Robertson Alex W, Lee Gun-Do, Lee Sungwoo, Buntin Parker, Drexler Matthew, Abdelhafiz Ali A, Yoon Euijoon, Warner Jamie H, Alamgir Faisal M
Department of Materials , University of Oxford , Parks Road , Oxford , OX1 3PH , United Kingdom.
Department of Materials Science and Engineering , Seoul National University , Gwanak-gu , Seoul 08826 , South Korea.
ACS Nano. 2019 Oct 22;13(10):12162-12170. doi: 10.1021/acsnano.9b06701. Epub 2019 Sep 26.
Platinum atomic layers grown on graphene were investigated by atomic resolution transmission electron microscopy (TEM). These TEM images reveal the epitaxial relationship between the atomically thin platinum layers and graphene, with two optimal epitaxies observed. The energetics of these epitaxies influences the grain structure of the platinum film, facilitating grain growth in-plane rotation and assimilation of neighbor grains, rather than grain coarsening from the movement of grain boundaries. This growth process was enabled due to the availability of several possible low-energy intermediate states for the rotating grains, the Pt-Gr epitaxies, which are minima in surface energy, and coincident site lattice grain boundaries, which are minima in grain boundary energy. Density functional theory calculations reveal a complex interplay of considerations for minimizing the platinum grain energy, with free platinum edges also having an effect on the relative energetics. We thus find that the platinum atomic layer grains undergo significant reorientation to minimize interface energy ( epitaxy), grain boundary energy ( low-energy orientations), and free edge energy. These results will be important for the design of two-dimensional graphene-supported platinum catalysts and obtaining large-area uniform platinum atomic layer films and also provide fundamental experimental insight into the growth of heteroepitaxial thin films.
利用原子分辨率透射电子显微镜（TEM）对生长在石墨烯上的铂原子层进行了研究。这些TEM图像揭示了原子级超薄铂层与石墨烯之间的外延关系，观察到了两种最佳外延情况。这些外延的能量学影响铂膜的晶粒结构，促进晶粒在平面内生长、旋转以及相邻晶粒的同化，而不是由晶界移动导致的晶粒粗化。由于旋转晶粒存在几种可能的低能中间态，即表面能最小的Pt-Gr外延以及晶界能最小的共格位错晶格晶界，使得这种生长过程得以实现。密度泛函理论计算揭示了为使铂晶粒能量最小化而进行的各种考虑之间的复杂相互作用，自由铂边缘也对相对能量学有影响。因此，我们发现铂原子层晶粒会发生显著的重新取向，以最小化界面能（外延）、晶界能（低能取向）和自由边缘能。这些结果对于二维石墨烯负载铂催化剂的设计以及获得大面积均匀的铂原子层薄膜具有重要意义，同时也为异质外延薄膜的生长提供了基本的实验见解。
