First-principles study on the structure and electronic properties of MCS (M = Sc, Ti, Y, Zr and Hf, = 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 MCS (M = Sc, Ti, Y, Zr, and Hf, = 1, 2) were investigated by density functional theory (DFT). Our results showed that the studied MCS except YCS are thermodynamically, dynamically, thermally, and mechanically stable. The p-d hybridization between the M-d state and the C/S-p state of MCS is stronger than that of the corresponding MCS. 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 YCS. This provides an explanation for the experimentally observed formation of non-stoichiometric TiCS. The room-temperature electron mobilities of semiconductor ScCS (YCS) along the and directions were determined to be 232.59 (818.51) and 628.22 (552.55) cm V s, and the room-temperature hole mobilities are only 88.32 (1.64) and 61.75 (17.80) cm V s. This work is expected to provide theoretical insights for the preparation and application of S-terminated MXenes.