[en] Short communication

[en] The critical current density in YBa₂Cu₃O_7-x (YBCO) thin films, which limits their application in high magnetic fields, can be enhanced by the introduction of artificial pinning centers as, e.g., provided by nanoparticles. An inert gas phase condensation process was used to prepare Y₂O₃ nanoparticles from an yttrium target by DC magnetron sputtering. With this method, both the size distribution and the areal density of the particles as determined from TEM investigations are independently controlled during deposition. Particles with a mean diameter of about 8 nm were deposited on SrTiO₃ substrates, which are terminated by TiO₂ through etching with BHF solution and subsequent annealing in 1 atm O₂ at 900 C. The behavior of the particles on the substrate at varying temperatures in an O₂ atmosphere of 0,7 mbar (YBCO deposition conditions) was studied by AFM and ICP-MS. A 300 nm thin YBa₂Cu₃O_7-x layer was deposited onto the likewise pre-coated substrates by off-axis pulsed laser deposition. Both inductive and resistive transport measurements at 77 K in magnetic fields of up to 9 T reveal the influence of the particles on the superconducting properties of YBa₂Cu₃O_7-x. (orig.)

[en] The influence of N content on the crystallization behavior of initially amorphous Ta-Si-N diffusion barriers deposited with a thickness of 10 nm between Cu and SiO₂ was investigated by means of glancing angle X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GD-OES), transmission electron microscopy (TEM), and graphite furnace atomic absorption spectrometry (GF-AAS) after annealing for various times at a temperature of T_an=600 deg. C. For a Ta₇₃Si₂₇ film, only Ta silicide phases (Ta₅Si₃, Ta₂Si) are formed, whereas all barriers containing nitrogen crystallize primarily into a Ta nitride. Si is not incorporated into this phase but diffuses mostly into the Cu film. Although the crystalline Ta nitride grows mainly within the original barrier region, it does not form a continuous layer. For barriers with a N content x_N≥25 at.%, the annealing time necessary to start the crystallization increases and the formed Ta nitride phases become N-richer (Ta₂N→Ta₅N₆). A Ta₃₀Si₁₈N₅₂ layer maintains its amorphous structure even after annealing for t_an=100 h. With increasing N content in the barrier, the thermal stability against Cu diffusion is improved

[en] The correlations among stoichiometry variation, preparation route, and microstructure as well as superconducting properties were investigated in MgB₂ bulk samples. We demonstrate that the different initial weight ratios of Mg and B between Mg_0.9B₂ and Mg_1.1B₂ are only slightly shifted towards Mg depletion during the mechanical alloying preparation at room temperature followed by a short annealing step. The samples with Mg surplus show the highest critical temperature T_c∼36 K, highest critical current density J_c∼1.5x10⁶ A/cm² at 7.5 K in self-field, and a homogeneous microstructure. In contrast, the Mg-depleted samples exhibit a rather porous and multiphase microstructure with a broad grain size distribution. A direct correlation of stoichiometry variation and superconducting properties was not found, but rather a strong influence of the Mg content on lattice strain and grain connectivity

[en] The forced crucible rotation technique has been applied to the solidification of Nd-Fe-B alloys. Specially sealed samples were subjected to well-defined forced rotation during induction heating and solidification. The resulting microstructure of the Nd-Fe-B alloys in consideration of melt convection has been investigated using scanning electron probe microscopy. The determination of the α-Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the α-Fe volume fraction in samples with high crucible rotation frequencies. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Surface acoustic wave devices are widely used as wireless sensors in different application fields. Recent developments aimed to utilize those devices as temperature sensors even in the high temperature range (T > 300 °C) and in harsh environmental conditions. Therefore, conventional materials, which are used for the substrate and for the interdigital transducer finger electrodes such as multilayers or alloys based on Al or Cu have to be exchanged by materials, which fulfill some important criteria regarding temperature related effects. Electron beam evaporation as a standard fabrication method is not well applicable for depositing high temperature stable electrode materials because of their very high melting points. Magnetron sputtering is an alternative deposition process but is also not applicable for lift-off structuring without any further improvement of the structuring process. Due to a relatively high Ar gas pressure of about 10"−"1 Pa, the sidewalls of the photoresist line structures are also covered by the metallization, which subsequently prevents a successful lift-off process. In this study, we investigate the chemical etching of thin tungsten films as an intermediate step between magnetron sputtering deposition of thin tungsten finger electrodes and the lift-off process to remove sidewall covering for a successful patterning process of interdigital transducers. - Highlights: • We fabricated Tungsten SAW Electrodes by magnetron sputtering technology. • An etching process removes sidewall covering of photoresist, which allows lift-off. • Tungsten etching rates based on a hydrogen peroxide solutions were determined.

[en] This article explores the potential of a scanning electron microscope with an energy dispersive X-ray spectrometer in combination with a new non-destructive 3D visualization technique, X-ray micro-computed tomography, as detection methods for siloxanes/silanes mixtures applied as wood preservatives. In order to have a higher contrast, bromine functional silane was added to the mixture. Scots pine and beech samples were dipped or impregnated with the mixture and subsequently scanned. Both silicon and bromine were easily detectable with both techniques. Dipped siloxanes/silanes covered the cell walls partly in beech and the lumen partly or completely in Scots pine. Impregnated siloxanes/silanes could be found in the cell walls of both wood species. From the results, it can be concluded that, under the circumstances as described in the article, impregnation with a siloxane is necessary to have cell wall penetration. The combination of scanning electron microscopy, energy dispersive X-ray spectroscopy and micro-computed tomography can offer important information concerning the localization of certain products inside wood. While the last of these can monitor changes in 3D, the other two techniques can provide detailed 2D information. Both techniques are complementary and provide important extra information

[en] The influence of rapid quenching on the phase formation of Cu-Si alloys was investigated for silicon contents between 10 and 30 at.%. Rapid quenching leads to formation of different meta-stable states depending on the chemical composition. High temperature phases η, δ and κ can be preserved at room temperature. The formation of the room temperature phase ε can be suppressed by rapid quenching from the melt. The crystal structure of the high temperature phases was analysed by X-ray powder diffraction. Annealing of the rapidly quenched alloys at T = 500 ^oC leads to the transformations of the meta-stable phases. The equilibrium states exhibit phase compositions, which are in agreement with the generally accepted phase diagram

[en] In this contribution we present systematic studies on the purification and subsequent functionalization of magnetically pure single-walled carbon nanotubes. We show through a combination of burning treatments and microwave digester treatments in aqua regia that single-walled carbon nanotubes can be purified without incurring any damage, with 90 wt% of catalyst material being removed. It is also shown that multiple microwave digester treatments lead to incremental functionalization of the nanotubes. The obtained functional groups are easily removed by annealing the sample in vacuum