Graphene grown on hBN by MBE and the deposition of hexacontane on hBN

Diez Albar, Juan and UNSPECIFIED (2020) Graphene grown on hBN by MBE and the deposition of hexacontane on hBN. PhD thesis, University of Nottingham.

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Abstract

This thesis discusses the growth of graphene on hexagonal boron nitride (hBN) by high temperature molecular beam epitaxy (MBE) with three different carbon sources: a carbon filament, an atomic carbon source consisting of a thin Ta cylinder and an e-beam source. The flakes were transferred into sapphire wafers previously to graphene growth in order to serve as a refractory support. Graphene layers grown with the different sources present common features but also significant differences which are discussed.

Full graphene monolayers are investigated using atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and conductive AFM. Samples exhibit hexagonal Moiré patterns with periods that tend to increase with the substrate growth temperature from ~14 nm, corresponding to rotationally aligned graphene on hBN, to much larger periods ~75 nm. Shifted Raman peaks, obtained from these areas indicate that the graphene is under tensile strain.

Moreover, at the highest temperatures ~1700 ºC, we observe domains where graphene and hBN are lattice matched and the hexagonal boundaries of the Moiré patterns become Frenkel-Kontorova walls that run along principal crystal axes and terminate at lattice defects. Previous theoretical studies indicate that graphene lattice matched to hBN exhibits a small ~50 mV gap due to inversion symmetry breaking of the two atoms in the unit cell of graphene. Conductive AFM measurements obtained at these Frenkel-Kontorova walls and at the areas between them, which we presume are lattice matched, show a lower conductance at the latter compared to the former which is consistent with the opening of a small bandgap.

These results represent new approaches to the introduction of strain in graphene as well as the possibility of local modification of its electronic properties which may be useful for the fabrication of graphene devices.

The deposition of hexacontane (C60H122) on hBN is also studied in chapter 7. We observed lamellar structures similar to that formed by alkanes on graphite. The orientation of the molecule with respect to the hBN lattice was also studied by obtaining high resolution AFM images and computer simulations.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Beton, Peter
Sergei, Novikov
Keywords: Hexagonal boron nitride, hbn, Graphene, Hexacontane
Subjects: Q Science > QC Physics
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 60385
Depositing User: Diez Albar, Juan
Date Deposited: 16 Jul 2021 15:02
Last Modified: 16 Jul 2021 15:02
URI: http://eprints.nottingham.ac.uk/id/eprint/60385

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