Tuning of the electronic and photocatalytic properties of Janus WSiGeZ 4 (Z = N, P, and As) monolayers via strain engineering.

Recently, MA 2 Z 4 materials have received tremendous attention due to their amazing electronic, spintronic, and optoelectronic properties. In this work, we propose a class of 2D Janus materials WSiGeZ 4 (Z = N, P, and As). It was found that their electronic and photocatalytic properties are sensitive to the change of the Z element. Biaxial strain results in an indirect-direct band gap transition in WSiGeN 4 and a semiconductor-metal transition in WSiGeP 4 and WSiGeAs 4 . Comprehensive studies demonstrate that these transitions as well as valley-contrasting physics are closely related to the crystal field induced orbital distribution. By taking into account several features of the excellent photocatalysts reported for water splitting, we predict three promising photocatalytic materials WSi 2 N 4 , WGe 2 N 4 , and WSiGeN 4 . Their optical and photocatalytic properties can be well modulated by applying biaxial strain. Our work not only provides a class of potential electronic and optoelectronic materials but also enriches the study of Janus MA 2 Z 4 materials.