UC San Diego

Modulation of chemical, photophysical, and electronic properties by controlling the type and concentration of carriers is an essential ability that enables semiconductor applications in a wide range of technologies. Colloidal semiconductor nanocrystals are an attractive class of solution processable and tunable semiconductor materials. Several doping strategies have been successfully applied to semiconductor nanocrystals, making them promising components of emerging technologies. Photochemical doping has emerged as a particularly attractive strategy for post-synthetic electronic doping of colloidal semiconductor nanocrystals because it is reversible, nondestructive and solution-stable. This dissertation focuses on the photochemical manipulation of nanoscale materials, including colloidal nanocrystals and cluster-based frameworks.Chapter 1 provides an introductory overview of electronic doping strategies. Furthermore, background on the classes of materials studied within, colloidal nanocrystals and cluster-based frameworks, is provided. Chapter 2 presents the photochemical reduction of colloidal maghemite nanocrystals as a means to access high-quality magnetite nanocrystals. The phase-transformation of iron oxide nanocrystal via introduction of excess carriers is analyzed by X-ray, optical, and magnetic characterization methods. Furthermore, the factors limiting photochemical reduction are discussed. Chapter 3 details the UV irradiation of colloidal 2H tungsten diselenide nanocrystals using lithium triethylborohydride. This phototreatment leads to a bleach of the band-edge absorption and an enhancement and blue-shift of the C-exciton absorption. Powder X-ray diffraction suggests that these changes are primarily due to lithium-ion intercalation into these two-dimensional materials. Chapter 4 extends the methods for electron-quantification in photochemically doped semiconductor nanocrystals do photochemically reduced cluster-based frameworks. The synthesis of cluster-based frameworks allows for in situ photodoping to access highly crystalline, reduced cluster-based frameworks. The results are used to demonstrates the unique stability of reduced Zn-bridged frameworks based on Mo-doped Preyssler clusters.