Quasi-two-dimensional NaCl crystals encapsulated between graphene sheets and their decomposition under an electron beam.
Quasi-two-dimensional NaCl crystals encapsulated between graphene sheets and their decomposition under an electron beam.
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DOI：
10.1039/d1nr04792b
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发表时间：
2021-11
期刊：
影响因子：
6.7
通讯作者：
T. Lehnert;S. Kretschmer;Fredrik Bräuer;A. Krasheninnikov;U. Kaiser
中科院分区：
文献类型：
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作者：
T. Lehnert;S. Kretschmer;Fredrik Bräuer;A. Krasheninnikov;U. Kaiser
采用生理盐水溶液过饱和法制备了石墨烯片间不同横向尺寸的准二维氯化钠（NaCl）晶体。用像差校正透射电子显微镜对晶体及其在80kv电子束下的分解进行了系统的原位研究。与直觉相反的是，更大的团簇在电子照射下分解得更快，但通常没有发现晶体尺寸和晶体分解的电子剂量之间的相关性。在破坏过程中，观察到晶体的突然分解，这可以用logistic衰减函数来描述。密度泛函理论分子动力学模拟提供了对破坏机制的深入了解，并表明即使不考虑电离和电子激发，由于原子在成像过程中从表面和边缘的弹道位移，独立的NaCl晶体也必须快速分解。然而，石墨烯片通过阻止移位的原子来减轻损伤的发展，并使晶体表面的缺陷能够立即重新组合。与此同时，一旦石墨烯中出现空穴，位移的原子就会逃逸，导致晶体迅速破坏。我们的研究结果提供了电子辐照下封装准二维NaCl晶体稳定性的定量数据，并允许在电子显微镜研究中得出只有高质量石墨烯适合用于保护离子晶体免受束损伤的结论。
Quasi-two-dimensional (2D) sodium chloride (NaCl) crystals of various lateral sizes between graphene sheets were manufactured via supersaturation from a saline solution. Aberration-corrected transmission electron microscopy was used for systematic in situ investigations of the crystals and their decomposition under an 80 kV electron beam. Counterintuitively, bigger clusters were found to disintegrate faster under electron irradiation, but in general no correlation between crystal sizes and electron doses at which the crystals decompose was found. As for the destruction process, an abrupt decomposition of the crystals was observed, which can be described by a logistic decay function. Density-functional theory molecular dynamics simulations provide insights into the destruction mechanism, and indicate that even without account for ionization and electron excitations, free-standing NaCl crystals must quickly disintegrate due to the ballistic displacement of atoms from their surface and edges during imaging. However, graphene sheets mitigate damage development by stopping the displaced atoms and enable the immediate recombination of defects at the surface of the crystal. At the same time, once a hole in graphene appears, the displaced atoms escape, giving rise to the quick destruction of the crystal. Our results provide quantitative data on the stability of encapsulated quasi 2D NaCl crystals under electron irradiation and allow the conclusion that only high-quality graphene is suitable for protecting ionic crystals from beam damage in electron microscopy studies.