Archivio della ricerca dell'Università di Modena e Reggio Emiliahttps://iris.unimore.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Tue, 20 Apr 2021 09:20:27 GMT2021-04-20T09:20:27Z101011Sliding friction of N2 on Pb(111)http://hdl.handle.net/11380/643308Titolo: Sliding friction of N2 on Pb(111)
Abstract: Molecular dynamics simulations of the sliding friction between two thick solid slabs are performed. The upper body is formed of light N2 particles and the substrate of heavy Pb atoms. Among the various mechanisms that are responsible for the friction, we consider the phonon–phonon interaction between the two blocks. To provide evidence of the phonon interaction, we compare two different systems. For the first we consider the substrate as formed of atoms fixed in the equilibrium (111) positions. In the second system the Pb atoms can be displaced from the ideal positions, under their mutual interactions. A comparison with recently obtained experimental data will be discussed.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/11380/6433082010-01-01T00:00:00ZAngle-Resolved Thermal Desorption and Time-of-flight spectra:Ne-Cu(111)http://hdl.handle.net/11380/452134Titolo: Angle-Resolved Thermal Desorption and Time-of-flight spectra:Ne-Cu(111)
Abstract: The angle-resolved thermal desorption flux, and time-of-flight spectrum have been computed for Ne-Cu( 111) using a microscopic description of the phonons of Cu( 1 I 1 ), and a realistic gas-solid potential. The angular distribution is narrower than cosine at 5 K, quasi-cosine at 10 K, and distinctly non-cosine at 20 and 30 K with the maximum away from the surface normal. The desorption is driven by long-wavelength phonons, but the precise angular dependence results from the temperature-dependent interplay of statistical and dynamical factors. He desorbing from graphite shows similar features.
Mon, 01 Jan 1990 00:00:00 GMThttp://hdl.handle.net/11380/4521341990-01-01T00:00:00ZMultiphonon Effects in Atom Surface Scattering: the Case of Pt(111)http://hdl.handle.net/11380/452135Titolo: Multiphonon Effects in Atom Surface Scattering: the Case of Pt(111)
Abstract: In this paper we show that the huge structures recently observed experimentally ith the He-surface atom scattering technique by using hot beams can be related with some confidence to multiphonon scattering events.
Mon, 01 Jan 1990 00:00:00 GMThttp://hdl.handle.net/11380/4521351990-01-01T00:00:00ZSurface Lattice Dynamics of Cu(111)http://hdl.handle.net/11380/452123Titolo: Surface Lattice Dynamics of Cu(111)
Abstract: We presnet a lattice dynamical calculation of the Cu(111) surface, based on the slab method in the framework of a force constant parametrization scheme that includes central and angular interactions.
Fri, 01 Jan 1988 00:00:00 GMThttp://hdl.handle.net/11380/4521231988-01-01T00:00:00ZSurface Resonant Phonons of Ag(110)http://hdl.handle.net/11380/452128Titolo: Surface Resonant Phonons of Ag(110)
Abstract: A study of the dynamics of the Ag(110) surface in the ḡGȲ direction is presented. The experimental TOF spectra show the existence of two low frequency modes with high scattering intensity and a dispersionless high frequency mode with a smaller intensity. The theoretical analysis based on a force constant model that contains long-range central interactions and short-range angular forces explains accurately both the dispersions and the scattering intensities of the three modes in terms of resonant and localized vibrations related to the modifications of the surface force constants caused by the different role played by the many-body forces in the surface region.
Sun, 01 Jan 1989 00:00:00 GMThttp://hdl.handle.net/11380/4521281989-01-01T00:00:00ZPhonons at the surface of the nearly-free-electron metal Al(111): realisation of an ideal surfacehttp://hdl.handle.net/11380/452124Titolo: Phonons at the surface of the nearly-free-electron metal Al(111): realisation of an ideal surface
Abstract: Surface phonons of the nearly-free-electron metal Al(111) have been measured by high-resolution He-atom time-of-flight experiments for four different directions. This is the first surface which shows no evidence for an anomalous resonant mode found on the noble metals and Pt and attributed to a strong (≊50%) reduction of surface lateral force constants. By fitting the time-of-flight spectra via a lattice-dynamical simulation the surface interlayer force constant is found to agree to within ±3% with the bulk value and the lateral force constant reduction is less than 20%.
Fri, 01 Jan 1988 00:00:00 GMThttp://hdl.handle.net/11380/4521241988-01-01T00:00:00ZSurface phonons on the Pt(111) surface: a comparison of He-scattering experiments with lattice dynamical calculationshttp://hdl.handle.net/11380/452127Titolo: Surface phonons on the Pt(111) surface: a comparison of He-scattering experiments with lattice dynamical calculations
Abstract: Angular distributions and surface-phonon dispersion curves have been measured by He-atom scattering for clean Pt between T=160 and 373 K and for Pt-H(1×1) at 160 K along the 〈110〉 and 〈112〉 azimuths. Inelastic-scattering intensities over a wide range of wave vectors are also reported for the clean surface. The results are analyzed with use of the distorted-wave Born approximation for a model potential describing the He-atom–Pt-surface potential. A set of 14 force constants adjusted to the bulk-phonon dispersion data cannot explain the measured time-of-flight spectra and the observed first-layer relaxation. However, by modifying at the surface the nearest-neighbor tangential force constants (α1’’=1.7α1b, and α1’=1.3α1b), the radial force constants (β1’’=0.39β1b), and the three-body force constant (γ1’’=0.037γ1b)— where the superscripts ∥ and ⊥ denote forces within the surface plane and between the first and second planes, respectively—a good fit to all the data is achieved. The new surface force constants are discussed in terms of electronic-charge redistribution within the first layer.
Sun, 01 Jan 1989 00:00:00 GMThttp://hdl.handle.net/11380/4521271989-01-01T00:00:00ZSurface lattice dynamics of Nickelhttp://hdl.handle.net/11380/452109Titolo: Surface lattice dynamics of Nickel
Abstract: In the framework of a central and angular force constants mode1,we have evaluated the phonon spectrum and the loss function of the Ni(111) surface covered with Oxigen. We explain quantitatively the main features of the observed electron energy loss spectra.
Thu, 01 Jan 1981 00:00:00 GMThttp://hdl.handle.net/11380/4521091981-01-01T00:00:00ZOn the detection of pseudo surface modes in Ag(111) with He-surface scatteringhttp://hdl.handle.net/11380/452117Titolo: On the detection of pseudo surface modes in Ag(111) with He-surface scattering
Abstract: We evaluate the surface phonon dispersion relations of Ag(111) within a force constants parametrization of the bulk dynamics. By changing the surface force constants we are able to explain all the salient features appearing in the experimental time of flight spectra. The parallel momentum Q has been considered along the direction [1-10] of the surface Brillouin zone. We show that the peaks of the time of flight spectra are related to the Rayleigh wave, to the pseudo Rayleigh wave and to a new resonance of longitudinal character. A comparison is made with the [11-2] direction.
Tue, 01 Jan 1985 00:00:00 GMThttp://hdl.handle.net/11380/4521171985-01-01T00:00:00ZCalculation of potential cut-off for one-phonon atom-surface scatteringhttp://hdl.handle.net/11380/452114Titolo: Calculation of potential cut-off for one-phonon atom-surface scattering
Abstract: A cluster calculation for Cu(111), Ag(111), and Au(111) shows that the lateral Fourier transform of the charge deformation due to a displacement of a single surface atom is a Gaussian exp(-Q2 / 2Qc2). This is proportional to the scattering amplitude for one-phonon exchange atom-surface scattering and produces a cutoff in the cross section. The values of Qc are evaluated for the above-mentioned surfaces, explaining very well the experimental observations. We also find a simple formula that should be useful to experimentalists in calculating the cutoff.
Sat, 01 Jan 1983 00:00:00 GMThttp://hdl.handle.net/11380/4521141983-01-01T00:00:00Z