Downscaling of non van der Waals Semimetallic W5N6 with Resistivity Preservation

TL;DR

This study successfully synthesizes ultrathin 2D W5N6 semimetallic nanosheets with preserved high electrical conductivity, providing new insights into their growth mechanism and expanding the 2D materials landscape.

Contribution

It introduces a novel synthesis method for 2D W5N6 with tunable thicknesses and elucidates the role of chalcogen vacancies and strain in the conversion process.

Findings

High crystallinity and smooth surfaces of 2D W5N6 flakes.

Electrical conductivity remains high down to 2.9 nm thickness.

Weak gate tuning indicates semimetallic behavior.

Abstract

The bulk phase of transition metal nitrides (TMNs) has long been a subject of extensive investigation due to their utility as coating materials, electrocatalysts, and diffusion barriers, attributed to their high conductivity and refractory properties. Downscaling TMNs into two-dimensional (2D) forms would provide valuable members to the existing 2D materials repertoire, with potential enhancements across various applications. Moreover, calculations have anticipated the emergence of uncommon physical phenomena in TMNs at the 2D limit. In this study, we use the atomic substitution approach to synthesize 2D W5N6 with tunable thicknesses from tens of nanometers down to 2.9 nm. The obtained flakes exhibit high crystallinity and smooth surfaces. Electrical measurements on 15 samples show an average electrical conductivity of 161.1 S/cm, which persists while thickness decreases from 45.6 nm to 2.9 nm. The observed weak gate tuning effect suggests the semimetallic nature of the synthesized 2D W5N6. Further investigation into the conversion mechanism elucidates the crucial role of chalcogen vacancies in the precursor for initiating the reaction and strain in propagating the conversion. Our work introduces a desired semimetallic crystal to the 2D material library with mechanistic insights for future design of the synthesis.