Effect of Substrate Type on Morphology of Silica Aerogel Film Prepared by Ambient Pressure Dry Method

Abstract:

Silica aerogel films were fabricated on five substrates, i.e., Ti, SiO₂, GaN, Al and Si, by ambient pressure dry method. The influence of the substrate type on the morphology of the silica aerogel films was investigated. X-ray photoelectron spectroscopy (XPS) was used to observe the interfacial bonding states between silica aerogel films and the substrates. The refractive index of each film was measured by fitting the reflectance spectrum using spectroscopic ellipsometry. The morphology and cross-section of each film were observed by atomic force microscope and field emission scanning electron microscope. Results show that the binding energy offset of 0.07 eV of the Al-O center peak and 0.43 eV of the Ti 2p_3/2 center peak are caused by the fabrication of the silica aerogel films, which suggests the formation of chemical bonds between the substrates and the silica aerogel films. The silica aerogel film prepared on the Ti substrate has the lowest refractive index of the films (1.17), and an approximate average porosity of 63.8% which is higher than that of the film on the Si substrate (57.2%). Effect of substrate type on the morphology of silica aerogel film is attributed to hydrophilicity. Owing to the best hydrophilicity of Ti substrate, more particles are accumulated on the Ti substrate to nucleate and grow, producing a silica aerogel film with larger surface roughness, particles and pores than other films.