CHEMICAL SCIENCE

Beijing University of Aeronautics and Astronautics has achieved a new breakthrough in two-dimensional material synthesis methods


On September 30, 2022, the team of Professor Gong Yongji of Beihang University and the team of Professor Wu Kai of Peking University published a research result entitled “Flux-assisted growth of atomically thin materials” in the journal Nature Synthesis.

The research group broke through the limitations of traditional methods to synthesize two-dimensional materials, and adopted the melt-assisted precipitation method to efficiently and controllably realize the synthesis of nearly 100 kinds of ultra-thin nanosheet materials, including complex multi-layered or non-layered ultra-thin two-dimensional single crystal materials that cannot be synthesized by traditional methods. The corresponding authors of the paper are Gong Yongji and Wu Kai; The first authors are Zhang Peng, Wang Xingguo, and Jiang Huaning.

Two-dimensional materials have attracted a lot of attention in recent years due to their special physical and chemical properties. In particular, these atomically thin materials provide an ideal platform for exploring catalytic, magnetic, superconductive, and topological properties at the two-dimensional limit level. Therefore, the controllable preparation of high-quality two-dimensional materials has become a prerequisite for its application in the electronics and information industries. Chemical vapor deposition (CVD) and mechanical stripping (ME) have been widely used in the preparation of various ultra-thin materials, but these methods are currently facing increasing challenges. The characteristics of CVD fumed phase reaction determine that when preparing multi-element materials, uneven gas phase distribution often leads to phase separation, so it is difficult to control the synthesis of complex multi-dimensional materials. In addition, for non-layered materials with some special properties, due to the high surface energy of the material or the strong bonding energy between the crystal planes, it can neither be synthesized by CVD, nor can it be mechanically peeled off by ME.

In view of this, in order to break through the limitations of traditional methods of synthesizing two-dimensional materials, the team of Professor Gong Yongji of Beijing University of Aeronautics and Astronautics, together with the team of Professor Wu Kai of Peking University, proposed a new, simple, powerful and efficient universal strategy for melt-assisted growth of two-dimensional materials. This method uses the melt precipitation process of classical growth single crystals supplemented by spatial limitation domains to successfully prepare a series of ultra-thin two-dimensional single crystals, including layered or non-layered, oligoprimal or multivariate two-dimensional single crystals. In addition, this method also shows the potential of preparing two-dimensional single crystal thin films. Different from the vapor deposition method, the melt precipitation method has the advantages of high efficiency and stability, controllable components and high repeatability. In particular, this method has a high tolerance to external growth conditions such as temperature, airflow size, number of precursors, etc.

Figure 1: a-d. Melt-assisted precipitation process and growth mechanism. e-h. Fe5GeTe2 and AgCrS2 repeat rate and thickness distribution statistics and condition tolerance.

The melt-assisted growth method has a high reproducibility rate and high tolerance to growth conditions. The growth repeat rate of two-dimensional materials, represented by Fe5GeTe2 and AgCrS2, is close to 100%, about 98%. In addition, the size of the growth gas flow can vary from 50 to 500 sccm, and the growth temperature range can reach close to 200 °C, showing the superiority of the melt auxiliary method.

Figure 2: Synthesized 80 ultra-thin two-dimensional single crystals and representative large-size single crystal and centimeter-level thin films.

The melt-assisted growth method is universal. Using the melt-assisted precipitation method, 80 representative ultra-thin two-dimensional single crystals were successfully prepared. These include layered and non-layered, oligoprimal and multivariate and large-size single crystal and thin film two-dimensional materials. In particular, non-layered materials represented by CuCrTe2, FeGe, BiFeO3, etc., are difficult to be synthesized by CVD or mechanically peeled off. The uniqueness and superiority of melt-assisted growth method are fully demonstrated.

Figure 3: Structure and scale analysis of representative materials Fe3GeTe2, Fe5GeTe2, MnPS3, and CuInP2S6.

The ratio of two-dimensional single crystal for melt precipitation is accurate and the performance is excellent. The test results of spherical electron microscopy show that the crystallization properties of the material are good and the proportion of elements is accurate. PFM test results prove that the growing ultra-thin In2Se3 has obvious ferroelectric properties, which can be compared with mechanically stripped In2Se3 nanosheets. The NbSe2 superconductivity test results are comparable to CVD and mechanically stripped NbSe2 two-dimensional sheets, indicating the excellent crystallinity of melt-precipitated samples.

Figure 4: Characterization of In2Se3 ferroelectric properties and NbSe2 superconductivity.

This study proposes a new universal method that is different from the traditional synthesis of two-dimensional materials, paving the way for the synthesis of more complex multi-dimensional materials, non-layered two-dimensional materials and large-sized thin films. (Source: Science Network)

Related Paper Information:https://doi.org/10.1038/s44160-022-00165-7



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