A custom-designed semifluorinated phosphonic acid, (9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,16-heptadecafluorohexadecyl)phosphonic acid (F8H8PA), and a normal hexadecylphosphonic acid (H16PA) were synthesized and used to generate self-assembled monolayers (SAMs) on commercially available yttrium barium copper oxide (YBCO) tapes. In this study, we wished to evaluate the effectiveness of these monolayer films as coatings for selectively etching YBCO. Initial films formed by solution deposition and manual stamping using a non-patterned polydimethylsiloxane stamp allowed for a comparison of the film-formation characteristics. The resulting monolayers were characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To prepare line-patterned (filamentized) YBCO tapes, standard microcontact printing (μ-CP) procedures were used. The stamped patterns on the YBCO tapes were characterized by scanning electron microscopy (SEM) before and after etching to confirm the effectiveness of the patterning process on the YBCO surface and energy-dispersive X-ray spectroscopy (EDX) to obtain the atomic composition of the exposed interface.

YBa2Cu3O7-delta (Y123) can have significant variation in oxygen content on a micron scale in superconducting devices, and this causes a range of superconducting properties-generally impairing the performance of the superconductor. This study initially aimed to determine variation in O content of Y123 using electron microprobe analysis. High-quality electron microprobe analysis requires flat, usually polished, samples. Polishing Y123 produces a change in O content in surface layers relative to that of the parent as polishing a ceramic involves partial to complete surface amorphization. The analyses are not appropriate for the parent (much lower O), evidence of inhomogeneity of oxygen is removed, and the resultant material absorbs oxygen from the environment. After ion milling, the new surface more reflects the parent; comparison of unprocessed materials with polished and milled ones suggests that milling does not seriously alter the O Ka peak shape. Furthermore, milled surfaces reveal inhomogeneities obscured in polished surfaces. O K alpha peaks derived from milled surfaces were compared with those from standard oxides; all standards were found to have peak shapes that do not conform to those of Y123. Because peak width: height is markedly different, the analytical assumption that peak height is proportional to peak area is violated. Alternative methods of determining peak area without mapping the entire peak are required to perform high-quality Y123 analyses; these are being developed.

To reduce ac losses of coated conductors (CCs), microcontact printing was employed as an alternative technology for processing striated tapes. All CCs possessed the same basic cross-sectional architecture: stainless steel/ABAD-YSZ/CeO2/PLD-YBCO. By magnetron sputtering, thin (100-300 nm) Au layers were deposited on bare (no cover layer on YBCO) tapes. Appropriate SAMs (self-assembled monolayers of alkanethiols) line patterns were printed with elastomeric stamps on the Au layer. A subsequent etching of Au, with ferri/ferrocyanide, and of YBCO, with phosphoric acid, was used to produce the desired filamentary structure. The sample performance was checked by angle-dependent measurements of the critical current density, J(c). Striating the CCs leads to a reduction of hysteretic ac losses of the HTS tapes, which according to E. H. Brandt's calculations depend on the width of the filaments. This was confirmed by AC SQUID measurements of the complex susceptibility and paves the way for long-length processing of low-loss CCs.

Submitted for the MAR11 Meeting of The American Physical Society Search for Superconductivity in Carbon Nanotubes Doped by Boron Ion Implantation NICHOLAS CORNELL, ALEX KUTSENOV, AUSTIN HOWARD, NATHANIEL MAYO, EDUARD GALSTAYAN, WEI KAN CHU, HERBERT FREYHARDT, ANVAR ZAKHIDOV, XUEMEI WANG, UNIVERSITY OF TEXAS AT DALLAS TEAM, UNIVERSITY OF HOUSTON TEAM — The boron doping of single wall carbon nanotubes(CNT) by laser ablation synthesis has been reported to create superconducting B-CNTs with Tc’s ranging from 12-19 Kelvin, depending on CNT inter-tube connection strength. We attempt to create boron doped multiwall CNT by ion implantation doping. Ion doping of boron(B) was performed at 60keV and 20keV, and low temperature transport combined with SQUID and ESR/LFMA was used in searching for SC. We have found that R(T) strongly depends on the metallic contact geometry. With thin film contacts on CNT sheets the R(T) shows no SC signatures, while when an Ag or Au paste penetrates the highly porous network of B doped multiwall CNT then R(T) drops and curvature changes are observed resembling SC transitions with Tc depending on B concentration and metallic electrode distances. We discuss these results in terms of possible SC in hybride “metal-CNT” system in which metal was predicted to supress phase fluctuation in one dimensional CNT network [1]. [1] Erez Berg, Dror Orgad, and Steven A. Kivelson, Phys. Rev. B 78, 094509(2008)

Submitted for the MAR11 Meeting of The American Physical Society Low Field Microwave Absorption Studies of Carbon Nanotubes Doped by Chemical and Ion Implantation Techniques AUSTIN HOWARD, ALEXANDER KUZNETSOV, NICHOLAS CORNELL, MYRON SALAMON, The University of Texas at Dallas, EDUARD GALSTAYAN, WEI KAN CHU, HERBERT FREYHARDT, The University of Houston, RAY BAUGHMAN, The University of Texas at Dallas, JUNJI HARUYAMA, JASON REPPERT, APPARAO RAO, Clemson University, ANVAR ZAKHIDOV, The University of Texas at Dallas — The motivation of this study is to develop a highly sensitive method of microwave absorption in low magnetic fields (LFMA), combined with SQUID magnetometry and resistivity, for searching for superconducting phases in in-situ doped nanomaterials; either chemically (by alkali metals or metalloids) or through Boron ion implantation. These methods have been applied to both MWNTs grown by CVD, as well as SWNTs which have been separated into metallic and semiconducting chiralities. Regardless of the doping technique or element, we have found a much higher rate of doping in the semiconducting SWNTs. Additionally, in the Boron doped SWNTs, we see two transitions at ∼8 K and ∼30 K, but the nature of the transition is not clear at the moment: it depends on the type of measurement. While SQUID and resistivity indicate a superconducting type transition, LFMA/ESR reveals that there is a clear magnetic transition at 30 K. Resolution of these differing results will be discussed. Austin Howard The University of Texas at Dallas Date submitted: 19 Nov 2010 Electronic form version 1.4

Large grain, (RE)BCO bulk superconductors fabricated by top seeded melt growth (TSMG) are able to generate large magnetic fields compared to conventional, iron-based permanent magnets. Following 20 years of development, these materials are now beginning to realize their considerable potential for a variety of engineering applications such as magnetic separators, flywheel energy storage and magnetic bearings. MgB2 has also continued to emerge as a potentially important bulk superconducting material for engineering applications below 20 K due to its lack of granularity and the ease with which complex shapes of this material can be fabricated. This issue of Superconductor Science and Technology contains a selection of papers presented at the 7th International Workshop on the Processing and Applications of Superconducting (RE)BCO Large Grain Materials, including MgB2, held 29th?31sy July 2010 at the Omni Shoreham Hotel, Washington DC, USA, to report progress made in this field in the previous three year period. The workshop followed those held previously in Cambridge, UK (1997), Morioka, Japan (1999), Seattle, USA (2001), Jena, Germany (2003), Tokyo, Japan (2005) and again in Cambridge, UK (2007). The scope of the seventh PASREG workshop was extended to include processing and characterization aspects of the broader spectrum of bulk high temperature superconducting (HTS) materials, including melt-cast Bi-HTS and bulk MgB2, recent developments in the field and innovative applications of bulk HTS. A total of 38 papers were presented at this workshop, of which 30 were presented in oral form and 8 were presented as posters. The organizers wish to acknowledge the efforts of Sue Butler of the University of Houston for her local organization of the workshop. The eighth PASREG workshop will be held in Taiwan in the summer of 2012.

The attractive perspectives offered by coated conductors, known as the 2nd generation of high temperature superconductors (2G-HTS), have triggered broad and fruitful R&D efforts to make them ready for the marketplace. The anisotropic features of YBCO and its weak-link behavior require the processing of almost single crystalline thin films into flat tapes of coated conductors by basically two different methods: RABiTS—rolling-assisted biaxially textured substrates; and IBAD—ion-beam assisted deposition. Reliable processing technologies are now at hand, and critical current carrying capacities can be raised to almost 10–20% of the theoretically possible limit by optimizing current transfer through grain boundaries as well as flux pinning through control and design of the microstructural landscapes. The optimization of the in-field properties of the 2G-HTS wires, as well as the manufacturing of coated conductors with low ac losses and of assembled conductors for high current application remain active development areas. Cost reduction and more economic processing are still an issue. However, coated conductors are now beginning to penetrate the market, particularly for power and electrical applications, where savings in energy are essential and where the unique features of high temperature superconducting materials can be utilized.

In this paper a 30 m long one-phase coaxial YBCO cable with 1 kA transport current and 10 kV operating voltage was designed for the Super3C project to check the feasibility of YBCO tapes for low-loss cables. The final design incorporates cryogenic, mechanical and electromagnetic aspects. The electromagnetic losses during normal operation must be minimized. The cryogenic design must also take into account the generation of heat during short circuit conditions. Mechanical restrictions set the minimum gaps between the coated conductor tapes and the minimum Jay angles in order to make the cabling feasible and to enable handling of the cable. The design of the electric insulation should be according to the international standard as far as applicable. The final design has to take into account all of the above restrictions.

We report on the fabrication of all-chemical YBa2Cu3O7 coated conductors on IBAD-YSZ (IBAD stands for ion beam assisted deposition; YSZ is yttrium stabilized zirconia) stainless steel substrates. YBCO films were grown by the trifluoroacetates route on top of CeO2 buffer layers made by metal-organic decomposition. The achievement of atomically flat CeO2 surfaces is found to be a key factor for obtaining clean interfaces with YBCO and high performance. Coated conductors with percolative critical currents of J(c)(GB)(65 K) = 1.8 MA cm(-2) were achieved. The determination of the intra-grain critical current J(c)(G) from inductive measurements suggests that the limiting factor for J(c)(GB) (65 K) is the YBCO in-plane texture, which is already of higher quality than that of the IBAD-YSZ cap layer.

The evolution from a partially oriented granular microstructure to a dense epitaxial one in CeO2 films deposited from chemical solutions on Y2O3-stabilized cubic ZrO2 (YSZ) has been investigated using cross-section transmission electron microscopy (XTEM), electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray reflectometry (XRR). In crystallization from chemical solutions, undercoolings are typically high enough to promote homogeneous and heterogeneous nucleation with equal probability. The desired texture is then transmitted from heterogeneously nucleated epitaxial grains throughout the volume of the film upon sintering. Crystallization of CeO2 under the reducing atmospheric conditions of Ar/5% H-2 results in a nanometric granular microstructure with a high concentration of C impurities decorating grain boundaries and interstitial cavities, which unexpectedly prevails after high-temperature annealing. Post-processing in oxidizing conditions removes C impurities and promotes grain growth resulting in a fully epitaxial film, as well as stabilizing the otherwise energetically prohibitive polar (001) planes. Misfit stresses in the post-processed epitaxial films are completely relieved by interfacial dislocations with b = (a/2) < 110 > and b = (a/2) < 011 > Burgers vectors. A mechanism that considers impurity-induced grain-boundary blocking and the stabilization of (001) planes via surface oxidation is proposed. Processing conditions to obtain high-quality CeO2 buffer layers can be adapted to YBa2Cu3O7-coated conductors.

We present atomic and magnetic force microscopy measurements on magnetic iron nanoparticles produced by a self-assembly method. The fabrication process is based on the thermal disintegration of iron nanowires deposited on faceted Al2O3 substrates. Arrangement and size of the particles depend on the annealing temperature. For iron this process yields particles with diameters in the range of 100–250 nm. The usage of the prepatterned substrates enforces a linear alignment of the particles. Magnetic force microscopy shows that the particles can be remanently magnetized with external fields of different orientations.