prof. dr hab. Janusz Sadowski
(Institute of Physics P.A.S., Department of Physics University of Warsaw,  Department of Physics and Electrical Engineering, Linnaeus University, Kalmar, Sweden)

Transition metal dichalcogenides and topological semimetals grown by Van der Waals epitaxy

Seminar on-line

Abstract

Recent research activity focused on transition metal dichalcogenide (TMD) layered materials, enabling acquiring extremely thin flakes via exfoliation from bulk crystals, brought attention of the research community to the possibilities of epitaxial growth of TMDs. Even though the exfoliated TMD flakes are suitable for research purposes, they are not much useful for application-ready optoelectronic devices, since it is not possible to control their shapes and dimensions. That's why the epitaxial growth techniques came into play. The lattice parameters of the most common TMDs are close to 0.35 nm, hence there is no suitale (cheap) substrate material for TMD deposition, but in contrast to the conventional epitaxy the lattice matching between TMD layer and the substrate is not important, the only condition is the common symmety of both lattices.

I will show two examples of TMDs - MoTe₂ and NiTe₂ grown by molecular beam epitaxy on GaAs(111) substrates, and an example of a transition meta pnictide (TaAs) grown on GaAs(001). TMDs grow on GaAs in a proper Van der Waals epitaxy mode. The case of TaAs can be described as a pseudo Van der Waals epitaxy, since the structure of this material is closed to but not completely layered. All three above mentioned materials are topological semimetals. MoTe2 in one of its polytypes is a Weyl semimetal (WSM), NiTe₂ is a Dirac semimetal (DSM), and TaAs is a WSM. Since the electrical properties of topological semimetals are to very much extent dependent on a magnetic field, the possibility of the epitaxial growth of DSM and WSM opens a way of integrating them in heterostructures with ferromagnets and antiferromagnets and use of magnetic proximity effects.

Link to video presentation