Optimizing experimental parameters of integrated differential phase contrast (iDPC) for atomic resolution imaging

Abstract

Integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) technique has been well developed for studying atomic structures at sub-Å resolution with the capability of simultaneously imaging heavy and light atoms even at an extremely low electron dose. As a direct phase contrast imaging technique, atomic resolution iDPC-STEM is sensitive to the imaging conditions. Although great achievements have been made both in aspect of theory and experiments, the influence of experimental parameters on the contrast of atomic resolution iDPC-STEM images has not been systematically investigated. Here, we perform the iDPC-STEM simulations on the prototypical example of SrTiO3 with respect to the routine experimental factors, including the defocus, specimen thickness, accelerating voltage, convergence angle, collection angle, sample tilt and electron dose. Through the evaluation of image contrast and atom column intensity, the parameters are discussed to improve the image contrast and the visibility of light elements. Moreover, the dose-dependent simulations demonstrate the advantage of low dose iDPC-STEM imaging over other conventional STEM modes. Our results provide a practical guideline to experimentally obtain accessible atomic resolution iDPC-STEM images.