| AVS 66th International Symposium & Exhibition | |
| 2D Materials | Tuesday Sessions |
| Session 2D+AS+MI+NS-TuM |
| Session: | 2D Materials Characterization including Microscopy and Spectroscopy |
| Presenter: | Sarah Haigh, University of Manchester, UK |
| Correspondent: | Click to Email |
Scanning Transmission Electron Microscopy (STEM) is one of the few techniques able to probe the structure and chemistry of 2D materials when these are stacked to form vertical heterostructures. By combining STEM with electron energy loss spectroscopy and energy dispersive X-ray spectroscopy it is possible to characterise individual point defects,[1] to measure interlayer distances for dissimilar materials [2] and to investigate the microstructure of mechanically deformed structures at the atomic scale [3]. We have extensively employed plan view and cross sectional STEM imaging to investigate complex 2D heterostructures. For example, we have shown that protruding defects prevent the realisation of pristine interfaces between transition metal selenides (MoSe2, WSe2, NbSe2) and boron nitride, unless exfoliation is performed in an inert environment.[2]
We have analysed microstructures produced when 2D van der Waals materials (graphite, boron nitride, MoSe2) are subjected to mechanical deformation and find that the types of defect can be predicted from just the bend angle and thickness of the materials.[3] In particular we find that above a critical thickness the materials exhibit numerous twin boundaries and for large bend angles these can contain nanoscale regions of local delamination. Such features are proposed to be important in determining how easily the material can be thinned by mechanical or liquid exfoliation.[3]
2D material heterostructures are also enabling new STEM imaging capabilities. We show they can be used as a platform to study real time reactions in liquid environments with unprecedented spatial resolution and spectroscopic capabilities [4]. We further demonstrate that graphene encapsulation allows imaging of point defect dynamics, structural degradation and mechanically induced stacking faults in 2D monochalcogenides, GaSe and InSe [1].
References
[1] D G Hopkinson et al, ACS Nano, (2019) 10.1021/acsnano.8b08253
[2] A P Rooney et al. Nano Letters, (2017) 17, 5222.
[3] A P Rooney et al. Nature Communications (2018) 9, 3597
[4] D J Kelly et al Nano Letters, (2018) 18, 2, 1168