title: Polarization-Resolved Raman Study of Bulk-like and Davydov-Induced Vibrational Modes of Exfoliated Black Phosphorus.
abstract: Owing to its crystallographic structure, black phosphorus is one of the few 2D materials expressing strongly anisotropic optical, transport, and mechanical properties. We report on the anisotropy of electron-phonon interactions through a polarization-resolved Raman study of the four vibrational modes of atomically thin black phosphorus (2D phosphane): the three bulk-like modes Ag1, B2g, and Ag2and the Davydov-induced mode labeled Ag(B2u). The complex Raman tensor elements reveal that the relative variation in permittivity of all Agmodes is irrespective of the atomic motion involved lowest along the zigzag direction, the basal anisotropy of these variations is most pronounced for Ag2and Ag(B2u), and interlayer interactions in multilayer samples lead to reduced anisotropy. The bulk-forbidden Ag(B2u) mode appears for n ≥ 2 and quickly subsides in thicker layers. It is assigned to a Davydov-induced IR to Raman conversion of the bulk IR mode B2uand exhibits characteristics similar to Ag2. Although this mode is expected to be weak, an electronic resonance significantly enhances its Raman efficiency such that it becomes a dominant mode in the spectrum of bilayer 2D phosphane.
authors.affiliation: Department of Engineering Physics, Polytechnique Montréal , Montréal, Québec H3C 3A7, Canada.
authors.forename: Anne-Laurence
authors.initials: AL
authors.lastname: Phaneuf-L'Heureux
authors.affiliation: Department of Physics, Université de Montréal , Montréal, Québec H3C 3J7, Canada.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Favron
authors.affiliation: Department of Engineering Physics, Polytechnique Montréal , Montréal, Québec H3C 3A7, Canada.
authors.forename: Jean-Francis
authors.initials: JF
authors.lastname: Germain
authors.affiliation: Department of Engineering Physics, Polytechnique Montréal , Montréal, Québec H3C 3A7, Canada.
authors.forename: Patrick
authors.initials: P
authors.lastname: Lavoie
authors.affiliation: Department of Engineering Physics, Polytechnique Montréal , Montréal, Québec H3C 3A7, Canada.
authors.forename: Patrick
authors.initials: P
authors.lastname: Desjardins
authors.affiliation: Department of Physics, Université de Montréal , Montréal, Québec H3C 3J7, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Leonelli
authors.affiliation: Department of Chemistry, Université de Montréal , Montréal, Québec H3C 3J7, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Martel
authors.affiliation: Department of Engineering Physics, Polytechnique Montréal , Montréal, Québec H3C 3A7, Canada.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Francoeur
keywords: Black phosphorus; Davydov effects; angle-resolved Raman spectroscopy; anisotropic properties; vibrational modes