(color online) (a) A topographic image of an in situ-cleaved surface of Ba Fe As . (b) A DOS map, measured on the same field of view as Fig. 1(a) at zero sample bias. (c) Enlarged view of the lower impurity in Fig. 1(b). (d) and (e) Tunneling spectra measured along the lateral and vertical trajectories in Fig. 1(c), respectively. (f) Spatial dependence of zero-bias conductance along the two trajectories. The solid line is a fit to Gauss function with characteristic width of nm. (g) Three typical spectra taken at the specific positions labeled in Fig. 1(c). All the data presented here were taken at sample bias mV and setting current pA with temperature T = 3 K.