Siregar N, Marlianto E, Gea S, Motlan . The Effect of Concentration of Structure and Optical Properties of Thin Films Synthesized by Sol-Gel Methods Spin Coating. IJSBAR. 2015;22(1):428-434. Accessed September 20, 2025. https://gssrr.org/JournalOfBasicAndApplied/article/view/3975