[en] The latest development of angle-resolved photoemission spectroscopy (ARPES) technique has seen extremely high energy resolution and momentum resolution, as well as multiple angle detection. These advancements have led to new findings through efficient Fermi surface mapping, fine electronic structure resolving, and direct determination of electron self-energy. In this paper, we will highlight some recent high resolution ARPES work on high temperature superconductors. These include: (1) charge-ordering and evolution of electronic structure with doping; (2) bilayer splitting and Fermi surface topology of Bi2212; and (3) strong electron-phonon coupling and electron-electron interaction in high temperature superconductors

[en] A refractory-metal-free C40 TiSi₂ phase formed by pulsed-laser annealing is identified experimentally by combined convergent beam electron diffraction (CBED) study and CBED pattern simulation. The simulation shows that the C40 TiSi₂ has a hexagonal structure with the space group P6₂22 (180) and lattice parameters a=0.471 nm and c=0.653 nm. Upon further furnace annealing or rapid thermal annealing, C54 TiSi₂ can be directly achieved from C40 TiSi₂ at low temperatures (600 - 700 degree C). This observation suggests that pulsed-laser annealing is promising for extension of TiSi₂ into the subquarter micron region in semiconductor device fabrication. [copyright] 2001 American Institute of Physics

[en] Photoemission spectroscopy measurements of MgB₂ are reviewed. From angle-resolved photoemission spectroscopy, band dispersion is observed as is theoretically predicted, suggesting that the electronic structure of MgB₂ is well described within band theory. From angle-integrated photoemission spectroscopy, a clear peak ascribed to the superconducting coherent peak is observed. The shape of the spectral line shape is consistent with the presence of s-wave gap(s). The estimated size of superconducting gap is close to the conventional BCS prediction, supporting the idea that this material is an electron-phonon mediated superconductor. At the same time, the presence of second gap with a smaller size is indicated by the high-resolution photoemission spectroscopy

[en] Pulse radiolysis of aqueous solutions of Pt₂(μ-P₂O₅H₂)₄^4- at pH 4 with added t-BuOH gives Pt₂(μ-P₂O₅H₂)₄H^4- via reaction with an electron and a proton. Pulsed-laser photolysis (Nd-YAG at 355 nm) of aqueous solutions of Pt₂(μ-P₂O₅H₂)₄^4- with added isopropyl alcohol, phosphorus acid, or hypophosphorous acid also gives Pt₂(μ-P₂O₅H₂)₄^4- by hydrogen atom abstraction. The mixed-valence hydride is similarly formed in methanolic solutions of (PPN)₄[Pt₂(μ-P₂O₅H₂)₄] from added triethylsilane or tributyltin hydride. The intermediacy of the Me₂COH radical is evidenced by the formation of both pinacol and acetone in the photochemically catalyzed dehydrogenation of isopropyl alcohol with Pt₂(μ-P₂O₅H₂)₄^4- in aqueous solution. The other radical, Pt₂(μ-P₂O₅H₂)₄H^4-, disproportionates to Pt₂(μ-P₂O₅H₂)₄H₂^4- and Pt₂(μ-P₂O₅H₂)₄^4-. The Bu₃Sn radical has been detected by transient difference laser spectroscopy in solutions containing Pt₂(μ-P₂O₅H₂)₄H₂^4- and Bu₃SnH. The quenching rates for hydrogen atoms donors with the ³A/sub 2u/ state of Pt₂(μ-P₂O₅H₂)₄^4-*, as measured by the Stern-Volmer equation, are given and compared

[en] This paper examines the effect of a maldistributed two-phase (gas/vapor-liquid) feed on the performance of a 1-1 feed-effluent heat exchanger. Equations are developed to predict the performance of a specified unit for cases in which the maldistribution of the feed is characterized by N classes of tubes, each having a given vapor-liquid feed ratio. A computer program has been developed to solve the sets of equations

[en] To develop effective water-soluble catalysts for aquathermolysis of heavy oil, in this paper, a series of complex was synthesized using phenyl hydroxamic acid and metallic chloride. The Ni(II) complex was characterized, and all the complexes were screened in aquathermolysis of heavy oil. The effects of water content and Ni(II) complex concentration on aquathermolysis were investigated. The effect of adding methanol as a reactant was examined and interpreted. With the catalyst and methanol, the reaction occurred at temperatures as low as 180?. The viscosity of the product was also substantially reduced by the decomposition of the large hydrocarbon molecules. (author)

[en] We describe valence-band and core-level photoemission data for copper oxide superconductors using the Anderson Hamiltonian applied to an impurity-cluster configuration-interaction model. We obtain experimental values of the parameters of the model the copper X oxygen charge transfer energy Δ∼0.4 eV, the d-d Coulomb interaction U∼6 eV, and the ligand-d hybridization T∼2.4 eV. Using these parameters, we evaluate the linear Cu-O-Cu superexchange interaction J and find it is dominated by the charge-transfer fluctuations. The magnitude obtained for J is much larger than typical Neel temperatures of these materials, and is somewhat larger than that estimated from applying the resonating-valence-bond picture to La₂CuO₄. We point out that for Δ<< U, ant T>>Δ, the charge-transfer degrees of freedom, and the lattice aspects of the Anderson lattice Hamiltonian, should not be neglected in constructing models for the high-T/sub c/ superconductivity. We also emphasize our resonant-photoemission result that the very small density of states at or near the Fermi level in all these materials has a substantial contribution from Cu 3d states, suggesting their importance for the superconductivity. We report other details of the resonant-photoemission data involving La and Ba states in the materials containing these elements

[en] We have studied the self-organized Ge/Si quantum dots (QD's) by Raman scattering under hydrostatic pressure near resonance and off resonance with confined Ge-like E₁ transition. The Raman spectra of Ge-Ge, Si-Ge, and the Si acoustic phonon (Si-2TA) modes were obtained as function of pressures in the range 1--70 kbar. Our results show that the Ge-Ge and Si-2TA modes can be easily resolved at low pressure due to a high degree of compressive built-in strain in the Ge layers. The mode Grueneisen parameter of the Ge-Ge phonon mode in QD's is found to be γ=0.81±0.01, which is smaller than the corresponding quantity in bulk Ge. Normalized Raman intensity profiles of Ge-Ge mode exhibit a resonance enhancement peak at ∼32 kbar. The pressure coefficient α of this resonating electronic transition thus obtained is ∼5±1meV/kbar. This value is smaller than the pressure shift of the E₁ transition in bulk Ge

[en] Polymer-silicate nanocomposites were prepared by polymer melt intercalation, an efficient and simple method. The starting materials included layered mica-type silicates (sodium- montmorillonite and organically modified bentonite), and poly(ethylene oxide). The polymer/ silicate mixtures were heated at 85 deg C and 95 deg C, and characterization of the nanocomposites was performed using XRD, DSC and SEM. The effects of various processing parameters on the materials synthesis are studied. Discussion focuses on the effects of heating temperature, time, and green body density on the intercalation process. A mechanism of melt intercalation is proposed. Copyright (1998) Australasian Ceramic Society

[en] The effects of Y₂O₃ content on σ_f and K₁ of TZP have been studied. It is found that the σ_f and K₁ of TZP increased first and then decreased with the increasing Y₂O₃ content. There is an optimal addition of Y₂O₃ in which σ_f and K₁ reach a maximum. Additions of Al₂O₃ could increase k_1c and σ_f of TZP at the same time. This interesting phenomenon is explained by the following mechanism, the crack deflection and branch toughening caused by Al₂O₃ grains could enhance the transformation toughening of ZrO₂. Controlling the content of AL₂O₃ and Y₂O₃ the authors obtained a TZP ceramic with K_1degree = 21.3 MPam^1/2 and σ_f = 1578 MPa