Structure and vibrational spectra of ReSe2nanoplates

Theoretical and experimental vibrational spectra of ReSe(2)nanocrystals, synthesized by self-limited chemical vapor deposition (CVD), are reported. Scanning electron microscopy reveals that the nanocrystals have the shape of polygon nanoplates (NPs), 20 nm thick and about 100-300 nm wide. X-ray diffraction studies determined their triclinic structure (space group, P-1 [no. 2]). The wavenumbers of the Raman- and infrared (IR)-active phonon modes were calculated using the density functional perturbation theory (DFPT), along with the dispersion curves and phonon density of states. The set of theoretical phonon wavenumbers is found to correlate well with the experimental Raman and IR spectra. We established that, unlike ReS2, ReSe(2)does not exhibit a phonon gap. Several extra bands in the experimental Raman spectrum of ReSe(2)are argued to be defect-induced contributions of phonons from F and Q critical points of the Brillouin zone. In addition, the effect of Fermi resonance is observed in the Raman spectrum of the ReSe(2)NPs, which manifests itself in an increase of the intensity of second-order bands due to their interaction with first-order phonons.