Atom probe tomography is a materials characterization technique that (electro-statically and/or thermally) evaporates ions off a sample tip at a controlled rate and measures the  mass to charge ratio (based on Time of Flight) and impact position (using a position sensitive detector) to reconstruct the sample in 3-D with atomic precision.

The atomic positioning of the reconstructed sample is ~ 0.1-0.3 nm in depth, and ~0.3-0.5 nm laterally.

Figure 1: www.cameca.com/instruments-for-research/atom-probe.aspx