Stoichiometry-Tunable Synthesis and Magnetic Property Exploration of Two-Dimensional Chromium Selenides

Emerging 2D chromium-based dichalcogenides (CrX_n (X = S, Se, Te; 0 < n ≤ 2)) have provoked enormous interests due to their abundant structures, intriguing electronic and magnetic properties, excellent environmental stability, and great application potentials in next generation electronics and spintronics devices. Achieving stoichiometry-controlled synthesis of 2D CrX_n is of paramount significance for such envisioned investigations. Herein, we report the stoichiometry-controlled syntheses of 2D chromium selenide (Cr_xSe_y) materials (rhombohedral Cr₂Se₃ and monoclinic Cr₃Se₄) via a Cr-self-intercalation route by designing two typical chemical vapor deposition (CVD) strategies. We have also clarified the different growth mechanisms, distinct chemical compositions, and crystal structures of the two type materials. Intriguingly, we reveal that the ultrathin Cr₂Se₃ nanosheets exhibit a metallic feature, while the Cr₃Se₄ nanosheets present a transition from p-type semiconductor to metal upon increasing the flake thickness. Moreover, we have also uncovered the ferromagnetic properties of 2D Cr₂Se₃ and Cr₃Se₄ below ∼70 K and ∼270 K, respectively. Briefly, this research should promote the stoichiometric-ratio controllable syntheses of 2D magnetic materials, and the property explorations toward next generation spintronics and magneto-optoelectronics related applications.