Chemical bonding in carbide MXene nanosheets

TL;DR

This study investigates the chemical bonding and surface chemistry of MXene nanosheets using X-ray photoelectron spectroscopy, revealing how surface modifications influence their electronic structure and properties.

Contribution

It provides new insights into the surface chemistry and electronic structure of MXenes, especially regarding the effects of oxidation and sputtering.

Findings

Band structure changes depend on nanosheet thickness.

Surface oxidation significantly alters electronic properties.

Adsorption sites influence surface chemistry.

Abstract

The chemical bonding in the carbide core and the surface chemistry in a new group of transition-metal carbides Tin+1Cn-Tx (n=1,2) called MXenes have been investigated by surface-sensitive valence band X-ray photoelectron spectroscopy. Changes in band structures of stacked nano sheets of different thicknesses are analyzed in connection to known hybridization regions of TiC and TiO2 that affect elastic and transport properties. By employing high excitation energy, the photoelectron cross-section for the C 2s - Ti 3d hybridization region at the bottom of the valence band is enhanced. As shown in this work, the O 2p and F 2p bands are shown to strongly depend both on the bond lengths to the surface groups and the adsorption sites. The effect of surface oxidation and Ar+ sputtering on the electronic structure is also discussed.