UC Riverside

One-dimensional (1-D) nanostructures, such as nanowires and nanotubes, are extremely attractive building blocks for electronics because of their small sizes, which provide for extremely high density devices, and their unique properties that emerge from increased surface to volume ratios. In addition their extremely high aspect ratios offer researchers the potential to build striped and coaxial structures with different components aligned along the cylindrical or radial axis of the wire, respectively. Composition modulation can be used to incorporate multiple functionalities from intrinsic properties of the material or through interfacial phenomena. However, spatial manipulation and the ability to assemble and position nanostructures in a controlled manner so they are registered to lithographically defined contacts is a critical step toward scalable integration in high-density nanodevices. In this dissertation a generalized template directed approach with ancillary assembly, contact, and displacement techniques were utilized to synthesize and characterize individual nanostructures from uniquely configured conducting polymer, magnetic, and semiconductor nanomaterials for sensor and spintronic applications.

Conducting polymers are particularly appealing because they exhibit tunable transport characteristics along with electronic, magnetic and optical properties of metals or semiconductors while retaining the attractive mechanical properties and processing advantages of polymers. In the first part of this work single component conducting polymer nanowires were electropolymerized, dielectrophoretically assembled, and contacted via maskless electrodeposition. Maskless electrodeposition was developed to selectively electrodeposit material on prefabricated microelectrode with no observable deposition on the conducting polymer nanowires, embedding the nanowire ends. Two different conducting polymers were investigated, polypyrrole (PPy) and polyethylendioxythiophene (PEDOT). Individual PPy nanowire devices demonstrated enhanced sensitivity to ammonia vapors, and PEDOT nanowire devices exhibited strong responses to volatile organic compounds. The gas sensing performances of these single nanowire devices were tuned by dopant type and synthesis conditions. Alternatively, single PEDOT nanowire devices were also completely coated in ferromagnetic material by implimenting non-selective electrodeposition. The magnetoresistance (MR) of these devices also displayed anomalous behavior, drastically deviating from typical anisotropic magnetoresistance responses. Additionally, multi-segmented noble/oxidizable nanowires were electrodeposited and subjected to galvanic displacement to create nanopeapod devices with Au peas and Te pods.