Navegando por Autor "Barrio, R. A."
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Artigo Effects of electron-electron correlations on defect and interface states in amorphous Si and Si02 systems(American Physical Society, 1986-07-15) Carriço, Artur da Silva; Barrio, R. A.; Elliot, R. J.The effects of electron-electron correlations are included in the nearest-neighbor tight-binding model of tetrahedrally coordinated covalent solids in the amorphous phase. The amorphous systems are represented by Bethe lattices and the electron-electron interactions are parametrized for a short- range interaction in a Hubbard-like Hamiltonian. Self-consistent solutions are obtained in the Hartree-Fock approximation. If defects are included the self-consistent energy parameters vary with distance away from the defect but the solution is still possible if this variation falls away rapid- ly over a few shells. The cases of dangling bonds in Si and Si02 are considered by terminating the Bethe lattice. The former shows localized states in the gap for two charge configurations, but Si02 shows only one. The interface between Si and Si02 is represented by joining two Bethe lattices. The self-consistent solution shows appreciable charge transfer on to the first 0 atom and consequential changes in the local density of states.Artigo Model of electronic states at the Si-Si02 interface(American Physical Society, 1986-07-15) Carriço, Artur da Silva; Barrio, R. A.; Elliot, R. J.The electronic properties of the interface between crystalline Si and its amorphous oxide SiO 2 have been studied within the tight-binding approximation by saturating the dangling bonds in three different surfaces (111), (110), and (100) of a semi-infinite Si crystal with SiO2 Bethe lattices. The localized states due to isolated dangling bonds in the interfaces (Pb centers) are found to be roughly at the same energy, in the Si gap for the (111) and (110) cases, but the (100) interface differs substantially from the other two. It is also found that the value of the site-energy interaction parameter on the Si defect site is important in determining the energy of the defect state.Artigo Modelling the raman spectrum of the amorphous- crystal Si system(Institute of Physics (the “Institute”) and IOPscience, 1986) Carriço, Artur da Silva; Barrio, R. A.; Elliot, R. J.A model to calculate the Raman response of small Si crystallites immersed in an amorphous Si matrix is developed. The structure of the system is modelled by an infinite crystalline slab of varying width, in which the atoms on the (111) surfaces on both sides of the slab are attached to Bethe lattices. The Raman response is obtained from a simple polarisability model using the Green function technique. The results are compared with recent experiments. The model can be used for Si crystallites with free and hydrogenated (111) surfaces.Artigo Vibrational properties of amorphous Si-N and Ge- N alloys(IOP Publishing Ltda, 1989) Carriço, Artur da Silva; Barrio, R. A.; Marques, F. C.; Sanjurjo, J.; Chambouleyron, I.A theoretical study of the vibrational density of states of amorphous alloys was developed by applying a simple effective-medium theory with a Born Hamiltonian. This theory is equivalent to the coherent-potential approximation, with the advantage that it is set in real space in a very simple way. With this theory, one can observe the differences in the spectra of amorphous Si and Ge when several concentrations of N atoms are added. The predictions of the theory are compared with data from Raman scattering experiments.