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 pi-conjugation. Besides the pi-pi conjugation, there exist hyperconjugative interactions arising from the delocalization of sigma 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 Pmn2(1)-BNO monolayer. Compared with monolayer hexagonal boron nitride, Pmn2(1)-BNO has a moderate direct band gap energy (3.32 eV) and better mechanical property along the armchair direction.