The Versatile Electronic, Magnetic and Photo-Electro Catalytic Activity of a New 2D MA2 Z4 Family*.

The recent successful growth of MoSi2 N4 and WSi2 N4 monolayers led to the discovery of a new class of the two-dimensional (2D) MA2 Z4 materials with no known 3D layered allotropes, which renders great possibilities to integrate diverse properties by proper design of sandwiched "MZ2 " building blocks and "A-Z" passivation layers. In this work, the dynamic stability, electronic properties, and surface reactivity of the new MA2 Z4 family, in which M is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, A refers to Si or Ge, and Z is N, P or As, is theoretically probed. Among the proposed 54 possible combinations, about 42 compositions are dynamically stable, which vary from non-magnetic, anti-ferromagnetic, to ferromagnetic semiconductors, metals and half-metals. In particular, the VB (V, Nb, Ta) MA2 Z4 possesses robust intrinsic ferromagnetism that is essential for spintronics applications. In regard to surface activity, most MA2 Z4 , particularly N- or P-terminated IVB and VB MA2 Z4 , have high catalytic potential for hydrogen evolution, and the ▵GH of non-magnetic MA2 Z4 is highly correlated to the highest occupied p electronic states of the surface Z atoms. The photocatalytic activity is also evaluated. MoSi2 N4 and WSi2 N4 within 4 % tensile strain are capable of photocatalytic overall water splitting. The findings indicate the new 2D MA2 Z4 family has fascinating properties and possesses strong potential for applications but not limited to electronics, spintronics and catalysts, which will stimulate the interests of experimental synthesis.