Preparation and properties of the nano-crystal and polymer composite film BIT/PEK-c with low scattering loss

Abstract

The polymers doped with the electro-optic active units have significant nonlinear optical effect after poling by an electric field. They have great potential for waveguide application in integrated optics and photoelectronics [1]. Bismuth titanate, Bi4Ti3O12 (BIT), is a typical ferroelectric material with useful properties for optical memory, piezoelectric and electrooptic devices. It has a high spontaneous polarization Ps (50 μC/cm2), a low coercive field (3.5 KV/cm), and a low dielectric constant (∼130) along the c-axis [2]. In our research, Bi4Ti3O12 nano-crystals were used as the nonlinear chromophore (guest), and the transparent polymer polyetherketone (PEK-c), which possesses a very high glass transition temperature and an intrinsic low dielectric coefficient, was selected as polymer host. By way of composition of the nano-crystals and the polymer, it is hopeful to improve the stability of the electro-optic polymer materials and obtain the materials with a high electro-optic figure of merit. We compounded Bi4Ti3O12 nano-crystals, the structure and size of which were analyzed by X-ray diffraction (XRD) and transmissive electron microscopy (TEM). The composite thin film of nano-crystal Bi4Ti3O12 and polymer PEK-c was prepared by spin coating method. The surface circumstance of BIT/PEKc composite film was observed by the atomic-force microscope. The values of refractive index and thickness of the film were determined by the quasi-waveguide coupling m-line method. And the loss due to scattering in BIT/PEK-c composite film was measured using photographic technique. Nanocrystalline Bi4Ti3O12 has been synthesized by the chemical solution decomposition (CSD) technique. Firstly bismuth nitrate penta-hydrate [Bi(NO3)3· 5H2O] was dissolved in 2-methoxyethanol. Then titanium butoxide [Ti(OC4H9)4] was added into the solution to form Bi4Ti3O12 precursor solution under stirring. The solution was baked to vaporize the solvent. So Bi4Ti3O12 ultrafine precursor powder was obtained. Finally the dried powder was annealed by rapid thermal processing (RTA) at 650 ◦C for 60 s and transformed into nanocrystalline Bi4Ti3O12. The crystal structure of the microcrystals was identified by XRD with Cu Kα1 (λ = 0.15406 nm) radiation operated at 40 KV and 20 mA. Fig. 1 shows the XRD pattern of Bi4Ti3O12 powder. It conforms to the standard XRD pattern of Bi4Ti3O12. The size of Bi4Ti3O12 microcrystals was evaluated by transmission electron microscopy (TEM; H-800 Uitachi). Fig. 2 is the TEM photograph