Large angle illumination enabling accurate structure reconstruction from thick samples in scanning transmission electron microscopy

Most reconstructions of the electrostatic potential of a specimen at atomic resolution assume a thin and weakly scattering sample, restricting accurate quantification to specimens only tens of Ångströms thick. We demonstrate that using large-angle-illumination scanning transmission electron microscopy (STEM)—a probe forming aperture with convergence angle larger than about 50 mrad—allows us to better meet the weak phase object approximation and thereby accurately reconstruct the electrostatic potential in samples thicker than the order of 100 Å.