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.Sat, 28 Nov 2020 20:30:26 GMT2020-11-28T20:30:26Z10801Interpretation of inelastic scattering of He from Cu surfaces in the anticorrugated potential modelhttp://hdl.handle.net/11380/305446Titolo: Interpretation of inelastic scattering of He from Cu surfaces in the anticorrugated potential model
Abstract: In this paper we demonstrate that inclusion of the anticorrugation effects in the pseudopotential describing the dynamic interaction of neutral He atoms with phonons of Cu(1 1 1) and Cu(1 0 0) surfaces can resolve the long standing discrepancy between the inelastic scattering intensities inferred from HAS-TOF and from the electron energy loss spectroscopy data.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/11380/3054462001-01-01T00:00:00ZThe interaction of intrinsic localized modes in the gap of doped semiconductors with plasmonshttp://hdl.handle.net/11380/305448Titolo: The interaction of intrinsic localized modes in the gap of doped semiconductors with plasmons
Abstract: We present a theoretical investigation of the interaction of intrinsic localized modes with plasmons. The anharmonic localized modes for a ID diatomic lattice are determined using a two-body potential which describes the interactions among particles in a zinc-blende structure material. The localized mode frequency is inside the gap between acoustic and optical phonons. Calculations have been performed for GaN because it has a large phonon gap, can be highly n-doped, and the plasma frequency of free carriers is in the range of phonon and intrinsic localized mode frequencies. To study the coupling we add to the equations of motion an electric field to simulate the plasmon. Solving the system we obtain the dynamical displacements pattern from which we evaluate the total polarization. From the polarization we determine the frequency of the combined mode for which the dielectric function is zero. In this investigation we have analysed both the case of small localized mode amplitudes and the case of larger amplitudes, obtaining different behaviour. In the first case the mixed mode has a frequency above the top of the optical branch, which can be explained in terms of the theory of the harmonic dielectric response of polar lattice vibrations. In the second case the coupled mode exists only for a finite slab, and its frequency is inside the phonon gap.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11380/3054482004-01-01T00:00:00ZEffects of the commensurability and disorder on friction for the system Xe/Cuhttp://hdl.handle.net/11380/692647Titolo: Effects of the commensurability and disorder on friction for the system Xe/Cu
Abstract: We present molecular dynamics simulations of static friction for a monolayer of Xe deposited on a thick slab of Cu for two different geometries. The interaction potential between Xe and Cu has been derived from DFT calculations. The first geometry is the commensurate adsorption geometry (√3 ×√3)R30◦ suggested by LEED, corresponding to a coverage 1/3, where all Xe atoms are on top positions. The second one corresponds to a coverage 0.36 and is characterized by a large surface unit cell, containing 9 Xe atoms in different disordered positions. This largeunit cell mimics an incommensurate case. Our analysis points out the effect of the order/disorder in tribological properties of a realistic three-dimensional system.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11380/6926472011-01-01T00:00:00ZAnharmonic effects in a finite Frenkel-Kontorova type chainhttp://hdl.handle.net/11380/305851Titolo: Anharmonic effects in a finite Frenkel-Kontorova type chain
Abstract: The features of the ground state and the phonon frequency spectrum of a finite Frenkel-Kontorova type model are investigated in presence of quartic anharmonic nearest-neighbor interactions. The different computational techniques used allow us to determine with great accuracy the critical parameter for the ground-state symmetry breaking transition, showing its dependence on the strength of the interatomic anharmonicity introduced. The phonon gap. the linearized vibrational modes and their parity are also studied in the vicinity of the transition point. (C) 2002 Elsevier Science B.V. All rights reserved.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/11380/3058512002-01-01T00:00:00ZThe phonons of the Al surfaces: comparison between semi-empirical and ab-initio calculationshttp://hdl.handle.net/11380/305689Titolo: The phonons of the Al surfaces: comparison between semi-empirical and ab-initio calculations
Abstract: We report inelastic He-atom surface scattering data for the low-index surfaces of aluminum. The experimental data are analyzed by using a semi-empirical Born-von Karman model in which both two-body and three-body interactions are taken into account and by using an ab initio pseudopotential approach. Our analysis shows that the semi-empirical model containing long-range forces agrees with great accuracy with the pseudopotential calculations for what concerns both the range of the interactions and the dispersion of the surface vibrational modes. The calculations of the reflection coefficients allow us to study the nature of the weak resonances observed in the time-of-flight spectra. These structures are related to a picking up of modes with polarization vector normal to the surface due to the modification introduced by the surface on the entire force field. Our analysis of Al proves that for simple metals an accurate semi-empirical model can reproduce with great accuracy both the surface lattice dynamics, without introducing new free parameters in the surface interatomic potential, as well as an ab initio pseudopotential calculation.
Wed, 01 Jan 1992 00:00:00 GMThttp://hdl.handle.net/11380/3056891992-01-01T00:00:00ZAnomalous linewidth behavior of the S3 surface resonance on Ag(110)http://hdl.handle.net/11380/305981Titolo: Anomalous linewidth behavior of the S3 surface resonance on Ag(110)
Abstract: We report detailed He atom scattering measurements of the phonon linewidth for the Rayleigh mode S-1 and the resonant mode S-3 of Ag(110) along the whole <(Gamma) over bar><(Y) over bar> side of the surface Brillouin zone as a function of the sample temperature. The novel behaviour observed for the resonance linewidth is explained by including the mixed-mode nature into the anharmonic calculations performed within the framework of the Born-von Karman model.
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/11380/3059811996-01-01T00:00:00ZElastic and inelastic interactions of He and Ne atoms with metals surfaceshttp://hdl.handle.net/11380/306544Titolo: Elastic and inelastic interactions of He and Ne atoms with metals surfaces
Abstract: The experimental information accumulated in recent years on elastic and inelastic scattering of He and Ne atoms from metal surfaces is analysed by describing the atom-surface interaction as a superposition of pseudo-pairwise potentials. These are chosen according to the quite accurate potentials presently available for van der Waals pairs and take a phenomenological account for many body effects. The emerging picture is quite satisfactory and allows the physical interaction of a given atom-surface system to be predicted with excellent accuracy. In particular the coupling of He atoms to the surface vibrational modes is considered with attention focused on He inelastic scattering from Cu(001).
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/11380/3065441993-01-01T00:00:00ZFar Infrared Vibrational Spectroscopy in CrSi_2http://hdl.handle.net/11380/307146Titolo: Far Infrared Vibrational Spectroscopy in CrSi_2
Abstract: We present and discuss reflectance and trasmittance measurements on CrSi, polycrystalline films in the (100 + 700) cm-' wavenumber range. The spectra show that the compound has a nonmetallic behaviour. The strong and sharp structures observed are interpreted on the basis of the symmetry properties of the normal modes of CrSie, and their strength is attributed to a dynamical charge. Moreover, preliminary lattice dynamicscalculations allow to explain the relative intensity of the infrared-active modes.
Mon, 01 Jan 1990 00:00:00 GMThttp://hdl.handle.net/11380/3071461990-01-01T00:00:00ZCalculation 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/11380/4521141983-01-01T00:00:00ZInelastic He scattering from metal surfaceshttp://hdl.handle.net/11380/452118Titolo: Inelastic He scattering from metal surfaces
Abstract: We present inelastic aton surface phonon scattering time of flight spectra for the reconstructed Au(111) and for the Pt(111) unreconstructed surface.
Wed, 01 Jan 1986 00:00:00 GMThttp://hdl.handle.net/11380/4521181986-01-01T00:00:00Z