Showing papers by "Fabrizio Cleri published in 2008"
TL;DR: In this paper, the atomic structure and energy-level alignment at a representative Si-molecule-metal interface was calculated, and a scheme for the vacuum level adjustment was proposed, consistent with the formation of interfacial dipoles and charge transfer to the molecular layer.
Abstract: We calculated the atomic structure and energy-level alignment at a representative Si-molecule-metal interface. The covalently bonded Si-molecule interface largely determines the overall band offset and the highest occupied molecular orbital position, while charge transfer across the metal-molecule interface induces localized π levels, even in the absence of covalent bonding to the metal. We propose a scheme for the vacuum level adjustment, consistent with the formation of interfacial dipoles and charge transfer to the molecular layer. The highest occupied π level of the molecule should be the main electronic state involved in the transport properties, while interface dipoles appear to be related to the interface-induced states.
6 citations
ENEA1
TL;DR: In this article, the atomic-level structure of a model Mg-MgH2 interface by means of the Car-Parrinello molecular dynamics method was characterized in terms of total energy calculations, and an estimate of the work of adhesion was given, in good agreement with experimental results on similar systems.
Abstract: We studied the atomic-level structure of a model Mg-MgH2 interface by means of the Car-Parrinello molecular dynamics method (CPMD). The interface was characterized in terms of total energy calculations, and an estimate of the work of adhesion was given, in good agreement with experimental results on similar systems. Furthermore, the interface was studied in a range of temperatures of interest for the desorption of hydrogen. We determined the diffusivity of atomic hydrogen as a function of the temperature, and give an estimate of the desorption temperature.
3 citations
TL;DR: In this article, the MgH2-Mg phase transformation in powder samples has been performed to gain detailed metallographic information, and a method for studying this phase transformation by cross sectional samples scanning electron microscopy observation of partially transformed material has been developed.
Abstract: The remarkable ability of magnesium to store significant quantities of hydrogen has fostered intense research efforts in the last years in view of its future applications where light and safe hydrogen-storage media are needed. Magnesium material, characterized by light weight and low cost of production, can reversibly store about 7.7 wt% hydrogen. However, further research is needed since Mg has a high operation temperature and slow absorption kinetics that prevent the use in practical applications. For these reasons a detailed study of the interface between Mg and MgH2 is needed. Further insights are gained by characterizing the Mg-MgH2 system from both the experimental and the numerical point of view. The study of the MgH2-Mg phase transformation in powder samples has been performed to gain detailed metallographic information. A method for studying this phase transformation by cross sectional samples scanning electron microscopy observation of partially transformed material has been developed. This method exploits the peculiar features of this system where the MgH2 phase is insulating and the Mg is a metallic conducting phase. This difference can induce a contrast between the two phases owing to the different secondary emission yield. Further insights are gained by characterizing Mg-MgH2 interfaces by means of accurate first-principle molecular dynamics simulations based on the density-functional theory. Extensive electronic structure calculations are used to characterize the equilibrium properties and the behavior of the surfaces in terms of total energy considerations and atomic diffusion.