Optimal experimental design of STEM measurement of atom column positions

A quantitative measure is proposed to evaluate and optimize the design of a high-resolution scanning transmission electron microscopy (STEM) experiment. The proposed measure is related to the measurement of atom column positions. Specifically, it is based on the statistical precision with which the positions of atom columns can be estimated. The optimal design, that is, the combination of tunable microscope parameters for which the precision is highest, is derived for different types of atom columns. The proposed measure is also used to find out if an annular detector is preferable to an axial one and if a C-s-corrector pays off in quantitative STEM experiments. In addition, the optimal settings of the STEM are compared to the Scherzer conditions for incoherent imaging and their dependence on the type of object is investigated. (C) 2002 Elsevier Science B.V. All rights reserved.