Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Tokyo 102-0076, Japan.
Nano Lett. 2023 Mar 8;23(5):1673-1679. doi: 10.1021/acs.nanolett.2c04048. Epub 2023 Feb 27.
Boron-based two-dimensional (2D) materials are an excellent platform for nanoelectronics applications. Rhombohedral boron monosulfide (r-BS) is attracting particular attention because of its unique layered crystal structure suitable for exploring various functional properties originating in the 2D nature. However, studies to elucidate its fundamental electronic states have been largely limited because only tiny powdered crystals were available, hindering a precise investigation by spectroscopy such as angle-resolved photoemission spectroscopy (ARPES). Here we report the direct mapping of the band structure with a tiny (∼20 × 20 μm) r-BS powder crystal by utilizing microfocused ARPES. We found that r-BS is a p-type semiconductor with a band gap of >0.5 eV characterized by the anisotropic in-plane effective mass. The present results demonstrate the high applicability of micro-ARPES to tiny powder crystals and widen an opportunity to access the yet-unexplored electronic states of various novel materials.
硼基二维（2D）材料是纳米电子学应用的理想平台。菱方硼单硫化物（r-BS）因其独特的层状晶体结构而备受关注，这种结构适合探索源于 2D 性质的各种功能特性。然而，由于只有微小的粉末晶体可用，因此对其基本电子态的研究在很大程度上受到限制，这阻碍了通过角分辨光电子能谱（ARPES）等光谱技术进行精确的研究。在这里，我们通过利用微聚焦 ARPES 直接绘制了微小（∼20×20μm）r-BS 粉末晶体的能带结构图。我们发现 r-BS 是一种 p 型半导体，具有>0.5eV 的带隙，其特点是各向异性的面内有效质量。本研究结果表明微 ARPES 对微小粉末晶体具有很高的适用性，并为探索各种新型材料尚未探索的电子态提供了机会。
