Kuo Cheng-Tai, Neumann Michael, Balamurugan Karuppannan, Park Hyun Ju, Kang Soonmin, Shiu Hung Wei, Kang Jin Hyoun, Hong Byung Hee, Han Moonsup, Noh Tae Won, Park Je-Geun
Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 151-742, Republic of Korea.
Department of Physics and Astronomy, Seoul National University (SNU), Seoul 151-742, Republic of Korea.
Sci Rep. 2016 Feb 15;6:20904. doi: 10.1038/srep20904.
The range of mechanically cleavable Van der Waals crystals covers materials with diverse physical and chemical properties. However, very few of these materials exhibit magnetism or magnetic order, and thus the provision of cleavable magnetic compounds would supply invaluable building blocks for the design of heterostructures assembled from Van der Waals crystals. Here we report the first successful isolation of monolayer and few-layer samples of the compound nickel phosphorus trisulfide (NiPS3) by mechanical exfoliation. This material belongs to the class of transition metal phosphorus trisulfides (MPS3), several of which exhibit antiferromagnetic order at low temperature, and which have not been reported in the form of ultrathin sheets so far. We establish layer numbers by optical bright field microscopy and atomic force microscopy, and perform a detailed Raman spectroscopic characterization of bilayer and thicker NiPS3 flakes. Raman spectral features are strong functions of excitation wavelength and sample thickness, highlighting the important role of interlayer coupling. Furthermore, our observations provide a spectral fingerprint for distinct layer numbers, allowing us to establish a sensitive and convenient means for layer number determination.
可机械剥离的范德华晶体涵盖了具有多样物理和化学性质的材料。然而，这些材料中很少有表现出磁性或磁有序的，因此提供可剥离的磁性化合物将为基于范德华晶体组装的异质结构设计提供非常有价值的构建单元。在此，我们报告了通过机械剥离首次成功分离出化合物三硫化镍磷（NiPS3）的单层和少层样品。这种材料属于过渡金属三硫化磷（MPS3）类别，其中几种在低温下表现出反铁磁有序，且迄今为止尚未有超薄片状形式的报道。我们通过光学明场显微镜和原子力显微镜确定层数，并对双层及更厚的NiPS3薄片进行了详细的拉曼光谱表征。拉曼光谱特征是激发波长和样品厚度的强函数，突出了层间耦合的重要作用。此外，我们的观察为不同层数提供了光谱指纹，使我们能够建立一种灵敏且便捷的层数确定方法。
