Raman scattering in In2Se3 and InSe2 amorphous films

Raman scattering (RS) in both In2Se3 and InSe2 amorphous films has been studied by micro-Raman in backscattering geometry at room temperature. The 40 μm thick films were prepared by thermal vacuum deposition onto a borosilicate glass substrate. The In2Se3 amorphous film was stripped off from the substrate. The recorded Raman spectra of both amorphous films reveal a general phonon density-of-states character, though some contribution of molecular-like character in the case of In2Se3 amorphous film is observed. The Raman spectra of In2Se3 film appear to be related to that of the α-In2Se3 crystal, while those of InSe2 seem to be related to the γ-In2Se3 crystal. The peaks in the frequency range from the Rayleigh line up to about 240 cm−1 are attributed to the folding of TA–LA and TO–LO crystal related modes. The strongest feature at 254 cm−1 and a shoulder at 235 cm−1 in the Raman spectrum of In2Se3 film are attributed to Se8 rings and Sen polymer molecules, while the one at 490 cm−1 is assigned to a second order contribution. The 150 cm−1 feature in InSe2 a-film is related to the zone center mode of the γ-In2Se3 crystal. The Raman spectra suggest that the structure of In2Se3 film is composed of linked InSe4 tetrahedral clusters with locally distributed Sen polymer and Se8 ring molecules. For InSe2, the structure of the film seems to be composed of InSe4 clusters linked by Se atoms at the corners shared by two vicinal tetrahedra.