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Adhesive-Based Atom Probe Sample Preparation


Surya S. Rout , 1 , 2 # * Philipp R. Heck , 1, 2, 3 Nestor J. Zaluzec , 4 Dieter Isheim , 5 Dean J. Miller , 6 and David N. Seidman 5 1 Robert A. Pritzker Center for Meteoritics and Polar Studies , T e Field Museum of Natural History , 1400 S . Lake Shore Dr .,


Chicago , IL 60605 2 Chicago Center for Cosmochemistry , T e University of Chicago , 5734 S . Ellis Ave ., Chicago , IL 60637 3 Department of the Geophysical Sciences , T e University of Chicago , 5734 S . Ellis Ave ., Chicago , IL 60637 4 Photon Science Division , Argonne National Laboratory , 9700 S . Cass Ave ., Argonne , IL 60439 5 Northwestern University Center for Atom-Probe Tomography , Department of Material Science & Engineering , Northwestern


University , Evanston , IL 60208 6 Center for Nanoscale Materials , Argonne National Laboratory , 9700 S . Cass Ave ., Argonne , IL 60439


# Present Address: Physics Institute, Space Research & Planetary Sciences, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland * surya.Rout@space.unibe.ch


Abstract: We present a specimen preparation procedure for atom-probe tomography using SemGlu from Kleindiek Nanotechnik, an adhesive that hardens under electron beam irradiation. The SemGlu adhesive is used in place of focused-ion-beam-induced deposition of organo-metallic Pt, W, or C to form a bond between the sample and the substrate during the specimen preparation procedure. We demonstrate the utility of this adhesive-based specimen preparation technique with a correlated atom-probe tomography-scanning transmission electron microscopy study of the iron-nickel alloy kamacite (ferrite, α -iron) in the Bristol iron meteorite and two steel specimens.


Keywords: atom-probe tomography (APT), specimen preparation, adhesive, scanning transmission electron microscopy ((S)TEM), Bristol iron meteorite


Introduction


Laser-assisted atom-probe tomography (APT) enables the acquisition of tomographic information on the elemental and isotopic composition of a broad range of specimens with near atomic-level spatial resolution and single-atom analytical sensitivity [ 1 , 2 ]. New generations of aberration-corrected scanning transmission electron microscopes (S)TEM have led to the study of the structure and composition of diff erent types of samples at sub-nm scale [ 3 – 5 ]. T e complementary use of both (S)TEM and APT is a powerful approach to generate detailed structural, chemical, and isotopic information on the near atomic scale. Correlative (S)TEM and APT studies show the synergies of the two methods in the study of grain boundaries, inclusions, impurities, segregation eff ects, defects, partitioning of elements, and phase transformations [ 6 – 14 ]. T is has been further enhanced by employing focused ion beam scanning electron microscope (FIB-SEM)-based specimen preparation techniques, which have facilitated site-specifi c studies of regions of interest (for example, inclusions, grain boundaries, heterophase interfaces). Additionally, various procedures have been developed especially for preparing site-specifi c specimens for correlative


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(S)TEM and APT studies [ 12 , 15 – 18 ], where the emphasis has been on methods to minimize sample damage during the (S) TEM and APT studies [ 12 , 17 , 18 ]. In this article we extend those works by adding an improved specimen preparation technique that reduces the use of focused-ion-beam-induced deposition of organo-metallic materials and also leads to very low sample damage during correlative (S)TEM and APT analyses. Organo-metallic deposition is frequently used in a FIB-SEM instrument to deposit different materials (for example, Pt, W, C) to form bonds between the FIB lift-out specimen and its supporting substrate (for example, Si posts, sharpened Cu or Mo grids, SiN films). This is done in order to produce mechanically stable specimens for APT analyses [ 15 , 16 ]. However, the bond produced during the organo-metallic (C, Pt, and W) deposition will be weak if the deposited connecting material is not sufficiently homoge- neous. Also these bonds are usually susceptible to fracture during APT analysis, particularly in experiments that employ high applied voltages to induce field evaporation of atoms from the specimen. To alleviate issues related to weak bonding between the specimen and the substrate, we have tested and successfully employed SemGlu (Kleindiek


Figure 1 : (a) Photograph showing the Widmanstätten pattern on an etched section of the Bristol iron meteorite (FMNH ME 2248). The plates of kamacite or ferrite (K) that grow with habit plane parallel to the (111) octahedral planes of the parent taenite or austenite (T) phase are marked with arrows. (b) SEM image of a region from the Bristol iron meteorite shown in (a). The interface between the kamacite and the taenite region is marked with dotted lines. Here a lamella is being extracted from the kamacite-taenite interface.


doi: 10.1017/S1551929518000238 www.microscopy-today.com • 2018 March


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