title: Raman and Brillouin scattering studies of bulk 2H-WSe2.
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(-1)was found not to be due to the A(1g) 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 [Formula: see text] 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.
authors.affiliation: Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St John's, NL, A1B 3X7, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Akintola
authors.forename: G T
authors.initials: GT
authors.lastname: Andrews
authors.forename: S H
authors.initials: SH
authors.lastname: Curnoe
authors.forename: M R
authors.initials: MR
authors.lastname: Koehler
authors.forename: V
authors.initials: V
authors.lastname: Keppens