Two-dimensional multiferroic material of metallic p-doped SnSe

Two-dimensional multiferroic material of metallic p-doped SnSe | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Two-dimensional multiferroic material of metallic p-doped SnSe Ruofan Du, Yuzhu Wang, Mo Cheng, Peng Wang, Hui Li, Wang Feng, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1583367/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Oct, 2022 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Two-dimensional (2D) multiferroic materials have garnered broad interests attributed to their fascinating magnetoelectric properties and energy-efficient multifunctional device applications. Multiferroic heterostructures have recently been realized, nevertheless, the direct coupling between ferroelectric and ferromagnetic order in a single material still remains a daunting challenge, especially for 2D materials. Herein, we develope a simple physical vapor deposition approach to synthesize 2D p-doped SnSe. The local phase segregation of SnSe2 microdomains and accompanying interfacial charge transfer result in the emergence of degenerate semiconductor and metallic feature in SnSe. Intriguingly, the room-temperature ferrimagnetism has been demonstrated first in 2D p-doped SnSe with the Curie temperature approaching to ~337 K. Meanwhile, the robust in-plane ferroelectricity is maintained even under the depolarizing field introduced by SnSe2. The coexistence of ferrimagnetism and ferroelectricity in 2D metallic p-doped SnSe verifies its multiferroic feature. This work presents a significant advance for exploring the magnetoelectric coupling in 2D limit and constructing high-performance logic devices to extend Moore's law. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The multiferroic materials, those simultaneously possess ferromagnetic and ferroelectric orders, have attracted increasing attention because of their emerging physical properties ( e.g. , magnetoelectric coupling 1–3 , nonreciprocity 4,5 , topological order 6 , and thermal Hall effect 7 , etc. ) and multifunctional applications in memory devices 8 , spintronic devices 9 , and nondestructive data storages 10 . In general, the electron spin order in partially filled d/f orbitals of transition metals results in the evolution of magnetism and breaks the time-reversal symmetry. However, the ferroelectricity often derives from the residual polarization due to the stable off-centered ion with empty d/f orbitals, which breaks the space-inversion symmetry 11 . In this regard, the exploration of multiferroism in low symmetry materials is promising and considerable efforts have also been made ( e.g. , NiI 2 1 , GaFeO 3 12 , BiFeO 3 13 , TbMnO 3 14 , and MnWO 4 15 , etc ). Although the two-dimensional (2D) multiferroic materials have long been sought for constructing high-performance magnetoelectric coupling devices, the progress is unsatisfactory. The group-IV monochalcogenides, such as SnSe, possess orthorhombic crystal structure 16,17 and have been predicted to be ferroelastic-ferroelectric multiferroics with spontaneous electric polarization and lattice strain 18,19 . Recently, the ferroelectricity has been experimentally validated in SnSe and SnS, respectively. For example, the shape-dependent in-plane piezoelectric response (with a piezoelectricity of ~19.9 pm V –1 ) was observed in solvent assistance synthesized SnSe nanowall/microsphere 20 . The room-temperature in-plane ferroelectricity was found to exist in physical vapor deposition (PVD) grown SnS nanosheet with the thickness below 15 layers 21 . The robust ferroelectricity with a critical temperature close to ~400 K was discovered in molecular beam epitaxy (MBE) synthesized monolayer SnSe film on graphene, and its ferroelectric domain could be manipulated by the bias voltage 22 . Notably, the ferromagnetism exploration of group-IV monochalcogenides is absent, although the ferromagnetic-ferroelectric multiferroics are promising for constructing magnetoelectric devices with efficient writing and lower energy-cost reading 8 . As a typical member, SnSe is a non-magnetic semiconductor, nevertheless, the magnetic moment can be induced through the hole doping 23,24 . Here we develop a high-throughput PVD method to synthesize 2D p-doped SnSe on mica in a controlled manner. A novel metallic feature is uncovered in 2D p-doped SnSe due to the local phase segregation of SnSe 2 microdomains and accompanying interfacial charge transfer. The room-temperature ferrimagnetism and robust in-plane ferroelectricity are found to exist in PVD-synthesized 2D p-doped SnSe simultaneously, highly suggestive of its multiferroic feature. By combining density functional theory (DFT) calculations and electrical transport/piezoresponse force microscopy (PFM) measurements, the internal mechanism is clarified unambiguously. Results Controlled synthesize thickness-tunable SnSe nanosheets on mica . 2D SnSe nanosheets were successfully synthesized on mica substrates by using an atmospheric pressure PVD method with SnSe powders as the precursors. The schematic diagram of growth process and crystal structure of SnSe along c -axis is depicted in Fig. 1a . The orthorhombic structure is distinguished in SnSe and the high Grüneisen parameter for such a structure results in anharmonic and anisotropic bonding. The freshly cleaved fluorphlogopite mica (KMg 3 (AlSi 3 O 10 )F 2 ) was selected as the growth substrate in view of its chemically inert feature and atomically smooth surface, as well as the weak van der Waal interaction with precursors that allows them to migrate with relatively low barrier, which is critical for the epitaxy growth of 2D materials. Other substrates ( e.g. , Au foil, soda-lime glass, SiO 2 /Si, and sapphire) were also used to synthesize SnSe, nevertheless, smaller and thicker nanosheets were obtained ( Fig. S1 ), reconfirming the advantage of mica substrate for growing large-domain and ultrathin SnSe. X-ray diffraction (XRD) measurements were then performed on as-grown samples to identify the phase structure of SnSe ( Fig. S2 ). Three main diffraction peaks at 15.4°, 31.1°, and 64.8° are assigned as (200), (400), and (800) planes of SnSe, respectively, according to the JCPDS card no. 48-1224, indicating the orthorhombic phase and layered structure along a -axis. Figure 1b displays the Raman spectrum of as-grown SnSe, the characteristic peaks at ~33.2, ~70.6, ~109.9, ~131.5, and ~150.0 cm −1 correspond to B1 3g, A1 g, B2 3g, A2 g, and A3 g modes of SnSe, respectively. Corresponding Raman intensity mappings of A1 g and B2 3g modes for a tetragonal SnSe nanosheet manifest a rather uniform color contrast, suggestive of its high thickness uniformity ( Fig. 1c and Fig. S3 ). Optical microscopy (OM) and atomic force microscopy (AFM) measurements were performed on as-grown samples to evaluate the morphology, domain size, and thickness evolution of 2D SnSe with the precursor-substrate distance. Apparently, the average edge lengths and thicknesses of SnSe nanosheets are tunable from ~17.3 to ~61.4 μm and from ~3.4 to ~116.4 nm, respectively, with increasing the precursor-substrate distance from 12 to 16 cm ( Fig. 1d − k and Fig. S4 ). Interestingly, tetragonal SnSe nanosheets with an average edge length of ~61.4 μm are synthesized as the distance is set as 12 cm ( Fig. 1d , h ), nevertheless, circle SnSe nanosheets (with an average edge length of ~17.3 μm) are evolved as the distance increased to 16 cm ( Fig. 1f , j ). The coexisting tetragonal and circle SnSe nanosheets are obtained at a distance of 14 cm, with the corresponding average edge lengths of ~29.7 and ~28.3 μm, respectively, as shown in Fig. 1e , i . Notably, the circle SnSe nanosheets possess a much thinner thickness than those of tetragonal analogs, as confirmed by the AFM results in Fig. 1g , k . The decreased SnSe vapor concentration with increasing the precursor-substrate distance results in a limited growth rate and kinetics. A similar growth behavior was also demonstrated in PVD synthesis of SnS on mica 21 . In brief, the domain size and thickness tunable SnSe nanosheets have been synthesized, which provides an ideal platform for exploring exotic physical properties ( e.g. , ferroelectricity, ferromagnetism, and superconductivity) and developing multifunctional applications in electronic devices. The atomic structure of PVD-synthesized 2D SnSe nanosheets . To determine the atomic structure and crystalline quality of PVD-synthesized 2D SnSe nanosheets, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements were performed on transferred samples. Figure 2a reveals the low-magnification TEM image of a well-shaped tetragonal SnSe nanosheet and its high crystalline quality is convinced by the regular morphology. A series of selected area electron diffraction (SAED) patterns captured from four random positions of such a SnSe nanosheet are shown in Fig. 2b . Only one set of arranged diffraction spots is observed, almost the same orientation verifies the single crystalline property and high crystallinity of PVD-synthesized 2D SnSe nanosheets. In addition, energy dispersive X-ray spectroscopy (EDS) measurements were carried out to identify the chemical constitutions and their distributions ( Fig. 2c – e ). The uniform color contrast within the nanosheet shows the high crystalline quality of 2D SnSe. Meanwhile, the perfect stoichiometric ratio of 1:1 for Sn and Se is also achieved according to the quantified analysis of EDS result ( Fig. 2f ). The typical atomic-resolution HAADF-STEM images and corresponding fast Fourier transform (FFT) pattern of tetragonal SnSe along [100] zone axis are depicted in Fig. 2g , h and Fig. S5 , respectively, a perfect lattice is obviously observed to show almost no visible defect, in line with the simulative result in Fig. 2i , suggestive of the high crystalline quality of 2D SnSe. Additionally, the lattice constant is measured to be ~2.1 Å, consistent with the (020) plane spacing of SnSe ( Fig. S6 ). The metallic feature of PVD-synthesized 2D p-doped SnSe . To investigate the electronic property and its anisotropy of PVD-synthesized 2D SnSe, a series of back-gate devices were thus constructed by transferring samples on Au electrodes, with the OM image shown in Fig. 3a . Notably, the electrode directions of 1‒2 and 3‒4 are identified as zigzag (ZZ) and armchair (AC) orientations of SnSe, respectively. The output characteristic curves (drain-source current ( I ds ) vs drain-source voltage ( V ds )) collected both along 1‒2 and 3‒4 directions show nearly linear and symmetric relationships under different back-gate voltages ( V gs ) from −60 to +60 V, indicating the Ohmic-type contacts between SnSe nanosheets and Au electrodes ( Fig. 3a ). Furthermore, the I ds values remain invariant with the V gs changing from −60 to +60 V, suggesting the metallic feature of SnSe ( Fig. 3b ), in contrast to intrinsically semiconducting behavior 25 . Interestingly, the much higher conductivity is clearly observed along the ZZ orientation (~9.76 × 10 3 S m −1 ) than that of the AC counterpart (~6.72 × 10 3 S m −1 ), manifesting the anisotropic electronic property of SnSe ( Fig. S7 ). The distinctive crystal structure of SnSe determines such an unusual phenomenon, as has been demonstrated in bulk SnSe 26 . Additionally, the metallic feature of PVD-synthesized 2D SnSe is also confirmed by the reduced longitudinal resistance ( R xx ) with decreasing the temperature from ~390 to ~2 K ( Fig. 3c ), as well as the intensive density of states (DOS) near the Fermi level ( Fig. S8 ). By precisely controlling the cooling rate during the sample growth process, SnSe 2 microdomains were evolved within SnSe, which resulted in a degenerate semiconductor and therefore a metallic behavior 24 . In consideration of the different thermal conductivities of SnSe (~0.69 W m −1 K −1 ) 16 and mica substrate (~0.183 W m −1 K −1 ) 27 , SnSe 2 microdomains could be segregated at the interfaces. Furthermore, the similar formation enthalpy between SnSe 2 (−0.43 eV/atom) and SnSe (−0.56 eV/atom) will be simple to induced the secondary phase (SnSe 2 ) in the host matrix phase (SnSe) or Sn vacancies in SnSe 28 . To confirm this speculation, X-ray photoemission spectroscopy (XPS) measurements were thus performed to characterize the chemical states of PVD-synthesized SnSe, with the results shown in Fig. 3d and Fig. S9 . The binding energies of ~485.4 and ~493.9 eV are attributed to Sn 2+ 3 d 5/2 and 3 d 3/2 , respectively. Interestingly, additional two characteristic peaks at ~486.6 and ~495.0 eV are obviously observed, which are assigned to Sn 4+ 3 d 5/2 and 3 d 3/2 , respectively, highly suggestive of the generation of Sn 4+ state in the as-grown sample. Additionally, the Ar plasma treatments and Raman characterizations were also executed to further determine the existence of SnSe 2 microdomains ( Fig. 3e and Fig. S10 ). Besides characteristic Raman peaks of SnSe at ~70, ~108, ~132, and ~150 cm –1 , a new peak (~180 cm –1 ) is obtained, which corresponds to the A 1g vibration mode of SnSe 2 , indicative of the formation of SnSe 2 microdomains. DFT calculations were performed to clarify the metallic feature of PVD synthesized SnSe. The band structure of SnSe/SnSe 2 is presented in Fig. 3f and the Fermi level is crossed by several bands, indicative of its metallic feature, echoing well with the experimental findings. Meanwhile, the electron transfer from SnSe to SnSe 2 is confirmed both by the energy band diagram and charge distribution in Fig. 3g , h , which convinces the formation of p-doped SnSe. In short, 2D metallic p-doped SnSe with high conductivity is confirmed because of the formation of SnSe 2 microdomains, which offers a playground for exploring the novel quantum phenomena, such as weak antilocalization effect ( Fig. S11 ), and multifunctional applications in electronic devices and energy-related fields. The ferrimagnetism in PVD-synthesized 2D p-doped SnSe . 2D multiferroic materials have attracted intensive interest due to their newfangled physical properties and multifunctional applications 1 . The ferroelectricity has been theoretically predicted and experimentally investigated in SnSe nanowalls 20 and films 22 . Nevertheless, the ferromagnetism exploration of 2D SnSe is still absent. Superconducting quantum interference device (SQUID) measurements were performed on transferred p-doped SnSe nanosheets (with an average thickness of ~41.4 nm) on SiO 2 /Si to determine the intrinsic magnetism. Zero-field cooled (ZFC) and field-cooled (FC) magnetization curves were collected with the magnetic field (100 Oe) vertical and parallel to c -axis, respectively ( Fig. 4a , c ). Interestingly, both these ZFC-FC curves present ferrimagnetic feature with the Curie temperature ( T c ) up to ~337 K ( Fig. S12 ), consistent with the theoretically predicted value (~325 K) 29 . Additionally, the maximum magnetic moments are obtained for ZFC curves at the temperatures of ~60 K (magnetic field vertical to c -axis) and ~75 K (magnetic field parallel to c -axis), and such a phenomenon is also observed in spin-glass 30 and superparamagnetic material 31 . The magnetic hysteresis loops of 2D p-doped SnSe nanosheets are clearly achieved at the temperatures of 5 and 300 K under the parallel and vertical magnetic fields ( Fig. 4b , d ), reconfirming the long-range ferrimagnetic order. Interestingly, the remanences are still observed even at ~300 K, highly suggestive of the room-temperature ferrimagnetism in 2D p-doped SnSe. Furthermore, the easy axis is assigned to in-plane due to its higher saturation magnetization and coercivity than those of the out-of-plane. DFT calculations were thus performed to provide further insights on the origin of ferrimagnetism in 2D p-doped SnSe. The differential charge density of SnSe/SnSe 2 in Fig. 4e shows the same electron orientation, indicating the appearance of ferrimagnetism state, consistent with the experimental results. The projected spin-polarized DOS in Fig. 4f reveals that the states around Fermi level are determined by Se atoms, and the asymmetric DOS of two spin channels results in a total magnetic moment of ~0.7881 μ B . Such theoretical results demonstrate that PVD-synthesized 2D p-doped SnSe nanosheets possess ferrimagnetic properties. To our knowledge, it is the first report regarding the ferrimagnetism of 2D SnSe, which lays a solid foundation for constructing high-performance spintronic devices. The determination of ferroelectricity in PVD-synthesized 2D p-doped SnSe . PFM is a noninvasive and powerful technology for determining ferroelectricity and thus is used for characterizing the transferred 2D p-doped SnSe nanosheets on Au/Si/ITO at room-temperature, with the schematic diagram shown in Fig. 5a . To eliminate the electrostatic effect between PFM tips and surface charges under high external electric fields 32 , the top Au electrodes were deposited on 2D p-doped SnSe nanosheets to avoid the local charge/ion accumulation 33 , with the OM image presented in Fig. S13 . The in-plane phase images are revealed in Fig. 5b , c under the sample bias voltage of 0 and 5 V, respectively, and the polarization reversal from downward to upward is obviously observed, tentatively indicative of the appearance of ferroelectricity. The topographic images of 2D tetragonal p-doped SnSe nanosheets with different thicknesses are shown in Fig. 5d and Fig. S14 , the corresponding amplitude hysteresis loops and phases are obtained ( Fig. 5e , f ). The well-defined butterfly loops of amplitude signals and the distinct 180° switching of phases confirm the robust ferroelectric polarization of 2D p-doped SnSe. The free energy of SnSe/SnSe 2 interface is calculated under different distortion angles (θ) along the AR direction and the single-well potential is thus obtained by the Landau model fitting ( Fig. S15 ) 29 . Interestingly, only one lowest energy point is obviously observed, indicating the ferroelectric spontaneous polarization in SnSe/SnSe 2 . Meanwhile, the free-energy contour of SnSe/SnSe 2 is also plotted in Fig. 5g , and the saddle point A corresponds to the paraelectric phase with central symmetry. The θ 1 and θ 2 are defined as the angles those measured along the AR direction of SnSe ( Fig. S16 ). Notably, the relationship between free energy and polarization can be established by calculating the polarization under different distortion angles ( Fig. 5h ). The E G is defined as the transfer potential barrier from ferroelectric phase (B) to paraelectric phase (A), and thus calculated to be ~164 meV, much higher than that of other 2D ferroelectric materials ( e.g. , α-In 2 Se 3 34 , CnInP 2 S 6 35,36 , and MoTe 2 37 ). Meanwhile, the spontaneous polarization intensity ( P s ) of SnSe/SnSe 2 interface is obtained to be ~0.58 × 10 −10 C/m, comparable to the monolayer SnSe 29 , which means that the in-plane ferroelectricity of SnSe is maintained even under the depolarizing field introduced by SnSe 2 . Such results suggest that PVD-synthesized 2D p-doped SnSe is a robust ferroelectric material, which opens the possibilities for the applications in sensors, actuators, and non-volatile memory devices 38 . Discussion In summary, large-domain and thickness-tunable SnSe nanosheets have been successfully synthesized on mica substrates by a simple PVD method. Given the similar formation enthalpy between SnSe 2 and SnSe, the local phase segregation of SnSe 2 microdomains and interfacial charge transfer are discovered, which result in the emergence of degenerate semiconductor and metallic feature in 2D p-doped SnSe. More interestingly, the room-temperature ferrimagnetism (with the Curie temperature approaching to ~337 K) and robust in-plane ferroelectricity have been verified in PVD-synthesized 2D metallic p-doped SnSe by combining DFT calculations, SQUID, and PFM measurements, and the multiferroic property is thus established. Such results present a breakthrough toward the controllable synthesis of 2D multiferroic materials, and open up a possibility for future industrial implementation of 2D multiferroic materials in the next-generation logic devices. Methods PVD synthesis of 2D metallic p-doped SnSe nanosheets on mica. The ambient pressure PVD was conducted to grow 2D metallic p-doped SnSe nanosheets in a dual heating zone furnace equipped with a 1-inch outer diameter quartz tube. The SnSe (~99.999%, 50 mg, Alfa Aesar) precursors were placed in a quartz boat and located in the center of upstream heating zone. The freshly cleaved mica substrates (10 × 10 × 0.2 mm, TaiYuan Fluorphlogopite Mica Company Ltd.) were located ~4 cm from the front of downstream heating zone. Notably, the SnSe powders were covered by molecular sieves to reduce the evaporation rate. Before conducting the PVD growth, the quartz tube was purged by ~500 sccm high-purity Ar gas and kept for ~5 min to remove the air and humidity. After that, the temperatures of upstream and downstream heating zone were heated to ~660 and ~430 °C, respectively, within 30 min. In addition, ~5 sccm H 2 and ~100 sccm Ar were introduced as the carrier gas during the PVD growth process. The target temperature was kept for 10 min. And then, the furnace was cooled down to room-temperature naturally. Etching-free transfer and characterization of 2D metallic p-doped SnSe nanosheets. The PVD-synthesized 2D metallic p-doped SnSe nanosheets were transferred by using the polystyrene assistant method 39 . The morphology, domain size, thickness, phase structure, optical property, and crystalline quality of 2D metallic p-doped SnSe nanosheets were characterized by OM (Olympus BX53M), AFM (Dimension Icon, Bruker), XPS (Thermo Scientific K-Alpha+ system, and the binding energies were calibrated by C1 s at ~284.8 eV), XRD (Rigaku Smartlab SE), Raman spectroscopy (Renishaw, with the excitation light of ~532 nm), and TEM (JEOL JEM-F200, with the acceleration voltage of ~200 kV). The atomic-resolution HAADF-STEM imaging was conducted on an aberration-corrected STEM JEOL ARM-200F with an acceleration voltage of ~80 kV. Ferroelectric characterization. PFM measurements were performed using a commercial AFM (Bruker Multimode 8) with a Pt/Ir-coated Si cantilever tip (spring constant: 3N/m). For the local electric measurements, a bias voltage of 5 V was applied to the sample. Electrical and ferrimagnetism measurements. The PVD-synthesized 2D metallic p-doped SnSe nanosheets with different thicknesses were transferred onto SiO 2 /Si substrates with pre-evaporated Au electrodes (~40 nm). The electrical transport measurements were performed under the vacuum (<1.3 mTorr) and dark conditions by using a semiconductor characterization system (Keithley 4200-SCS). The ferrimagnetism properties of 2D metallic p-doped SnSe nanosheets were measured by SQUID (Quantum Design, MPMS3) using the reciprocating sample option (RSO). The magnetic hysteresis loops were measured using the max slope position and linear regression fitting parameters to eliminate centering errors at zero moment. Temperature-dependent magnetic moment of 2D metallic p-doped SnSe nanosheets was measured using ZFC and FC modes with the cooling rate of 3 K min – 1 . Magnetic calculation. All DFT calculations within a spin-polarized frame were carried out with the Vienna ab initio Simulation Package (VASP) 40 . The elemental cores and valence electrons were represented by the projector augmented wave (PAW) method. The generalized gradient approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional was employed for all the calculations 41 . During the calculation, the energy cutoff and precision energy were set to 700 and 10 – 6 eV, respectively. And the force convergence criterion was 10 – 2 eV/Å for each atom. Monkhorst-Pack k -points of 2 × 6 × 1 and 1 × 6 × 1 were applied for all the surface calculations of SnSe and SnSe/SnSe 2 , respectively. For the ferromagnetism of SnSe and SnSe/SnSe 2 , the initial magnetic moments of Sn atoms were set as +2 μ B . Ferroelectric calculation. All the calculations were performed by VASP with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional and PAM method. The plane wave cutoff energy was set as 600 eV. The interface was constructed based on the 1 × 3 supercell of SnSe and 1 × 2 supercell of SnSe 2 . Monkhorst-Pack k -points of 14 × 14 × 1 and 14 × 5 × 1 were used for monolayer SnSe and SnSe/SnSe 2 , respectively. The atomic structures were relaxed until the energy and force reach less than 10 − 6 eV and 10 – 2 eV Å − 1 , respectively. A vacuum layer of ~20 Å was added to minimize the interaction between the periodic images. The van der Waals interaction between SnSe and SnSe 2 was corrected by the DFT-D3 method of Grimme. The macroscopic electronic polarization was calculated according to the modern theory of polarization based on the Berry phase. References Song, Q. et al . Evidence for a single-layer van der Waals multiferroic. Nature 602 , 601–605 (2022). Herng, T. S. et al . 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Novel intelligent devices: Two-dimensional materials based memristors. Front. Phys. 17 , 23602 (2022). Cheng, M. et al . Phase-tunable synthesis and etching-free transfer of two-dimensional magnetic FeTe. ACS Nano 15 , 19089–19097 (2021). Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50 , 17953 (1994). Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77 , 3865 (1996). Declarations Acknowledgments This work was financially supported by National Key R&D Program of China (Nos. 2018YFA0703700 and 2021YFA1200800), National Natural Science Foundation of China (Nos. 91964203 and 92164103), the Beijing National Laboratory for Molecular Sciences (No. BNLMS202001), and the Fundamental Research Funds for the Central Universities (No. 2042021kf0029). Author contributions J.S. and J.H. conceived and supervised the research project. R.D. and Y.W. developed and conducted the PVD growth and transfer of 2D metallic p-doped SnSe with M.C., P.W., H.L., W.F. and L.S.’s assistance. Y.W. constructed the device and electrical transport measurements. R.D., Y.W., M.C., P.W., H.L., W.F. and L.S carried out the OM, XPS, XRD, Raman, AFM, and TEM characterizations. R.D. performed the ferroelectric and ferrimagnetic measurements. All the authors discussed the results and commented on the manuscript. Additional information Supplementary information accompanies this paper at XXX. Competing interests: The authors declare no competing financial interests. Reprints and permission information are available online at XXX. Additional Declarations There is NO Competing Interest. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-1583367","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":101931130,"identity":"d9579ed8-4aa2-46e5-aa5d-3e3f07830a3e","order_by":0,"name":"Ruofan Du","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ruofan","middleName":"","lastName":"Du","suffix":""},{"id":101931131,"identity":"38ec8a1f-ace7-4489-9bea-20b218dd9727","order_by":1,"name":"Yuzhu Wang","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuzhu","middleName":"","lastName":"Wang","suffix":""},{"id":101931132,"identity":"d6468e15-0fa4-4eba-8e01-db3102664ea7","order_by":2,"name":"Mo Cheng","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mo","middleName":"","lastName":"Cheng","suffix":""},{"id":101931133,"identity":"6b8044c5-9207-45c4-b46e-3cc4d1c439e3","order_by":3,"name":"Peng Wang","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Peng","middleName":"","lastName":"Wang","suffix":""},{"id":101931134,"identity":"8365439d-28f0-4a4f-8371-306ba45396ff","order_by":4,"name":"Hui Li","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hui","middleName":"","lastName":"Li","suffix":""},{"id":101931135,"identity":"ea1c02d1-21d4-44d6-8611-3fa3895f0581","order_by":5,"name":"Wang Feng","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Wang","middleName":"","lastName":"Feng","suffix":""},{"id":101931136,"identity":"4ef5af1c-06cc-42d0-93e5-9e9f674d4808","order_by":6,"name":"Luying Song","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Luying","middleName":"","lastName":"Song","suffix":""},{"id":101931137,"identity":"add35e46-adb2-4675-aea7-c5fbc19946f4","order_by":7,"name":"Jianping Shi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYBACxmYQaQDEEoyNDxgbQLwE4rU0GxClBQEkGNgkiNLC3M787HFBwR27+bOb26p5dxxm4GfPMWD4uQOfw9jMjWcYPEvecOdg223eM4cZJHveGDD2nsHrFzNpHoPDyQYSiW23c9sOMxjcyDFgZmzDp4X9G1iL/IzEtmKQFnvCWnjAttgx3EhsYwbbIkFYS5n0DIPDCQY3Epul/7al80iceVZwsBePFsP+49ukC/4ctpefkf7w48w2azn+9uSND37i09IADGggndgAFeABEQdwa2BgkGeAaLHHp2gUjIJRMApGOAAAOdRQJvPna2AAAAAASUVORK5CYII=","orcid":"","institution":"Wuhan University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Jianping","middleName":"","lastName":"Shi","suffix":""},{"id":101931138,"identity":"bc70ae37-03bd-4a2d-aa46-fb046327dd50","order_by":8,"name":"Jun He","email":"","orcid":"","institution":"Wuhan University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"He","suffix":""}],"badges":[],"createdAt":"2022-04-22 07:45:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1583367/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1583367/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-022-33917-2","type":"published","date":"2022-10-17T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":20843749,"identity":"4db92de4-823d-4504-a03a-1a5a5b9c521e","added_by":"auto","created_at":"2022-04-27 18:28:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":332916,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eControllable synthesis of thickness-tunable SnSe nanosheets on mica.\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e (a) Schematic diagram of the growth process and crystal structure of SnSe on mica. (b) Raman spectrum of as-grown SnSe on mica. (c) Raman intensity mapping image of A1 g mode for a tetragonal SnSe nanosheet, showing its thickness uniformity. (d–f) OM images of as-grown SnSe that synthesized at different precursor-substrate distances of 12, 14, and 16 cm, respectively, revealing variable domain sizes and morphologies. (g–i) Corresponding edge length distributions. (j,k) AFM images and corresponding height profiles analysis of tetragonal and circle SnSe nanosheets on mica.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/aad71c0bafa032f0190db622.png"},{"id":20843748,"identity":"3d438ae1-601a-4fda-afa2-dc68b0c4771b","added_by":"auto","created_at":"2022-04-27 18:28:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":467075,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAtomic structure of PVD-synthesized 2D SnSe nanosheets.\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e (a) Low-magnification TEM image of a typical tetragonal SnSe nanosheet. (b) Corresponding SAED patterns captured from the random positions labeled with numbers 1−4 in (a). (c) Low-magnification TEM image of a tetragonal SnSe nanosheet. (d,e) Corresponding EDS mapping images of Sn and Se, respectively, showing the uniform element distribution. (f) Quantified analysis of EDS result. (g) Atomic-resolution HAADF-STEM image of a tetragonal SnSe nanosheet. (h) Zoomed-in HAADF-STEM image. (i) Atomic structure model of tetragonal SnSe viewed along a-axis.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/6acbef5318c4c676e750242a.png"},{"id":20843752,"identity":"c786384d-8b86-4cc8-a46e-7170d682ad0f","added_by":"auto","created_at":"2022-04-27 18:28:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":144463,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eMetallic behavior of PVD-synthesized 2D p-doped SnSe.\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e (a) Output characteristic curves of SnSe, collected both along 1–2 and 3–4 directions. Inset is the corresponding OM image of a back-gate device. (b) Transfer characteristic curves of SnSe back-gate device. (c) Temperature-dependent longitudinal resistance of SnSe (with the thickness of ~46 nm). Inset is the corresponding OM image of a Hall bar device. (d) XPS spectrum of transferred 2D p-doped SnSe nanosheets on SiO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/Si, showing the coexistence of Sn\u003c/em\u003e\u003csup\u003e\u003cem\u003e2+\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e and Sn\u003c/em\u003e\u003csup\u003e\u003cem\u003e4+\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e. (e) Raman spectra captured from four random positions in Ar plasma treated sample. The characteristic peaks of SnSe\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e are indicated by the blue rectangle. Inset is the corresponding OM image. (f,g) Calculated band structure and energy band diagram of SnSe/SnSe\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e. (h) Differential charge density of SnSe/SnSe\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e (isosurface value of 0.001 e/A\u003c/em\u003e\u003csup\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e). Yellow and blue isosurface contours represent the charge accumulation and depletion, respectively. All scale bars are 20 µm.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/0f40ebb4593a628adda68a31.png"},{"id":20843751,"identity":"1239a9ac-f8c7-49cb-b800-996b88763f6b","added_by":"auto","created_at":"2022-04-27 18:28:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":127865,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFerrimagnetism of PVD-synthesized 2D p-doped SnSe nanosheets.\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e (a,c) Temperature-dependent magnetic moment of 2D p-doped SnSe nanosheets with a vertical and parallel magnetic field at 100 Oe. T\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e is defined as the temperature at which the maximum magnetic moment is obtained during the ZFC process.\u003c/em\u003e \u003cem\u003e(b,d) Magnetic hysteresis loops of 2D p-doped SnSe at 5 and 300 K with the magnetic field vertical and parallel to c-axis, respectively. (e) Differential charge density of SnSe/SnSe\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e (isosurface value of 0.03705 e Bohr\u003c/em\u003e\u003csup\u003e\u003cem\u003e–3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e).\u003c/em\u003e \u003cem\u003eYellow isosurface contours represent the charge accumulation. The same direction of electron indicates the appearance of ferromagnetism. (f) Projected spin-polarized DOS of SnSe/SnSe\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e. The Fermi level is set to zero.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/e6110d115b061082c8d48ef4.png"},{"id":20843750,"identity":"49f331ec-c3e8-4ef8-8ae2-ae11de30d34f","added_by":"auto","created_at":"2022-04-27 18:28:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":243930,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eThe ferroelectricity determination of PVD-synthesized 2D p-doped SnSe nanosheets.\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e (a) Schematic diagram of the PFM measurement. (b,c) PFM in-plane phase images of 2D p-doped SnSe at the sample bias voltage of 0 and 5 V, respectively. (d) AFM image and corresponding height profile analysis of a 57-nm-thick tetragonal SnSe nanosheet with a top Au electrode. (e,f) Corresponding PFM amplitude hysteresis loops and phases captured from the selected positions labeled in (d). (g) Free-energy contour plot of SnSe/SnSe\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e interface according to the tilting angles (θ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e and θ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e). The paraelectric phase (A) and ferroelectric phase (B) are marked. (h) Polarization-dependent single-well potential. E\u003c/em\u003e\u003csub\u003e\u003cem\u003eG\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e and P\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e are defined as the ground-state energy (potential barrier) and spontaneous polarization, respectively.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/68b8cdc13d98d7fa3a42cb50.png"},{"id":27909964,"identity":"014be9b7-1a4f-464a-8fef-d2044e35a619","added_by":"auto","created_at":"2022-10-18 07:13:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1752513,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/2ba8a061-91bb-4c7a-9ee4-a3e703f83dde.pdf"},{"id":20843753,"identity":"abf87b54-d3b2-4ec2-8666-18d3bbab6207","added_by":"auto","created_at":"2022-04-27 18:28:56","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":6163365,"visible":true,"origin":"","legend":"","description":"","filename":"DuetalsupplementaryInformation0422.docx","url":"https://assets-eu.researchsquare.com/files/rs-1583367/v1/fdb295f9385c8d0cb08b3056.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Two-dimensional multiferroic material of metallic p-doped SnSe","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe multiferroic materials, those simultaneously possess ferromagnetic and ferroelectric orders, have attracted increasing attention because of their emerging physical properties (\u003cem\u003ee.g.\u003c/em\u003e, magnetoelectric coupling\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e, nonreciprocity\u003csup\u003e4,5\u003c/sup\u003e, topological order\u003csup\u003e6\u003c/sup\u003e, and thermal Hall effect\u003csup\u003e7\u003c/sup\u003e, \u003cem\u003eetc.\u003c/em\u003e) and multifunctional applications in\u0026nbsp;memory devices\u003csup\u003e8\u003c/sup\u003e, spintronic devices\u003csup\u003e9\u003c/sup\u003e, and nondestructive data storages\u003csup\u003e10\u003c/sup\u003e. In general, the electron spin order in partially filled \u003cem\u003ed/f\u0026nbsp;\u003c/em\u003eorbitals of transition metals results in the evolution of magnetism and breaks the time-reversal symmetry. However, the ferroelectricity often derives from the residual polarization due to the stable off-centered ion with empty \u003cem\u003ed/f\u003c/em\u003e orbitals, which breaks the space-inversion symmetry\u003csup\u003e11\u003c/sup\u003e. In this regard, the exploration of multiferroism in low symmetry materials is promising and considerable efforts have also been made (\u003cem\u003ee.g.\u003c/em\u003e, NiI\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e1\u003c/sup\u003e, GaFeO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e12\u003c/sup\u003e, BiFeO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e13\u003c/sup\u003e, TbMnO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e14\u003c/sup\u003e, and MnWO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e15\u003c/sup\u003e,\u0026nbsp;\u003cem\u003eetc\u003c/em\u003e). Although the two-dimensional (2D) multiferroic materials have long been sought for constructing high-performance magnetoelectric coupling devices, the progress is unsatisfactory.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe group-IV monochalcogenides, such as SnSe, possess orthorhombic crystal structure\u003csup\u003e16,17\u003c/sup\u003e and have been predicted to be ferroelastic-ferroelectric multiferroics with spontaneous electric polarization and lattice strain\u003csup\u003e18,19\u003c/sup\u003e. Recently, the ferroelectricity has been experimentally validated in SnSe and SnS, respectively. For example, the shape-dependent in-plane piezoelectric response (with a piezoelectricity of ~19.9 pm V\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) was observed in solvent assistance synthesized SnSe nanowall/microsphere\u003csup\u003e20\u003c/sup\u003e. The room-temperature in-plane ferroelectricity was found to exist in physical vapor deposition (PVD) grown SnS nanosheet with the thickness below 15 layers\u003csup\u003e21\u003c/sup\u003e. The robust ferroelectricity\u0026nbsp;with a critical temperature close to ~400 K was discovered in molecular beam epitaxy (MBE) synthesized monolayer SnSe film on graphene, and its ferroelectric domain could be manipulated by the bias voltage\u003csup\u003e22\u003c/sup\u003e. Notably, the ferromagnetism exploration of group-IV monochalcogenides is absent, although the ferromagnetic-ferroelectric multiferroics are promising for constructing magnetoelectric devices with efficient writing and lower energy-cost reading\u003csup\u003e8\u003c/sup\u003e. As a typical member, SnSe is a non-magnetic semiconductor, nevertheless, the magnetic moment can be induced through the hole doping\u003csup\u003e23,24\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHere we develop a high-throughput PVD method to synthesize 2D p-doped SnSe on mica in a controlled manner. A novel metallic feature is uncovered in 2D p-doped SnSe due to the local phase segregation of SnSe\u003csub\u003e2\u003c/sub\u003e microdomains and accompanying interfacial charge transfer. The room-temperature ferrimagnetism and robust in-plane ferroelectricity are found to exist in PVD-synthesized 2D p-doped SnSe simultaneously, highly suggestive of its multiferroic feature. By combining density functional theory (DFT) calculations and electrical transport/piezoresponse force microscopy (PFM) measurements, the internal mechanism is clarified unambiguously.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eControlled synthesize thickness-tunable SnSe nanosheets on mica\u003c/strong\u003e. 2D SnSe nanosheets were successfully synthesized on mica substrates by using an atmospheric pressure PVD method with SnSe powders as the precursors. The schematic diagram of growth process and crystal structure of SnSe along \u003cem\u003ec\u003c/em\u003e-axis is depicted in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1a\u003c/strong\u003e. The orthorhombic structure is distinguished in SnSe and the high Gr\u0026uuml;neisen parameter for such a structure results in anharmonic and anisotropic bonding. The freshly cleaved fluorphlogopite mica (KMg\u003csub\u003e3\u003c/sub\u003e(AlSi\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e)F\u003csub\u003e2\u003c/sub\u003e) was selected as the growth substrate in view of its chemically inert feature and atomically smooth surface, as well as the weak van der Waal interaction with precursors that allows them to migrate with relatively low barrier, which is critical for the epitaxy growth of 2D materials. Other substrates (\u003cem\u003ee.g.\u003c/em\u003e, Au foil, soda-lime glass, SiO\u003csub\u003e2\u003c/sub\u003e/Si, and sapphire) were also used to synthesize SnSe, nevertheless, smaller and thicker nanosheets were obtained (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS1\u003c/strong\u003e), reconfirming the advantage of mica substrate for growing large-domain and ultrathin SnSe.\u0026nbsp;X-ray diffraction (XRD) measurements were then performed on as-grown samples to identify the phase structure of SnSe (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS2\u003c/strong\u003e).\u0026nbsp;Three main diffraction peaks at 15.4\u0026deg;,\u0026nbsp;31.1\u0026deg;, and\u0026nbsp;64.8\u0026deg; are assigned as\u0026nbsp;(200), (400), and (800) planes of\u0026nbsp;SnSe, respectively,\u0026nbsp;according to the JCPDS card no. 48-1224, indicating the orthorhombic phase and layered structure along \u003cem\u003ea\u003c/em\u003e-axis.\u0026nbsp;\u003cstrong\u003eFigure\u003c/strong\u003e \u003cstrong\u003e1b\u003c/strong\u003e displays the Raman spectrum of as-grown SnSe, the characteristic peaks at ~33.2, ~70.6, ~109.9, ~131.5, and ~150.0 cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e correspond to B1 3g, A1 g, B2 3g, A2 g, and A3 g modes of SnSe, respectively. Corresponding Raman intensity mappings of A1 g and B2 3g modes for a tetragonal SnSe nanosheet manifest a rather uniform color contrast, suggestive of its high thickness uniformity (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1c\u003c/strong\u003e and \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS3\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOptical microscopy (OM) and atomic force microscopy (AFM) measurements were performed on as-grown samples to evaluate the morphology, domain size, and thickness evolution of 2D SnSe with the precursor-substrate distance. Apparently, the average edge lengths and thicknesses of SnSe nanosheets are tunable from ~17.3 to ~61.4 \u0026mu;m and from ~3.4 to ~116.4\u0026nbsp;nm, respectively, with increasing the precursor-substrate distance from 12 to 16 cm\u0026nbsp;(\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1d\u003c/strong\u003e\u0026minus;\u003cstrong\u003ek\u003c/strong\u003e and \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS4\u003c/strong\u003e). Interestingly,\u0026nbsp;tetragonal SnSe nanosheets with an average edge length of ~61.4 \u0026mu;m are synthesized as the distance is set as 12 cm (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1d\u003c/strong\u003e,\u003cstrong\u003eh\u003c/strong\u003e), nevertheless, circle SnSe nanosheets (with an average edge length of ~17.3 \u0026mu;m) are evolved as the distance increased to 16 cm (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1f\u003c/strong\u003e,\u003cstrong\u003ej\u003c/strong\u003e). The coexisting tetragonal and circle SnSe nanosheets are obtained at a distance of 14 cm, with the corresponding average edge lengths of ~29.7 and ~28.3 \u0026mu;m, respectively, as shown in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1e\u003c/strong\u003e,\u003cstrong\u003ei\u003c/strong\u003e. Notably, the circle SnSe nanosheets possess a much thinner thickness than those of tetragonal analogs, as confirmed by the AFM results in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e1g\u003c/strong\u003e,\u003cstrong\u003ek\u003c/strong\u003e. The decreased SnSe vapor concentration with increasing the precursor-substrate distance results in a limited growth rate and kinetics. A similar growth behavior was also demonstrated in PVD synthesis of SnS on mica\u003csup\u003e21\u003c/sup\u003e. In brief, the domain size and thickness tunable SnSe nanosheets have been synthesized, which provides an ideal platform for exploring exotic physical properties (\u003cem\u003ee.g.\u003c/em\u003e, ferroelectricity, ferromagnetism, and superconductivity) and developing multifunctional applications in electronic devices.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe atomic structure of PVD-synthesized 2D SnSe nanosheets\u003c/strong\u003e. To determine the atomic structure and crystalline quality of PVD-synthesized 2D SnSe nanosheets, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements were performed on transferred samples. \u003cstrong\u003eFigure\u003c/strong\u003e \u003cstrong\u003e2a\u003c/strong\u003e reveals the low-magnification TEM image of a well-shaped tetragonal SnSe nanosheet and its high crystalline quality is convinced by the regular morphology. A series of selected area electron diffraction (SAED) patterns captured from four random positions of such a SnSe nanosheet are shown in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e2b\u003c/strong\u003e. Only one set of arranged diffraction spots is observed, almost the same orientation verifies the single crystalline property and high crystallinity of PVD-synthesized 2D SnSe nanosheets.\u003c/p\u003e\n\u003cp\u003eIn addition, energy dispersive X-ray spectroscopy (EDS) measurements were carried out to identify the chemical constitutions and their distributions (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e2c\u003c/strong\u003e\u0026ndash;\u003cstrong\u003ee\u003c/strong\u003e). The uniform color contrast within the nanosheet shows the high crystalline quality of 2D SnSe. Meanwhile, the perfect stoichiometric ratio of 1:1 for Sn and Se is also achieved according to the quantified analysis of EDS result (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e2f\u003c/strong\u003e). The typical atomic-resolution HAADF-STEM images and corresponding fast Fourier transform (FFT) pattern of tetragonal SnSe along [100] zone axis are depicted in \u003cstrong\u003eFig. 2g\u003c/strong\u003e,\u003cstrong\u003eh\u003c/strong\u003e and \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS5\u003c/strong\u003e, respectively, a perfect lattice is obviously observed to show almost no visible defect, in line with the simulative result in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e2i\u003c/strong\u003e, suggestive of the high crystalline quality of 2D SnSe. Additionally, the lattice constant is measured to be ~2.1 \u0026Aring;, consistent with the (020) plane spacing of SnSe (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS6\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe metallic feature of PVD-synthesized 2D p-doped SnSe\u003c/strong\u003e. To investigate the electronic property and its anisotropy of PVD-synthesized 2D SnSe, a series of back-gate devices were thus constructed by transferring samples on Au electrodes, with the OM image shown in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3a\u003c/strong\u003e. Notably, the electrode directions of 1‒2 and 3‒4 are identified as zigzag (ZZ) and armchair (AC) orientations of SnSe, respectively. The output characteristic curves (drain-source current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e)\u0026nbsp;\u003cem\u003evs\u0026nbsp;\u003c/em\u003edrain-source voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e)) collected both along 1‒2 and 3‒4 directions show nearly linear and symmetric relationships under different back-gate voltages (\u003cem\u003eV\u003c/em\u003e\u003csub\u003egs\u003c/sub\u003e) from \u0026minus;60 to +60 V, indicating the\u0026nbsp;Ohmic-type\u0026nbsp;contacts between SnSe nanosheets and Au electrodes (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3a\u003c/strong\u003e). Furthermore, the \u003cem\u003eI\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e values remain invariant with the \u003cem\u003eV\u003c/em\u003e\u003csub\u003egs\u003c/sub\u003e changing from \u0026minus;60 to +60 V, suggesting the metallic feature of SnSe (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3b\u003c/strong\u003e), in contrast to intrinsically semiconducting behavior\u003csup\u003e25\u003c/sup\u003e. Interestingly, the much higher conductivity is clearly observed along the ZZ orientation (~9.76\u0026nbsp;\u0026times; 10\u003csup\u003e3\u003c/sup\u003e S m\u003csup\u003e\u0026minus;1\u003c/sup\u003e) than that of the AC counterpart (~6.72 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e S m\u003csup\u003e\u0026minus;1\u003c/sup\u003e), manifesting the anisotropic electronic property of SnSe (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS7\u003c/strong\u003e). The distinctive crystal structure of SnSe determines such an unusual phenomenon, as has been demonstrated in bulk SnSe\u003csup\u003e26\u003c/sup\u003e. Additionally, the metallic feature of PVD-synthesized 2D SnSe is also confirmed by the reduced longitudinal resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003exx\u003c/sub\u003e) with decreasing the temperature from ~390 to ~2 K (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3c\u003c/strong\u003e), as well as the intensive density of states (DOS) near the Fermi level (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS8\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBy precisely controlling the cooling rate during the sample growth process, SnSe\u003csub\u003e2\u003c/sub\u003e microdomains were evolved within SnSe, which resulted in a degenerate semiconductor and therefore a metallic behavior\u003csup\u003e24\u003c/sup\u003e. In consideration of the different thermal conductivities of SnSe (~0.69 W m\u003csup\u003e\u0026minus;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;1\u003c/sup\u003e)\u003csup\u003e16\u003c/sup\u003e and mica substrate (~0.183 W m\u003csup\u003e\u0026minus;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;1\u003c/sup\u003e)\u003csup\u003e27\u003c/sup\u003e, SnSe\u003csub\u003e2\u003c/sub\u003e microdomains could be segregated at the interfaces. Furthermore, the similar formation enthalpy between SnSe\u003csub\u003e2\u003c/sub\u003e (\u0026minus;0.43 eV/atom) and SnSe (\u0026minus;0.56 eV/atom) will be simple to induced the secondary phase (SnSe\u003csub\u003e2\u003c/sub\u003e) in the host matrix phase (SnSe) or Sn vacancies in SnSe\u003csup\u003e28\u003c/sup\u003e. To confirm this speculation, X-ray photoemission spectroscopy (XPS) measurements were thus performed to characterize the chemical states of PVD-synthesized SnSe, with the results shown in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3d\u003c/strong\u003e and \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS9\u003c/strong\u003e. The binding energies\u0026nbsp;of ~485.4 and ~493.9 eV are attributed to Sn\u003csup\u003e2+\u003c/sup\u003e 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e, respectively. Interestingly, additional two characteristic peaks at ~486.6 and ~495.0 eV are obviously observed, which are assigned to Sn\u003csup\u003e4+\u003c/sup\u003e 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e, respectively, highly suggestive of the generation of Sn\u003csup\u003e4+\u003c/sup\u003e state in the as-grown sample. Additionally, the Ar plasma treatments and Raman characterizations were also executed to further determine the existence of SnSe\u003csub\u003e2\u003c/sub\u003e microdomains (\u003ca href=\"https://pubs.acs.org/doi/full/10.1021/acsnano.0c10250#fig4\"\u003e\u003cstrong\u003eFig.\u003c/strong\u003e\u003c/a\u003e \u003cstrong\u003e3e\u003c/strong\u003e and \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS10\u003c/strong\u003e). Besides characteristic Raman peaks of SnSe at ~70, ~108, ~132, and ~150 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, a new peak (~180 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) is obtained, which corresponds to the A\u003csub\u003e1g\u003c/sub\u003e vibration mode of SnSe\u003csub\u003e2\u003c/sub\u003e, indicative of the formation of SnSe\u003csub\u003e2\u003c/sub\u003e microdomains. DFT calculations were performed to clarify the metallic feature of PVD synthesized SnSe. The band structure of\u003cem\u003e\u0026nbsp;\u003c/em\u003eSnSe/SnSe\u003csub\u003e2\u003c/sub\u003e is presented in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3f\u003c/strong\u003e and the Fermi level is crossed by several bands, indicative of its metallic feature, echoing well with the experimental findings. Meanwhile, the electron transfer from SnSe to SnSe\u003csub\u003e2\u003c/sub\u003e is confirmed both by the energy band diagram and charge distribution in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e3g\u003c/strong\u003e,\u003cstrong\u003eh\u003c/strong\u003e, which convinces the formation of p-doped SnSe. In short, 2D metallic p-doped SnSe with high conductivity is confirmed because of the formation of SnSe\u003csub\u003e2\u003c/sub\u003e microdomains, which offers a playground for exploring the novel quantum phenomena, such as weak antilocalization effect (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS11\u003c/strong\u003e), and multifunctional applications in electronic devices and energy-related fields.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe ferrimagnetism in PVD-synthesized 2D p-doped SnSe\u003c/strong\u003e. 2D multiferroic materials have attracted intensive interest due to their newfangled physical properties and multifunctional applications\u003csup\u003e1\u003c/sup\u003e. The ferroelectricity has been theoretically predicted and experimentally investigated in SnSe nanowalls\u003csup\u003e20\u003c/sup\u003e and films\u003csup\u003e22\u003c/sup\u003e. Nevertheless, the ferromagnetism exploration of 2D SnSe is still absent. Superconducting quantum interference device (SQUID) measurements were performed on transferred p-doped SnSe nanosheets (with an average thickness of ~41.4 nm) on SiO\u003csub\u003e2\u003c/sub\u003e/Si to determine the intrinsic magnetism. Zero-field cooled (ZFC) and field-cooled (FC) magnetization curves were collected with the magnetic field (100 Oe) vertical and parallel to \u003cem\u003ec\u003c/em\u003e-axis, respectively (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e4a\u003c/strong\u003e,\u003cstrong\u003ec\u003c/strong\u003e). Interestingly, both these ZFC-FC curves present ferrimagnetic feature with the Curie temperature (\u003cem\u003eT\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e) up to ~337 K (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS12\u003c/strong\u003e), consistent with the theoretically predicted value (~325 K)\u003csup\u003e29\u003c/sup\u003e.\u0026nbsp;Additionally, the maximum magnetic moments are obtained for ZFC curves at the temperatures of ~60 K (magnetic field vertical to \u003cem\u003ec\u003c/em\u003e-axis) and ~75 K (magnetic field parallel to \u003cem\u003ec\u003c/em\u003e-axis), and such a phenomenon is also observed in spin-glass\u003csup\u003e30\u003c/sup\u003e and superparamagnetic material\u003csup\u003e31\u003c/sup\u003e.\u0026nbsp;The magnetic hysteresis loops of 2D p-doped SnSe nanosheets are clearly achieved at the temperatures of 5 and 300 K under the parallel and vertical magnetic fields (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e4b\u003c/strong\u003e,\u003cstrong\u003ed\u003c/strong\u003e), reconfirming the long-range ferrimagnetic order. Interestingly, the remanences are still observed even at ~300 K, highly suggestive of the room-temperature ferrimagnetism in 2D p-doped SnSe. Furthermore, the easy axis is assigned to in-plane due to its higher saturation magnetization and coercivity than those of the out-of-plane.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDFT calculations were thus performed to provide further insights on the origin of ferrimagnetism in 2D p-doped SnSe. The differential charge density of SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e4e\u003c/strong\u003e shows the same electron orientation, indicating the appearance of ferrimagnetism state, consistent with the experimental results. The projected spin-polarized DOS in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e4f\u003c/strong\u003e reveals that the states around Fermi level are determined by Se atoms, and the asymmetric DOS of two spin channels results in a total magnetic moment of ~0.7881 \u0026mu;\u003csub\u003eB\u003c/sub\u003e. Such theoretical results demonstrate that PVD-synthesized 2D p-doped SnSe nanosheets possess ferrimagnetic properties. To our knowledge, it is the first report regarding the ferrimagnetism of 2D SnSe, which lays a solid foundation for constructing high-performance spintronic devices.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe determination of ferroelectricity in PVD-synthesized 2D p-doped SnSe\u003c/strong\u003e. PFM is a noninvasive and powerful technology for determining ferroelectricity and thus is used for characterizing the transferred 2D p-doped SnSe nanosheets on Au/Si/ITO at room-temperature, with the schematic diagram shown in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e5a\u003c/strong\u003e. To eliminate the electrostatic effect between PFM tips and surface charges under high external electric fields\u003csup\u003e32\u003c/sup\u003e, the top Au electrodes were deposited on 2D p-doped SnSe nanosheets to avoid the local charge/ion accumulation\u003csup\u003e33\u003c/sup\u003e, with the OM image presented in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS13\u003c/strong\u003e. The in-plane phase images are revealed in\u003cstrong\u003e\u0026nbsp;Fig.\u003c/strong\u003e \u003cstrong\u003e5b\u003c/strong\u003e,\u003cstrong\u003ec\u003c/strong\u003e under the sample bias voltage of 0 and 5 V, respectively, and the polarization reversal from downward to upward is obviously observed, tentatively indicative of the appearance of ferroelectricity. The topographic images of 2D tetragonal p-doped SnSe nanosheets with different thicknesses are shown in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e5d\u003c/strong\u003e and \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS14\u003c/strong\u003e, the corresponding amplitude hysteresis loops and phases are obtained (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e5e\u003c/strong\u003e,\u003cstrong\u003ef\u003c/strong\u003e). The well-defined butterfly loops of amplitude signals and the distinct 180\u0026deg; switching of phases confirm the robust ferroelectric polarization of 2D p-doped SnSe.\u003c/p\u003e\n\u003cp\u003eThe free energy of SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e interface is calculated under different distortion angles (\u0026theta;) along the AR direction and the single-well potential is thus obtained by the Landau model\u0026nbsp;fitting\u0026nbsp;(\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS15\u003c/strong\u003e)\u003csup\u003e29\u003c/sup\u003e. Interestingly,\u0026nbsp;only one lowest energy point is obviously observed, indicating the ferroelectric spontaneous polarization in SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e. Meanwhile, the free-energy contour of SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e is also plotted in \u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e5g\u003c/strong\u003e, and the saddle point A corresponds to the paraelectric phase with central symmetry. The \u0026theta;\u003csub\u003e1\u003c/sub\u003e and \u0026theta;\u003csub\u003e2\u003c/sub\u003e are defined as the angles those measured along the AR direction of SnSe (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003eS16\u003c/strong\u003e). Notably, the relationship between free energy and polarization can be established by calculating the polarization under different distortion angles (\u003cstrong\u003eFig.\u003c/strong\u003e \u003cstrong\u003e5h\u003c/strong\u003e). The \u003cem\u003eE\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e is defined as the transfer potential barrier from ferroelectric phase (B) to paraelectric phase (A), and thus calculated to be ~164 meV, much higher than that of other 2D ferroelectric materials (\u003cem\u003ee.g.\u003c/em\u003e,\u0026nbsp;\u0026alpha;-In\u003csub\u003e2\u003c/sub\u003eSe\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e34\u003c/sup\u003e, CnInP\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e6\u003c/sub\u003e\u003csup\u003e35,36\u003c/sup\u003e, and MoTe\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003e). Meanwhile, the spontaneous polarization intensity (\u003cem\u003eP\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e) of SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e interface is obtained to be ~0.58 \u0026times; 10\u003csup\u003e\u0026minus;10\u003c/sup\u003e C/m, comparable to the monolayer SnSe\u003csup\u003e29\u003c/sup\u003e, which means that the in-plane ferroelectricity of SnSe is maintained even under the depolarizing field introduced by SnSe\u003csub\u003e2\u003c/sub\u003e. Such results suggest that PVD-synthesized 2D p-doped SnSe is a robust ferroelectric material, which opens the possibilities for the applications in sensors, actuators, and non-volatile memory devices\u003csup\u003e38\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, large-domain and thickness-tunable SnSe nanosheets have been successfully synthesized on mica substrates by a simple PVD method. Given the similar formation enthalpy between SnSe\u003csub\u003e2\u003c/sub\u003e and SnSe, the local phase segregation of SnSe\u003csub\u003e2\u003c/sub\u003e microdomains and interfacial charge transfer are discovered, which result in the emergence of degenerate semiconductor and metallic feature in 2D p-doped SnSe. More interestingly, the room-temperature ferrimagnetism (with the Curie temperature approaching to ~337 K) and robust in-plane ferroelectricity have been verified in PVD-synthesized 2D metallic p-doped SnSe by combining DFT calculations, SQUID, and PFM measurements, and the multiferroic property is thus established. Such results present a breakthrough toward the controllable synthesis of 2D multiferroic materials, and open up a possibility for future industrial implementation of 2D multiferroic materials in the next-generation logic devices.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003ePVD synthesis of 2D metallic p-doped SnSe nanosheets on mica.\u003c/strong\u003e The\u0026nbsp;ambient pressure PVD was conducted to grow 2D metallic p-doped SnSe nanosheets in a dual heating zone furnace equipped with a 1-inch outer diameter quartz tube. The SnSe (~99.999%, 50 mg, Alfa Aesar) precursors were\u0026nbsp;placed in a quartz boat and located in the center of upstream heating zone. The freshly cleaved mica substrates (10 \u0026times; 10 \u0026times; 0.2 mm, TaiYuan Fluorphlogopite Mica Company Ltd.) were located ~4 cm from the front of downstream heating zone. Notably, the SnSe powders were covered by molecular sieves to reduce the evaporation rate. Before conducting the PVD growth, the quartz tube was purged by ~500 sccm high-purity Ar gas and kept for ~5 min to remove the air and humidity. After that, the temperatures of upstream and downstream heating zone were heated to ~660 and ~430 \u0026deg;C, respectively, within 30 min. In addition, ~5 sccm H\u003csub\u003e2\u003c/sub\u003e and ~100 sccm Ar were introduced as the carrier gas during the PVD growth process. The target temperature was kept for 10 min. And then, the furnace was cooled down to room-temperature naturally.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEtching-free transfer and characterization of 2D metallic p-doped SnSe nanosheets.\u003c/strong\u003e The PVD-synthesized 2D metallic p-doped SnSe nanosheets were transferred by using the polystyrene assistant method\u003csup\u003e39\u003c/sup\u003e. The morphology, domain size, thickness, phase structure, optical property, and crystalline quality of 2D metallic p-doped SnSe nanosheets were characterized by OM (Olympus BX53M), AFM (Dimension Icon, Bruker), XPS (Thermo Scientific K-Alpha+ system, and the binding energies were calibrated by C1\u003cem\u003es\u003c/em\u003e at ~284.8 eV), XRD (Rigaku Smartlab SE), Raman spectroscopy (Renishaw, with the excitation light of ~532 nm), and TEM (JEOL JEM-F200, with the acceleration voltage of ~200 kV). The atomic-resolution HAADF-STEM imaging was conducted on an aberration-corrected STEM JEOL ARM-200F with an acceleration voltage of ~80 kV.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFerroelectric characterization.\u003c/strong\u003e PFM measurements were performed using a commercial AFM (Bruker Multimode 8) with a Pt/Ir-coated Si cantilever tip\u0026nbsp;(spring constant: 3N/m). For the local electric measurements, a bias voltage of 5 V was applied to the sample.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrical and ferrimagnetism measurements.\u003c/strong\u003e The PVD-synthesized 2D metallic p-doped SnSe nanosheets with different thicknesses were transferred onto SiO\u003csub\u003e2\u003c/sub\u003e/Si substrates with pre-evaporated Au electrodes (~40 nm). The electrical transport measurements were performed under the vacuum (\u0026lt;1.3 mTorr) and dark conditions by using a semiconductor characterization system (Keithley 4200-SCS). The ferrimagnetism properties of 2D metallic p-doped SnSe nanosheets were measured by SQUID (Quantum Design, MPMS3) using the reciprocating sample option (RSO). The magnetic hysteresis loops\u0026nbsp;were measured using the max slope position and linear regression fitting parameters to eliminate centering errors at zero moment. Temperature-dependent magnetic moment of 2D metallic p-doped SnSe nanosheets was measured using ZFC and FC modes with the cooling rate of 3 K min\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMagnetic calculation.\u003c/strong\u003e All DFT calculations within a spin-polarized frame were carried out with the Vienna \u003cem\u003eab\u003c/em\u003e initio Simulation Package (VASP)\u003csup\u003e40\u003c/sup\u003e. The elemental cores and valence electrons were represented by the projector augmented wave (PAW) method. The generalized gradient approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional was employed for all the calculations\u003csup\u003e41\u003c/sup\u003e. During the calculation, the energy cutoff and precision energy were set to 700 and 10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e6\u003c/sup\u003e eV, respectively. And the force convergence criterion was 10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e2\u003c/sup\u003e eV/\u0026Aring; for each atom. Monkhorst-Pack \u003cem\u003ek\u003c/em\u003e-points of 2 \u0026times; 6 \u0026times; 1 and 1 \u0026times; 6 \u0026times; 1 were applied for all the surface calculations of SnSe and SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e, respectively. For the ferromagnetism of SnSe and SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e, the initial magnetic moments of Sn atoms were set as +2 \u0026mu;\u003csub\u003eB\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFerroelectric\u0026nbsp;calculation.\u003c/strong\u003e All the calculations were performed by VASP with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional and PAM method. The plane wave cutoff energy was set as 600 eV. The interface was constructed based on the 1 \u0026times; 3 supercell of SnSe and 1 \u0026times; 2 supercell of SnSe\u003csub\u003e2\u003c/sub\u003e. Monkhorst-Pack \u003cem\u003ek\u003c/em\u003e-points of 14 \u0026times; 14 \u0026times; 1 and 14 \u0026times; 5 \u0026times; 1 were used for monolayer SnSe and SnSe/SnSe\u003csub\u003e2\u003c/sub\u003e, respectively. The atomic structures were relaxed until the energy and force reach less than 10\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csup\u003e6\u003c/sup\u003e eV and 10\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003csup\u003e2\u003c/sup\u003e eV \u0026Aring;\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e, respectively. A vacuum layer of ~20 \u0026Aring; was added to minimize the interaction between the periodic images. The van der Waals interaction between SnSe and SnSe\u003csub\u003e2\u003c/sub\u003e was corrected by the DFT-D3 method of Grimme. The macroscopic electronic polarization was calculated according to the modern theory of polarization based on the Berry phase.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSong, Q. \u003cem\u003eet al\u003c/em\u003e. Evidence for a single-layer van der Waals multiferroic. 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Generalized gradient approximation made simple. Phys. Rev. Lett. \u003cb\u003e77\u003c/b\u003e, 3865 (1996).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by National Key R\u0026amp;D Program of China (Nos. 2018YFA0703700 and 2021YFA1200800), National Natural Science Foundation of China (Nos. 91964203 and 92164103), the Beijing National Laboratory for Molecular Sciences (No. BNLMS202001), and the Fundamental Research Funds for the Central Universities (No. 2042021kf0029).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ.S. and J.H. conceived and supervised the research project. R.D. and Y.W. developed and conducted the PVD growth and transfer of 2D metallic p-doped SnSe with M.C., P.W., H.L., W.F. and L.S.\u0026rsquo;s assistance. Y.W. constructed the device and electrical transport measurements. R.D., Y.W., M.C., P.W., H.L., W.F. and L.S carried out the OM, XPS, XRD, Raman, AFM, and TEM characterizations. R.D. performed the ferroelectric and ferrimagnetic measurements. All the authors discussed the results and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u003c/strong\u003e accompanies this paper at XXX.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e The authors declare no competing financial interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReprints and permission information\u003c/strong\u003e are available online at XXX.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-1583367/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1583367/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Two-dimensional (2D) multiferroic materials have garnered broad interests attributed to their fascinating magnetoelectric properties and energy-efficient multifunctional device applications. Multiferroic heterostructures have recently been realized, nevertheless, the direct coupling between ferroelectric and ferromagnetic order in a single material still remains a daunting challenge, especially for 2D materials. Herein, we develope a simple physical vapor deposition approach to synthesize 2D p-doped SnSe. The local phase segregation of SnSe2 microdomains and accompanying interfacial charge transfer result in the emergence of degenerate semiconductor and metallic feature in SnSe. Intriguingly, the room-temperature ferrimagnetism has been demonstrated first in 2D p-doped SnSe with the Curie temperature approaching to ~337 K. Meanwhile, the robust in-plane ferroelectricity is maintained even under the depolarizing field introduced by SnSe2. The coexistence of ferrimagnetism and ferroelectricity in 2D metallic p-doped SnSe verifies its multiferroic feature. This work presents a significant advance for exploring the magnetoelectric coupling in 2D limit and constructing high-performance logic devices to extend Moore's law.","manuscriptTitle":"Two-dimensional multiferroic material of metallic p-doped SnSe","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-04-27 18:28:54","doi":"10.21203/rs.3.rs-1583367/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5a27550a-1610-4bcc-8f7f-40d4501c7333","owner":[],"postedDate":"April 27th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2022-10-18T07:12:56+00:00","versionOfRecord":{"articleIdentity":"rs-1583367","link":"https://doi.org/10.1038/s41467-022-33917-2","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2022-10-17 04:00:00","publishedOnDateReadable":"October 17th, 2022"},"versionCreatedAt":"2022-04-27 18:28:54","video":"","vorDoi":"10.1038/s41467-022-33917-2","vorDoiUrl":"https://doi.org/10.1038/s41467-022-33917-2","workflowStages":[]},"version":"v1","identity":"rs-1583367","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1583367","identity":"rs-1583367","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}