Two Dimensional MOene: From Superconductors to Direct Semiconductors and Weyl Fermions.

Yan, Luo; Zhu, Jiaojiao; Wang, Bao-Tian; He, Junjie; Song, Hai-Zhi; Chu, Weibin; Tretiak, Sergei; Zhou, Liujiang · Nano Lett · 2022

basic_science · Level V

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Abstract

The number of semiconducting MXenes with direct band gaps is extremely low; thus, it is highly desirable to broaden the MXene family beyond carbides and nitrides to expand the palette of desired chemical and physical properties. Here, we theoretically report the existence of the single-layer (SL) dititanium oxide 2H-Ti<sub>2</sub>O MOene (MXene-like 2D transition oxides), showing an Ising superconducting feature. Moreover, SL halogenated 2H- and 1T-Ti<sub>2</sub>O monolayers display tunable semiconducting features and strong light-harvesting ability. In addition, the external strains can induce Weyl fermions via quantum phase transition in 2H-Ti<sub>2</sub>OF<sub>2</sub> and Ti<sub>2</sub>OCl<sub>2</sub> monolayers. Specifically, 2H- and 1T-Ti<sub>2</sub>OF<sub>2</sub> are direct semiconductors with band gaps of 0.82 and 1.18 eV, respectively. Furthermore, the carrier lifetimes of SL 2H- and 1T-Ti<sub>2</sub>OF<sub>2</sub> are evaluated to be 0.39 and 2.8 ns, respectively. This study extends emerging phenomena in a rich family of 2D MXene-like MOene materials, which provides a novel platform for next-generation optoelectronic and photovoltaic fields.