Transmission infrared study of acid-catalyzed sol-gel silica coatings during room ambient drying

Abstract

Sol-gel solutions prepared from tetraethylorthosilicate (TEOS) hydrolyzed in acidic conditions were used to make thin films on Si wafers via spin coating. Solutions with H2O/TEOS ratios of 2, 5, and 10 were prepared and aged at room temperature in sealed containers for times ranging from <2.5 h to 1 month. Transmission Fourier transform infrared spectra acquired around 1 min after spinning showed peaks characteristic of both SiO2 and SiOH. Additional features at ≍580, 1093, and 1130 cm−1 were observed and possible origins are discussed. Peaks at ≍580 and 1130 cm−1, which increased in intensity with solution age time, are attributed to cyclic Si–O, e.g., 4-member rings. When films were exposed to room air, ring concentration decreased significantly within 30 min. Rings were stable for hours, however, when films were kept in N2. The feature at 1093 cm−1, most sensitive to H2O/TEOS, is attributed to residual Si–O–C.