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https://hdl.handle.net/2142/84325
Description
Title
Optically-Assisted Scanning Tunneling Microscopy
Author(s)
Carmichael, Erin Suzanne
Issue Date
2008
Doctoral Committee Chair(s)
Martin Gruebele
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Scanning tunneling microscopy (STM) consistently provides the highest spatial resolution among the scanning probe methods, allowing surfaces to be investigated on the atomic level. With the addition of optical excitation, STM promises to become a powerful technique for single molecule spectroscopy, enabling one to examine the response of single molecules on a surface. Atomic scale laser-assisted STM has thus far remained an elusive goal, with few recent experiments reaching sub-nanometer resolution. This is due to the many difficulties faced as a result of light perturbing the tunneling junction. The combination of a novel rear-illumination geometry with frequency-modulated laser excitation allows measurement of single molecule optical absorption by detecting modulations in the local electronic density of states with near atomic resolution. This new technique is used to probe the optical absorption of single-walled carbon nanotubes on silicon surfaces, providing data that illustrates unambiguous detection of single molecule optical absorption. Additionally, the deposition of ultrathin gold films is investigated as a potential transparent conductive substrate for use in optical STM experiments performed at visible excitation wavelengths. Roughness is evaluated as a function of film thickness and trends demonstrate a transition from kinetic roughening to thermal roughening that is highly dependent on the deposition temperature profile.
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