Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2009)

Science technologies have been in pursuit of smaller, faster and more efficient devices and enormous efforts made by myriad numbers of scientists have provided us with electronics in reduced volumes with improved performances. Miniaturization of electronic circuits down to micrometer scale has been well-developed as industrial processes and it is easy to witness electronic products containing integrated circuits consisted of microstructures in our everyday life. However, miniaturization of circuit components down to nanometer scale has revealed new challenges not only for difficult handling of diminutive structures but also for unusual physical properties of nanomaterials.

Countless numbers of conventional chemical and physical studies have been dedicated to exploit the benefit of the unique properties of nanostructures by developing efficient techniques for controlled synthesis and assembly of nanostructures. However, environmental concerns of using toxic solvent systems and high energy-consuming processes, and pursuit of highly selective molecular interactions for highly precise assemblies have averted the eyes of scientists to biological materials. Biorecognition properties of biological materials are attractive for achieving programmed self-assembly of nanostructures and biomolecules with metal-reducing ability are very inviting for developments of environmentally-acceptable synthesis processes.

In the light of above discussion, this thesis takes the advantages of biological approaches to assemble and synthesize inorganic nanostructures in a controlled manner. DNA was used for the assembly processes due to their facilities of sequence programming and chemical modifications. Spatially controlled assembly of multi-segmented Au/Pd/Au nanowires across gold electrodes has been demonstrated using thiolated DNA strands functionalized on the gold surface of nanowires and electrodes. Electron transport properties of DNA-assisted assembled nanowires were demonstrated showing negligible blocking effect by DNA layers hybridized between nanowires and electrodes. The assembled Au/Pd/Au nanowire was used for hydrogen sensing manifesting the applicability of DNA-assisted assembly to build functional nanodevices.

Amino acids are essential as building blocks for proteins and for metabolisms. Recently, amino acids have been given another important role as a reducing and capping agent for the synthesis of gold nanostructures. Amino acid-mediated synthesis of gold nanostructures has been demonstrated showing the capability of biological approaches to synthesize single crystalline gold nanostructures in 0-D, 1-D and 2-D dimensions by manipulating the reaction environment. Structural changes of gold nanostructures due to the speciation of gold complexes were systematically demonstrated by altering solvent conditions. The effect of the side chains of amino acids on the structural features of gold nanostructures was systematically demonstrated. Distinguished electron transport properties were observed for single crystalline nanoribbons showing resistivity lower by an order of magnitude than polycrystalline counterparts. Rapid reversible room temperature H2S gas sensor was fabricated using AC aligned gold nanoparticle ar

    Cover page: Biological Assembly and Synthesis of Inorganic Nanostructures
    • Article
    • Peer Reviewed
    UC Santa Barbara Previously Published Works (2015)
    The optical resonances of plasmonic nanostructures depend critically on the geometrical details of the absorber. We show that this unique property of plasmons can potentially be used to create panchromatic absorbers covering most of the useful solar spectrum, by measuring the light-to-hydrogen conversion capabilities of a series multielectrode photocatalytic devices, based on functionalized gold nanorods of appropriately chosen aspect ratios. Judiciously combining nanorods of various aspect ratios almost doubles the H2 production of the device over what is optimally possible with a device using gold nanorods of a single aspect ratio (all other key parameters being equal). The estimated quantum efficiency (absorbed photons-to-hydrogen) averaged over the entire solar spectrum of the best performing plasmonic multielectrode array was approximately 0.1%, and the measured H2 production rate for all of the devices was found to be approximately proportional to the hot electron generation. The device was monitored continuously for over 200 hr of operation without measurable diminution in the rate.
      Creative Commons 'BY-NC-ND' version 4.0 license
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2014)
      The conversion of sunlight into electricity by photovoltaics is currently a mature science and the foundation of a lucrative industry. In conventional excitonic solar cells, electron-hole pairs are generated by light absorption in a semiconductor and separated by the "built in" potential resulting from charge transfer accompanying Fermi-level equalization either at a p-n or a Schottky junction, followed by carrier collection at appropriate electrodes. Here we report a stable, wholly plasmonic photovoltaic device in which photon absorption and carrier generation take place exclusively in the plasmonic metal. The field established at a metal-semiconductor Schottky junction separates charges. The negative carriers are high-energy (hot) electrons produced immediately following the plasmon's dephasing. Some of the carriers are energetic enough to clear the Schottky barrier or quantum mechanically tunnel through it, thereby producing the output photocurrent. Short circuit photocurrent densities in the range 70-120 μA cm(-2) were obtained for simulated one-sun AM1.5 illumination with devices based on arrays of parallel gold nanorods, conformally coated with 10 nm TiO2 films and fashioned with a Ti metal collector. For the device with short circuit currents of 120 μA cm(-2), the internal quantum efficiency is ∼2.75%, and its wavelength response tracks the absorption spectrum of the transverse plasmon of the gold nanorods indicating that the absorbed photon-to-electron conversion process resulted exclusively in the Au, with the TiO2 playing a negligible role in charge carrier production. Devices fabricated with 50 nm TiO2 layers had open-circuit voltages as high as 210 mV, short circuit current densities of 26 μA cm(-2), and a fill factor of 0.3. For these devices, the TiO2 contributed a very small but measurable fraction of the charge carriers.
        Creative Commons 'BY-NC-ND' version 4.0 license
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2013)
        Efficient and cost-effective conversion of solar energy to useful chemicals and fuels could lead to a significant reduction in fossil hydrocarbon use. Artificial systems that use solar energy to produce chemicals have been reported for more than a century. However the most efficient devices demonstrated, based on traditionally fabricated compound semiconductors, have extremely short working lifetimes due to photocorrosion by the electrolyte. Here we report a stable, scalable design and molecular level fabrication strategy to create photoelectrochemically active heterostructure (PAH) units consisting of an efficient semiconductor light absorber in contact with oxidation and reduction electrocatalysts and otherwise protected by alumina. The functional heterostructures are fabricated by layer-by-layer, template-directed, electrochemical synthesis in porous anodic aluminum oxide membranes to produce high density arrays of electronically autonomous, nanostructured, corrosion resistant, photoactive units (~10(9)-10(10) PAHs per cm(2)). Each PAH unit is isolated from its neighbor by the transparent electrically insulating oxide cellular enclosure that makes the overall assembly fault tolerant. When illuminated with visible light, the free floating devices have been demonstrated to produce hydrogen at a stable rate for over 24 h in corrosive hydroiodic acid electrolyte with light as the only input. The quantum efficiency (averaged over the solar spectrum) for absorbed photons-to-hydrogen conversion was 7.4% and solar-to-hydrogen energy efficiency of incident light was 0.9%. The fabrication approach is scalable for commercial manufacturing and readily adaptable to a variety of earth abundant semiconductors which might otherwise be unstable as photoelectrocatalysts.
          Creative Commons 'BY-NC-ND' version 4.0 license
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2018)
          Tin-based chalcogenide semiconductors, though attractive materials for photovoltaics, have to date exhibited poor performance and stability for photoelectrochemical applications. Here, a novel strategy is reported to improve performance and stability of tin monosulfide (SnS) nanoplatelet thin films for H2 production in acidic media without any use of sacrificial reagent. P-type SnS nanoplatelet films are coated with the n-CdS buffer layer and the TiO2 passivation layer to form type II heterojunction photocathodes. These photocathodes with subsequent deposition of Pt nanoparticles generate a photovoltage of 300 mV and a photocurrent density of 2.4 mA cm-2 at 0 V versus reversible hydrogen electrode (RHE) for water splitting under simulated visible-light illumination (λ > 500 nm, Pin = 80 mW cm-2). The incident photon-to-current efficiency at 0 V versus RHE for H2 production reach a maximum of 12.7% at 575 nm with internal quantum efficiency of 13.8%. The faradaic efficiency for hydrogen evolution remains close to unity after 6000 s of illumination, confirming the robustness of the heterojunction for solar H2 production.
            Cover page: Earth‐Abundant Tin Sulfide‐Based Photocathodes for Solar Hydrogen Production
            • Article
            • Peer Reviewed
            UC Santa Barbara Previously Published Works (2013)
            Nanostructured Schottky inorganic-organic solar cells provide overall power conversion efficiencies exceeding 3%, with extremely large short-circuit photocurrents. The device EQE faithfully tracks the absorptance of the CdSe nanorods, and the IQE is approximately constant over the entire visible spectrum as opposed to a p-n junction hybrid solar cell fabricated with a highly absorbing organic polymer.
              Cover page: High‐Efficiency Panchromatic Hybrid Schottky Solar CellsCreative Commons 'BY-NC-ND' version 4.0 license
              • Article
              • Peer Reviewed
              UC Santa Barbara Previously Published Works (2017)
              We present a sensitive and quantitative protein detection assay that can efficiently distinguish between specific and nonspecific target binding. Our technique combines dual affinity reagents with surface-enhanced Raman spectroscopy (SERS) and chemometric analysis. We link one Raman reporter-tagged affinity reagent to gold nanoparticles and another to a gold film, such that protein-binding events create a "hot spot" with strong SERS spectra from both Raman reporter molecules. Any signal generated in this context is indicative of recognition by both affinity labels, whereas signals generated by nonspecific binding lack one or the other label, enabling us to efficiently distinguish true from false positives. We show that the number of hot spots per unit area of our substrate offers a quantitative measure of analyte concentration and demonstrate that this dual-label, SERS-linked aptasensor assay can sensitively and selectively detect human α-thrombin in 1% human serum with a limit of detection of 86 pM.
                Cover page: Dual-reporter SERS-based biomolecular assay with reduced false-positive signalsCreative Commons 'BY-NC-ND' version 4.0 license
                • Article
                • Peer Reviewed
                LBL Publications (2017)
                We report on the synthesis and characterization of bent-core liquid crystal (LC) compounds and the preparation of mixtures that provide an optically isotropic antiferroelectric (OI-AFLC) liquid crystal display mode over a very wide temperature interval and well below room temperature. From the collection of compounds synthesized during this study, we recognized that several ternary mixtures displayed a modulated SmCaPA phase down to below -40 °C and up to about 100 °C on both heating and cooling, as well as optical tilt angles in the transformed state of approximately 45° (optically isotropic state). The materials were fully characterized and their liquid crystal as well as electro-optical properties analyzed by polarized optical microscopy, differential scanning calorimetry, synchrotron X-ray diffraction, dielectric spectroscopy, and electro-optical tests.
                  • Article
                  • Peer Reviewed
                  UC Santa Barbara Previously Published Works (2014)
                  An approach based on a solution-based synthesis that produces a thermally stable Ag/oxide/S₂ Te₃ -Te metal-semiconductor heterostructure is described. With this approach, a figure of merit of zT = 1.0 at 460 K is achieved, a record for a heterostructured material made using wet chemistry. Combining experiments and theory shows that the large increase in the material's Seebeck coefficient results from hot carrier filtering.
                    Cover page: Hot carrier filtering in solution processed heterostructures: a paradigm for improving thermoelectric efficiency.Creative Commons 'BY-NC-ND' version 4.0 license
                    Top