Figure 3: (a–d) Schematic field ion images of single-atom 𝑊 (110) tips produced from a hemispherical starting tip (radius 8 nm) via field evaporation according to highest-field, image-force (with/without polarization), and Kreuzer-Nath criteria; (e–h) experimental field ion images (voltage ~8.8 kV) showing the formation of an SAT and evaporation of atoms from below the apex. Arrows indicate features which change between (g) and (h).