抄録
Introduction : Two-dimensional (2D) materials show unique properties such as unique electronic states and a large surface area. Therefore, they have potential applications in the development of superior electronic devices and catalysts. Among them, rhombohedral boron sulfide (r-BS) is a nonmetallic layered material composed of boron and sulfur that has been experimentally shown to exhibit excellent performance as an OER catalyst when mixed with graphene [1]. In addition to this, r-BS is theoretically predicted to exhibit excellent thermal conductivity [2] and high hydrogen storage performance via alkali modification [3]. It has also been shown experimentally that r-BS can be easily exfoliated from the bulk into nanosheets and that its band gap depends on the number of layers [4]. These properties make r-BS promising for applications. On the other hand, it is not yet clear experimentally which type of carrier properties r-BS exhibits as a semiconductor. The purpose of this study is to synthesize r-BS and evaluate its carrier properties by measuring Seebeck coefficient and electrochemical measurements using photocurrent.
Method : Powdered amorphous boron and sulfur were mixed at an atomic ratio of 1 : 1 and formed into pellets. The sample pellets were then packed into an h-BN cell, and high-pressure synthesis was conducted using a belt-type high-pressure synthesis apparatus at 5.5 GPa and 1873 K for 40 minutes. After synthesis, the cell was quenched and sample was taken from the cell. The sample was used to evaluate the structure by X-ray diffraction measurements, and its carrier properties were evaluated by Seebeck coefficient measurements and linear sweep voltammetry (LSV) using the sample as an electrode.
Result : X-ray diffraction results show that the peaks shown by the obtained sample indicate that the synthesized sample is r-BS single-phase. The measured Seebeck coefficient was in the range of 500~520 μV/K, suggesting that the r-BS carrier is a hole. In addition, a p-type rectification profile was observed in the LSV in the dark condition (Figure). The current was larger for the positive bias condition because the holes contributed to the current, while the photo-electrochemical current was more pronounced for the negative bias condition. These results indicate that r-BS is a material with p-type semiconductor properties.
Conclusion : In this study, we synthesized r-BS and clarified its physical properties by measurement. Specifically, the Seebeck coefficient and LSV results indicate that r-BS is a p-type semiconductor. Details of other measured properties will be discussed on the presentation day.
References:
[1] L. Li, et al., Chemical Engineering Journal 471 (2023) 144489.
[2] P. Mishra, et al., Sustain. Energy Fuels 4 (2020) 2363-2369.
[3] P. Mishra, et al., J. Appl. Phys. 123 (2018) 135903.
[4] H. Kusaka, et al., J. Mater. Chem. A 9 (2021) 24631-24640.
