Date of Award

1-1-2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Nanoscale Science and Engineering

Program

Nanoscale Sciences

Content Description

1 online resource (xiv, 87 pages) : color illustrations.

Dissertation/Thesis Chair

Carl A. Ventrice, Jr.

Committee Members

Nathaniel Cady, Anton deVilliers, Hassaram Bakhru, Vincent LaBella

Keywords

Decomposition, Disordering, Electron, Irradiation, Low-Energy, Self-Assembly, Monomolecular films, Self-assembly (Chemistry), Electrons, Thiols, Extreme ultraviolet lithography, Vapor-plating, Gold films

Subject Categories

Materials Science and Engineering

Abstract

Understanding the interaction of low energy electrons with organic thin films is important for the development of many technological applications, one of which is extreme ultra-violet (EUV, 92 eV) lithography. At this energy, the photon will produce an electron cascade that induces most of the chemical changes within the photoresist. In order to better understand these interactions, electron scattering experiments have been performed on self-assembled monolayers (SAMs) of the aliphatic molecule 1-decanethiol and the aromatic molecule 1,1’-biphenyl-4-thiol grown on Au(111) via vapor phase deposition. The molecules take on either a lying down (LD) or standing up (SU) geometry depending on coverage. The techniques used to explore these interactions include low-energy electron diffraction (LEED), temperature programmed desorption (TPD), and ex-situ X-ray photoelectron spectroscopy (XPS). The interaction of low energy electrons with the SAM can displace the molecules from their equilibrium positions and/or break bonds (C-S, C-C, C-H) within the molecule. From LEED, the crystal structure of both the LD phase and SU phase SAMs grown from both types of molecules is easily disrupted upon electron irradiation. For the LD phase of the aliphatic SAM, some of this disorder is reversible, whereas for the LD phase of the aromatic SAM it is permanent. Upon electron irradiation, changes in peak intensities and positions of the TPD and XPS spectra indicate that the C-S bonds are cleaved for both molecules. The sensitivity of the bonds within the hydrocarbon body of aliphatic molecule to electron beam damage depends on its orientation. In the SU phase, a large chemical shift in the C-1s and large reduction in the hydrocarbon fragments of the TPD spectra are observed, which indicates a large cross section for electron beam damage. The LD phase of the aliphatic molecule and both phases of the aromatic molecule show only subtle changes to the spectra. The relative insensitivity of these SAMs to electron beam damage is attributed to charge delocalization effects. For the LD phase of the aliphatic molecule, it is in direct contact with the metallic substrate. For the aromatic molecule, conjugated double bonds within the aromatic rings allow for excess charge delocalization, resulting in a lower probability for C-C bond breakage.

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