Ti 3 C 2 T x MXene intercalated with Li + ions was produced and ion-exchanged with a series of trimethylalkylammonium (AA) cations of increasing alkyl chain length. A discontinuous expansion in the MXene layer spacing was observed, attributed to complete packing of the interlayer space at a critical chain length. The latter was used to estimate the number of cations per Ti 3 C 2 formula unit, which was found to be in good agreement with a similar quantification obtained from X-ray photoelectron spectroscopy, energy-dispersive spectroscopy, and elemental analysis. The system was also modeled using density functional theory and molecular dynamics, arriving at cation concentrations in the same range. The intercalated AA cations led to tunable increases in resistivity of the normally highly electrically conductive MXene and were investigated as interlayer pillars in electrochemical capacitors.

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Niobium-carbide nanocomposite coatings with a carbon content varying from 43 -64 at.% were deposited by dual DC magnetron sputtering. X-ray diffraction, x-ray photoelectron spectroscopy and electron microscopy showed that all coatings consisted of nanometer sized NbC grains embedded in a matrix of amorphous carbon. Mechanical properties and electrical resistivity showed a strong dependency on the amount of amorphous carbon (a-C) and NbC grain size in the coating. The highest hardness (23 GPa), elastic modulus (295 GPa) and the lowest resistivity (260 µΩcm) were measured for the coating with about 15 % of a-C phase.Contact resistance measurements using a crossed cylinder set-up showed lowest contact resistance for the coating containing 33 % a-C (140 µΩ at a contact force of 100 N), which is comparable to a Ag reference (45 µΩ at a contact force of 100 N). Comparison with TiCbased nanocomposites studied under similar conditions showed that the Nb-C system has less tendency to form a-C and that lowest contact resistance is obtained at comparable amounts of a-C phase in both material systems (33 % for Nb-C compared to 35 % for Ti-C). With these good electrical contact properties, the Nb-C nanocomposites can be considered as a potential material for electrical contact applications.

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