Reconstructing Lattice Vibrations of Crystals with Electron Ptychography

Abstract: While capable of imaging the atoms constituting thin slabs of material, the achievable resolution of conventional electron imaging techniques in a transmission electron microscope (TEM) is very sensitive to the partial spatial coherence of the electron source, lens aberrations and mechanical instabilities of the microscope. The desire to break free from the limitations of the apparatus spurred the popularity of ptychography, a computational phase retrieval technique that, to some extent, can compensate for the imperfections of the equipment. Recently it was shown that ptychography is capable of resolving specimen features as fine as the blurring due to the vibrations of atoms, a limit defined not by the microscope, but by the investigated sample itself. Here we report on the successful application of a mixed-object formalism in the ptychographic reconstruction that enables the resolution of fluctuations in atomic positions within real space. We show a reconstruction of a symmetric {\Sigma}9 grain boundary in silicon from realistically (molecular dynamics) simulated data. By reconstructing the object as an ensemble of 10 different states we were able to observe movements of atoms in the range of 0.1-0.2 \AA in agreement with the expectation. This is a significant step forward in the field of electron ptychography, as it enables the study of dynamic systems with unprecedented precision and overcomes the resolution limit so far considered to be imposed by the thermal motion of the atoms.