No abstract

Using Rutherford backscattering technique, we have measured the angular distribution of the composition and thickness of the Y-Ba-Cu oxide film deposited by firing excimer laser (30 ns, 248 nm) pulses at a stoichiometric Y1Ba2Cu3O7−x pellet. The angular distribution consisted of two distinct components: one a cos θ component, a result of evaporation, and the other a highly forward directed component, a result of a secondary ejection process. The evaporated component is nonstoichiometric, as one would expect, whereas the forward-directed component has a composition close to that of the pellet. Further, the forward-directed stoichiometric component increases with the laser energy density in comparison with the evaporated component. These observations are discussed in the context of current models of laser-induced material ejection at surfaces.The laser energy dependence of the deposition is of critical importance in controlling the film stoichiometry.

The frequency-dependent conductivity of laser-deposited YBa2Cu3C>7-s thin films shows an onset of midinfrared absorption at -140 cm -1 and structure in the 400-500-cm ~! region. These low-energy absorptions occur both above and below 7V, making them unlikely to be the superconducting gap in the usual BCS sense. The absorption across the gap is weak because the high-r c materials are in the clean limit; this weak absorption is masked by the midinfrared absorption.

Thin-film heterostructures of Bi(4)Ti(3)O(12)Bi(2)Sr(2)CuO(6+x), have been grown on single crystals of SrTiO(3), LaAlO(3), and MgAl(2)O(4) by pulsed laser deposition. X-ray diffraction studies show the presence of c-axis orientation only; Rutherford backscattering experiments show the composition to be close to the nominal stoichiometry. The films are ferroelectric and exhibit a symmetric hysteresis loop. The remanent polarization was 1.0 microcoulomb per square centimeter, and the coercive field was 2.0 x 10(5) volts per centimeter. Similar results were obtained with YBa(2)Cu(3)O(7-x) and Bi(2)Sr(2)CaCu(2)O(8+x), and single-crystal Bi(2)Sr(2)CuO(6+x)as the bottom electrodes. These films look promising for use as novel, lattice-matched, epitaxial ferroelectric film/electrode heterostructures in nonvolatile memory applications.

No abstract