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The electronic band structure probed by angle-resolved photoemission spectroscopy on thin epitaxial La 2−x Sr x CuO 4 films under extreme tensile strain shows anomalous features compatible with c-axis dispersion. This result is in striking contrast with the usual quasi-two-dimensional ͑2D͒ dispersion observed up to now in most superconducting cuprates, including relaxed and compressively strained La 2−x Sr x CuO 4 films grown under the same conditions. The data were analyzed using a 3D tight-binding dispersion for a body-centeredtetragonal lattice. We relate the enhancement of the c-axis dispersion to the significant displacement of the apical oxygen induced by epitaxial strain.

The correlated 3d sulphide BaVS 3 exhibits an interesting coexistence of one-dimensional and threedimensional properties. Our experiments determine the electronic band structure and shed light on this puzzle. High-resolution angle-resolved photoemission measurements in a 4-eV-wide range below the Fermi energy level uncover and investigate the coexistence of a 1g wide-band and e g narrow-band d electrons, which lead to the complicated electronic properties of this material. We explore the effects of strong correlations and the Fermi surface instability associated with the metal-insulator transition.

Angle-resolved photoemission spectroscopy reveals very surprising strain-induced effects on the electronic band dispersion of epitaxial La(2-x)Sr(x)CuO(4-delta) thin films. In strained films we measure a band that crosses the Fermi level (E(F)) well before the Brillouin zone boundary. This is in contrast to the flat band reported in unstrained single crystals and in our unstrained films, as well as in contrast to the band flattening predicted by band structure calculations for in-plane compressive strain. In spite of the density of states reduction near E(F), the critical temperature increases in strained films with respect to unstrained samples. These results require a radical departure from commonly accepted notions about strain effects on high temperature superconductors, with possible general repercussions on superconductivity theory.

We report on the fabrication, Raman characterization and electron emission behavior of cold electron cathodes that are specifically designed to be used in miniature X-ray sources. The cathodes are fabricated by screen-printing a nanocomposite paste comprising multiwall carbon nanotubes as fillers in a matrix of graphite, glass and bentonite clay. The cathodes can resist high temperatures up to 880 C and, as such, can survive most high-temperature brazing steps required for vacuum-tight sealing of the sources. We demonstrate peak emission current densities around 300 mA cm À2 at an applied electric field of 175 kV cm À1 and stable emission around 50 mA cm À2 at 125 kV cm À1 for at least 5 hours without significant degradation. X-rays were successfully generated at 3.2 watts of peak power (80 mA, 40 kV) with a commercial X-ray tube modified to accommodate a paste cathode.