4s Band Research Articles

X-ray absorption measurements on Tl 1− xBi xSr 2CuO 5 and Tl 0.5Bi 0.5Sr 2CaCu 2O 7 Valences of Bi, Tl and Cu

Near-edge X-ray absorption spectroscopy measurements of Bi and Tl L3-edges and Cu K-edge in a series of compounds Tl 1− x Bi x Sr 2CuO 5 and Tl 0.5Bi 0.5Sr 2CaCu 2O 7 have been presented. The results provides strong evidence for the existence of mixed-valent Bi and Tl in these compounds. Moreover, the formal valence of copper in Tl 1− x Bi x Sr 2CuO 5 and Tl 0.5Bi 0.5Sr 2CaCu 2O 7 appears to be much higher than 2+. It is suggested that the Tl(Bi) 6s band could cross the Fermi level, resulting in electronic correlations between the Tl(Bi)-O and Cu-O layers, which is significant in determining the physical properties of these compounds.

Effects of Ce and F substitutions on the electronic structure of Nd2CuO4 superconductors.

The changes incurred by the replacement of Nd (or O) by Ce (or F) atoms on the electronic energy states of the superconducting ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$ compounds have been investigated in a tight-binding approximation. A minimum number of parameters have been employed in the calculation. The various peaks observed in the direct and inverse photoemission data of Reihl et al. are well explained. The calculated shift in Fermi level with x (or y) in ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ (or ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{F}}_{\mathit{y}}$) is seen to be in agreement with the experiment. Further, our model detects an unoccupied Cu 4s band just at the conduction-band edge, as has been detected in electron-spin-resonance experiments.

S-wave pairing mediated by double excitation of triplet in two band systems with intermediate electron correlation

A two band system, composed of a half-filled insulating band and a metallic band, with no hybridization in between, is studied as a model for Cu-O type high-Tc ceramics. In the case of hole-type ceramics, these two bands correspond to the 3d band of Cu and the 2pπ band of O, while, in the case of electron-type newly found ceramics, they correspond to the 3d and 4s bands of Cu. The intraband electron-electron repulsions are assumed to be intermediate strength, while the interband repulsion V is assumed to be weak. It is shown, however, that V results in an attraction between electrons in the metallic band, through a virtual excitation of two triplet excitons which are low lying excitations in the correlation gap of the half-filled band. Because of its retardation effect, this attraction can overcome the direct repulsion between electrons, only at around the Fermi level, and can give Tc of about 50K≈100K. A large damping of this excitation is also obtained, in agreement with experimental results.

Structural and electronic properties of crystalline and glassy calcium-zinc compounds. II. Electronic density of states

For pt.I, see ibid., vol.1, p.8277 (1989). The authors report self-consistent calculations of the electronic structure of crystalline and amorphous Ca-Zn alloys using a linearised muffin-tin orbital supercell method. Strong similarities between the electronic densities of state of the metallic glasses and the corresponding crystalline compounds are found. This supports previous conclusions from molecular dynamics studies of the atomic structure that the local order in the metallic glasses is similar to that in the trigonal prismatic inter-metallic compounds. In the Ca-rich phases the s,p conduction band splits into a fully occupied Zn 4s band and a valence band that is of pure 4p character on the Zn sites and of a strongly s,p,d-hybridised character on the Ca sites. The consequences of this result for the chemical bonding and the electronic properties are discussed.

Quantum Chemical Calculations of Ground Electronic State of High-TcCopper Oxides

Carrier locations of hole-doped and electron-doped high- T c copper oxides in their ground states were determined by quantum chemical calculations. We have used a cluster surrounded by point charges. The used point charge arrangement produces a potential which simulates the functional form of the Madelung potential completely. Our calculation includes electronic correlations especially of on-site Coulomb repulsion of the Cu atom, which is the most important near the half-filling of the ground state. The doped hole will occupy the oxygen 2p π band. The doped electron will occupy the Cu 4s band. In the hole-doped and the electron-doped copper oxide, a moment on the Cu 3d x 2 – y 2 orbital will remain.

Oxygen 1s x-ray-absorption edges of transition-metal oxides.

The oxygen 1s x-ray-absorption edges of a series of 3d-transition-metal oxides have been measured. The structures at the edge arise from covalent mixing of the metal and oxygen states, which introduces oxygen p character in unoccupied states of mainly metal character. The spectra can be divided into two regions: The first is a double-peaked sharp structure near threshold, which can be related to the metal 3d states; the second is a broader structure 5--10 eV above the edge and is related to the metal 4s and 4p bands. We attribute the oxygen p character up to 15 eV above threshold to mainly oxygen 2p character. The data are analyzed in terms of ligand-field and exchange splittings. It is shown that the splitting between the two sharp peaks near threshold is related closely to the ligand-field splitting, but the relative intensities of the peaks are not fully explained at the present time.

The X-Ray Photoelectron Spectra of 1:1 and 1:2 Salts Formed from Triethylammonium and 7,7,8,8-Tetracyanoquinodimethane

Abstract The X-ray photoelectron spectra of the 1:1 and 1:2 salts formed from the triethylammonium cation (TEAH+) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been measured and analyzed in order to investigate the electronic structures and conformations of the salts. The N 1s band (398.2 eV) degenerated in the free TCNQ molecule splits into two bands (398.4 eV and 400.3 eV) in the 1:1 salt. This is due to the unequal interactions of the nitrogen atoms of the TCNQ anion radical (TCNQ\ewdot) with TEAH+. In the 1:2 salt, the degenerated N 1s bands of two free TCNQ molecules split into three bands (398.5, 400.0, and 401.8 eV). This implies that the negative charge is inhomogeneously distributed over two TCNQ molecules, supporting the idea that the electronic structure of the 1:2 salt can be represented approximately as TEAH+–TCNQ\ewdot–TCNQ0. It is found that, in the 1:2 salt, the neutral TCNQ molecule (TCNQ0) is weakly bound to the TCNQ anion radical (TCNQ\ewdot) of the strongly bound 1:1 salt, with their molecular planes parallel.

Structural and Electronic Relationships in the High-Temperature Copper-Based Superconductors

ABSTRACTAtomic displacements from the ideal rock-salt positions in the Tl-, Bi-, and Pb-O layers of the Cu-based high-Tc super-conductors affect the electronic nature of these oxides. When distortions in the Bi-O layers of Bi2Sr2CaCu2O8 are considered, the bottom of the Bi 6p band is found to lie more than 1 eV above the Fermi level. Displacements in the double Tl-O layers of Tl2Ba2Can−1CunO2n+4 places the bottom of the Tl 6s bands significantly below the Fermi level showing that electrons can be removed from the x2-y2 bands of the CuO2 layers. However, this is not the case for the thallium-oxygen single layers of Tl2Ba2Can−1CunO2n+3. Correlations between the superconducting transition temperatures, Tc, and the in-plane Cu-O bond lengths, rCu−O', of the Tl- and Bi- based copper-oxide super-conductors reveal Tc vs rCu−O characteristics similar to those found for La2−xSrxCuO4.

Group Specific Component Subtyping in Bloodstains by Separator Isoelectric Focusing in Micro-Ultrathin Polyacrylamide Gels Followed by Immunoblotting

The identification of group specific component (Gc) subtypes derived from blood-stains by separator isoelectric focusing in micro-ultrathin polyacrylamide gels (interelectrode distance: 50 mm) containing 4.5 to 5.4 pharmalytes is described. The separation achieved between Gc 1F and Gc 1S bands is compared favorably with that obtained using separator isoelectric focusing in conventional polyacrylamide gels dimensions (interelectrode distance: 110 to 120 mm). The technique is rapid and economical, and the immunoblotting method described is more sensitive than immunofixation followed by silver staining.

Electronic-structure and local-order study of GexSe

X-ray photoelectron spectroscopy (XPS) and tight-binding calculations are used to study the electronic structure and the local order in ${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{Se}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ glasses (0lxl0.42). The shape of the valence electronic density of states in Ge-Se compounds is discussed in terms of (4:2)- or (3:3)-coordinated local structures and Ge-Se, Ge-Ge, and Se-Se bonds. It is shown that Ge 4s and Se 4s band shapes are very sensitive to the presence of Ge-Ge and Se-Se bonds, respectively. Se-rich glasses (xl0.33) can be described with 4:2 coordination and Ge-Se and Se-Se bonds whereas Ge-rich glasses (xg0.33) can be described with 4:2 and 3:3 coordinations and Ge-Se bonds.

Group‐specific component subtyping: A high resolution method employing short run cathodic drift

AbstractA high resolution polyacrylamide gel isoelectric focusing method is described for group‐specific component (Gc) subtyping. With this method all the common Gc subtypes can be identified and the Gc variant 1A1 bands are clearly resolved from the Gc 1F and 1S bands. The run time of 90 min represents a substantial saving in time when compared to many other methods reported in literature.

Photoemission satellites and electronic structure of Fe2O3.

The electronic structure of \ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ with the high-spin ${d}^{5}$ ground-state configuration has been studied by ultraviolet photoemission spectroscopy with use of synchrotron radiation as well as by x-ray photoemission and Auger-electron spectroscopy. The results are interpreted in terms of the configuration-interaction theory based on a ${\mathrm{FeO}}_{6}$-cluster model. The main lines of the valence-band photoemission spectra are identified with Fe?d sup 5 ndash---ligand-hole final states produced by ligand-to-3d charge-transfer screening of 3d holes (3${d}^{4}$ states), whereas the satellite at higher binding energies is assigned to unscreened (or poorly screened) 3${d}^{4}$ final states. The Fe 3d versus O 2p partial density of states and symmetry characteristics of 3d-derived peaks are found to be quite different from assignments based on ligand-field theory or band theory. These results indicate that ${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ cannot be considered as a Mott-Hubbard insulator in its original sense but is classified as a charge-transfer-type insulator according to a theory of Zaanen, Sawatzky, and Allen. A possibility is suggested that the lowest unoccupied state is not Fe?d ndash---like but is the bottom of the Fe 4s band. The large exchange energy of the high-spin 3${d}^{5}$ configuration is shown to greatly stabilize the localized 3d states relative to the itinerant state.

Electronic Band Structure of C8K Studied by Angle-Resolved Ultraviolet Photoelectron Spectroscopy

Angle-resolved ultraviolet photoelectron spectroscopy has been performed for a C 8 K single crystal. The dispersive π * -band near the \(\tilde{K}\) point and the so-called K 4s band around the Γ point are experimentally identified. The experimentally determined band structure has been compared with two different band calculations to discuss the charge transfer in C 8 K. The observed difference in the spectral feature of the `K 4s' band between the experiment and the calculation are also discussed.

Electronic structure of the alkali-metal overlayers on the π-bonded Si(111)2×1 surface

We calculate the surface band structures of the Cs and K covered Si (111)2×1 surfaces by first-principles LCAO-Xα-slab method. It is shown that the bonding π-band of the substrate Si is stable upon alkali-metal adsorption, and that partially occupied Cs 6s (K 4s) band is newly formed near the Γ-J' axis in the surface Brillouin zone. The results are in good agreement with the recent photoemission experiment. The present study suggests the stability of Pandey's π-bonded chain structure against the alkali-metal adsorption.

XPS analysis of iron aluminum oxide systems

XPS spectra of Fe 2O 3 and Al 2O 3 oxides are reported. The main emphasis is placed on the quantitative analysis of Ar + ion reductive effects on Fe 2O 3 surfaces in terms of n o/ n Fe atomic ratios achieved by use of the “First Principles Model”. No Fe metal is found in etched Fe 2O 3. Quantitative results show that the reduction: Fe 2O 3 → 2 FeO+ 1 2 O 2 occurs in the etching conditions used. Evidence of this reduction is found in the photoelectron spectra of the pure oxide as well as in those of Fe 2O 3+Al 2O 3 mixtures. A quantitative approach is proposed to derive Ar +-induced modifications at Fe 2O 3 surfaces in the mixtures. This approach permits the derivation of n o/ n Fe changes on the basis of intensity ratio measurements I O(Al)/ I O(Fe) between the two oxide components in the O 1s band of the mixtures. The correlation of derived n Al/ n Fe atomic ratios is very high in a vast range of composition of the mixtures analyzed either in the as received condition and in the etched condition. A sensitivity factor for the Fe 2p 3 2 transition is given: S Fe2p 3 2 = 2.50 (with respect to S F1s taken as the unity), which applies to the VG Esca 3 MkII apparatus used in this work. Comparison with previous quantitative XPS analysis of Fe 2O 3 and Al 2O 3 is presented.

Subtyping group‐specific component or esterase D using the same ultrathin‐layer polyacrylamide gel format

AbstractAn ultrathin‐layer polyacrylamide isoelectric focusing gel is described for obtaining highly resolved, nondistorted, reproducible patterns for group‐specific component (Gc) or esterase D (EsD) subtyping. The 1F, 1S, 2 and 1A1 bands of the Gc system were all typeable by isoelectric focusing alone. All common EsD allelic products were easily resolved. Typing Gc or EsD derived from bloodstains was also demonstrated.

Different effects of tubulin ligands on the intrachain cross-linking of beta 1-tubulin.

When bovine brain tubulin purified in the absence of GTP and MgCl2 is reacted with N,N'-ethylene-bis(iodoacetamide) (EBI), a bifunctional analogue of iodoacetamide, three new electrophoretically distinct species of tubulin are generated, migrating ahead of beta 1-tubulin on gels containing Na dodecyl sulfate. All three bands appear to be derived from the beta 1 subunit of tubulin and not from the alpha or beta 2 subunit. Accordingly, the bands have been designated beta 1 s, beta 1, and beta 1s in order of increasing electrophoretic mobility. EBI appears to introduce two intrachain cross-links into beta 1-tubulin; the beta 1s band contains one of these cross-links, designated beta s, the beta 1 band contains the other cross-link, designated beta s, and the beta 1 s band contains both cross-links. Both cross-links appear to involve sulfhydryl groups. Colchicine, podophyllotoxin, and nocodazole completely inhibit beta formation while GTP, vinblastine, and maytansine enhance it. It contrast, formation of beta s is completely blocked by guanine nucleotides and by maytansine, while vinblastine inhibits this by 70%. Colchicine, podophyllotoxin, and nocodazole enhance beta s formation. These results show that tubulin has the unusual property of having two discrete sites which can be targeted by an alkylating agent with each site having its alkylation inhibited by a different set of ligands. The results are consistent with several models, including one where vinblastine and maytansine have overlapping binding sites on the beta-subunit of tubulin relatively close to the GTP binding site.

Electron impact spectroscopy of methane and methane–d4

Electron impact spectra of methane and methane-d4 have been obtained employing electrons of 200 eV incident energy at scattering angles of 2° to 15° over an energy-loss range that includes the second ionization potential. In the bound state spectrum evidence is presented for the existence of at least one additional state in the region of the 3s transition. A new vibrational progression has been found on the side of a conjectured 4s band lending support to that assignment. One diffuse structure and three new optically forbidden vibrational progressions have been found in a 4 eV range below the 2A1 ion threshold. Evidence indicates that the first three transitions belong to the symmetry forbidden Rydberg series (2a1, ns)←(2a1)2 where n=3, 4, and 5. It is suggested that the fourth transition is the first member of a series converging to an excited ion state.

A deficiency mutant of the Gc system.

In the course of a paternity investigation an apparent mother-child incompatibility was observed in the Gc system. An extensive family study was undertaken to test the hypothesis of a silent gene or null allele responsible for the contrary phenotypes: the mother had the type Gc 2, the son was GC 1. The apparent incompatibility was due to a "pseudo" silent allele, called Gc * 1, which controlled a group-specific component with extremely reduced serum concentrations. This double-band mutant could be differentiated from the Gc 1S bands by two-dimensional electrophoresis: isoelectric focusing (IEF)/6 M urea IEF. The allele Gc * 1 was found in 12 persons from this family, it was not associated with any apparent disease state. Also present in this family was the variant Gc 1C1. Pedigree analysis revealed a possible (not significant) distorted segregation ratio for the allele Gc * 1C1, which was found in 22 of 33 offspring from marriages with one parent heterozygous for Gc * 1C1.

Distribution of Hp, Tf, Gc and Pi Polymorphisms in a Japanese Population Sample from San-in District

Distribution of Hp, Tf, Gc and Pi systems was studied in 225 serum samples from a Japanese population in the central region of San-in District of Japan. The frequencies of Hp1, TfC1 and PiM1 alleles were found to be somewhat but not significantly low as compared with other Japanese populations. A new variant type of Gc was observed to be located between the Gc 1S and 1C2 bands. The obtained gene frequencies are as follows: Hp1=0.2183, Hp2=0.7817; TfC1=0.7448, TfC2=0.2456, TfVar=0.0096; Gc1F=0.4411. Gc1S=0.2823, Gc2=0.2645, Gc1A2=0.0121; PiM1=0.6742, PiM2=0.2793, PiM3=0.0465.