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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2017)

This thesis describes three experimental thrusts applying nanotechnology to develop novel tools for the life sciences.

Part I (chapters 2 and 3) covers the development of a graphene based nanofluidic platform for in-situ electron microscopy. The Graphene Flow Cell (GFC), as we have referred to it, consists of a nanofluidic channel integrated into a SiN/SiO2/SiN stack on a Silicon chip, with a layer of graphene sealing the channel. The graphene serves as an electron transparent membrane as well as a scavenger of oxidative radicals during imaging. We discuss the fabrication and testing of the GFC, as well as a few demonstrations of its capabilities. The GFC outperforms commercial nitride cells in resolution and contrast, and allows for the introduction of reactants

during imaging and precise control of sample concentration, features sealed liquid cell architectures lack. These advantages have already allowed for advances in our understanding of nanobubble geometry and stability, as well nanoparticle dynamics. Finally, we discuss some future applications and improvements for the GFC.

Part II (chapters 4 and 5) discusses work towards carbon nanotube intracellular neural electrodes. Due to their nanoscale nature, extreme aspect ratios, and unique mechanical and electrochemical properties, carbon nanotubes make an ideal electrophysiological probe. We demonstrated their capability using a single-unit probe device, and further demonstrated that such a probe is scalable, having the potential to record from a high-density of neurons in a small volume. We walk through the micro- and nano-fabrication considerations in developing such a probe, and progress we have made towards this aim. Finally, we discuss an alternative application of CNTs as neural probes, using them to bias plasmonic nanoparticles to create a voltage sensitive optical probe.

Finally, Part III (chapters 6 and 7) covers ongoing work applying atomically precise nanopores in hexagonal boron nitride (hBN) to DNA sequencing. Previous work out of our lab has demonstrated that defects in hBN introduced by electron beam irradiation grow in atomically-quantized metastable triangles. Taking advantage of this property, it is possible to produce individual triangular nanopores in hBN with atomically precise diameters. This precision allows us to create nanopores for DNA sequencing in which the pore size is tailored to the size of DNA strands. Currently, solid-state nanopore sequencing has been limited by the speeds at which DNA passes through the pore, as well as limited blocking current signatures of the nucleotide bases. Atomically precise pores address both of these issues and will likely mark a significant advance in the field. We cover the progress we have made towards this goal, as well

as aims that are still outstanding.

    Cover page: Applications of Nanotechnology to the Life Sciences
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    We demonstrate the fabrication of individual nanopores in hexagonal boron nitride (hBN) with atomically precise control of the pore size. Previous methods of pore production in other 2D materials create pores of irregular geometry with imprecise diameters. By taking advantage of the preferential growth of boron vacancies in hBN under electron beam irradiation, we are able to observe the pore growth via transmission electron microscopy, and terminate the process when the pore has reached its desired size. Careful control of beam conditions allows us to nucleate and grow individual triangular and hexagonal pores with diameters ranging from subnanometer to 6nm over a large area of suspended hBN using a conventional TEM. These nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation. Furthermore, the chemical edge-groups along the hBN pores can be made entirely nitrogen terminated or faceted with boron-terminated edges, opening avenues for tailored functionalization and extending the applications of these hBN nanopores.
      Cover page: Fabrication of Atomically Precise Nanopores in Hexagonal Boron Nitride
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2017)
      We demonstrate the fabrication of individual nanopores in hexagonal boron nitride (h-BN) with atomically precise control of the pore shape and size. Previous methods of pore production in other 2D materials typically create pores with irregular geometry and imprecise diameters. In contrast, other studies have shown that with careful control of electron irradiation, defects in h-BN grow with pristine zig-zag edges at quantized triangular sizes, but they have failed to demonstrate production and control of isolated defects. In this work, we combine these techniques to yield a method in which we can create individual size-quantized triangular nanopores through an h-BN sheet. The pores are created using the electron beam of a conventional transmission electron microscope; which can strip away multiple layers of h-BN exposing single-layer regions, introduce single vacancies, and preferentially grow vacancies only in the single-layer region. We further demonstrate how the geometry of these pores can be altered beyond triangular by changing beam conditions. Precisely size- and geometry-tuned nanopores could find application in molecular sensing, DNA sequencing, water desalination, and molecular separation.
        Cover page: Fabrication of Subnanometer-Precision Nanopores in Hexagonal Boron Nitride
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2016)
        Chemists have developed mechanistic insight into numerous chemical reactions by thoroughly characterizing nonequilibrium species. Although methods to probe these processes are well established for molecules, analogous techniques for understanding intermediate structures in nanomaterials have been lacking. We monitor the shape evolution of individual anisotropic gold nanostructures as they are oxidatively etched in a graphene liquid cell with a controlled redox environment. Short-lived, nonequilibrium nanocrystals are observed, structurally analyzed, and rationalized through Monte Carlo simulations. Understanding these reaction trajectories provides important fundamental insight connecting high-energy nanocrystal morphologies to the development of kinetically stabilized surface features and demonstrates the importance of developing tools capable of probing short-lived nanoscale species at the single-particle level.
          Cover page: Single-particle mapping of nonequilibrium nanocrystal transformations
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