Fig. 2: Simulation of convergent beam electron diffraction patterns with a 9 mrad convergence angle (corresponding to a 1.3 Å diameter probe) moving across a gold nanocuboid into vacuum (position 1–7).

A Pure gold nanocuboid. B Equivalent simulation with the last two layers replaced by Cu atoms. Model thickness is the average size of gold nanocuboids, 25 nm. The probe step size is 2.04 Å so that the probe positions coincide with the atomic column positions. Central discs are masked for better observation of the intensity distribution beyond the central disc (unmasked raw diffraction patterns are shown in Supplementary Fig. S11). The coloured intensity scale, common to all diffraction patterns, ranges from 0 to 0.005% of the maximal vacuum probe intensity. Blue boxes indicate the features that are sensitive to copper atoms but are insensitive to the vacuum interface. Yellow boxes indicate the features arising from the nanocuboid-vacuum interface. The interface breaks the mirror symmetry in the direction perpendicular to the surface, indicated by the differences in reference to the dashed yellow line.