Abstract
Finding the structure of nanocrystals to atomic scale can provide a greater understanding of the properties of nano-materials which may realize in many different applications. It has been widely studied that high resolution transmission electron microscope (HRTEM) can provide the information to a finer scale. However, atomic resolution tomography has not yet proposed. Electrons interact with atoms strongly which cause hundreds of diffractions simultaneously resulting in multiple scattering. Therefore, the exit wave function does not reveal the structure information exactly. Dynamical scattering in the crystal can be described from the multislice theory and the channelling theory. The multislice theory presents the electrons are transmitted through a set of N two dimensional phase- and amplitude-objects in equal separation distances. The channelling theory derives the motion of electrons passing through an atom column in real space. This motion can be fairly expressed only by the most bound state of the electrons. This thesis discusses the potential of structure reversion from exit wave based on the two methods: reverse multislice method and reverse channelling method. From the reverse multislice method, it is intended to find the number of slices of atomic planes perpendicular to the incident electron beam direction. The reverse channelling method is mainly retrieving the thickness and the bound eigenenergy of the atom column. These two methods apply to analyze the number of atoms in every atom column and to distinguish chemically the different elements. Both methods are tested with a simulated wedge-shaped crystal NiSi2 and an experimental SrTiO3 [110] exit wave. The results show that these two methods can effectively determine the number and the type of the atoms. A primary concept of discrete tomography is introduced. At the atomic level materials are made out of a discrete set of atoms. By representing the structure projection information as matrices, atomic resolution tomography can be obtained.