Fresnel effect in high-resolution TEM imaging of small particles

Abstract

It is established that analysis of Fresnel contrast visible at the edges of nanoparticles in the high resolution electron microscope provides a valuable tool for determining the size of the particles with near atomic spacing accuracy.Methods based on the Fresnel effect are enjoying increased use in the study of flat precipitates, multilayers, and grain boundaries. In profile imaging studies of solid surfaces, Fresnel effects have been observed by Marks, and by O'Keefe et al. who showed that image structure within Fresnel fringes from MgO cubes can produce “ghost” atoms far outside the specimen surface. However, consequences of the Fresnel effect appear not to have been included in the study of small particles at atomic resolution. In this work, we have used HRTEM image simulation to explore the changes in images of a nanoparticle under various imaging conditions, in particular to relate the model particle size and its apparent size as derived from the HRTEM image.