Abstract
Coherent diffractive imaging (CDI) is a new technique for the structural analysis of materials at a resolution limited by the wavelength of the radiation involved. Due to the strong interaction of electrons with matter and short de Broglie wavelength of electrons, electron CDI offers, in principle, atomic-scale resolution of nano-objects in coherent diffraction experiments. In addition, for nanocrystals, coherent diffraction in Bragg geometry allows for the recovery of a three-dimensional (3D) structure of the sample using an angular range of crystal tilt within a few degrees. In this thesis, a detailed theoretical and experimental investigation of the electron CDI technique is presented. The well-known nanocrystals of MgO smoke were used as a test nano-object. For diffraction experiments, we used a highly coherent illumination from a field-emission gun as a source of electrons. In our data analysis, we developed an algorithm to reconstruct a complex exit wave from the electron diffraction pattern alone. Results of the two-dimensional (2D) CDI reveal a crystal lattice with 0.15 nm resolution using Bragg reflections, and characterize the crystal boundary with a resolution of about 3 nm using diffuse scattering measured in the vicinity of the Bragg peak. In 3D electron CDI, we, for the first time, experimentally determined the morphology of a single MgO nanocrystal using Bragg diffraction geometry. The iterative algorithm developed was applied to invert the 3D diffraction pattern about a (200) reflection of the nanoparticle measured at an angular range of 1.8º, which revealed a 3D image of the sample at about 8-nm resolution. Computer simulations verified the results of 2D and 3D reconstructions. The described technique offers a powerful way to image crystals, disordered materials and biological samples of nanometer size with atomic-scale resolution