Near-forward Raman scattering intensity in ZnO

We have measured the Raman scattering intensities of the E₁ (TO) polariton mode in ZnO, a wurtzite type crystal, at room and liquid nitrogen temperatures. These results reveal a novel behavior in contrast to that observed for ZnSe. These results confirm earlier theoretical considerations.     

Effects of X-ray absorption in the analysis of thick target samples by XRF

The accuracy of the quantitative analysis of thick targets by XRF is impaired by effects due to the absorption of X-rays in the matrix associated with the non-uniformity of the X-ray beam and the lack of knowledge of the actual distribution of trace elements in the target. The uncertainty in the elemental mass associated to a definite number X-rays detected is discussed in the paper. A correction factor is derived to account specifically for the effect of the absorption of X-rays and the non-uniformity of the X-ray beam. Work partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico, Financiadora de Estudos e Projetos and International Atomic Energy Agency.     

Self-consistent-field CNDO/BW cluster model of covalent solids

We have suggested a parametrization scheme for the self -consistent CNDO/BW method suitable to model the electronic structure of perfect and locally perturbed covalent solids. By working on small clusters we have carried out calculations for diamond perfect crystal and for nitrogen replacing a carbon atom in the lattice. The results show that the methos is accurate to calculate one electron energy-eigenvalues and total energies.     

Hot electron and hot phonon contributions to radiative emission spectra in CdS at high excitation intensities

The dependence of excitation frequency of photoluminescence spectral shape of CdS at high excitation intensities allowed discrimination between hot phonon and hot electron contributions to the broadening of the emission band on one side and the broadening due to many body effects on the other. It was found that the shift towards lower energies of the emission peak is mainly due to induced high carrier density and that the broadening is related to the presence of high densities of optical phonons and hot carriers.     

Photoexcited hot phonons and phonon lifetimes in GaAs

A study of optical lifetimes as determined from surface conditions is made through Raman lineshape analysis and non-equilibrium phonon distributions induced by energetic photoelectrons. Results indicate that first-order Raman scattered linewidths are lifetime determined and that phonon lifetimes depend upon surface conditions. Our observations also give strong support to the mechanism and analysis proposed earlier for hot phonon generation through photoelectron relaxation.     

Multiple scattering mass operator method for molecular orbital calculations

An exchange-correlation potential model to be used in connection with the multiple scattering method is presented. Retaining the main advantages of the multiple scattering method with the Xα potential, particularly its low computational requirements, this new formalism does not require any adjustable parameter. Test calculations on the NiF₆^4? system are reported and compared with experimental and ab initio results.     

Defect-molecule parameters for the divacancy in silicon

The hamiltonian eigenvalue problem is solved for a diva cancy in silicon within the framework of the defect-molecule model. A direct connection between the solution of this problem and a self-consistent multiple-scattering cluster calculation is established in order to determine the parameters of the model. The obtained results provide a quantitative confirmation of the currently accepted microscopic picture of the divacancy.     

Stable colloidal suspensions of nanostructured zirconium oxide synthesized by hydrothermal process

Nanocrystalline zirconium oxide was synthesized by hydrothermal treatment of ZrO(NO₃)₂ and ZrOCl₂ aqueous solutions at different temperatures and time in presence of hydrogen peroxide. Hydrothermal treatment of zirconium salts (0.25 and 0.50 mol L^?1) produced nanocrystalline monoclinic ZrO₂ powders with narrow size distribution, which were formed by the attachment of the smaller particles with crystallites size of 3.5 nm, estimated by means of the Scherrer’s equation and confirmed by transmission electronic microscopy. Typical monoclinic zirconium oxide X-ray powder diffraction patterns and Raman spectra were obtained for all the crystalline powders. It was observed that the crystallization depends strongly on the temperature, resulting in amorphous material when the synthesis was realized at 100 °C, and crystalline with monoclinic phase when synthesized at 110 °C, independently of the salt used. Zirconium oxide colloidal nanoparticles were formed only at hydrothermal treatments longer than 24 h. The stability of the colloids was successfully characterized of zeta potential, showing an initial value of + 59.2 mV in acid media and isoelectric point at pH = 5.2, in good agreement with previous studies.