Two-dimensional transition-metal dichalcogenides (TMDCs) possess unique electronic and optical properties, which open up a new opportunity for atomically thin optoelectronic devices. Synthesizing large-scale monolayer TMDCs on the SiO 2 /Si substrate is crucial for practical applications, however, it remains a big challenge. In this work, a method which combines chemical vapor deposition (CVD) and thermal evaporation was employed to grow monolayer tungsten disulfide (WS 2 ) crystals. Through controlling the density and the distribution of W precursors, a wafer-scale continuous uniform WS 2 film was achieved, with the structural and spectral characterizations confirming a monolayer configuration and a high crystalline quality. Wafer-scale field-effect transistor arrays based on the monolayer WS 2 were fabricated. The devices show superior electrical performances, and the maximal mobility is almost 1 order of magnitude higher than those of CVD-grown large-scale TMDC devices reported so far.

Among large numbers of transition metal dichalcogenides (TMDCs), monolayer rhenium disulfide (ReS2) is of particular interest due to its unique structural anisotropy, which opens up unprecedented opportunities in dichroic atomical electronics. Understanding the domain structure and controlling the anisotropic evolution of ReS2 during the growth is considered critical for increasing the domain size toward a large-scale growth of monolayer ReS2. Herein, by employing angle-resolved Raman spectroscopy, we reveal that the hexagonal ReS2 domain is constructed by six well-defined subdomains with each b-axis parallel to the diagonal of the hexagon. By further combining the first-principles calculations and the transmission electron microscopy (TEM) characterization, a dislocation-involved anisotropic evolution is proposed to explain the formation of the domain structures and understand the limitation of the domain size. Based on these findings, growth rates of different crystal planes are well controlled to enlarge the domain size, and moreover, single-crystal domains with a triangle shape are obtained. With the improved domain size, large-scale uniform, strictly monolayer ReS2 films are grown further. Scalable field-effect transistor (FET) arrays are constructed, which show good electrical performances comparable or even superior to that of the single domains reported at room temperature. This work not only sheds light on comprehending the novel growth mechanism of ReS2 but also offers a robust and controllable strategy for the synthesis of large-area and high-quality two-dimensional materials with low structural symmetry.

We perform a systematic investigation of MnPSe3/CrBr3 two-dimensional (2D) van der Waals heterostructures through first-principles calculations. The most stable stacking configuration of MnPSe3/CrBr3 heterostructures is found to have an indirect type-II band structure. Biaxial tensile strain is employed to tailor the spin–valley properties of the heterostructures in terms of the momentum, energy and spin components of the valleys. A novel opposite spin splitting evolution appears at the K and K′ valleys of the top valance band (TVB) with increasing tensile strain. A change from an indirect to a direct band gap is found at 7% tensile strain. A maximum spin splitting of 34.7 meV at the K′ valley is produced simultaneously with valley polarization under a tensile strain of 10%. The spin components distributed at the TVB are found to be controlled by strain-related competition between direct exchange interaction and indirect superexchange interaction of Se (px  +  py ) and Se pz orbitals. Spin polarization precisely regulated by strain can facilitate the manipulation of valley and spin degrees of freedom in MnPSe3/CrBr3 heterostructures, which opens up great potential for novel applications, such as strained sensor, spintronic and valleytronic devices.

Resonant plasmonic coupling has been considered as a promising strategy to enhance the optical response and manipulate the polarization of two-dimensional (2D) layer materials toward the practical applications. Here, a hybrid structure with periodic Ag nanoprism arrays was designed and fabricated on 2D GaSe layers to enhance these optical properties. By using the optimized hybrid structure with well-matched resonance, significant enhanced Raman scattering and band edge emission were successfully realized, and it is also interestingly found that the higher enhancement would be achieved while decreasing the thickness of GaSe layers. Theoretical simulation indicated that the strongly enhanced local field and the modified charge densities are the main reasons. By further introducing the patterned gratings on the plasmonic hybrid structure, selective excitation with controllable polarization was readily realized, besides the strongly enhanced photoluminescence intensity. This work provides a strategy for the plasmonic engineering of polarization controllable 2D optoelectronic devices.

In this work, the electronic and spintronic properties of GaSe/HfSe2 heterostructure under different strains are investigated through first-principles calculations. The results indicate that GaSe/HfSe2 heterostructure has an intrinsic type I band alignment, and the band structure is sensitive to the strain. A transition from type-I to type-II band alignment is found under a tensile stress. The evolution of the band structures is analyzed by the decomposed-projected band structures. Moreover, switchable spin textures of GaSe/HfSe2 heterostructure with different strains are also predicted. The controllable electronic spintronic properties of GaSe/HfSe2 heterostructure hold a great promise in applications of nanoelectronics and spintronics.

Considerable enhancements of room temperature circular polarization and anisotropic optical response in 2D GaSe are achieved through the strain manipulation.

Development of two-dimensional (2D) nanoelectronics is appealing for electrically tunable properties in 2D materials. By means of density functional theory computations, we systematically study the modulation of vertical electric field on the electronic structure and spintronic properties of monolayer GaGeTe. A transition from indirect to direct bandgap is realized with an electric field of 0.11 V Å −1 . The direct bandgap monotonously diminishes due to the giant Stark effect with a Stark coefficient of 3.68 Å. A critical electric field of 0.43 V Å −1 is predicted, at which the semiconductor-to-metal transition occurs, and the effective mass of holes is correspondingly tuned to as low as 0.16 m 0 . Electric-field-induced SOC plays an important role in the spintronic properties of monolayer GaGeTe so that a widely tunable SOC splitting from 0 to 78.3 meV is achieved, and switchable spin-polarization features are also predicted in the spin texture. The spin splitting is attributed to the Rashba effect with the Rashaba contribution coefficients tuned from 0 eVÅ to 0.15 eVÅ. As the all-electrical control method is demonstrated, the physical mechanism related to the redistribution of the electronic states is further revealed. The outstanding electronic and transport features as well as the widely controllable spintronic properties of monolayer GaGeTe hold a great promise for their applications in the field of 2D nanoelectronics and spintronics.

Spin injection performance in GaN film was systematically investigated through the three-terminal Hanle spin precession measurements with the comparison of varied tunnel barrier thickness, spin injector materials, and channel widths. Spin relaxation time and diffusion length were optimized to 37.3 ps and 139.0 nm at room temperature, respectively. With the optimal spin injector, a 12% spin polarization was obtained in a four-terminal non-local spin valve device. By applying the optimized spin injector structure to the spin-light emitting diodes, room temperature circular polarization ratios of 6.2% and 9.2% for Co and Fe spin polarizers were respectively achieved at surface-emission.