β‐In2S3 is a natural defective III–VI semiconductor attracting considerable interests but lack of efficient method for its 2D form fabrication. Here, for the first time, this paper reports controlled synthesis of ultrathin 2D β‐In2S3 flakes via a facile space‐confined chemical vapor deposition method. The natural defects in β‐In2S3 crystals, clearly revealed by optical spectra and optoelectronic measurement, strongly modulate the (opto)‐electronic of as‐fabricated β‐In2S3 and render it a broad detection range from visible to near‐infrared. Particularly, the as‐fabricated β‐In2S3 photodetector shows a high photoresponsivity of 137 A W−1, a high external quantum efficiency of 3.78 × 104%, and a detectivity of 4.74 × 1010 Jones, accompanied with a fast rise and decay time of 6 and 8 ms, respectively. In addition, an interesting linear response to the testing power intensities range is observed, which can also be understood by the presence of natural defects. The unique defective structure and intrinsic optical properties of β‐In2S3, together with its controllable growth, endow it with great potential for future applications in electronics and optoelectronics.

Infrared light detection is generally limited by the intrinsic bandgap of semiconductors, which suppresses the freedom in infrared light photodetector design and hinders the development of high‐performance infrared light photodetector. In this work, for the first time infrared light (1030 nm) photodetectors are fabricated based on WS2/MoS2 heterostructures. Individual WS2 and MoS2 have no response to infrared light. The origin of infrared light response for WS2/MoS2 comes from the strong interlayer coupling which shrinks the energy interval in the heterojunction area thus rendering heterostructures longer wavelength detection ability compared to individual components. Considering the low light absorption due to indirect bandgap essence of few layers WS2/MoS2 heterostructures, its infrared responsivity is further enhanced with at most ≈25 times but the fast response rate is maintained via surface plasmon resonance (SPR). Such an interlayer coupling induced infrared light response and surface plasmon resonance enhancement strategy paves the way for high‐performance infrared light photodetection of infinite freedom in design.

Two dimensional (2D) magnetic materials display enormous application potential in spintronic fields. However, most of currently reported magnetic materials are van der Waals layered structure that is easy to be isolated via exfoliation method. By contrast, the studies on non-van der Waals ultrathin magnetic materials are rare, largely due to the difficulty in fabrication. Rhombohedral Cr 2 S 3 , an intensively studied antiferromagnetic transition metal chalcogenide with Neel temperature of ≈120 K, has a typical non-van der Waals structure. Restricted by the strong covalent bonding in all the three dimensions of non-van der Waals structure, the synthesis of ultrathin Cr 2 S 3 single crystals is still a challenge that is not achieved yet. Besides, the study on the Raman modes of rhombohedral Cr 2 S 3 is also absent. Herein, by employing space-confined chemical vapor deposition strategy, ultrathin rhombohedral Cr 2 S 3 single crystals with a thickness down to ≈2.5 nm for the first time are successfully grown. Moreover, a systematically investigation is also conducted on the Raman vibrations of ultrathin rhombohedral Cr 2 S 3 . With the aid of angle-resolved polarized Raman technique, the Raman modes of rhombohedral Cr 2 S 3 for the first time based on crystal symmetry and Raman selection rules are rationally assigned.

Transition metal dichalcogenides (TMDs) consist of dozens of ultrathin layered materials that have significantly different properties due to their varied phases, which determine the properties and application range of TMDs. Interestingly, a controllable phase transition in TMDs is achieved extensively with the use of several methods. Thus, phase control is a promising way to fully exploit the potential of TMDs. This review introduces the recent rapid development of the study of the TMD phase control, starting from the basic conception of the phase and phase transition in TMDs to the strategies for obtaining phase control. The different strategies are roughly classified into several types based on their characteristics: doping, synthesis method, strain, thermal method, and interlayer coupling. Finally, an evaluation on the prospect of the emergent strategies is provided.

GaTe is an important III-VI semiconductor with direct bandgap; thus, it holds great potential in the field of optoelectronics. Although it is known that GaTe can exist both in monoclinic and hexagonal phases, current studies are still exclusively restricted to the monoclinic phase of two dimensional (2D) GaTe owing to the difficulty in the fabrication of 2D hexagonal GaTe. Both monoclinic and hexagonal GaTe are demonstrated in this work, which can be selectively synthesized via a physical vapor deposition method, under precisely controlled growth temperatures. The pristine Raman and non-linear optical properties of hexagonal GaTe has been systematically explored for the first time; moreover, a novel selected-area phase transition from hexagonal to monoclinic of GeTe has been achieved via fs-laser irradiation. This work may pave the way for widely use of 2D GaTe in various fields in future.a strategy for selected-area phase transition from h-GaTe to m-GaTe, which may pave the way for wide applications of GaTe in future.

layer-dependent bandgap, [10] valley selective circular dichroism, [11] high on/off ratio, [12] and high thermostability [12] of the 2D MoS 2 . The performance of these novel devices significantly depends on the intrinsic optical properties (especially the dielectric function) of the 2D MoS 2 , which exhibit an intriguing layer dependency due to the enhanced quantum confinement effect and the absence of inversion symmetry. Therefore, the effective characterization of the layer-dependent optical properties of MoS 2 is critical for the performance improvement and the optimal design of those photoelectric devices based on MoS 2 .Layer-dependent optical properties of MoS 2 , including absorbance, [1] photoluminescence spectra, [10] Raman spectra, [13] and second-harmonic generation effect, [14] have been measured and discussed previously. However, these studies can hardly gain the basic optical constants, such as dielectric function, complex refraction index, etc., which play an important role in the quantitative design and optimization of those MoS 2 -based photoelectric devices. [15] Beyond these researches, there are also some reports on the dielectric function of the 2D MoS 2 , where the techniques they used can be roughly divided into three types: ellipsometry, [16][17][18][19][20][21][22][23][24][25][26] reflection (or absorption) spectrum method, [27,28] and contrast spectrum or differential reflection (or transmission) spectrum method. [29,30] By using of ellipsometry, Li et al. investigated the optical properties of the monolayer and bulk MoS 2 , and identified some critical points (CPs) in their dielectric function spectra. [22] The frequency-dependent reflection (transmission) spectra and corresponding differential spectra of the monolayer MoS 2 were simultaneously measured by Morozov et al., then the dielectric function was extracted. [27] Li et al. measured the reflection spectra of the mechanical exfoliation monolayer MoS 2 flake and the bulk MoS 2 , then their dielectric functions were calculated combined with a Kramers-Kronig constrained variational analysis. [28] Nevertheless, these published experimental reports on the dielectric function of MoS 2 mainly focus on the monolayer and bulk counterpart and the spectral range is relatively narrow. Apart from these experimental studies, some researchers have also devoted to predict the dielectric properties of the 2D MoS 2 with the help of theoretical calculations. [31,32] For example, Johari et al. studied the dielectric properties of monolayer, bilayer, and bulk MoS 2 by computing the electron Wafer-scale, high-quality, and layer-controlled 2D MoS 2 films on c-sapphire are synthesized by an innovative two-step method. The dielectric functions of MoS 2 ranging from the monolayer to the bulk are investigated by spectroscopic ellipsometry over an ultra-broadband (0.73-6.42 eV). Up to five critical points (CPs) in the dielectric function spectra are precisely distinguished by CP analysis, and their physical origins are identified in the band structures with ...

The important role of p-n junction in modulation of the optoelectronic properties of semiconductors is widely cognized. In this work, for the first time the synthesis of p-GaSe/n-MoS heterostructures via van der Waals expitaxial growth is reported, although a considerable lattice mismatching of ≈18% exists. According to the simulation, a significant type II p-n junction barrier located at the interface is expected to be formed, which can modulate optoelectronic properties of MoS effectively. It is intriguing to reveal that the presence of GaSe can result in obvious Raman and photoluminescence (PL) shift of MoS compared to that of pristine one, more interestingly, for PL peak shift, the effect of GaSe-induced tensile strain on MoS has overcome the p-doping effect of GaSe, evidencing the strong interlayer coupling between GaSe and MoS . As a result, the photoresponse rate of heterostructures is improved by almost three orders of magnitude compared with that of pristine MoS .

Chemical vapor deposition growth of 1T' ReS Se alloy monolayers is reported for the first time. The composition and the corresponding bandgap of the alloy can be continuously tuned from ReSe (1.32 eV) to ReS (1.62 eV) by precisely controlling the growth conditions. Atomic-resolution scanning transmission electron microscopy reveals an interesting local atomic distribution in ReS Se alloy, where S and Se atoms are selectively occupied at different X sites in each Re-X octahedral unit cell with perfect matching between their atomic radius and space size of each X site. This structure is much attractive as it can induce the generation of highly desired localized electronic states in the 2D surface. The carrier type, threshold voltage, and carrier mobility of the alloy-based field effect transistors can be systematically modulated by tuning the alloy composition. Especially, for the first time the fully tunable conductivity of ReS Se alloys from n-type to bipolar and p-type is realized. Owing to the 1T' structure of ReS Se alloys, they exhibit strong anisotropic optical, electrical, and photoelectric properties. The controllable growth of monolayer ReS Se alloy with tunable bandgaps and electrical properties as well as superior anisotropic feature provides the feasibility for designing multifunctional 2D optoelectronic devices.