Investigating Band Structure Modifications in 2D Materials and Heterostructures via Scanning Tunneling Microscopy and Spectroscopy

Abstract

This thesis explores structural and electronic properties of 2D crystals and van der Waals heterostructures (vdWH) at the nanometre scale. In particular, the experiments presented characterize modifications to the local density of states induced by defects, moiré potentials, or by disrupted topological order of surface states. Such structures can be utilized as part of a platform to explore physics phenomena by tuning interlayer interactions, which can lead to emergent properties previously only accessible in more complicated systems. Bulk 2D crystals are explored using scanning-probe techniques, with the intent of learning and applying their characteristics to tailored van der Waals heterostructures. Room temperature and low temperature ultrahigh vacuum scanning probe microscopy (scanning tunneling microscopy and spectroscopy) is used as the primary characterization method.

The main results in this thesis are: (a) observations and characterization of the local lattice defects in bulk semiconducting transition metal dichalcogenides (TMDs) by scanning tunneling microscopy and spectroscopy (STM/S), (b) the development of a fabrication technique for creating atomically clean van der Waals heterostructures, (c) an example of such a device through STM/S measurement of a graphene-rhenium disulfide heterostructure, and (d) scanning tunneling microscopy and spectroscopy study of bulk crystals of antiferromagnetic topological insulator, MnBi₂Te₄, where the spatial heterogeneity of the spectroscopic features are investigated.

Altogether, these results establish groundwork for building more complex heterostructures which are suitable for scanning probe experiments and assist in exploring fundamental physics phenomena through the moiré framework.