Implantation, damage, and regrowth of high Tc superconductors
Abstract We have observed superconductivity in thin films of (La1−xSrx)2CuOy which are fabricated by implanting evaporated La/Cu multilayer films with Sr and annealing in oxygen. The films are insulating and partially transparent as-implanted, but they darken and become conducting at annealing temperatures as low as 500°C. The resistive behavior is very sensitive to the annealing conditions and the superconducting layer appears to be buried beneath the surface. Similarly, implantation of F, O, and Ne into single crystals and high quality (χmin
Lattice recovery of oxygen‐implanted YBa2Cu3O7−δ superconductor
The regrowth of an oxygen‐implanted YBa2Cu3O7−δ thin film was studied by Rutherford backscattering, ion channeling, and x‐ray diffraction studies. The atomic composition of the thin film was preserved even after a 1 h anneal at 990 °C, reflecting the high chemical stability of the material obtained by the pulsed laser deposition technique. Two distinct activation energies were determined during the regrowth process: 0.42±0.04 eV at lower temperatures, corresponding to epitaxial growth from the interface, and 0.18±0.03 eV at higher temperatures, presumably associated with homogeneous nucleation and reorientation.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.