Three-Dimensional Microstructural Characterization Using Focused Ion Beam Tomography
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5/7/07
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Three-Dimensional
Microstructural Characterization Using Focused Ion Beam Tomography
Michael D. Uchic, Lorenz Holzer, Beverley J. Inkson, Edward L. Principe, and Paul Munroe Abstract This article reviews recent developments and applications of focused ion beam (FIB) microscopes for three-dimensional (3D) materials characterization at the microscale through destructive serial sectioning experiments. Precise ion milling—in combination with electron-optic–based imaging and surface analysis methods—can be used to iteratively section through metals, ceramics, polymers, and electronic or biological materials to reveal the true size, shape, and distribution of microstructural features. Importantly, FIB tomographic experiments cover a critical size-scale gap that cannot be obtained with other instrumentation. The experiments encompass material volumes that are typically larger than 1000 mm3, with voxel dimensions approaching tens of nanometers, and can contain structural, chemical, and crystallographic information. This article describes the current state of the art of this experimental methodology and provides examples of specific applications to 3D materials characterization.
Introduction The importance of material microstructure and its subsequent influence on properties is a basic tenet of materials science. Therefore, one might reasonably expect to find a suite of mature materials characterization methodologies that provide an unbiased, accurate, and complete description of microstructural features at length scales over which microstructural features are generally observed, i.e., from nanometers to millimeters in size. Unfortunately, this is often not the case. Many commonly used characterization methodologies at the microscale, such as scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), energy dispersive spectroscopy (EDS), and scanning probe microscopy and its derivatives such as
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atomic force microscopy, all provide near-surface information but cannot inform the user about the exact nature of microstructural features except in selected cases where the feature geometry is symmetric, highly idealized, or a priori known. To achieve truly quantitative materials characterization, it is imperative that modern characterization methodologies provide three-dimensional information.1 Specifically, 3D characterization enables the measurement of a number of important geometric properties that cannot be obtained using a 2D analysis, such as the number of features per unit volume, feature connectivity, real feature shapes and sizes, and spatial distribution information.2
One well-established method for obtaining 3D information from instruments that only provide 2D data, such as those listed above, is by serial sectioning.2 Serial sectioning experiments are conceptually simple. The first step is to create a planar surface through careful removal of a known volume of material. This process is typically accomplished via mechanical sectioning, mechanical grinding and polish
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