Investigation of the Ga-rich GaAs(001) Surface Reconstructions Stability and Interaction with Halogens

Atomic and electronic structures for a number of GaAs(001) surface geometries were studied within the density functional theory in order to re-examine the energy stability of surface reconstructions in the Ga-rich limit. It was shown that among geometries with (42) symmetry so-called ζ-model is most stable but the energetically favored Ga-rich (24) reconstructions are stabilized by dimerized Ga and As atoms. Our calculations predict the coexistence of (24) and (44) reconstructions on GaAs(001) in the Ga-rich limit. Comparative study of the halogens (F, Cl, I) adsorption on the -GaAs(001)-(42) surface were performed. The energetically preferable positions for all considered halogens are found on-top sites above dimerized and nondimerized Ga atoms. The electronic properties of the semiconductor surface and its change upon halogen adsorption are discussed. It was shown that the interaction of halogen with the Ga dimerized at-oms leads to the weakening of the chemical bonds between surface atoms that determines the initial stage of surface etching. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3531

Influence of Fluorine and Oxygen Adsorption on the Electronic Properties of the InAs(111)A-(2*2) Surface

Atomic and electronic structures of the reconstructed InAs(111)A-(2*2) surface are studied within den-sity functional theory. The most stable adsorption positions of oxygen and fluorine on the surface are de-termined. Our calculations show that oxygen adsorption leads to appearance of electronic states in band gap and the structure of these surface states strongly depends on adsorption geometry. An increase of oxy-gen concentration and its coadsorption with fluorine leads to substantial structural changes in the surface and subsurface layers due to adsorbate penetration into semiconductor. Evolution of the electronic struc-ture upon oxygen and fluorine adsorption on the reconstructed InAs(111)A-(2*2) surface in dependence on adsorbate geometry is analyzed. It is shown that surface states induced by oxygen adsorption can be par-tially removed by fluorine, when it forms bonds with the surface indium atoms. The formation of the indi-um–fluorine or indium–oxygen bonds proceeds due to charge transfer from arsenic atoms to indium ones in the surface layers. The microscopic mechanism of fluorine influence on the interface states at InAs–oxides interface is suggested. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3529

Influence of Interstitial Impurities (H, B, C) on Grain Boundary Cohesion in B2 Ti-based Alloys

The investigation of hydrogen, boron and carbon sorption properties at the Σ5(310) symmetrical tilt grain boundary (GB) and (310) free surface (FS) in B2 Ti-based alloys was carried out by the plane-wave pseudopotential method within density functional theory. The most preferential positions for interstitial impurities at GB were determined. It was shown that impurities sorption energies at GB depend strongly on their local environment. The analysis of electronic properties allows us to establish the microscopic na-ture of chemical bonding of all considered impurities at GB. It was shown that H decreases more signifi-cantly the surface energies than the GB energy in contrast to B and C. This results in decreasing the Grif-fith work that indicates also the decrease of the strength of grain boundary. The segregation of H at the GB makes intergranular fracture much easier because the bonding between metal atoms, which are neigh-bors of H, is weakened. The segregation behavior of hydrogen confirms it as an embrittler for B2 Ti-based alloys. At the same time boron and carbon segregation contrast to hydrogen increase the GB cohesion. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3551

Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems

We report a theoretical study of the quasiparticle lifetime and the quasiparticle mean free path caused by inelastic electron-electron scattering in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based on spin-polarized calculations, which are performed within the $GW$ approximation for equiatomic and Co- and Ni-rich compounds, as well as for their constituents. We mainly focus on the spin asymmetry of the quasiparticle properties, which leads to the spin-filtering effect experimentally observed in spin-dependent transport of hot electrons and holes in the systems under study. By comparing with available experimental data on the attenuation length, we estimate the contribution of the inelastic mean free path to the latter.Comment: 10 pages, 10 figure

The investigation of electronic properties of Ti-based alloys

The self-consistent band structure calculations of the ordered and disordered intermetallic titaniumbased alloys were performed using full-potential linearized augmented plane wave (FLAPW) method and Korringa-Khon-Rostoker -coherent potential approximation (KKR-CPA) The electronic structure of the (001) surfaces are also calculated. The alteration of the electronic properties in the three TiMe series (Me=Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) are discussed in the dependence of a number of valence electrons. The changes of the electronic structure during martensitic transformation, with disordering and alloying are analyzed. The calculated emission, absorption, electron energy loss spectra and optical properties are found to be in good agreement with experiment

The adsorption of hydrogen on B2TiFe surfaces

We investigate the interaction of hydrogen with the B2 TiFe (001)and (110) surfaces using the full-potential linearized augmented plane wave (FLAPW) method, The changes in the electronic structures in the different B2 TiFe surfaces in comparison with the bulk ground state are analyzed, Ferromagnetic order is found in the Fe-terminated (001) surface with the magnetic moment 2.27mu(B),3, which quickly diminishes inside the film. The absorption of hydrogen onto the Fe/TiFe (001) surface results in a decrease in the magnetic moment. For the fully relaxed surfaces interacting with hydrogen, the driving bonding mechanisms for different adsorption sites are discussed. A microscopic explanation of the local surface reactivity is given. It is found that the hydrogen atoms form stronger chemical bonds with the iron atoms than with the titanium atoms in the B2 TiFe surfaces. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reservedclose272

Electronic structure of binary and ternary Ti-based shape-memory alloys

The electronic and structural properties for TiMe (Me = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) alloys are studied using the full-potential linearized augmented plane wave (FLAPW) method. The alteration of electronic structure with disorder and alloying with a third element is analyzed. The calculated emission, absorption X-ray and electron energy-loss spectra are found to be in good agreement with experiments. (C) 2001 Elsevier Science Ltd. All rights reservedclose161