Emerging oxidized and defective phases in low-dimensional CrCl₃

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) magnets, specifically chromium trihalides (CrX3), are promising for spintronics.
• Chromium chloride (CrCl3) offers relative stability compared to other CrX3 materials.
• Understanding the atomic and electronic structure of CrCl3 is vital for its application.

Purpose of the Study:

• To characterize mechanically exfoliated CrCl3 flakes at the atomic scale.
• To investigate the electronic structures of pristine, oxidized, and defective monolayer CrCl3.
• To explore the effects of oxidation and defects on the electronic band structure of CrCl3.

Main Methods:

• Density functional theory (DFT) calculations.
• Scanning tunneling spectroscopy (STS).
• X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS).
• Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis.

Main Results:

• CrCl3 flakes exhibit spontaneous surface oxidation and amorphous chromium oxide formation upon air exposure.
• CrCl3 is thermally stable up to 200 °C and possesses tunable chlorine vacancy defects up to 400 °C.
• Pure monolayer CrCl3 is an insulator (2.6 eV band gap); oxidized and defective phases show in-gap spin-polarized states.

Conclusions:

• Surface oxidation and intrinsic chlorine vacancies significantly alter the electronic band structure of CrCl3.
• These defects introduce spin-polarized states, modifying the insulating properties of monolayer CrCl3.
• The findings are crucial for designing and utilizing 2D CrCl3-based spintronic devices.