Preparation of opal photonic crystal infrared stealth materials

With the development of infrared detection technology, the survival of military target is now under serious threat. Therefore, new infrared stealth technologies and materials are now in an urgent demand. The photonic crystal (PhC) possesses regularly repeating structure which results in band-gap and diffraction satisfying Bragg's law of diffraction. The PhC presents unique optical properties and functionality. The PhC with band-gap located in visible band is used widely as biosensor, chemical sensor, optical filter, reflector, modulator, metasurface and solar cell. The PhC with band-gap located in infrared band can be used to control the propagations of the electromagnetic waves of infrared band, and could be used as a promising material in the infrared stealth technology. Photonic structure used to tune the infrared radiation usually has a one-dimensional layer-by-layer stack or three-dimensional wood pile structure. However, the poor flexibility, low strength, small area coverage, complicated fabrication process and high cost can prevent this new infrared stealth technology from being applied and developed. In this report, a simple and cost-effective method of preparing the opal PhC materials is proposed, and this infrared stealth material forbids electromagnetic waves of infrared band to propagate on account of band-gap.In this paper, opal PhCs materials with high quality are assembled from SiO2 colloidal microspheres with micrometer size by using optimized vertical deposition method. We calculate the relation between the diameter of SiO2 colloidal microsphere and the frequency of opal PhCs band-gap in theory and verified in experiment, which operates in the working band of infrared detector. The results show that the diameters of SiO2 colloidal microspheres should be 1.33-2.22 m and 3.56-5.33 m. A series of monodispersed micrometer SiO2 colloidal microspheres is prepared by the modified Stber method, and bigger microspheres are prepared by using the seeded polymerization method. Then, we choose the diameters of 1.5 m and 4.3 m SiO2 microspheres to prepare the opal PhCs materials. The PhCs materials assembled by 1.5 m SiO2 microspheres are prepared in alcohol under 60 ℃ or in acetone under 40 ℃; while the PhCs material assembled by 4.3 m SiO2 microspheres is prepared in alcohol/dibromomethane =3:1 under 60 ℃. Finally, the opal PhC materials with band-gap located in 2.8-3.5 m and 8.0-10.0 m are successfully prepared, and the widths of band-gap are 0.7 m and 1.9 m, respectively. These opal PhCs materials could change the infrared radiation characteristics of the target in infrared waveband, and meet the requirements of wide band-gap for infrared stealth materials.