1,721,001 research outputs found
Thermodynamic properties of FCC metals: Cu and Al
No full textIsothermal bulk modulus, linear coefficient of thermal expansion, thermodynamic Gruneisen parameter and constant pressure specific heat have been computed for Cu and Al throughout a wide range of temperatures. The authors use a perturbative Helmholtz free energy as a function of the strain parameters. The Brillouin sums are carried out exactly. The atomic interactions are modelled according to a force constant potential: angular forces and long-range central forces are included in the harmonic part of the potential, while the anharmonic part is first-neighbours ranged. The model is shown to be successful in describing both the thermoelastic and the caloric properties
Anharmonicity on Al(100) and Al(111) surfaces -- Presentazione poster by R Zivieri - Conferenza nazionale
No full textWe present a molecular-dynamics analysis of the stable non-melting (100) and (111) surfaces of Al.
An expansion of (111) surface and a contraction of (100) surface result from the calculations. At
low temperature, the vertical mean-square vibrational amplitude is larger than the in-plane
component, while at higher temperature the in-plane component approaches the vertical one. The
evaluated linewidths and the energy shifts for the Rayleigh surface phonon are in good agreement
with the He-surface scattering data. The effect of surface anharmonicity is much larger for the static
properties than for the dynamical properties.--Presentazione poster by R Zivieri - Conferenza nazional
Influence of graphene coating on the adsorption and tribology of Xe on Au(111) substrate
No full textThe adsorption and tribological properties of graphene have received increasing attention for the further development of graphene-based coatings in applications. In this work, we performed first principles calculations with the inclusion of the nonlocal van der Waals correction to study the effect of graphene coating on the adsorption geometries, sliding frictions and electronic properties of Xe monolayer on the Au(1 1 1) substrate. The calculated activation energies indicate that Xe becomes movable on pure Au(1 1 1) surface at a temperature of around 30 K, whereas its motion can be activated only at a high temperature of similar to 50 K on graphene and on graphene-coated Au(1 1 1) substrates, in good agreement with recent experimental measurements by quartz crystal microbalance technique
Determination of corrugation and friction of Cu(111) toward adsorption and motion of Ne and Xe
No full textThe corrugation feature of potential energy surfaces (PESs) for rare-gas (RG) adlayers on metal surfaces has been extensively explored in the positive adsorption energy part. Here, we show that opposite corrugation features may also happen in the negative adsorption energy side for Ne and Xe on Cu(111). While the PES of Ne/Cu(111) is corrugated near the equilibrium adsorption geometry, i.e., Ne prefers the hollow site, the PES of Xe/Cu(111) is anticorrugated, i.e., Xe prefers the atop site. The weak hybridization of RG p and Cu d states is critical for this qualitative difference. Furthermore, the calculated activation energies indicate that Ne may move on Cu(111) at a very low temperature, whereas Xe motion can be activated only above 35 K. We found that the inclusion of the nonlocal van der Waals correction is essential for the correct determination of adsorption and motion energetics for RG adatoms on metals through density functional calculations
The Vacancy Formation Energy for Zirconium.
No full textThe vacancy formation energy of zirconium has been calculated by means of a microscopic model which takes into account the electron-electron and electron-ion interaction. The result obtained is in reasonable agreement with the presently available experimental data. The connection between the vacancy formation energy and the basic mechanism for irradiation creep in this materials are discussed
Premelting of Al(110) surface from a local perspective -- Presentazione poster by R. Zivieri - Conferenza internazionale
No full textA molecular-dynamics analysis of local disorder on Al(110) surface near the melting point has been
performed. Premelting process has been studied calculating the surface extended X-ray absorption fine
structure (SEXAFS) Debye-Waller factor which has an anisotropical behaviour above 800 K for the
range of temperatures up to the melting point. Theoretical results have been compared with recent
SEXAFS measurements. The calculations show that bonds between Al atoms , for temperatures higher
than 800 K, are broken along the direction normal to the surface, while they remain intact on the
surface. A loss of coordination number is present as an evidence of structural disorder for temperatures
near melting. -- Presentazione poster by R. Zivieri - Conferenza internazional
Atomic holography: does a polarized light beam improve the image?
No full textPerforming three measurements (holograms) on the same sample with the same beam but different polarization, spurious spots can be reduced and the holographic image appears to be better. The change of polarization requires nothing more than a rotation of the sample around the beam's direction. For the reconstruction of the image one applies the standard Fourier transform (FT) techniques on a combination of the holograms obtained. The resulting image is better than that obtained with an unpolarized beam
Thermodynamic Properties of Alkali Metals
No full textAbstract - We have calculated the equation of state at O K for the various alkali metals starting from a theoretical description of the volume dependence of their dynamical matrix. We also obtain a detailed knowledge of the individual Grueneisen parameters which also allow us to calculate temperature effects like the thermal pressure and the thermal expansion coefficient. The agreement with the experimental data is satisfactory and it can be considered as a test of validity of the quasi-harmonic approximation
Strong Interference Effects in Surface Brillouin Scattering from a Supported Transparent Film
No full textA measurement of surface Brillouin scattering from a 2250-Å film of silica grown on (001) silicon is presented. The spectrum shows many structures related to Rayleigh, Sezawa, and Lamb waves. We calculate the Brillouin cross section taking the ripple and the elasto-optic coupling mechanisms into account in the two media. Both the mechanisms are found to be important and there is evidence of strong interference effects between the ripple and the elasto-optic contributions to the scattering amplitude
Dielectric matrix and covalent charge distribution of silicon
No full textAbstract. The valence charge density associated with the nearly free electron dielectric matrix of silicon is computed. The part arising from the off-diagonal dielectric elements is shown to contain the effects of covalency and displays the piling up of bonding charge between the ions
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