TWO-DIMENSIONAL MATERIALS BEYOND GRAPHENE: SYNTHESIS, ATOMIC-SCALE CHARACTERIZATION, AND APPLICATIONS

Restricted (Penn State Only)
Author:
Azizi, Amin
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 05, 2016
Committee Members:
  • Nasim Alem, Dissertation Advisor
  • Nasim Alem, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Joan Marie Redwing, Committee Member
  • Joshua Alexander Robinson, Outside Member
Keywords:
  • Two-dimensional materials
  • Chemical vapor deposition (CVD)
  • Electron microscopy
  • Two-dimensional alloys
  • van der Waals heterostructures
  • Atomic Structure
  • Defects
Abstract:
Two-dimensional (2D) crystals are atomically thin materials that enable fabrication of flexible and unconventional devices. They offer a wide range of physical and chemical properties that can be engineered for practical applications, such as ultrafast transistors, efficient catalysts and solar cells, flexible and transparent displays, and LEDs. Advances in designing new structures from 2D crystals promise to extend this field even further. This thesis will present tunable synthesis of 2D crystals, atomic-scale characterization of 2D structures and their defects, in addition to their applications in energy storage devices. Large-area 2D hexagonal boron nitride (h-BN) crystals with tunable morphology and thickness are synthesized using a controlled low-pressure chemical vapor deposition (LPCVD). State-of-the-art aberration-corrected electron microscopy with sub-angstrom resolution is used to probe atomic structure, chemistry and optical properties of 2D structures. Different approaches, by which the already remarkable properties of 2D crystals can be further tuned, based on understanding defect structures and dynamics in 2D crystals, creating vertical heterostructures by stacking individual 2D crystals one atop the other, and doping/alloying of 2D crystals, will be discussed. Additionally, this thesis will present a potential application of the CVD-synthesized h-BN films in capacitive energy storage devices. A simple and versatile approach for coating polymer dielectrics with large-area CVD-grown h-BN films will be demonstrated, through which their capacitive energy storage performance at high temperatures is significantly improved in comparison to pristine polymer materials.