Growth of 2D MoP single crystals on liquid metals by chemical vapor deposition
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Published online 13 November 2020 | https://doi.org/10.1007/s40843-020-1521-0
Growth of 2D MoP single crystals on liquid metals by chemical vapor deposition 1
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Feifei Cao , Shuting Zheng , Jingjing Liang , Zhi Li , Bin Wei , Yiran Ding , Zhongchang Wang , 2* 1* 1,2* Mengqi Zeng , Nan Xu and Lei Fu ABSTRACT Two-dimensional (2D) transition metal phosphides (TMPs) are predicted with many novel properties and various applications. As a member of TMPs family, molybdenum phosphide (MoP) exhibits many exotic physicochemical properties. However, the synthesis of high-quality 2D MoP single crystals is not reported due to the lack of reliable fabrication method, which limits the exploration of 2D MoP. Here, we report the growth of high-quality ultrathin MoP single crystals with thickness down to 10 nm on liquid metals via chemical vapor deposition (CVD). The smooth surface of liquid Ga is regarded as a suitable growth substrate for producing 2D MoP single crystals. The Mo source diffuses toward the Ga surface due to the high surface energy to react with phosphorus source, thus to fabricate ultrathin MoP single crystals. Then, we study the second harmonic generation (SHG) of 2D MoP for the first time due to its intrinsic noncentrosymmetric structure. Our study provides an new approach to synthesize and explore other 2D TMPs for future applications. Keywords: 2D materials, transition metal phosphides, molybdenum phosphides, liquid metals, chemical vapor deposition
INTRODUCTION Researches in two-dimensional (2D) materials have increasingly grown triggered by pioneering studies on graphene [1–4]. As an emerging family of 2D materials, 2D transition metal phosphides (TMPs) are predicted with novel properties, which are appealing for many applications, including optical, thermal insulating materials, magnetic material and catalysts [5,6]. Thus the reliable synthesis of 2D TMPs is highly demanded.
As a member of TMPs family, molybdenum phosphide (MoP) exhibits many exotic properties with the presence of novel three-component fermions, such as intrinsic non-centrosymmetric structure, high conductivity, strong anisotropic lattice thermal conductivity, superconductivity, and the transformation to a direct bandgap semiconductor in monolayer MoP [7–11]. Yet, traditional solution approaches usually obtain polycrystalline nanoparticles [12,13]. The preparation of high-quality 2D MoP single crystals has not yet been reported due to the lack of reliable fabrication methods. Chemical vapor deposition (CVD) approach is considered to be one of the most promising methods to obtain high-quality 2D single crystals [14]. The emerging liquid metals possess atomically smooth surface, which are regarded as suitable growth substrates for producing 2D materials [15]. In this study, we firstly report the successful growth of high-quality 2D MoP single crystals via CVD by using liquid gallium (Ga) surface as the growth substrate. Our group has successfully prepared a series of 2D materials on liquid metal surface [16–19]. Mo source s
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