First-principles study on the structure and electronic properties of M2CSx (M = Sc, Ti, Y, Zr and Hf, x=1, 2)

Two-dimensional (2D) transition metal carbides/nitrides, known as MXenes, have attracted extensive attention due to their rich elemental composition and diverse surface chemistry. In this study, the crystal structure, electronic, mechanical, and electronic transport properties of M2CSx (M = Sc, Ti, Y, Zr, and Hf, x = 1, 2) were investigated by density functional theory (DFT). Our results showed that the studied M2CSx except Y2CS2 are thermodynamically, dynamically, thermally, and mechanically stable. The p-d hybridization between the M-d state and the C/S-p state of M2CS is stronger than that of the corresponding M2CS2. However, the antibonding state would appear near the Fermi level and thus reduce the thermal stability of the material due to the introduction of sulfur vacancies in the Y-free MXenes studied. In contrast, sulfur vacancies would significantly enhance the bonding states of Y-C and Y-S bonds and improve the stability of Y2CSx. This provides an explanation for the experimentally observed formation of non-stoichiometric Ti2CS1.2. The room-temperature electron mobilities of semiconductor Sc2CS (Y2CS) along the x and y directions were determined to be 232.59 (818.51) and 628.22 (552.55) cm(2) V-1 s(-1), and the room-temperature hole mobilities are only 88.32 (1.64) and 61.75 (17.80) cm(2) V-1 s(-1). This work is expected to provide theoretical insights for the preparation and application of S-terminated MXenes.