Raman tensor studies on defective non-van der Waals Bi₂O₂Se

The Raman tensors of the three modes at ∼55, ∼80, and ∼160 cm−1 for the non-van der Waals layered material Bi2O2Se, which were assigned to Eu, Eg, and A1g, respectively, were experimentally investigated. Two modes at ∼55 and ∼80 cm−1, which were not observable in perfect crystal Bi2O2Se in the backscattering configuration, owing to the Raman selection rule, were activated by defects. These two modes exhibit strong polarization dependence at line defects and the excitation energy; thus, their Raman polarizability tensors exhibit strong dependence on the defect morphology and geometric characteristics of Bi2O2Se. The results of this study confirm that the Raman tensors of nanocrystalline structures can be modulated by defects.