  The standard technique for sub-pixel estimation of atom positions from atomic
resolution scanning transmission electron microscopy images relies on fitting
intensity maxima or minima with a two-dimensional Gaussian function. While this
is a widespread method of measurement, it can be error prone in images with
non-zero aberrations, strong intensity differences between adjacent atoms or in
situations where the neighboring atom positions approach the resolution limit
of the microscope. Here we demonstrate mpfit, an atom finding algorithm that
iteratively calculates a series of overlapping two-dimensional Gaussian
functions to fit the experimental dataset and then subsequently uses a subset
of the calculated Gaussian functions to perform sub-pixel refinement of atom
positions. Based on both simulated and experimental datasets presented in this
work, this approach gives lower errors when compared to the commonly used
single Gaussian peak fitting approach and demonstrates increased robustness
over a wider range of experimental conditions.
