New Workfl ows
Figure 10 : High-resolution imaging of PZT. (a) TEM image acquired using a 4k × 4k camera. (b) Digitally magnifi ed region from the white box in (a) showing atomic columns. (c) Fourier transform of the full 4k × 4k TEM image with a circle indicating the information limit of 0.12 nm.
or FRAMs), pyroelectric sensors, and electro-optical applica- tions [ 9 ]. A variety of PZT-based materials compatible with these applications has been developed via various composi- tional modifi cations and changes in the methods of chemical synthesis and processing. It is well established that doping with cations, such as La, in PZT thin fi lms and PZT ceramics causes their dielectric and ferroelectric properties to change. In this example, bismuth is examined as a new dopant for
PZT thin fi lms in the hope that a large, reversible, and sponta- neous polarization exhibited by the doped material makes it an attractive candidate for FRAM applications. In the present analysis, it was of interest to study the nanostructure formed inside the domains of these ceramics, as well as the structure of the domain boundaries. Workflow . The guided workflow here followed the same steps as above: the user/system selects the area of interest, deposits a protective layer of platinum, mills two large trenches on either side of the region of interest, and cleans up the surfaces of the cross section while applying slight tilt to maintain parallel side walls ( Figure 8 ). The sample is then attached to the nanomanipulator, lifted out of the bulk sample, and attached to a TEM sample grid. Final cleaning
of the cross section was applied to both sides of the lamella using a 30 kV ion beam energy and tilting the sample into the beam. To complete the sample, a low-energy cleaning step was applied to both sides of the lamella to remove any residual amorphous material ( Figure 9 ). Imaging and analysis . Aſt er the semi-automated workfl ow was used to prepare the sample in the SEM/FIB system (T ermo Scientifi c Helios DualBeam), the operator transfered the sample to the electron microscope (T ermo Scientifi c Talos F200X S/ TEM) for high-resolution TEM and STEM-EDS spectrum imaging analysis. T e high-resolution TEM image in Figure 10a was acquired using a 4k × 4k T ermo Scientifi c Ceta camera and shows the PZT crystal. Figure 10b shows the digital magnifi - cation of a region of Figure 10a , which reveals the crystalline structure of PZT. T e corresponding Fourier transform of the image ( Figure 10c ) contains spatial frequencies corresponding to 0.12 nm, which is the specifi ed information limit of the Talos F200X S/TEM. Figure 11 shows the spectra from two areas of the X-ray spectrum image. T e raw X-ray spectral data indicate the presence of two phases; one containing Ti, Pb, Nb, Zr, Al, and Mg (area 1) and one rich in Si, Mg, and O (area 2). T e elements in these phases are also shown in the X-ray maps of Figure 12 . Compositional information could be obtained with the SuperX detector despite the small acquisition time of only 3 minutes. T ese fi gures show that the sample prepared using the semi-automated workfl ow is suitable for TEM and STEM characterization.
Figure 11 : STEM image of PZT phases acquired using a Talos F200X S/TEM at 200 keV. (left) Image recorded in parallel with the STEM X-ray spectrum image. (right) X-ray spectra of the two phases within the fi eld of view.
24
Conclusion T e characterization of materials via high-resolution STEM (HR-STEM) requires sample preparation meeting a range of distinct criteria: the preparation must repeatably deliver high-quality thin sections that precisely capture the
www.microscopy-today.com • 2018 January
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