1,721,064 research outputs found
Il contributo di Maria Famigletti alla Formazione degli Insegnanti
No full textPer moltissimi anni la Prof. Maria Famiglietti ha partecipato alla progettazione e attuazione di percorsi di formazione degli Insegnant principalmente negli ambiti delle Tecnologie e delle Scienze nella Scuola Secondaria di Primo grado
La formazione iniziale e permanente degli Insegnanti di tecnologia
No full textParlare di Formazione iniziale e in itinere degli insegnanti di Educazione tecnica e di Scienze nella scola di base significa parlare obbligatoriamente della figura di Maria Famiglietti e della sua ricerca didattica
Single-phonon scattering from clean flat metal surfaces
No full textIn this paper we review the recent advances of the He atom scattering experiments and the theoretical interpretation of the time-of-flight (TOF) spectra relative to clean flat metal surfaces in the one-phonon regime. We discuss the atom-surface scattering mechanism, including the anomalies in the metal surface phonon spectrum and the details of the atom-surface interaction potential. In particular we focus the discussion on the anticorrugating effects in the TOF intensities
Surface States of the (110) Surface of GaAs
No full textResults are presented of a new calculation of the surface states at the (110) surface of GaAs. By using Koster-Slater parameters fitted to bulk optical and photoemission data, the surface band structure has been calculated with a LCAO method. The main conclusion is the existence of two surface bands, one inside the band gap at about 1 eV from the top of the valence band and the other a few tenths of an eV below it. The results show good agreement with the available experimental data
Intrinsic Surface States in III-V Compounds
No full textThe electronic structure of the (110) face of GaAs, GaP and InSb is investigated using a realistic tight-binding model. Calculations of the surface band structure are presented and the nature of the various surface bands is discussed. The results are in agreement with the experimental data and provide a quantitative description of the cation-derived surface states lying in the bulk band gap
Brillouin Scattering and Surface Acoustic Phonons
No full textIn this work we present the theory of the scattering of light from an anisotropic semiinfinite medium. We show that the Brillouin scatterin can occour with two different mechanisms. The first one is related to the surface corrucation induced by the thermal phonons. The ripple effect is dominant in the scattering from metalli surfaces where the penetration depth of the light is very small. The second scattering mechanism is due to the modulation of the dielectric function of the whole medium induced by the phonons. It results particularly important for opaque semiconductors (elastooptic effect). In order to investigate the effects of the anisotropy of the medium we prent results for various faces of clean semiconductors
Hysteretic behaviour in driven Frenkel-Kontorova chains on irregular substrates
No full textThe hysteretic dynamics of a Frenkel-Kontorova chain subject to irregular substrate potentials and driven by an external dc force is studied both in the underdamped and in the overdamped regime at zero temperature. The choice of a rigid external potential defined by the sum of two sinusoidal functions with different periodicity allows us to simulate microscopic sliding over quasiperiodic and multiple-well periodic substrates. We analyse, for different parameter values of the model, the behaviour of the centre of mass average velocity of the chain as a function of an adiabatic increase and decrease of the applied driving. For small damping coefficients (negligible dissipative forces), at a fixed value of the substrate potential amplitude, the width of the hysteresis region is markedly influenced by the chain stiffness. As expected, in the overdamped dynamical regime no hysteresis is observed. We comment on the nature of the dynamical states displayed during the chain motion at different strengths of the dc driving
Anticorrugation in inelastic He-atom scattering from Rh(111) surfaces
No full textRecent measurements supported by nb initio calculations have shown that the interaction of He atoms with transition metal surfaces is anticorrugating, i.e., the electron density seen by He is higher in the bridge positions than in the on-top positions. By shifting the electron charge density away from the atomic positions and using the Esbjerg-Norskov approach to determine the interaction potential, we evaluate the inelastic reflection coefficients of He with Rh(lll). The structure factor introduced by the anticorrugation explains, in a simple way, the high intensity observed for the resonant mode
Reconstruction and Dynamics of the W(100), Mo(100) and Cr(100) Surfaces
No full textA model has been developed that is capable of describing the structural and lattice dynamical properties of the reconstructed W(100), and the closely related Mo(100) and Cr(100), surfaces. In particular the different reconstructions (both commensurate and incommensurate) that are seen on the clean neutral surface, on a high-field FIM tip and on H-covered surfaces, are found to belong to the same T equals O surface ′′phase diagram′′
Surface Density of Acoustic Phonons in GaAs
No full textWe calculate the surface density of acoustic phonons for GaAs(110) and relate it to the Brillouin elasto-optic cross section. A continuum of surfacelike excitations is found in good agreement with the position and the shape of the surface structure observed in the measured Brillouin spectrum. The role played by the optical absorption coefficient in determining different scattering mechanisms is also discussed
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