Peking University, May 22, 2019: A team of Peking University researchers including Liu Kaihui, Yu Dapeng, Wang Enge and their collaborators have published their latest discovery entitled “Epitaxial growth of a 100-square-centimetre single-crystal hexagonal boron nitride monolayer on copper” on Nature. In the paper, the growth of a large single-crystal hexagonal boron nitride (hBN) monolayer film on symmetry-broken substrate has been reported for the first time, whose growth mechanism is expected to be universal and can be applied to the synthesis of large-area single crystals of other two-dimensional (2D) materials in general.
It is well known that materials are the very foundation for the development of modern high-tech industries. Various advanced devices based on silicon have led the revolution of information industry, which impacts on the international politics and economics to a great extent. In recent years, with the continuous decrease of key circuit component size, the short channel effect, thermal effect, etc. have taken place and obstructed the further development of microelectronics engineering. Thus, searching on brand new quantum material family has become a research focus nowadays, to realize the breakthrough for future devices. As a significant representative, 2D materials possess atomic thickness, perfect surface and interface, excellent physical properties, including conductors (graphene), semiconductors (transition metal dichalcogenides, black phosphorus, etc.), and insulators (hBN), which are highly promising towards future revolutionary technology. As highly-integrated and high-end devices require the large-area, high-quality single-crystal materials, the preparation of 2D single-crystal materials has been under urgent pursuit both in scientific and technological communities.
Epitaxial growth of large-area, high-quality 2D single-crystal materials on single-crystal substrate has always been a hot topic in nanotechnology research but of enormous challenges. In 2017, for the first time in the world, the same PKU research team and their collaborators reported the preparation of meter-sized single-crystal Cu (111) and according epitaxial growth of single-crystal graphene on it (Science Bulletin 2017, 62, 1074). Dissimilar to graphene, most other 2D materials such as hBN have the lattice without central inversion symmetry, which leads to twin grain boundary problems during the epitaxial growth. Specifically, there are two equivalent orientations (with rotation angle of 180°) of hBN domains on ordinary single-crystal substrates, and defective grain boundaries would be generated during the coalescence of which.
The key to solve this problem is to find a single-crystal substrate with suitable surface symmetry, and Prof Kaihui Liu’s team and their collaborators just did it. By using the patented method, the industrial polycrystalline copper foil was first annealed into single-crystal Cu (110) with a small-angle inclined (which is commonly known as the “vicinal surface”), with only C1 symmetry on the surface. The coupling between Cu<211> step edge and zigzag-edge of hBN domain with different termination (B- or N-) has different formation energy, which break the equivalence of lattice orientation between hBN domains with rotation angle of 180°. Thereby, unidirectionally aligned hBN domains have been obtained and then seamless stitched into an entire piece of single crystal with large area and high quality. Such method can be broadly extended to the epitaxial growth of other large-area 2D single crystals, and is expected to establish the materials foundation for the high-tech applications based on new 2D materials.
Figure. Realization and mechanism of epitaxial growth of single-crystal hBN on vicinal Cu (110)
Wang Li, Xu Xiaozhi, Zhang Leining, and Qiao Ruixi are the co-first authors of the paper; Liu Kaihui, Ding Feng (Ulsan National Institute of Science and Technology), Wang Zhujun (Eidgenössische Technische Hochschule in Zürich), and Bai Xuedong (Institute of Physics, Chinese Academy of Sciences) are the corresponding authors of the paper. The research projects have been supported by the Ministry of Science and Technology, the National Natural Science Foundation of China, the Beijing Municipal Science and Technology Commission, the Quantum Materials Science 2011 Collaborative Innovation Center, the State Key Laboratory of Artificial Microstructures and Mesoscopic Physics, and the Electron Microscopy Laboratory of Peking University, etc..
Edited by: Zhang Jiang
Source: School of Physics
