Self Injection length in La0.7 Ca0.3 Mno3-YBa 2Cu3O7-d ferromagnet- superconductor multi layer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-d (YBCO). The heterojunctions were grown in situ by sequentially growing LCMO and YBCO films on LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 microns width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, Ic, was measured at 77K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a Jc of ~2 x 10E6 A/ cm2 the LCMO side showed about half the value for the same thickness (1800 A). The difference in Jc indicates that a certain thickness of YBCO has become 'effectively' normal due to self-injection. From the measurement of Jc at two different thickness' (1800 A and 1500 A) of YBCO both on the LAO as well as the LCMO side, the value of self-injection length (at 77K) was estimated to be ~900 A self-injection length has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection.Comment: 6 pages, one figure in .ps forma

Application of the Taguchi analytical method for optimization of effective parameters of the chemical vapor deposition process controlling the production of nanotubes/nanobeads

Seven variable parameters of the chemical vapor deposition system have been optimized with the help of the Taguchi analytical method for getting a desired product, e.g., carbon nanotubes or carbon nanobeads. It is observed that almost all selected parameters influence the growth of carbon nanotubes. However, among them, the nature of precursor (racemic, R or Technical grade camphor) and the carrier gas (hydrogen, argon and mixture of argon/hydrogen) seem to be more important parameters affecting the growth of carbon nanotubes. Whereas, for the growth of nanobeads, out of seven parameters, only two, i.e., catalyst (powder of iron, cobalt, and nickel) and temperature (1023 K, 1123 K, and 1273 K), are the most influential parameters. Systematic defects or islands on the substrate surface enhance nucleation of novel carbon materials. Quantitative contributions of process parameters as well as optimum factor levels are obtained by performing analysis of variance (ANOVA) and analysis of mean (ANOM), respectively

Multiferroic Bi(0.7)Dy(0.3)FeO(3) thin films directly integrated on Si for integrated circuit compatible devices

Magnetoelectric multiferroic Bi(0.7)Dy(0.3)FeO(3) (BDFO) thin films deposited on p-type Si (100) substrate using pulsed laser deposition technique demonstrated a saturated ferroelectric and ferromagnetic hysteresis loop at room temperature. More interestingly, the observed change in electric polarization with applied magnetic field in these films indicated the presence of room temperature magnetoelectric coupling behavior. Using high-frequency capacitance-voltage measurements, the fixed oxide charge density, interface trap density and dielectric constant were estimated on Au/BDFO/Si capacitors. These results suggest the integrated circuit compatible application potential of BDFO films in the field of micro-electro-mechanical systems and nonvolatile memories.

Direct injection of spin-polarized carriers across YBa2Cu3O7-delta-La0.3Ca0.7MnO3 interface at 77 K

We report here injection of spin-polarized carriers from a half-metallic La0.3Ca0.7MnO3 (LCMO) colossal magnetoresistive (CMR) thin film into a high-temperature superconducting YBa2Cu3O7-delta (YBCO) thin film studied using a micro-bridge. The LCMO and YBCO films were grown on LaAlO3 (LAO) substrate sequentially using pulsed laser deposition (PLD). I-V measurements carried out at 77 K show that while normal critical current, l(c)(n), of the micro-bridge is 80 mA, the critical current, l(c)(p), through the micro-bridge when injected from the CMR layer is 38 mA. This clearly shows that spin-polarized quasiparticles injected from the CMR layer into the YBCO layer suppress the critical current of the superconductor via the pair-breaking phenomena

Aqueous sol-derived ferroelectric thin films of PbTiO3 directly on Si(100) substrate

Ferroelectric thin films of PbTiO3 are prepared directly on Si(100) substrate for the first time by spin coating an aqueous sol of lead and titanium hydroxy complex and post annealing at various temperatures. The X-ray diffraction patterns show that the films are polycrystalline in nature. Scanning electron microscopy reveals that the films 0.3 mu m in thickness are essentially crack-free. Since there is no organic content in the precursor solution, post deposition shrinkage is reduced. This helps to decrease the possibility of film cracking. The ferroelectric properties of the films are comparable to those obtained by the complex alkoxide route and other expensive techniques. Copyright (C) 1997

GROWTH AND MICROSTRUCTURAL STUDY OF RADIO-FREQUENCY MAGNETRON SPUTTERED MGO FILMS ON SILICON

Microstructure of magnesium oxide films radio frequency (rf) sputtered on silicon substrates at various argon: oxygen (9:1) gas pressures in the range 1-6.7 Pa and at various substrate temperatures up to 700-degrees-C have been studied using x-ray diffraction and scanning electron microscopy. The films have shown a tendency for oriented structure with growth orientation perpendicular to the planes. The tendency for columnar growth has been found to be strong at high argon pressures and has been found to persist to higher substrate temperatures. This observation is consistent with the structure zone model proposed by Movchan and Demchishin [Phys. Met. Mettallogr. 28, 83 (1969)] and later studied by Thornton [J. Vac. Sci. Technol. 11, 666 (1974)]. Annealing of films at 900-degrees-C in oxygen which is needed to reduce oxygen deficiencies and strain generated during growth, and to improve crystallinity by increasing grain size, has been found to cause microcracks in the films depending upon the microstructure and thickness. Films with columnar structure have shown microcracks and the threshold thickness at which microcracks develop has been found to be strongly dependent on the nature of the columnar structure. Dense MgO films deposited at 600-degrees-C at a low pressure of 1 Pa have not shown microcracks upto a thickness of 600 nm. Such films should be potentially applicable as buffer layers for the growth of high quality Y1Ba2Cu3O7-delta films on silicon

LARGE CRITICAL CURRENTS AND IMPROVED EPITAXY OF LASER-ABLATED AG-DOPED YBA2CU3O7-DELTA THIN-FILMS

Microstructure and critical current densities of laser ablated YBa2Cu3O7-delta thin films doped with 2-20 wt. % Ag have been studied. A critical current density as high as 1.4 X 10(7) A cm-2 at 77 K has been realized on [100] SrTiO3 substrates with YBaCuO films doped with 5 wt. % Ag which has been found to be the optimum. Evidence indicates that the improved microstructure and epitaxy which is a consequence of grain enlargement and alignment caused by Ag is responsible for the high values of critical currents observed

SUPERCONDUCTIVITY AND VALENCE STATE OF TB IN LU1-XTBXBA2CU3O7-DELTA (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.7)

Although both lutetium and terbium do not form superconducting REBa2Cu3O7-delta, we report here the formation of superconducting phase in thin films. Films are highly c-axis oriented with high current densities (3.0x10(6) A cm-2 at 77 K) observed in Lu0.5Tb0.5Ba2Cu3O7-delta. X-ray photoelectron spectroscopic analysis of Tb in the above film indicates that Tb is in a trivalent state. Further, as the redox potential of Tb (Tb4+ +e- --> Tb3+:E0 = 3.1 V) is close to that of Pr (Pr4+ +e- -->Pr3+:E0 = 3.2 V), we suggest that Pr also would be in a trivalent state and the mechanism by which the latter depresses T(c) must be of trivalent origin

Silver doping and its influence on the oxygenation during in-situ growth of yba2cu3o7-x thin-films

The influence of Ag doping on both oxygenation and deoxygenation during growth of YBa2Cu3O7-x films at 700-degrees-C by pulsed laser deposition has been studied. Experiments show that undoped and Ag-doped films grown at 200 mTorr oxygen pressure and quenched immediately after termination of growth have a superconducting transition temperature T(c) of 61 and 86 K, respectively. The high T(c) of 86 K obtained with quenched Ag-doped films is thought to be due to both enhanced oxygen incorporation and reduced deoxygenation associated with Ag doping. These results show that Ag-doped YBa2Cu3O7-x films could be crucial for realizing devices based on multilayer structures