Molecular spintronics: design, fabrication, and characterization Public Deposited

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  • March 21, 2019
Creator
  • Niskala, Jeremy Russell
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • A great deal of organic spintronics has been centered on spuncoat polymeric or thermally deposited organic materials. In contrast, few studies have focused on spin behavior through molecular layers covalently bound to electrodes such as with self-assembled monolayers (SAMs) formed on ferromagnetic metals. The reason for this is twofold; a) SAM formation methods on ferromagnetic electrodes have not been thoroughly developed, and b) forming electrical contact to molecular layers is not a trivial pursuit. The work herein is dedicated to the design, fabrication, and characterization of metal-molecule-metal (MMM) junctions for their eventual application in molecule-based spin-electronics. Firstly, SAM formation via thiol and isocyanide attachment chemistry on Ni, Co, and Fe thin films was examined under both inert and atmospheric conditions in an attempt to form pristine, oxide free monolayers. In addition, a broadly applicable electrochemical technique was developed to remove native oxides from ferromagnetic surfaces prior to the formation of high surface coverage SAMs on thin, evaporated metal films. The SAMs prepared under electroreduction conditions were found to rival those prepared under inert conditions in a glovebox. MMM junctions were fabricated by forming SAM arrays in lithographically defined wells within a photoresist followed by coating with the conductive polymer blend poly(3,4-ethylenedioxythiophene) stabilized with poly(4-styrenesulphonic acid) (PEDOT:PSS). PEDOT:PSS protected the monolayer prior to the thermal deposition of a top metal electrode and yielded promising tunneling characteristics through alkanedithiols; however, magnetotransport was never witnessed. A soft lithographic technique called nanotransfer printing (nTP) was developed to print metal thin film electrodes (Au, Ni, and Co) directly atop molecular monolayers formed on SAM coated metal electrodes. Junctions by this technique were studied by conductive atomic force microscopy and showed scalable tunneling characteristics through alkanedithiols monolayers based on tunneling distance (i.e., molecule length) and tunneling area (i.e., printed feature size). Permanent MMM junctions by nTP were fabricated by registered lithography atop large area (greater than or equal to 50 mu m) printed electrodes followed by the deposition of a top gold electrode. Tunneling characteristics were interpreted using the Simmons model.
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  • "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry."
Advisor
  • Meyer, Thomas
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  • Chapel Hill, NC
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  • Open access
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