Chemical bonding in carbide MXene nanosheets

The valence band of a new 2D material called MXene is probed by X-ray photoelectron spectroscopy. Changes in the Ti-C bond strength of the carbide core is shown to depend on the atomic layer thickness. The O 2p and the F 2p band positions of the termination groups depend both on the adsorption sites and bond lengths. Due to a different bonding, the binding energy from the Fermi level of the F 2p band (∼9 eV) is larger than for the O 2p band (∼6 eV). The samples must be freshly made to avoid surface oxidation and Ar+ sputtering should be avoided.