Multimodal Spectroscopic Study of Surface Termination Evolution in Cr₂TiC₂T_x MXene

Control of surface functionalization of MXenes holds great potential, and in particular, may lead to tuning of magnetic and electronic order in the recently reported magnetic Cr₂TiC₂T_x. Here, vacuum annealing experiments of Cr₂TiC₂T_x are reported with in situ electron energy loss spectroscopy and novel in situ Cr K-edge extended energy loss fine structure analysis, which directly tracks the evolution of the MXene surface coordination environment. These in situ probes are accompanied by benchmarking synchrotron X-ray absorption fine structure measurements and density functional theory calculations. With the etching method used here, the MXene has an initial termination chemistry of Cr₂TiC₂O_1.3F_0.8. Annealing to 600 °C results in the complete loss of -F, but -O termination is thermally stable up to (at least) 700 °C. These findings demonstrate thermal control of F termination in Cr₂TiC₂T_x and offer a first step toward termination engineering this MXene for magnetic applications. Moreover, this work demonstrates high energy electron spectroscopy as a powerful approach for surface characterization in 2D materials.