Horacio Alves | Universidade Federal de São João del Rei (original) (raw)

Papers by Horacio Alves

Journal of Physics: Condensed Matter, 1998

ABSTRACT We report first-principles studies of the stability and electronic properties of a layer... more ABSTRACT We report first-principles studies of the stability and electronic properties of a layer of Te atoms at an InAs/GaAs(001) interface. The calculations are performed within the LDA approximation. Our results indicate that the formation of half a monolayer of Te atoms is energetically unstable against phase segregations, indicating that the Te atoms do not reduce the GaAs/InAs interface energy. However, a GaAs/Te(0.5)/InAs interface can be formed on the basis of a kinetic process. The Te atoms occupying As sites have strongly covalent character, and give rise to a half-filled band at 0.15 eV below the conduction band. The calculated valence-band offset, with the inclusion of half a monolayer of Te atoms, presents a good agreement with experimental results.

In this work, we have performed spin-polarized calculations for the structural and electronic pro... more In this work, we have performed spin-polarized calculations for the structural and electronic properties of vacancies and anti-site defects in the rocksalt PbTe. Our obtained results have shown that both the Pb and Te antisites are the favorable defects in Pb and Te rich conditions, respectively. Moreover, in the perfect stoichiometry condition, the antisites, as well as the Te vacancy, are equally probable to find. Considering the charge injection in the system, all the defects change from the 2+ charge state to the 2one within 14 meV, at around 80 meV from the valence band edge within the bandgap. This feature makes it difficult to experimentally characterize these defects in PbTe.

Proceedings of Brazilian Workshop on Semiconductor Physics, 2017

Brazilian Journal of Physics

In this work we h a ve calculated the electronic structure of point defects in cubic silicon carb... more In this work we h a ve calculated the electronic structure of point defects in cubic silicon carbide(3C-SiC) using the Molecular Cluster Model within the framework of the ab initio LCAO-MO Unrestricted Hartree-Fock method. The following point defects were studied: vacancies, anti-sites, Si and C interstitials at both tetrahedral and hexagonal sites. Our results show good agreement with both experimental and other theoretical calcula-tions. From the total energy evaluation, without including relaxation and/or local distortion eeects, we found that carbon anti-site and silicon vacancy are the most energetically stable point defects in both C-rich and stoichiometrically 3C-SiC, while for Si-rich material, silicon anti-site and carbon vacancy are the most stable ones.

physica status solidi (c), 2010

ABSTRACT In this work, we present our theoretical results for the relaxation of the rutile TiO2 (... more ABSTRACT In this work, we present our theoretical results for the relaxation of the rutile TiO2 (110), as well as for the adsorption of benzene over this surface. Our results are in good agreement with both the available theoretical and experimental data, whenever these comparisons were possible. Based on our obtained results, we show that the interaction between the adsorbate and the TiO2 (110) surface shows a van der Waalslike character, with the calculated adsorption energies at the order of 43 to 173 meV. In this adsorption process, the H atoms of the benzene prefer to bind with the surface Ti atoms. As a result, two occupied electronic levels appear at the surface bandgap, which are responsible for the optical absorption peaks at the blue-violet region of the electromagnetic spectra. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

physica status solidi (b), 2009

ABSTRACT In this work, theoretical results for the equation of state, the phonon dispersions and ... more ABSTRACT In this work, theoretical results for the equation of state, the phonon dispersions and their pressure dependence of MnAs and MnN are presented. The results show that the inclusion of spin-polarization effects in the calculations is important in order to give the correct energy ordering of the possible structures, and are in good agreement with the experimental results whenever this comparison is possible. Based on the obtained results, it is found that the phonon frequencies of these materials are very sensitive to the applied pressure. Moreover, the pressure dependence of the vibrational modes of both MnAs and MnN show a negative bowing which has its value increased when we go from a structure with lower symmetry to a high symmetric one.