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In order to study the possible advantage of photo-assisted MOCVD compared with thermal MOCVD during the annealing process after film growth, a piece of c-axis oriented YBa2Cu3O7−δ film on Φ1″ LaAlO3 (1 0 0) substrate was prepared by photo-assisted MOCVD. It has well in-plane alignment and high critical current density (Jc > 2.5 MA/cm2, @ 0 T, 77 K, thickness ≈ 430 nm). Small pieces cut from it were annealed by photo-assisted or thermal annealing process to realize deoxidization or oxidization respectively. By monitoring the c-axis lattice constant, it was found that oxidization rate of photo-assisted annealing is obviously higher than that of thermal annealing. Inversely, the deoxidization rate of photo-assisted annealing is lower than that of thermal annealing. And a phenomenon that the long-time stable c-axis lattice constant is related to the temperature, unrelated to annealing process has been observed. It conforms to the thermodynamic equilibrium which is relative to annealing temperature and oxygen partial pressure, irrespective to whether photo activation or thermal activation.

Pure GdBa 2 Cu 3 O 7− δ (GdBCO) films were deposited on (1 0 0)-oriented LaAlO 3 (LAO) substrates by photo-assisted metal organic chemical vapor deposition (PhA-MOCVD) technique. The effects of substrate temperature ( T s ) and oxygen partial pressure (Po 2 ) on microstructure, growth rate and superconducting critical current density ( J c ) were investigated. A dense and no grain boundary visible, single-crystal-like cross-sectional morphology was observed. For the GdBCO film sample obtained at T s of 810 °C and Po 2 of 4 Torr, the full width at half-maximum were 0.08° and 0.41° for out-of-plane and in-plane orientations, respectively. Such low values were similar to that of single crystal GdBCO. Optimally processed GdBCO samples exhibited J c of 2.5 MA/cm 2 at 77 K in self-field. A relatively high growth rate of 0.104 μm/min for the GdBCO film is realized by the PhA-MOCVD technique.

Y 2 O 3 nanodots were fabricated on vicinal substrate (1 0 0)-oriented LaAlO 3 (LAO) by photo-assisted metalorganic chemical vapor deposition (PhA-MOCVD). Nucleation and growth processes of Y 2 O 3 nanodots self-assembled as rows along the terraces of LAO were investigated with various growth parameters. It is found that density and size of Y 2 O 3 nanodots can be tuned and well controlled by varying substrate temperature ( T s ), oxygen partial pressure and growth time. At lower T s , the morphologies of Y 2 O 3 nanodots are characterized by small and dense solid cones. With elevating T s , the dots gradually grow larger and sparser. This phenomenon could be illustrated by two competitive kinetic processes, i.e. surface diffusion of adatoms and yttrium desorption. Morphologies of these nanodots were also influenced by variation of oxygen partial pressure. To further discuss the growth kinetics, a more clearly quasi-linear distribution was obtained and the coarsening effect is modified by varying growth time.

Normally, surface of c -axis oriented YBCO films grown by MOCVD are found to be populated by micron-sized outgrowths with elemental compositions such as Ba–Cu–O and Cu–O. For both low and high current applications with the YBCO films, these surface outgrowths should be eliminated. In this study, it is found that by using a simple processing technique of decreasing appropriately the sublimation temperature of the Cu-based precursor, the surface outgrowths can be essentially subdued. At the same time it is qualitatively predictable that J c of these smoother YBCO films will be lowered. However, experimentally, it is found that at appropriate YBCO film growth conditions, the lowered J c value is acceptable for most applications. Actually, a surface outgrowth covered YBCO film made by photo-assisted MOCVD, with film composition Y:Ba:Cu as 1:1.2:1.5, has its J c being 3.4 MA/cm 2 (0 T , 77 K). As composition of YBCO film is changed to 1:0.9:1.2 by lowering the sublimation rate of the Cu-based precursor, then there are no more outgrowths on surface, with its J c being 2.6 MA/cm 2 .

It is well-known that there is a relatively small temperature window for the growth of epitaxial and c -axis oriented YBCO thin films by various methods. In this study, this window was more precisely examined for YBCO film growths by photo-assisted MOCVD. At specified total reactor pressure of 4.6 torr, and specified respective partial pressures for the oxidizing agents, O 2 and N 2 O at 1.7 torr and 1.1 torr, the film growths were tested at several substrate temperature ( T s ) points from 780 °C to 864 °C. The film growth time for each test was 3 min. As to compositional purity, purity in c -axis orientation, and crystal structural quality of these tested films by using photo-assisted MOCVD technique, it was found that for the growth of purely c -axis oriented YBCO thin films with high crystalline quality, the appropriate growth temperature range (or “ T s window”) was from about 800 °C to 830 °C, at relevant pressures as specified above. T c and J c of a typical YBCO film sample grown within this “ T s window”, i.e., 810 °C, were found as 90 K and 1.32 MA/cm 2 (77 K, 0 Oe) respectively by magnetization measurements. It is noticeable that this film, and other purely c -axis oriented YBCO films are all single-crystal like and dense, with no SEM visible grain boundary or void. The causes of precipitates found on top surface of these c -axis oriented YBCO films are also discussed.

High-quality superconducting YBa2Cu3O7−δ (YBCO) thick films with thickness over 2 μm were grown on LaAlO3 (LAO) substrates by photo-assisted metalorganic chemical vapor deposition (PhA-MOCVD) with a single liquid precursor delivery system. The YBCO thick films fabricated are single-crystal like with no visible grain boundaries or voids. Surface and interface microstructures of YBCO thick films have been systematically investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. Large precipitates were observed on the surface of these films. These precipitates are mostly composed of crystalline BaCu3O4, along with some polycrystalline and amorphous YBCO phases, and were found to exist only on top of the YBCO films, with no penetration into the films. The high quality of the prepared YBCO thick films was confirmed further by the results of X-ray diffraction and Tc/Jc measurements. Thus, these thick YBCO films prepared by PhA-MOCVD have promising application potential in fields such as coated conductors.

Epitaxial, high-quality YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films were grown by a photoassisted metal-organic chemical vapor deposition technique with a single liquid precursor delivery system, and characterized by X-ray diffraction (XRD), scanning electron microscopy, and low-high-resolution transmission electron microscopy techniques. Very dense and single-crystal-like film structure was observed in all of these YBCO thick films. Large precipitates on these thick films were identified as BaCu/sub 3/O/sub 4/, sprinkled only at surface of these YBCO thick films. YBCO thick films with high crystalline and superconductive quality were confirmed by data of XRD analyses and superconductivity measurements. At the same time, the reason why epitaxial YBCO thick films with high-quality single-crystal-like structure can be grown up to about 4.5 /spl mu/m thick is illustrated from the point of view of photoactivation. It is also found that these thick films were optimally oxygenated with their superconductive properties in concern.

High quality superconducting YBa 2 Cu 3 O 7− x (YBCO) films were deposited on LaAlO 3 ( 1 0 0 ) substrates at a high growth rates of 0.2–1 μm /min with high reproducibility by a novel photo-assisted metalorganic chemical vapor deposition process with single liquid precursor delivery technique. The photo irradiation technique can dramatically increase the growth rate and the single liquid precursor delivery technique can significantly improve the process reproducibility. X-ray diffraction analysis indicated that single phase, c -axis oriented and well ab-aligned YBCO films were high reproducibly prepared. The as-grown YBCO films showed critical temperatures ( T c ) of 91 K with the transition width ( ΔT c ) less than 1 K, and self-field critical current densities ( J c ) of 4.6×10 6 A/cm 2 at 77 K.

YBa 2 Cu 3 O 7-x films have been deposited by photo-assisted MOCVD at commercially viable rates on both single crystal oxide substrates and atomically textured metallic substrates. CeO 2 and YSZ buffer layers have also been developed by photo-assisted MOCVD for deposition on metallic substrates at rates approaching 1 μm/min. The resulting buffer layers show good duplicate of the moderate atomic order of the underlying metallic substrates, and the subsequent YBCO layers show similar moderate atomic order with resulting J c ∼ 5 x 10 5 A/cm 2 .

Intrinsically, the thin-film preparation technique of metalorganic chemical vapor deposition involves a large number of control variables which are especially critical in work with quaternary or higher high- T c materials. Thus, effective methods are needed to optimize variable settingsin the preparation of high- T c films. A matrix experimental plan and robust design methodology has been employed for this purpose. The first design phase was based on existing knowledge regarding growth temperature, pressure and annealing temperature for photo-assisted preparation of YBCO thin films on LaAlO 3 (100) substrates. A battery of only nine experiments plus three confirmation depositions were then used to optimize the process control parameters of precursor oven temperature, carrier gas (Ar) flow rate, and the flow rates of two oxidizing gases, O 2 and N 2 O, with respect to critical current density ( J c ) of the films. J c (77 K, zero field) values for deposited YBCO films (with thickness in the 0.4–0.6 μm range) were found to be improved from about 1 to 3 × 10 6 A/cm 2 . J c for a thinner sample (0.15 μm) reached 5.0 × 10 6 A/cm 2 . It was found that under these processing conditions the most significant process control parameter affecting J c is the flow rate of O 2 , or more precisely, the oxidizing agent flow-rate ratio of O 2 and N 2 O. Analysis of the variance of the J c data indicated that there likely exist interactions among some of the control variables, most obviously between the flow rates of O 2 and N 2 O.

The growth of purely a -axis oriented YBCO thin films on LaAlO 3 (100) substrates with no template layer addition has been accomplished by photo-assisted MOCVD. In addition to the requirement of lattice-matched substrates, the difficulty of growth of purely a -axis oriented YBCO films with this processing technique has been overcome by utilizing three appropriate processing/growth factors: substrate temperature ( T s ), total partial pressure of oxidizing gases O 2 and N 2 O ( P (O 2 + N 2 O)), as well as high film growth rate. A high growth rate (up to 7000 a/min) has been accomplished through MOCVD growth assisted by photo-irradiation with tungsten-halogen lamps. Variance of the three factors leads to tailored growth of either a -axis, c -axis or [110] oriented growth for YBCO. The growth of a -axis YBCO thin films under different precursor flow rates also affects the film morphology.

ZrO2 nanodots are successfully prepared on LaAlO3 (LAO) (100) substrates by photo-assisted metal-organic chemical vapor deposition (MOCVD). It is indicated that the sizes and densities of ZrO2 nanodots are controllable by modulating the growth temperature, oxygen partial pressure, and growth time. Meanwhile, the microwires are observed on the surfaces of substrates. It is found that there is an obvious competitive relationship between the nanodots and the microwires. In a growth temperature range from 500 ?C to 660 ?C, the microwires turn longest and widest at 600 ?C, but in contrast, the nanodots grow into the smallest diameter at 600 ?C. This phenomenon could be illustrated by the energy barrier, decomposition rate of Zr(tmhd)4, and mobility of atoms. In addition, growth time or oxygen partial pressure also affects the competitive relationship between the nanodots and the microwires. With increasing oxygen partial pressure from 451 Pa to 752 Pa, the microwires gradually grow larger while the nanodots become smaller. To further achieve the controllable growth, the coarsening effect of ZrO2 is modified by varying the growth time, and the experimental results show that the coarsening effect of microwires is higher than that of nanodots by increasing the growth time to quickly minimize ZrO2 energy density.

YBa2Cu3O7 (YBCO) films have been deposited by photo-assisted MOCVD at rates of greater than 0.3μm/min on both single crystal oxide substrates and atomically textured metallic substrates. The YBCO films of thickness from 0.5μm to 3μm deposited on LaAlO3 substrates are shown to be highly atomically ordered with Jc> 1 × 106 A/cm2. CeO2 buffer layers have also been developed by photo-assisted MOCVD for the integration of YBCO with metallic substrates. The CeO2 layers were found to be crack-free when grown on nickel even above 1 micron thickness, and exhibited crystal orientation and in-plane alignment similar to that of the atomically textured Ni substrates. YBCO films grown on the thick CeO2 buffer layers on nickel substrates have shown promising results with Jc∼6 × 105 A/cm2.

High-quality GdBa2Cu3O7-δ (GdBCO) films with thicknesses of 0.14-1.62 μm were deposited on (100)-oriented LaAlO3 substrates by photo-assisted metal-organic chemical vapor deposition technique. Evaluation of film microstructure and strain-relaxation phenomenon in the growing films and their effects on the crystallographic and superconducting properties of the GdBCO films have been investigated. A single-crystal-like cross-sectional morphology with dense and crack-free surface and no grain boundary visible was observed. The c-axis lattice parameters of the GdBCO films grown with different thicknesses were used to determine the out-of-plane strain. The result shows that the strain could be gradually relieved as film thickness increases. Highly biaxially textured GdBCO films have been obtained. For a 0.31-μm GdBCO film sample, the full-widths at half-maximum were 0.08° and 0.47° for out-of-plane and in-plane orientations, respectively. Such low values were similar to that of single-crystal GdBCO. The highest critical current density (Jc) value is ~ 2.5MA/cm2 (77 K and 0 T). As films were getting thicker, their Jc values decrease gradually. This is mainly attributed to a lack of pinning centers in the thicker films.

Metalorganic chemical vapor deposition (MOCVD) is emerging as a practical high Tc superconducting thin film preparation technique for industrial application. Intrinsically this technique involves a large number of variable parameters. This is especially critical for the quarternary or higher high Tc materials. Thus, effective methods are required to optimize the parameters for the preparation of high Tc films. A matrix experimental design named Robust Design has been employed for this purpose. The first-phase design was based on a starting knowledge of growth temperature and pressure, and annealing temperature for MOCVD preparation of YBCO thin films. A minimum lab effort of only nine deposition experiments was then used to optimize the process control parameters of precursor oven temperature, carrier gas (Ar) flow rate, O2 flow rate and N2O flow rate. The results were then followed by three confirmation depositions. The Robust Design resulted in the growth of YBCO film with Tc consistently in the range of 87.0 K to 90.2 K and Jc improved from about 1.0 × 106 A/cm2 to 3–5 × 106 A/cm2.