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 (SiO2) mineral stone as raw material using magnesium-thermic chemical reduction method. The synthesis process involves extraction of silica (SiO2) powder from the raw material and then Si-NPs was prepared by chemical reduction of silica (SiO2) powder using the magnesium-thermic process. Two processes were done for synthesis: (a) magnesium-thermic reaction and annealing at T = 500 degrees C, 600 degrees C and 700 degrees C at N-2 gas and (b) acid washing via HCl and HF. The stoichiometric ratio of Mg/SiO2 = 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 degrees C, T = 600 degrees C and T = 700 degrees C, respectively. Also, the direct band gap was determined for nanopowders.