Interlayer coupling in two-dimensional titanium carbide MXenes

Success in the exfoliation of the stacked T-functionalized titanium carbide MXenes Tin+1CnT2 (T = OH, O, and F) would potentially extend their application scope, which requires an understanding of the nature of interlayer coupling. Here, we report for the first time the intrinsic interlayer coupling in pristine MXenes on the basis of first-principles calculations by taking long-range interaction into account. It is demonstrated that the functional terminations (OH, O, and F) weaken the interlayer coupling as compared with the bare counterparts, whereas the coupling is significantly stronger than van der Waals bonding as specified by the fact that the binding energies of stacked Tin+1CnT2 are 2-6 times those of well-known graphite and MoS2 with weak interlayer coupling. With binding energies in the range of 1-3.3 J m(-2), the successful exfoliation of stacked Tin+1CnT2 into monolayers invariably requires further weakening of the interlayer coupling.