Technical: This project will address the challenge of introducing complexity in photonic slab arrangements. Vertical variation throughout the thickness of quasi-2D slabs will be introduced via colloidal processing under confinement. Freezing between two and three dimensions accesses structural transitions in gap regions incommensurate with integral layer spacing of thin particulate films. From confocal microscopy of fluorescent-shell modified particles in wedge cell geometry, the real space phase organization will be investigated as a function of particle morphology, system density and cell height. The synthesis of shape anisotropic colloids will be performed to prepare building blocks for unconventionally ordered solids in addition to crystals under the imposed packing constraints. Quantitative evaluation of order parameters and correlation functions determined experimentally and from Monte Carlo simulations of the confined states will inform simulation models to evaluate the optical properties of the slab patterns and their various inverse embodiments¯ for example, residual volume-, shell-, and skeleton inverse structures. Sol-gel and nanoparticle precursors for solution processing as well as vapor phase depositions will be applied in backfilling and co-assembly routes to inversion to obtain high-refractive index contrast. The project will enhance the understanding of how reduced symmetry, expanded dimensionality, and novel classes of partial order structuring impact light-matter interactions in photonic crystal slabs. To this aim, photonic band structures will be calculated and the relative influence of structural parameters such as positional ordering, orientation ordering, motif morphology, basis complexity, dielectric filling fraction, refractive index contrast on the behavior of photonic bands at high symmetry points in reciprocal space will be explored. Complimentary analysis of mode field distributions will be applied to rationalize the formation of full 2D photonic band gaps. A powerful experimental technique in its infancy for application to photonic slab structures will be used to confirm stop band and band gap frequencies, modified density of photonic states, in addition to the experimental field distribution of photonic modes. Namely, the Electron Energy Loss Spectroscopy technique applied in a Scanning Transmission Electron Microscope will enable the photonic characterization at high spatial resolution. For investigation of refraction properties of the slabs, equal frequency contour plots will also be calculated and the light propagation in-plane through atypical structures will be simulated to determine frequency and directions for left-handed, right-handed, positive- and negative refraction behavior as a function of structural parameter variants. Point source imaging for appropriately indicated configurations defined by self-assembly will be studied to evaluate resolution in the flat lens application of the photonic slab materials. Through this project the structure-property-processing-performance relationships will be established.
This award will enhance undergraduate research opportunities for students in Historically Black Colleges and Universities as well as Women's Colleges. The PI plans to engage undergraduates to conduct research from these institutions through the REU programs associated with the Cornell Shared Facilities. Enrichment will also be offered through conference support for presenting research and for professional development workshops. Lasting relationships with researchers in the home institution will be sought for continued collaboration involving the visiting student and potentially providing additional recruiting opportunities to Cornell's graduate programs. An informal public education project is planned around a distributed research and "Science as Art" model to place images of materials research in public library exhibits which will promote the field. As well, the organization of seminar series hosted by URM graduate fellows to invite distinguished underrepresented minority (URM) faculty for research talks and professional development.
