Effect of disorder on the optical properties of colloidal crystals

Abstract

Colloidal crystals offer a promising route for the formation of three-dimensional photonic crystals. The primary constraint in working with these materials is the disorder present in these self-assembled materials. Sphere vacancies, line dislocations, and random position errors all lead to a degradation in the optical properties. It is important to characterize these effects so as to guide further developments in colloidal crystal optics. Here, we report a systematic and quantitative study of disorder in colloidal crystals with visible diffractive properties. Using optical spectroscopy and digital imaging we have correlated several measures of structural disorder with variations in the transmissive and reflective optical properties. We observe a critical size distribution above which rapid deterioration of the lowest stop band is observed. Below this critical size distribution, we observe excellent optical quality, nearly independent of the size distribution. Single sphere vacancies also increase in crystals formed from more polydisperse spheres. The primary effect of this type of defect is to increase the broadband diffuse scattering.

Perfect absorption and no reflection in disordered photonic crystals

“…Increasing degrees of structural disorder, even orders of magnitude larger than those for the geometric case, do not destroy the crystal which remains periodic on average, hence exhibiting still efficient reflectivity resonances (Bragg peaks). In the case of geometric disorder, already a few percent level [61][62][63][64][65][66][67]. As a matter of fact, geometric disorder is especially detrimental to our setup as it implies a concomitant variation in the phase mismatch between atomic distribution N j (z) and dynamic shift δ ds (z); this point is clearly confirmed in Fig.…”

Relation between growth dynamics and the spatial distribution of intrinsic defects in self-assembled colloidal crystal films

“…The presence of such imperfections largely affects the optical properties of these lattices. 5,6 Although the effect of having different types of intrinsic defects has been studied in some detail both theoretically 7,8 and experimentally, [9][10][11][12][13] no strict correlation between the growth dynamics of colloidal crystal films and the presence of imperfections has been established up to date. This is mainly due to the lack of a model describing the colloidal crystal film formation.…”

Broadband coherent backscattering spectroscopy of the interplay between order and disorder in three-dimensional opal photonic crystals

“…In our experiments we investigate the behavior around the stop- gap at L, which is located at φ = 0 • angle of incidence and has a bandwidth of 6% as predicted by band structure calculations and measured in many reports on opals elsewhere. 12,25,31,50,51 By tilting the sample, we gain access to directions away from the L-gap corresponding to LK, LU, and LW in the band diagram. In the experiments we average over many crystalline regions with random orientations in the (111) plane, and the crystal is spun around its ΓL-axis to average individual speckle.…”

“…All crystals have some degree of intrinsic disorder due to polydispersity of the building blocks or imperfections in fabrication. [4][5][6][7][8][9][10][11][12] In order to realize random multiple scattering without relying on intrinsic disorder, another route has been explored to intentionally design disorder in three-dimensional photonic crystals of very high quality. 13 The role of disorder has recently been investigated in photonic crystal waveguides.…”