An investigation of the effect of the nearest surroundings on the formation of V Lα emission bands for solid solutions of rare earth orthovanadates—orthophosphates

The V Lα, P Kβ and O Kα X-ray emission spectra for solid solutions YVO₄—YPO₄ and EuVO₄—EuPO₄ have been studied. It is shown that with an increase in concentration of orthophosphate in a substitutional solid solution a hump appears in the low energy part of the V Lα spectrum, corresponding in energy to the P Kβ spectrum. The cluster calculation of the electronic structure of solid solutions YVO₄—YPO₄, carried out by the Extended Hückel method, explains this effect as due to the hybridization of V 3d and P 3p states when [PO₄ ] complexes are introduced into the orthovanadate tetrahedral lattice.     

Linear and nonlinear optical properties of Ca3(VO4)2

Single crystals of Ca₃ (VO₄)₂ have been grown by the Czochralski method. The refractive indices show that the crystals are phasematchable between 1.72 μm and 2.94 μm with favourable values for acceptance angle and spectral width of the incident laser beam in the entire phasematching range. The nonlinear optical coefficients have been measured by the Maker fringe method at a fundamental wavelength of 1.064 μm. They are comparable to those of KDP. Thus the crystals are potentially useful for frequency conversion of broadband or tunable laser sources as semiconductor and F-center lasers. They may also be installed in high f-number IR image converters.     

A study of the adsorption of several oxygen-containing molecules (O2, CO,NO, H2O) on Re(0001) by XPS,UPS and temperature programmed desorption

We have studied the adsorption of oxygen, carbon monoxide, nitric oxide, and water vapour on Re(0001), using X-ray and ultra-violet photo electron spectroscopies (XPS and UPS) and temperature-programmed desorption. As on polycrystalline rhenium, adsorbed oxygen is completely dissociated, even at room temperature. Furthermore, the formation of a superficial oxide at room temperature seems probable. Carbon monoxide is almost completely molecularly adsorbed, only a very small fraction being dissociatively adsorbed in a single β- state. However, an attractive interaction still exists between the adsorbed atoms in this β- state. Nitric oxide is adsorbed in a dissociated β₂ state and a molecular β₁ state. The population is smaller than on polycrystalline rhenium, corresponding to half a monolayer. Mathematical treatment of the desorption spectra allowed us to determine the activation energy for desorption of nitrogen resulting from the decomposition of adsorbed species. These quantities were found to be similar to those measured for polycrystalline rhenium.     

XPS study of the exchange-splitting in the s-levels of Mn and R in RMn2Si2 (R = La to Nd,Sm and Gd)

Exchange (or multiplet) splitting, ΔE_s of the 3s core-level of Mn in RMn₂Si₂ (R = La to Nd, Sm and Gd) has been observed using XPS technique. The measured value of ΔE_s is used to determine the magnetic moment on Mn ion in RMn₂Si₂. ΔE_s has also been measured for the 4s and 5s levels of R in RMn₂Si₂ and it is found that the value of ΔE_s increases with increase in the number of unpaired spins (La to Gd).     

A study of the interaction between perylene and the TiO2(1 1 0)-(1 × 1) surface-based on XPS, UPS and NEXAFS measurements

The interaction between a semi-large aromatic hydrocarbon compound (perylene) and the TiO₂(1 1 0)-(1 × 1) surface under ultra high vacuum conditions has been probed by X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) methods. UPS measurements of the adsorbate system have been compared with an experimental UPS spectrum of perylene in the gas phase and a calculated spectrum obtained by means of density functional theory (DFT) methods. NEXAFS results of perylene molecules adsorbed on TiO₂(1 1 0)-(1 × 1) were compared with data from an α-phase perylene single crystal. A novel analysis of the valence data has been employed to show that no strong chemical interaction takes place between perylene and the TiO₂(1 1 0)-(1 × 1) surface. Furthermore, angle-dependent NEXAFS measurements and the growth curve results suggest that the perylene molecules are oriented flat down onto the TiO₂ substrate due to weak van der Waals interactions.