Strain Analysis Using STEM Moiré Method
JEOL Ltd. EM business unit
Abstract: Strain measurement using a moiré fringe in scanning transmission electron microscopy (STEM) is reported. The moiré fringe in STEM arises as an interference fringe of a crystal lattice and a scanning raster, due to under-sampling effect. The moiré spacing is magnified with the factor determined by the ratio of the raster spacing with respect to crystal lattice spacing, when they are parallel. The width of the fringe is controllable, since we can arbitrarily select the spacing and direction of the raster. The strain map of the crystal is calculated with the phase shift of the moiré fringe. And the calculation is based on a phase analysis procedure developed for holography. The specimen drift compensation, using a non-strained reference region, was applied to improve the final accuracy. And the averaging of resulted multiple phase maps derived from moiré patterns was also applied to the final results to improve the accuracy. The accuracy of the strain map, examined with a non-strained Si crystal, was approximately 0.2 % in standard deviation of the strain map with a spatial resolution of several nanometers.
Key words: Moire, STEM, Strain, Phase analysis, strain device