Probing the Electronic Properties in Superatomic Van der Waals Semiconductors

Wed, Apr 10, 2019, 11:00 am

Two-dimensional van der Waals materials built from clusters featuring atomic precision instead of simple atoms have attracted great attention due to their emergent physical properties and flexibility of surface functionalization. In this talk, I will describe two van der Waals materials derived from the Chevrel phases. The strong in-plane covalent bonding and weak interlayer interactions allow exfoliating them down to few layers. Their unique electronic properties are characterized by using scanning tunneling microscopy/spectroscopy, photoluminescence, polarization dependent Raman spectroscopy and first principles calculations. In Re6Se8Cl2, I determine the electronic bandgap, optical bandgap and thus the exciton binding energy. The latter is as large as 100 meV, which is consistent with the partially 2D nature of the exciton. In Mo6S3Br6, I determine its robust 2D semiconducting character and strong in-plane structural and electronic anisotropy. The complex, hierarchical structures with 2D characters in these two materials suggest an exciting new strategy to design 2D materials with multi-functionality and desired electronic properties.