Thin films superconductors

Figure 9.15. Influence of sample cleaning on XPS scans taken on a thin-film superconductor, (a) Survey scan from an as-received surface, (b) Survey scan from surface after ion-beam (sputter) cleaning. Note the reduction in the Cls peak after cleaning, (c) Comparative Ba3d scans from both cases. Note the change in shape and size as the surface contaminant layers (probably containing carbonates and hydroxides of Ba in addition to other components) are removed. The peak shapes and intensities of other cations change, too. Initial data represent the composition and chemistry of the contaminant layer, whereas that from sputtered sample represents those of the pure underlying superconductor (possibly with sputter-induced changes that need to be accounted for).

The alkaline-earth metal -diketonates are less volatile than other metal / -diketonates because they exist as oligomers. For example, one Ba / -diketonate consists of a clnster of five metal ions bridged by S-drketonate carbonyl O atoms and H2O. Several such metal /3-diketonates which are used for metallorganic chemistry vapor deposition (MOCVD) of thin-film superconductors were characterized by GC-MS as well as by TGA and MS. It was proved that the addition of the -diketone to the carrier gas stream improves the GC behavior of these alkaline earth metal chelates, probably owing to adduct formation accompanying the dissociation of the oligomers . 

The patentees examined the delivery of a variety of reagents used to make thin film superconductors. The reagents, metal complexes of Y(THD)3, Ba(THD)3, Cu(THD)3,... 

The physical principles of LTSEM applied to superconductors were first discussed by Clem Huebener [5.2]. The minimum beam diameter which can be achieved in commercial scanning electron microscopes is typically about 10 nm. On the other hand, the spatial resolution of LTSEM is limited by the spreading of the beam-induced sample perturbation. In thin-film superconductors it is essentially the thermal perturbation (local heating effect) which... 

New ceramic technologies have been developed for the preparation of thin-film superconductors YBa2Cu307-x (YBGO) on a monocrystalline SrTiOj substrate, as well as superconductor powders by Pb-doped Bi2Sr2Ga30io + Y (BSCCO) as a top-quality material (Binder and Gunther 1999). 

Tumipseed, S. B., Barkley, R. M., and Sievers, R. E., Synthesis and characterization of alkaline-earth-metal P-diketonate complexes used as precursors for chemical vapor deposition of thin-film superconductors, Inorg. Chem., 30, 1164 (1991). 

A good example of the power of synchrotron source radiation is found in the study of the thin-film superconductors that are required for applications of high-temperature superconductors (HTSC) in microelectronics technology [77]. An example of such work [78] involves the analysis of HTSC films produced by laser evaporation of elements in the Y-Ba-Cu-0 system. Ten films were simultaneously deposited with various target-to-substrate distances allowing study to be made of the laser plasma expansion in vacuo. A very important advantage of this method is that it allows extremely low detection limits to be achieved. As an example, in the referenced study [78] the authors claim a detection limit of 5 x lO atoms/cm. ... 

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