title: Exfoliation and Raman Spectroscopic Fingerprint of Few-Layer NiPS3 Van der Waals Crystals.
abstract: 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.
authors.affiliation: 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.
authors.forename: Cheng-Tai
authors.initials: CT
authors.lastname: Kuo
authors.affiliation: 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.
authors.forename: Michael
authors.initials: M
authors.lastname: Neumann
authors.affiliation: 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.
authors.forename: Karuppannan
authors.initials: K
authors.lastname: Balamurugan
authors.affiliation: 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.
authors.forename: Hyun Ju
authors.initials: HJ
authors.lastname: Park
authors.affiliation: 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.
authors.forename: Soonmin
authors.initials: S
authors.lastname: Kang
authors.affiliation: National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan.
authors.forename: Hung Wei
authors.initials: HW
authors.lastname: Shiu
authors.affiliation: Department of Chemistry, Seoul National University (SNU), Seoul 151-742, Republic of Korea.
authors.forename: Jin Hyoun
authors.initials: JH
authors.lastname: Kang
authors.affiliation: Department of Chemistry, Seoul National University (SNU), Seoul 151-742, Republic of Korea.
authors.forename: Byung Hee
authors.initials: BH
authors.lastname: Hong
authors.affiliation: Department of Physics, University of Seoul, Seoul 130-743, Republic of Korea.
authors.forename: Moonsup
authors.initials: M
authors.lastname: Han
authors.affiliation: 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.
authors.forename: Tae Won
authors.initials: TW
authors.lastname: Noh
authors.affiliation: 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.
authors.forename: Je-Geun
authors.initials: JG
authors.lastname: Park