Identifying the Atomic Layer Stacking of Mo 2 C MXene by Probe Molecule Adsorption.

A density functional theory study is presented here aimed at investigating whether the atomic stacking on the new family of two-dimensional MXene materials has an influence on their adsorption properties and whether these properties can provide information about this structural feature. To this end, the Mo 2 C MXene, exhibiting two nearly degenerate crystal structures with either ABC or ABA atomic stacking, is chosen as a case study. The study of the adsorption of CO, CO 2 , and H 2 O on both polymorphs of Mo 2 C reveals substantial differences that could be used in experiments to provide information about the atomic stacking of a given sample. Particularly, we show that the asymmetric and symmetric stretching modes of the adsorbed CO 2 and the CO stretching mode are clear features that allow one to identify the stacking of atomic layers of the Mo 2 C MXene. The present finding is likely to apply to other MXenes as well.