The effect of impurities on TL emission wavelengths of NaCl crystals

This paper is devoted to studying the influence of Ca, Si, Pb, and Cr impurities (possessing no absorption bands at the wavelength of acting laser irradiation) on the value of bulk laser damage threshold and UV absorption in KDP single crystals. It is shown that for the investigated concentration range (1 divided by 10<SUP>-5</SUP> 1 divided by 10<SUP>-2 mass%</SUP> laser damage threshold essentially decreases with raising the concentration of impurity ions in the crystal lattice. The maximal value of the said characteristic (approximately 40 J/cm<SUP>2</SUP>) is found to be achieved in the case when the concentration of impurities is not less than 1 divided by 10<SUP>-5</SUP> mass%.

: This is a report on the progress in theoretical calculations of scanning tunneling microscopy spectra near impurities in superconductors. Calculations have been performed for Zn and Ni impurities in BSCCO, and compared with recent scanning tunneling microscopy spectra near those impurities. Good quantitative agreement has been found. The Zn atom appears to locally destroy superconductivity. New experiments involving two Ni atoms and a Ni and Zn atom have been proposed to clarify the range of this effect from Zn, and also to observe the spin-spin correlation function in the superconducting state.

Tuning the microstructure of biomass-derived hard carbons by controlling the impurity removal process for enhanced Na ion storage performance

Anomalous Zn- and Ni-substitution effects on superconductivity in the superconducting weak ferromagnets RuSr2RCu2O8 (R = Gd, Eu)

It has been observed that the catalytic activity of MoS2 crystals is enhanced when either Co or Ni atoms are added. The presence of these atoms leads to electronic rearrangements, which are considered the source of catalytic improvement. However, the relation between the electronic properties and the enhancement of the catalytic activity is not yet fully understood. In order to get insight into the electronic-level changes that affect the catalyst performance, a solid-state density functional study has been carried out for Mo, Co/Mo, and Ni/Mo sulfides, using bulk and surface models. The MoS2 crystallize in a well-known layered structure, which has been used together with the supercell model to simulate the \documentclass{article}\pagestyle{empty}\begin{document}$(10\ \bar{1}\ 0)$\end{document} edge surface of MoS2. The binary sulfides were obtained substituting Co or Ni by Mo from the original MoS2 bulk model. The electronic structure in a nonmagnetic state is analyzed and, in particular, the density of states of metal and sulfur atoms for the surface and bulk are compared. Finally, we discuss the important role that these properties play in the hydrodesulfurization reaction and concluded that Mo at the surface remains the relevant reactive atomic center in the bimetallic systems, whereas Co and Ni are responsible for increasing the Mo reactivity at the surface. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 406–415, 2000

The modified embedded atom method (MEAM) is used to investigate the geometry and energetics of Si ad-dimers and adatoms on the reconstructed Si(001) surface. Site stability and saddle point energies are predicted for a large number of possible mechanisms. The calculations predict the relative stability of parallel and normal ad-dimers to be 80 meV, in excellent agreement with from experiment, the barrier to rotation of these dimers to be 0.66 eV compared with , and the activation energy for diffusion parallel to the dimer rows to be 0.74 eV compared with . These calculations are the first of any kind to predict quantitative agreement with experiment. We also predict substitutional Ni atoms near the surface are bound to the second and first layer below the dimer layer by 0.65 and 0.47 eV relative to bulk substitutional Ni atoms. The effect of these Ni impurities on the ad-dimer stability is predicted. A parallel ad-dimer is repelled by a substitutional Ni impurity by 30 meV compared with the 20 - 35 meV observed in experiment for an unknown substrate defect.

Ni Impurity Effect on the Transport Properties and Carrier Concentration of Bi2212

Effect of Ni and Co impurities on the electronic structure and magnetic properties of BCC iron

The scope of this paper is to analyse the effect of Au and Cr impurities, diffused onto GaSb substrates on the formation of nanodots created by LEIS using Ar+ ions It is concluded that oblique incidence in rotating configuration delays the formation of the nanodots compared to previously reported normal incidence experiments. The presence of cracks induced by the sputtering process has been observed both in the Au and Cr diffused samples. Cathodoluminescence (CL) spectra obtained in irradiated samples both pure and Crdiffused have revealed no difference between them, showing the usual three band encountered in this material (Band Gap at 798 meV, A Band at 777 meV and tail-states at 815 meV). However, a fourth band has been detected in the Au sample centered at 769 meV.

Effect of the chemical impurities on the luminescence emission of natural apatites

First-principles calculation of structural energetics of Al–TM (TM = Ti, Zr, Hf) intermetallics

High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using57Co/Fe Mossbauer and111In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of ∼5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mossbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.

The progress possible in the analysis of refractory powders such as ZrO2, SiC and Al2O3 by the use of new sample preparation, processing and introduction techniques elaborated for AAS, ICP-OES and ICP-MS with low and high mass resolution is demonstrated. For optimized sample preparation techniques based on dissolution of ZrO2, e.g. fusion with (NH4)2SO4, it is shown to what extent impurities present in (NH4)2SO4 determine the detection limit. Hydraulic high pressure nebulization with and without matrix removal by complexing the impurities with dithiocarbamates (Cu, Co, Cr and Ni) or oxine (Fe, Mn and Mo) and fixing them on a C18 solid phase for subsequent solid phase extraction coupled with flame atomic absorption was used to determine Fe, Cu, Cr, Mn, Ni, Co and Mo impurities in (NH4)2SO4 in the 10–100 ng/g range. Further a method to synthesize (NH4)2SO4 with higher purity than some commercially available high-purity (NH4)2SO4 with respect to Fe, Cu, Cr and Mn using high-purity NH3 and chlorosulphonic acid is shown. Reliable determinations of Fe and Al at the 100 μg/g level in ZrO2 with ICP-OES with matrix removal as well as with ICP-MS without matrix removal are reported. For the direct analysis of Al2O3 powders, slurry nebulization ICP-MS sample introduction is shown to improve detection limits and to reduce sample preparation, if the leachable and non-leachable fractions are analyzed separately. For powders such as SiC, the matrix or solvents can cause spectral interferences. Matrix removal is shown to be useful to improve detection limits for the interfered elements. High resolution ICP-MS can be used to control the completeness of matrix removal techniques and to overcome limitations due to spectral interferences even in case of complex materials.

Using the LCAO recursion approach, we investigate the microscopic properties of a Σ=9 (011) tilt grain boundary in silicon. The atomic configurations around the boundary are determined by using the modified (quenched) molecular dynamics method. The segregation energies are calculated for both dopant (B, P and As) and transitional (deep level; Ti, V, Cr, Mn, Fe, Co, Ni and Cu) impurities. In general, we have found that these impurity atoms tend to segregate to the tilt grain boundaries, except for B impurity (smallest segregation energy). The formation or shift of the band gap states plays an important role in determining the segregation energy of the impurity atoms. From the calculated energy levels of the segregated impurity atoms, we further discuss the electrical properties of the polycrystalline semiconductors.KeywordsImpurity AtomMolecular Dynamic MethodAtomic ConfigurationBoundary SegregationBand Structure EnergyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

F-aggregate colour centres in LiF crystals with divalent impurities (M = Ni, Co, Be, Mg) are investigated by optical and thermally stimulated depolarization current (TSDC) spectroscopy methods. The F+2 centres accumulation in the LiF:M2+ crystals is similar to the F+2 centres accumulation in undoped LiF. Accumulation of F+2-like colour centres was observed only in the LiF:Mg2+ crystals at the first stage of low temperature irradiation with radiation doses exceeding 107 R. F+2-like centres are not formed in LiF with Ni, Be and Co impurity ions. The difference between the properties of the magnesium on one hand and the nickel, beryllium or cobalt doped crystals on the other is discussed in terms of the Hayes-Nickols mechanism with extra anion vacancy generation in the case of the LiF:Mg2+ crystal. The absence of the mechanism in LiF:Ni2+ and LiF:Be2+ is connected to the reduction of the impurity Ni2+ and Be2+ ion valence state and in LiF:Co2+ to the small concentration of single Co2+V-c dipoles as a result of extensive dipole aggregation. The destruction of the F+2 and F+2-like centres takes place in LiF:Mg2+ crystals at the second stage of aggregation, at which other F-aggregated centres are formed, with the impurity-vacancy (IV) dipoles included in their composition. The two-band structure of the TSDC curve of irradiated LiF:Mg2+, with relaxation parameters close to those of single IV dipole reorientation bands, is in accordance with the above mechanism of aggregation. The creation mechanisms and models of laser active colour centres (F+2-like and F3Mg2+V-c `red' colour centres) are discussed.