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Direct Correlation of MXene Surface Chemistry and Electronic Properties

MXenes are a class of 2D materials with the chemical formula Mn+1XnTx (M = transition metal element, X = C and/or N, and T = surface termination, e.g. –O, –OH, –F) with currently 20+ members and the potential for many more. Despite their recent discovery in 2011, MXenes have already demonstrated state-of-the-art performance in fields such as electromagnetic interference shielding, chemical sensing, and energy storage[1]. To a large extent, this exceptional performance is due to MXenes’ high metallic conductivity. Methods to further improve conductivity, and thus performance, are a central objective of MXene research. A promising approach is through surface chemistry engineering; density functional theory has predicted a strong influence of surface terminations on MXene conductivity[2]. To date, such predications lack experimental validation. Here, we directly correlate MXene surface chemistry and electronic transport through novel microscopy techniques: direct-detection electron energy-loss spectroscopy[3] (EELS) and simultaneous in situ heating (up to 775 °C) and electric biasing. Our experiments uncover important chemistry-property relationships which advance our fundamental understanding of MXenes and provide clear guidelines for the optimization of MXene devices.