X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in Cu_{x}TiSe_{2} as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. The results show a CDW incommensuration arising at an intercalation value coincident with the onset of superconductivity at around x=0.055(5). Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up to x=0.091(6), the highest copper concentration examined in this study. The phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.

MXenes comprise a class of 2D materials with attractive properties for use in electronically functional composites. However, a fundamental understanding of these properties at the scale of individual flakes is necessary. Here, we use resonance Raman scattering of Ti3C2T x MXenes to study their vibrational modes as a function of the flake thickness and surface terminations. Enhancement enables a precise comparison of the peak shifts in MILD/HF-method etching environments that produce different functional group densities on the MXene layer surfaces. We find that the enhanced Raman modes are sensitive to the different electron-withdrawing character of the surface functional groups.

Unambiguous determination of the optical dynamics in MXenes is necessary for their reliable development into applications such as EMI shielding, energy storage, and laser systems. Here, simultaneous ultrafast transmission and reflection (SUTR) is used to determine the temporal change in refractory index (n) and extinction coefficient (k) of Ti 3 C 2 T x from 450 to 1300 nm which is dominated by intraflake mechanisms. We assign the dynamics for wavelengths below 600 nm with interband transitions, while those at 800 nm are assigned to a plasmon resonance. The response from 1000 to 1300 nm shows changes in index of refraction with no changes in extinction coefficient, consistent with free carriers.