TY - JOUR
T1 - Estimating soft-mode frequencies of surface overlayers by means of photoelectron diffraction: The (2×2) surface-V2O 3/Pd(111)
AU - Sambi, M
AU - Surnev, Svetlozar L.
AU - Kresse, Georg
AU - Netzer, Falko P.
AU - Granozzi, G
N1 - Zeitschrift: Physical Review B - Condensed Matter and Materials Physics
Coden: PRBMD
Art-Nr: 155417
Affiliations: Dipartimento di Chimica Inorganica, Unità di Ricerca INFM, Università di Padova, Via Loredan 4, 35131 Padova, Italy; Institut für Experimentalphysik, Karl-Franzens-Universität Graz, A-8010 Graz, Austria; Institut für Materialphysik, Universität Wien, Sensengasse 8/12, A-1090 Wien, Austria
Adressen: Sambi, M.; Dipartimento di Chimica Inorganica; Unità di Ricerca INFM; Università di Padova; Via Loredan 4 35131 Padova, Italy; email: [email protected]
Import aus Scopus: 2-s2.0-4544254026
22.10.2007: Datenanforderung 1935 (Import Sachbearbeiter)
22.10.2007: Datenanforderung 1936 (Import Sachbearbeiter)
PY - 2003
Y1 - 2003
N2 - The (2×2) surface-V2O3 layer, an interface-mediated vanadium oxide phase observed on Pd(111) in the submonolayer coverage range, has been investigated by means of angle scanned x-ray photoelectron diffraction (XPD), which gives a direct experimental confirmation of the model derived by scanning tunnelling microscopy (STM) and density functional calculations (DFT), with a quantitative determination of the V-O interlayer spacing. In addition, XPD measurements compared to single scattering cluster-spherical wave (SSC-SW) simulations revealed a peculiar broadening of V-O forward scattering (FS) maxima that is limited to azimuthal scans and that cannot be accounted for by isotropic Debye-Waller attenuation of the diffraction features. However, the existence of a soft phonon mode in the overlayer, associated with substantial in-plane displacements from equilibrium of O scatterers with respect to V emitters, could explain the experimental observation. The existence of such a soft mode has been confirmed by DFT calculations. It consists of an in-plane quasirotation around the V emitter of the three nearest-neighbor O atoms, and the estimated DFT frequency amounts to 15 cm-1. The XPD data have been analyzed by means of SSC-SW simulations wherein a harmonic oscillator model has been employed to approximate the effect of the soft phonon mode on XPD curves. As a result, an experimental determination of the frequency of the mode has been obtained (40‘25 cm-1), which is of the same order of magnitude as the DFT predicted frequency. Moreover, the sensitivity of XPD scans to the correlation of soft-mode atomic displacements has been studied, leading to the estimate of a "soft-mode XPD coherence length" for the system under investigation. This work therefore explores an application of XPD as a surface spectroscopy sensitive to vibrational soft modes.
AB - The (2×2) surface-V2O3 layer, an interface-mediated vanadium oxide phase observed on Pd(111) in the submonolayer coverage range, has been investigated by means of angle scanned x-ray photoelectron diffraction (XPD), which gives a direct experimental confirmation of the model derived by scanning tunnelling microscopy (STM) and density functional calculations (DFT), with a quantitative determination of the V-O interlayer spacing. In addition, XPD measurements compared to single scattering cluster-spherical wave (SSC-SW) simulations revealed a peculiar broadening of V-O forward scattering (FS) maxima that is limited to azimuthal scans and that cannot be accounted for by isotropic Debye-Waller attenuation of the diffraction features. However, the existence of a soft phonon mode in the overlayer, associated with substantial in-plane displacements from equilibrium of O scatterers with respect to V emitters, could explain the experimental observation. The existence of such a soft mode has been confirmed by DFT calculations. It consists of an in-plane quasirotation around the V emitter of the three nearest-neighbor O atoms, and the estimated DFT frequency amounts to 15 cm-1. The XPD data have been analyzed by means of SSC-SW simulations wherein a harmonic oscillator model has been employed to approximate the effect of the soft phonon mode on XPD curves. As a result, an experimental determination of the frequency of the mode has been obtained (40‘25 cm-1), which is of the same order of magnitude as the DFT predicted frequency. Moreover, the sensitivity of XPD scans to the correlation of soft-mode atomic displacements has been studied, leading to the estimate of a "soft-mode XPD coherence length" for the system under investigation. This work therefore explores an application of XPD as a surface spectroscopy sensitive to vibrational soft modes.
U2 - 10.1103/PhysRevB.68.155417
DO - 10.1103/PhysRevB.68.155417
M3 - Article
SN - 1098-0121
VL - 68
JO - Physical Review B
JF - Physical Review B
IS - 15
M1 - 155417
ER -