Charge Density Waves in Exfoliated Films of van der Waals Materials: Evolution of Raman Spectrum in TiSe2

A number of the charge-density-wave materials reveal a transition to the macroscopic quantum state around 200 K. We used graphene-like mechanical exfoliation of TiSe2 crystals to prepare a set of films With different thicknesses The transition temperature to the charge-density-wave state was determined Via modification of Raman spectra of TiSe2 films It was established that the transition temperature can increase from its bulk value to similar to 240 K as the thickness of the van der Waals films reduces to the nanometer range. The obtained results are important for the proposed applications of such materials in the collective-state information processing, which require room-temperature operation.