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Torsional instability in the single-chain limit of a transition metal trichalcogenide

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Science  20 Jul 2018:
Vol. 361, Issue 6399, pp. 263-266
DOI: 10.1126/science.aat4749

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Oscillating one-dimensional chains

The confinement of materials to nanoscale dimensions often reveals properties not seen in bulk materials. Pham et al. confined NbSe3 within carbon nanotubes (a conductor) or boron nitride nanotubes (an insulator). Transmission electron microscopy revealed an oscillatory motion of the confined chains not observed in bulk crystals. Electronic structure calculations showed that charge transfer drives the torsional wave instability, and the limited covalent bonding between the chains and the nanotube sheath allows unhindered dynamics. Application of an external potential applied to the nanotube should directly affect the torsion and thus lead to different optical and electron transport properties.

Science, this issue p. 263

Abstract

The scientific bounty resulting from the successful isolation of few to single layers of two-dimensional materials suggests that related new physics resides in the few- to single-chain limit of one-dimensional materials. We report the synthesis of the quasi–one-dimensional transition metal trichalcogenide NbSe3 (niobium triselenide) in the few-chain limit, including the realization of isolated single chains. The chains are encapsulated in protective boron nitride or carbon nanotube sheaths to prevent oxidation and to facilitate characterization. Transmission electron microscopy reveals static and dynamic structural torsional waves not found in bulk NbSe3 crystals. Electronic structure calculations indicate that charge transfer drives the torsional wave instability. Very little covalent bonding is found between the chains and the nanotube sheath, leading to relatively unhindered longitudinal and torsional dynamics for the encapsulated chains.

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