摘要:

Vapor‐deposited thin films of YBa2Cu3Oywith complete superconducting transition temperatures as high as about 90.8 K have been fabricated using a triple e‐beam vapor deposition system. Resistive transition widths of about 0.7 K have been observed. While a variety of substrates have been used, the highest Tcand Jcare generally obtained on single crystal SrTiO3. Lithographic patterning of the films has been accomplished, producing the first superconducting electron devices (DC SQUIDs) operating in the liquid nitrogen temperature range, up to about 78 K.

ISSN:0094-243X    

DOI:10.1063/1.37111

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have used metal molecular beam epitaxy, sputter deposition with single composite target, and spin‐on/pyrolysis with metallo‐organic precursors to prepare thin films of high Tcoxide superconductors mostly in the Y‐Ba‐Cu‐O system. We report the superconducting properties and the structural characteristics of the films. The processing parameters of these thin‐film techniques are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.37100

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

YBa2Cu3O7−xfilms are produced through a combination electron‐beam/thermal evaporation process. The resistivity behavior and structures of the prepared films are correlated to as‐deposited compositions, annealing temperatures and substrate temperatures. In particular, ‘‘ab’’‐oriented YBa2Cu2O7−xfilms are observed to grow both on (001) SrTiO3and (11¯02) Al2O3. Also, under some conditions, ‘‘c’’‐oriented YBa2Cu3O7−xfilms are grown on (001) SrTiO3. Plasma oxidation is shown to sharpen the transitions but can produce a resistive foot due to oxidation of non‐stoichiometric compositions at grain boudaries.

ISSN:0094-243X    

DOI:10.1063/1.37110

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Thin film processes for the high Tc superconductors of perovskite‐type oxides are classified into three: (1) deposition at a low substrate temperature followed by a post‐annealing at around 900°C; (2) deposition at a crystallization temperature 600–800°C, followed by the post‐annealing; (3) deposition at the crystallization temperature under oxidizing atmosphere. The process (3) possibly lowers the synthesis temperature. It was confirmed that the superconducting thin films of Er‐Ba‐Cu‐O were successfully grown at 650°C by the sputtering deposition owing to the process (3). Their onset temperature was 92K with zero‐resistivity at 86K.

ISSN:0094-243X    

DOI:10.1063/1.37070

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Thin YBa2Cu3O7−xsuperconducting films have been grown by several sputtering techniques including single target rf glow discharge sputtering, multi‐target rf sputtering, ion beam sputtering, and rf magnetron sputtering. A variety of substrates were used for the deposition and the best superconducting properties were obtained on single crystal (100) MgO and (100) SrTiO3substrates. RF sputtering was studied in detail because some very unique effects were observed during the sputtering. These effects, i.e., substrate heating, resputtering and stoichiometric deposition, were investigated. Substrate heating was found to be mainly due to secondary electron impingement. Resputtering may be mostly due to energetic neutral particle bombardment; however, negative ion bombardment cannot be ruled out. Ba deficiency in substoichiometric films may be due to the formation of Ba+ion formation and recapture by the cathode and due to intense substrate heating. Films grown by rf diode sputtering had to be compensated with excess Ba to maintain stoichiometry.

ISSN:0094-243X    

DOI:10.1063/1.37080

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Thin films of Y‐Ba‐Cu‐O have been fabricated using rf diode sputtering from a single mixed‐oxide powder target. The target consisted of about 200 grams of mixed reacted CuO, BaCO3, and Y2O3powders spread over an 8‐inch Cu plate, and mounted horizontally in a standard‐model sputtering system. Such a target was used for repeated rf‐diode depositions in a ‘‘sputter‐up’’ mode to a substrate hanging face‐down, with deposition rate of order 50–100 A˚/minute. Substrates investigated include sapphire and yttria‐ stabilized zirconia. Well‐cooled substrates yielded films close to the composition of an YBa2Cu3O7target. In contrast, uncooled or heated substrates yielded films dramatically deficient in Cu relative to the target. Sputtering for several hours in Ar plasma with 10% O2yielded shiny, black films ≊1 &mgr;m thick. Subsequent processing of films on zirconia substrates up to 850 °C in pure O2yielded an onset of superconductivity at ≊87 K, with a broad transition to zero resistance at ≊50 K. Improvements in this transition are expected as process parameters are refined. Effects of varying substrate temperature, rf power, target composition, and post‐deposition annealing treatment will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.37081

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Thin films of Y‐Ba‐Cu‐O superconductors were grown using a single‐target DC diode sputtering technique. A variety of substrates were employed, including quartz, alumina, MgO, and strontium titanate. As‐deposited films were amorphous. Formation of the superconducting structure was accomplished by post‐deposition high‐temperature anneals in oxygen. Deposition parameters leading to superconducting films from a single mixed‐oxide target are discussed. Electron spectroscopy has been employed to non‐destructively determine that the surface of the films are oxygen depleted, which may contribute to the high contact resistance measured in these films.

ISSN:0094-243X    

DOI:10.1063/1.37082

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Thin films of Y1Ba2Cu3Oxhave been produced on sapphire substrates by d.c. diode sputtering in Ar atmosphere followed by annealing O2at 850 C. X‐ray diffraction and resistivity show the films are amorphous and insulating as sputtered but become polycrystalline and conductive upon annealing, whereupon resistance begins to fall at 98 K, becoming fully superconductive at 69 K with a mid‐point at 86 K. Four‐point resistance measurements are made using low frequency phase sensitive detection. Electron microprobe analysis indicates that the 1‐2‐3 composition of this oxide can be obtained in the film by using a Y1Ba3.2Cu3.9Oxtarget, suggesting that resputtering of Ba and Cu occurs during the deposition. A strong interaction (most likely diffusive) can occur with the sapphire substrate which degrades the superconducting transition, necessitating shorter annealing times and lower temperatures than used for bulk powders.

ISSN:0094-243X    

DOI:10.1063/1.37083

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have studied the morphology, structure and superconducting properties high Tcoxide films, mostly in the Y‐Ba‐Cu‐O sytem, prepared by various sputtering techniques (diode and magnetron sputtering) and molecular beam epitaxy (MBE). In the as‐deposited condition the chemical homogeneity both across the film and through the thickness is excellent as measured by Rutherford backscattering spectrometry (RBS). Post oxygen annealing at temperature above 800°C yields the orthorhombic superconducting phase as revealed by the x‐ray diffraction. High‐quality epitaxially grown Y1Ba2Cu3O7−xfilms deposited on single‐crystal SrTiO3substrates with various orientations were obtained with a narrow rocking curve (<0.3°) in the direction perpendicularly to the film plane. Also, for the first time we observed the electron channeling in this class of materials. Sharp superconducting resistive transitions with Tc(R=0) above 89K and critical current density at 77K have been reproducibly achieved.

ISSN:0094-243X    

DOI:10.1063/1.37084

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

DC planar magnetron sputtering from a composite target has been used to produce films of YBa2Cu3O7−xwith zero resistance at 77K. Various aspects of the deposition process are addressed with a view to scaling up the process for production purposes.

ISSN:0094-243X    

DOI:10.1063/1.37085

出版商:AIP    

年代:1988

数据来源: AIP