Synthesis and structural characterization of the single chain limit of van der Waals materials

The successful isolation of a single layer of van der Waals (vdW) materials, such as graphene and transition metal dichalcogenides (TMDs), and the renewed interests in their emergent properties in the atomically thin limit have motivated the exploration of other vdW materials. Transition metal trichalcogenides (TMTs), such as niobium triselenide (NbSe₃), are closely related quasi one-dimensional (1-D) vdW materials consisting of trigonal prismatic chains binding together by weak vdW interaction. The bulk TMTs abound with peculiar properties, such as sliding charge density wave and superconductivity.
In our talk, I will present our recent effort in isolation and study of the single chain of these 1-D vdW materials encapsulated within carbon and boron nitride nanotubes. In the single chain limit of NbSe₃, we found an unusual structural helical torsional wave not seen in bulk NbSe₃ crystal, by aberration-corrected transmission electron microscopy (TEM). Density functional theory (DFT) calculation shows that the charge transfer from the encapsulating nanotubes to the single chain induces such torsional wave. We term the phenomenon Charge-induced Torsional Wave (CTW). I will also discuss our efforts in synthesis of other TMTs, beyond NbSe₃, in the single chain limit.