Tunable type-II lateral MoSi 2 N 4 /WSi 2 N 4 heterostructures for photocatalytic applications.

Combining various two-dimensional crystals has emerged as an exciting way to tailor the properties of lateral heterostructures for new-generation optoelectronic devices. Herein, a seamless lateral heterostructure based on MoSi 2 N 4 and MoSi 2 N 4 monolayers along armchair interfaces is predicted, and its electronic and optical properties are investigated by using first principles calculations. Our calculations indicate that the MoSi 2 N 4 /WSi 2 N 4 lateral heterostructures (HSs) possess excellent stability due to the very small lattice mismatch. In contrast to their parent monolayers with wide indirect band gaps, all (MoSi 2 N 4 ) m (WSi 2 N 4 ) n lateral HSs are direct gap semiconductors, and their direct gap nature is independent of compositions and strains. The band alignment of (MoSi 2 N 4 ) m (WSi 2 N 4 ) 16- m lateral HSs undergoes a quasi-type-I to type-II to quasi-type-II to quasi-type-I band transition with an increase in m . (MoSi 2 N 4 ) 8 (WSi 2 N 4 ) 8 is a type-II semiconductor, and the band arrangement changes from type-II to quasi-type-I upon applying tensile strain. Compared with pristine materials, the band edges of MoSi 2 N 4 /WSi 2 N 4 lateral HSs are more favorable for photocatalytic water splitting. Furthermore, MoSi 2 N 4 /WSi 2 N 4 lateral HSs exhibit higher visible light absorption. These results greatly expand the optoelectronic applications of Mxenes in the 2D realm.