Plane waves Point defects

Abstract The surfaces of model metal oxides offer many fundamental examples where the outcome of a specific chemical reaction might be linked to the surface structure and local electronic properties. In this work the reaction of simple molecules such as ammonia, alcohols, carboxylic and amino acids is studied on two metal oxide single crystals rutile TiO CllO) and (001) and fluorite UOj(l 11). Studies are conducted with XPS, TPD, and Plane Wave Density Functional Theory (DFT). The effect of surface structure is outlined by comparing the TiOj(llO) rutile surface to those of TiOjCOOl), while the effect of surface point defects is mainly discussed in the case of stoichiometric and substoichiometric UOjClll). 

The Fa(11)-centre is an F-centre, where one of the nearest cations of the lattice is replaced by a different alkali ion. There is the combination of two point defects, which means that its point symmetry is axial rather than cubic, and so is the potential well, which is a single well with a diameter close to the pure F-centre in the x and y directions and slightly expanded in the z-direction, provided the disturbing cation is smaller than that of the host lattice (Fig.2.4a and 2.5a). This situation will hardly affect the ground state of the electron wave function, since it will remain mainly spherically symmetric, (close to a s-like electron function), however, after excitation, the n = 2 electron distribution can orient its nodal plane to coincide either with the xy-plane, which is favorable, or with the two perpendicular planes leading... 

The calculation schemes usually used for point defect include 1. the choice of the model of the defective crystal 2. the choice of the Hamiltonian (Hartree-Fock, DFT or hybrid, semiempirical) 3. the choice of the basis for the one-electron Bloch functions decomposition hnear combination of atomic orbitals (LCAO) or plane waves (PW). 

As in any semiconductors, point defects affect the electrical and optical properties of ZnO as well. Point defects include native defects (vacancies, interstitials, and antisites), impurities, and defect complexes. The concentration of point defects depends on their formation energies. Van de WaHe et al. [86,87] calculated formation energies and electronic structure of native point defects and hydrogen in ZnO by using the first-principles, plane-wave pseudopotential technique together with the supercell approach. In this theory, the concentration of a defect in a crystal under thermodynamic equilibrium depends upon its formation energy if in the following form ... 

Many choices for carrying out an inspection with guided waves can be obtained from the dispersion curves. Many different combinations of phase velocity and frequency might work equally well for finding specific cohesive or adhesive type defects. As an example, wave structures for two specific points are illustrated in Fig. 10. In Fig. 10a, for example, the in-plane displacement component, which could be quite sensitive to certain kinds of defects along the interface or in the adhesive layer, is quite dominant along the interface and in the adhesive layer. In Fig. 10b, however, from the power distribution, it is expected to have best results for substrate inspection only if needed. This point would not be selected for adhesive bond inspection. Theoretical results are useful primarily for establishing... 

---