Duy Thien, Nguyen, Tu, Nguyen, Hoa, Nguyen, Doanh, Sai, AND Vu, Le. " Fabrication, Characterization of SiO2 Nanospheres and SiO2 Opal Photonic Crystals" VNU Journal of Science: Mathematics - Physics [Online], Volume 37 Number 1 (12 March 2021)