Angle-resolved Raman scattering study of anisotropic two-dimensional tellurium nanoflakes

Abstract

As an elemental crystal, anisotropic two-dimensional (2D) tellurium (Te) flakes have recently garnered significant attention due to their exceptional chemical stability, tunable bandgap, low thermal conductivity, and high carrier mobility. To further investigate the anisotropic properties of Te nanoflakes, a rapid and effective method of determining their crystal axes is essential. In this study, it is demonstrated that the intensity of the Raman-active mode in Te nanoflakes exhibits a laser-polarization-dependence, varying periodically with the polarization angle. The crystal axis in two-dimensional Te nanoflakes can be identified using angle-resolved polarized Raman spectroscopy. Specifically, the Raman intensity of the A1 mode is the highest when the incident light is polarized along the [12¯10] direction and the lowest when polarized along the [0001] direction. This identification of the crystal axis via Raman spectroscopy is further verified by transmission electron microscopy measurements. In addition, theoretical simulations reveal that anisotropic Raman scattering is closely associated with the interference effect in a multilayer stacking system, as well as anisotropic absorption and anisotropic electron–phonon coupling in Te nanoflakes. This discovery not only provides a rapid method for locating the crystal axes in Te nanoflakes but also offers new insights into the scattering phenomenon in anisotropic materials beyond Te nanoflakes.