ARTICLE DOI: 10.1038/s41467-017-02077-z OPEN A two-dimensional Fe-doped SnS2 magnetic semiconductor Bo Li1,2, Tao Xing3, Mianzeng Zhong1, Le Huang4, Na Lei3, Jun Zhang 1, Jingbo Li1 & Zhongming Wei 1 Magnetic two-dimensional materials have attracted considerable attention for their sig- nificant potential application in spintronics. In this study, we present a high-quality Fe-doped SnS2 monolayer exfoliated using a micromechanical cleavage method. Fe atoms ∼ fi 1234567890 were doped at the Sn atom sites, and the Fe contents are 2.1%, 1.5%, and 1.1%. The eld- effect transistors based on the Fe0.021Sn0.979S2 monolayer show n-type behavior and exhibit high optoelectronic performance. Magnetic measurements show that pure SnS2 is diamag- netic, whereas Fe0.021Sn0.979S2 exhibits ferromagnetic behavior with a perpendicular aniso- tropy at 2 K and a Curie temperature of ~31 K. Density functional theory calculations show that long-range ferromagnetic ordering in the Fe-doped SnS2 monolayer is energetically stable, and the estimated Curie temperature agrees well with the results of our experiment. The results suggest that Fe-doped SnS2 has significant potential in future nanoelectronic, magnetic, and optoelectronic applications. 1 State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences & College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100083, China. 2 Department of Applied Physics, School of Physics and Electronics, Hunan University, Changsha 410082, China. 3 Fert Beijing Institute, School of Electronic and Information Engineering, BDBC, Beihang University, Beijing 100191, China. 4 School of Materials and Energy, Guangdong University of Technology, Guangzhou, Guangdong 510006, China. Correspondence and requests for materials should be addressed to Z.W. (email: [email protected]) NATURE COMMUNICATIONS | 8: 1958 | DOI: 10.1038/s41467-017-02077-z | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-017-02077-z wo-dimensional (2D) layered transition metal dichalco- Results genides (TMDs), e.g., MoS2,WS2, and SnS2, are promising Characterization of Fe-doped SnS2. Figure 1a shows an optical T fl functional materials due to their peculiar structural and image of a mechanically exfoliated Fe0.021Sn0.979S2 ake on a Si/ 1–10 fi electronic properties . Signi cant efforts, such as doping, SiO2 substrate. Atomic force microscopy (AFM) and magnetic strain, and chemical functionalization, have been used to obtain force microscopy (MFM) were used to characterize the height and distinctive optical and electrical properties by tuning the band magnetism of the samples, respectively. MFM is a valuable tool – alignments of 2D materials11 14. Doping, which is the intentional that can potentially be used to detect magnetic interactions introduction of impurities into a material, plays a significant role between a magnetized AFM tip and samples36. Recently, MFM in functionalizing 2D materials by changing the intrinsic prop- has been employed to characterize the magnetic response of 15–17 37, erties of pristine atomic layers . For example, wolfram and single- or few-layer 2D nanosheets, such as graphene and MoS2 38 selenium chemical doping of MoS2 is an effective way to engineer . However, it has been reported that MFM signals have non- 18–23 the optical bandgap , and Nb-, Co-, and Mn-doped MoS2 few magnetic contributions due to capacitive and electrostatic inter- layers exhibit diverse transport properties11, 12, 24. Magnetic atom actions between the nanosheets and the conductive cantilever 38, 39 (e.g., Mn, Fe, Co, and Ni)-doped 2D TMDs are promising as 2D- tip . In this study, AFM and MFM images of Fe0.021Sn0.979S2 25–29 diluted magnetic semiconductors (DMS) , and many have and pure SnS2 were obtained under the same test condition. The been predicted to exhibit ferromagnetic behavior at room tem- AFM images show that the obtained Fe0.021Sn0.979S2 and pure 25, 27 perature . DMS, such as Mn-doped InAs and GaAs, have SnS2 are monolayers (Fig. 1b, Supplementary Fig. 1a). The MFM distinctive physical properties and provide the possibility of images show that the Fe0.021Sn0.979S2 monolayer has a larger 30–33 o electronic control of magnetism . To date, Co- and Mn- negative phase shift (523 m ) than that of the pure SnS2 mono- o doped MoS2 nanosheets have been synthesized via the chemical layer (51 m ) (Supplementary Fig. 1b, c) by approximately ten vapor deposition method, and understanding their magnetic times, which should largely contribute to the difference in the 11, 24 properties requires more research . Recently, Zhang et al. and magnetic and electrical properties between the Fe0.021Sn0.979S2 Xu et al. reported the magnetic properties of Cr2Ge2Te6 and CrI3 and SnS2 monolayers. Raman spectroscopy has been widely used monolayers via high-resolution and high-sensitivity magneto- in 2D TMD alloys, and it changes with the composition of the 34, 35 18, 40 optic microscopy . However, further investigation into the alloy . The Raman peaks of the Fe0.021Sn0.979S2 and pure SnS2 −1 magnetism and functional properties of high-quality magnetic monolayers are located at 314 cm , corresponding to the A1g 3, 10 atom-doped 2D TMDs is warranted. mode of SnS2 . The A1g mode of the Fe0.021Sn0.979S2 monolayer In this work, we synthesized different Fe-doped SnS2 is broader than that of the pure SnS2 monolayer (Fig. 1c). This (Fe0.021Sn0.979S2,Fe0.015Sn0.985S2, and Fe0.011Sn0.989S2) bulk crys- broadening behavior, which is due to the doped atoms, has also tals via a direct vapor-phase method, and we obtained been observed in other 2D alloys20. fl Fe0.021Sn0.979S2 monolayer akes via mechanical exfoliation. The crystallinity of the Fe0.021Sn0.979S2 was further character- fi Monolayer Fe0.021Sn0.979S2 exhibits high-quality optoelectronic ized using high-angle annular dark- eld scanning transmission properties. Magnetic measurements show that Fe0.021Sn0.979S2 electron microscopy (HAADF-STEM) and transmission electron exhibits ferromagnetic behavior with a perpendicular anisotropy microscopy (TEM). Figure 1e shows a low-resolution HAADF- ∼ at 2 K and a Curie temperature of 31 K. The experimental results STEM image of a few layers of Fe0.021Sn0.979S2. Energy-dispersive agree well with the theoretical calculations. X-ray spectroscopy (EDS) of the nanosheet (Fig. 1f) shows that ab c d Fe–SnS2 ML 0.83 nm SnS2 ML 314 cm–1 Intensity (a.u) 305 310 315 320 –1 Intensity (a.u.) Remain shift (cm ) 5 μm 2 μm 290 300 310 320 500 510 520 530 540 550 560 Raman shift (cm–1) ef g h S Sn Sn Sn Fe S S SS S S Sn (a.u.) Z Counts (a.u.) Sn S Fe Fe 1 μm 1 nm 2 3 4 5 6 7 0.0 0.4 0.8 1.2 1.6 Energy (KeV) Distance (nm) Fig. 1 Characterization of the Fe0.021Sn0.979S2 flakes. a Optical image of the Fe0.021Sn0.979S2 flake. b AFM and c Raman spectra of the Fe0.021Sn0.979S2 and SnS2 monolayers. The height of the flake in b was obtained along the white dotted line. The inset in c shows the expanded view of the Raman spectra around the A1g mode of the Fe0.021Sn0.979S2 and SnS2 monolayers. d SnS2 atomic structure. e Low-resolution HAADF-STEM image of the Fe0.021Sn0.979S2 flake. f EDS of the Fe0.021Sn0.979S2 flake. g High-resolution STEM image of the Fe0.021Sn0.979S2 flake; the red circles are Fe atoms. h Z-contrast mapping in the areas marked with yellow rectangles in g 2 NATURE COMMUNICATIONS | 8: 1958 | DOI: 10.1038/s41467-017-02077-z | www.nature.com/naturecommunications NATURE COMMUNICATIONS | DOI: 10.1038/s41467-017-02077-z ARTICLE a 1E–5 b 9 0 V 8 1E–6 1.1 nm 1 V 6 2 V 3 V 1E–7 6 3 4 V 5 V A) 1E–8 μ A) 10 m μ μ (A) 0 ( 4 ( sd sd I sd I 1E–9 I –3 1E–10 2 –6 1E–11 0 –9 1E–12 –4 –20 24 –1.0 –0.50.0 0.5 1.0 V (V) g Vsd (V) c 0.25 d 1 V 0.21 Experimental data 2 V Fitting curve 0.20 3 V 0.18 V =3V A) 0.15 sd –6 0.15 R = 0.098P–0.245 (10 sd 0.10 I 0.12 0.05 Photoresponsivity (A/W) 0.09 0.00 050 100 150 200 0.0 0.5 1.0 1.5 2.0 2.5 Time (s) Light power (μW) Fig. 2 Electrical characteristics and photoresponse of the Fe0.021Sn0.979S2 monolayer. a Transfer and b output characteristics of Fe0.021Sn0.979S2. The inset shows an optical image of one typical device and the AFM image of the corresponding sample used for fabricating the device. c Time-dependent Isd of the transistor based on Fe0.021Sn0.979S2 during the light (638 nm, 2.63 μW) switching on/off under a positive source–drain voltage, Vsd, from 1 to 3 V. d Photoresponsivity (R) as a function of light power (P) with a Vsd of 3 V the nanosheet contains S, Sn, and Fe elements. Using a high- (Fig. 1g), and each Fe atom is surrounded by six S atoms to resolution STEM image and the Z-contrast intensity distribution, form an octahedral coordination. The oxidation state of the Fe = = = the Sn (Z 50), Fe (Z 26), and S (Z 16) atoms were directly atom should be +4, leading to a high binding energy for Fe 2p3/2 distinguished, as shown in Fig. 1g, h. Fe atoms were doped at the in Fe0.021Sn0.979S2. Furthermore, quantitative analysis of the XPS – ∼ Sn atom sites.