Studies Of SiO₂ Optical Thin Films Prepared By Electrostatic Self-Assembly Multilayer Method

Optical films are of importance as parts of optical elements and can be used to improve the performances of optical elements and apparatus. Electrostatic self-assembly multiplayer (ESAM) method has advantages in preparing films and develops fast in recent years. In this work, PDDA/SiOa complex films and SiO2 anti-reflective films were prepared by ESAM method, and their optical properties in the visible light spectrum range and anti-scratching performance were investigated.In this paper, the property difference of SiO2 sols used for preparing thin films by ESAM method or Sol-gel process has been discussed. Three kinds of SiO2 sols were prepared, catalyzed by HCl or NH3 H2O only, or HCl first and then NH3 H2O respectively (please note: in following text, the SiO2 sol catalyzed by HC1 first and then NH3 H2O and its correspondent films will benamed SiO2 sol 1# and film 1 ; the SiO2 sol catalyzed by NH3 H2O only and itscorrespondent films will be named SiO2 sol 2# and film 2#). Through investigating the assembling properties of the sols, observing thin films' microscopic structure with TEM and testing their transmissivity with 721 spectrophotometer, we find that the first kind of sol is not suitable for preparing ESAM films, but the last two, i.e. sol 1# and sol 2#, are good. Fourier transform infrared spectrum (FT-IR) and DTA-TG heat analysis of the gels were carried out.PDDA/SiO2 complex films were prepared with ESAM method. The optical properties of the films were studied in the visible light spectrum range and their anti-scratching performance were investigated. The effects of the size of the colloidal particles on the optical properties and their anti-scratching performance of the thin films were studied. The optical properties of thin films following the bilayer numbers and the light wavelengths, and the light transmittance of films following the humidity were studied. Composition of the thin films was carried out with FT-IR and surface analysis of the films, e.g. the distribution of SiO2particles on the last PDDA layer, was analyzed with XPS.SiO2 optical anti-reflective thin films with micropores were prepared with ESAM method. The optical properties of PDDA/SiO2 complex films against the changes in temperature in the processof heat treatment were studied.After heat treated at 520 C, the light transmittance at certain wavelengths of the thin improved greatly. The chemical bond structures of the optical thin films was studied with FT-IR, and surface analysis of the thin films was carried out using XPS and their anti-scratching performances were studied. The result indicates that thin film 2# possesses very good anti-scratching performance. Its surface can't be destroyed obviously even scraped with a blade. However, that of film 1# is smaller, even smaller than that of the corresponding PDDA/SiO2 complex films.