Li Huanhuan, Zhao Ruiqi
Henan Key Laboratory of Materials on Deep-Earth Engineering, School of Materials Science and Engineering, Henan Polytechnic University, Henan 454003, China.
Phys Chem Chem Phys. 2022 May 25;24(20):12226-12235. doi: 10.1039/d1cp05957b.
The chemical vapor deposition method is widely used in preparation of graphene, hexagonal boron nitride (h-BN) and other 2D materials. To improve the quality of h-BN, it is essential to learn details of the growth mechanism including dissociation of precursors, the initial nucleation, the stabilities of various clusters and the origins behind them. Here, the dissociation process of ammonia borane (AB) and its later nucleation on the Ru(0001) surface were simulated with density functional theory. The results show that the key step before dissociation is the chemical adsorption of AB molecule on the Ru(0001) surface. In the approaching process of AB molecule to Ru(0001), all bonds connected with H, irrespective of B-H or N-H, are stretched by the underlying metal surface. The H atoms connected with boron prefer to be dissociated followed by those connected to nitrogen. After full dehydration, BN dimer accumulates by forming chain-like, ring-shaped and honeycomb clusters. The chain-like geometries are energy-favoured in BN clusters with size lower than 6. Beyond this, the honeycomb configuration becomes the energy-favoured one, resulting in a geometry evolution from chain-like to honeycomb. The nucleation barrier and the critical nuclei size of BN clusters on Ru(0001) at different chemical potentials are discussed, which can be realized by tuning ratios of B to N in the feedstock. The growth mode observed for h-BN on Ru(0001) can be easily extended to growth on other transition metals and other 2D materials, thus should provide important information in optimizing experimental schemes.
化学气相沉积法广泛应用于石墨烯、六方氮化硼（h-BN）及其他二维材料的制备。为提高h-BN的质量，了解生长机制的细节至关重要，包括前驱体的解离、初始成核、各种团簇的稳定性及其背后的原因。在此，采用密度泛函理论模拟了氨硼烷（AB）在Ru(0001)表面的解离过程及其随后的成核过程。结果表明，解离前的关键步骤是AB分子在Ru(0001)表面的化学吸附。在AB分子靠近Ru(0001)的过程中，与H相连的所有键，无论B-H键还是N-H键，均受到底层金属表面的拉伸。与硼相连的H原子比与氮相连的H原子更倾向于解离。完全脱水后，BN二聚体通过形成链状、环状和蜂窝状团簇而聚集。在尺寸小于6的BN团簇中，链状结构在能量上更有利。超过这个尺寸，蜂窝状结构成为能量有利的结构，导致几何结构从链状向蜂窝状演变。讨论了不同化学势下Ru(0001)表面BN团簇的成核势垒和临界核尺寸，这可以通过调整原料中B与N的比例来实现。在Ru(0001)上观察到的h-BN生长模式可以很容易地扩展到在其他过渡金属和其他二维材料上的生长，因此应为优化实验方案提供重要信息。
