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Title: Characterisation of buried interfaces in van der Waals materials by cross sectional scanning transmission electron microscopy
Author: Rooney, Aidan
ISNI:       0000 0004 7225 3285
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Graphene and other two-dimensional materials can be stacked together to form vander Waals heterostructures: synthetic crystals composed of different atomically thin layers with a bespoke electronic band structure. Structural characterisation of vander Waals heterostructures is difficult using conventional methods as the properties are almost entirely defined by the nature of the buried interfaces between dissimilar crystals. These methods also fall short of resolving the atomic structure of buried defects in van der Waals materials such as graphite. This work demonstrates the refinement and successful application of ion beam specimen preparation to produce cross sectional slices through these unique crystals so that they can be characterised by high resolution scanning transmission electron microscopy (STEM). Cross sectional specimen were prepared using in situ lift-out in a focused ion beam (FIB) dual-beam instrument. The fine polishing steps were optimised to prevent damage to the core of the specimen. High resolution STEM imaging of twin defects in graphene, hexagonal boron ni-tride and MoSe2 revealed that the boundaries are not atomically sharp but extended across many atoms. Advanced processing and analysis of these images uncovered fundamental mechanics which govern their geometry. This technique was further applied to complex transition metal dichalcogenide heterostructures to quantitatively determine the properties of buried interfaces between atomically thin crystals.
Supervisor: Haigh, Sarah Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TEM ; Nanomaterials ; FIB ; 2D materials ; Graphene ; Electron Microscopy