Large-Area Atomic Layers of the Charge-Density-Wave Conductor TiSe2

Abstract

Layered transition metal (Ti, Ta, Nb, etc.) dichalcogenides are important prototypes for the study of the collective charge density wave (CDW). Reducing the system dimensionality is expected to lead to novel properties, as exemplified by the discovery of enhanced CDW order in ultrathin TiSe₂. However, the syntheses of monolayer and large-area 2D CDW conductors can currently only be achieved by molecular beam epitaxy under ultrahigh vacuum. This study reports the growth of monolayer crystals and up to 5 × 10⁵ µm² large films of the typical 2D CDW conductor—TiSe₂—by ambient-pressure chemical vapor deposition. Atomic resolution scanning transmission electron microscopy indicates the as-grown samples are highly crystalline 1T-phase TiSe₂. Variable-temperature Raman spectroscopy shows a CDW phase transition temperature of 212.5 K in few layer TiSe₂, indicative of high crystal quality. This work not only allows the exploration of many-body state of TiSe₂ in 2D limit but also offers the possibility of utilizing large-area TiSe₂ in ultrathin electronic devices.

Large-area 2D charge-density-wave (CDW) conductor TiSe₂ films are synthesized under ambient pressure by chemical vapor deposition. Low-temperature Raman measurement provides spectroscopic evidence that CDW order still emerges in monolayer TiSe₂ and survives to a higher temperature than thick samples. This work offers the possibility of utilizing large-area TiSe₂ in ultrathin electronic devices.

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