Optically-Active Microcrystals and Devices through DNA-Programmable Assembly

Sun, Lin

doi:https://doi.org/10.21985/n2-wayz-hs21

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Optically-Active Microcrystals and Devices through DNA-Programmable Assembly

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Colloidal crystals are promising candidates for nanophotonic applications due to their strong interactions with light and the capability to tailor such interactions through crystal design and engineering. DNA-programmable assembly, in particular, allows for precise structural control down to the sub-nanometer length scale. In this thesis, ways of designing, synthesizing, and utilizing DNA-assembled crystals as optical devices or components are presented. Chapter 1 provides a brief overview of the uses of DNA-programmable assembly in nanophotonics, with a focus on how its control over crystal structure parameters makes it attractive for optical microdevice designs. Chapter 2 shows how such control can be exploited to study and determine the effects of nanoscale structure and lattice parameters on the light-matter interactions in colloidal crystals. Specifically, a comparison of the macroscopic optical properties of crystals with the same bcc lattice symmetry and macroscopic rhombic dodecahedron crystal habit but composed of octahedral and spherical nanoparticles, respectively, is provided. The first use of DNA-assembled crystals in making photonic crystals is presented and discussed in Chapter 3. The use of DNA molecules as spacer groups is a novel design parameter for photonic crystals, and a new set of design rules have emerged through simulations, which are detailed in this chapter. Importantly, a crystal composed of cubic nanoparticles is made according to these design rules, and it shows a broad reflectance stopband in the red and infra-red region, which underscores the advantages and utility of using DNA-programmable assembly techniques to make the photonic crystals predicted by simulation. While the above two applications have benefited from the structural control at the nanoscale, control of mesoscale structural parameters, such as crystal orientation, size, shape and location on a substrate is equally crucial for integrating DNA-assembled crystals into devices. Chapter 4 describes a method for controlling colloidal crystal size and shape through the use of lithographically defined patterns to guide DNA-mediated assembly. Through a layer-by-layer assembly process on designated areas, the crystal’s two-dimensional size and shape and height in the third dimension can be precisely controlled. Chapter 5 reports the incorporation of two-dimensional nucleation interfaces on a substrate to guide DNA-mediated nanoparticle crystallization into arrays of Wulff-shaped constructs with their orientation, shape and location dictated by the design of the interface. This unprecedented level of structural control is a significant step towards realizing complex, integrated devices based upon colloidal crystals. Finally, a brief conclusion and future outlook are given in Chapter 6. Taken together, the work reported in this dissertation has expanded the scope and capabilities of using DNA-programmable assembly in optical device fabrication.

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