Tem Investigation of Growth Temperature Dependence in Pulsed-Laser Ablated PLZT Films for Pyroelectric Applications
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563 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
(ao=0.395 nm) and the cubic LAO (a0=0.379 nm). Excluding the LSCO layer results in only a 4% mismatch between film and substrate and promises easier and more accurate study of electron diffraction patterns (DPs) and images. Investigation of PLZT grown directly on LAO therefore simplifies TEM analysis, while also providing intuitive speculation to the situation when LSCO electrodes are incorporated. Careful steps were taken to insure non-destructive TEM sample preparation. An M-bond adhesive was used to glue cross-sectional samples film to film prior to curing via addition of heat. A standard tripod polisher was then used to mechanically thin samples down to approximately 20 •.tm with diamond lapping sheets. The last and most crucial step involved Argon ion bombardment using a Bal-Tech RES 010 Ion Mill. Depending on the thickness of the mechanically polished samples, this procedure may take from 1.5 to 3 hrs operating at 6.5 KV and 1.5 mA at a 150 beam angle. To minimize damage from the ion beam (i.e., redeposition of unwanted species), the process is done with a continuous flow of liquid Nitrogen, to reduce milling temperatures. A Rigaku theta-2theta diffractometer with Cu radiation source was used to obtain X-ray data and a JEOL 4000FX electron microscope (operated at 300 KV) was used to carry out TEM analysis. RESULTS Figure 1 shows standard 0-20 XRD spectra for four films grown at substrate heater temperatures of 5500, 6000, 6500, and 7000 C. The 200-LAO peaks are constant for all tempera40000
35000
002 PLZT
A50
IA 600C0I1 10o6500C
30000 =
25000
o0
-C
0
•
A
A A
A
200 LAO~
Ai,
520000
44
45
46
47
48
49
20 (deg)
FIGURE 1. Theta-2theta x-ray diffraction for varying deposition temperatures. 002 peaks correspond to c-lattice parameter in PLZT. tures and correspond to a lattice parameter of 0.379 nm, which agrees precisely with the accepted value. Since La 3÷ doping results in a slight decrease in the tetragonality of PZT, the decreased cparameters ranging from 0.401 nm to 0.406 nm (indicated by the 002-PLZT peaks) are to be expected [6]. However, it should be noted that the 002 peak at 650 °C represents both the highest intensity and corresponds to the largest c-parameter. At 700 °C, a significant decrease in the peak intensity indicates that the film begins to lose its c-axis domain dominance. It is important to acknowledge here, that though the XRD spectra show no evidence of a-axis domain orientation, we may not conclude that the films are fully c-axis oriented. Theoretically, a -2.9o tilting of (h00)
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planes away from the [001] substrate direction may result in the disappearance of (hOO) type peaks in PZT [7]. This important point is most likely responsible for certain spots in TEM electron diffraction patterns as discussed below. Figure 2 shows electron diffraction patterns (along a [hOO] zone axis) for films deposited at substrate heater temperatures of 5000, 5500, 6000, and 650 'C. The most obvious feature
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