The XPS valence band spectra of NbC

The x-ray photoemission valence band spectra of NbC have been measured and are compared with the x-ray emission spectra and with the results from band structure calculations. This comparison leads to a large enhancement of theC2 _p photoabsorption cross section (at=1,487 eV) compared to the value calculated for the free atom. The effect of the nonmetal vacancy in the valence band can be described very well with vacancy cluster calculations.     

The XPS valence band of nickel metal

The XPS valence band spectrum of evaporated nickel is compared with a theoretical density of states curve and with a synthetic density of states curve obtained by adding two XPS valence band spectra of copper shifted by 0.3eV with respect to each other. Both calculated curves agree with the main features of the XPS valence band spectrum.     

High resolution core and valence band XPS spectra of non-conductor pyroxenes

High resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of the non-conductor pyroxene minerals, bronzite ((Mg_0.8,Fe_0.2)₂Si₂O₆) and diopside (Ca(Mg_0.8Fe_0.2)Si₂O₆) have been obtained with the Kratos magnetic confinement charge compensation which minimizes differential charge broadening. Observed Si 2p, O 1s, Mg 2p and Ca 2p total linewidths are all about 1.3 eV, very similar to those observed previously with the same instrument for SiO₂ and olivines ((Mg,Fe)₂SiO₄); and we consider that these widths are within 0.05 eV of the minimum room temperature linewidths for these samples with the experimental resolution of this instrument of 0.35 eV. These linewidths are all determined by vibrational broadening due to the M-O symmetric stretch in the ion states. The Si 2p binding energies (BE) are intermediate between the quartz and olivine Si 2p binding energies; but the O 1s spectra resolve the bridging oxygen (BO) and non-bridging oxygen (NBO) in the unit, with the NBO O 1s very close in BE to the O in olivine, and the BO very close to the BO in SiO_2. Indeed in both diopside and bronzite, it is possible to separate the three structurally inequivalent O atoms in the O 1s spectra: the BO at a BE of about 532.6 eV, a NBO peak from the MgOSi moiety (Mg in the M1 site) at about 531.3 eV, and a NBO peak at 531 eV from the CaOSi or the FeOSi moieties (Ca and Fe in the M2 site). The O 1s BE increases with the increase in the electronegativity Ca < Mg < Fe < Si. Moreover, the linewidths of these peaks increase when Fe and Mg are both present in either M1 (diopside) or M2 (bronzite) sites.The valence band spectra for the two pyroxenes are rather similar, and quite different from the VB spectra of quartz and olivines. The dispersion of the pyroxene VB spectra is intermediate between the VB spectra of quartz and olivines; the valence band spectrum of pyroxenes are more dispersed than in olivines by about 1.5 eV but less dispersed than quartz by about 1.5 eV. These VB spectra can be assigned using the previous olivine VB spectra and high quality pseudopotential density functional theoretical calculations in the generalized gradient (GGA) approximation. As for the olivine VB spectra, the Fe 3d t_2g and e_g orbitals in M1 and M2 sites of the pyroxene are located at the top of the pyroxene valence band, and the BE of the Fe 3d peaks from M1 are about 0.7 eV smaller than the Fe 3d peaks in M2. The theoretical XPS valence band spectra using the theoretical density of states and the Gelius intensity approximation are is in good semi-quantitative agreement with the experimental spectra. This intermediate dispersion of pyroxenes is due to the partial polymerization of the Si-O units in pyroxenes, and the intermediate charge on the Si atoms as indicated by the Si 2p BE.     

Comparison of the background corrected valence band XPS spectra of Fe and Co aluminides and silicides with their electronic structures

The background corrected valence band XPS spectra and the electronic structures of FeAl, FeSi, CoAl and CoSi were studied. Clean surfaces of the polycrystalline samples were obtained by in situ fracturing of the samples in an XPS spectrometer. The energy loss parts of the Fe 2p, Co 2p and valence band spectra were removed by the deconvolution method using Al 2s or Si 2s spectra as response functions. CoAl exhibited a satellite peak in the Co 2p region, but the other compounds had no clear satellite peaks in the Co 2p and Fe 2p regions. The experimentally background corrected valence band spectra were compared with the calculated spectra using the first-principle band calculation. There were large discrepancies between the spectra above the binding energy of 5 eV. These indicated that the experimental spectra could not be explained by the electronic structures of the ground states alone.     

XPS valence band spectra of Nb3Sn,Nb and Sn

XPS valence band spectra of Nb₃Sn, Nb and Sn have been obtained under high resolution. The 4d band structure in the Nb₃Sn spectrum is similar to that seen in Nb metal.     

Electron correlation effects in the valence band photoemission spectra of cooper dichloride

He I, He II and Al Kα photoemission measurements of the valence band of CuCl₂ are reported. The presence of the 3d⁸-like satellite indicates the strong correlation effects in the final state and the breakdown of the one-particle model. It is shown that the reduction of the satellite intensity in the valence band compared with the core hole emission is caused by the delocalization of the photo-hole. The satellite intensity in resonance with the super-Coster-Kronig decay is calculated.     

Determination of equilibrium composition of C x H y O z N t plasmas out of thermodynamic equilibrium

In this paper, we determine the composition of C_xH_yO_zN_t plasmas out of thermodynamic equilibrium using a more rigorous thermodynamic derivation of the Saha equation modified to two-temperature plasma system proposed by Chen et al. The calculation is made for these plasmas in pressure range 0.1-1 MPa and for electron temperature range 5 000-30 000 K. A great attention is given to the evolution of the major species such as hydrogen components (H, H₂), carbon monoxide (CO) and electrons. We compared the results obtained with our previous experimental and theoretical studies; the latter one has been carried out in equilibrium situation. We also compared our results with those given by the method based on the minimization of the Gibbs free energy widely used in the literature. Received 29 December 2000 and Received in final form 28 August 2001     

The Effect of Water Vapor on the Conductivity and Emission Properties of the Formed Mo–Si x N y O z –Al Structure

The effect of water-vapor partial pressure on the conductivity and emission properties of the formed Mo–Si _x N _y O _z –Al sandwich-structure with a 40-nm thick dielectric and a 15-nm thick aluminium electrodes is studied. It is shown that an inflow of water-vapor into a degassed vacuum chamber results in the occurrence of a region of negative differential resistance in the volt-ampere characteristic and an increase in emission current in MIM-structures. The increase in conductivity is attributable to the formation of a delocalized impurity state band in local regions of dielectric surface due to water molecule adsorption.     

A Mössbauer study of hyperfine interaction in the systems Co x Mn3−x−y Fe y O4 and Ni x Mn3−x−y Fe y O4

A Mössbauer study of systems Co _x Mn_3?x?y Fe _y O₄ and Ni _x Mn_3?x?y Fe _y O₄ for values ofx=0·1, 0·5, 1·0 andy ranging from 0·1 to 2·0 in steps of 0·2 have been made. At room temperature samples fory values ranging in between 0·1 to 0·5 exhibit paramagnetic behaviour while all spectra for values ofy between 0·6 to 0·8 show relaxation effects. Well-defined hyperfine Zeeman spectra are observed for all the samples withy>0·8 and resolved in two sextets corresponding to octahedral and tetrahedral site symmetries and a central doublet probably due to the presence of super-paramagnetic particles in the system. The hyperfine field at⁵⁷Fe nucleus reduces with decreasing iron cobalt and nickel concentration. These observations have been explained in terms of site preference of cations and exchange interactions.     

The photoelectron spectra of some heterocyclic compounds which contain N,O, Cl and Br

The photoelectron spectra of 19 heterocyclic compounds, several of which are germicidal agents, containing N, O, Cl and Br have been investigated. Complete band assignments have been made for the lone-pair regions of the spectra for future reference in structure/biological-activity correlations. A detailed comparison of the carbonyl-oxygen lone-pair splitting patterns in the spectra indicates that succinimide is skeletally planar, while N-chlorosuccinimide and N-bromosuccinimide are substantially nonplanar in the gas phase.     

The superconductivity,structure and magnetic susceptibility of Nb y Au x -Pt(1−x)A-15 type phases

Measurements of the superconducting transition temperature, lattice parameter and magnetic susceptibility are made on ternary Nb-Au-Pt alloys in the as cast and annealed conditions. Annealing reduced most of the alloys to A-15 structure as observed by X-ray diffraction, but metallographic microstructures of some of these alloys showed them to be still inhomogeneous. This inhomogeneity affects the values ofT _c and χ- All the alloys are found to be nearly paramagnetic in nature, and χ follows the variation inT _c for most of the alloys. The experimental results are discussed in their relationship to other low temperature properties e.g. the electron-phonon interaction constant, the electron density of states and the lattice volume.     

Ascertaining the values of sigma x,sigma y,and sigma z of a polarization qubit

In the 1987 spin-retrodiction puzzle of Vaidman, Aharonov, and Albert one is challenged to ascertain the values of sigma(x), sigma(y), and sigma(z) of a spin-1/2 particle by utilizing entanglement. We report the experimental realization of a quantum-optical version in which the outcome of an intermediate polarization projection is inferred by exploiting single-photon two-qubit quantum gates. The experimental success probability is consistently above the 90.2% threshold of the optimal one-qubit strategy, with an average success probability of 95.6%.     

Absorption spectra and magneto-optic figures of merit in the Bi x Sm3-x Fe5-y Ga y O12 system

The absorption (α) and Faraday rotation (θ) spectra of 14 garnets belonging to the series Bi _x Sm_3-x Fe_5-y Ga _y O₁₂ (0<x<1.05, 0.8<y<1.15) have been measured between 15 000 cm⁻¹ and 19 000 cm⁻¹. The figure of merit (θ/α) at 17 850 cm⁻¹ (560 nm) increases linearly with increasing bismuth concentration up tox∼0.6 where it begins to increase less rapidly. For operation of magneto-optic display devices at 17 850 cm⁻¹ there is no advantage in using garnets in this series withx>0.8. The Faraday rotation at 17 850 cm⁻¹ increases linearly with bismuth concentration whereas the absorption coefficient increases more rapidly. The presence of Bi³⁺ increases the intensity of all Fe³⁺ pair transitions in the garnet system as a result of the increased superexchange induced by Bi³⁺. This is in keeping with the observation that the intensity of the⁶A_1g (S)→⁴T_1g (G) transition in (RE)₃Fe₅O₁₂ (RE=Er, Y, Dy, Gd, Eu) increases on traversing the above RE series as do the Curie temperatures of these iron garnets.     

Microwave absorption spectra and the problem of the crystal field in tetragonal compounds HoBa2Cu3O x (x = 6.0, 6.3)

The resonance microwave absorption at wavelengths 871, 406, 305, and 118 μm in tetragonal layered perovskites HoBa₂Cu₃O _x (x = 6.0, 6.3) in pulsed magnetic fields up to 40 T has been detected. This absorption is caused by the electronic transitions between low lying levels of the Ho³⁺ ion in the crystal field. The positions and intensities of the basic resonance absorption lines for the crystal with x = 6.0 in the magnetic field oriented along the tetragonal axes are adequately described in terms of the tetragonal crystal field with known interaction parameters. To explain the weaker absorption lines, it is necessary to take into account the effect of the inhomogeneous orthorhombic and monoclinic components of the crystal field, which are due to disorder in the oxygen subsystem. This effect is more pronounced in the absorption spectra of the crystal with x = 6.3 for which the oxygen disorder is more pronounced.     

The thermodynamic properties and special features of spectra of elementary excitations of unstable valence Sm-and Ce-based compounds

The experimental data on the spectra of elementary excitations measured by inelastic neutron scattering and on the heat capacity and the coefficient of thermal expansion are used to analyze the correlation between the spectral characteristics of the electron and phonon subsystems and the special features of the temperature dependence of the thermodynamic properties of a number of unstable valence Sm-and Ce-based compounds. The anomalous behavior of the thermodynamic properties of these compounds is defined by the special features of their phonon and electron (4f and conduction electrons) spectra. The rearrangement of the 4f-electron spectrum as a result of temperature variation plays a decisive part in the formation of temperature dependences of the heat capacity and the coefficient of thermal expansion of unstable valence systems.     

He II spectra of La,Ce and Yb: Novel features in the valence band region

He II photoelectron spectra of La, Ce and Yb show features which cannot be explained in terms of single electron excitations. It is proposed that these are due to formation of electron-hole paris. Communication No. 227.