Center for Functional Nanomaterials Seminar

Abstract Interest in layered heterostructures of two-dimensional materials has generated many investigations of interlayer transport phenomena. Tunneling transport between two layers of graphene or 2D semiconducting transition metal dichalcogenides (TMDs) separated by a thin insulator can exhibit negative differential resistance, and steep-switching in transistor applications. However, these tunneling characteristics are highly dependent on atomic details of the heterostructure interfaces. Low-energy electron microscopy (LEEM) is a fast method for probing the top few atomic layers of crystalline surfaces with 10-nm-scale lateral resolution and sensitivity to such details. In this study, LEEM is employed to measure crystal orientation, electrostatic potential variations, and interfacial dipole formation in heterostructures of graphene and TMDs. For MBE-formed WSe2 on epitaxial graphene on SiC in particular, I show that work function differences between the graphene and TMD depend on the surface reconstruction of the SiC below. Furthermore, interlayer transport between the graphene and WSe2 is rectifying in some cases and ohmic in others, with LEEM revealing the underlying mechanism. Interlayer tunneling is similarly expected to depend on properties measurable in LEEM, and these LEEM methods are broadly applicable to many 2D heterostructures of general interest. Host: Jurek Sadowski