Focused ion beam and scanning electron microscopy for 3D materials characterization
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Introduction A focused ion beam (FIB) system coupled with a scanning electron microscope (SEM) on the same platform, often referred to as an FIB-SEM microscope, is a powerful combination for three-dimensional (3D) microstructural analysis. The FIB is used serially to remove layers of material, while the electron beam is used to illuminate the freshly exposed surface. While early FIB-SEM imaging yielded 3D data stacks from measured electron signals (secondary electrons or backscattered electrons), more recent developments have integrated diffraction and x-ray spectroscopy with 3D FIB-SEM imaging. This article briefly reviews recent developments in acquisition and analysis of 3D FIB-SEM electron backscatter diffraction (EBSD) and x-ray microanalysis. A related review was recently published by Holzer and Cantoni,1 and the interested reader is directed there for more details on imaging and microanalytical developments.
Three-dimensional orientation mapping Automated EBSD, which makes it possible to accumulate a map of crystal orientations on a surface, has had a transformative effect on the study of grain boundaries in polycrystals. It is currently possible to measure several hundred orientations per second, enabling the determination of the shapes and
orientations of thousands of grains in a reasonable amount of time. However, EBSD reveals information only on nearsurface crystallography. Three-dimensional details extending beneath the surface requires serial sectioning (sequentially removing layers of material).2,3 The experimental solution for serial sectioning has been made possible by dual beam microscopes that contain both an electron beam for EBSD mapping and an FIB for milling away layers of material. Efforts to fully automate the sequence of orientation mapping and FIB milling have obviated user intervention in the imaging cycle, enabling the collection of large 3D orientation maps of materials from which statistical information can be derived.4–10 For example, a 3D orientation map of a ferritic steel is shown in Figure 1. Three-dimensional orientation maps, compared to 2D images, occupy large banks of memory and are time consuming to measure. A typical 3D map will take several days to measure, where the time demand scales with the field of view and the number of parallel sections examined. In a conventional FIB-SEM microscope, orientation mapping and milling require comparable amounts of time. To balance the cost of the instrument time with the desire to collect as much useful information as possible, it is important to consider the choices for the spacing of the orientation points both within planes and
Paul G. Kotula, Sandia National Laboratories; [email protected] Gregory S. Rohrer, Carnegie Mellon University; [email protected] Michael P. Marsh, Marsh Imaging and Visualization; [email protected] DOI: 10.1557/mrs.2014.55
© 2014 Materials Research Society
MRS BULLETIN • VOLUME 39 • APRIL 2014 • www.mrs.org/bulletin
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FOCUSED ION BEAM AND SCANNING ELECTRON MICROSCOPY FOR 3D MATERIALS CHARACT
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