Mark Lelental

Preparation of silver behenate coatings to provide low- to mid-angle diffraction calibration

A method for the preparation of a well aligned silver behenate sample is described. Multiple (0 0 l) diffraction peaks, (0 0 1) to (0 0 48), are easily observed using a conventional laboratory X-ray diffraction instrument.

Effect of amine borane structure on activity in electroless plating

Abstract The effect of substituents on the activity of amine boranes in nickel electroless plating has been studied. The minimum coverages of evaporated palladium, silver, gold, and copper catalysts necessary for initiation of plating by solutions incorporating these reductants have been determined. A dissociative mechanism for nickel electroless plating with amine boranes is proposed. A relationship between the strength of the donor-acceptor (NB) bond and minimum coverage of catalyst necessary for initiation of nickel deposition is proposed.

Microstructure of 110 K superconducting Bi-Sr-Ca-Cu-O thin films grown on (100)MgO by metallo-organic decomposition

Abstract 1-, 2-, 4- and 6-layer superconducting Bi-Sr-Ca-Cu-O (BSCCO) thin films have been prepared on (100) MgO substrate by metallo-organic decomposition. The 4- and 6-layer films reach zero resistance state at T >100 K. X-ray diffraction shows the oxide films to consist of three phases identifiable by their unique c -axis values of 24, 30 and 38 A. These films show a high degree of orientation in which the c -axis of the grains are aligned perpendicular to the substrate surface. In the 2-layer film, transmission electron microscopy indicates the oriented grain growth to be primarily either (130)BSCCO(100)MgO or (100)BSCCO (100)MgO. Ion channeling measurements using He ++ at energies ranging between 1 to 4.5 MeV, show that the polycrystalline grains in the film have a highly oriented mosaic structure, and among all the films, the 2-layer system exhibits the highest degree of alignment with (100)MgO.

The effect of X-ray penetration depth on structural characterization of multiphase Bi-Sr-Ca-Cu-O thin films by X-ray diffraction techniques

Abstract X-ray diffraction has been used extensively to assess the crystalline phase composition of superconducting ceramics. In instances where randomly oriented powders are available, X-ray diffraction provides a means of identifying not only the phases present but also the volume fraction of each phase. In instances where ultrathin films ( 0.2 μm) the ability to measure phase composition by X-ray diffraction is hampered by the fact that due to the limited effective X-ray penetration depth the X-ray beam may not sample all depths of the film equally. This phenomenon could result in a lessening of the contribution to the final diffraction pattern by phases concentrated near the substrate-film interface. This paper describes the characterization of Bi-Sr-Ca-Cu-O superconducting films by X-ray diffraction. Reactive beam ion etching experiments made it possible to observe the change in the relative volume fraction of three superconducting phases as a function of etch depth.

In situ high-temperature x-ray diffraction studies of antimony-doped tin oxide thin films formed by metallo-organic decomposition

Abstract Thin films of antimony-doped SnO 2 coated on stainless steel were fabricated by metallo-organic decomposition (MOD) techniques. A novel method for thermal fabrication of SnO 2 type films utilizing in situ high-temperature x-ray diffraction (HTXRD) found crystallization onset occurred between 400 and 500°C. Processing at fixed temperatures of 500, 700, and 900°C provided a high degree of crystallization after approximately 2 hr. The resulting crystallites after 6 hr of heating ranged in size from 36 A at 500°C to 205 A at 900°C. It has been observed that prolonged thermal processing of these samples leads to oxidation of the stainless steel substrate.

The use of X-ray diffraction rocking curve methodology for assessment of the c-axis orientation in BiSrCaCuO superconducting thin films

Abstract An X-ray diffraction theta scan rocking curve analysis method has been developed which allows one to assess the relative degree of c -axis preferred orientation of BiSrCaCuO superconducting ceramic thin films deposited on (100) MgO and Ag foil substrates. The full width at half maximum (FWHM) of the rocking curve peak is taken as a relative measure of c -axis orientation. Precision measurements of the data collection parameters, sample holder mounting, and instrument loading of the sample were performed. Defocusing of the X-ray beam was characterized using random α-Al 2 O 3 powder and a (100) Si wafer. Rocking curves of the BiSrCaCuO 37 A-110 K superconducting phase (00 14 ) peak for a random powder, thin film on Ag substrate, and thin film on (100) MgO were obtained with FWHM values of > 20° ∼ 5° and ∼0.3°θ, respectively.

XPS studies on copper valence in 85 K and 110 K mixed phase lead-free Bi-Sr-Ca-Cu-O superconducting thin films prepared by MOD techniques

Abstract The oxidation states of copper ions in mixed phase Bi-Sr-Ca-Cu-O superconducting thin films were investigated by X-ray photoelectron spectroscopy. Films containing various volume fractions of the 85 K and the 110 K phases were prepared by metallo-organic deposition techniques. Analysis of the Cu 2p 3 2 photoelectron peak revealed that both Cu 2+ and Cu 1+ states exist in these films. With increasing 110 K transition depth, the Cu 2+ /Cu 1+ ratio decreased as shown by a reduction in the copper shake-up satellite intensity.

Semiquantitative assessment of 2223/2212 phase homogeneity in Bi(Pb)SrCaCuO superconducting thin films using XRD techniques

Abstract Phase segregation in multiphasic Bi(Pb)SrCaCuO (BSCCO) films deposited on a silver foil substrate by m metallo-organic decomposition (MOD) has been observed using X-ray diffraction (XRD) techniques. The concept of a phase inhomogeneity factor (PIHF), developed in this work, has been applied to a semiquantitative assessment of the distribution of the 2223 and 2212 phases in the bulk versus film-substrate interface region. On the basis of the XRD-PIHF analyses, we conclude that the silver substrate tends to promote the 2212 to 2223 phase transformation with 2223-rich compositions being formed at the film-substrate interface. This phase transformation was shown to occur at lower temperatures for thinner films. These films contain higher volume-fractions of the 2223 phase and exhibit a higher degree of phase homogeneity. Moreover, the film-substrate interactions seem to induce the lowering of the melting point of the system in the interfacial region and lead to an increase in the degree of c -axis orientation by promoting partial melt textured grain growth.

Effects of cold rolling and thermal annealing on superconducting properties of 2212 Bi-Sr-Ca-Cu-O/Ag tapes

Abstract High-temperature superconducting (HTS) tapes were fabricated by doctor-blade coating of a BSCCO 2212 dispersion in Butvar-B76 binder, and thermal processing in a three-zone belt furnace. The crystalline properties of these HTS layers were studied by X-ray diffraction techniques. The superconducting properties of HTS tape conductors were examined using AC susceptometry. The effects of sintering, cold rolling, and thermal annealing were monitored by following the temperature dependence of the AC susceptibility and process-induced changes in the crystalline microstructure. A significant degradation of the superconducting properties due to cold rolling has been observed. This degradation is attributed to inferior intergranular coupling and appears to be reversible. Thermal annealing of the cold-rolled samples leads to the full recovery of the AC susceptibility versus temperature response.

A vibrational spectroscopic study of metal chalcogenide spin-on-glasses

Abstract Thin films of germanium diselenide have been prepared by a spin-on-glass technique from ethylenediamine solutions. The solutions and the films at various stages of processing have been characterized using infrared and Raman spectroscopies. The results indicate that amorphous GeSe 2 films are formed after complete processing. At stages prior to the formation of the final film several chemically distinct species are observed. The identification of some of these species offers insight into the formation of solid GeSe 2 networks.