Frequency‐doubled Nd:YAG laser (532 nm) pulses of 1.7 J/cm2 and 10 ns duration were used to deposit thin films of YBa2 Cu3 O7−δ by laser ablation on NdGaO3 , LaGaO3, and SrTiO3 substrates held at 725±5 °C in 0.2 Torr of O2 ambient. Electrical resistivities versus temperature of all films show normal metallic behavior and sharp superconducting transitions with Tc (R=0) at 92–93 K. Critical current densities in 0.3–0.6 μm thick, 200 μm long, and 10–30 μm wide strips were measured to be 106 A/cm2 at 60, 77, and 80 K in the films on LaGaO3, NdGaO3, and SrTiO3, respectively. X‐ray diffraction patterns show that all films grew epitaxially, with domains of only two crystalline orientations rotated 90° with respect to each other in the a‐b plane (consistent with twins), and the c axis perpendicular to the substrates. The closely matched lattice constants of the film and substrates (0.8–2.1%) result in epitaxial growth of the films.

Epitaxial films of YBa2Cu3O7−δ on NdGaO3, LaGaO3, and SrTiO3 substrates deposited by laser ablation

YBa2Cu3O7−δ thin films were deposited onto (100) SrTiO3 substrates using 1064, 532, 355, 248, and 193 nm laser ablation. Transport measurements show lower normal‐state resistivities and higher critical currents in films deposited by the shorter wavelength lasers. The surface morphology of the films was rough with large particulates when the 1064 nm laser was used whereas much smoother surfaces with fewer and smaller particulates were obtained with the UV lasers. It is suggested that the better film quality obtained when the UV lasers are used is due to a small absorption depth of the UV photons in the ceramic target and to higher absorption by the ablated fragments. This leads to smaller ablated species and further fragmentation in the hotter plume and, therefore, to smoother and denser films.

Laser wavelength dependent properties of YBa2Cu3O7−δ thin films deposited by laser ablation

We report the formation of excellent quality epitaxial YBa2Cu3O7 films on (100) SrTiO3 and (100) ZrO2 (yttria stabilized) substrates in the temperature range of 500–650 °C by XECl excimer laser ablation in a 0.2 Torr oxygen ambient. By applying a dc bias voltage of +300 V to an interposing ring, we were able to reduce the substrate temperatures from 650 to 500 °C for obtaining epitaxial films. The quality of the epitaxial films was found to decrease with temperature, particularly below 550 °C. The thickness of the superconducting films was varied from 500 to 5000 A with superconducting transition temperatures Tc (zero resistance) varying from 87 to 90 K for 650 °C deposits. The critical current density Jc of films was found to vary linearly with temperature with values of (zero magnetic field at 77 K) 5.0×106 and 1.0×106 for films deposited at 650 °C on (100) SrTiO3 and (100) yttria‐stabilized zirconia substrates, respectively. X‐ray diffraction, transmission electron microscopy, electron channeling patte...

In situ processing of epitaxial Y‐Ba‐Cu‐O high Tc superconducting films on (100) SrTiO3 and (100) YS‐ZrO2 substrates at 500–650 °C

Interaction of laser radiation with solid materials and its significance to analytical spectrometry: a review

We describe our procedure for fabricating YBa2Cu3Ox‐SrTiO3‐YBa2Cu3Ox thin‐film trilayer structures. Each film is grown in situ by excimer laser deposition onto a heated (100)MgO substrate. The geometrical configuration of each layer is defined by a metal mask; the vacuum chamber is opened between depositions to allow the targets and masks to be changed. The lower and upper YBa2Cu3Ox films in the best trilayer structure had transition widths of 1 and 3 K (10–90%), respectively, and transition temperatures (zero resistance) of 87 K. The resistance between the YBa2Cu3Ox films at 77 K was 108 Ω for an overlapping area of 0.2 mm2, corresponding to a SrTiO3 resistivity of 4×109 Ω cm.

Multilayer YBa2Cu3Ox‐SrTiO3‐YBa2Cu3Ox films for insulating crossovers

KrF excimer laser ablation of an Y1Ba2Cu3O7−δ pellet in 0.1–0.2 Torr of O2 ambient was used to deposit thin superconducting films onto SrTiO3, yttria‐stabilized zirconia (YSZ), and silicon substrates at 600–700 °C. The as‐deposited 1‐μm‐thick films at 650–700 °C substrate temperature were superconducting, without further high‐temperature annealing. All films had a similar Tc onset of ∼92 K but different zero‐resistance Tc of 90, 85, and 70 K for the films on SrTiO3, YSZ, and Si substrates, respectively. Angular x‐ray diffraction analysis showed that all the films were highly oriented with the c axis perpendicular to their surface. Critical current densities at 77 K were about 40 000 and 10 000 A/cm2 for the films on SrTiO3 and YSZ, respectively. Smooth surface morphology was observed in all films, with occasional defects and cracks in the films on YSZ, which seems to explain the lower critical current in these films.

G. Kimel

Papers

Highly oriented as-deposited superconducting laser ablated thin films of Y1Ba2Cu3O7−δ on SrTiO3, zirconia, and Si substrates