Graphether: a two-dimensional oxocarbon as a direct wide-band-gap semiconductor with high mechanical and electrical performances.

Although many graphene derivatives have sizable band gaps, their electrical or mechanical properties are significantly degraded due to the low degree of π-conjugation. Besides the π-π conjugation, there exist hyperconjugative interactions arising from the delocalization of σ electrons. Inspired by the structural characteristics of a hyperconjugated molecule, dimethyl ether, we design a two-dimensional oxocarbon (named graphether) by the assembly of dimethyl ether molecules. Our first-principles calculations reveal the following findings: (1) monolayer graphether possesses excellent dynamic and thermal stabilities as demonstrated by its favourable cohesive energy, the absence of soft phonon modes, and high melting point. (2) It has a direct wide-band-gap energy of 2.39 eV, indicating its potential applications in ultraviolet optoelectronic devices. Interestingly, the direct band gap feature is rather robust against the external strains (-10% to 10%) and stacking configurations. (3) Due to the hyperconjugative effect, graphether has the high intrinsic electron mobility. More importantly, its in-plane stiffness (459.8 N m-1) is even larger than that of graphene. (4) The Pt(100) surface exhibits high catalytic activity for the dehydrogenation of dimethyl ether. The electrostatic repulsion serves as a driving force for the rotation and coalescence of two dehydrogenated precursors, which is favourable for the bottom-up growth of graphether. (5) Replacement of the C-C bond with an isoelectronic B-N bond can generate a stable Pmn21-BNO monolayer. Compared with monolayer hexagonal boron nitride, Pmn21-BNO has a moderate direct band gap energy (3.32 eV) and better mechanical property along the armchair direction.