Xe+ Plasma FIB: 3D Microstructures from Nanometers to Hundreds of Micrometers
T. L. Burnett , 1 , 2 * B. Winiarski , 1 , 2 R. Kelley , 3 X. L. Zhong , 4 I. N. Boona , 5 D. W. McComb , 5
K. Mani , 3 M. G. Burke , 4 and P. J. Withers 1 1 T e Henry Moseley X-ray imaging facility , School of Materials , T e University of Manchester , M13 9PL , UK 2 FEI Company , Achtseweg Noord 5 , Bldg 5651 GG , Eindhoven , T e Netherlands 3 FEI Company , 5350 Northeast Dawson Creek Drive , Hillsboro , OR 97124 4 Materials Performance Centre , School of Materials , T e University of Manchester , Materials Department , Manchester , M13 9PL , UK
5 Center for Electron Microscopy and Analysis, T e Ohio State University, 1305 Kinnear Road, Columbus, OH 43212
*
timothy.burnett@manchester.ac.uk
Abstract : Xenon plasma focused ion beam (FIB) technology has the potential to investigate large volumes, hundreds of micrometers in size whilst retaining the high resolution of SEM imaging. Three different materials, an aluminum alloy, a zirconium-based metallic glass, and a tungsten carbide-cobalt hard metal, were subject to serial section- ing to build up 3D microstructural images. Lastly a sample of human dentine was shaped into a pillar for analysis using nanoscale X-ray CT. The plasma FIB broadens the range of length scales, which can be investigated and holds signifi cant promise for bringing new understanding of complex microstructures.
Introduction T ere is a critical need to analyze many material systems in three dimensions (3D), for example to understand the connectivity of phases, porous networks, and complex shapes. Fortunately, there are now several tools available for 3D charac- terization, for example, X-ray computed tomography (CT) [ 1 ], serial section SEM Tomography (SST) [ 2 – 4 ], transmission electron tomography [ 4 ], and atom probe tomography [ 5 , 6 ], each covering diff erent length scales (see Figure 1 ). FIB-SEM SST . T e emergence of focused ion beam scanning electron microscopy (FIB-SEM) using a gallium ion FIB has provided a means of accessing volumes of interest (VoI) using SST. T e Ga + FIB-SEM is also an important tool for the creation of transmission electron microscopy (TEM) samples. In practice, acquisition times limit the method to volumes about (50 μ m) 3 for site-specifi c 3D analysis using SST close to the surface with slice thicknesses down to ~10 nm. Despite its destructive nature, SST enables detailed 3D imaging of phases, grain structure (via electron backscatter diff raction (EBSD)), and chemistry (by energy dispersive X-ray spectroscopy (EDS)) [ 8 ]. However there are many cases where it would be of interest to probe large VoIs that are submerged deeper within the sample. In an eff ort to respond to this challenge, the concept of correlative tomography, the 3D equivalent of correlative microscopy, has been proposed as a way of studying a VoI over multiple scales by coupling X-ray CT and SST to acquire multiple types of data (structural, crystallographic, chemical, etc.) that can be brought into registry for the same region [ 9 ]. Plasma FIB . Recently Xe + plasma FIBs [ 10 , 11 ] have emerged, demonstrating faster materials removal rates compared to Ga + liquid metal ion source FIBs [ 12 ]. In this article, we examine the capabilities of a Xe + Plasma FIB (PFIB)-SEM dual-beam system for 3D analysis across a range of materials and applications.
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T e FEI Helios PFIB used in this study has a maximum current of 1.3 μ A compared to a maximum current of ~65 nA for many Ga + FIB systems. In addition to a higher maximum current, which is useful for coarse milling duties, we can operate the PFIB at currents up to 180 nA for the preparation of high-quality cross sections for imaging. In addition, the Xe + PFIB avoids potentially harmful chemical reactions, such as those that can result from Ga + FIB milling [ 13 ]. We are continuing to build our understanding of this technology to enable us to apply it to a large range of potential applications. Here we present four example applications where we have successfully applied the PFIB: describing the size of the volumes interrogated, the resolution, and the 3D reconstruction.
Three different serial sectioning results are presented:
a stress corrosion crack tip in a 7000 series Al alloy, a Zr-based bulk metallic glass (BMG) with embedded dendrites, and a tungsten carbide hard metal with a cobalt binder phase (WC-11 wt% Co) analyzed by 3D EBSD. A fourth example shows the preparation of a site-specific pillar of human dentine for nanoscale X-ray CT.
Figure 1 : 3D imaging methods for materials science. Non-destructive methods are represented by dashed lines. Microtomy is typically only for soft material [ 7 ].
doi: 10.1017/S1551929516000316
www.microscopy-today.com • 2016 May
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