Invited Paper AS+AC-TuM1
Progress Toward Atomic-Scale Tomography

Tuesday, November 8, 2016, 8:00 am, Room 101B

There have been efforts of late to produce three-dimensional images at the atomic scale where every atom is accounted for and the position information is quite precise. All atoms in a two-dimensional thin film of boron nitride were imaged and identified by Krivanek et al. [1]. Scott et al. were able to produce three-dimensional images using electron tomography that show every atom in a gold nanoparticle containing over 7000 gold atoms [2]. Using atom probe tomography (APT), Moody et al. have shown three-dimensional images of several million atoms in an aluminum alloy where each atom is positioned correctly in a face-centered cubic lattice and 60% of the atoms are detected [3]. These are all impressive and important developments. They suggest what atomic-scale microscopy might ultimately achieve: recording with high precision the position and identity of every atom in a technologically relevant structure. This capability can fairly be termed atomic-scale tomography (AST).

If AST is to be achieved, it appears that APT and electron microscopy should be used synergistically to capture the strengths of one technique to overcome the limitations of the other. This question has been explored in detail [4] and the conclusion is that there are some ways that AST can be achieved. The instrumental developments needed to reach AST with APT and (S)TEM as a basis include: trajectory corrections for precise atom placement and detecting 100% of the atoms without ambiguity in identity. The former may be achieved by imaging the specimen apex to enable precise ion trajectory simulation toward the detector. An electron column integrated into an atom probe can, in principle, record the specimen apex shape throughout an entire atom probe experiment. Detectors for recording all atoms might be based on superconducting materials [5]. If these detectors also record an ion’s kinetic energy, then most time of flight-based ambiguities in peak identification can be eliminated [6].

Once these instruments are combined, the full analytical capabilities of each can be used synergistically. This presentation will outline approaches that should be pursued to reach this end and review the current plans to build an atomic-scale tomograph.

[1] O. L. Krivanek, et al., Nat. Lett, vol. 464, p. 571, 2010.

[2] M. C. Scott et al., Nature, vol. 483, pp. 444–447, 2012.

[3] M. P. Moody et al., Micros Microanal, vol. 17, pp. 722–723, 2011.

[4] T. F. Kelly et al., Microsc. Microanal., vol. 19, pp. 652–664, 2013.

[5] R. F. McDermott, J. R. Suttle, and T. F. Kelly, “Unpublished research,” 2015.

[6] T. F. Kelly, Micros Microanal, vol. 17, pp. 1–14, 2011.