PLD System Research Articles

Increase of production rate of RE-123 film by PLD system with the hot-wall type heating

We have studied two types of heating systems to produce thick GdBa 2Cu 3O 7− X (Gd123) films with high critical current ( I c) stably at a high speed by the PLD method. Material yields of both PLD systems reached about 50–60% by optimization of evaporation condition. Hot-wall heating type (type 2) could fabricate the thicker Gd123 film with the higher I c compared to contact heating type (type 1) and maximum I c reached 1040 A at about 6 μm thick. Furthermore, it was estimated that type 2 could fabricate Gd123 film with an I c of about 700 A at about twice speed compared to type 1. Finally, it was considered that the hot-wall heating type was very advantageous to prepare thick Gd123 film with high I c at a high speed from the system structure.

Effective thickness of CeO2 buffer layer for YBCO coated conductor by advanced TFA-MOD process

YBCO films were fabricated on PLD-CeO2/IBAD-Gd2Zr2O7/Hastelloy substrates using the advanced TFA-MOD process. The effective thickness of the CeO2 buffer layer for obtaining high Ic was investigated in short samples of YBCO films. The CeO2 buffer layer was epitaxially grown on an IBAD-Gd2Zr2O7 template tape with 18° of Δϕ by a reel-to-reel PLD system. The in-plane grain alignment of PLD-CeO2 buffer layers rapidly improved with the thickness and saturated at a critical thickness of 0.8μm. The size of CeO2 grains was about 1μm at the saturated thickness of Δϕ. YBCO films with the thickness of 1μm were deposited by the TFA-MOD on the CeO2 buffer layer with different thickness films. Improvement of the CeO2 in-plane grain alignment resulted in increase of Ic. The Ic values of 250–290A were obtained with the CeO2 layer thicker than 0.8μm. The CeO2 thickness, at which the intensity ratio of the BaCeO3 was saturated, corresponded to the critical thickness. From the view points of achieving higher production rates and to obtain the CeO2 Δϕ value of 5° as well as considering the reaction between YBCO and CeO2, the optimum thickness of the CeO2 buffer layer on the IBAD-Gd2Zr2O7 with 18° of Δϕ was found to be at least 0.8μm.

Fabrication of Y1−xRExBa2Cu3Oy films on single crystalline substrates and IBAD buffered metallic tapes by advanced TFA-MOD process

We fabricated Y1−xSmxBa2Cu3Oy and YSmxBa2Cu3Oy (YSmBCO) films on SrTiO3 (STO) single crystalline substrates and IBAD buffered metallic tapes (PLD-CeO2/IBAD-GZO/Hastelloy) by the advanced TFA-MOD process by mixing TFA salts of Y, Sm, Ba and Cu naphthenate, and tried to improve the superconductivity properties compared with those of the pure YBa2Cu3O7−δ (YBCO).As a result, Jc values of Y1−xSmxBa2Cu3Oy films with x=0.05 or 0.3, which were fabricated on STO substrates, were improved under the high magnetic fields compared with those of the YBCO without substitution. However, Sm segregation was detected near the STO substrate which was obtained by the TEM–EDS (transmission electron microscopy–energy-dispersive X-ray spectroscopy) analysis.On the other hand, Y1−xSmxBa2Cu3Oy films with x=0.05 and YSmxBa2Cu3Oy films with x=0.3, which were fabricated on IBAD buffered metallic substrates, also improved Ic value under the high magnetic fields compared with those of the YBCO without substitution. Moreover, from the TEM-EDS analysis, Y or Sm segregation was not found.The difference in the Sm segregation behavior between the film on STO and CeO2 buffered substrates could be explained by the difference in the ratios of the misfit parameters between YBCO/substrate and SmBCO/substrate. Additionally, it was considered that the above phenomenon might be unique in the MOD system and could not be observed in the PLD system, because of the difference in the crystal growth mechanism.In the film of YSm0.3Ba2Cu3Oy, we observed the grains of (Y,Sm)2O3 and (Y,Sm)2Cu2O5 by TEM observation. We will further investigate the origin of pinning centers.

Rapid Production of Buffered Substrates and Long Length Coated Conductor Development Using IBAD, PLD Methods and “Self-Epitaxial” Ceria Buffer

Activities at SRL-Nagoya Coated Conductor Center (NCCC) are presented including rapid production of 100 to 220 m buffered substrate tapes and a 46 m YBCO coated conductor using reel-to-reel equipment of both IBAD and PLD systems. A 220 m long IBAD and a 100 m long CeO/sub 2/ capped substrate have been successfully and stably produced. Furthermore, the PLD-CeO/sub 2/, which we call the "Self-Epitaxial" method, is found to be effective to increase a production rate. The combination of IBAD and PLD-CeO/sub 2/ enhanced the overall buffer processing rate up to 2 m/h. This is much higher than the rate of 0.5 to 1 m/h of the conventional IBAD method. We also recently introduced a new PLD system for YBCO, which utilizes a multi-plume and multi-turn deposition, MPT-PLD method. This system is now successfully operating and then very recently we have achieved the record of I/sub c//spl times/L (critical current times length) of 8335 Am. A 45.8 m long YBCO coated conductor carried the high I/sub c/ of 182 A. The MPT-PLD method is also effective to increase the thickness of YBCO with high J/sub c/. Consequently, I/sub c/ as high as 300 A was also obtained for a short sample test. Therefore, the new system of MPT-PLD is very promising for long YBCO tape fabrication.

Pore formation in YBCO films deposited by a large-area pulsed laser depositionsystem

The surface morphology of YBCO films deposited by a large-area PLD system ischaracterized by pores of varying depths and sizes. The presence of these pores has beencorrelated to the yttrium-rich composition in the films. In-depth studies on the interplay ofparameters including oxygen background pressure, target–substrate distance, filmcomposition, and target stoichiometry on the porosity of the YBCO films deposited onLAO (100) substrates have been conducted. Off-stoichiometry in the composition of thefilms has been attributed to the scattering of the ablated species with the oxygen ambient.The relative excess of yttrium in the films causes the segregation of yttrium-rich secondaryphases, one of which has been identified for the first time as barium yttrium oxide(BaY2O4). From structural characterizations, it has been found that the nucleation and enlargementof the barium yttrium oxide phase obstructs the YBCO growth and eventually causesthe pores in the film to develop. Considering the deposition conditions whicheither promote or hinder the formation of this secondary phase during YBCOgrowth, a reasonably good control of pore size and density has been achieved.

Relationship between composition and surface morphology in YBCO films deposited by large-area PLD

YBCO films deposited from a stoichiometric (Y123) target via a large-area PLD system have consistently been found to be Y-rich in composition as well as characterized by pores. Use of an off-stoichiometric target with increased Ba and Cu content proved to be an effective method to compensate for the deficiency in barium and copper in the films. Films with composition closer to the ideal stoichiometric ratio have been obtained from the off-stoichiometric target, including significantly reduced pore density, improved microstructure and higher critical current density ( J c) in excess of 2 MA/cm 2 at 77.3 K over a 2 ″-diameter area. Furthermore, it was found out that the dense and smooth YBCO film deposited from the off-stoichiometric target needed ex situ oxygen annealing to reach fully-oxygenated state.

Current status of pulsed laser deposition YBCO coated conductors in SRL using bufferlayers by ion-beam assisted deposition GZO and self-epitaxy pulsed laser depositionCeO2

For a long coated conductor fabrication, SRL-Nagoya Coated Conductor Center (NCCC) hasinstalled reel-to-reel equipment for IBAD and PLD systems. A 60 m long IBAD and a 55 mCeO2 capped substrate have been successfully produced. ThePLD-CeO2, which we call the self-epitaxial method, is found to be effective to increase the in-planealignment and processing rate of buffer layers. PLD-YBCO layers on the self-epitaxialPLD-CeO2 cap layer exhibited a high degree of in-plane texturing about3° andthus high Jc up to 4.4 MA cm−2 and high Ic of 276 A cm−1 width. Long YBCO conductor fabrication using reel-to-reel PLD equipment is nowunderway.

Progress of PLD and IBAD processes for YBCO wire in the SRL-Nagoya CoatedConductor Centre—new method for a coated conductor using a self-epitaxialPLD-CeO2 buffer

The Nagoya Coated Conductor Centre (NCCC) in SRL has installed new reel-to-reel IBADand PLD systems for the fabrication of long, coated conductors. A 53 m long ion-beamassisted deposition (IBAD) substrate has been successfully produced. The degree of bi-axialtexturing was improved by the newly found buffer deposition technique of pulsed laserdeposition- (PLD)-CeO2, which we call the self-epitaxial method. ThePLD-CeO2 layer brought about a high degree of in-plane texturing up to2.6° in a few minutes on an IBAD seed layer. The resultant YBCO coated conductor on theCeO2 layer showedhigh Jc valuesof up to 4.4 MA cm−2. The reel-to-reel PLD equipment with a high power laser of200 W is now being applied to long-conductor fabrication andCeO2 buffer layer deposition with a high deposition rate.

次世代超電導線材の開発と特性評価 ＹＢＣＯのマルチ‐プルーム・マルチ‐ターンＰＬＤ成膜

We have investigated the high-speed deposition of YBa2Cu3O7-x (YBCO) using PLD on a CeO2-capped IBAD buffer layer. In order to speed up the coated conductor process, we introduced a continuous PLD system mainly consisting of high-power laser equipment and a vacuum chamber with a reel-to-reel substrate transfer system. The laser system was designed so that the laser beam scans YBCO targets during deposition and raises plural and discrete plumes (multi-plume). The aim of this is to perform high-speed production of YBCO layers. Although high laser pulse frequency deposition makes high-speed deposition possible, it causes roughening of the surface morphology and lowers the Jc. The multi-plume gave us a high Jc during low laser pulse frequency deposition and high-speed deposition at a higher frequency. The substrates were turned three times to enlarge the deposition area (multi-turn). Within 15 degrees aslant to a plume center, we obtained a high Jc for all turns. Using this multi-plume and multi-turn PLD equipment, we have succeeded in deposition of a 21m-long YBCO layer with a high end-to-end critical current (Ic) of 85 A and high Jc exceeding 1 MA/cm2. Ic data measured in 1.4m intervals showed good uniformity, with a standard deviation of 3.43%. This layer also showed high in-plane alignment, attaining 5.2 degrees of full-width-at-half-maximum as observed by X-ray phi scans. These results indicate the availability of utilizing multi-plume and multi-turn PLD for YBCO-coated conductor preparation.

In-situ monitoring of the growth of oxide thin films in PLD using high-pressure reflection high energy electron diffraction

Reflection high-energy electron diffraction (RHEED) is very surface sensitive and often used for the analysis and monitoring of thin film growth in ultrahigh vacuum deposition system (for instance, Molecular Beam Epitasis). In order to in-situ monitor the growth of oxide thin films at high oxygen pressure up to 50Pa, a high-pressure RHEED designed and fabricated by our group was used for first time in our pulsed laser deposition system (PLD). Using the PLD system the Nb-doped SrTiO3 (STNO) and Y1Ba2Cu3O7 (YBCO) thin films have been epitaxially grown on SrTiO3 (001) substrates. T he RHEED patterns of the STNO and YBCO films and the oscillation of the intensity of the pattern have been measured by the high-pressure RHEED during deposition. In addition,the surface morpholoyg of the films and the dynamic analysis of film growth process were discussed.

Control of film orientation: a parametric study of laser ablated FTO films on a-, c- and r-cut sapphire substrates by X-ray diffraction

Parametric work has been done to prepare FeTiO3 (FTO) thin films on A-, C-, and R-cut sapphire substrates. We have found that the preparation of highly oriented FTO films on different cut substrates is strongly dependent on substrate temperature, laser energy density and gas pressure. The orientations of FTO thin film can be controlled both by varying substrate cut direction and laser energy density. By varying the substrate cut directions, epitaxial thin films with high quality have been successfully grown on both A- and C-cut sapphire substrates with different substrate temperatures. The orientation control can also be realized by changing laser energy density, and we have grown both (112̄0) and (0006) oriented films on A-cut substrates with different laser energy densities. Higher laser energy density developed the tendency of film growth along the (0006) direction on A-cut substrates. At the same time, higher laser energy density enhances (0006) film growth on C-cut sapphire too. We have also found that epitaxial films can be grown on A-cut sapphire substrates in a quite large temperature range from 450 to 600°C. However, we have not got epitaxial film on R-cut sapphire substrate in a quite wide temperature range from 300 to 600°C. Probably it can be grown at a higher temperature which now is not accessible to our PLD system.

ATP- and EGF-stimulated phosphatidulinositol synthesis by two different pathways, phospholipase D and diacylglycerol kinase, in A-431 epidermoid carcinoma cells.

The [(3)H]inositol incorporation into the membrane fraction of A-431 human epidermoid carcinoma cells was markedly increased by stimulation of the cells with either epidermal growth factor (EGF), ATP, bradykinin, or a calcium ionophore A23187 in the presence of 1 mM extracellular calcium ions; most incorporated [(3)H]inositol was found to have accumulated as phosphatidylinositol (PI). The EGF- and ATP-stimulated PI synthesis was inhibited by two protein kinase C inhibitors, staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), and an intracellular calcium chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA/AM), but not by the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). Pretreatment of cells with pertussis toxin (IAP, islet-activating protein) inhibited the PI synthesis, [Ca(2+)]i elevation, and inositol trisphosphate (IP(3)) production by ATP, suggesting that the phospholipase C(PLC) system coupled with IAP-sensitive G protein is involved in the ATP-stimulated PI synthesis. On the other hand, the ATP stimulation increased the release of [(3)H]choline and [(32)P)phosphatidic acid (PA) from radiolabeled cells, and such release was not inhibited by IAP. In the presence of n-butyl alcohol, which prevents the production of PA by generation of phosphatidylbutanol, the ATP-stimulated PI synthesis was reduced. Because n-butyl alcohol did not inhibit IP(3) production and [Ca(2+)]i elevation, this fact suggests that the lAP-insensitive PLD system is involved in the ATP-stimulated PI synthesis. In A-431 cells, the stimulation of P(2)-purinergic receptors appears to activate the IAP-sensitive PLC system and IAP-insensitive PLD system, both of which are essential for the stimulation of PI synthesis. The present results imply the general prospect that ligand stimulation, which mobilizes second messengers and consumes their precursors, simultaneously provokes the pathway to synthesize and salvage the second messenger precursors as well.

1D and 2D Monte Carlo Simulations of Pulsed Laser Ablation of Si/Ga Into Ar/O2with a Substrate

ABSTRACTThe Direct Simulation Monte Carlo (DSMC) method is applied to the problem of pulsed laser deposition in both ID and 2D axisymmetric simulations. A source of target atoms expands into a cylindrical volume containing a background gas at room temperature and pressures up to 100 mTorr in the presence of a diffusely reflecting substrate. At regular intervals, the density and temperature of each species are computed. Particle flux and energy per particle incident on the substrate are also monitored as functions of time. The simulation results qualitatively compare, well with experimental plume diagnostics, with measured film growth rates as a function of background gas pressure, and with measured changes in film growth stoichiometry resulting from the introduction of a background gas into a two-component PLD system.

1D and 2D Monte Carlo Simulations of Pulsed Laser Ablation Of Si/Ga Into Ar/O2With A Substrate

AbstractThe Direct Simulation Monte Carlo (DSMC) method is applied to the problem of pulsed laser deposition in both 1D and 2D axisymmetric simulations. A source of target atoms expands into a cylindrical volume containing a background gas at room temperature and pressures up to 100 mTorr in the presence of a diffusely reflecting substrate. At regular intervals, the density and temperature of each species are computed. Particle flux and energy per particle incident on the substrate are also monitored as functions of time. The simulation results qualitatively compare well with experimental plume diagnostics, with measured film growth rates as a function of background gas pressure, and with measured changes in film growth stoichiometry resulting from the introduction of a background gas into a two-component PLD system.

Progress in Phosphate Glass Dosimetry: Experiences and Routine Monitoring with a Modern Dosimetry System

Abstract The modern, commercially available PLD system type Toshiba FGD-10, with flat glass dosemeters and a full automatic readout system, type tested at the PTB, allows for the measurement of Hpown to photon energies of 10 keV and, in addition, the indication of radiation quality below 100 keV as well as the direction of the radiation incidence. Due to the intrinsic pre-dose subtraction, doses of 0.03 mSv up to 8 Sv can be measured with a random uncertainty of 10%. The paper discusses long-term monitoring results on a monthly and yearly basis. Experiences in routine monitoring as well as intercomparison experiments, showed an excellent long-term stability of the system with an accuracy of measurement in the order of 1% not previously obtained with other solid state dosimetry systems. The system allows for a reliable routine evaluation also under unfavourable readout and environment conditions.

Modern Automatic Readout Systems for Phosphate Glass Dosemeters Using UV Laser Excitation

The new automatic readout systems FGD-10 and FGD-20 for flat glass dosemeters using pulsed UV laser excitation are applicable in the photon energy range 15 keV - 1.3 MeV and in the dose range above 0.03 mSv. Using the automatic readout mode for vertical and horizontal scanning of the glass, both systems allow interpretation of radiation conditions in personnel monitoring. The fully automatic systems make use of a dosemeter encapsulation unlocked and opened automatically within the reader. Separate code numbers of the capsule and the glass card are registered. The reader FGD-10 (FGD-20) is capable of continuously reading out 500 dosemeters (20 dosemeters) in magazines within a readout time of 20 s (10s) per dosemeter. FGD-10 exchanges automatically high-dosed by annealed glass cards and allows data handling for 50,000 dosemeters. The microprocessor controlled evaluation technique provides intrinsic subtraction of pre-dose during readout, automatic calibration using the same dosemeter during the monitoring period, simultaneous indication of different dose quantities and interpretation of radiation quality and incidence. The fully automatic PLD systems optimised in the readout procedure and prototype-tested are expected to be reliable dosimetry systems for application in individual and environmental monitoring.

Modern Automatic Readout Systems for Phosphate Glass Dosemeters Using UV Laser Excitation

Abstract The new automatic readout systems FGD-10 and FGD-20 for flat glass dosemeters using pulsed UV laser excitation are applicable in the photon energy range 15 keV - 1.3 MeV and in the dose range above 0.03 mSv. Using the automatic readout mode for vertical and horizontal scanning of the glass, both systems allow interpretation of radiation conditions in personnel monitoring. The fully automatic systems make use of a dosemeter encapsulation unlocked and opened automatically within the reader. Separate code numbers of the capsule and the glass card are registered. The reader FGD-10 (FGD-20) is capable of continuously reading out 500 dosemeters (20 dosemeters) in magazines within a readout time of 20 s (10s) per dosemeter. FGD-10 exchanges automatically high-dosed by annealed glass cards and allows data handling for 50,000 dosemeters. The microprocessor controlled evaluation technique provides intrinsic subtraction of pre-dose during readout, automatic calibration using the same dosemeter during the monitoring period, simultaneous indication of different dose quantities and interpretation of radiation quality and incidence. The fully automatic PLD systems optimised in the readout procedure and prototype-tested are expected to be reliable dosimetry systems for application in individual and environmental monitoring.

How Accurately do Thermoluminescence and Photoluminescence Dosimetry Systems Indicate the New ICRU Dose Quantities for Individual Monitoring?

Abstract In 1985, the German-Swiss radiation protection association and the PTB organised an intercomparison programme for individual monitoring systems to find out whether these systems are able to measure the new dose equivalents H'(10) and H'(0.07) specified in ICRU Report 39. Twelve laboratories from Switzerland, Austria, England and the Federal Republic of Germany participated with 30 dosimetry systems including TLD systems for whole-body monitoring (13), TLD systems for extremity dosimetry (5), PLD systems (2), and film dosimetry systems (6). The dosemeters were irradiated with photons on the surface of an Alderson human phantom or an ICRU sphere. The range of the mean photon energy was 26 keV to 662 keV. It was observed that there are already some dosimetry systems of every type (TLD, PLD, etc) whose response, with respect to H'(10) and H'(0.07), does not vary appreciably with photon energy. However, in general, special effort is needed to implement the new dose quantities in routine monitoring.