Multi-modal Spectroscopic Study of Surface Termination Evolution in\n Cr2TiC2Tx MXene

Control of surface functionalization of MXenes holds great potential, and in\nparticular, may lead to tuning of magnetic and electronic order in the recently\nreported magnetic Cr2TiC2Tx. Here, vacuum annealing experiments of Cr2TiC2Tx\nare reported with in situ electron energy loss spectroscopy and novel in situ\nCr K-edge extended energy loss fine structure analysis, which directly tracks\nthe evolution of the MXene surface coordination environment. These in situ\nprobes are accompanied by benchmarking synchrotron X-ray absorption fine\nstructure measurements and density functional theory calculations. With the\netching method used here, the MXene has an initial termination chemistry of\nCr2TiC2O1.3F0.8. Annealing to 600 C results in the complete loss of -F, but -O\ntermination is thermally stable up to (at least) 700 C. These findings\ndemonstrate thermal control of -F termination in Cr2TiC2Tx and offer a first\nstep towards termination engineering this MXene for magnetic applications.\nMoreover, this work demonstrates high energy electron spectroscopy as a\npowerful approach for surface characterization in 2D materials.\n