Source of information: School of Physics

On May 27, 2020, Researcher Liu Kaihui, Academician Wang Enge of the School of Physics of Peking University, Academician Yu Dapeng of Southern University of Science and Technology, and Professor Ding Feng of the Ulsan Institute of Science and Technology in South Korea made important progress in the manufacturing of high-index single crystal copper foil. The research team creatively proposed the "variation and inheritance" growth mechanism regulated by the interface of the crystal surface, for the first time in the world to realize the manufacture of the most complete and largest size high-index single crystal copper foil library. Related research results were published online in the journal Nature with the title "Seeded growth of large single-crystal copper foils with high-index facets".

Copper plays an extremely important role in the modern information society and is widely used in key fields such as electrical, electronic, communications, and national defense. However, the commercial copper currently on the market is basically polycrystalline copper, and various defects in it cause the efficiency of electron and phonon transport to be greatly reduced. In theory, single-crystal copper with a perfect crystal structure can maximize the intrinsic electrical and thermal performance of copper, and it is expected to have an important impact in the direction of low-loss, high-heat dissipation power and electronic device applications. In addition, with the rise of two-dimensional material research in recent years, copper has been widely used in the epitaxial preparation of two-dimensional single crystal materials. A single crystal copper foil substrate with various index crystal planes is the basis for the epitaxial growth of two-dimensional single crystal materials with different structures. Therefore, the preparation of single crystal copper foil with large size and multiple index crystal planes is a scientific and technical problem to be solved urgently in industry and scientific research.

In materials science, single crystal copper foil can be divided into two categories according to the crystal plane index: low index crystal plane and high index crystal plane. As shown in Figure 1, there are only three types of low-index crystal planes: Cu (001), Cu (011), and Cu (111), while there are theoretically unlimited types of high-index crystal planes. Since 2016, Liu Kaihui and collaborators have made a series of progress in the research of low-index copper single crystals: ultra-fast epitaxial preparation of single-meter graphene single crystals on single crystal Cu(111) (Nature Chemistry 2019, 11 , 730; Science Bulletin 2017, 62, 1074; Nature Nanotechnology 2016, 11, 930); decimeter-scale two-dimensional hexagonal boron nitride single crystal epitaxy on the neighboring Cu(110) single crystal (Nature 2019, 570, 91 ). Compared with the low-index crystal plane, the high-index crystal plane copper foil can provide a richer surface structure, which can greatly broaden the types of epitaxial preparation of two-dimensional material systems. However, the traditional annealing method can usually only obtain the Cu(111) single crystal with the lowest surface energy, and the high-index crystal plane structure is not dominant in thermodynamics and kinetics, and its control preparation is extremely challenging.

In response to this problem, the research team developed a new annealing technology to achieve thermodynamic and kinetic control of the copper foil recrystallization process (Figure 2a). Different from the traditional annealing process, a layer of oxide can be formed on the surface of the copper foil through the designed pre-oxidation process. The formation of the interface between copper and copper oxide makes the traditional "minimum surface energy principle" no longer the main driving force for the formation of crystal planes. , So as to greatly increase the formation probability of high-index crystal plane "nucleus"; through the designed reducing atmosphere annealing process to eliminate the dynamic grain boundary, the abnormal growth of the high-index crystal plane "nucleus" can be achieved, thereby preparing A4 paper The size of the high-index crystal plane single crystal has more than 30 types of crystal planes (Figure 2b-c). At the same time, using the prepared single crystal copper foil as a "seed crystal" can induce the conversion of polycrystalline copper foil into a single crystal having the same crystal orientation as the "seed crystal", thereby realizing a large-size single crystal copper foil with a specific crystal plane Oriented "replication" manufacturing of single crystal copper ingots. In addition, this method is universal for the preparation of other single crystal metal foils.

This research achievement is the first to realize the controllable preparation of the single crystal copper foil library with the largest size and the most complete crystal face index in the world. In single crystal metal research, two-dimensional material growth, surface interface catalysis, low-loss electrical transmission, high frequency The fields of circuit boards and high heat sinks are of pioneering significance.

Wu Muhong, Zhang Zhibin, Xu Xiaozhi and Zhang Zhihong are the co-first authors of the paper, and Liu Kaihui, Ding Feng, Yu Dapeng and Wang Enge are the corresponding authors. The research results have been strongly supported by the Natural Science Foundation of China, the Ministry of Science and Technology, Beijing Science and Technology Commission and other related projects, Peking University State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Collaborative Innovation Center for Quantum Matter Science and Electron Microscope Laboratory, etc. .