Angstrom-scale imaging of 2D molecular materials via scanning transmission electron microscopy and ptychography
Kharel, Priti
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/127332
Description
Title
Angstrom-scale imaging of 2D molecular materials via scanning transmission electron microscopy and ptychography
Author(s)
Kharel, Priti
Issue Date
2024-10-23
Director of Research (if dissertation) or Advisor (if thesis)
Huang, Pinshane
Doctoral Committee Chair(s)
Murphy, Catherine Jones
Committee Member(s)
Lopez, Joaquin Rodriguez
Zuo, Jian-Min
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
structure determination
molecular crystals
covalent organic framework
3D structure
scanning transmission electron microscopy
atomic resolution
stacking disorder
Abstract
Accurate structural determination of 2D molecular materials is crucial for their development and application across diverse fields, including biomedicine, energy storage, and electronics. However, conventional diffraction-based techniques often provide limited structural information, particularly for systems such as thin films, polycrystalline particles, and nanopowders— forms in which many 2D molecular materials are commonly synthesized. This thesis presents a direct approach for resolving structures of such 2D molecular materials using scanning transmission electron microscopy (STEM) to image atomic connectivity and higher-order 3D structures. We address the longstanding challenges of radiation damage and weak electron scattering through a multi-pronged strategy that includes using protective graphene substrates, low-dose imaging, maximizing signal to noise ratio in the images, and advanced data processing. In atomically thin 2D small molecular crystals, our methods yield elementally sensitive images with a resolution of up to 1.3 Å, enabling the distinction of light elements such as carbon and nitrogen. When applied to 2D covalent organic frameworks (2D COFs), we uncover significant disorder in inter-layer stacking with nanometer-scale offsets, challenging their previous depictions as average eclipsed structure. Using multi-slice electron ptychography, we extend our imaging to three dimensions, revealing the 3D arrangement of COF layers and distortions in the shape of the pore channels that are critical for their charge and mass transport applications. Overall, this thesis introduces powerful new direct techniques for the structural characterization of 2D molecular materials, providing synthetic chemists and materials scientists with an invaluable tool for ab initio structure determination and accurate exploration of structure-property relationships.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.