FROM VAN DER WAALS TO COULOMBIC HETEROSTRUCTURES: UNDERSTANDING CHARGE TRANSFER IN 2D MATERIALS

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  • March 20, 2019
Creator
  • Woomer, Adam
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Innovations in semiconductor technologies, such as transistors, photovoltaics, and light-emitting diodes, require materials with highly designed properties. Zero-dimensional quantum dots and one-dimensional conjugated polymers are ideal building blocks for engineered three-dimensional materials because of their size-dependent quantum-confined optoelectronic properties, however, two-dimensional materials have been largely unexplored. Here I show that reassembled films of 2D semiconductors retain their quantum-confined properties due to turbostratic disorder and interlayer contaminants, yet are still electrically conductive. I designed uniaxially pressure and temperature-dependent van der Pauw conductivity measurements to determine that charge transport proceeds via hopping, with an activation energy expected for nanoparticle systems. In this manner, we can design 3D materials with virtually any optoelectronic propertie with the appropriate choice of 2D material and thickness. I next introduce a new class of materials, called Coulombic heterostructures. As opposed to the familiar van der Waals heterostructures, in which van der Waals forces dominate the interlayer space of stacked 2D materials, Coulombic heterostructures exhibit massive charge transfer and Coulombic forces between layers. These materials take advantage of the ultra-low work function and anionic electron gas of electrenes to form quasi-bonds between adjacent flakes. With interlayer distances smaller than van der Waals bonds yet larger than ionic and covalent bonds, Coloumbic heterostructures fall within the van der Waals gap, a largely unexplored region of materials. I then highlight the exciting new properties that can result from the assembly of Coulombic heterostructures, including superlubricity, defect free doping, formation of electron-donor adducts, and tuning of intercalation voltages for battery applications.
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  • In Copyright
Advisor
  • Warren, Scott
  • You, Wei
  • Cahoon, James
  • Dingemans, Theo
  • Atkin, Joanna
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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