Browsing by Subject "Functional materials"
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Item Creating more effective functional materials: altering the electronics of conducting metallopolymers for different applications.(2014-05) Raiford, Matthew Thomas; Holliday, Bradley J.; Humphrey, Simon M; Anslyn, Eric V; Jones, Richard A; Freeman, Benny DConducting metallopolymers possess attractive electronic properties for use in sensors, photoelectronic devices, catalysts, and other applications. Modification of the conducting polymer backbone, through chemical or electrochemical methods, enables control of catalytic, electronic, and optical properties of the metal via inductive modulation of the electron density. Understanding in detail the relationship between the metal and polymer backbone could lead to more effective metallopolymer materials. We hope to study this relationship by probing the band gaps, excited state energy levels, catalytic activity, and sensor function in four metallopolymer systems. Devices with sub-stochiometric ratios of Cu2ZnSnS4 NPs (CZTS: (Cu2Sn)1-xZn1/xS)(0≥x≥0.75)) grown in Cu(II) conducting metallopolymers were produced to study band gap tuning in hybrid materials. The valence and conductance bands of CZTS (x = 0.60) aligned with the HOMO/LUMO of the Cu(II) metallopolymer. Changing the alignment facilitated charge transfer in the hybrid material, leading to photovoltaic materials with efficiencies of ~0.1%. Chemoresistive ionophore sensors were developed by incorporating selective binding groups, such as thiourea, into conducting polymer backbones. Thiourea monomers and polymers showed high selectivity for Pb(II) ions over many competitive ions. XPS experiments demonstrated that reversible chelation of Pb(II) ions could be achieved through a simple uptake/rinse process. The conductivity of the thiourea polymer increased fifty-fold, from 7.75×10−2 S/cm2 to 3.5 S/cm2, after Pb(II) exposure. Sensitivity measurements indicated the sensors have limits of detection near 10−10 M. Highly conjugated ligands were synthesized to explore effective sensitization of visible and near-IR emitting lanthanides. (3,4-ethylenedioxy)thiophene was appended to dipyridophenazine and dipyridoquinoxaline to introduce a group that could be easily electropolymerized. These bi-functional ligands emitted from π-π* and an inter-ligand charge transfer excited states, and therefore, two distinct triplet states were observed. These separate energy pathways allowed for efficient sensitization of both visible (Tb(III), Eu(III), Dy(III)) and near-IR emitting (Nd(III), Yb(III), Er(III)) ions. Finally, we explored the oxidation of a rhodium-containing conducting metallopolymer and the subsequent effect on the activity of the metal center. Oxidation of the backbone led to ancillary ligand attenuation, allowing for control of the catalytically active species in the conducting metallopolymer. Rh(I,III) monomer and metallopolymer catalytic studies showed potential for new heterogenous/homogeneous hybrid catalysts.Item Nanoelectronics based on epitaxial oxides(2015-08) Hu, Ph. D., Chengqing; Yu, Edward T.; Lee, Jack C; Register, Leonard F; Ekerdt, John G; Sun, NanCrystalline oxide materials and heterostructures have been under extensive investigation owing to the richness of the physical, chemical, and electrical properties they exhibit, including ferromagnetism, ferroelectricity, ferrotoroidicity, superconductivity, metal-insulator transition, multiferroics, and 2-dimensional electron liquids. In recent years, the advancement of thin film growth techniques such as molecular beam epitaxy and atomic layer deposition has made possible monolithic integration of these crystalline oxide materials with mainstream semiconductor substrate materials such as Si and Ge, which opens new avenues for improving existing device performance and provides many opportunities for adding various solid-state device functionalities to electronic devices that are unachievable with conventional semiconductor materials. Epitaxial oxide heterostructures with a perovskite crystal structure are emerging as outstanding candidates for realization of devices in which diverse material properties - ferromagnetism, piezoelectricity, ferroelectricity, and others - are flexibly coupled to achieve new functionality. In the first part of this dissertation, the strain-dependent ferromagnetism in LaCoO3, piezoelectric response in SrTiO3, and their strain coupling in a single-crystal oxide heterostructure grown on Si (001) are employed to enable a novel approach to modulating ferromagnetism and magnetoresistance by application of a gate voltage in a suitably fabricated device. The second part of the dissertation addresses the resistive switching behavior and physics of epitaxial single-crystal anatase TiO2 on silicon and demonstrates several unique advantages of using single-crystal metal oxide films as an active switching layer, including a high ON/OFF ratio, a great potential for device scaling, highly linear current-voltage characteristics, and room-temperature, reproducible quantization of conductance, etc. Finally, epitaxial SrHfO3-based gate stacks for Ge metal-oxide-semiconductor devices are investigated as an approach to alleviate the gate dielectric interface quality problem that has tremendously hampered the adoption of next-generation Ge-based transistors. Different methods are shown to effectively decrease the interface trap density, and the gate stacks developed in this dissertation represent the state of the art in terms of the combination of equivalent oxide thickness and gate leakage. In summary, this dissertation presents several results in the design and modeling, process integration, characterization, and analysis of device prototypes for functional and nano- electronics applications using epitaxial oxide films. These results provide a foundation for further exploration of solid-state device applications using epitaxial crystalline oxide materials.