The outstanding difference between high temperature superconductors and low temperature superconductors is the sign of the Hall coefficient, properly understood. Since the Lorentz force acts on particles, not voids nor immobile ions, we propose that the experimental positive coefficient is due to dispersion dynamics in valence bands, i.e. on electrons with positive charge/mass ratio, but with negative charge and negative effective mass. In HiT ccompounds, anionic and cationic doping creates holes that substitute for the lattice distortions that bind Cooper pairs in metallic superconductors such as Nb. In both types of superconductor, the conventional notion of antiparallel spins S = 0, with paired wave vectors k and -k, is maintained; but in the ceramics “holes” h, produced by chemical doping and measured in the normal state, are available to bond super-conducting Boson pairs via h− or h02 excitons.
An apparatus is described to measure the optical excitation spectrum of a material whilst it is under X-ray bombardment. Results are presented in the form of the excitation spectra from two distinct optical emissions from a mixed-powder specimen of ZnS and ZnSe. From these spectra site selection in the EXAFS structure above the zinc K edge is demonstrated.
The chemical behaviour of both YBa2Cu3O6.5+y (123) and Bi2Sr2CaCu2O8+y (2212) in various solvents was studied in a comparative manner. In both compounds superconductivity apparently depends on a high-oxidation state of Cu. Electrochemical corrosion rates were measured by a variety of techniques and are related to the concentration of labile Cu3+ ions in the specimens. Generally (2212) is the more stable compound, except in strongly basic solutions owing to the amphoteric nature of Bi. In the presence of acidic or basic solutions Bi3+ is oxidised to Bi4+ or Bi5+ by the high-oxidation state of Cu in (2212) (similar to oxidation by Na2O2), demonstrating a common feature of cuprate superconductors. The concentration of labile ions was determined by the volumetric measurement of evolved oxygen from acid solution, and the technique was extended to measure the concentration of undecomposed or re-formed carbonates after sintering.
Abstract Abstract The technique of extended electron energy loss fine structure (EXELFS) using an electron energy loss spectrometer fitted to a transmission electron microscope (TEM) has been applied to a study of the structure of the thin layer of amorphous alumina (Al2O3) which is formed on aluminium by anodic oxidation in neutral sodium tartrate solution. The EXELFS spectrum above the oxygen K-edge gives an Al-O bond length of 1–89 A, which is in good agreement with a previous measurement obtained from the electron-yield surface extended X-ray absorption fine structure (EXAFS) above the aluminium K-edge. The Al-O bond length derived from EXELFS measurements for the oxide film after crystallization in the electron beam shows that the structure of the crystalline phase is consistent with the reported structure of γ-alumina. Electron-yield surface EXAFS is generally a broad-beam technique, more applicable to in aitn studies of surface films. TEM EXELFS requires the films to be detached from their substrates, but the electron beam probes the specimen with high spatial resolution. The relative merits of these two techniques for structural studies of thin oxide layers are discussed.
New chemical information has been obtained which explains “footing” and “bottom pinching” effects in chemically amplified (CA) resists on a silicon nitride surface. X-ray photoelectron spectroscopy measurements indicate that the residual alkaline molecules on the nitride surface play a major role in the formation of nitride footing. It appears that the organic contaminants are not responsible for nitride footing. O2 and N2O/SiH4 plasma treatment are used to modify the silicon nitride surface. Less severe footing is observed if the nitride surface is treated with N2O/SiH4 plasma. This is attributed to the deposition of a thin oxide cap on the nitride substrate, which suppresses the surface basicity. However, extended N2O plasma treatment causes resist bottom pinching. This is ascribed to the surface acidity of a newly formed oxide cap which enhances the CA resist development process. Results show that the N (1s) peak, after extended N2O/SiH4 plasma treatment, has shifted to a higher binding state which suggests that the nitride surface becomes acidic, causing bottom pinching.
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