Reflectivity of Photonic Crystals Self-assembled with Silica Spheres

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We investigate the spectral reflectivity of photonic crystals assembled with silica spheres. The propagation of electromagnetic wave can be controlled by periodic structures known as photonic crystals. Therefore photonic crystals are anticipated for advanced control of thermal radiation beyond solid state properties. The close-packed photonic crystals well-defined thickness are rapidly made on a Si wafer by using self-assembly of colloidal silica spheres. We measure spectral reflectivities of the samples with an FT-IR (Fourier Transform - Infrared Spectroscopy). The spectral reflectivity is enhanced at specific wavelength designed with numerical analysis. The peak of spectral reflectivity shifts to shorter wavelength with increasing incident angle. The angular dependency of the spectral reflectivity can be roughly calculated by the modified Bragg's equation taking into account Snell's law of refraction. We show that the reflectivity in infrared range is well enhanced by using large photonic crystals assembled with silica micro-spheres.