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Van der Waals (vdW) heterojunctions constructed by vertical stacking two-dimensional transition metal dichalcogenides hold exciting promise in realizing future atomically thin electronic and optoelectronic devices. Recently, a Janus WSSe structure has been successfully synthesized by using chemical vapor deposition, selective epitaxy atomic replacement, and pulsed laser deposition methods. Herein, based on first-principles calculations, we introduce the structures and performances of MoS2/WSSe vdW heterojunctions with different interfaces and stacking modes. The vdW heterojunctions possess indirect band gaps for S–S interfaces, while direct band gaps for Se–S interfaces. Besides, the potential drop indicates an efficient separation of photogenerated charges. Interestingly, the opposite built-in electric fields formed in the vdW heterojunctions with a S–S interface and a Se–S interface suggest different charge transfer paths, which would motivate further theoretical and experimental investigations on charge transfer dynamics. Moreover, the electronic property is adjustable by applying external in-plane strains, accomplishing with indirect to direct bandgap transition and semiconductor to metal transition. The findings are helpful for the design of multi-functional high-performance electronic and optoelectronic devices based on the MoS2/WSSe vdW heterojunctions. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) heterojunctions constructed by vertical stacking two-dimensional transition metal dichalcogenides hold exciting promise in realizing future atomically thin electronic and optoelectronic devices. Recently, a Janus WSSe structure has been successfully synthesized by using chemical vapor deposition, selective epitaxy atomic replacement, and pulsed laser deposition methods. Herein, based on first-principles calculations, we introduce the structures and performances of MoS 2 /WSSe vdW heterojunctions with different interfaces and stacking modes. The vdW heterojunctions possess indirect band gaps for S-S interfaces, while direct band gaps for Se-S interfaces. Besides, the potential drop indicates an efficient separation of photogenerated charges. Interestingly, the opposite built-in electric fields formed in the vdW heterojunctions with a S-S interface and a Se-S interface suggest different charge transfer paths, which would motivate further theoretical and experimental investigations on charge transfer dynamics. Moreover, the electronic property is adjustable by applying external in-plane strains, accomplishing with indirect to direct bandgap transition and semiconductor to metal transition. The findings are helpful for the design of multi-functional high-performance electronic and optoelectronic devices based on the MoS 2 /WSSe vdW heterojunctions., (© 2021 IOP Publishing Ltd.)

Alumina (Al 2 O 3 ) is one of the most widely used ceramic materials for innumerable applications, due to its unique combination of attractive physical and mechanical properties. These intrinsic properties are dictated by the numerous phases that Al 2 O 3 forms and its related phase transformations. Transition metal (TM) cation dopants (iron (Fe), cobalt (Co), nickel (Ni) and manganese (Mn)), even in sparse amounts, have been shown to significantly affect the phase transformation and microstructural evolution of Al 2 O 3 . Small concentrations of TM cation dopants have successfully been incorporated to synthesize magnetically active Al 2 O 3 , while reducing the θ to α phase transformation temperature by 150 °C, and maintaining the outstanding mechanical properties. In addition, first-principle calculations based on density-functional theory with hybrid functional (HSE06) and the PBE+U methods have provided a mechanistic understanding of the formation energy and magnetism of the TM-doped α and θ phases of Al 2 O 3 . The results reveal a potential route for phase transition regulation and external magnetic field-induced texturing of Al 2 O 3 ceramics.