Vertical strain and electric field tunable band alignment in type-II ZnO/MoSSe van der Waals heterostructures.

The van der Waals heterostructure (vdWH) has attracted widespread attention as a unique structure for future electronic and optoelectronic devices. In this paper, we constructed the ZnO-SeMoS and ZnO-SMoSe vdWHs and systematically investigated their electronic structures and band alignments considering vertical strain and external electric field effects. It is found that the ZnO-SeMoS and ZnO-SMoSe vdWHs both exhibit type-II band alignment with indirect band gaps of 1.31 and 0.63 eV respectively, depending on the interface characteristics. What's more, the band alignment of these two heterostructures can be tuned to type I or type III, and their band gap can be modified to direct feature by applying vertical strain and an electric field. The results reveal that ZnO/MoSSe vdWHs have promising potential in multi-functional nanodevices, and provide a way to modify the electronic properties of Janus-based heterojunctions using interface characteristics.

Two-Dimensional In2X2X' (X and X' = S, Se, and Te) Monolayers with an Intrinsic Electric Field for High-Performance Photocatalytic and Piezoelectric Applications.

Two-dimensional (2D) materials with excellent photocatalytic properties and unique piezoelectric response have attracted great attention. However, these characters are rare for traditional 2D structures. With an intrinsic electric field, the Janus 2D materials show great promise in photocatalytic and out-of-plane piezoelectric applications. Herein, we show that Janus In2X2X' (X and X' = S, Se, and Te) monolayers are desirable in the overall water splitting and piezoelectric devices. Comprehensive investigations reveal that the band gaps of these Janus monolayers are from 0.34 to 2.27 eV. With proper band edge positions, strong solar absorption, fast transfer and efficient separation of carriers, and high solar to hydrogen (STH) efficiencies (reaching 37.70%), eight members of them stand out. Besides, the electrons and holes have sufficient driving forces in the process of redox reaction. The piezoelectric response for in- and out-of-plane is superior for all monolayers. These compelling features make them suitable for photocatalysts, sensors, actuators, and energy conversion devices.