Figure 4: Simultaneous atomic-resolution ADF STEM image and electric field vector map and electric field strength map of Au single atoms.

(a) ADF STEM image. (b,c) Electric field vector and electric field strength maps constructed from the segmented-detector STEM images. The dwell time is 300 μs per pixel. The inset colour wheel indicates how colour and shade denote the electric field orientation and strength. Magnified images from three isolated Au atom positions (3), identified from the ADF image but extractable from all the simultaneously acquired images, are shown to the right of the full images. The enlarged sections of the electric field vector and electric field strength maps show the distinctive contrast features seen at the column locations in Fig. 2. Simulated single Au atom images are also shown, which include a 10 nm-thick amorphous carbon substrate beneath the single Au atom. Because of the random structure of amorphous carbon, the diffraction effect is weak and thus the single Au atom contrast stands out from the background amorphous carbon contrast. (d) Comparison between the projected electric field strength line profile of Au atom number 2 and the simulated projected electric field strength line profiles of a single Au atom. For the experimental electric field strength line profile, the zero CoM angle is set to the average intensity of the nearby amorphous carbon region, and thus the comparison simulations do not include an amorphous carbon substrate. The experimental electric field strength using the eCoM approximation (blue line) and the simulated electric field profile assuming the same eCoM approximation (light green) are in good quantitative agreement. For comparison, the ideal atomic electric profile (including finite temperature effect) blurred by the diffraction-limited probe intensity profile and incoherent source size (red dashed line) is also shown. It is seen that the eCoM is a quantitatively good approximation to the (probe-blurred) atomic electric field.