Observation of crystal structures by image restoration in electron holography

Abstract

Off-axis electron holography has been applied to crystal structure images using digital image processing.Three important factors pertaining to the correction of aberrations in electron holography are:(1)interference fringes narrower than one third of the required resolution,(2)a Signal to Noise (S-N) ratio in the hologram which is high enough for high resolution reconstruction, and(3)the estimation of the amount of aberrations.We have obtained interference fringes with a spacing of below 0.03 nm , which is sufficient for a resolution of 0.1 nm in the reconstructed image. The S-N ratio depends on the instrument used to record the hologram and whether the specimen causes strong scattering or weak scattering.Some ways of estimating the amount of aberration have been proposed. Here we adopted an algorithm which involves minimizing the contrast of the reconsturcted image by optimizing the processing parameters (Cs and df), because it is applicable not only to weak phase objects but also to general phase objects and, in principle, only one hologram is needed to determiner the parameters.