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This dissertation introduces scanning probe microscopy (SPM) and describes the construction and design of a home built low temperature magnetic force microscope (MFM). Then the magnetic coatings on atomic force microscope cantilevers with a focused ion beam (FIB) will be explained. This technique allows the convenient deposition of complex or expensive materials such as CoCrPt. With the MFM tip coated by FIB, the ferromagnetic domain structure of a La[subscript 0.67]Ca[subscript 0.33]MnO₃ film is studied as a function of an in-plane magnetic field below room temperature. Next I will discuss the use of chemically-synthesized FePt nanocrystals as a good candidate for high density storage media. This nanocrystal film showed sintering problems during the annealing process, which is essential to make FePt a hard ferromagnet. A silica overcoating method was used to prevent nanocrystal sintering, which allowed the MFM study of films made from these nanocrystals. I will also discuss resistance measurements of the FePt nanocrystals.

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As a material whose applications are many and growing, zinc oxide still remains a complex system whose photoluminescent (PL), structural, electrical, and photocatalytic properties have not been fundamentally understood. The luminescent properties of zinc oxide (ZnO) nanocrystals (NCs) are very sensitive to crystal structure, and defect states in zinc oxide, which in turn is very sensitive to preparation methods, post-synthesis workup, and thermal treatments. Understanding and managing this rich defect chemistry is critical to controlling ZnO properties. As the surface-to-volume ratio of ZnO increases as materials enter the quantum regime, the surface defects play a stronger role. The exact role of the defect states and their contribution to the physical and chemical properties of ZnO has been studies in great lengths yet still remains controversial.

Half of the sun’s power lies in the infrared. As a result, the optimal bandgaps for solar cells in both the single-junction and even the tandem architectures lie beyond 850 nm. However, progress in low-cost, large-area, physically-flexible solar cells has instead been made in organic and polymer materials possessing absorption onsets in the visible. Recent advances have been achieved in solution-cast infrared photovoltaics through the use of colloidal quantum dots. Here we report stable solution-processed photovoltaic devices having 3.6% power conversion efficiency in the infrared. The use of a strongly-bound bidentate linker, benzenedithiol, ensures device stability over weeks. We investigate in detail the physical mechanisms underlying the operation of this class of device. We find that diffusion of electrons and holes over hundreds of nanometers through our PbSe colloidal quantum dot solid is chiefly responsible for the high external quantum efficiencies obtained in this new class of devices.

Colloidal semiconductor nanocrystals have shown great promise in functional devices such as solar cells and LEDs, but still relatively little is understood about the chemistry of their formation and resulting structure. In this thesis, we describe the results of our study of ultrathin Bi2S3 nanowires, part of the emerging class of materials at the transition from molecular scale clusters to nanowires, from a chemical perspective. Using a complementary suite of techniques, we propose an atomically precise model of the nanowires accounting for both the inorganic core structure and ligand-surface interaction for purified dispersions. The growth process of the nanowires was studied using in situ NMR on reaction mixtures and information on the growth and reactivity not attainable with purified dispersions was gained. The small molecule reactivity of the sulfur-oleylamine precursor was elucidated and it was shown that H2S is produced in situ leading to the formation of Bi2S3. This knowledge allowed for the extension of the sulfur-oleylamine precursor to SemSn-oleylamine, which produces H2S and H2Se in situ leading to the formation of homogeneous solid-solution PbSxSe1-x nanocrystals with tunable stoichiometry. Through this work, we elucidated each stage of the nanowire formation from small molecule reactivity, to growth process, to solution phase structure.

Colloidal semiconductor nanocrystals have shown great promise in functional devices such as solar cells and LEDs, but still relatively little is understood about the chemistry of their formation and resulting structure. In this thesis, we describe the results of our study of ultrathin Bi2S3 nanowires, part of the emerging class of materials at the transition from molecular scale clusters to nanowires, from a chemical perspective. Using a complementary suite of techniques, we propose an atomically precise model of the nanowires accounting for both the inorganic core structure and ligand-surface interaction for purified dispersions. The growth process of the nanowires was studied using in situ NMR on reaction mixtures and information on the growth and reactivity not attainable with purified dispersions was gained. The small molecule reactivity of the sulfur-oleylamine precursor was elucidated and it was shown that H2S is produced in situ leading to the formation of Bi2S3. This knowledge allowed for the extension of the sulfur-oleylamine precursor to SemSn-oleylamine, which produces H2S and H2Se in situ leading to the formation of homogeneous solid-solution PbSxSe1-x nanocrystals with tunable stoichiometry. Through this work, we elucidated each stage of the nanowire formation from small molecule reactivity, to growth process, to solution phase structure.