| Summary: | Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> 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 Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti<sub>3</sub>C<sub>2</sub> layer acting as surface functional groups. The surface functional groups on the Ti<sub>3</sub>C<sub>2</sub> layer were determined to include O<sup>2−</sup>, OH<sup>−</sup>, F<sup>−</sup> and O<sup>−</sup>–F<sup>−</sup>, among which F atoms could also desorb from Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene easily. The schematic atomic structure of Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> 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.
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