Phase Formation Studies and Structural Properties of Laser Ablated (Pb,La)(Zr, Ti)O 3 -Thin-Films on Stainless Steel
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high and controllable deposition rate [2]. In order to understand the growth mechanisms for PZT on stainless steel in detail, we investigated the covering of these substrates with La-doped PZT, (Pbo.98La 0os)(Zro065Ti 0 35)03. This ferroelectric oxide ceramic offers excellent dielectric, piezoelectric and ferroelectric properties [3,4]. In this paper, the formation of perovskite PZT on stainless steel substrates with different compositions was investigated. The present study firstly focuses on the interface between stainless steel and the ferroelectric film. The existence and characteristics of oxide layers at the substrate surface have been examined by XRD, TEM / X-TEM, SIMS and RBS. To study the influence of an oxide layer on the phase formation (ferroelectric perovskite phase, secondary nonferroelectric phases) of the subsequently grown PZT films, XRD measurements were carried out. Variations in the stoichiometry of the films have been analyzed by EDX. Finally, the microstructure and texture of the PZT films was investigated by SEM and X-ray pole figure measurements and correlations to above mentioned experiments were outlined. EXPERIMENT The PZT thin films were prepared by pulsed laser deposition (PLD). The light of a KrF Excimer laser (Lambda Physik, ? = 248 nm, E = 0.6 J/pulse, repetition rate = 16 Hz) was focussed on the cylindrical rotating targets (Roditi/Vemitron, IJS Ljubljana) to ablate PZT. The substrates 283 Mat. Res. Soc. Symp. Proc. Vol. 596 ©2000 Materials Research Society
were chosen with respect to their Ni contents. We used three different kinds of steel as substrate material: first, Hastelloy steel, second, High-Temperature Steel and third, VA Steel. They are heated conventionally by a resistive heater, consisting of heating wires integrated between hightemperature stainless steel top- and bottom-elements. An important factor is to maintain constant heating conditions [5]. These are monitored by a thermocouple fixed on the top-element of the heater near the substrate-intake. The films were deposited at heater temperatures of 650'C at oxygen pressures of 0.1 mbar. Oxidation of the stainless steel substrates was carried out at the same conditions. The substrate surface was examined by Rutherford Backscattering Spectroscopy (RBS, 3.5 MeV He++ / 1.5 MeV He+), Transmission Electron Microscopy (TEM / X-TEM, plane-view / cross-section, 300 kV), X-Ray Diffraction (XRD, Cu-Kail, grazing angle, 0-20 scan) and Secondary Ion Mass Spectroscopy (SIMS, primary beam: Cs, 3 kV, 460 nA, 500 [Im raster). The phase formation and texture of the subsequently grown PZT films were investigated by XRD (Cu-KI, 0-20 scan, pole figure) and the stoichiometric quality of the films by Energy Dispersive X-ray spectroscopy (EDX, 15 keV). The microstructure and morphology of the films was imaged by Scanning Electron Microscopy (SEM, 15 keV). RESULTS Interface At the beginning of film growth, the conditions at the substrate surface essentially influence the phase formation of the deposited material. Therefore, a modification o
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