Characterizing the Chemical Structure of Ti₃C₂T_x MXene by Angle-Resolved XPS Combined with Argon Ion Etching

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti₃C₂T_x MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti-C bond. XPS results obtained after argon ion etching indicated staggered distribution between C-Ti-C bond and O-Ti-C, F-Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti₃C₂T_x MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti₃C₂ layer acting as surface functional groups. The surface functional groups on the Ti₃C₂ layer were determined to include O^2-, OH^-, F^- and O^--F^-, among which F atoms could also desorb from Ti₃C₂T_x MXene easily. The schematic atomic structure of Ti₃C₂T_x MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.