Aberration Correction Based on Focus Modulation Transmission Electron Microscopy and its Applications

Three techniques of wave field reconstruction using focus modulation transmission electron microscopy are reviewed based on a fundamental concept of three-dimensional optical transfer properties. These techniques use a set of through-focus images for the processing and enable not only correction of spherical aberration but also separate imaging of the phase and amplitude components of the sample. Defocus-image modulation processing enables real-time correction of spherical aberration by combining techniques such as high-speed control of focus and high-speed image processing. Three-dimensional Fourier filtering enables correction of all Seidel aberrations including spherical aberration and higher-order aberrations with high signal-to-noise ratios. Dynamic hollow-cone illumination combined with image processing using Fourier filtering has the possibility of reducing the degradation of spatial resolution caused by chromatic aberration. Experimental data obtained by these methods are presented describing the inherent characteristics of the respective methods.