Advanced Image Reconstruction for Electron Ptychography and Tomography
Abstract: Aberration-corrected optics have made electron microscopy a widespread and essential tool for 2D/3D material characterization at the atomic scale. The resolution of conventional imaging modes is fundamentally limited by the aperture size (α) and beam voltage, with state-of-the-art reaching just below 0.5 Å at 300 kV. By combining full-field ptychography and a new electron microscope pixel array detector, we recently increased the numerical aperture and spatial resolution beyond the limitation of the lens. At 80 kV beam voltage, our ptychographic reconstruction significantly improved image contrast of single-atom defects in MoS2 and achieved an information limit close to 5α, corresponding to a 0.39 Å Sparrow resolution. This technique has potential applications in low-dose imaging and extends to crystalline structures with strong dynamic scattering. In electron tomography (ET), traditional reconstruction often suffers from artifacts due to insufficient measurements and limited tilt range. Recently, optimization-based algorithms that utilize the notion of sparsity have shown potentials in improving reconstruction quality with reduced sampling. The second part of my talk will review several sparsity-exploiting algorithms and explore their limitations in ET.