Self-Assembly of Colloidal Diamond and Related Lattices for 3-D Photonic Band Gap Materials
Abstract
The goal of this research is to use colloidal self-assembly to construct photonic crystals that possess a full omnidirectional three-dimensional (3D) photonic band gap at optical frequencies. Three-dimensional photonic crystals are materials with a periodically varying dielectric constant in all three dimensions. Such crystals are said to have a photonic band gap if they prohibit the propagation of light in all directions over some finite range of frequencies. Technological and scientific interest in such materials is stimulated by their potential to enhance the efficiency of lasers, integrate and miniaturize optical components, control the flow of light to unprecedented levels, and inhibit spontaneous emission. The first step of this research program will be to self-assemble a colloidal superlattice that consists of two interpenetrating sublattices, one with a diamond structure and the other pyrochlore. Both sublattices are predicted to have large robust band gaps that open up for low dielectric contrast and are insensitive to disorder. Once this structure is assembled, one of the sublattices will be removed, either pyrochlore or diamond, leaving behind the other sublattice. In one scenario, the remaining sublattice is made from high-dielectric (refractive index) titania and the process stops there, with the result being a photonic crystal with a full 3D photonic band gap. In a second scenario, the crystal made from the remaining sublattice is backfilled with high-dielectric titania using sol-gel chemistry, and the remaining sublattice is removed leaving behind an inverse diamond or pyrochlore structure, which has a full 3D photonic band gap that can be superior to the equivalent direct structure. The target lattice constant for the crystal structure is 200-400 nm, which will produce a photonic band gap at optical wavelengths (400-700 nm). Using a new approach to colloidal self-assembly, the target superlattice has already been demonstrated to self-assemble with colloidal particles having a lattice constant of approximately 2 micrometers. The approach starts from a design principle that uses preassembled components of the desired superstructure, which are programmed to interact with particles around them in a way that builds up otherwise unattainable structures using only nearest-neighbor interactions. Here the pre-assembled components are tetrahedral clusters of overlapping colloidal spheres mixed with singlet colloidal spheres. The pairwise nearest-neighbor interactions between the pre-assembled components are programmed by coating the clusters and spheres with DNA having "sticky ends" thus creating attractive pairwise interactions between only the clusters and spheres, while leaving the sphere-sphere and cluster-cluster interactions unchanged from their usual hard-sphere interactions. The programmability of the DNA-mediated interactions between particles also opens up the possibility of building defects into the photonic crystal, which can be used for precision optical waveguides, laser cavities, or optical modulation. The optical properties of the photonic crystals, including band gaps, defect states, and optical waveguides will be characterized using optical transmission and reflection experiments.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 17, 2018
- Source ID
- W911NF1710328
Entities
People
- David J. Pine
Organizations
- Army Contracting Command
- New York University
- United States Army