Thursday 21 May 2015: Scanning transmission electron microscope imaging and analysis for optimising 2D crystal -graphene device heterostructures
Dr Sarah Haigh - University of Manchester, School of Materials Material Science Centre
HAR/170 (3D Visualisation Suite) 14:00-15:30
Sarah Haigh , Fred Withers , Aidan Rooney  , Roman Gorbachev , Andre Geim , Konstantin Novoselov 
School of Materials, University of Manchester, Manchester, UK
 School of Physics and Astronomy, University of Manchester, Manchester, UK
By combining different two dimensional crystals within a Van der Waals heterostructure stack it is possible to produce devices with bespoke electronic bandstructures and advanced functionality. The individual crystal layers are produced by mechanical exfoliation and layered sequentially onto a Si substrate. Despite the necessity of employing polymeric support layers that are deposited and removed as part of the transfer procedure, our cross sectional high resolution scanning transmission electron microscope (STEM) imaging has revealed that the heterostructure stacks form large areas of pristine synthetic crystal, free from hydrocarbon contaminants at the atomic scale (Haigh, et al. Nat Mater, 2012, 11, 764; Georgiou et al. Nat. Nano., 2013, 8, 100). More recently we have applied this technique to study photonic devices incorporating transition metal dichalcogenides. For example, we demonstrate that STEM imaging is unique in being able to obtain critical information on the width of the h-BN tunnelling barriers as well as on the thickness and uniformity of MoS2 layers for a multiple quantum well LED heterostructure (Withers et al., Nat Mater, 2015). Examples of high resolution STEM characterisation to study nanoscale compositional segregation in 3D and transformations during in situ heating for noble metal nanoparticles will also be presented.