Raman Spectroscopy of the Trapezoidal Bi2O2Se

The 2D Bi2O2Se has recently attracted significant interest with large Hall mobility at low temperature due to the depressed electron-phonon scattering. However, the phonon properties of Bi2O2Se are not well explored, and some Raman modes are under debate. Here, substrate engineering is used to grow an unexplored trapezoidal Bi2O2Se, which facilitates the Raman measurements in different orientation planes. Two additional Raman modes at 55 and 429 cm(-1) are detected on the slope of the trapezoid besides the 159 and 362 cm(-1) modes found on the top plane of the trapezoidal Bi2O2Se. Based on the polarized Raman spectroscopy, density functional theory calculations, and group theory analysis, the Raman modes of 55, 159, 362, and 429 cm(-1) are assigned to the E-g, A(1g), B-1g, and E-g modes, respectively. There are two distinct types of angle-resolved polarized Raman spectroscopy for the A(1g) mode on the top and edge planes of Bi2O2Se, which can be used to determine the crystal orientation unambiguously. Furthermore, strong thermal anisotropy is found in the top and edge planes of trapezoidal Bi2O2Se, as reflected from the first-order temperature coefficient of A(1g) phonon mode. The novel growth strategy and interesting anisotropic phonon properties may open up potential applications of Bi2O2Se in nanoelectronics.