Photonic crystal properties of packed submicrometric SiO2 spheres (original) (raw)
Related papers
Physical Review Letters, 1999
We report observations of the optical stop band of periodic planar arrays of submicron silica spheres, and of macroporous polymers grown from these silica templates. The stop-band width and peak attenuation depend on the number of layers and on the dielectric contrast between the spheres and the interstitial regions, both of which are experimentally controlled. The results are compared to the predictions of the scalar wave approximation. This is the first systematic study of the thickness dependence of the stop band in colloidal photonic band gap structures.
A comparative study of colloidal silica spheres: Photonic crystals versus Bragg's law
Physics Letters a, 2008
A comparative study of colloidal crystals made of silica spheres using Bragg's law and a model including a photonic band gap (PBG) was demonstrated. Optical properties of the crystals annealed at various temperatures were characterized by a procedure similar to X-ray diffraction technique. Experimentally, the PBG obtained from the transmission spectra agrees with the model of the photonic bands using two parameters, sphere size and the effective index. This procedure gives a better description than the traditional way using just the Bragg's expression without a band gap, commonly referred to as Zone-folding.
Colloidal crystals as photonic crystals
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005
Colloidal crystals (CC) are closely related to photonic crystals (PC) as both of them can be considered as composite materials with a spatial periodic distribution of building blocks. In the case of CC those building blocks are submicrometric particles. Here we will report on recent advances made in our laboratory to fabricate new colloidal crystals with the aim to find new optical properties in relation to PC. We will focus on the following novel topics: (1) Non-close packed face centred cubic (FCC) structures by chemical etching techniques. Most results on solid colloidal crystals concern close packed systems. However, theory predicts that a non-close packed crystal structure presents stronger light scattering properties as compared to the close packed one. Here we shall show results on the fabrication method and optical characterization of non-close packed FCC colloidal crystals. (2) Diamond structures made from nanorobotics. This technique helps to build up complicate 3D crystal structures not achievable, so far, from colloidal self-assembly methods. We will report on the construction method of a crystal aggregate with diamond symmetry.
Influence of Optical Band Structures on the Diffraction of Photonic Colloidal Crystals
Photonic Band Gap Materials, 1996
We have performed optical diffraction studies on colloidal crystals with large refractive index mismatches up to 1.45 and polarizibilities per volume as large as 0.6. These conditions push colloidal crystals into the regime where strong coupling between photonic crystals and the light field occurs. It is found that the photonic band structures result in apparent Bragg spacings that strongly depend on the wavelength of light. The dynamical diffraction theory that correctly describes weak photonic effects encountered in X-ray diffraction, also breaks down. Two simple models are presented that give a much better description of the diffraction of photonic crystals.
Langmuir, 2006
A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the facecentered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.
Characterization of Photonic Colloidal Single Crystals by Microradian X-ray Diffraction
Advanced Materials, 2006
Photonic crystals (PCs) can provide unprecedented control over both the emission and the propagation of light, allowing important applications in, for example, infrared telecommunications. However, fabrication and characterization of PCs is challenging owing to the large refractive-index contrast that is needed to open up a photonic bandgap. Here we demonstrate that microradian X-ray diffraction can be used to characterize various (inverse) PCs with lattice spacings as large as 1.3 lm at different stages of their fabrication. We have even fabricated non-close-packed (non-cp) PC structures by selfassembly of colloidal microspheres in an external electric field. Inverse PCs have been obtained by infiltration of the colloidal-crystal templates with amorphous silicon. The size of the colloidal particles allows us to characterize the internal 3D structure of these crystal templates in both real and reciprocal space.