Materials Science Research Lecture
Abstract: 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 both peculiar ground state and unusual collective excitation, such as sliding charge density wave and superconductivity.
In my 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 transferred 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.
More About the Speaker: Thang Pham is currently a postdoc researcher at MIT working with Prof. Frances M. Ross on developing a new gas-phase in-situ transmission electron microscopy technique to study the growth of various quantum oxide nanowires via vapor-liquid-solid mechanism. He earned his B.S. (Summa Cum Laude) in Materials Science and Engineering from Hanoi University of Technology, Vietnam in 2011. He then obtained his M.S. and Ph.D. in Materials Science and Engineering at the University of California at Berkeley under the guidance of Prof. Alex Zettl. His doctoral work focused on synthesis and transmission electron microscopy of hexagonal boron nitride nanostructures and transition metal trichalcogenides in the single chain limit. His awards include Intel Awards for Young Engineers, Honda Young Engineers and Scientists (Honda YES) Award, R&D 100 Award, and Outstanding Graduate Student Instructor at UC Berkeley.