Phonon properties of 2D Ti3C2Cl2 MXenes

Abstract Tailoring the surface chemistry of MXenes is crucial for tuning their electronic, optical, catalytic, and mechanical properties. Phonons play a particularly important role in determining thermal properties, while they can also influence mechanical properties and electronic behavior, e.g., through electron–phonon coupling. Here, we report the synthesis of high-quality Ti ₃ C ₂ Cl ₂ MXenes, enabling the investigation of their intrinsic vibrational and thermal properties using a combination of in situ Raman spectroscopy, specific heat measurements, and ab initio calculations. The assessment of vibrational modes and their symmetries was based on polarized Raman spectroscopy, which revealed strong anisotropy between in-plane E and out-of-plane A ₁ modes. These observations are supported by density functional perturbation theory (DFPT) calculations, showing excellent agreement with the experimental results. We demonstrate that temperature induces reversible shifts and broadening of Raman peaks, which we attribute to anharmonic effects. Specific heat measurements further provide insights into the thermal behavior and acoustic phonon modes of Ti ₃ C ₂ Cl ₂ . We separate electron and phonon contributions to the specific heat and find evidence of the two-dimensional character of MXenes in the low temperature range — an effect often suppressed in other low-dimensional systems.