When 10:00 AM - 12:00 PM Jul 08, 2022
Where 1017 H.H. Dow/Virtual
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PhD defense: “Additive and Fiber Nano-manufacturing of Multi-material, Dielectric Photonic Crystals”

Brian Iezzi

Many of the colors we see in the natural world are not the result of portions of the visible spectrum being absorbed by pigmentation, but rather the result of light being reflected and refracted due to structural arrangements of micro and nanoscale matter. These arrangements, referred to as photonic crystals (PCs), provide a means to design spectral properties across virtually any wavelength of electromagnetic radiation, leading to PCs’ increasing use in many applications, from advanced biomedical imaging to high-speed fiber optic communications. Today, most PC fabrication is largely limited to “subtractive” manufacturing techniques, where material is removed to create a desired structure. These mature technologies are generally capital intensive, have slow prototyping cycles, are inherently wasteful, and are limited to creatingonly certain 3D geometries. In contrast, this dissertation considers a “bottom-up” approach to creating PCs, using micro- and nano-scale additive manufacturing (AM) and fiber drawing (FD).

Electrohydrodynamic jet (e-jet) printing, a high- resolution AM technique, is first investigated for use in fabricating multi-layered, multi-polymer one-dimensional photonic crystals (1DPCs). The combination of multiple layers, and dielectrics with differing refractive indices, can be used to precisely control constructive and destructive interference at specific wavelengths. Engineering favorable combinations of ink surface tension and substrate surface energy to promote uniform spreading was found to be critical in the creation of smooth nanoscale layers. Building on the understanding of surface wetting dynamics, drop-on- demand e-jet printing was also used to create two-dimensional PC arrays using colloidal inks with high index germanium nanoparticles (2DPCs). Low aspect ratio, hemispherical meta- atom structures, created through tuning ink and surface dynamics, were found to have favorable photonic properties compared to geometries created via subtractive methods.

Finally, the 1DPC concept is applied to multi-material, thermally drawn photonic fibers, where, for the first time, a strong infrared reflectance response is engineered using N>100 all-polymer constituent layers. Electromagnetic simulations guide fabrication of fibers having a unique photonic “barcode” with high signal to noise ratio versus a woven carrier fabric. These barcode fibers may find applications in garment authentication and life cycle textile tracing and sorting. The AM and FD techniques described also enable convenient in-situ measurement of the structure’s photonic properties during the manufacturing process, permitting on-the-fly adjustment of printing (and drawing) parameters through reinforcement learning algorithms. This real-time adjustment can be performed rapidly and with low cost, thus enabling an important move toward an autonomous manufacturing paradigm for the creation of novel photonic structures.

 Zoom link: https://umich.zoom.us/j/91886631158, passcode: summer