Il Morgante maggiore

Oprawa półskórek

Morgante , di Luigi Pulci. [Li Fatti di Carlo Magno et de i Palatini de Francia]

[Morgante

First-principles study of acetylene adsorption on Si(100): The end-bridge structure

We present the results of a first-principles study of the adsorption of acetylene on Si(100). In particular, we focus on a recent controversial issue concerning the occurrence of the "end-bridge" configuration in which an acetylene molecule bridges two adjacent surface Si dimers. At variance with recent theoretical calculations, we find that the lowest-energy "end-bridge" structure is stable and nonmetallic both at 0.5 ML and at 1.0 ML coverage. This leads to the conclusion that this configuration can be one of those observed in experiments. The results of first-principles calculations of the optical properties of different configurations of acetylene on Si(100) are also presented and discussed

Electronic and optical properties of acetylene and ethylene on Si(001)

In this work, we present the results of ab-initio theoretical calculations concerning the electronic and optical properties of Si(001) surface covered by small hydrocarbon molecules, namely acetylene and ethylene. As a result of the adsorption process, both molecules are covalently bonded to the surface, and we point out analogies and differences of the two systems under study. The most stable configurations have been taken into account at different coverages. We will show how band structure and reflectance anisotropy spectra calculations supply additional indirect information concerning the adsorption geometry and the saturation coverage, that have been longly debated. (C) 2008 Elsevier Ltd. All rights reserved

Amorphous steel coatings deposited by cold-gas spraying

Cold-gas spray (CGS) deposition of amorphous steel coatings starting from a commercial feedstock powder containing boron, tungsten, and silicon was investigated. Microstructural characterization, carried out by X-ray diffraction (XRD), transmission electron microscopy, and backscattered electron diffraction (EBSD) analysis, confirmed the amorphous nature of deposited coatings. The amorphization phenomenon is related to high-strain/strain-rate deformation with shear instability caused by very high particle kinetic energy, with a mechanism that resembles the severe plastic deformation process. The CGS coatings were heat-treated at temperatures ranging from 650 to 850 ◦C to induce partial recrystallization. The effect of nanocrystal nucleation and growth on the hardness of the coatings was investigated, and the hardness of heat-treated samples was found to increase with respect to as-sprayed coatings, outperforming conventional high-velocity oxy-fuel (HVOF) deposits. Hardness was found to decrease after prolonged (<90 min) or higher temperature (>750 ◦C) exposures