Exploration of Materials and Mesostructures Accessible via Inorganic Phototropic Growth

Citation

Hamann, Kathryn Rose (2022) Exploration of Materials and Mesostructures Accessible via Inorganic Phototropic Growth. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/z725-v841. https://resolver.caltech.edu/CaltechTHESIS:05212022-202251527

Abstract

Biological systems have evolved complex methods to interact with and adapt to a given environment to optimize fitness, and replication of these natural mechanisms in artificial systems has been a long-standing area of research interest with significant potential utility. Phototropic growth is a natural phenomenon wherein an organism spatially orients biomass addition to optimize light collection. An artificial analog, inorganic phototropic growth, has been demonstrated and relies on a similar process: semiconductor mass is selectively added near regions of high light absorption, thus optimizing light collection and instructing further localized material addition. Inorganic phototropic growth effected via light-mediated electrodeposition has been used to generate anisotropic Se-Te mesostructures with optically-defined morphologies by capitalizing on inherent asymmetries in light absorption at structured, semiconducting interfaces to direct anisotropic growth. This thesis broadens the previous understanding of inorganic phototropic growth via a series of investigations that expand both the material library and complex morphologies accessible and includes detailed analyses of associated structural evolutions and the underlying optical phenomena. First, inorganic phototropic growth of highly ordered and periodic PbSe and CdSe mesostructures with optically-defined morphologies is demonstrated. Second, deposition using temporally varying illumination inputs to generate Se-Te mesostructures with tunable morphological complexity in both the in-plane and out-of-plane directions is examined. Third, the use of single, static, short wavelength (green to ultraviolet) inputs to simultaneously define two orthogonal sets of periodic features in Se-Te deposits is explored. A suite of optically-based simulations is used throughout to model the growth processes and elucidate the fundamental light-matter interactions which defined the empirically observed morphologies.

Thesis Files