Conversion of Solution‐Derived Perhydropolysilazane Thin Films into Silica in Basic Humid Atmosphere at Room Temperature

Abstract

Spin‐on perhydropolysilazane (PHPS) thin films were converted into mechanically hard silica thin films by an exposure to the vapor from aqueous ammonia. Infrared absorption and X‐ray photoelectron spectroscopic analyses were conducted to clarify the details of the PHPS‐to‐silica conversion and the nature of the silica thin film products. The PHPS‐to‐silica conversion was found to proceed rapidly between 2 and 3 h of exposure via a reaction‐limited process, where the refractive index and the pencil hardness greatly decreased and increased, respectively. Finally, the O/Si mole ratio close to 2 was achieved, which has never been realized in literature for PHPS‐derived silica thin films. It was also found that the condensation of Si–OH groups proceeds in films immediately after PHPS hydrolysis, which is similar to the base‐catalyzed hydrolysis–condensation reaction of silicon alkoxides. Although the silica thin films obtained had refractive indices similar to that of silica glass, high pencil hardness over 9H on Si(100) substrates, and O/Si mole ratios close to 2, it was concluded that they are nonidentical to silica glass, containing trace amounts of Si–OH and Si–H groups.

Perhydropolysilazane derived silica for flexible transparent barrier foils using a reel-to-reel wet coating technique: Single- and multilayer structures

“…The layer thickness of all films was approximately 500 nm (uncured) with only minor changes after the conversion. The decrease of the refractive indices determined by ellipsometry with approximately 1.56 for PHPS as deposited, 1.51 after one VUV scan and 1.47 for SiO x after the second and third VUV scans is in agreement with values of the literature [21]. After a first VUV-run absorption bands of SiH, NH and SiNSi still appear.…”

“…This will be part of the ongoing research. The mechanical proof and the potential of the SiO x -layers are already described in literature [13,15,21,25,32] .…”

“…water/ammonia vapor, catalysts, ozone, UV) [18][19][20][21]. A rapid thermal conversion at temperatures above 200°C is not applicable to most polymer substrates.…”

Hydrophobic, transparent and hard silicon oxynitride coating from perhydropolysilazane

“…The absorption bands located at 3380 cm −1 and 1176 cm −1 correspond to the stretching vibration and bending vibration of the NH bond, respectively, while the absorption band at 2160 cm −1 is due to the stretching vibration of the SiH bond. The broad absorption band between 820 cm −1 and 1020 cm −1 is attributed to overlap of the vibrations of the SiNSi bond …”

Ultrathin silica film derived with ultraviolet irradiation of perhydropolysilazane for high performance and low voltage organic transistor and inverter

“…To measure the degree of PHPS-to-silica conversion, the atomic contents of the obtained film were provided in Fig. S1, where the O/Si mole ratio of 1.97 indicates the high efficiency of this conversion method [38]. Crystallization state of silica has strong influence on the dielectric properties.…”