Evidence for the shear horizontal phonon mode on the NaCl(001) surface

The structure and dynamics of the NiO͑100͒ and CoO͑100͒ surfaces have been studied by high-resolution He atom scattering. Both crystals were cleaved in UHV providing unreconstructed surfaces of high quality. For both materials the surface phonon dispersion curves were measured over the entire Brillouin zone along the high-symmetry azimuthal directions. In addition to the Rayleigh mode, the Lucas mode (S 4 ) and a longitudinal gap mode (S 6 ) have been observed. Although both materials are very similar they reveal significantly different surface phonon spectra. A detailed lattice dynamical analysis indicates a charge redistribution at the surface that is presumably driven by the lower coordination of the outermost atoms. ͓S0163-1829͑98͒00743-7͔

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“…39,54 This is nicely confirmed by the direct comparison between theory and experimental data in Fig. 7.…”

Section: Lattice Dynamical Analysissupporting

confidence: 86%

Helium-atom-scattering study of the structure and phonons of the NiO(100) and CoO(100) surfaces

1998

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“…This polarization was chosen since with HAS the probability for exciting the SP Ќ modes is usually greater than for exciting the SP ʈ mods, 27 whereas the excitation of the shear horizontal modes is forbidden along high-symmetry directions. 25 Doubling the unit cell has the important effect that the Rayleigh wave is folded back into the reduced first-Brillouin zone and, thus, gives rise to a nearly flat band at around 3 Table I͒. Even though the calculated phonon bands of Fig. 6͑b͒ do not acount for the librational modes, they nicely reproduce several of the experimental features summarized in Fig.…”

Section: Calculation Of the Dispersion Curvessupporting

confidence: 55%

“…24 The relative signal intensity of these peaks indicates that the surface studied has a relatively low density of defects and that the quality of the surface is comparable with other previously studied single-crystal dielectric and semiconductor surfaces. 25,26 Besides the diffuse elastic peak, each spectrum has a number of other fairly sharp peaks at positive-and negativeenergy transfers. The peaks at the positive-energy side correspond to the annihilation of single phonons, while those on the negative side are due to single phonon excitations.…”

Section: Measurements Of the Phonon Dispersion Curvesmentioning

confidence: 99%

Low-frequency phonon dynamics of theC60(111)surface

Glebov¹,

Senz²,

Toennies³

et al. 1997

Phys. Rev. B

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High-quality C 60 films, with a thickness of about 100 Å, were epitaxially grown on in vacuo cleaved GeS͑001͒ single crystal surfaces and characterized with helium atom diffraction. Phonon dispersion curves of the C 60 (111) surface were obtained from high-resolution inelastic helium atom time-of-flight ͑TOF͒ spectra. Pronounced inelastic peaks corresponding to the Rayleigh modes and to the frustrated rotations ͑librations͒ of the C 60 molecules were observed along the ͗110͘ and ͗112͘ directions. The anharmonicity of the librations was found to be slightly larger than in the bulk C 60 . The contribution of the C 60 vibrations ͑without librons͒ to the inelastic TOF peak intensities was estimated from lattice dynamic calculations based on the intermolecular potential of Girifalco ͓J. Phys. Chem. 92, 858 ͑1992͔͒. ͓S0163-1829͑97͒08939-X͔

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“…The dispersion of the Rayleigh modes of NaCl͑100͒ is well known and was measured using helium-atom scattering in earlier experiments. 30 As a simple model, these modes are presented in Fig. 2 as sine curves, with an amplitude of 10 meV corresponding to the energy at the Brillouin-zone boundary (M point͒.…”

Section: Inelastic Helium Atom Scattering Resultsmentioning

confidence: 99%

Phonon-libron dynamics of acetylene adsorbed onNaCl(001)

et al. 1998

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The phonon-dispersion curves of the high-temperature (3ͱ2ϫͱ2)R45°phase of acetylene on NaCl͑001͒ have been measured using high-resolution time-of-flight inelastic helium-atom scattering and compared with semiempirical calculations. The observed two Einstein vibrational modes at 8 and 14 meV are assigned to a collective perpendicular motion of the molecule centers of mass in the monolayer and to a collective librational motion of the molecular axes, respectively. With the same semiempirical potential used in the dynamical calculations, the 0 K adsorbate monolayer structure is predicted to be (ͱ2ϫͱ2)R45°which is at variance with the (7ͱ2ϫͱ2)R45°structure determined at TϽ80 K by helium diffraction. The results are compared with structure assignments based on infrared spectroscopy and ab initio calculations.

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Evidence for the shear horizontal phonon mode on the NaCl(001) surface

Cited by 24 publications

References 27 publications

Helium-atom-scattering study of the structure and phonons of the NiO(100) and CoO(100) surfaces

Helium-atom-scattering study of the structure and phonons of the NiO(100) and CoO(100) surfaces

Low-frequency phonon dynamics of theC60(111)surface

Phonon-libron dynamics of acetylene adsorbed onNaCl(001)

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