Transition metal dichalcogenides (TMDs) are layered materials with the general chemical formula of MX2, where M is a transition metal (e.g. Mo, Ti, Ta, V) and X is a chalcogen (S, Se, Te). Each slab is composed of a covalently bonded sandwich of a sheet of metal atoms and two hexagonal planes of the calcogen atoms. The adjacent layers are held together by week Van der Waals interactions to form the bulk crystal in different polytopes which vary in stacking orders and metal atom coordination.
This chemically versatile family of materials spans the entire range of electronic structures, from insulator to metal, and hosts a number of interesting properties such as charge density wave (CDW) modulations, orbital ordering and superconductivity. These materials are the subject of intense studies both in bulk and exfoliated few layer forms.
Similarly to graphene, dichalcogenides can be exfoliated to few layer thin forms. The reduced thickness results in confinement and inverse pressure effects that drive changes in various physical properties. The chemical diversity of this family allows the tuning of these properties.
We study thickness dependent properties like electronic bandgap and CDW formation temperature, e.g. in MoS2 and VSe2. In-situ and ex-situ micro-mechanically exfoliated specimens are both in the scope of interest as well as gated structures of thin films grown by chemical vapor deposition.