New Workfl ows
Figure 2 : Lift-out of the bulk chunk. (a) Attaching the nanomanipulator probe to the sample, and (b) lifting the “chunk” out of the bulk material. Figure 2b is an FIB image, and thus the rotation of the image is different.
• T inness: T e sample must be thin enough for the beam to pass through to the detector, ideally with most electrons interacting no more than once with a sample atom.
• Surface quality: T e surface of the samples should be fl at and free from topographic artifacts or defects introduced by the milling process (for example, material sputtering). Amorphous surface damage from the thinning process must be minimized. T is is important to ensure that the analysis of the sample is not compromised by changing the composition or structure of the initial material during the sample preparation process. T e existence of amorphous surface damage will also degrade the contrast and resolu- tion of TEM images.
• T ickness uniformity: T e thickness of the created samples should be uniform so that analytical techniques that depend on the number of events occurring over the electron path length through the specimen, including many chemical and elemental analysis methods, can yield valid point-to-point comparisons of elemental distribu- tion or particle/precipitate distribution across the sample.
• Parallelism: Closely related to thickness uniformity, the parallelism of the top and bottom surfaces plays a critical role in electron holography.
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Figure 3 : Grid attachment. (a) TEM grid is moved into position near the sample. (b) Sample attached to the TEM grid.
Semi-automated workfl ow . Recent advances in instrument design, particularly in the automation of both setup and operating routines, now permit the execution of a guided, semi-automated workfl ow for sample preparation that can rapidly and routinely prepare high-quality samples for high-resolution imaging techniques like S/TEM or atom probe microscopy [ 6 ]. Although the ability to automate certain portions of the preparation process has evolved steadily since FIB-based sample preparation was introduced, it has only now reached the point where essentially the entire process can be incorporated into a repeatable and easily executed guided routine. T e workfl ow can be applied to a wide range of diff erent materials, including silicon, steel, aluminum, ceramics, and soſt materials. It is especially well-suited to multi-user facilities, even those serving operators with many levels of expertise. By automating segments of the process that do not require operator interaction and providing guidance for those segments that do require interaction, a well-designed workfl ow can: (a) help users of all experience levels routinely prepare site-specifi c, ultra-thin, high-quality in-situ lamellas for S/TEM analysis, (b) enable the user to achieve predictable results for a wide range of materials, typically in under an hour, (c) assist the user with low-energy polishing to improve the quality of fi nal lamellas, and (d) dramatically increase TEM data acquisition, productivity, and quality.
www.microscopy-today.com • 2018 January
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