Raman Tensor of WSe₂ via Angle-Resolved Polarized Raman Spectroscopy

Abstract

Tungsten selenide (WSe2) as a van der Waals layered crystal has anisotropic light absorption and light scattering on its out-of-plane surface. However, the Raman tensor of WSe2, which determines the anisotropy of inelastic light scattering, is still unknown without being carefully studied. Here, via establishing angle-resolved polarized Raman spectroscopy measurement, we obtained the experimental Raman tensor of WSe2. Additionally, theoretical Raman tensors under different incident laser line excitations from ultraviolet to infrared were calculated via the first-principles density functional approach, coinciding fairly well with the experimental ones. The first-principles results also reveal that WSe2 has different Raman tensor forms under different laser line excitations, especially the phase difference between Raman tensor elements of the A1g mode. It is suggested that the photon-energy dependent phase differences are determined by the dispersion and absorption of WSe2 on different pump lights.

2D Octagon-Structure Carbon and Its Polarization Resolved Raman Spectra

“…The Raman tensor was obtained with the finite displacement method [ 31 , 32 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ]: where V is the volume of unit cell, M μ is the atomic mass of atom μ , χ αβ / r l ( μ ) is the first derivative of the electric polarizability tensor with respect to the atomic displacement. It equals the derivative of dielectric tensor ε αβ divided by 4 π because χ αβ ( ω ) = ( ε αβ ( ω ) − δ αβ )/4 π .…”

“…The Raman tensor was obtained with the finite displacement method [31,32,[41][42][43][44][45][46][47][48][49][50][51][52]]:…”

Laser tuning in AlN single crystals

“…The measurement geometry is shown in Fig. 1a [24][25][26][27][28][29][30][31][32][33][34], where a polarizer with fixed polarization direction was placed in the collecting optical path to ensure that the polarization direction of scattering light was strictly consistent with that of pump light. In order to avoid the influences of pump light absorption and resonance Raman scattering on the intensity of scattering light, 488-nm Ar+ gas laser was used as pump light and focused on the AlN surface through a 50× quartz lens [35][36][37][38][39].…”

Raman tensor of layered black phosphorus

“…Angle-resolved polarized Raman (APR) spectroscopy, as an undamaged tool, is powerful to measure Raman tensor. It has been performed in our previous work which studied the Raman polarization characteristic of anisotropic crystal, such as MoS 2 , black arsenic and AlN [2,[15][16][17][18][19][20][21]. Recently, BP has attracted much attention in the aspects of optical and electrical anisotropy.…”