Investigation of the Pb depletion in single and dual pulsed laser deposited epitaxial PZT thin films and their structura
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Investigation of the Pb depletion in single and dual pulsed laser deposited epitaxial PZT thin films and their structural characterization Devajyoti Mukherjee, Robert Hyde, Tara Dhakal, Hariharan Srikanth, Pritish Mukherjee and Sarath Witanachchi Department of Physics, University of South Florida, Tampa, Florida. ABSTRACT We have investigated the Pb depletion in laser ablated PZT (PbZr1-xTixO3) films through a systematic study of PZT target-laser interactions for both single laser and dual-laser ablation methods. The study includes films deposited from a stoichiometric and an excess PbO PZT targets. The films were deposited on single crystal SrTiO3 [100] substrates at 550˚C with a background oxygen pressure of 500 mT. Single laser deposited films at a laser fluence of 5J/cm2 produced the highest Pb content while dual-laser ablated films where an excimer and a CO2 pulsed lasers were synchronized for ablation produced high Pb content for an excimer laser fluence of less than 2J/cm2. This enabled the growth of particulate-free PZT films with high Pb content. ICCD imaging of the plasma plumes showed variations in the expansion profiles at different laser fluencies that correlated well with the Pb content observed in the deposited films. INTRODUCTION Pulsed laser deposition (PLD) technique offers unique advantages in the growth of thin films of multi-component ferroelectric materials such as PZT. The most promising characteristics of the PLD technique is the stoichiometric transfer of materials from the target to the substrate. However, for oxides such as PZT which involve volatile elements like Pb, ablation of stoichiometric PZT targets causes preferential evaporation of Pb from the target at low laser fluences. In addition, Pb depletion in films was observed for typical growth temperatures of 500˚C to 600˚C necessary for getting crystalline films [1]. This Pb deficiency is responsible for the coexistence of a pyrochlore phase with the perovskite PZT phase, degrading the ferroelectric properties of the films. To compensate for the Pb loss it is a general practice to add excess PbO during the preparation of the dense ceramic PZT targets. Our investigations have shown that the preferential evaporation of Pb from target is suppressed at high laser fluences, but with the undesirable increase in the particulate density. On the other hand the advantages of growth of multi-component materials using dual laser ablation had been demonstrated earlier [2]. In this work we report the effectiveness of the dual laser ablation technique in producing particulate free high Pb content PZT films. Not only have the films grown by dual laser ablation retained the crystalline quality and high Pb content like the high excimer fluence single laser ablated films but also there has been a reduction in particulates on film surface. EXPERIMENTAL DETAILS The dual laser ablation system used in our experiments has been described in detail elsewhere [3]. Briefly, a 20-ns FWHM KrF laser pulse at 248 nm overlapped a 200-ns FWHM CO2 laser pu
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