YBCO Target Research Articles

Synthesis and properties of YBa 2Cu 3O 7−δ made by a modified hydroxycarbonate method

YBa 2Cu 3O 7−δ was synthesised using a solution method. The coprecipitation of the stoichiometric amounts of nitrate solution of yttrium, barium and copper was performed using a mixture of NaOH, Na 2CO 3 and H 2C 2O 4 in a molar ratio 5:1:1 as precipitation agent. The as-obtained precursors have a copper deficiency of 0.1 with respect to the nominal stoichiometry of the starting solution. The mechanistic study of the product formation has revealed that in these atomically mixed precursors the individual components have a different behaviour with respect to those in a mechanical mixture. The final products was obtained after heat treatment at 950°C for 6 h in oxygen atmosphere. The product was analyzed by XRD, SEM, EDXS and four probe DC resistivity measurements. The as-synthesised YBCO has shown good superconducting properties T c( R = 0) = 90.5 K and ΔT = 1 K. This method was used with success in the fabrication of YBCO target for laser ablation.

Optical spectroscopy study of the role of Ag in laser ablated YBa2Cu3O7−δ thin films

We have found evidence through optical spectroscopy that AgO is indeed generated in the laser plume during pulsed laser deposition of YBa2Cu3O7−δ (YBCO) thin films using Ag-doped YBCO targets. This supports our earlier conjecture that formation of AgO in the plume and its subsequent dissociation at the elevated substrate temperature (since AgO is unstable above 350 °C) provides active oxygen to the YBCO lattice, thereby increasing oxygen incorporation during growth of YBCO thin films.

High pressure d.c. sputtering of high Tc superconducting films: properties and deposition conditions

We used high pressure d.c. sputtering to deposit superconducting thin films (YBa 2Cu 3O 7 − δ (YBCO) and Bi 2Sr 2CaCu 2O 8 + x). With a.c. susceptibility measurements one can not only quickly characterize the superconducting properties of the sample, but also identify the layered growth of the films. Measurements of the gas phase composition of the sputter deposition show an unexpectedly high oxygen/metal ratio. The reason for this ratio is investigated. Measurements of the evaporation of YBCO target material yield spectra are presented, where the most important metal and metal-oxygen species are identified.

Spectroscopic analysis of plasma during rf magnetron sputtering of a YBCO target: Evidence for oxidation on the surface of the cathode

In this article, we present spectroscopic analysis of plasma during reactive rf magnetron sputtering of a YBa2Cu3O7 target. Particular attention is paid to the influence of oxygen pressure on the emission lines of cationic species. From the optical response of barium and copper resonance lines, we have deduced that the oxidation of barium into barium oxide BaO (or BaO2) is complete for an oxygen content up to 10% whereas the oxidation of copper into copper oxide CuO needs an oxygen content of up to 30% which corresponds to the value of the gas composition generally used by different groups. We have shown that these oxidation reactions are represented by a mass law in the vapor phase. These results are confirmed by x-ray photon spectroscopy analysis and give the experimental process for mixed valence copper oxide sputtering deposition.

The effect of YBa 2Cu 3O 7− x target properties on the superconducting characteristics of laser ablation deposited thin films

Pulsed-laser deposition has been demonstrated to be an advantageous technique for producing high-quality superconducting YBCO thin films. In this technique, the quality of the YBCO thin films is strongly dependent on various processing conditions such as substrate temperature, laser energy density, ambient oxygen pressure, and pulse repetition rate, all of which have been previously investigated. However, it has been also found that the laser target is one of the key factors in the fabrication of high-quality YBa 2Cu 3O 7− x (YBCO) thin films. In the systematic identification of this effect, nine different YBCO targets have been studied. Both the YBCO targets from various sources and the corresponding YBCO thin films deposited under optimized conditions have been characterized and compared by their structure, composition and electronic properties. This investigation has indicated that impurity phases (liquid phase, 211 and CuO) in the targets play different roles, though the sintered targets as a whole were stoichiometric. The superconducting transition temperature ( T c) of YBCO thin films decreased as the liquid phase (BaCuO 2CuO, which is yttrium deficient) in the YBCO bulk target increased. T c of the thin films may also be decrease with the presence of the 211 phase in the targets, however, the CuO phase in the YBCO target may actually increase T c of the thin films.

Two-dimensional growth model for laser-ablated Ag-doped YBa2Cu3O7−x thin films

Ag-doped YBa2Cu3O7−x (YBCO) thin films using 2–20 wt % Ag-doped YBCO targets have been grown in situ by the laser ablation technique. The improvement in properties in normal and superconducting states of Ag-doped YBCO films has been interpreted using a two-dimensional growth model. The model is simple and is based on widely accepted characteristics of Ag such as its flux action at high temperatures and its nonreactivity with YBCO phase. Experimental evidence in support of the growth model is presented by carrying out microstructural studies and measurements of room-temperature resistivity, critical current density, and microwave surface resistance in superconducting state.

On the role of Ag in enhancement of Jc in YBa 2Cu 3O 7−δ thin films

The role of Ag in the enhancement of J c in YBa 2Cu 3O 7−δ (YBCO) thin films is investigated. Studies show that the concentration of Ag in laser-ablated films made from YBCO targets containing 1–20 wt.% Ag, is less than 0.1%. J c has been found to improve with Ag doping by a factor of 8 in the films which were prepared from targets containing 5 wt.% Ag. A theoretical model based on the reduction in the resistive grain-boundary size is proposed to explain the observed enhancement of J c.

Preparation of Y-Ba-Cu-O films by ion-beam sputtering with a hollow cathode oxidation

Deposition of as-grown high Tc superconducting films by ion beam sputtering was investigated. In order to improve the superconductivity, oxygen should be activated. For this purpose, we developed a hollow cathode activation system to deposit superconducting YBCO films. When the current of hollow cathode was 100mA, we obtained the Tc of 87K for YBCO film on (100) SrTiO 3 substrate at 730°C. YBCO targets with varying composition were used and resulting YBCO films were examined by X-ray diffraction. The result showed optimum target to obtain pure YBCO film was Ba and Cu rich one (YBa 2.2Cu 4O x). IBS are suitable to deposit various materials such as insulator, the YBCO-Y 2O 3-YBCO trilayer structures were also succecfully formed.

In-Situ Plume Diagnosis During Pulsed Laser Deposition of Epitaxial-Oxide Thin Films

ABSTRACTThe visible plume, induced during pulsed-laser deposition (PLD) of epitaxial La0.5.jSr0.5 5CoO3/Ba0.4Sr0.6TiO3/La0.5Sr05CoO3/YBa2Cu3O7/YSZ heterostructures on silicon (100) wafers, was studied by optical-emission spectroscopy (OES). These films are suitable for the fabrication of ferroelectric capacitors and pyroelectric-sensor devices. A YAG laser, at 266 nm, is used for ablation. A collection lens transfers the PLD-plume emission into an optical fiber and onto a diffraction grating and a CCD array, for time-averaged spectroscopy from 410 to 640 nm. Plume emissions from ablated targets in the presence of an oxygen ambient, due to various atomic (Ba, Co, Cu, Sr, Ti, Y, Zr), ionic (Ba+, La+, Sr+, Y+), and a diatomic oxide (YO) species were identified. Emission intensity and evolution of ablated species are reported for distance away from the target surface, oxygen pressures, and laser fluences (1 to 4 J/cm2). The behavior of reactive-product species, especially YO for plumes from yttria-stabilized zirconia (YSZ) and YBCO targets, is discussed. This simple and inexpensive OES system is suitable for use as a plume-quality monitor on routine PLD film synthesis.

Behavior of the droplets ejecting from the YBCO target during the pulsed laser deposition

The droplets density of the YBa 2Cu 3O 7-x thin film was increased considerably at a certain laser shot number. Until 100 laser shots of cumulative irradiation, the films have the droplets density of ∼10 3 mm −2 and the YBCO target surface smoothness was maintained. However, after 100 laser shots, the density was increased more than 10 times and the target surface morphology modified to conical structure. This result has explained by the change of the droplets ejecting behavior with the development of the canonical structure at the target surface.

Ion-beam sputter deposition process for Y1Ba2Cu3O7-δ thin-film structures

Ion-beam sputter deposition (IBS) has been developed to a fully oxygen-compatible technology for growth of complex oxides, such as Y1Ba2Cu3O7−δ (YBCO) thin films. The IBS system consists of an rf-plasma ion source with molybdenum grids for sputtering, a dc-plasma electron source for space charge compensation, stoichiometric YBCO and NGO targets, a beam chopper with BaO2, Cu, and Nd blades for stoichiometry control, and an ECR-oxygen-plasma source for in situ film oxidation and photoresist removal. Due to its complexity the IBS process is fully computer-controlled. A salient feature of IBS is the excellent crystallographic and morphological properties of thin (100)/(010)- and (103)-oriented YBCO films on SrTiO3 (STO) and NdGaO3 (NGO) substrates. Sharp interfaces and good superconducting properties render this technology feasible for the fabrication of SIS-ramp-junction SQUID's.

Investigation of precipitate formation on laser-ablated YBa2Cu3O7- delta thin films.

We have investigated systematically the particle formation on the surface of high-quality ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (YBCO) epitaxial films grown by pulsed laser deposition. Scanning-Auger-electron spectroscopy identified two types of precipitates, i.e., ${\mathrm{BaCuO}}_{2}$ and CuO, on the films deposited from a stoichiometric YBCO target. The coexistence of these two phases with a YBCO matrix film is well explained by the pseudoternary phase diagram of ${\mathrm{YO}}_{1.5}$-BaO-CuO, assuming a slight Y deficiency in the film. The precipitate formation was reduced when the films were grown under conditions slightly deviated from the optimum for the formation of well-equilibrated, highly crystalline, and high-${\mathit{T}}_{\mathit{c}}$ and high-${\mathit{J}}_{\mathit{c}}$ films. Under such thermodynamically off-equilibrated conditions, the phase separation into YBCO and secondary phases is presumed to be kinetically prevented to give solid-soluted films and off-stoichiometric compositions and inferior crystallinity and superconductivity. The film-thickness dependences of the precipitate density and size were quantitatively analyzed by scanning electron microscopy to indicate that the nucleation of precipitates occurred by the initial 50 nm growth of the film to be followed by the increase of the precipitate's size. The use of off-axis polished substrates could successfully suppress the nucleation of the precipitates. A possible mechanism of precipitate formation is proposed.

Novel YBa2Cu3O7−x and YBa2Cu3O7−x/Y4Ba3O9 multilayer films by bias-masked ‘‘on-axis’’ magnetron sputtering

In situ YBa2Cu3O7−x (YBCO) films have been fabricated on SrTiO3 (001) and LaAlO3 (001) substrates by on-axis biased-radio-frequency magnetron sputtering in Ar-10% O2 at total pressures as low as 3 Pa (3×10−2 mbar) and a deposition rate 210 nm/h. Negative oxygen ion-resputtering has been considerably reduced by introducing a biased copper mask between the substrate and target. The surface morphology and physical properties of the films are greatly improved on applying a positive dc substrate bias with respect to the grounded deposition chamber. We have obtained superconducting YBCO films with transport critical current as high as 106 A/cm2 at 77 K and low normal-state resistivity by this approach. Scanning tunneling microscopy analyses of the films with the best superconducting properties reveal a spiral growth mechanism. However, films deposited by negative dc bias under identical sputtering conditions are insulating. From x-ray θ-2θ and rocking curve measurements, we identify the insulating films to be c-axis oriented Y4Ba3O9 (YBO) films. Furthermore, YBCO films could be grown on the YBO layers without any degradation of TC and c-axis orientation. This novel bias sputtering feature gives us a unique opportunity to produce superconductor/insulator, YBCO/YBO, multilayers from a single YBCO target.

Large area, low microwave surface resistance thin films of YBa 2Cu 3O 7 prepared by pulsed laser ablation

YBa 2Cu 3O 7 (YBCO) superconducting thin films were deposited on (100)LaAlO 3 substrates 35 mm in diameter by pulsed laser ablation. The substrates were heated resistively during deposition by a single-crystal Si heater and the laser beam was scanned on the rotating YBCO target. The films exhibited a thickness variation of ±3.7%, with zero resistance temperature T c0 =90.6±0.6 K, critical current density J c =2.9±0.9×10 6 A/ cm 2 at 77 K, and at 10 GHz a surface microwave resistance of <250μΩ at 77 K. The above-mentioned properties showed that high-quality YBCO thin films over a large substrate area can be obtained with this laser ablation system.

Effect of processing conditions on superconductive properties of laser-deposited YBCO thin films

Thin superconductive films of YBa2Cu3O7−x have been deposited on (100) single crystal SrTiO3 substrates by using technique of ArF pulse excimer laser evaporation of bulk YBCO target in a vacuum, followed by slow cooling in an oxygen atmosphere. Thin-film properties are strongly influenced by the processing conditions. The effect of pulse repetition rate, beam power, beam size on the target surface and oxygen pressure on the surface morphology and superconductive properties of deposited films has been investigated. Film characterization has been performed by using X-ray diffractometry, scanning electron microscopy and four-point probe electrical instruments.

Selective etching of YBCO targets by ion — plasma sputtering

Abstract Single-phase ceramics YBa2Cu3O7 produced by the solid-state sintering and used as a target at ion-plasma deposition of films was studied by the X-rays analysis, optical microscopy and microhardness measurement. Following changes occurred in the target during its use: 1. 1-grains having the orientation along the normal to the surface of the target were predominantly etched away by sputtering from the surface of the target; 2. 2 — Y2BaCuO5 compound appeared; 3. 3 — nonuniform distribution of oxygen appeared along the cross-section of the target.

Laser ablation of YBCO: utilizing /sup 18/O to investigate the incorporation of oxygen into the laser plume

/sup 18/O has been used as a tracer to measure the transfer of oxygen from the chamber atmosphere into the laser induced plume. The amount of oxygen incorporated into the plume was found by laser ablating from a polycrystalline YBCO target onto a room temperature carbon substrate in an atmosphere of 50% /sup 16/O and 50% /sup 18/O. A series of such samples was prepared using deposition pressures ranging from 0.5 to 260 mTorr. The film stoichiometry, including, most importantly, the atomic fraction of /sup 18/O, for each sample was determined using Rutherford backscattering. The results show that the incorporation of /sup 18/O from the deposition atmosphere increases with increasing deposition pressure (50% /sup 16/O and 50% /sup 18/O) up to approximately 25 mTorr and then, unexpectedly, decreases for higher pressures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Selective etching of YBCO target by ion-plasma sputtering

Single-phase ceramics YBa 2Cu 3O 7 produced by the solid-state sintering and used as a target at ion-plasma deposition of films was studied by the X-rays analysis, optical microscopy and microhardness measurement. Following changes occured in the target during its use: 1 - grains having the < 00 l orientation along to the normal to the surface of the target were predominantly etched away by sputtering from the surface of the target; 2 - Y 2BaCuO 5 compound appeared; 3 - nonuniform distribution of oxygen appeared along the cross-section of the target.

Fast-Iccd Photography and Gated Photon Counting Measurements of Blackbody Emission from Particulates Generated in The KrF-Laser Ablation of BN and YBCO

ABSTRACTFast intensified CCD photography and gated photon counting following KrF-laser irradiation of YBCO and BN targets reveal the first observations of very weak emission from slow-moving ejecta up to 2 cm from the target and times extending to ∼1.5 ms. Time-of-flight velocities inferred from the emission measurements indicate velocities (v ˜ (0.45−1.2) x 104 cm s−1) comparable to those measured for the large particles which often accompany the pulsed laser deposition process. Gated photon counting is employed to obtain temporally resolved spectra of this weak emission. The spectral shape is characteristic of blackbody emission, which shifts to longer wavelengths as the particles cool during flight in vacuum. Estimates of the temperature of the particles are made based on the emissivity of a perfect blackbody and range from 2200 K to 3200 K for both BN and YBCO when irradiated at Φ248 = 3.5 J cm−2 and 1.5 J cm−2, respectively. The temperature decrease of the particles in vacuum is compared to a radiative cooling model which gives estimates of the initial surface temperature and radii of the particles.

In-situ sputtering of YBCO films for microwave applications

RF magnetron sputtering from a single YBCO target onto a heated substrate ( approximately=700 degrees C) was used to obtain c-axis-oriented 1-2-3 films that are superconducting without a subsequent annealing or oxygenation step, with T/sub c/(R=0) as high as 88 K on MgO and LaAlO/sub 3/ substrates. This process uses an 8-in-diameter target in the sputter-up configuration, with a central grounded shield to eliminate negative ion bombardment. It can reproducibly and uniformly cover substrates as large as 3-in across at rates exceeding 1 AA/s. Maintaining film composition very close to stoichiometry is essential for obtaining films with good superconducting properties and surface morphology. Optimum films have critical currents of approximately=1 MA/cm/sup 2/ at 77 K. Measurements of microwave surface resistance based on a stripline resonator indicate low surface resistance for unpatterned YBCO ground planes, but excess loss and a strong power dependence in a patterned center strip.