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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2018)

Chip-scale integrated light sources are a crucial component in a broad range of photonics applications. III-V semiconductor nanowire emitters have gained attention as a fascinating approach due to their superior material properties, extremely compact size, and capability to grow directly on lattice-mismatched substrates including silicon. However, their practical applications are still in the early stages due to the difficulties in achieving high-performance nanowire emitters and integrating nanowire emitters with photonic platforms. In this dissertation, we demonstrate III-V nanowire-based lasers monolithically integrated on silicon-on-insulator (SOI) platforms, which can be potentially employed for chip-scale optical communications and photonic integrated circuits. For this, selective-area epitaxy of InGaAs nanowires on 3D structured SOI platforms is developed by catalyst-free metal-organic chemical vapor deposition. Nanowires are precisely positioned on 3D structures, including waveguides and gratings, with nearly 100 % nanowire growth yield and wide bandgap tuning ranges. Next, nanowire array-based bottom-up photonic crystal cavities are demonstrated on SOI substrates. InGaAs/InGaP core/shell nanowire arrays form 1D and 2D photonic crystal cavities on SOI layers, and single-mode room-temperature lasing from these bottom-up cavities is achieved by optically pumping the nanowire arrays. We also show that the nanowire array lasers are effectively coupled with SOI waveguides, which is achieved by integrating bottom-up nanowires on pre-patterned SOI platforms. The lasing wavelengths of nanowire array lasers are in the ranges of 1,100–1,440 nm, which covers telecommunication wavelengths, all operating at room temperature. It is also shown that arrays of proposed lasers with individually tunable wavelengths can be integrated on a single chip by lithographically tuning the cavity geometries. In summary, the III-V nanowire lasers on silicon demonstrated in this dissertation represent a new platform for ultracompact and energy-efficient light sources for silicon photonics and unambiguously point the way toward practical and functional nanowire lasers.

    Cover page: III-V semiconductor nanowire lasers on silicon
    • Article
    • Peer Reviewed
    LBL Publications (2021)
    Sulfur(VI) fluoride exchange (SuFEx) click chemistry has offered a facile and reliable approach to produce polysulfates and polysulfonates. However, the current SuFEx polymerization methods lack precise control of target molecular weight and dispersity. Herein, we report the first chain-growth SuFEx polycondensation process by exploiting the unique reactivity and selectivity of S-F bonds under SuFEx catalysis. Given the higher reactivity of iminosulfur oxydifluoride versus fluorosulfate, the chain-growth SuFEx polycondensation is realized by using an iminosulfur oxydifluoride-containing compound as the reactive chain initiator and deactivated AB-type aryl silyl ether-fluorosulfates bearing an electron-withdrawing group as monomers. When 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was utilized as the polymerization catalyst, precise control over the polymer molecular weight and polydispersity was achieved. The resulting polymers possess great thermal stability but are easily degradable under mild acidic and basic conditions.
      Cover page: Chain-Growth Sulfur(VI) Fluoride Exchange Polycondensation: Molecular Weight Control and Synthesis of Degradable Polysulfates
      • Article
      • Peer Reviewed
      LBL Publications (2021)
      Sulfur(VI) fluoride exchange (SuFEx) is a category of click chemistry that enables covalent linking of modular units through sulfur(VI) connective hubs. The efficiency of SuFEx and the stability of the resulting bonds have led to polymer chemistry applications. Now, we report the SuFEx click chemistry synthesis of several structurally diverse SOF4-derived copolymers based on the polymerization of bis(iminosulfur oxydifluorides) and bis(aryl silyl ethers). This polymer class presents two key characteristics. First, the [-N=S(=O)F-O-] polymer backbone linkages are themselves SuFExable and undergo precise SuFEx-based post-modification with phenols or amines to yield branched functional polymers. Second, studies of individual polymer chains of several of these new materials indicate helical polymer structures. The robust nature of SuFEx click chemistry offers the potential for post-polymerization modification, enabling the synthesis of materials with control over composition and conformation.
        Cover page: SuFExable polymers with helical structures derived from thionyl tetrafluoride
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2023)
        High capacity polymer dielectrics that operate with high efficiencies under harsh electrification conditions are essential components for advanced electronics and power systems. It is, however, fundamentally challenging to design polymer dielectrics that can reliably withstand demanding temperatures and electric fields, which necessitate the balance of key electronic, electrical and thermal parameters. Herein, we demonstrate that polysulfates, synthesized by sulfur(VI) fluoride exchange (SuFEx) catalysis, another near-perfect click chemistry reaction, serve as high-performing dielectric polymers that overcome such bottlenecks. Free-standing polysulfate thin films from convenient solution processes exhibit superior insulating properties and dielectric stability at elevated temperatures, which are further enhanced when ultrathin (~5 nm) oxide coatings are deposited by atomic layer deposition. The corresponding electrostatic film capacitors display high breakdown strength (>700 MV m-1) and discharged energy density of 8.64 J cm-3 at 150 °C, outperforming state-of-the-art free-standing capacitor films based on commercial and synthetic dielectric polymers and nanocomposites.
          Cover page: High-performing polysulfate dielectrics for electrostatic energy storage under harsh conditionsCreative Commons 'BY' version 4.0 license
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