Procedure to count atoms with trustworthy single-atom sensitivity

We report a method to reliably count the number of atoms from high-angle annular dark field scanning transmission electron microscopy images. A model-based analysis of the experimental images is used to measure scattering cross sections at the atomic level. The high sensitivity of these measurements in combination with a thorough statistical analysis enables us to count atoms with single-atom sensitivity. The validity of the results is confirmed by means of detailed image simulations. We will show that the method can be applied to nanocrystals of arbitrary shape, size, and atom type without the need for ap rioriknowledge about the atomic structure. Atomic resolution high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) enables one to obtain projection images of the atomic columns of crystalline nanoparticles. These images are highly sensitive for the number of projected atoms in these columns. 1,2 Therefore, this imaging technique is appealing to count the number of atoms in each column with single-atom sensitivity being of great importance to help determining the three-dimensional (3D) arrangement of all atoms. Previous quantification attempts often assume a linear dependence of the HAADF STEM intensities on the number of atoms using mass standards with