Retrieval of material’s 3D structure using new phase-contrast STEM methods

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Phase-contrast imaging techniques applied for scanning transmission electron microscope (STEM) not only improve the efficiency of electron dose compared with conventional imaging modes, but also provide more possibilities to investigate nanomaterials. The techniques for phase-contrast imaging were proposed in the 1970s and have been developed in recent years. These phase-contrast imaging techniques are mainly classified in three categories: (a) differential phase contrast (DPC) preferred for investigating dislocations, the magnetic structure, or the electronic structure; (b) differentiated DPC (DDPC) preferred for measuring charge density distribution; (c) integrated DPC (IDPC) method for generating the potential map of the scanned sample surface. Most DPC-based methods cannot produce an isotropic contrast transfer function and are usually applied for investigating thin samples. We find the IDPC method promising and would like to improve the current IDPC mode for thickness-dependent study in this project. Furthermore, based on theoretical studies we plan to retrieve the inner structure of a thick sample from a minimum number of exposures by applying a pixelated detector in STEM. Combining the theoretical work with our dose-dependent study on (S)TEM imaging, we would like to develop an IDPC-based method to acquire the three-dimensional structure of a sample with the minimal input of electron dose and realize it experimentally.