Emerging oxidized and defective phases in low-dimensional CrCl 3 .

Two-dimensional (2D) magnets such as chromium trihalides CrX ₃ (X = I, Br, Cl) represent a frontier for spintronics applications and, in particular, CrCl ₃ has attracted research interest due its relative stability under ambient conditions without rapid degradation, as opposed to CrI ₃ . Herein, mechanically exfoliated CrCl ₃ flakes are characterized at the atomic scale and the electronic structures of pristine, oxidized, and defective monolayer CrCl ₃ phases are investigated employing density functional theory (DFT) calculations, scanning tunneling spectroscopy (STS), core level X-ray photoemission spectroscopy (XPS), and valence band XPS and ultraviolet photoemission spectroscopy (UPS). As revealed by atomically resolved transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis, the CrCl ₃ flakes show spontaneous surface oxidation upon air exposure with an extrinsic long-range ordered oxidized O-CrCl ₃ structure and amorphous chromium oxide formation on the edges of the flakes. XPS proves that CrCl ₃ is thermally stable up to 200 °C having intrinsically Cl vacancy-defects whose concentration is tunable via thermal annealing up to 400 °C. DFT calculations, supported by experimental valence band analysis, indicate that pure monolayer (ML) CrCl ₃ is an insulator with a band gap of 2.6 eV, while the electronic structures of oxidized and Cl defective phases of ML CrCl ₃ , extrinsically emerging in exfoliated CrCl ₃ flakes, show in-gap spin-polarized states and relevant modifications of the electronic band structures.
Competing Interests: There are no conflicts to declare.
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