Thermodynamic Favorability of the 1T Phase over the 1H Phase in Group III Metal Monochalcogenide Zigzag Nanoribbons

TL;DR

This study uses ab initio simulations to show that 1T phase nanoribbons of group III-VI materials are more thermodynamically stable than 1H phase, with implications for their synthesis and optoelectronic properties.

Contribution

It provides the first systematic comparison of thermodynamic stability between 1T and 1H phase nanoribbons of group III-VI materials using density functional theory.

Findings

1T phase nanoribbons are more stable than 1H phase up to 34 nm width.

1T nanoribbons remain semiconducting with Mexican-hat-shaped valence bands.

Hydrogenation energies of 1T InSe nanoribbons are positive.

Abstract

Owing to the promising optoelectronic and thermoelectric properties of two-dimensional (2D) group III-VI materials (MXs), their nanoribbons (NRs) have attracted notable attention as an emerging class of quasi-one-dimensional (quasi-1D) nanostructures. Due to the fact that the most stable 2D monolayer polymorph of MXs is the 1H phase, to date, existing studies in the literature have predominantly focused on the NRs formed from 1H phase MXs. Nevertheless, NRs of the 1T phase have received little to no attention. Employing ab initio simulations based on density functional theory, we systematically compared the thermodynamic stability of hydrogen passivated and unpassivated 1T and 1H ZNRs of GaS, GaSe, and InSe. Our results reveal that non-polar 1T phase MX ZNRs are thermodynamically more favorable than polar 1H MX ZNRs at widths up to 34 nm, a range that is realizable through contemporary experimental fabrication techniques. Furthermore, unlike metallic 1H ZNRs, 1T ZNRs remain semiconductor and retain a Mexican-hat-shaped top valence bands. Complementarily, hydrogenation energies of 1T InSe ZNRs are positive, and due to the edge-localized states, the 1T unpassivated ZNRs possess nearly flat top valence bands. Our findings serve as a compass for subsequent synthesis pathways of group III-VI NRs.