Halogenation induced transition of superconductor-to-semiconductor in MXene-like MOene with direct band gap and long carrier lifetime

Abstract

Traditional MXenes with intriguing mechanical and electronic properties, together with the fertilities of elemental compositions and chemical decorations have aroused much attentions. However, the semiconducting traits with direc band gap are extremetely rare among reported MXenes. Thus, broadening the family of MXene beyond carbides and nitrides with unique behaviors is still an extraordinary and fascinating field. By using the first-principles calculations, the most stable single-layer (SL) dititanium oxide Ti 2 O with edge-sharing trigonal prisms (labled as 1H-Ti 2 O) has been obtained with particle-swarm optimization methods. Similar to the SL 1T-Ti 2 O MOene proposed in our previous work, here, 1H-Ti 2 O monolayer is also an electride material that anionic electron existis on its surface, and an intrinsic Ising superconductor with transition temperature T c of ∼ 4.7 K. Moreover, the electronic properties of SL 1Hand 1T-Ti 2 O are strongly assocated with the functional groups. In particular, halogenated 1H-and 1T-Ti 2 O monolayers, namely, 1H-and 1T-Ti 2 OX 2 (X=F, Cl) are semiconductors with direct band gap of 0.58−1.18 eV, indicating their attractive performance in optoelectronic and photovoltaic fields. The absorption spectra indicate that SL 1H-and 1T-Ti 2 OX 2 have strong light harvest ability from ultraviolet to nearinfrared region, favoing their potential applications in solar cells and infrared detectors. Furthermore, via the ab initio nonadiabatic molecular dynamics, the carrier lifetimes of 1H-and 1T-Ti 2 OF 2 monolayer are evaluated to be 0.39 and 2.8 ns, respectively, which are comparable to that of MoS 2 monolayer (0.39 ns) and multilayer halide perovskites (0.65−1.04 ns). Here, the SL 1T-Ti 2 OF 2 with a larger band gap and a weaker nonradiative coupling exhibits a prolonged electron-hole recombination when compared with 1H-Ti 2 OF 2 monolayer. This finding further broadens the family of traditional MXenes to MOenes with multifunctional and adjustable properties, and would motivate more efforts in theories and experiments about MOenes family.