Advances in 3D focused ion beam tomography
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Introduction For a fundamental understanding of microstructure effects on materials properties, it is essential to characterize the threedimensional (3D) topology by means of tomography and image processing. For many modern functional materials, the characteristic length of important topological features, which influence the effective materials properties, is in the range of 10 to 100 nm. As shown in Figure 1, focused ion beam (FIB) tomography covers this important size range in resolution, which makes it the method of choice for 3D investigations in many materials science disciplines.1 The method is based on an alternating procedure of FIB-slicing and scanning electron microscopy (SEM) imaging to acquire stacks of images. The method is also described in the literature with equivalent terms such as “FIB-serial sectioning,” “FIB-SEM tomography,” “3D-FIB,” “FIB-slice and view,” and “FIB-nanotomography (FIB-nt).” FIB tomography started more than 10 years ago using single beam machines.2,3 With the introduction of commercial dual platform FIB-SEM machines, the serial sectioning could be performed without stage tilting and repositioning. This was the basis for automated stack acquisition with reproducible slicing distances down to the 10 nm-range.4–6 However, the method initially suffered from some other important limitations, in particular with respect to the size of the image window (that
limited the ability to provide representative views of the sample), slow acquisition times (that limited the number of slices), and image quality and drift problems (that limited reliability of quantitative analysis). The method rapidly evolved, and user-friendly automation procedures were introduced. In addition, it was combined with new detection modes for chemical analysis (x-ray energy dispersive spectrometry7,8 [3D-XEDS]) and for crystallographic information (electron backscatter diffraction9–12 [3D-EBSD]). Today, FIB tomography provides excellent contrast for many different material types, which is also due to recent advances in detector technology. FIB tomography has been successfully applied to numerous research disciplines. From the wide range of successful applications of FIB tomography, we describe three examples in order to illustrate the importance of 3D information, which in many cases can currently only be obtained by FIB tomography. The first is the important field of energy materials. FIB tomography has been used to distinguish between active and inactive electrochemical reaction sites (i.e., internal surfaces and three phase boundaries). This information is essential for understanding the influence of microstructures on the performance of electrodes in fuel cells and batteries and for the improvements in corresponding materials design.13–20 The second example is research on porous materials (e.g., membranes, catalysts,
Marco Cantoni, Materials and Basic Science, Swiss Federal Institute of Technology EPFL; marco.cantoni@epfl.ch Lorenz Holzer, Institute of Computational Physics, Zurich University of Applied Sciences; lor
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