Scanning transmission electron microscopy (STEM) is emerging as fundamentally new kind of tool for the direct assembly of nanostructures. Atomically precise manipulation with STEM relies on recent advances in instrumentation that have enabled non-destructive atomic-resolution imaging at lower electron energies. Graphene, the atomically thin layer of hexagonally bonded carbon, is the ideal sample for such experiments. In an effort to control its properties, heteroatom dopants have been introduced into graphene both during growth and using post-growth methods, with ion implantation being a particularly promising example of the latter technique.
While momentum transfer from highly energetic electrons often leads to atom ejection, interesting dynamics can be induced when the transferable kinetic energies are comparable to bond strengths in the material . Operating in this regime, very recent experiments have revealed the potential for single-atom manipulation of Si heteroatoms in the graphene lattice using the Ångström-sized electron beam . In our latest experiments, we have achieved 36 controlled single-site jumps with a manipulation rate already comparable to state-of-the-art in fully automated scanning tunneling microscopy. Sample quality thus appears to be the principal challenge in creating 2D nanostructures from multiple Si atoms in the near future .
To enable such successes, it has been vital to understand the relevant atomic-scale phenomena through accurate dynamical simulations. Although excellent agreement between experiment and theory for the specific case of atomic displacements from graphene has been recently achieved using density functional theory molecular dynamics , in many other cases quantitative accuracy remains a challenge. I will discuss our recent reanalysis of available experimental data on beam-driven dynamics of N, B, and Si heteroatoms in light of such simulations , and present our latest manipulation trials with implanted P and Ge.
 Susi, T., Kotakoski, J., Kepaptsoglou, D., Mangler, C., Lovejoy, T.C., Krivanek, O.L., Zan, R., Bangert, U., Ayala, P., Meyer, J.C., Ramasse, Q., Phys. Rev. Lett. 113, 115501 (2014). doi:10.1103/PhysRevLett.113.115501
 Susi, T., Meyer, J.C., Kotakoski, J., Ultramicroscopy 180, 163-172 (2017). doi:10.1016/j.ultramic.2017.03.005
 Nosraty Alamdary, D., Kotakoski, J., Susi, T., Physica Status Solidi B, 1700188 (2017).
 Susi, T., Hofer, C., Argentero, G., Leuthner, G.T., Pennycook, T.J., Mangler, C., Meyer, J.C., Kotakoski, J., Nat. Commun. 7:13040 (2016), doi: 10.1038/ncomms13040
 Susi, T., Kapaptsoglou, D., Lin, Y.-C., Ramasse, Q., Meyer, J.C., Suenaga, K., Kotakoski, J., 2D Materials 4, 042004 (2017). doi:10.1088/2053-1583/aa878f