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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2019)

This dissertation is divided into two segments. The first segment focuses on the structural and electronic characterization of one-dimensional (1D) and two-dimensional (2D) nanostructures using scanning tunneling microscopy (STM) and spectroscopy (STS). The second segment focuses on the investigation of unique optical behavior in 1D-2D heterosystems using scattering-scanning near-field optical microscopy (s-SNOM).

Bottom-up synthesis from molecular precursors provides a useful methodology for designing and fabricating interesting nanomaterials. The first part describes application of bottom-up synthesis techniques to fabricate 1D nanostructures (graphene nanoribbons (GNRs)) and 2D networks (covalent organic frameworks (COF)). Following the synthesis, the structural and electronic properties of these nanomaterials were studied using STM and STS. In this dissertation, two specific GNR projects are discussed that provide in-detail investigation of the manipulation of the electronic properties of GNRs through the site-specific introduction of dopant atoms. The first project describes the detailed study of boron-doped N=7 AGNRs, where the AGNRs are substitutionally doped with boron atoms in their backbone. The second project focuses on the study of sulfur-doped N=13 GNRs, where the sulfur atoms substitutionally dope the edges of the GNRs. This dissertation also describes two COF projects that demonstrate the strong dependence of the electronic structure of single-layer COFs on the chemical bond arrangement within the covalent network. Specifically, the synthesis and characterization of two different porphyrin-based single-layer 2D COFs that exhibit symmetric (COF-366-OMe) and asymmetric (COF-420) bonding environments are studied.

The second part of the thesis describes investigation of the coupling between 1D plasmon polaritons in silver nanowires with 2D phonon polaritons of the silicon carbide (SiC) substrate. The silver nanowire-SiC hybrid structure was investigated using near-field infrared spectroscopy. A significant change in the 1D plasmon dispersion by the 2D phonon polaritons in SiC was observed upon approaching the SiC phonon polariton energies.

    Cover page: Local Probe Analysis of the Structural, Electronic, and Optical Properties of Nanomaterials
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2015)
    A fundamental requirement for the development of advanced electronic device architectures based on graphene nanoribbon (GNR) technology is the ability to modulate the band structure and charge carrier concentration by substituting specific carbon atoms in the hexagonal graphene lattice with p- or n-type dopant heteroatoms. Here we report the atomically precise introduction of group III dopant atoms into bottom-up fabricated semiconducting armchair GNRs (AGNRs). Trigonal-planar B atoms along the backbone of the GNR share an empty p-orbital with the extended π-band for dopant functionality. Scanning tunneling microscopy (STM) topography reveals a characteristic modulation of the local density of states along the backbone of the GNR that is superimposable with the expected position and concentration of dopant B atoms. First-principles calculations support the experimental findings and provide additional insight into the band structure of B-doped 7-AGNRs.
      Cover page: Site-Specific Substitutional Boron Doping of Semiconducting Armchair Graphene Nanoribbons
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2018)
      Bottom-up fabrication techniques enable atomically precise integration of dopant atoms into the structure of graphene nanoribbons (GNRs). Such dopants exhibit perfect alignment within GNRs and behave differently from bulk semiconductor dopants. The effect of dopant concentration on the electronic structure of GNRs, however, remains unclear despite its importance in future electronics applications. Here we use scanning tunneling microscopy and first-principles calculations to investigate the electronic structure of bottom-up synthesized N = 7 armchair GNRs featuring varying concentrations of boron dopants. First-principles calculations of freestanding GNRs predict that the inclusion of boron atoms into a GNR backbone should induce two sharp dopant states whose energy splitting varies with dopant concentration. Scanning tunneling spectroscopy experiments, however, reveal two broad dopant states with an energy splitting greater than expected. This anomalous behavior results from an unusual hybridization between the dopant states and the Au(111) surface, with the dopant-surface interaction strength dictated by the dopant orbital symmetry.
        Cover page: Concentration Dependence of Dopant Electronic Structure in Bottom-up Graphene Nanoribbons
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2016)
        Layer-stacking domain walls in bilayer graphene are emerging as a fascinating one-dimensional system that features stacking solitons structurally and quantum valley Hall boundary states electronically. The interactions between electrons in the 2D graphene domains and the one-dimensional domain-wall solitons can lead to further new quantum phenomena. Domain-wall solitons of varied local structures exist along different crystallographic orientations, which can exhibit distinct electrical, mechanical and optical properties. Here we report soliton-dependent 2D graphene plasmon reflection at different 1D domain-wall solitons in bilayer graphene using near-field infrared nanoscopy. We observe various domain-wall structures in mechanically exfoliated graphene bilayers, including network-forming triangular lattices, individual straight or bent lines, and even closed circles. The near-field infrared contrast of domain-wall solitons arises from plasmon reflection at domain walls, and exhibits markedly different behaviours at the tensile- and shear-type domain-wall solitons. In addition, the plasmon reflection at domain walls exhibits a peculiar dependence on electrostatic gating. Our study demonstrates the unusual and tunable coupling between 2D graphene plasmons and domain-wall solitons.
          Cover page: Soliton-dependent plasmon reflection at bilayer graphene domain walls
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2016)
          Substitutional doping of graphene nanoribbons (GNRs) with heteroatoms is a principal strategy to fine-tune the electronic structure of GNRs for future device applications. Here, we report the fabrication and nanoscale characterization of atomically precise N = 13 armchair GNRs featuring regioregular edge-doping with sulfur atoms (S-13-AGNRs) on a Au(111) surface. Scanning tunneling spectroscopy and first-principle calculations reveal modification of the electronic structure of S-13-AGNRs when compared to undoped N = 13 AGNRs.
            Cover page: Bottom-Up Synthesis of N = 13 Sulfur-Doped Graphene Nanoribbons
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