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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2023)

Plasmonic nanoparticles are known for their unique optical properties originating from the localized surface plasmon resonance. Assembling plasmonic nanoparticles into secondary superstructures induces plasmonic coupling, producing tunable optical properties. However, current assembly strategies lack dynamic control over the assembly, limiting real-time applications. Magnetic assembly has proven to be an effective strategy to manipulate the interaction between magneto-plasmonic nanoparticles, generating dynamically tunable optical properties featuring fast response, full reversibility, and remote control. This dissertation focuses on developing optically functional nanostructures by magnetically assembling plasmonic nanoparticles into secondary superstructures. In the first part, one-dimensional (1D) plasmonic photonic crystals with angular-dependent structural colors are fabricated by assembling magneto-plasmonic nanoparticles under an external magnetic field. Different from conventional 1D photonic crystals, the assembled 1D nanochains show angular-dependent colors from the selective activation of photonic diffraction and plasmonic scattering. In the second part, we develop magnetically tunable plasmonic chiral nanostructures by assembling magneto-plasmonic nanoparticles under a helical magnetic field from a cubic permanent magnet. The handedness and magnitude and position of the resulting circular dichroism (CD) spectra can be dynamically tuned by the orientation and strength of the helical magnetic field. In addition, we find that the chiral nanostructures are not formed from the helical alignment of magneto-plasmonic nanoparticles, but instead, the nanoparticles align along the magnetic field direction to form 1D linear periodic nanochains, which further assemble into chiral superstructures under the helical magnetic field. This assembly incorporates plasmonic coupling, photonic diffraction, and chirality into a single system, allowing multi-mode colors with selective activation and dynamic tunability. Furthermore, this helical magnetic assembly method is developed to fabricate chiral luminescent nanostructures by assembling magneto-luminescent hybrid clusters under the helical magnetic field, realizing magnetically tunable circularly polarized luminescence. In the last part, we develop a general strategy for fabricating plasmonic chiral nanostructures by stacking polymer films containing magnetically assembled linear plasmonic nanochains and further demonstrate dynamic control over the chiral optical properties by controlling the stacking angle. Overall, the magnetic assembly of plasmonic nanoparticles generates novel optical properties with dynamic tunability, promising for color displays, sensors, and optical devices.

    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2023)
    The wide accessibility to nanostructures with high uniformity and controllable sizes and morphologies provides great opportunities for creating complex superstructures with unique functionalities. Employing anisotropic nanostructures as the building blocks significantly enriches the superstructural phases, while their orientational control for obtaining long-range orders has remained a significant challenge. One solution is to introduce magnetic components into the anisotropic nanostructures to enable precise control of their orientations and positions in the superstructures by manipulating magnetic interactions. Recognizing the importance of magnetic anisotropy in colloidal assembly, we provide here an overview of magnetic field-guided self-assembly of magnetic nanoparticles with typical anisotropic shapes, including rods, cubes, plates, and peanuts. The Review starts with discussing the magnetic energy of nanoparticles, appreciating the vital roles of magneto-crystalline and shape anisotropies in determining the easy magnetization direction of the anisotropic nanostructures. It then introduces superstructures assembled from various magnetic building blocks and summarizes their unique properties and intriguing applications. It concludes with a discussion of remaining challenges and an outlook of future research opportunities that the magnetic assembly strategy may offer for colloidal assembly.
      Cover page: Magnetically Induced Anisotropic Interaction in Colloidal Assembly.
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2023)
      Steelmaking contributes 8% to the total CO2 emissions globally, primarily due to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable performance because the dominant gas-solid reduction mechanism is set by the defects and pores inside the mm- to nm-sized oxide particles that change significantly as the reaction progresses. While these governing dynamics are essential to establish continuous flow of iron and its ores through reactors, the direct link between agglomeration and chemistry is still contested due to missing measurements. In this work, we directly measure the connection between chemistry and agglomeration in the smallest iron oxides relevant to magnetite ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we resolve the formation and consumption of wüstite (Fe1-xO)-the step most commonly attributed to whiskering. Using X-ray diffraction, we resolve crystallographic anisotropy in the rate of the initial reaction. Complementary imaging demonstrated how the particles self-assemble, subsequently react, and grow into elongated whisker structures. Our insights into how morphologically uniform iron oxide particles react and agglomerate in H2 reduction enable future size-dependent models to effectively describe the multiscale aspects of iron ore reduction.
        Cover page: Correlating chemistry and mass transport in sustainable iron production.
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