The structures of the various phases endow In 2 Se 3 unique properties as well as a broad range of potential applications. However, the controversy on the structures of In 2 Se 3 strongly hinders the exploitation of its properties and potentially gives rise to misdirection of its applications. Here, taking advantage of state-of-the-art aberration-corrected scanning transmission electron microscopy, we demonstrate the atomic-scale structures of lab-created and purchased In 2 Se 3 compounds. Six phases in three polymorphs at room temperature have been observed among all the samples, which include 2H and 3R α-In 2 Se 3 , 1T, 2H, and 3R β-In 2 Se 3 , and none-layered γ-In 2 Se 3 . Raman spectra are directly correlated to individual In 2 Se 3 phases, providing fingerprints for identifying various phases of In 2 Se 3 . In addition, obvious out-of-plane ferroelectricity of 2H α-In 2 Se 3 was also observed by piezoresponse force microscopy, enabling its potential application in ferroelectric devices.

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Multiferroics materials, which exhibit coupled magnetic and ferroelectric properties, have attracted tremendous research interest because of their potential in constructing next-generation multifunctional devices. The application of single-phase multiferroics is currently limited by their usually small magnetoelectric effects. Here, we report the realization of giant magnetoelectric effects in a Y-type hexaferrite Ba0.4Sr1.6Mg2Fe12O22 single crystal, which exhibits record-breaking direct and converse magnetoelectric coefficients and a large electric-field-reversed magnetization. We have uncovered the origin of the giant magnetoelectric effects by a systematic study in the Ba2-xSrxMg2Fe12O22 family with magnetization, ferroelectricity and neutron diffraction measurements. With the transverse spin cone symmetry restricted to be two-fold, the one-step sharp magnetization reversal is realized and giant magnetoelectric coefficients are achieved. Our study reveals that tuning magnetic symmetry is an effective route to enhance the magnetoelectric effects also in multiferroic hexaferrites.

mechanical transfer method. [28][29][30] However, low yield, multiple steps, and interface contaminations usually accompany the mechanical transfer method, undermining the performance of 2D heterostructures and impeding their applications. In contrast, chemical vapor deposition (CVD) is a low-cost and highly efficient method compatible with the traditional semiconductor manufacturing technique, which has been widely used in the fabrication of 2D heterostructures. [31][32][33] Very recently, WS 2 -MoS 2 , WS 2 -WSe 2 , and MoSe 2 -WSe 2 heterostructures have been successfully synthesized using the CVD growth technique. [25,34] Compared with the onestep CVD method, the two-step epitaxial growth method can avoid forming alloy compounds (MX 2−x X x or M 1−x M x X 2 ) that significantly influence the properties of the interface. [35] As reported in a previous study, [36] the lateral monolayer MoS 2 -WS 2 heterostructure is a type-II heterostructure in which free electrons and holes are confined in different materials and can be spontaneously separated, owning innate superiority for optoelectronics. In addition, bilayer TMCs possess a relatively large band gap that is beneficial for the suppression of dark current and the elevation of responsivity. However, the synthesis of large-scale and high-quality lateral heterostructures with controllable thicknesses remains a major challenge.In this work, lateral bilayer (LBL) WS 2 -MoS 2 heterostructures were successfully synthesized via a two-step CVD growth method. The structural and optical properties of the as-grown LBL WS 2 -MoS 2 heterostructures are thoroughly examined by Raman and photoluminescence (PL) spectroscopy, secondharmonic generation (SHG) imaging, atomic force microscopy (AFM), spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), and Kevin probe force microscopy (KPFM). Additionally, a photodetector device based on LBL WS 2 -MoS 2 heterostructures is also fabricated. The performance of the LBL WS 2 -MoS 2 heterostructure photodetector has also been fully investigated. Figure 1a depicts the two-step CVD method employed here for the growth of LBL WS 2 -MoS 2 heterostructures. As indicated in Figure 1a, the WS 2 bilayer crystals are first prepared on a Si/ SiO 2 substrate using WO 3 and S as precursors ( Figure S1a, Supporting Information). Figure 1b,c presents the images of optical 2D heterostructures combining different layered semiconductors have received great interest due to their intriguing electrical and optical properties. However, the arbitrary growth of layers in a lateral heterostructure remains a challenge. Here, the synthesis of large-scale lateral bilayer (LBL) WS 2 -MoS 2 heterostructures is reported by a two-step chemical vapor deposition route. Raman, photoluminescence, and second-harmonic generation images show the sharp boundaries between WS 2 and MoS 2 domains in the heterostructure. Atomically resolved scanning transmission electron microscopy further reveals that sharp boundaries are formed by seamless connecti...

The coexistence and coupling between magnetization and electric polarization in multiferroic materials provide extra degrees of freedom for creating next-generation memory devices. A variety of concepts of multiferroic or magnetoelectric memories have been proposed and explored in the past decade. Here we propose a new principle to realize a multilevel nonvolatile memory based on the multiple states of the magnetoelectric coefficient (α) of multiferroics. Because the states of α depends on the relative orientation between magnetization and polarization, one can reach different levels of α by controlling the ratio of up and down ferroelectric domains with external electric fields. Our experiments in a device made of the PMN-PT/Terfenol-D multiferroic heterostructure confirm that the states of α can be well controlled between positive and negative by applying selective electric fields. Consequently, two-level, four-level, and eight-level nonvolatile memory devices are demonstrated at room temperature. This kind of multilevel magnetoelectric memory retains all the advantages of ferroelectric random access memory but overcomes the drawback of destructive reading of polarization. In contrast, the reading of α is nondestructive and highly efficient in a parallel way, with an independent reading coil shared by all the memory cells.