On August 7, the international academic journal "Science" published online the latest progress in new two-dimensional materials by the Advanced Carbon Materials Research Department of the National Research Center for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, "Layered two-dimensional MoSi2N4 materials "Chemical vapor deposition of layered two-dimensional MoSi2N4 materials".
Two-dimensional van der Waals layered materials represented by graphene have unique electrical, optical, mechanical, thermal and other properties, and have broad application prospects in the fields of electronics, optoelectronics, energy, environment, aerospace and other fields. Currently widely studied two-dimensional layered materials, such as graphene, boron nitride, transition metal chalcogenides, black phosphorene, etc., all have known three-dimensional matrix materials. The exploration of two-dimensional layered materials without known three-dimensional matrix materials can greatly expand the physical properties and applications of two-dimensional materials, which has important scientific significance and practical value.
In 2015, the team of Ren Wencai and Cheng Huiming of the Shenyang National Research Center for Materials Science of the Institute of Metals invented the bimetal substrate chemical vapor deposition (CVD) method to prepare a variety of non-layered two-dimensional transition metal carbide crystals with different structures. Such as orthogonal Mo2C, hexagonal WC and cubic TaC, and found that ultra-thin Mo2C is a two-dimensional superconductor (Nature Materials, 2015). However, constrained by surface energy, non-layered materials rich in surface dangling bonds tend to grow in islands, so it is difficult to obtain a single layer material with uniform thickness.
The team recently discovered that in the process of growing non-layered two-dimensional molybdenum nitride by CVD, the introduction of silicon can passivate the dangling bonds on the surface, thereby preparing a new two-dimensional van der Waals layer without known parent materials. Shape material MoSi2N4, and obtained centimeter-level single-layer film. A single layer of MoSi2N4 contains 7 atomic layers of N-Si-N-Mo-N-Si-N, which can be seen as a single layer of MoN (N-Mo-N) sandwiched between two Si-N layers. Using a similar method, a single layer of WSi2N4 was also prepared.
On this basis, they cooperated with the Chen Xingqiu research group and Sun Dongming research group of the Institute of Metals and found that the single-layer MoSi2N4 has semiconducting properties (band gap is about 1.94 eV) and the theoretical carrier mobility is better than that of MoS2. The mechanical strength and stability of single-layer semiconductor materials such as MoS2; and more than a dozen two-dimensional layered materials with the same structure as single-layer MoSi2N4 have been predicted through theoretical calculations, including semiconductors, metals and magnetic semi-metals with different band gaps. .
This work has not only opened up a new family of two-dimensional layered MoSi2N4 materials, expanded the physical properties and applications of two-dimensional materials, but also opened up the research direction of preparing new two-dimensional van der Waals layered materials, providing more new two-dimensional materials New ideas.