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Xe Plasma FIB

and shape distribution of the WC grains. A practical volume of (100 μ m) 3 is possible in the PFIB-SEM compared to a typical volume of (50 μ m) 3 captured in the Ga + FIB-SEM. Based on an average grain size in this material of 11.5 μ m, determined from the PFIB-SEM dataset, it is possible to capture ~660 grains compared to ~80 grains possible in the Ga + FIB-SEM. T is material was specifi cally chosen for this 3D EBSD study because it has presented signifi cant problems when investigated at a smaller scale within the Ga + FIB-SEM. T e WC phase is resistant to FIB machining and is diffi cult to prepare damage- free. Figures 4 b to 4 d show a series of maps collected from a single slice prepared during an automated EBSD procedure. It has been possible to prepare a large cross section of this material using PFIB at 30 kV and 59 nA with a time of only 51 s to create each new slice. T e EBSD results show the indexing rate is over 80%. An issue facing this large-volume EBSD analysis is the time taken to collect the EBSD maps. In this study acquisition of 33 slices took ~30 hours, although it should be noted that much faster acquisition rates would be possible on many other materials such as ferrite, austenite, nickel, copper, etc. with mapping times of less than 10 minutes, depending on the map size and resolution required. T e speed and quality of the PFIB cut opens up volumes of real signifi cance, but time has to be spent optimizing the EBSD mapping for maximum speed. Despite the current level of optimization we have achieved, we need further hardware and soſt ware developments to alleviate this bottleneck in acquisition of large-volume, high-resolution 3D EBSD datasets.

Preparation of human dentine for X-ray CT . Lastly, by connecting the non-invasive X-ray techniques to the destructive 3D imaging techniques within a correlative framework, there is a need to locate, excavate, and analyze sub-volumes in further detail. As well as providing high-resolution images of volumes, the PFIB promises to be able to excavate regions of interest, for example, creating samples for nanoscale X-ray CT. This is especially challenging for materials science specimens as an ideal sample size (in this case determined by the X-ray energy and their penetration) with a pillar that is 20–100 μ m in diameter and approximately 100 μ m tall. To achieve this, milling to a depth of over 100 μ m is required, as well as a milled radius of the hole equal to the pillar height. T ese dimensions put this task beyond the practical means of the Ga + FIB-SEM. The ability to create these samples from a site-specifi c location and then create a sample of the desired dimensions makes this an important capability, combining the precision of the cutting with the fast material-removal rate.

Figure 5a shows a pillar of human dentine prepared by the PFIB. This study had two aims: one was the desire to understand better the 3D morphology of the dentine tubules, and the second was to determine the accurate orientation of the tubules with respect to the subsequently prepared TEM lamellae. Understanding the detailed geometry of the dentine tubules at the sub-micron level is exceptionally difficult to appreciate from 2D cross sections. The quality of the NanoCT results was ensured by predicting the X-ray


Figure 5 : Human dentine. (a) SEM image of the PFIB-prepared dentine pillar attached to the NanoCT holder. (b) 3D rendering of the NanoCT data showing the same orientation of the pillar as the SEM image. (c) Sub-volume showing three orthogonal views of the tubules and the enhanced density material (shown in red) that surrounds the tubules. The fi nal diameter of the dentine pillar was ~45 µm, and the diameter of the dentine tubules was 2–2.5 µm.

absorption of the sample and then specifically machining a pillar of the required dimensions using the PFIB. Figures 5 b and 5 c show the results of the nanoscale X-ray CT scan providing a (120 nm) 3 voxel size and the ability to see the tubules and the increased density along the walls of the tubules.

Discussion T ese results give an overview of some applications where we have successfully applied the PFIB-SEM. T e ability to prepare high-quality cross sections at high currents has meant that large volumes can be quickly captured with nanoscale resolution. T is is an exciting area for development because many important engineering materials have grain structures many tens of micrometers and can only be charac- terized eff ectively over volumes hundreds of micrometers in size. In addition to the results presented here, we have also examined several other materials, including steel, aluminum, zirconium, titanium, alumina, various coatings, and an olivine rock sample. In each case, the parameters had to be optimized. With each new material comes a learning curve to optimize the conditions used. In addition we are continuing to push the • 2016 May

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