Direct Peritectic Growth of c-Axis Textured YBa2Cu3Ox on a Flexible Metallic Substrate

Previous work in the development of YBa₂Cu₃O _x (YBCO) superconducting wires and tapes has been focused on the deposition of YBCO on buffered metallic substrates. Although such an approach has proved successful in terms of achieving grain texturing and high transport current density, critical issues involving continuous processing of long-length conductors and stabilization of the superconductor have not yet been entirely settled. We have developed a novel process, the so-called direct peritectic growth (DPG), in which textured YBCO thick films have been successfully deposited directly onto a silver alloy substrate. No buffer layer is employed in the film deposition process. The textured YBCO grains have been obtained through peritectic solidification over a wide range of temperatures and times. The substrate materials have not demonstrated any observable reaction with the YBCO melt at the maximum processing temperature near 1010°C. The transport J _c has reached a respectable value of 10⁴ A/cm² at 77 K and zero magnetic field. Based on the experimental results in this work, we show that the DPG method offers an effective alternative for the fabrication of long-length YBCO conductors. Also reported is a physical explanation of the texturing mechanism on the metal substrate.     

Structure and dielectric properties of sputtered bismuth magnesium niobate thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O₂/(O₂ + Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O₂/(O₂ + Ar) mixing ratio of sputter atmosphere was required. The deposited Bi_1.5MgNb_1.5O₇ cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~ 50% at a maximum applied bias field of 1.5 MV/cm, with low dielectric loss of ~ 0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films.     

Crystal engineering of high-T c and related oxide films for future electronics

Advanced technology and future prospect of oxide-based electronic materials are described with a focus on the significance of atomically controlled epitaxy of high-T _c superconductors and related oxide films. Problems in suitably forming the oxides whose power is potentially superior to silicon’s are discussed to stimulate technology development for engineering oxide film growth on an atomic scale. Our experimental results on controlled epitaxial growth of oxide films are presented with respect to pulsed laser deposition of YBa₂Cu₃O_{7 −δ} films as well as laser MBE growth of SrTiO₃ homoepitaxy and CeO₂ heteroepitaxy on Si substrates.     

Structural and mechanical characterization of BCxNy thin films deposited by pulsed reactive magnetron sputtering

BC_xN_y thin films deposited at 250 °C by pulsed reactive magnetron sputtering of a B₄C target in an Ar/N₂ plasma were studied by elastic recoil detection analysis, Fourier transform infrared, Raman, and photoelectron spectroscopy, electron microscopy, and nanoindentation. In the concentration range of 6% to 100% N₂ in the sputter plasma the segregation into nanocrystalline hexagonal boron nitride and amorphous sp² carbon is the dominant process during the film growth. The stoichiometric ratio and structural details of the major phases depend on the N₂ concentration in the plasma and have significant influence on the Young′s modulus and the elastic recovery of the BC_xN_y thin films.     

Photoluminescence characterization of β-FeSi2 prepared by ion beam sputter deposition (IBSD) method

Photoluminescence (PL) measurement technique was found to be effective in revealing the unique characteristics of β-FeSi₂ film formation on Si substrates by means of ion beam sputter deposition (IBSD) method. A strong photoluminescence peak at around 0.8 eV was observed for β-FeSi₂ samples and also for Si substrates that were sputter etched by Ne⁺, and then thermally annealed in air at elevated temperature. Comparison with literature data indicated that the PL peak at 0.8 eV observed in this study was mainly from D1 emission bands in Si substrate, whose intensity was enhanced by the sputter etching and the subsequent annealing of the substrate. Furthermore, comparison between CZ-Si and FZ-Si results indicated that the energy of 0.8 eV peak observed in this study was affected by the presence of oxygen in the Si bulk as well.     

Radio frequency sputtering and the deposition of high-temperature superconductors

This paper reviews the background to glow-discharge sputter deposition of thin films and the deposition of YBCO superconducting thin films in particular. The background to sputtering is briefly reviewed with reference to the recent literature on analytical and numerical techniques for investigating radiofrequency (r.f.) plasmas, magnetron sputtering and hysteretic behaviour in reactive sputtering. Low-energy, ion-assisted deposition techniques are briefly reviewed, and the effect of ion-beam interactions on film nucleation and growth is also discussed. The background to the sputter deposition of high-temperature superconductors (HTS) is given along with the choice of sputtering system for HTS deposition. Resputtering effects, off-axis andin-situ/ex-situ processing are also discussed. The sputter deposition of YBa₂Cu₃O _x is considered in detail along with theP-T-x oxidation conditions and the tetragonal/orthorhombic line. Typical experimental arrangements and results for YBCO sputtered onto SrTiO₃ and MgO are given. The problem of producing high-critical-current-density polycrystalline films by sputtering is also discussed.     

Material properties and growth control of undoped and Sn-doped In2O3 thin films prepared by using ion beam technologies

Undoped (IO) and Sn-doped In₂O₃ (ITO) films have been deposited on glass and polymer substrates by an advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. Relationships between structural and electrical properties in ITO films on glass substrates were intensively investigated by using the IBSD method with changing ion energy, reactive gas environment, and substrate temperature. Smooth-surface ITO films (R_rms ≤ 1 nm and R_p-v ≤ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. The different dependence of IO and ITO films' properties on the experimental parameters, such as ion energy and oxygen gas environment, will be intensively discussed.     

Crystal growth of orthorhombic BaSi2 by the vertical Bridgman method

Melt growth of BaSi₂ by the vertical Bridgman (VB) growth method was initiated from barium metal (3 N grade) and semiconductor-grade silicon. Because Ba is highly reactive at the growth temperature (≈1500 K), the crucible materials were chosen to avoid chemical reactions and sticking between the crucibles and the molten and vapor Ba. Crucibles made of molybdenum, quartz, alumina, SiN_x-coated quartz, chemical vapor deposition (CVD) pyrolytic graphite (PG), and chemical vapor deposition SiC-coated graphite were examined, and the semiconductor orthorhombic BaSi₂ was obtained in quartz, alumina, and molybdenum crucibles. The crystalline forms of the grown crystals depend on the crucible materials and growth conditions.     

Chemical solution deposition of YBa2Cu3O7−x coated conductors

At present, the development of superconducting YBa₂Cu₃O_7−x coated conductors attracts much attention due to their enormous application potential in electric power systems. Worldwide research is focused on the investigation and improvement of buffer materials and YBa₂Cu₃O_7−x superconducting properties as well as low-cost manufacturing processes in cooperation with industrial companies. Accordingly, chemical solution deposition has emerged as a highly competitive, versatile, and cost-effective technique for fabricating coated conductors of high performance. New chemical solution approaches are under development for buffer layer deposition. In order to achieve high critical current carrying YBa₂Cu₃O_7−x layers, the established trifluoroacetate route is favored. This paper reviews the most recent work on chemical solution deposition within the IFW Dresden while also considering achievements on this specific research topic worldwide.     

Coating material innovation in conjunction with optimized deposition technologies

Concentrating on physical vapour deposition methods several examples of recently developed coating materials for optical applications were studied for film deposition with optimized coating technologies: mixed evaporation materials for ion assisted deposition with modern plasma ion sources, planar metal and oxide sputter targets for Direct Current (DC) and Mid-Frequency (MF) pulsed sputter deposition and planar and rotatable sputter targets of transparent conductive oxides (TCO) for large-area sputter deposition.Films from specially designed titania based mixed evaporation materials deposited with new plasma ion sources and possible operation with pure oxygen showed extended ranges of the ratio between refractive index and structural film stress, hence there is an increased potential for the reduction of the total coating stress in High-Low alternating stacks and for coating plastics.DC and MF-pulsed sputtering of niobium metal and suboxide targets for optical coatings yielded essential benefits of the suboxide targets in a range of practical coating conditions (for absent in-situ post-oxidation ability): higher refractive index and deposition rate, better reproducibility and easier process control, and the potential for co-deposition of several targets.Technological progress in the manufacture of rotatable indium tin oxide (ITO) targets with regard to higher wall-thickness and density was shown to be reflected in higher material stock and coater up-time, economical deposition rates and stable process behaviour. Both for the rotatable ITO targets and higher-dense aluminum-doped zinc oxide (AZO) planar targets values of film transmittance and resistivity were in the range of the best values industrially achieved for films from the respective planar targets. The results for the rotatable ITO and planar AZO targets point to equally optimized process and film properties for the optimized rotatable AZO targets currently in testing.     

Growth and Characterization of PrBa2Cu3O7?x Thin Film Used as Template Layer on SrTiO3 Substrate

We have grown PrBa₂Cu³O_7–x (PBCO) thin films on (100) SrTiO₃ substrates using pulsed laser deposition (PLD). X-ray diffraction (XRD) studies indicate that the orientation of PBCO films varied with increasing deposition temperature: b axis oriented films can be grown at 680°C, and a axis oriented films at the temperature between 692°C and 705°C. Atomic force microscopy (AFM) reveals that a good flatness of the films was obtained with surface mean roughness of less than 24 Å, indicating that it is suitable for use as template layers in a axis oriented epitaxial YBa₂Cu₃O_7–y /PBCO and YBCO/tetragonal–YBCO/PBCO multilayer structures.     

Review of Applications of High-Temperature Superconductors

Since the discovery of high-T _c superconductor oxides in 1986, much research and development have been carried out, and much progress has been made. In the last ten years our efforts have been devoted to the development of materials technologies for these difficult materials, and remarkable progress has been made. This is a great contribution not only for application but also for fundamental research on high-T _c superconductors. In this paper, we will present a review of applications of high-T _c superconductors discovered in the last ten years. At present, it can be said that we are in the transition period from the period of growth to the period of specialization, looking for future applications of high-T _c superconductivity.     

Characteristics of stacked CuInS2 and CuGaS2 layers as determined by the growth sequence

CuInS₂ and CuGaS₂ thin films have been prepared sequentially from elemental evaporation sources onto conventional soda lime glass substrates heated at 350 °C during the deposition process. The gradient in the structure and composition of the stacked layers has been investigated for the two possible growth sequences. Structural depth profiling and crystallographic phase analysis were performed by grazing incidence X-ray diffraction. The atomic distribution in the films depth was analyzed by X-ray photoelectron spectroscopy combined with sputter etching. Formation of the quaternary compound CuIn_1 − xGa_xS₂, with a high Ga content x > 0.80, has been detected with different distribution depending on the growth sequence.     

Growth and structure of electron beam evaporated V2O5 thin films

The growth, structure and room temperature electrical conductivity of electron beam evaporated V₂O₅ thin films were studied in detail as a function of deposition temperature. The films deposited at T_s≈553 K and subsequently annealed in oxygen atmosphere at 693 K exhibited orthorhombic layered structure.     

Gasochromic switching of reactively sputtered molybdenumoxide films: A correlation between film properties and deposition pressure

Molybdenumoxide (MoO_x) thin films can change their optical properties upon exposure to hydrogen. Since the film properties strongly depend on process parameters we have studied how the films are affected by the total pressure during deposition. Stoichiometric and sub-stoichiometric MoO_x films were prepared by reactive direct current magnetron sputtering in an atmosphere of argon and oxygen. Substoichiometric films were coated with platinum as a catalyst and were colored in diluted hydrogen atmosphere and bleached in air. Optical spectroscopy, X-ray reectometry, spectroscopic ellipsometry and simulations of the measured spectra were used to characterize the films ex situ. In situ switching characteristics as revealed by optical spectroscopy and changes in stress were measured as well. We find that the total pressure during sputter deposition has a strong influence on the optical constants, the film density, and the sputter rate. The mechanical stresses and switching Preprint submitted to Elsevier Science 10 March 2006 cycles during the film coloration and bleaching also strongly depend on the total pressure. The influence of the sputter pressure on film properties is explained by the kinetics during the sputter process.     

Chemical vapor deposition of the superconductor YBa2Cu3O7?x(s) from the gas phase

The deposition of the condensed phase YBa₂Cu₃O_7–x from a gas mixture composed of YCl₃, BaCl₂, Cu₃Cl₃, and Ar reacting with another consisting of O₂ and Ar in a flow system at elevated temperatures was investigated by means of the virtual equilibrium model, and the deposition rates were computed as a function of input gas stream compositions. The optimum growth conditions were identified.     

Photocatalytic performance of very thin TiO2/SnO2 stacked-film prepared by magnetron sputtering

TiO₂/SnO₂ stacked-layers are synthesized by reactive sputter deposition on the glass substrate. Very thin TiO₂/SnO₂ bilayer-photocatalysts exhibited a very high photocatalytic activity for a degradation of gaseous acetaldehyde. Both the control of an electronic structure of TiO₂ overlayer in the near-surface region and the interfacial separation of photogenerated electrons/holes in the TiO₂/SnO₂ stacked-layer are keys to improve the photocatalytic performance.     

Study of (Bi4−x La x ) Ti3O12 Powders and Ceramics Prepared by Sol-Gel Method

La-modified (Bi_4–x La _x )Ti₃O₁₂ (abbreviated as BLT) powders were prepared by sol-gel processing methods. The powders were characterized by differential thermal analysis (DTA) and laser-diffraction particle-size analysis. The (Bi_4–x La _x )Ti₃O₁₂ ceramics were prepared from the powders and characterized by X-ray diffraction (XRD). The results indicate that the sol-gel method can be used to prepare nanometer powder for the new types of BLT ferroelectric ceramics. The solid reaction of BLT powders occurs at 730°C approximately resulting in the growth of BLT grain. The average grain size may be varied in the range 60–500 nm, depending on the calcination temperature of the powders. The (Bi_4–x La _x )Ti₃O₁₂ ceramics prepared from the powders were polycrystalline materials with completely monoclinic (Bi_4–x La _x )Ti₃O₁₂ phase.     

Effect of praseodymium substitution on the growth and properties of Y1−x Pr x Ba2Cu3O7−δ (o <x < 0·4) single crystals

In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium substituted (partially) large single crystals of high temperature superconducting Y_1−x Pr _x Ba₂Cu₃O_7−δ (x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm³ and 4 × 1 × 1 mm³, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y_0·8Pr_0·2Ba₂Cu₃O_7−δ and Y_0·6Pr_0·4Ba₂Cu₃O_7−δ materials are ≈ 2 × 3 × 0·1 mm³ and 5 × 1 × 1 mm³ and ≈ 1 × 1·5 × 0·1 mm³ and 7 × 0·2 × 0·1 mm³, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T _c) of the oxygenated crystals were found to depend on the Pr-content. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995