Vapor phase synthesis and Raman spectroscopy of two-dimensional cobalt oxide nanoflakes
To explore antiferromagnetic materials,two-dimensional cobalt oxide nanoflakes were synthesized on sapphire(Al2O3)and mica substrates via chemical vapor deposition(CVD)using cobalt chloride hexahydrate(CoCl2·6H2O)as the precursor.By adjusting the oxygen flux during the growth process,the synthesis of two-dimensional tricobalt tetraoxide(Co3O4)and cobaltous oxide(CoO)nanoflakes was achieved.The morphology,thickness,phase structure,magnetism,and stability of the synthesized cobalt oxide nanoflakes were characterized by optical microscopy,atomic force microscopy and Raman spectroscopy.The results revealed that both Co3O4 and CoO nanoflakes had a triangular shape.The lateral size of Co3O4 nanoflakes could reach up to 18 μm with a thickness of approximately 24 nm.Similarly,the lateral size of CoO nanoflakes could reach up to 20 μm with a minimum thickness of 12 nm.At low temperatures,CoO nanoflakes exhibited magnetic Raman peaks,indicating their response to low-temperature magnons.Raman spectra at different laser powers demonstrated the transformation of CoO phase into Co3O4 under 12 mW excitation.Additionally,the CoO nanoflakes remained unoxidized after being kept at room temperature for a month,demonstrating excellent stability at room temperature.
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