Ambipolar two-dimensional bismuth nanostructures in junction with bismuth oxychloride
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Ambipolar two-dimensional bismuth nanostructures in junction with bismuth oxychloride Xianzhong Yang§, Shengnan Lu§, Jun Peng, Xiangchen Hu, Nan Wu, Congcong Wu, Chao Zhang, Yifan Huang, Yi Yu, and Hung-Ta Wang () School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China § Xianzhong Yang and Shengnan Lu contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 20 August 2020 / Revised: 23 September 2020 / Accepted: 30 September 2020
ABSTRACT Despite the unique properties of bismuth (Bi), there is a lack of two-dimensional (2D) heterostructures between Bi and other functional 2D materials. Here, a coherent strategy is reported to simultaneously synthesize rhombohedral phase Bi nanoflakes and bismuth oxychloride (BiOCl) nanosheets. The delicate balance between several reactions is mediated mainly for the reduction and chlorination in the chemical vapor transport (CVT) process. The Bi-BiOCl lateral heterostructures have been constructed via the coalescence of the two different 2D nanostructures. The characteristics of ambipolar conducting Bi and insulator-like BiOCl are elaborated by scanning microwave impedance microscopy (sMIM). This work demonstrates a way to construct a 2D Bi nanostructure in junction with its oxyhalide.
KEYWORDS Bi, ambipolar, BiOCl, chemical vapor transport, nanostructures
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Introduction
Two-dimensional (2D) materials of Group-15 elements have remarkable physical and chemical properties [1–3]. For instance, black phosphorus monolayer is complementary to graphene and molybdenum disulfide (MoS2) monolayer because of its direct bandgap and carrier mobility [4]. As the last and heaviest pnictogen, bismuth (Bi) is a prototypical semimetal with highly-anisotropic and tiny Fermi surfaces, providing peculiar properties such as the suppressed carrier concentration, the small effective mass, and the long carrier mean free path [5–7]. By scaling down the dimension of Bi to a few tens of nanometers or less, several intriguing physical phenomena were observed, including semimetal-to-semiconductor transition [8, 9], enhanced magnetoresistance [10], quantum Hall effect [7], etc. Recent attention has been focused on its non-degenerate edge states and surface states [11, 12], strain-induced bandgap opening [13], and homojunctions of its two different crystal phases [14]. For advances in electronics and other device-level applications, it is essential to construct a 2D Bi nanostructure in junction with another functional 2D material [15–17]. Although various Bi nanostructures are available, Bi-associated heterojunction is currently lacking. One of the reasons is that Bi epitaxial growth is complex. Bi owns multiple crystal phases [18–20]; even the most stable rhombohedral phase has a few polytypes [21]. A further complication is the low melting point, ~ 271 C. Thus, it often requires a sophisticated system for the epitaxy. For example, molecular beam epitaxy [13, 14] and thermal evaporation in ultr
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