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Applied Surface Science, Vol.504, 2020
Exfoliation, lattice vibration and air stability characterization of antiferromagnetic van der Waals NiPS3 nanosheets
Layered NiPS3 compound belongs to interesting two dimensional magnetic van der Waals (vdW) crystals, which provide the ideal platform for understanding two dimensional magnetism. Here high-quality NiPS3 single crystals of millimeter size are synthesized through the chemical vapor transport method. The layered structure and weak vdW interaction between layers lead to exfoliation down to a single layer. The atomic force microscope (AFM) and optical contrast are combined to determine the layer thickness. The lattice vibrations are further probed by Raman spectroscopy in detail and exhibit significant dependence on thickness of nanosheets. By Raman spectroscopy and AFM, the stability of monolayer NiPS3 has been discussed when exposed to air at room temperature. It is estimated that the exposure to air induces degradation gradually and the monolayer NiPS3 is roughly stable within 3 days after exfoliation. The surface suffers from oxidation in air, as confirmed by XPS measurements.