LAUSR

The development of fast acquisition cameras allows for the collection of a series of convergent beam electron diffraction (CBED) patterns at each scanning position during conventional STEM at a speed as fast as s/frame. Thus, a 4D-STEM dataset (2D in real space as a function of probe position and 2D diffraction pattern in each real space position) is generated while high-angle annular dark field (HAADF)STEM images of the sample are acquired. By analyzing the 4D-STEM dataset, we can achieve more accurate structural information than conventional STEM images acquired at a lower electron dose, i.e., imaging both the heavy (conventionally seen by annular dark field – ADF) and light (conventionally seen by annular bright field – ABF) elements at atomic resolution simultaneously. Moreover, 4D-STEM dataset analysis can reveal the field information of the sample such as the electric field, magnetic field, atomic potential, and strain. There are several techniques that have been commonly used to extract information from scanning CBED patterns, such as differential phase contrast (DPC) ptychography. By calculating the center of mass (COM) of the CBED patterns, which is the derivative of the first moment, DPC generates a qualitative solution that is linear to the electromagnetic field of the sample [1-3]. Ptychography is a more complicated phase retrieval method that either employs iterative algorithms [4-6] or phases up the transfer function of the 4D-STEM dataset [7] [8] to quantify the projected potential.