Peking University has developed a single-crystal layered high-dielectric material Bi2SeO5

On March 9, 2023, Professor Peng Hailin’s research team from the School of Chemical and Molecular Engineering of Peking University published a research paper entitled “Single-crystalline van der Waals layered dielectric with high dielectric constant” online in Nature Materials. A van der Waals layered high dielectric constant single crystal material Bi2SeO5 was reported.

Professor Peng Hailin of Peking University is the corresponding author of the paper, and the first authors include Zhang Congcong, Tu Teng, postdoctoral fellow Wang Jingyue of the School of Chemistry and Molecular Engineering of Peking University, Zhu Yongchao, a doctoral student jointly trained by Central South University in Peking University, and Jianbo Yin, a researcher at Beijing Graphene Research Institute/School of Electronics, Peking University.

High-performance dielectric materials have broad application prospects in electronics, electrical, energy conversion and dielectric energy storage. The development of advanced dielectric materials with high dielectric constant and high dielectric strength is attracting attention. In the field of new nanomaterials and electronic devices, hexagonal boron nitride (hBN), commonly known as “white graphite”, is widely used as electronic packaging materials and dielectric materials. hBN block single crystal can be dissociated into two-dimensional insulating materials due to its good electrical insulation and van der Waals layered structure, and as an atomic-level flat encapsulation and dielectric layer, it plays an important role in the exploration of various novel physical properties of two-dimensional materials. For example, important physical phenomena such as fractional quantum Hall effect, two-dimensional ferromagnetism, and two-dimensional superconductivity have been observed in hBN-encapsulated two-dimensional materials. However, the dielectric constant of hBN is low (κ ≈ 3.5), resulting in insufficient electric field regulation ability and weak coulomb shielding. More importantly, high-quality hBN bulk single crystals require harsh preparation conditions such as high temperature (> 1500 °C) and high pressure (about 40,000 atmospheres), slow growth rate, and the obtained single crystal size is small. At present, only a few research institutions can synthesize high-quality hBN bulk single crystals through high temperature and high pressure, which seriously limits its wide application. Therefore, it is of great significance to efficiently and conveniently prepare new layered single crystal dielectric materials with high dielectric constant.

Peng Hailin’s research group in the School of Chemistry and Molecular Engineering of Peking University developed a high-mobility two-dimensional semiconductor (Bi2O2Se) and its ultra-thin natural oxide gate medium Bi2SeO5 (Nature Nanotech. 2017, 12, 530; Nature Electron. 2020, 3, 473; Nature Electron. 2022, 5, 643)。 Recently, Peng Hailin’s research group reported an efficient and convenient preparation method for Bi2SeO5, a layered single crystal material with high dielectric constant. They prepared Bi2SeO5 layered large single crystals by chemical vapor transport with a transverse size of centimeters. The interlayer bonding force of Bi2SeO5 single crystal is weak, and large-area uniform and atomically flat nanosheets can be prepared by mechanical cleavage. Capacitance-voltage measurement combined with scanning probe microwave imaging technology shows that the room temperature permittivity of Bi2SeO5 two-dimensional single crystal is as high as 16.5, which is much higher than hBN. Electrical measurements show that Bi2SeO5 two-dimensional single crystal has high dielectric strength, and its breakdown field strength is as high as 10~30 MV/cm, which is better than hBN samples. Theoretical calculations also show that the strong ion polarization in high-quality layered Bi2SeO5 leads to both high dielectric constant and high breakdown field strength.

Figure 1: Structure and properties of Bi2SeO5 in a single crystal layered high κ-gate medium. (a) the crystal structure of layered Bi2SeO5; (b) Optical photograph of Bi2SeO5 cm single crystal prepared by gas phase transport method; (c) Optical photograph of mechanical cleavage of large-area Bi2SeO5 nanosheets; (d) Typical high-resolution transmission electron microscopy imaging of lamellar Bi2SeO5; (e) Dielectric constant and breakdown field strength of layered Bi2SeO5 and comparison with other common layered gate media.

Bi2SeO5 two-dimensional single crystal with high dielectric performance is used in electrical devices to obtain strong gate regulation ability. The research team used two-dimensional material transfer technology to construct a high-mobility two-dimensional semiconductor Bi2O2Se field-effect Hall device in Bi2SeO5 two-dimensional nanosheet packaging. Low-temperature quantum transport measurements show that the carrier mobility of the two-dimensional semiconductor Bi2O2Se is significantly improved by the packaging of Bi2SeO5, and the low-temperature Hall mobility is as high as 470000 cm2/Vs (the highest mobility of Bi2O2Se systems to date), and the quantum Hall effect of Bi2O2Se is observed for the first time. The two-dimensional single-crystal dielectric material Bi2SeO5 can not only be used as an ideal encapsulation material and gate medium for two-dimensional Bi2O2Se, but also suitable for other two-dimensional material systems, such as MoS2 and graphene.

Figure 2: Evaluation of encapsulation and gatekeeping capability of layered single-crystal Bi2SeO5 nanosheets. (a) Schematic diagram of electrical transport test devices; (b) Ultra-high Hall mobility of Bi2SeO5-encapsulated two-dimensional Bi2O2Se nanosheets; (c) Increased mobility of Bi2SeO5 package two-dimensional MoS2; (d) Comparison of the gate control ability of layered single crystal Bi2SeO5 and hBN.

The research and development of Bi2SeO5, a layered single crystal material with high dielectric properties, provides excellent packaging materials and gate dielectric materials for nanodevice research, which makes the carrier mobility and carrier concentration of two-dimensional materials highly controllable, and can effectively reduce the power consumption of two-dimensional transistors, which is of great significance in the development of micro-nano electronic devices in the future. In addition, the development of Bi2SeO5, a dielectric material with high dielectric constant and high dielectric strength, is expected to break through the dielectric bottleneck and achieve ultra-high energy storage density and efficiency. Therefore, the research and development of Bi2SeO5, a new layered single crystal material with high dielectric properties, has important basic scientific significance and application value.

The research collaborators also include Prof. Xiaosong Wu, Prof. Zhimin Liao, Prof. Peng Gao from the School of Physics, Prof. Qianqian Huang from the School of Integrated Circuits of Peking University, Prof. Binghai Yan from the Weizmann Institute of Science in Israel, Prof. Hai Xu and Prof. Hu Huiping from Central South University, and Prof. Keji Lai from the University of Texas at Austin.

The research has been supported by the National Natural Science Foundation of China, the Ministry of Science and Technology, the Beijing National Research Center for Molecular Science, the Tencent Foundation, the Peking University Liberal Arts Postdoctoral Fellow, and the instrumental platform of the Laboratory of Molecular Materials and Nanoprocessing (MMNL) of the School of Chemistry and Molecular Engineering of Peking University. (Source: Science Network)

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