Exploring structural and electronic heterogeneity in nanoscale systems using scanning tunneling microscopy
Wallum, Alison
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https://hdl.handle.net/2142/122159
Description
Title
Exploring structural and electronic heterogeneity in nanoscale systems using scanning tunneling microscopy
Author(s)
Wallum, Alison
Issue Date
2023-11-30
Director of Research (if dissertation) or Advisor (if thesis)
Gruebele, Martin
Doctoral Committee Chair(s)
Gruebele, Martin
Committee Member(s)
Lyding, Joseph W
van der Veen, Renske M
Girolami, Gregory S
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
scanning tunneling microscopy
excited state imaging
low-dimensional carbon materials
quantum dots
Abstract
In this thesis, we outline application of scanning tunneling microscopy (STM) to investigate local variations in the structural and electronic characteristics of materials on the nanoscale. The high spatial resolution of STM combined with its ability to simultaneously collect structural and electronic measurements allows for comprehensive characterization of materials at sub-nm resolution. These features make STM particularly well suited for investigating heterogeneities inherent in nanomaterials and functionalized surfaces, which often make it difficult to develop a complete picture of structure-property relationships from ensemble properties. The following research focuses on applying STM and optically-assisted STM to probe local changes in electronic and optical properties of (1) inorganic nanocrystals, (2) low-dimensional carbon materials, and (3) functionalized and patterned surfaces.
We begin by discussing applications of STM and the broader field of excited state imaging, outlining the motivation and challenges of studying nanomaterials and patterned surfaces using these techniques (Chapter 1). We then present application of single-molecule absorption STM (SMA-STM) to investigate excited state interactions of nanomaterials, highlighting experiments probing and modeling interactions between carbon nanotubes and optically excited quantum dots. This work ultimately identifies local features of these systems that dictate the polarization of CNTs in the presence of a proximally excited quantum dot (Chapter 2). Following this, we outline studies focused on showing local changes in the band structure and enhanced absorption of PbS nanocrystals decorated with PDI ligands. Alongside probing properties of functionalized nanocrystals, this work demonstrates early examples of applying ambient SMA-STM for single- particle excited state imaging experiments (Chapter 3). Next, we map structural and electronic features of anthracene functionalized silicon surfaces to better understand how electronic coupling contributes to the energetic landscape of these systems, and then characterize quantitative structural features of patterned metallic glasses (Chapter 4). We then discuss efforts to probe optical and electronic characteristics of low-dimensional carbon materials. This includes deconvoluting optical and electronic properties of carbon dots from properties associated with byproducts produced during bottom-up solvothermal syntheses, followed by structural characterization of carbon nitride and furan-derived nanothreads (Chapter 5). Finally, in addition to research centered around STM, we outline the development and implementation of a modern teaching laboratory in collaboration with local community colleges. This work takes data science techniques used in our research to analyze and simplify complicated data and adapts them to a teaching lab for early undergraduate education (Chapter 6).
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