UC Berkeley

Fine control over material synthesis on the nanoscale can facilitate the stabilization of competing crystalline structures. Here, we demonstrate how carbon nanotube reaction vessels can be used to selectively create one-dimensional TaTe₃ chains or two-dimensional TaTe₂ nanoribbons with exquisite control of the chain number or nanoribbon thickness and width. Transmission electron microscopy and scanning transmission electron microscopy reveal the detailed atomic structure of the encapsulated materials. Complex superstructures such as multichain spiraling and apparent multilayer moirés are observed. The rare 2H phase of TaTe₂ (1H in monolayer) is found to be abundant as an encapsulated nanoribbon inside carbon nanotubes. The experimental results are complemented by density functional theory calculations for the atomic and electronic structure, which uncovers the prevalence of 2H-TaTe₂ due to nanotube-to-nanoribbon charge transfer and size confinement. Calculations also reveal new 1T' type charge density wave phases in TaTe₂ that could be observed in experimental studies.