Which chromium-sulfur compounds exist as 2D material?

TL;DR

This study reports the synthesis and characterization of two novel 2D chromium-sulfide materials, revealing their structures, stability, and potential magnetic properties, expanding the family of 2D transition metal chalcogenides.

Contribution

First experimental synthesis and structural characterization of two new 2D chromium-sulfides, with insights into their electronic and magnetic properties via first-principles calculations.

Findings

Identified two new 2D chromium-sulfide phases: Cr₂S₃-2D and Cr₂⅔S₄-2D.

Both materials are structurally stable under ambient conditions.

Cr₂S₃-2D and Cr₂⅔S₄-2D are predicted to be magnetic.

Abstract

Two-dimensional (2D) chromium-sulfides are synthesized by molecular beam epitaxy using graphene as a substrate. Structure characterization by employing scanning tunneling microscopy and low energy electron diffraction indicates that there are two 2D phases, Cr$_2$S$_3$-2D and Cr$_{2\frac{2}{3}}$S$_4$-2D, which have not been reported before. Cr$_{2\frac{2}{3}}$S$_4$-2D is related to bulk Cr$_5$S$_6$, but thinner than a bulk unit cell. For Cr$_2$S$_3$-2D, an even thinner material, no bulk counterpart exists. Both 2D materials are found to be structurally stable under ambient conditions and exhibit interesting electronic properties. Extensive first-principles calculations provide further insight into the electronic structure of these systems and indicate that they should be magnetic. Although single layers of CrS$_2$ were predicted to be stable by density functional theory calculations and reported in previous experimental studies, we were unable to synthesize CrS$_2$ under our range of experimental conditions.