Time-of-flight Emission Profiles of the Entire Plume Using Fast Imaging During Pulsed Laser Deposition of YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7−x\u3c/sub\u3e

Emission time-of-flight (TOF) profiles have been obtained using gated imagery to further the process control during the pulsed laser deposition of the high temperature superconductor, YBa2Cu3O7−x⁠. An intensified charge coupled device array was used to obtain a sequence of plume images at 10ns temporal resolution and 0.2mm spatial resolution. Plume imagery is transformed to TOF profiles and pulse-to-pulse variations removed using physically based smoothing techniques. Comparison with non-imaging sensors establishes excellent agreement, with systematic uncertainties in streaming speed and temperatures of less than 15% and 8%, respectively. The resulting streaming speeds of 0.4–1.2×106 cm/s and characteristic temperatures of 20000–200000K are characterized across the full plume. This new imaging TOF technique enables the monitoring of the complete evolution of speed distributions. Indeed, significant deviations from the forward-directed Maxwellian speed distributions are observed

The pulsed-laser ablation plume dynamics: Characterization and modeling

High quality thin films (100 nm to several 1000 nm) of many complex material systems such as the high temperature superconductor YBCO, have been deposited using pulsed laser ablation. Long lengths of high quality YBCO on metallic conductors are needed to meet industrial and government requirements. Although, pulsed laser deposition (PLD) grows the best YBCO films on meter lengths of metallic conductors, it has not been proven to be a consistent manufacturing process. PLD is simple in concept but has quite complicated plume and growth dynamics which are not well understood. In this study we use in-situ time-resolved mesurements of collision-driven plume emissions to characterize critical deposition parameters and to develop a computational model which includes these dynamics in a reacting PLD plume

The pulsed-laser ablation plume dynamics: Characterization and modeling

High quality thin films (100 nm to several 1000 nm) of many complex material systems such as the high temperature superconductor YBCO, have been deposited using pulsed laser ablation. Long lengths of high quality YBCO on metallic conductors are needed to meet industrial and government requirements. Although, pulsed laser deposition (PLD) grows the best YBCO films on meter lengths of metallic conductors, it has not been proven to be a consistent manufacturing process. PLD is simple in concept but has quite complicated plume and growth dynamics which are not well understood. In this study we use in-situ time-resolved mesurements of collision-driven plume emissions to characterize critical deposition parameters and to develop a computational model which includes these dynamics in a reacting PLD plume

Effect of Grain Orientation and Local Strain on the Quality of Polycrystalline YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7\u3c/sub\u3e Superconductive Films

The critical current densities of superconducting thin films and their dependence on the film structural characteristics has been a major research interest for more than a decade. Controlling this relationship is crucial if large-scale high-quality YBa 2 Cu 3 O 7 (YBCO) tapes are to be produced. Two major keystones of information have been established in this field. Firstly, there is a direct relationship between the critical current density and the grain-boundary angle in polycrystalline YBCO films. Grain boundaries with a mismatch angle higher than 5° usually result in reduced critical current densities. This detrimental effect of large-angle grain boundaries to the quality of YBCO films has been attributed to strain fields resulting from such grain boundaries. Secondly, the quality of the YBCO film can be enhanced by straining its lattice in specific direction. Here, we report, for the first time, direct experimental results coupling local grain orientation and local strain maps of thin YBCO films deposited on a (001) biaxially textured nickel substrate. These results were correlated to the quality of the film and showed how grain structure in the nickel substrate affects the grain structure in the YBCO films even in the presence of several buffer layers. More importantly, the data show that highquality films with high critical current densities can be produced, in spite of large-angle grain boundaries, if the film is compressed in the range of 0.5% strain normal to the a axis

Effect of Grain Orientation and Local Strain on the Quality of Polycrystalline YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7\u3c/sub\u3e Superconductive Films

The critical current densities of superconducting thin films and their dependence on the film structural characteristics has been a major research interest for more than a decade. Controlling this relationship is crucial if large-scale high-quality YBa 2 Cu 3 O 7 (YBCO) tapes are to be produced. Two major keystones of information have been established in this field. Firstly, there is a direct relationship between the critical current density and the grain-boundary angle in polycrystalline YBCO films. Grain boundaries with a mismatch angle higher than 5° usually result in reduced critical current densities. This detrimental effect of large-angle grain boundaries to the quality of YBCO films has been attributed to strain fields resulting from such grain boundaries. Secondly, the quality of the YBCO film can be enhanced by straining its lattice in specific direction. Here, we report, for the first time, direct experimental results coupling local grain orientation and local strain maps of thin YBCO films deposited on a (001) biaxially textured nickel substrate. These results were correlated to the quality of the film and showed how grain structure in the nickel substrate affects the grain structure in the YBCO films even in the presence of several buffer layers. More importantly, the data show that highquality films with high critical current densities can be produced, in spite of large-angle grain boundaries, if the film is compressed in the range of 0.5% strain normal to the a axis

Local Grain Orientation and Strain in Polycrystalline YBa\u3cem\u3e\u3csub\u3e2\u3c/sub\u3e\u3c/em\u3eCu\u3cem\u3e\u3csub\u3e3\u3c/sub\u3e\u3c/em\u3eO\u3cem\u3e\u3csub\u3e7−δ\u3c/sub\u3e\u3c/em\u3e Superconductor Thin Films Measured by Raman Spectroscopy

We report direct measurements of local grain orientation and residual strain in polycrystalline,C-axis oriented thin YBa2Cu3O7−δ superconducting films using polarized Raman spectroscopy. Strain dependence of the Ag Raman active mode at 335 cm−1 was calibrated and used to measure local strain in the films. Our data showed that high quality films are associated with the connected path of uniform grain orientation (single crystal-like) across the film and uniform residual strain in the range of −0.3%. Nonuniform grain orientation or high angle grain boundaries and nonuniform local strains were associated with low quality films

Local Grain Orientation and Strain in Polycrystalline YBa\u3cem\u3e\u3csub\u3e2\u3c/sub\u3e\u3c/em\u3eCu\u3cem\u3e\u3csub\u3e3\u3c/sub\u3e\u3c/em\u3eO\u3cem\u3e\u3csub\u3e7−δ\u3c/sub\u3e\u3c/em\u3e Superconductor Thin Films Measured by Raman Spectroscopy

We report direct measurements of local grain orientation and residual strain in polycrystalline,C-axis oriented thin YBa2Cu3O7−δ superconducting films using polarized Raman spectroscopy. Strain dependence of the Ag Raman active mode at 335 cm−1 was calibrated and used to measure local strain in the films. Our data showed that high quality films are associated with the connected path of uniform grain orientation (single crystal-like) across the film and uniform residual strain in the range of −0.3%. Nonuniform grain orientation or high angle grain boundaries and nonuniform local strains were associated with low quality films

Local Dielectric and Strain Measurements in YBa2Cu3O7−δ Thin Films by Evanescent Microscopy and Raman Spectroscopy

The near-field evanescent microwave microscope is based on a coaxial transmission line resonator with a silver-plated tungsten tip protruding through an end-wall aperture. The sensor is used to measure local dielectric properties of thin-film YBa2Cu3O7−δ deposited on three different SrTiO3 bi-crystal substrates having mismatch grain boundary angles of 3°, 6°, and 12°. The measurements in the superconducting state are below critical temperature at T = 79.4 K. The dielectric property of the superconductor within the near field of the tip frustrates the electric field and measurably changes the transmission line\u27s resonant frequency. The shift of the resonator\u27s frequency is measured as a function of tip–sample separation and associated changes in quality factor (ΔQ) image scans of the thin film are presented. A quantitative relationship between the real and imaginary parts of the local dielectric constant and the frequency shift using the method of images is established. The comparison between experimental data and theory based on this method is given and discussed. Raman measurements of the intergranular strain within the YBa2Cu3O7−δ thin film deposited on each SrTiO3 substrate in the region of the bi-crystal junction showed excellent correlation between grain boundary mismatch and induced grain boundary strain. Compressive strains normal to the aaxis (i.e. tensile strains normal to the b axis) were detected across the grain boundary. The magnitude of induced strain as well as its spread away from the grain boundary increased as the mismatch angle increased