2014/01/03 by Xin Luo, Yanyuan Zhao, Luo, Xin +11
Engineering · Materials Science · Physics and Astronomy · #2D Materials and Applications #FOS: Physical sciences #Graphene research and applications #Materials Science (cond-mat.mtrl-sci) #Perovskite Materials and Applications #cond-mat.mtrl-sci
paper · pdf · doi:10.48550/arxiv.1401.0626
arxiv created 2014/01/03 · openalex publication_date 2014/01/03 · arxiv updated 2014/01/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We report the observation and interpretation of new Raman peaks in few-layer tungsten diselenide (WSe2), induced by the reduction of symmetry going from 3D to 2D. In general, Raman frequencies in 2D materials follow quite closely the frequencies of corresponding eigenmodes in the bulk. However, while the modes that are Raman active in the bulk are also Raman active in the thin films, the reverse is not always true due to the reduced symmetry in thin films. Here, we predict from group theory and density functional calculations that two intra-layer vibrational modes which are Raman inactive in bulk WSe2 in our experimental configuration become Raman active in thin film WSe2, due to reduced symmetry in thin films. This phenomenon explains the Raman peaks we observe experimentally at ~310 cm-1 and 176 cm-1 in thin film WSe2. Interestingly, the bulk mode at ~310 cm-1 that is Raman inactive can in fact be detected in Raman measurements under specific wavelengths of irradiation, suggesting that in this case, crystal symmetry selection rules may be broken due to resonant scattering. Both theory and experiment indicate that the and modes blue-shift with decreasing thickness, which we attribute to surface effects. Our results shed light on a general understanding of the Raman/IR activities of the phonon modes in layered transition metal dichalcogenide materials and their evolution behavior from 3D to 2D.