MBE Growth and Characterization of Graphene on Well-Defined Cobalt Oxide Surfaces: Graphene Spintronics without Spin Injection Page: I

Olanipekun, Opeyemi B. MBE Growth and Characterization of Graphene on Well-
Defined Cobalt Oxide Surfaces: Graphene Spintronics without Spin Injection. Doctor of
Philosophy (Chemistry), August 2017, 88 pp., 3 tables, 49 figures, chapter references.
The direct growth of graphene by scalable methods on magnetic insulators is important
for industrial development of graphene-based spintronic devices, and a route towards substrate-
induced spin polarization in graphene without spin injection. X-ray photoelectron spectroscopy
(XPS), low energy electron diffraction LEED, electron energy loss spectroscopy (EELS) and
Auger electron spectroscopy (AES) demonstrate the growth of Co304(1 11) and CoO(1 11) to
thicknesses greater than 100 A on Ru(0001) surfaces, by molecular beam epitaxy (MBE). The
results obtained show that the formation of the different cobalt oxide phases is 02 partial
pressure dependent under same temperature and vacuum conditions and that the films are
stoichiometric. Electrical I-V measurement of the Co304(111) show characteristic hysteresis
indicative of resistive switching and thus suitable for advanced device applications. In addition,
the growth of Coo.5Feo.50(111) was also achieved by MBE and these films were observed to be
OH-stabilized. C MBE yielded azimuthally oriented few layer graphene on the OH-terminated
CoO(111), Coo.5Feo.50(111) and Co304(111). AES confirms the growth of (111)-ordered sp2 C
layers. EELS data demonstrate significant graphene-to-oxide charge transfer with Raman
spectroscopy showing the formation of a graphene-oxide buffer layer, in excellent agreement
with previous theoretical predictions. XPS data show the formation of C-O covalent bonding
between the oxide layer and the first monolayer (ML) of C. LEED data reveal that the graphene
overlayers on all substrates exhibit C3V. The reduction of graphene symmetry to C3V -
correlated with C-O bond formation - enables spin-orbit coupling in graphene. Consequences
may include a significant band gap and room temperature spin Hall effect - important for

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Olanipekun, Opeyemi B. MBE Growth and Characterization of Graphene on Well-Defined Cobalt Oxide Surfaces: Graphene Spintronics without Spin Injection, dissertation, August 2017; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc1011813/m1/2/ocr/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; .

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