基於單原子電子源之低能量同調電子繞射成像術

Abstract

在這項工作中，我們建造了一個使用單原子電子源的低能量同調電子繞射成像顯微鏡。它包括一個單原子場發射源，一組三極式的靜電透鏡、結合奈米尺度步進器的樣品台，和一個可前後移動之延遲線偵測器，使用此偵測器可以在樣品後方不同距離記錄繞射圖案。此顯微鏡的設計非常適合對3奈米厚度以下的極薄樣品進行成像。我們分析了其中用於聚焦電子束的非對稱三極式靜電透鏡，並以2千電子伏特的電子能量在樣品平面取得直徑為87奈米的聚焦束斑。利用此儀器，我們成功地記錄到對應0.62埃解析度的石墨烯樣品高角度繞射圖案，我們同時進行了數值模擬，並以此模擬結果與實驗結果進行比對。這項工作展示了操作電壓在1-10千伏時，同調電子繞射成像術在超薄二維材料、生物分子和奈米材料等方面的潛力。該儀器的最終目標是取得這些材料的高對比、原子解析度影像。

In this work, a transmission-type, low-kilovolt coherent electron diffractive imaging instrument was constructed. It comprised a single-atom field emitter, a triple-element electrostatic lens, a sample holder, and a retractable delay line detector to record the diffraction patterns at different positions behind the sample. It was designed to image materials thinner than 3 nm. We analyzed the asymmetric triple-element electrostatic lens for focusing the electron beams and achieved a focused beam spot of 87 nm on the sample plane at the electron energy of 2 kV. High-angle coherent diffraction patterns of a suspended graphene sample corresponding to (0.62 Å)-1 were recorded. The simulated results were calculated to compare with the experimental results. This work demonstrated the potential of coherent diffractive imaging of thin 2D materials, biological molecules, and nano-objects at voltage between 1-10 kV. The ultimate goal of this instrument is to achieve atomic resolution of these materials with high contrast and little radiation damage.