Subnanometer-Wide Indium Selenide Nanoribbons.

Indium selenides (InSe) have been shown to retain several desirable properties, such as ferroelectricity, tunable photoluminescence through temperature-controlled phase changes, and high electron mobility when confined to two dimensions (2D). In this work we synthesize single-layer, ultrathin, subnanometer-wide InSe by templated growth inside single-walled carbon nanotubes (SWCNTs). Despite the complex polymorphism of InSe we show that the phase of the encapsulated material can be identified through comparison of experimental aberration-corrected transmission electron microscopy (AC-TEM) images and AC-TEM simulations of known structures of InSe. We show that, by altering synthesis conditions, one of two different stoichiometries of sub-nm InSe, namely InSe or β-InSe, can be prepared. Additionally, AC-TEM heating experiments reveal that encapsulated β-InSe undergoes a phase change to γ-InSe above 400 °C. Further analysis of the encapsulated species is performed using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and Raman spectroscopy, corroborating the identities of the encapsulated species. These materials could provide a platform for ultrathin, subnanometer-wide phase-change nanoribbons with applications as nanoelectronic components.