三維原子分辨電子成像學之研發與應用

Development and Application of Electron Tomography at Atomic Resolution

此文章中，我們展示由像差修正之高分辨電子顯微鏡得到全息像進而重構材料表面形貌與內部三維原子結構的分析法。目前穿透式電子顯微鏡（transmission electron microscopy，TEM）因球面像差修正器（Cscorrector）的發展，其穿透式電子顯微影像已經能達到次埃（sub-Å）等級的空間解析度，進一步提升分析原子結構的能力。然而，傳統穿透式電子顯微鏡影像分析受限投影於二維尺度，無法真實反映待測樣品的形狀與結構，而材料性質又與原子間的排列及交互作用有關，因此電子顯微術發展的最終目標將扮演材料性質與材料結構的重要分析橋梁，而如何從二維影像找回材料之三維資訊是極為重要的課題，本文中以模擬的雙層石墨烯（bilayer graphene）、油酸單分子（oleic acid molecule）以及實驗的鍺奈米晶粒（Ge nanocrystal）、氧化鎂（MgO）晶粒與奈米金橋（nano Au bridge）全息像重構回三維原子結構為例。 In this article, we introduce an atomic resolution tomography method using electron holography reconstructed from Cs corrected electron microscope. This method is allowed for quantitative analysis of three-dimensional atomic structure and surface topography from only one projected direction. Recently, TEM has capability to analyze material with sub-Å resolution with a Cs corrector. However, the real structure in three dimensions(3D) and the whole shape of material still can not be directly revealed from electron micrographs due to the limitation of two dimensional projected image. Certainly, materials properties can be corrected with the atomic arrangement in three dimensions. The ultimate goal of electron microscopy is to act as a communication channel between structure and properties of materials. It is therefore a very important issue how to determine the atomic positions in three dimensions from two dimensional projected images. We demonstrated our methodology using the simulated exit wave functions of a bilayer graphene, oleic acid molecules and experimental cases including of Ge nano-crystal、 MgO and nano Au bridge.