Nitrogen incorporation at the SiO2/SiC interface via high temperature nitric oxide annealing leads to the passivation of electrically active interface defects, yielding improved inversion mobility in the semiconductor. However, we find that such nitrided oxides can possess a larger density of hole traps than as-grown oxides, which is detrimental to the reliability of devices (e.g., can lead to large threshold voltage instabilities and to accelerated failure). Three different charge injection techniques are used to characterize this phenomenon in metal–oxide–semiconductor structures: x-ray irradiation, internal photoemission and Fowler–Nordheim tunneling. Some nitrogen-based atomic configurations that could act as hole traps in nitrided SiO2 are discussed based on first-principles density functional calculations.

With extensive first-principles calculations, we investigated the geometric structure, phase transition, and electronic properties of orthorhombic, monoclinic, and tetragonal K 1x Na x NbO 3 (KNN) as functions of the Na content. We found that KNN undergoes an orthorhombic-to-monoclinic-to-orthorhombic phase transition when the Na content is gradually increased. We also found that the polarization vector of the monoclinic phase can be rotated more easily than those of the orthorhombic and tetragonal phases, giving rise to an enhanced piezoelectric response of the monoclinic KNN. Furthermore, our calculations provide an interpretation for the experimentally observed unusual broad peak of the KNN piezoelectric parameters.S. B. Sinnott-contributing editor Manuscript No. 35030.

Ab initio density-functional theory and thermodynamics calculations are combined to establish a microscopic mechanism for the oxidation of the α(2)-Ti(3)Al(0001) surface. The surface energies as functions of the chemical potentials, as well as structural relaxations and electronic densities of states, are determined. The surface phase diagram (SPD) of the α(2)-Ti(3)Al(0001) systems with different defects and at various oxygen coverages is constructed. It is found that the Al antisite defect prefers to segregate on the α(2)-Ti(3)Al(0001) surface and oxygen adsorption enhances the segregation with the formation of the surface with three Al antisites per unit surface cell (i.e. the top surface layer is full of Al atoms) at the initial stage of oxidation, accounting for the aluminum selective oxidation observed experimentally. After the initial stage of oxidation, the O-α(2)-Ti(3)Al(0001) system manifests itself with a non-uniform double-phase SPD, suggesting the competition between oxidations of the Al and Ti elements in the oxidation process. This result explains the experimentally observed second regime of oxidation in which both metal elements are oxidized.

Articles you may be interested in Transition-metal and metalloid substitutions in L10-ordered FeNiThe effect of 3d transition elements ͑such as V, Cr, Mn, Fe, Co, and Ni additions͒ on material properties in L1 0 TiAl has been studied using the first-principles DMol and discrete variational method within the framework of the density-functional theory. The transfer energy calculation indicates that all these 3d elements show a tendency to substitute for Al sites in the stoichiometric TiAl alloy, with the increasing order V Ͻ CrϽ MnϽ NiϽ FeϽ Co. Our results show that the local distortion of crystal lattice around an impurity atom is nonuniform, and it is found that the important influencing factors on the local lattice distortion are the impurity atom size and the site preference. Based on the effects of the doped alloying elements on the structural parameters and mechanical properties, we conclude that the larger bond strength and the smaller axial ratio benefit the ductility.

By using first-principles DMol and the discrete-variational method (DVM) based on density functional theory, we investigated the effect of some light impurities, H, B, C, N and O, on the electronic structure of their corresponding different impurity-doped systems in γ-TiAl. The impurity formation energy, Mulliken occupation, bond order and charge density difference have been calculated to study the impurity-induced changes in the energetics and electronic structure. According to the impurity formation energy, it is found that the impurities energetically prefer to occupy the Ti-rich octahedron interstitial sites in the order H