A METHOD FOR RECONSTRUCTING AND LOCATING ATOMS ON THE CRYSTAL-LATTICE IN 3-DIMENSIONAL ATOM-PROBE DATA

The physical process of field evaporation introduces lateral aberrations in the ion trajectories toward an atom probe detector. In three-dimensional atom probes, these aberrations blur information describing the 3D atomic stacking in the material. This work reports progress that has been made using Fourier transform and pattern recognition techniques to reconstruct an original lattice structure from simulated atom probe data and to subsequently force atoms to the nearest lattice point. Usually Fourier transform techniques are used in image processing to separate image noise from periodic information not to actually shift features in the image. The present technique analyzes a 2D data set and determines the statistically best lattice parameters, lattice orientation, lattice position and site occupation with no free parameters in the analysis. A randomly oriented Gaussian blurring function is used to simulate trajectory aberrations. For 151 atoms originally on a square lattice, atom locating errors are less than 4% when the mean displacement is one quarter of the lattice parameter. The repositioning efficiency increases rapidly with increasing data set size and decreases rapidly with increasing aberration magnitude.