Dimer‐Based Three‐Dimensional Photonic Crystals

Abstract

The self‐assembly of polystyrene dimer‐ and spherocylinder‐shaped colloids is achieved via controlled drying on glass and silicon substrates. 3D monoclinic colloidal crystal structures are determined from scanning electron microscopy images of sections prepared using focused ion‐beam (FIB) milling. Full photonic bandgaps between the eighth and ninth bands are found for a systematic range of colloidal dimer shapes explored with respect to the degree of constituent lobe fusion and radius ratio. The pseudogap between bands 2 and 3 for spherocylinder‐based monoclinic crystals is also probed using normal incidence reflection spectroscopy.

Phase diagram of hard asymmetric dumbbell particles

“…In a rotator phase (also referred to as a plastic crystal in the literature), the particle center of mass positions are on average located on a lattice but the particles can still rotate. Free rotation of a particle can be hindered by the surrounding particles, and at high densities correlations between the instantaneous particle positions and orientations can develop [17,30]. Periodic crystals have both periodic positional ordering of the particle centers of mass and periodic orientational ordering of the particles' major axes, and as such both the small and large constituent spheres are also periodically ordered even for nontangential AD particles.…”

“…Dimer particles are not only fundamentally interesting, e.g., as a model for diatomic molecules, but also have practical applications, e.g., in the production of colloidal crystals with useful optical properties [16,17]. Dimers consist of two connected spheres, and they can be synthesized with a range of different constituent sphere diameter ratios and separations [4,[18][19][20][21][22][23][24][25].…”

Polarizability and alignment of dielectric nanoparticles in an external electric field: Bowls, dumbbells, and cuboids

“…Self-assembly of the particles is an important process by which large-scale nano-structures can be formed. This self-assembly process can be spontaneous in the case of favorable thermodynamic conditions and suitable effective particle-particle interactions, [3][4][5][6][7][8][9][10] but can also be steered and further manipulated by external fields. Rodlike particles in a liquid dispersion, for instance, can spontaneously align at sufficiently high concentrations solely due to their excluded volume interactions, 11 but their self-organisation has also been driven by external magnetic or electric fields, [12][13][14][15][16] by substrates that preferentially orient the rods, 17,18 or by fluid flow.…”

Using shape for self-assembly

“…The literature provides beautiful examples of the effect of aspect ratio on the packing structure: low-aspect-ratio dimers will pack very similarly to spheres [103], while high-aspect-ratio nanorods will show liquid-crystal-like (i.e. smectic or nematic) structures [101,104] and high-aspect-ratio platelets will stack in columns [105].…”