title: Phonon modes at the 2H-NbSe2 surface observed by grazing incidence inelastic x-ray scattering.
abstract: We have determined the dispersion of acoustic and optical surface phonon modes 2H-NbSe2 at the by inelastic x-ray scattering under grazing incidence conditions. Already, at room temperature, an anomaly is observed close to the charge density wave -vector position located at about one-third along the Gamma-M direction of the Brillouin zone. Our results indicate that the anomaly for the surface mode occurs at a lower energy than that measured in bulk sensitive geometry in the same experiment, showing evidence of a modified behavior in the uppermost layers. We demonstrate that inelastic x-ray scattering in grazing incidence conditions provides a unique tool to selectively study either surface or bulk lattice dynamics in a single experiment.
authors.affiliation: Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität, D-24098 Kiel, Germany.
authors.forename: B M
authors.initials: BM
authors.lastname: Murphy
authors.forename: H
authors.initials: H
authors.lastname: Requardt
authors.forename: J
authors.initials: J
authors.lastname: Stettner
authors.forename: J
authors.initials: J
authors.lastname: Serrano
authors.forename: M
authors.initials: M
authors.lastname: Krisch
authors.forename: M
authors.initials: M
authors.lastname: Müller
authors.forename: W
authors.initials: W
authors.lastname: Press