Growth Towards Light: Translation of Optical Inputs into Mesostructured Outputs via Inorganic Phototropism

Citation

Carim, Azhar Iqbal (2021) Growth Towards Light: Translation of Optical Inputs into Mesostructured Outputs via Inorganic Phototropism. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/mn62-wc26. https://resolver.caltech.edu/CaltechTHESIS:04202021-164652779

Abstract

Palm trees exhibit phototropic growth wherein physical extension of the plant guides the crown towards the time-averaged position of the sun to maximize solar harvesting. In analogous fashion, the directed growth and resultant nanoscale morphology of an evolving inorganic semiconductor deposit can be precisely defined in three-dimensional space using incoherent, uncorrelated light with spatially-invariant intensity. Maskless, photo-driven electrochemical deposition of semiconductor films generates highly ordered, periodic mesostructures with anisotropic, nanoscale features conformally over macroscale areas. This inorganic phototropic growth process does not utilize any physical nor chemical templating agents. Rather, as with natural phototropism, wherein the morphological phenotype expressed by an organism is a function of the light available in the habitat during growth, the precise mesostructures are set by the deposition illumination. Structural complexity and anisotropy result as consequences of inherent asymmetry in the light-material interactions during growth. Here, the morphological outcomes defined by specific illumination inputs are explored and the microscopic optical phenomena underpinning this physical recording of light information is interrogated via both experimental and computational methodologies.

Thesis Files