Niefind Falk, Mao Qian, Nayir Nadire, Kowalik Malgorzata, Ahn Jung-Joon, Winchester Andrew J, Dong Chengye, Maniyara Rinu A, Robinson Joshua A, van Duin Adri C T, Pookpanratana Sujitra
Nanoscale Device Characterization Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA.
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD, 20742, USA.
Small. 2024 Mar;20(11):e2306554. doi: 10.1002/smll.202306554. Epub 2023 Nov 2.
Intercalation forms heterostructures, and over 25 elements and compounds are intercalated into graphene, but the mechanism for this process is not well understood. Here, the de-intercalation of 2D Ag and Ga metals sandwiched between bilayer graphene and SiC are followed using photoemission electron microscopy (PEEM) and atomistic-scale reactive molecular dynamics simulations. By PEEM, de-intercalation "windows" (or defects) are observed in both systems, but the processes follow distinctly different dynamics. Reversible de- and re-intercalation of Ag is observed through a circular defect where the intercalation velocity front is 0.5 nm s ± 0.2 nm s. In contrast, the de-intercalation of Ga is irreversible with faster kinetics that are influenced by the non-circular shape of the defect. Molecular dynamics simulations support these pronounced differences and complexities between the two Ag and Ga systems. In the de-intercalating Ga model, Ga atoms first pile up between graphene layers until ultimately moving to the graphene surface. The simulations, supported by density functional theory, indicate that the Ga atoms exhibit larger binding strength to graphene, which agrees with the faster and irreversible diffusion kinetics observed. Thus, both the thermophysical properties of the metal intercalant and its interaction with defective graphene play a key role in intercalation.
嵌入形成异质结构，超过25种元素和化合物被嵌入到石墨烯中，但这一过程的机制尚未得到很好的理解。在此，利用光发射电子显微镜（PEEM）和原子尺度的反应分子动力学模拟，对夹在双层石墨烯和SiC之间的二维Ag和Ga金属的脱嵌过程进行了跟踪研究。通过PEEM，在两个系统中都观察到了脱嵌“窗口”（或缺陷），但过程遵循明显不同的动力学。通过一个圆形缺陷观察到Ag的可逆脱嵌和再嵌入，其中嵌入速度前沿为0.5 nm/s±0.2 nm/s。相比之下，Ga的脱嵌是不可逆的，其动力学更快，受缺陷的非圆形形状影响。分子动力学模拟支持了Ag和Ga这两个系统之间的这些显著差异和复杂性。在脱嵌的Ga模型中，Ga原子首先堆积在石墨烯层之间，直到最终移动到石墨烯表面。由密度泛函理论支持的模拟表明，Ga原子对石墨烯表现出更大的结合强度，这与观察到的更快且不可逆的扩散动力学一致。因此，金属嵌入剂的热物理性质及其与缺陷石墨烯的相互作用在嵌入过程中都起着关键作用。
