[en] Niobium zirconium nitride nanocrystalline films were deposited by DC unbalanced magnetron sputtering on silicon substrates with a growth temperature of 450 deg. C and an RF bias voltage of -70 V. The concentration of zirconium and niobium was regulated by controlling the power to the sputtering guns. The nitrogen concentration was controlled by varying the nitrogen flow rate and, hence, partial pressure. These films were investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, spectroscopic ellipsometry (SE), and nanoindentation. XRD revealed that these films formed a solid solution and that the grain size, deduced from the width of the XRD peaks using the Scherrer formula, did not vary with niobium content. The elemental composition was determined from XPS measurements. The optical constants were measured using SE and were found to correlate well with film structure and composition using a Drude-Lorentz (DL) model. The mechanical properties of the coatings were evaluated using nanohardness testing and were found to depend on composition. Optimum mechanical properties were achieved for a niobium content of 12%

[en] Coatings of tantalum nitride with various compositions were deposited on silicon substrates using unbalanced reactive magnetron sputtering. An optical emission spectrometer was used to monitor the ratio of tantalum to nitrogen particles in the plasma in real time. The coatings were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). The primary nitride phases (Ta, Ta₂N, TaN) in the films were determined using XRD and XPS. The elemental composition was revealed from XPS measurements. The refractive indices were deduced from analysis of the SE data, which were subsequently simulated using the Drude-Lorentz model. The resistivity and electron mean free paths were deduced from this simulation and were correlated to the film composition and microstructure. The resistivity increased whereas the electron mean free path decreased with an increase in nitrogen content or a decrease in grain size

[en] Li and Sc are two of the 23 elements which only superconduct under high pressure. In previous studies T_c for Li reaches 14 K at 30 GPa, but for Sc only 0.35 K at 21 GPa. We determined T_c(P) for Sc to be 74.2 GPa and found that T_c increases monotonically with pressure to 8.2 K. Changes in the superconducting phase diagram of monovalent Li are studied upon alloying with 10% divalent Mg

[en] Of the 52 known elemental superconductors among the 92 naturally occurring elements in the periodic table, fully 22 only become superconducting under sufficiently high pressure. In the rare-earth metals, the strong local magnetic moments originating from the 4f shell suppress superconductivity. For Eu, however, Johansson and Rosengren have suggested that sufficiently high pressures should promote one of its 4f electrons into the conduction band, changing Eu from a strongly magnetic (J=7/2) 4f⁷-state into a weak Van Vleck paramagnetic (J=0) 4f⁶-state, thus opening the door for superconductivity, as in Am (5f⁶). We report that Eu becomes superconducting above 1.8 K for pressures exceeding 80 GPa, T_c increasing linearly with pressure to 142 GPa at the rate +15 mK/GPa. Eu thus becomes the 53rd elemental superconductor in the periodic table. Synchrotron x-ray diffraction studies to 92 GPa at ambient temperature reveal four structural phase transitions.

[en] The stability of charge stripe order in La_2-xBa_xCuO₄ (LBCO) is still poorly understood. At x=1/8 LBCO exhibits a pronounced suppression of superconductivity and a static ordering of of spins and charge into a stripe pattern. At the same doping a structural transition from the usual orthorhombic phase (LTO) into the low temperature tetragonal phase (LTT) is observed. By the application of pressure the stability of the LTT and the LTO phase can be tuned and thus the influence of these structural distortion on the stripe order be studied. Using high energy X-ray diffraction the presence of charge stripes in a lattice without long range distortions could be found, indicating that electronic effects also contribute to the stablity if stripe order.

[en] Of the 52 known elemental superconductors among the 92 naturally occurring elements in the periodic table, fully 22 only become superconducting under sufficiently high pressure. In the rare-earth metals, the strong local magnetic moments originating from the 4f shell suppress superconductivity. For Eu, however, Johansson and Rosengren have suggested that sufficiently high pressures should promote one of its 4f electrons into the conduction band, changing Eu from a strongly magnetic (J=7/2) 4f⁷-state into a weak Van Vleck paramagnetic (J=0) 4f⁶-state, thus opening the door for superconductivity, as in Am (5f⁶). We report that Eu becomes superconducting above 1.8 K for pressures exceeding 80 GPa, T_c increasing linearly with pressure to 142 GPa at the rate +15 mK/GPa. Eu thus becomes the 53rd elemental superconductor in the periodic table. Synchrotron x-ray diffraction studies to 92 GPa at ambient temperature reveal four structural phase transitions.