Lateral and Vertical Graphene/Hexagonal Boron Nitride Heterostructures Grown by Molecular Beam Epitaxy

Thomas, James C. (2021) Lateral and Vertical Graphene/Hexagonal Boron Nitride Heterostructures Grown by Molecular Beam Epitaxy. PhD thesis, University of Nottingham.

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This thesis discusses the investigation of graphene/ hexagonal Boron Nitride (hBN)heterostructures grown by Sergei V. Novikov and Tin S. Cheng using molecular beam epitaxy (MBE), with a focus on measurements recorded using atomic force microscopy (AFM), in particular conductive AFM (CAFM). MBE is a relatively uncommon deposition technique for graphene growth that offers a route to scaleable high quality material. In this thesis three different carbon sources have been used to grow strained graphene samples at high temperature (up to ~ 1700 degC) on exfoliated hBN flakes. These samples have been subsequently analysed using a range of techniques including AFM, CAFM, lateral force microscopy (LFM), Raman spectroscopy, and angle resolved photoemission spectroscopy (ARPES). A particular focus is placed on the recorded strain of these structures, measured with the aid of the hexagonal graphene/hBN moiré superlattice pattern formed at the interface of the stacked 2D structure. In order to carry out the CAFM measurements shown, electrical contacting procedures have been developed as part of this work in order to measure electrically isolated graphene/ hBN regions. The most prominent of these methods has been the deposition of a conductive silver nanowire networking layer.

During AFM contact mode scanning the appearance of a graphene/ hBN moiré pattern deformation that follows the tip scan direction was observed and has been investigated. Large differences between trace (forward scan) and retrace (backwards scan) imaging have been seen in the resulting moiré pattern. These differences have been explained by considering the strong tip-surface interaction between the probe and the graphene surface, along with the large locally applied pressure exerted by the tip that increases the graphene/ hBN van derWaals interaction.

Using an electron beam carbon source for MBE graphene growth, a high level of precision has been achieved that has allowed for narrow graphene bands with uniform and tuneable widths below 20 nm to be grown along hBN step edges and around hBN islands. These graphene nanoribbons have formed lateral graphene/ hBN junctions on hBN material produced within the same system using plasma assisted MBE,

demonstrating successful sequential growth of these heterostructures. Investigations of these samples are carried out within this thesis, along with a potentially useful hydrogen etching method for hBN that could be used as a lithographic technique in conjunction with these samples.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Beton, Peter H.
Novikov, Sergei V.
Keywords: Graphene, conductive AFM, CAFM, atomic force microscopy, AFM, Boron Nitride, hBN, MBE growth, high strain, heterostructure, lattice matching, moire pattern, moire deformation, step-flow growth, lateral heterostructures
Subjects: Q Science > QC Physics > QC501 Electricity and magnetism
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 64262
Depositing User: Thomas, James
Date Deposited: 18 Jan 2024 16:08
Last Modified: 18 Jan 2024 16:08

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