Matthias Batzill
In this tutorial talk, I am introducing the concept of van der Waals epitaxy of transition metal dichalcogenides (TMDs) and the endeavor of finding potentially ferromagnetic 2D materials. Epitaxial mono- or few-layer films allow detailed measurement of electronic structure by angle resolved photoemission and thus determine layer dependent properties and the role of interlayer interactions of the properties. In addition, scanning tunneling microscopy can give information on the growth process and defect structures in the films. We discuss selected cases of TMDs. For VSe2 we suggest a competition between charge density and ferromagnetic ordering for the ground state. While in CrTe2 the ground state may be the semiconducting 1H-phase rather than the sought metallic and possibly ferromagnetic 1T-phase. Formation of ultrathin intercalation compounds are also discussed as a potential ultrathin ferromagnets. Finally, we discuss properties of defects in TMDs and how these may help in inducing magnetic properties. The incorporation of magnetic dopants may be one approach and recent reports suggest the possibility of diluted ferromagnetic 2D semiconductors. While there are many unanswered questions, a controlled vacuum synthesis and characterization of monolayer materials is an important aspect to find new materials.