Highly stable two-dimensional α1-MA2Z4 (M = Mg, Ca, Sr; A = Al; Z = S, Se) monolayers with promising photocatalysis and piezoresistive effect

The fundamental properties of two-dimensional α1-MA2Z4 (M = Mg, Ca, Sr; A = Al; Z = S, Se) monolayers have been systematically investigated based on the first principles calculations. Our results show that the α1-MA2Z4 monolayers have mixed ionic-covalent bonding character. The structural stability analyses reveal that all structures are dynamically stable and sustain stability below 800 K. All α1-MA2Z4 monolayers exhibit semiconducting property. The suitable bandgaps and the band edges alignment strides the redox potentials of water splitting, having potential as the candidates of the photocatalyst. All structures are predicted to possess isotropic electron-dominated mobility, which increases from 340.79 to 591.84 cm2 s−1 V−1 with the increase in atomic number of the alkaline-earth metal and chalcogen group. Further imposing the strain along the armchair direction, the electron mobility of α1-MA2Z4 can be enhanced to ∼103 cm2 V−1 s−1, especially the electron mobility of α1-MgA2S4 even increases to ∼2 × 103 cm2 V−1 s−1. The increased electron mobility indicates the reduced resistivity, which shows that the α1-MA2Z4 monolayers possess a remarked piezoresistive effect. The outstanding properties indicate that the α1-MA2Z4 is promising in photocatalysis and flexible electronics fields.