesium-thermic chemical reduction process using the SiO2 precursor

In this paper, silicon nanoparticles (Si-NPs) were prepared using silica (SiO 2 ) mineral stone as raw material using magnesium-thermic chemical reduction method. The synthesis process involves extraction of silica (SiO 2 ) powder from the raw material and then Si-NPs was prepared by chemical reduction of silica (SiO 2 ) powder using the magnesium-thermic process. Two processes were done for synthesis: (a) magnesium-thermic reaction and annealing at T = 500 °C, 600 °C and 700 °C at N 2 gas and (b) acid washing via HCl and HF. The stoichiometric ratio of Mg/SiO 2 = 1:1, 1.5:1, 2:1 and 2.5:1 was also investigated in the chemical reduction conditions. To study the structure and morphology of nanoparticles, X-ray Diffraction (XRD) and Field Emission-Scanning Electron Microscope (FE-SEM) were used. Grown nanoparticles have a polycrystalline structure with spherical form with crystalline size of 20–40 nm. To study the optical band gap of Si-NPs and type of direct or indirect semiconductor, energy gap and absorption behavior of nanoparticles was investigated using the UV–Vis spectroscopy. The indirect band gap and blue shift comparison to bulk was observed at 3.62 eV, 3.47 eV and 3.43 eV for the samples synthesized in the temperatures of T = 500 °C, T = 600 °C and T = 700 °C, respectively. Also, the direct band gap was determined for nanopowders.