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Abstract
This thesis focuses on the development of chemical approaches for direct optical patterning of colloidal nanomaterials. In Chapter 1, we introduce colloidal nanomaterials and their device applications. We then discuss the need for new methods to pattern nanomaterials which motivate the development of direct optical lithography of functional inorganic nanomaterials (DOLFIN). Chapter 2 discusses the establishment of a library of photosensitive ligands and additives for DOLFIN. We demonstrate the use of these photosensitizers to pattern a variety of NCs and study their photodecomposition pathways and products. We also discuss the various chemical mechanisms that enable the solubility of NCs to be modulated by the decomposition of the photosensitizers. In Chapter 3, we directly optically pattern oxide nanoparticles (NPs) by mixing them with photosensitive diazo-2-naphthol-4-sulfonic acid and irradiating with widely available 405 nm light. We demonstrate the direct optical lithography of ZrO2, TiO2, HfO2, and ITO NPs and investigate the chemical and physical changes responsible for this photoinduced decrease in solubility. Micron-thick layers of amorphous ZrO2 NPs were patterned with micron resolution and shown to allow 2π phase control of visible light. We also show multilayer patterning and use it to fabricate features with different thicknesses and distinct structural colors. Upon annealing at 400 °C, the deposited structures have excellent optical transparency across a wide wavelength range (0.3-10 μm), a high refractive index (n=1.84 at 633 nm) and are optically smooth. We then fabricate diffractive optical elements, such as binary phase diffraction gratings, that show efficient diffractive behavior and good thermal stability. Different oxide NPs can also be mixed prior to patterning, providing a high level of material tunability. Chapter 4 involves the direct photo-patterning approach for lead halide perovskite (LHP) NCs through the binding and subsequent cleavage of a photosensitive oxime sulfonate ester. The photosensitizer binds to the NCs through its sulfonate group and is cleaved at the N‒O bond during photo-irradiation with 405 nm light. This bond cleavage decreases the solubility of the NCs which allows patterns to emerge upon development with toluene. Post-patterning ligand exchange results in photoluminescence quantum yields up to 76%, while anion exchange provides tunability in the emission wavelength. The patterned NC films show photoconductive behavior, demonstrating that good electrical contact between the NCs can be established. In Chapter 5, we introduce the direct optical patterning of bare NCs that does not require any additional photosensitive ligands or additives. We determined that photo-exposure of ligand-stripped, bare NCs in air significantly reduces their solubility in polar solvents due to photo-oxidation of surface ions. This approach enabled the patterning of bare ZnSe, CdSe, ZnS, InP, CeO2 NCs as well as mixtures of ZnSe with ZrO2, HfO2, or CdSe/ZnS NCs. The photo-oxidation process was studied by various methods including UV-vis and X-ray photoelectron spectroscopy. We also demonstrate porosity and refractive index modulation of patterned NC films. This allowed the refractive index of the ZnSe NC film to be modulated between n=1.87 and n=2.10. Our findings showcase an easily accessible patterning method for bare NCs.