Preparation Of Gradient Colloidal Photonic Crystals And Application Research

Photonic crystal (photonic crystal), also known as photonic band gap crystals, isan ordered structure in which the dielectric constant (or refractive index) areperiodically distributed. Due to the interaction between Mie scattering and Braggdiffraction of light transmitted, certain frequencies of light can not pass through;mixed with some defect states, the light localized in specific regions. These featuresmake the photonic crystal easily and powerfully to limit, regulate of photons, whichmay cause the transformation of human society from the electronic to the photon age.In the second chapter, we use the classical emulsion polymerization and soap-freeemulsion polymerization to prepare monodisperse polymer colloidal particles. Wewere able to characterize particle size and morphology by scanning electronmicroscopy, transmission electron microscopy. By differential scanningcalorimeter(DSC) and thermogravimetric analyzer(TGA), we characterized the glasstransition temperature and the temperature of thermal decomposition of these particles.Monodisperse particles self-assembled into three-dimensional colloid crystals. We usespin-coating, dispensing, single or double substrate vertical deposition,253nm,343nm, and490nm colloids self-assemble into three-dimensional colloidal crystals. Weuse UV-visible-near-infrared spectrograph to test reflection and transmission spectraof three-dimensional colloidal crystal film. From the spectra, we can obtain thephotonic band gap of the photonic crystal structure. Colloidal photonic crystals withcontrollable layers were prepared using the dip-coating method. By controlling thepreparation conditions, such as the pulling speed, solution concentration, height ofcurved liquid surface, we can get thin colloidal crystals films with1-30layers. SEMwas used to the characterization of the crystal morphology, and we found thatas-prepared colloidal crystals were hexagonal close-packed. As thickness increase,more regular colloidal crystals with a larger area were formed. We studied thespectroscopic properties of the colloidal crystal film with different layers. Besides,based on the colloidal crystals, we put them in isotropic oxygen plasma chamber, andadjusted the photonic band gap of colloidal photonic crystal film. At the same time, gradient colloidal photonic crystals with different layers were thus prepared. Wediscussed the relationship between photonic band gap and particle size in gradientstructure. Compared with non-gradient structure, the gradient colloidal crystals wereblue-shift obviously. With the appearance of the disordered structure by the etchingduration, the photonic band intensity decreased.In the third chapter, we prepared gradient colloidal photonic crystals with differentlayers. And then, we applied Au film on the surface of gradient and non-gradedcolloidal photonic crystal surface by vacuum thermal evaporation. Depending onthickness of the Au film and angular of the Au flux, photonic band gap differs fromeach other. Au is the noble metal in which local surface plasmonic resonance effectexists. We can effectively regulate the photonic band FWHM and peak position by Aufilm and nanostructure. Upon filling into colloidal crystal, Au increased the averagerefractive index of colloidal crystal films, and thus the photonic band gap is red shift.This effect is more obvious with decreasing the crystal thickness. The averagerefractive index changes little in thick colloidal crystal film, and thus the photonicband gap shift is small. In gradient colloidal crystals, with the increase of Audeposition angle, due to the LSPR effect between hemisphere gold shell on thecolloids and nanoparticles, photonic band gap blue shift. And what’s more, wedeposited Si film on the gradient and non-gradient structure of colloidal crystalsthrough the magnetron sputtering technique. Si is a high refractive index materialcompared with the colloidal particles. Upon the filling of Si, red shift of the photonicband gap in gradient colloidal photonic crystal is not obvious. For the non-gradientstructure, due to the formation of a continuous Si film, Bragg diffraction peaksgradually being masking, while some of the Fabry-Perrot interferometer peak isenhanced. We use gradient colloidal photonic crystal to enhance the fluorescent signal.By adjusting the position of photonic band gap, we enhanced the fluorescence of RB.