Raman and Brillouin scattering studies of bulk 2H-WSe2

Author: Akintola K   Andrews G T   Curnoe S H   Koehler M R   Keppens V  

Publisher: IOP Publishing

E-ISSN: 1361-648X|27|39|395401-395406

ISSN: 0953-8984

Source: Journal of Physics: Condensed Matter, Vol.27, Iss.39, 2015-10, pp. : 395401-395406

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Abstract

Raman and Brillouin spectroscopy were used to probe optic and acoustic phonons in bulk 2H-WSe2. Raman spectra collected under different polarization conditions allowed assignment of spectral peaks to various first- and second-order processes. In contrast to some previous studies, a Raman peak at  ∼259 cm−1was found not to be due to the A1g mode but to a second-order process involving phonons at either the M or K point of the Brillouin zone. Resonance effects due to excitons were also observed in the Raman spectra. Brillouin spectra of 2H-WSe2 contain a single peak doublet arising from a Rayleigh surface mode propagating with a velocity of &$1340pm 20$ ; m s−1. This value is comparable to that estimated from Density Functional Theory calculations and also to those for the transition metal diselenides 2H-TaSe2 and 2H-NbSe2. Unlike these two materials, however, peaks arising from scattering via the elasto-optic mechanism were not observed in Brillouin spectra of WSe2 despite its lower opacity.