Showing papers by "S. R. Foltyn published in 1990"
TL;DR: In this article, the authors studied the film growth mechanism as a function of deposition rate using pulsed laser deposition and observed the outgrowths nucleating at coalescence and proposed that certain defects related to the c-axis growth habit may be the fundamental cause of outgrowth formation.
Abstract: One problem with the growth of high quality c‐axis oriented YBa2Cu3O7−x films is the tendency of the film surface to become rough. We studied the film growth mechanism as a function of deposition rate using pulsed laser deposition. These films form by the classic nucleation and growth process; the thickness at which the nucleated islands coalesce increased with decreasing deposition rate. The film has pinholes prior to coalescence and nucleates outgrowths during coalescence. The outgrowths enlarge rapidly because they contain materials and crystallographic directions with growth rates faster than that of the c‐axis film. A smooth surface is obtained if the substrate temperature and deposition rate are chosen such that coalescence is just completed at the final film thickness. We observed the outgrowths nucleating at coalescence and propose that certain defects, related to the c‐axis growth habit, may be the fundamental cause of outgrowth formation. Outgrowths have not been observed in a‐axis films. Outgrowths are easily confused with the particulate deposition problem associated with laser deposition. In these experiments, the particulate problem was essentially eliminated by using freshly polished targets for each run.
138 citations
TL;DR: In this article, a broad angular distribution was observed for XeCl laser ablation plumes used in the deposition of YBa2Cu3O7−δ thin films.
Abstract: Broad angular distributions have been observed for XeCl laser ablation plumes used in the deposition of YBa2Cu3O7−δ thin films. Distributions (inferred from film thickness) and film stoichiometry were measured as a function of laser fluence, beam shape, and oxygen pressure. Parallel to the long axis of the laser spot, plumes exhibited a cos3.5(θ) spread and composition varied with angle; in the perpendicular direction, more diffuse [cos1.5(θ)] plume distributions were associated with stoichiometric deposition. The observed phenomena are consistent with formation of a Knudsen layer near the target surface.
131 citations
TL;DR: In this article, superconducting thin films of YBa2Cu3O7−δ on (100)SrTiO3 are prepared in situ by a pulsed laser deposition technique at deposition rates from 1 to 145 A/s.
Abstract: Superconducting thin films of YBa2Cu3O7−δ on (100) SrTiO3 are prepared in situ by a pulsed laser deposition technique at deposition rates from 1 to 145 A/s. Crystallinity of the films is examined by Rutherford backscattering in the channeling mode using a 2.2 MeV He+ ion beam. The backscattering minimum yield (χmin) increases with the deposition rate. A χmin of 3% is observed in the films deposited at the lowest deposition rate. Even at a deposition rate of 145 A/s, the films show good crystallinity with χmin of 15%, indicating epitaxial growth. The x‐ray diffraction measurements show that the films have strong c‐axis orientation normal to the substrates. The films have metallic resistance versus temperature behavior with zero resistance temperatures of 90 K. The results indicate that the pulsed laser deposition technique could be used to deposit large‐area films efficiently with adequate substrate movement.
86 citations
TL;DR: In this article, critical current densities (Jc) in YBa2Cu3O7−x films made at deposition rates from 0.1 to 14.5 nm/s (∼50 μm/h) were measured using a direct transport method.
Abstract: Critical current densities (Jc) in YBa2Cu3O7−x films made at deposition rates from 0.1 to 14.5 nm/s (∼50 μm/h) were measured using a direct transport method. As the deposition rate was increased by two orders of magnitude, the films exhibited no marked degradation in current carrying capability with Jc of ∼4×106 A/cm2 at 77 K and zero field. Jc for all the films showed similar behavior under a magnetic field up to 8 T, although extra structural defects were found in the films deposited at the higher rates. The results from this experiment indicate the feasibility for coating wires, tapes, and other macroscopic shapes with high Tc superconductors using proper vapor deposition techniques.
63 citations
TL;DR: In this article, superconducting films of YBa 2 Cu 3 O 7−δ have been prepared on yttrium stabilized cubic zirconia in situ by laser ablation.
16 citations
TL;DR: In this paper, target modification by excimer laser exposure has been investigated and significant physical and chemical modifications occur on the target surface, but these modifications do not inhibit congruent evaporation.
Abstract: Target modification by excimer laser exposure has been investigated. Under conditions typical in the fabrication of superconducting thin films, deposition rate decreases with exposure and significant physical and chemical modifications occur on the target surface. These modifications do not inhibit congruent evaporation.
13 citations
TL;DR: Pulsed laser deposition (PLD) has been widely used for deposition of high Tc superconducting thin films, and is recognized as one of the best physical vapor techniques for the preparation of these films.
Abstract: Pulsed laser deposition (PLD) has been widely used for deposition of high Tc superconducting thin films, and is recognized as one of the best physical vapor techniques for the preparation of these films. The most important advantage of this technique is stoichiometric deposition; films can be made with the same composition as the target. Utilizing PLD, not only thin films but also multilayers and superlattices of high Tc superconductors have been fabricated. In this paper, the performance of the technique will be reviewed, and speculations regarding the future would be made.
11 citations
TL;DR: In this paper, the authors present a process control and diagnostics relevant to achieving the required scaling and reproducibility of a 3-in. wafer with high temperature superconductors.
Abstract: High quality thin films of high temperature superconductors (HTS) have been fabricated using pulsed or cw lasers as physical vapor deposition sources. There is current interest in scaling the pulsed laser deposition (PLD) technique to coat 3-in. wafers with HTS. Process control and diagnostics relevant to achieving the required scaling and reproducibility will be reviewed.
5 citations
TL;DR: In this paper, the authors report on the pulsed laser deposition of high quality, superconducting, 200 nm thick films of YBa2Cu3O7-x at rates approaching 15 nm/s.
Abstract: We report here on the pulsed laser deposition of high quality, superconducting, 200 nm thick films of YBa2Cu3O7-x at rates approaching 15 nm/s. Film crystallinity and electrical properties were studied as a function of deposition rate from 0.1 to 14.5 nm/s. Though some degradation in the film crystallinity is observed by RBS channeling and X-ray rocking curve measurements, critical current densities (Jc = 4 × 106 A/cm2, 77 K, B = 0) are effectively unchanged in going to the higher deposition rates.
3 citations
TL;DR: In this article, a pulsed excimer laser was used to ablate aluminum metal into an oxygen-containing atmosphere, and the resulting fine powder was collected on a 0.1 µm filter and analyzed to determine structure and composition.
Abstract: A pulsed excimer laser was used to ablate aluminum metal into an oxygen-containing atmosphere. The resulting fine powder was collected on a 0.1 µm filter and analyzed to determine structure and composition. Using a combination of TEM, EELS, and thermal analysis techniques, the product was found to be amorphous aluminum oxide, Al2O3. The morphology of the powders was investigated using SEM, TEM, and surface area measurements. The resulting powder was crystallized and examined by x-ray diffraction.
1 citations
TL;DR: In this paper, the XeCl excimer laser was used to ablate high-temperature superconductor thin films, at a laser fluence of {approx} 4J/cm{sup 2}.
Abstract: Y{sub 2}O{sub 3} pressed powders were ablated by pulses from a XeCl excimer laser, operating at 308 nm, 150 mJ/pulse, {approx}15 nsec/pulse and 20 Hz. Emission spectra from Y* and YO* were recorded as a function of ambient oxygen pressure in the range 10{sup {minus}5} -- 4 {times} 10{sup {minus}1} Torr, at a laser fluence of {approx} 4J/cm{sup 2}. A kinetic model is developed to describe the results, and the application to production of laser-deposited high-temperature superconductor thin films is discussed. 13 refs., 4 figs.
TL;DR: In this article, two aspects of non-chemical, post-deposition processing of laser-deposited superconducting Yba2Cu3O7-δ thin films are reported.
Abstract: We report here on two aspects of non-chemical, post-deposition processing of laser-deposited superconducting Yba2Cu3O7-δ thin films. One patterning process consists of placing a contact mask over the film and removes the surrounding material by excimer laser ablation. Good edge definition for 30–100 μm etch features is obtained. However, some redeposition of material is observed. In separate patterning experiments, oxygen-deficient films were re-oxygenated by a direct-write laser heating method. This process produces very smooth edges between the superconducting patterns and the surrounding material.