We investigate the optical properties of photonic crystals consisting of both metal and dielectric. In the optical region metals are highly absorptive and reflective; namely exhibit high refractive index resulting in wider bandgaps. Silver spheres are employed in this study as silver has low losses in the optical region. We calculate the band gap structure with the KKR(Korringa-Kohn-Rostoker) method which use the multiple scattering process.
First, we investigate the surface modes of monolayers of silver spheres due to the two dimensional periodicity. Electromagnetic waves are normally incident on the plane of periodically arrayed structure. The transmission spectra of triangular lattices of spheres are calculated when the radius of sphere is much smaller than the wavelength of the incident light. The surface modes of silver spheres are observed when the real part of dielectric constant of metal is -2as a dip in the transmittance spectra at the wavelength of 353nm. As the radius of sphere becomes larger, the resonant wavelength moves toward the longer wavelength region. The transmission spectra are calculated varying the radius of spheres with the distance between adjacent spheres fixed. As two spheres gets closer, the surface mode splits into two modes due to the coupling between the localized surface modes. Reflection and absorption spectra of the monolayer structure are also studied. Absorption does not affect the mode splitting but another resonant mode is observed originating from the reflection. Calculations obtained for the square lattice of monolayer structure yield similar results as the triangular lattice case.
Second, we investigate the transmission spectra of a 3D photonic crystal which is made by stacking silver monolayers. The transmittance spectrum for shorter wavelength region shows the same shape as for the monolayer but the value of transmittance gets smaller as the number of layers increases. In the long wavelength region additional band gap appears due to the periodicity along the propagation direction of the incident light. The position and size of this gap are dependent on the distance between the monolayers while the gap at around 353 nm is not affected.
광자 결정에서 큰 폭의 밴드갭을 얻기 위해서 금속을 이용한 광자 결정에 많은 연구가 이루어 지고 있다. 그 중 3차원의금속 광자 결정은 제작상의 어려움이 존재하여 이론적인 연구가 함께 진행되고 있다. 본 논문에서는 3차원 금속 광자 결정의 광학적인 특성을 연구하기 위해서 KKR방법을 이용하여 전자기파의 진행 특성을 계산하였다. 이 때 2차원 주기적인 구조에서 표면모드가 발생되는 것을 알아보았다. 그리고 표면모드에 의한 투과율 특성이 3차원적으로 배열된 구조에서 어떠한 영향을 미치는 보고 3차원 구조에서의 전자기파의 진행 특성을 살펴보았다.
