One-dimensional and branched gold nanostructures grown directly on surfaces: Assembly, patterning, alignment, formation of heterojunctions, and analytical applications.

摘要

This dissertation describes (1) the wet chemical synthesis, patterning, and alignment of Au nanorods (Au NRs) and synthesis of branched Au nanostructures directly on surfaces by seed-mediated growth, (2) the direct growth of nanoscale one-dimensional heterojunctions between Au NRs, carbon nanotubes, and GaAs nanowires (GaAs NWs) directly on surfaces by combining seed-mediated growth and chemical assembly with vapor-phase synthesis, and (3) the use of Au nanorods and branched Au structures in electrochemical, electronic-based sensing, and surface-enhanced Raman spectroscopy (SERS) applications. These studies are important for realizing the goal of future incorporation of one-dimensional (1D) nanostructures into functional nanodevices.; We synthesized Au NRs from surface-attached Au nanoparticles (Au NPs), controlling the length and aspect ratio (AR) by variation of the synthetic conditions as well as the growth time. We also manipulated Au NRs on surfaces by pushing short and breaking long AR NRs. Control over the shape of nanostructures to form branched structures occurs by seed alteration or further modification of the synthetic conditions.; Patterning of Au NP seeds led to the fabrication of well-defined patterns of Au NRs over large areas and the yield of NRs was greatly improved from 8 to 38% by removal of other shapes with the use of adhesive tape.; We used a simple surface chemical amidation reaction to grow Au NRs with controlled orientation. This procedure led to alignment of 80% of Au NRs on the surface within a range of 30°. The alignment is influenced by the surface chemistry and type of substrate used.; Seed-mediated growth on vapor phase grown carbon nanotubes and GaAs NWs led to metal-carbon and metal-semiconductor junctions. We also combined particle assembly and vapor growth to form carbon-semiconductor junctions.; Finally, electrochemical sensing of FeCN64-, dopamine, and ascorbic acid with Au NRs grown on carbon fiber (CF) electrodes show a high reduction in capacitive current when compared to bare CF. The resistance of an individual Au NR connected electrochemically with nanoscale contacts was highly sensitive to chemisorbed molecules, which could serve as an electronic-based sensor. SERS revealed a greater enhancement of the Raman signal by branched Au nanostructures versus Au NRs.