Self-Assembled Binary Photonic Crystals under the Active Confinement and Their Light Trapping

The
self-assembly of oppositely charged colloidal ellipsoids and
spheres under active confinement is first proposed to achieve long-range
ordered photonic crystals. Compared with the conventional passive
confinement, a characteristic of the active confinement is that boundaries
are movable. Our Brownian dynamics simulations show that dynamic steady
structures, similar to quasi-2D colloidal crystals, can be obtained
under the strong confinement when the two boundaries periodically
oscillate together. The in-plane structures can be regulated by changing
the charge ratio of the two kinds of particles. These dynamic steady
structures are determined by the minimum electrostatic energy with
the aid of increased mobility of confined particles, which are not
available in equilibrium. Numerical simulations verify that light
can be perfectly confined in this dielectric binary photonic slab
without any radiation, which corresponds to a typical optical bound
state with divergent lifetime and ultrasharp spectral profile. Given
the changeable geometry of this photonic slab, the trapped optical
field might be applicable to enhanced light–matter interactions.
In addition, for thicker layers, layer-by-layer ordered structures
occur spontaneously, driven by the active confinement, while no global
order occurs in the passive confinement. Our results show that the
boundary motion can become an important factor affecting self-assembled
structure and function.