Formation and electronic properties of oxide and sulphide films of Co,Ni and Mo studied by XPS

Dry O₂ oxidation up to 400°C, water immersion at room temperature or H₂S sulphidation at 400°C forms oxide or sulphide films on polycrystalline Co and Ni foils. X-ray photoelectron spectra (XPS) of the Co 2p and Ni 2p core levels and valence band (VB) structure changes allow the identification of the chemical state of such films and their electronic properties. They are compared with the films obtained on Mo in similar conditions. Ni appears less reactive than Co during O₂ or water oxidation and is considered as a more noble metal. Dry oxidation mainly induces CoO while water immersion induces formation of CoO(OH). For Ni, phases like Ni₂O₃, Ni(OH)₂ and/or NiO(OH) are the most probable products, respectively. H₂S sulphidation always produces a sulphur-rich Co or Ni phase. The VB response to sulphidation of the three studied metals shows that Co or Ni sulphides are potential electron-donors to MoS₂. Such results are relevant to the synergy observed in hydrotreating catalysis with these sulphides.     

Anisotropy and scale effect in the microhardness of crystals of Bi-based superconducting phases

Microhardness studies are carried out on the (001) plane of faceted crystals of the Bi₂Sr₂CuO₆ (2201) and Bi₂Sr₂CaCu₂O₈ (2212) phases with the help of a Knoop indenter. Peculiarities in the effect produced on the microhardness by the indenter orientation relative to crystal faces, the presence of lead in the structure, and the force applied to the indenter (scale effect) are detected. It is found that crystals of the 2212 phase exhibit the strongest dependence of the microhardness on the above factors.     

Determination of N and O‐atoms and N2 (A) Metastable Molecule Densities in the Afterglows of N2‐H2, Ar‐N2‐H2 and Ar‐N2‐O2 Microwave Discharges

Early afterglows of N₂‐H₂, Ar‐N₂‐H₂ and Ar‐N₂‐O₂ flowing microwave discharges are characterized by optical emission spectroscopy. The N and O atoms and the N₂ (A) metastable molecule densities are determined by optical emission spectroscopy after calibration by NO titration for N and O‐atoms and measurements of NO and N₂ band intensities. If an uncertainty of 30% is estimated on N‐atomic density, an inaccuracy of one order of magnitude is obtained on the O and N₂ (A) densities. In N₂‐(0.05‐2.5%)H₂ and Ar‐(1‐50%)N₂‐(0.05‐2.5%) H₂ gas mixtures, the O‐atoms are coming from O₂ impurities in the discharge. Concentrations of N and O‐atoms and of N₂ (A) densities are compared to the ones obtained in Ar‐(5‐50%)N₂‐(0.2‐2.5%) O₂ gas mixtures in which a controlled amount of O₂ is added. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Upper critical fields of cubic and tetragonal single crystal and polycrystalline Nb3Sn in DC fields to 30 tesla

Measurements of the upper critical field, H_c2(T), in single crystal Nb₃Sn were extended to 30 tesla (300 kG) with dc fields produced by a Hybrid magnet. Observations of H_c2(T) were made for materials which remain in the cubic (c) phase and those which show a martensitic transformation at the tetragonal (t) phase. H_c2(T) measurements of Nb₃Sn for a pure crystal for which the de Haasvan Alphen (DHVA) effect was observed and for polycrystalline (t) phase and (c) phase materials are also reported. Measured values of H_c2(4.2 K) and calculated values of H_c2(0) are: 1) along the [100] direction for our earlier Nb₃Sn, H_c2(4.2 K) = 26 T for the (c) phase and 21.5 T for the (t) phase; H_c2(0) = 29T for the (c) phase and 24 T for the (t) phase; 2) along the [100] direction for the DHVA material H_c2(4.2 K) = 18 T and H_c2(0) = 20 T; 3) for polycrystalline Nb₃Sn (t) phase material H_c2(4.2 K) = 23 T and H_c2(0) = 25 T and for (c) phase material H_c2(4.2 K) = 26 T and H_c2(0) = 29 T. The values of (dH_c2/dT)_T=Tc vary from 2.4T/K for the highest H_c2(T) material to 1.6T/K for the DHVA material. The anisotropy for various Nb₃Sn single crystal materials is small and independent of temperature from T_c to 0.1 T_c. δT_c between the (c) and (t) phase is <0.3 K. Within experimental error excellent fits of H_c2(T) with theory are obtained assuming a dirty or clean Type II superconductor with no Pauli paramagnetic limiting. Experimental details and strong-coupling effects are discussed. When strong-coupling is included, the effects of any paramagnetic limiting would be small and not detectable within our present experimental error. Brief comments also are made concerning H_c2 of V₃Si.     

Electronic structure of amino acids and ureas

The outer electronic levels of glycine, alanine, glycine ethyl ester, urea, and thiourea have been investigated by means of photoelectron spectroscopy using He I (584 Å) and He II (304 Å) radiation and CNDO/2 molecular orbital calculations. In the amino acids the molecular orbital (MO) ordering ha been found to be [σ core and carbonyl π > a″(O) a′(O) > a″(N)] with a first ionization potential of ～8.8 eV. Glycine and alanine are foun to exist as the undissociated amino carboxylic acids rather than zwitterions in the high temperature vapor. In urea the three lowest energy molecular o are near-degenerate [σ(4b₁) ～ π(1a₂) ～ π(2b₂)] while in thiourea only the two lowest energy MO's are near-degenerate [π(1a₂ σ(4b₁) ～ π(2b₂)]. The first ionization potentials of urea and thiourea are 9.7 and 7.9 eV respectively.     

Pd@SnO2 and SnO2@Pd Core@Shell Nanocomposite Sensors

Pd@SnO₂ and SnO₂@Pd core@shell nanocomposites are prepared via a microemulsion approach. Both nanocomposites exhibit high‐surface, porous matrices of SnO₂ shells (>150 m² g^?1) with very small SnO₂ crystallites (<10 nm) and palladium (Pd) nanoparticles (<10 nm) that are uniformly distributed in the porous SnO₂ matrix. Although similar by first sight, Pd@SnO₂ and SnO₂@Pd are significantly different in view of their structure with Pd inside or outside the SnO₂ shell and in view of their sensor performance. As SMOX‐based sensors (SMOX: semiconducting metal oxide), both nanocomposites show a very good sensor performance for the detection of CO and H₂. Especially, the Pd@SnO₂ core@shell nanocomposite is unique and shows a fast response time (τ₉₀ < 30 s) and a very good response at low temperature (<250 °C), especially under humid‐air conditions. Extraordinarily high sensor signals are observed when exposing the Pd@SnO₂ nanocomposite to CO in humid air. Under these conditions, even commercial sensors (Figaro TGS 2442, Applied Sensor MLC, E2V MICS 5521) are outperformed.     

Two salts and the salt cocrystal of ciprofloxacin with thiobarbituric and barbituric acids: The structure and properties

Ciprofloxacin (CfH, C₁₇H₁₈FN₃O₃) crystallizes with 2‐thiobarbituric (H₂tba) and barbituric acid (H₂ba) in the aqueous solution to yield salt CfH₂(Htba)·3H₂O ( 1 ), salt cocrystal CfH₂(Hba)(H₂ba)·3H₂O ( 2 ), and salt CfH₂(Hba)·H₂O ( 3 ). The compounds are structurally characterized by the X‐ray single‐crystal diffraction. The numerous intermolecular hydrogen bonds N–H?O and O–H?O formed by water molecules, Htba^?/Hba^? and CfH₂⁺ ions, and H₂ba molecules stabilize the crystal structures of 1 to 3 . Hydrogen bonds form a 2D plane network in the salts of 1 and 3 and a 3D network in the salt cocrystal of 2 . There are different π‐π interactions in 1 to 3 . The compounds have been characterized by powder X‐ray diffraction, thermogravimetry/differential scanning calorimetry, and Fourier transform infrared spectroscopy. The compounds dehydration ends at 130°C to 150°C, and their oxidative decomposition is observed in the range of 250°C to 275°C.     

Electromagnetic properties and decays of Dirac and Majorana neutrinos in a general class of gauge theories

We discuss the electromagnetic properties and decays of Dirac and Majorana neutrinos in a general class of gauge theories. Specific results for the standard SU(2)_L × U(1) and a (not necessarily left-right symmetric) SU(2)_L × SU(2)_R × U(1) theory are analyzed.     

Molecular structure and IR spectra of bromomethanes by DFT and post-Hartree-Fock MP2 and CCSD(T) calculations

The molecular parameters (geometries, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of bromomethanes (CH₃Br, CH₂Br₂, CHBr₃, CBr₄) are predicted by a density functional theory with the hybrid Becke3-LYP functional (DFT) and post-Hartree-Fock methods (MP2, CCSD(T)) using a 6-311G(2d,2p)-type basis set. The MP2 calculations are carried out with different numbers of frozen core orbitals to find how the number of bromine orbitals used for electron correlation influences the predicted molecular parameters and IR spectra of the species in question. Three options were used: (a) all electrons (full), with both the core and valence orbitals considered; (b) partial frozen core option (pfc), when the orbitals up to 3p of bromine were frozen; and (c) full frozen core option (ffc), when all core orbitals up to 3d were frozen. The CCSD(T) calculations for geometric parameters were carried out with both the pfc and ffc options, while for the prediction of the IR spectra only the ffc option was used. In addition, the calculations at the DFT and MP2(pfc) levels with inclusion of f functions on carbon and bromine atoms in bromomethanes (and also the CCSD(T)(pfc) calculations for CH₃Br) were carried out to predict the changes in the geometric parameters and/or vibrational IR spectra of the molecules upon inclusion of f functions The geometries of bromomethanes (particularly the CBr bond lengths) are predicted better by the DFT and CCSD(T) calculations when the f functions (in particular on bromine atom) are included, while the MP2 calculations without f functions are good enough for correct predictions of the molecular geometries. The molecular parameters and vibrational IR spectra of bromomethanes in question and their deuterated species predicted by the DFT, MP2(ffc) and CCSD(T)(ffc) with the 6-311G(2d,2p) basis set agree well with the available experimental data.     

The oscillator strengths for C1s and O1s excitation of some saturated and unsaturated organic alcohols,acids and esters

Electron energy loss Spectroscopy (ISEELS) under dipole scattering conditions is used to obtain the carbon and oxygen K-shell oscillator strength spectra of methanol (CH₃OH), propanol (CH₃CH₂CH₂OH), propenol (CH₂=CHCH₂OH), propargyl alcohol (HC≡CCH₂OH), propanoic acid (CH₃CH₂COOH), acrylic acid (CH₂=CHCOOH) and propiolic acid (HC≡CCOOH). A detailed interpretation of these spectra is presented, along with a comparison with the NEXAFS spectra of multilayers of these molecules adsorbed on a Si(111) surface, as recently reported by Outka et al. (Surf. Sci., 185 (1987) 53). Good agreement is found between the multilayer NEXAFS and the gas phase ISEEL spectra, except for the carboxylic acids which differ dramatically in the discrete portion of the O1s spectrum. Possible origins for this difference are discussed. The C1s and O1s spectra of methyl formate (HCOOCH₃) are also reported and interpreted in comparison with the spectra of formic acid and methanol.     

Electronic structure and optical properties of the red and yellow mercuric iodides

With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI₂ and yellow HgI₂. It is found that the red HgI₂ has a direct gap of 1.22834 eV and the yellow HgI₂ has an indirect gap of 2.11222 eV. For the red HgI₂, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε ₂ (ω ) are discussed. Our calculated anisotropic dielectric function of the red HgI₂ is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI₂. Finally, the different optical properties are discussed.     

Sonochemical synthesis of silver, copper and lead selenides

Ag₂Se, CuSe and PbSe were prepared by irradiating the mixtures of AgNO₃, CuI or PbCl₂ with selenium in ethylenediamine (en) with ultrasound at 18 kHz, using a commercial ultrasonic cleaner, respectively. X-ray powder diffraction (XRD) patterns and transmission electron microscope (TEM) images show that the products are orthorhombic Ag₂Se, hexagonal CuSe and cubic PbSe, respectively, and all are well crystallized in nanometers.     

Phonons and electronic transitions in the Raman spectra of FeCl2·2H2O and isomorphic compounds

The Raman spectra in FeCl₂ · 2H₂O (FC2) and the isomorphic compounds FeCl₂ · 2D₂O (FC2D), MnCl₂ · 2H₂O (MC2) and CoCl₂ · 2H₂O (CC2) were observed at 2 K to obtain the frequencies of all 12 optical phonons of even symmetry at the zone center. The lowest of these phonons is known to be coupled resonantly to the magnons below T_N. This coupling and other important magnetic properties of the iron salts are determined by the influence of the crystal field. The electronic transitions of the Fe²⁺-ion in a crystal field are identified after a thorough assignment of the phonon lines in the four isomorphic compounds to symmetry types, using back-scattering and 90°-scattering techniques.     

Reaction kinetics and magnetic properties of Ba and Sr ferrites

This Mössbauer study is concerned with the formation mechanism of hexaferrites (n=6) and of monoferrites (n=1) in the systems (1) BaCO₃+nFe₂O₃, (2) SrCO₃+nFe₂O₃ and (3) 0.5BaCO₃+0.5SrCO₃+nFe₂O₃. With a molar ratio of 1∶1 for the starting materials one gets final reaction products with different crystalline structures. The experimental results indicate that the thermodynamical final state of the hexaferrite formation is reached on different routes. Various reaction models are discussed.     

Anisotropy of the ionic conductivity and dielectric response in orthorhombic and monoclinic inorganic fluorides

The anisotropy of the ionic conductivity and permittivity of (1) BaR₂F₈ (R=rare earth element) single crystals with monoclinic BaTm₂F₈ structure and of (2) (β-YF₃ structured) rare earth trifluorides is studied. Single crystals, eutectic composites and ceramics are investigated in a broad temperature range. In the monoclinic BaR₂F₈ crystals, a pronounced anisotropy of the ionic conductivity and a slight anisotropy of the permittivity are found. The fastest ionic transport with the lowest activation energy (0.563 eV) and the highest value of the permittivity are observed along thea axis. The temperature dependencies of the fluoride ion conductivities of various orthorhombic rare earth trifluorides differ only slightly from one another. For the bulky single crystals, the conductivity at 500 °C and the conduction activation enthalpy are equal to 1.1(4)×10⁻⁵ S/cm and 0.75(3) eV, respectively. The ionic conductivity is almost isotropic, but the anisotropy of the permittivity is significant. For the fluorides of both structural types, plausible conduction mechanisms are proposed, networks of most probable conduction paths are presented and the origin of the observed anisotropy of the ionic conductivity is elucidated. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

First-principles study of electronic properties and stability of Nb5SiB2（001） surface

The density functional calculations are performed to study the electronic structure and stability of Nb 5 SiB 2(001) surface with different terminations.The calculated cleavage energies along the(001) planes in Nb 5 SiB 2 are 5.015 J · m 2 and 6.593 J · m 2 with the break of Nb-Si and Nb-NbB bonds,respectively.There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy:the larger the cleavage energy,the larger the surface relaxation.Moreover,the surface stability of the Nb 5 SiB 2(001) with different terminations has been investigated by the chemical potential phase diagram.From a thermodynamics point of view,the four terminations can be stabilized under different conditions.In chemical potential space,NbB(Nb) and Nb(Si) terminations are just stable in a small area,whereas Si(Nb) and Nb(NbB) terminations are stable in a large area(the letters in brackets represent the subsurface atoms).     

Cross-section and rate coefficient calculation for electron impact excitation, ionisation and dissociation of H2 and OH molecules

The weighted total cross-section (WTCS) theory is used to calculate electron impact excitation, ionisation and dissociation cross-sections and rate coefficients of OH, H₂, OH⁺, H₂ ⁺, OH^- and H₂ ^- diatomic molecules in the temperature range 1500–15000 K. Calculations are performed for H₂(X, B, C), OH(X, A, B), H₂ ⁺(X), OH⁺(X, a, A, b, c), H₂ ^-(X) and OH^-(X) electronic states for which Dunham coefficients are available. Rate coefficients are calculated from WTCS assuming Maxwellian energy distribution functions for electrons and heavy particles. One and two temperature (θ_e and θ_g respectively for electron and heavy particles kinetic temperatures) results are presented and fitting parameters (a, b and c) are given for each reaction rate coefficient: k(θ) = a (θ^b)exp (-c/θ).     

Properties and structure of oxidized coatings deposited onto Al-Cu and Al-Mg alloys

The results of new studies of creating protective oxide coatings based on Al₂O₃ (Si, Mn) and deposited onto aluminum alloys using electrolyte-plasma oxidation are presented. An analysis is performed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction, Rutherford backscattering of ⁴He⁺ and protons, nanoindentation, scratching, friction coefficient measurements, and acoustic emission measurements. The results demonstrate that the deposited coatings have a high quality, hardness, and wear resistance and a low thermal diffusivity. Apart from Al₂O₃, the coatings are found to have Si, Mn, C, and Ca. The stoichiometry of the coatings is determined. The density and hardness of the coatings are close to those of ??-Al₂O₃ in the coating on an Al-Cu (D-16) substrate, and these values of the coating on an Al-Mg (S006) are lower by a factor of 1.5.     

Hypersensitivity in the Luminescence and 4f?C4f Absorption Properties of Mono- and Dinuclear EuIII and ErIII Complexes Based on Fluorinated ??-Diketone and Diimine/ Bis-Diimine Ligands

The results of our investigation on the sensitized luminescence properties of three Eu(III) ??-diketonate complexes of the form [Eu₂(fod)₆(??-bpm)], [Eu(fod)₃(phen)] and [Eu(fod)₃(bpy)] and 4f?C4f absorption properties of their Er(III) analogues ( fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2??-bipyrimidine, phen = 1,10-phenanthroline and bpy = 2,2??-bipyridyl) in a series of non-aqueous solvents are presented. The Eu(III) complexes are highly luminescent and their luminescence properties (intensity and band shape) are sensitive to the changes in the inner coordination sphere of the Eu(III) ion. The luminescence intensity of the mononuclear complexes in pyridine is drastically decreased. The coordination structure of the complexes in pyridine is transformed into a more symmetrical one which results into a slow radiative rate of the emission from the complexes. The ancillary ligands, phen and bpy are found better co-sensitizers as compared to the bpm to sensitize Eu(III)-luminescence. The 4f?C4f absorption properties (oscillator strength and band shape) of the Er(III) complexes demonstrate that ⁴G_11/2 ?? ⁴I_11/2 and ²H_11/2 ?? ⁴I_15/2 hypersensitive transitions of Er(III) are very sensitive in some coordinating solvents which reflects complex?Csolvent interaction in solution. The hypersensitive transitions of [Er(fod)₃(phen)] remain unaffected in any of the solvents and this complex retains its bulk composition in solution. The erbium complexes as well as the Er(fod)₃ chelate are invaded by DMSO. This solvent enters the inner coordination sphere by replacing heterocyclic ligand and the complexes acquire similar structure [Er(fod)₃(DMSO)₂] in this solvent. The results reveal that the luminescence and absorption properties of lanthanide complexes in solution can be controlled by tuning the coordination structure through ancillary ligands and donor solvents. This work shall prove useful in designing new biological applications with such probes.     

On the bonding and reactivity of CO2 on metal surfaces

We present ab-initio valence-bond calculations on free and coordinated CO₂. By analogy to transition-metal complexes with coordinated CO₂ three different coordination geometries for the CO₂ molecule are considered: (a) pure carbon coordination, (b) pure oxygen coordination, (c) mixed carbon-oxygen coordination. It is shown that pure oxygen ((b) geometry) and mixed carbon-oxygen coordination ((c) geometry) are more favourable than pure carbon coordination. In all cases studied, the bonding between the CO₂ moiety and the metal atom is described best as a CO₂⁻ anion interacting with a Ni cation. On the basis of the theoretical calculations, many observed and expected features (some already known and some predicted) of the interaction of CO₂ and metal surfaces can be discussed. The electron transfer to the CO₂ moiety drives the observed bent geometry of the coordinated CO₂ molecule and is accompanied by an elongation of the CO bond distance with respect to the free molecule. The bond elongation leads to a drastic lowering of the asymmetric CO stretching frequency, and a change in the relative energy position of the photoelectron peaks. We also consider intermolecular interaction between the CO₂⁻ anion and surrounding neutral CO₂ molecules via “solvation” in analogy to results of recent gas-phase cluster experiments. On the basis of the deduced metal-CO₂ bonding scheme the reactivity of coordinated CO₂ is investigated. Three reaction channels are considered: (a) dissociation into CO and O⁻, (b) oxidation to CO₃⁻ and CO₃²⁻, (c) disproportionation of CO₂⁻ + CO₂ to CO₃⁻ and CO. On the basis of energetic considerations we argue that dissociation is likely to occur on transition-metal surfaces, while oxidation to carbonate species is more likely on noble metals due to the low binding energies for the dissociation products, namely oxygen and CO on these surfaces.