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Modifying the Fermi level density of states in graphene

Lingmei Kong, University of Nebraska - Lincoln

Abstract

My investigation of graphene on different substrates demonstrates that there is a large variation of interfacial charge transfer between graphene and various substrates. Inverse photoelectron spectroscopy (IPES) measurements of CVD grown single layer graphene on BN(0001)/Ru(0001), Ru, Ni(poly), and Cu(poly) indicate a substrate-to-graphene charge transfer of approximately 0.07, 0.06, 0.03 e- per carbon atom respectively and a charge transfer of 0.02 e- from graphene to the MgO substrate per carbon atom. Investigation of graphene on two different oxide substrates demonstrates that graphene on MgO could be used as the extreme limit of a narrow channel semiconductor and may have application in a field effect transistor (FET) because of a 0.5-1.0 eV band gap. This band gap is induced in graphene on MgO, but this is not evident for graphene on CO3O4/Co. There is induced antiferromagnetic ordering for the graphene on Co3O 4(111)/Co(111) structure.^ Five different p-quinonoid zwitterionic type molecules, with a large intrinsic dipole of 10 Debyes, were also deposited on graphene on Cu to study the modification on the electronic structures of graphene. The investigation of three such adsorbates (butyl zwitterion, methoxybenzyl zwitterion and methylbenzyl zwitterion) indicates photoemission and inverse photoemission final states are more weakly screened for these dipolar molecules on graphene than that on gold. This is evident in the much larger highest occupied molecular orbitals (HOMO) to the lowest unoccupied molecular orbital (LUMO) gap for the molecules on graphene than that on gold. This suggested that graphene is chemically inert, which was also confirmed by the very slight changes in the graphene Raman peak position and relative intensities with the adsorption. However, the adsorption of TCNE and TCNQH functionalized butyl zwitterion molecules exhibit strong intermolecular interactions and island growth pattern, which is consistent with the electronic structure seen in photoemission and inverse photoemission. The HOMO-LUMO gaps adsorbed on graphene are more or less the same as that on gold for both of the two cases, indicating the almost equal strong interaction with the both gold and graphene, but in fact suggestive of far stronger intermolecular interactions.^

Subject Area

Physics, Condensed Matter|Engineering, Materials Science

Recommended Citation

Kong, Lingmei, "Modifying the Fermi level density of states in graphene" (2012). ETD collection for University of Nebraska - Lincoln. AAI3546675.
http://digitalcommons.unl.edu/dissertations/AAI3546675

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