  We have developed a physically-intuitive method to calculate the local
lattice constant as a function of position in a high-resolution transmission
electron microscopy image by performing a two-dimensional fast Fourier
transform. We apply a Gaussian filter with appropriate spatial
full-width-half-max (FWHM) bandwidth to the image centered at the desired
location to calculate the local lattice constant (as opposed to the average
lattice constant). Fourier analysis of the filtered image yields the vertical
and horizontal lattice constants at this location. The process is repeated by
stepping the Gaussian filter across the image to produce a set of local lattice
constants in the vertical and horizontal direction as a function of position in
the image. The method has been implemented in a freely available tool on
nanoHUB.
