E. W. Chase

As‐deposited high Tc and Jc superconducting thin films made at low temperatures

2000 A as‐deposited high Tc superconducting Y1Ba2Cu3O7−x films with zero‐resistance temperatures of ∼89 K and critical current densities about 0.7×106 A/cm2 at 77 K have been reproducibly fabricated at a substrate holder temperature of 650 °C, using pulsed laser deposition, with no post‐annealing. One key to these results is the injection of gaseous oxygen into the laser‐produced plume just in front of the target. In this way, the correct amount of oxygen is incorporated into the as‐grown film so that post‐deposition treatment becomes unnecessary. The in situ growth of such high Tc and Jc films is an important step in the use of the laser deposition technique to fabricate multilayer structures such as Josephson junctions.

Low‐temperature preparation of high Tc superconducting thin films

Thin superconducting films of Y‐Ba‐Cu‐O were prepared at 650 °C using the pulsed laser deposition technique. The as‐deposited films were fully superconducting at low temperature (30 K). After annealing in oxygen at 450 °C for 3 h, the films exhibited superconductivity with zero resistance at temperatures as high as 83 K. Film‐substrate interface reaction was minimal as revealed by Rutherford backscattering and Auger electron spectrometry. These films processed at such low temperatures are also found to have excellent planar surface morphology and high critical current density.

EPITAXIAL ORDERING OF OXIDE SUPERCONDUCTOR THIN-FILMS ON (100) SRTIO3 PREPARED BY PULSED LASER EVAPORATION

Thin films of Y‐Ba‐Cu‐O superconductors on (100) SrTiO3 were prepared using the pulsed excimer laser evaporation technique. After an annealing treatment in oxygen the films exhibited superconductivity with zero resistance at 85 K with transition widths (90%–10%) as narrow as a 2 K. A considerable amount of orientation of the films with respect to the substrates was observed by x‐ray diffraction and ion channeling techniques. Interface reaction revealed by Rutherford backscattering and Auger electron spectrometry resulted in a thickness dependence of the superconducting properties of the films.

Superconducting Y1Ba2Cu3O7−x films on Si

By depositing YBaCuO films at low substrate holder temperatures (600 °C) using a pulsed laser, films with the orthorhombic phase exhibiting superconductivity with high zero resistance temperatures (Tc0) were produced. Tc0 values as high as 50 and 80 K were seen on films deposited directly on Si and on Si with only a 50 nm ZrO2 buffer layer, respectively. The key to the successful film deposition is the low processing temperatures involved, which minimized the interface reactions as observed by Auger electron spectrometry.By depositing YBaCuO films at low substrate holder temperatures (600 /sup 0/C) using a pulsed laser, films with the orthorhombic phase exhibiting superconductivity with high zero resistance temperatures (T/sub c//sub 0/) were produced. T/sub c//sub 0/ values as high as 50 and 80 K were seen on films deposited directly on Si and on Si with only a 50 nm ZrO/sub 2/ buffer layer, respectively. The key to the successful film deposition is the low processing temperatures involved, which minimized the interface reactions as observed by Auger electron spectrometry.

Superconducting Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub x/ films on Si

By depositing YBaCuO films at low substrate holder temperatures (600 °C) using a pulsed laser, films with the orthorhombic phase exhibiting superconductivity with high zero resistance temperatures (Tc0) were produced. Tc0 values as high as 50 and 80 K were seen on films deposited directly on Si and on Si with only a 50 nm ZrO2 buffer layer, respectively. The key to the successful film deposition is the low processing temperatures involved, which minimized the interface reactions as observed by Auger electron spectrometry.By depositing YBaCuO films at low substrate holder temperatures (600 /sup 0/C) using a pulsed laser, films with the orthorhombic phase exhibiting superconductivity with high zero resistance temperatures (T/sub c//sub 0/) were produced. T/sub c//sub 0/ values as high as 50 and 80 K were seen on films deposited directly on Si and on Si with only a 50 nm ZrO/sub 2/ buffer layer, respectively. The key to the successful film deposition is the low processing temperatures involved, which minimized the interface reactions as observed by Auger electron spectrometry.

Optical spectroscopy: An in situ diagnostic for pulsed laser deposition of high Tc superconducting thin films

High oxygen partial pressure has been found to be an important parameter for the pulsed laser deposition of as‐deposited superconducting thin films with high Tc and Jc. The optical emissions from both elemental and oxide species ejected from the target of YBa2Cu3O7−x during the pulsed laser deposition process increase with the oxygen pressure, with the oxide emission showing a stronger pressure dependence than the elemental emission. The dynamics of the interaction between the oxygen atoms and the species in the laser‐produced plume were studied by a wavelength and time‐resolved measurement. The results are qualitatively explained using a simple model based on optical emission arising from inelastic and recombination collision between the elemental species and electronically excited oxygen atoms. The formation of oxides in the plume is shown to be essential for the production of higher quality superconducting films, indicating the value of optical spectroscopy as a diagnostic tool.

Properties of Oriented Oxide Superconductor Thin Films Prepared by Pulsed Laser Evaporation from High Tc Bulk Material

We report on the preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of bulk material. Rutherford back-scattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 1 nm per laser shot. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques. After an annealing treatment in oxygen the films exhibited superconductivity with zero resistance in the range 55 K – 85 K, depending on the annealing conditions and the type of substrate. In particular, films prepared on SrTiO3〈l00〉 showed transition widths as narrow as 2 K, and a considerable amount of orientation, as observed by X-ray diffraction and ion channeling techniques. There is evidence for strong interface reaction with in-diffusion of Ba and Cu and out-diffusion of Ti and Sr, resulting in a thickness dependence of the superconducting properties of the films.

Infrared spectra and the energy gap in thin film YBa2Cu3O7-delta

Interpretations of IR and millimeter wave measurements in superconductors are generally carried out in terms of the Mattis-Bardeen calculations, which apply either to the anomalous skin effect regime or to the dirty limit regime. In high temperature superconductors neither limit applies. Reflectance measurements on high quality, epitaxially-grown, laser-deposited films indicate that these samples are in the clean-limit, normal skin effect regime. Features that have been previously identified as the gap appear in both the superconducting and the normal-state spectra, although obscured by the free carrier absorption above Tc. Below Tc these features become more evident as the free carrier contribution condenses into a delta function at zero frequency.

As-deposited near-single crystalline high Tc and Jc superconducting thin films by a pulsed lased deposition process

Abstract As-deposited high T c superconducting Y 1 Ba 2 Cu 3 O 7− x films with zero resistance temperatures of ≃89 K and critical current densities about 0.7×10 6 A/cm 2 at 77 K have been reproducibly fabricated at a substrate holder temperature at 650°C, using pulsed laser deposition, without post-annealing. One key to these results is the injection of gaseous oxygen into laser produced plume just in front of the target. In this way, the correct amount of oxygen is incorporated into the as-grown film so that post-deposition treatment becomes unnecessary. Axial ion channeling in these as-deposit high T c superconducting films on (100) SrTiO 3 and X-ray photoelectron spectroscopy (XPS) on the film surfaces were performed. Angular yield profile near the film surface for Ba, and the surface peak intensity were measured using 3 MeV He ions. For channeling normal to the substrate a minimum yield of 7%, compared to ≃3% for single crystals, was obtained. The results of ion channeling and XPS studies indicate that the as-deposited films have good crystallinity as well as toichiometry to within ≃1 nm of the film surface. The in-situ growth of such high T c and J c films is an important step in the use of the laser deposition technique to fabricate multilayer structures and the surface perfection is of importance in tunneling devices such as Josephson junctions.