a,b) Scanning tunneling microscopy (STM) images of a Cu(111) surface with iron atoms being assembled (a) into a circular quantum corral structure (b) (Crommie et al. 1993). The STM experiments require low temperatures and ultra-high vacuums. c,d) STEM images of a silicon atom embedded in the graphene lattice, being non-destructively moved by one lattice position by a beam-driven silicon-carbon bond inversion (Susi et al. 2014). e,f) The corresponding simulated structures. (Panels a and b courtesy of Michael Crommie / University of California at Berkeley.)