Magnesiothermic reduction of silica glass substrate—Chemical states of silicon in the generated layers

• Published in: Journal of Asian Ceramic Societies 2017-09, Vol.5 (3), p.341-349
• Main Authors: Tsuboi, Yuki, Ura, Shogo, Takahiro, Katsumi, Henmi, Takashi, Okada, Arifumi, Wakasugi, Takashi, Kadono, Kohei
• Format: Article
• Language: English
• Subjects: Magnesiothermic reduction; Magnesium silicide; Silica glass; Silicon; Silicon monoxide
• ISSN: 2187-0764; 2187-0764
• DOI: 10.1016/j.jascer.2017.06.010

•Magnesiothermic reduction was applied to SiO2 glass substrate in various conditions.•Highly oriented Mg2Si was obtained in the solid state reaction at 600–700°C.•Silicon was obtained in the reaction with Mg film deposited on the glass substrate.•Amorphous layer was formed on the SiO2 glass in the reaction with Mg vapor at 575°C.•Chemical state of silicon in the amorphous layer was investigated by XPS. We applied magnesiothermic reduction to silica glass substrates at various conditions including solid state or solid-Mg liquid reaction, and solid-Mg vapor reaction. Magnesium silicide with highly oriented to the 〈110〉 direction against the substrate surface was obtained in the solid state reaction at temperatures from 600°C to 700°C using Mg grains while Si crystallites were obtained in the reaction with Mg film deposited on the glass substrate at 560°C. On the other hand, in the reduction with Mg vapor at 575°C, brown and amorphous layer was formed on the surface of the silica glass substrate. The layer was transparent in the visible and near-infrared regions, and showed an interference pattern in the transmission spectra, indicating the homogeneity of the layer. The thickness and refractive index were estimated as 770nm and 1.94, respectively. As the reaction with Mg vapor proceeded further, Mg2Si and MgO crystallites were formed. Oxidation states and their depth profiles of silicon atoms in the layers were investigated by X-ray photoelectron spectroscopy. The silicon atoms in the brown and amorphous layer existed in intermediate oxidation states, −2 and +3. The reaction proceeding, the formal charge of the silicon atoms varied to −4 corresponding to Mg2Si and +2.