Raman scattering from ZnO incorporating Fe nanoparticles: Vibrational modes and low-frequency acoustic modes

Nanocrystaline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe2O3, ZnFe2O4) and the mean crystalline size (8–52 nm). In this paper we report the experimental spectra of Raman scattering. Main characteristics of experimental Raman spectrum in 200–1600 cm−1 spectral region are: sharp peak at 436 cm−1 and broad two-phonon structure at ∼1150 cm−1, typical for ZnO; broad structure below 700 cm−1 that has different position and shape in case of ZnFe2O4 or Fe2O3 nanoparticles. Low-frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum approximation, which considers nanoparticle as homogeneous elastic sphere.

Research highlightsNanocrystaline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe2O3, ZnFe2O4) and the mean crystalline size (8–52 nm). Small amount (5 wt.%) of Fe2O3 at the beginning of the synthesis results in forming of ZnFe2O4 nanoparticles. Large amount (90 wt.%) of Fe2O3 at the beginning of the synthesis results in forming Fe2O3 nanoparticles. Both samples contain ZnO phase which is not registered by XRD, but is clearly seen in the Raman spectra. Main characteristics of experimental Raman spectrum in 200–1600 cm−1 spectral region are: sharp peak at 436 cm−1 and broad two-phonon structure at ∼1150 cm−1, typical for ZnO; broad structure below 700 cm−1 that has different position and shape in case of ZnFe2O4 or Fe2O3 nanoparticles. In low-frequency Raman spectra of ZnFe2O4 nanoparticles registered peaks agree well with the calculated frequencies of acoustic phonons. As a result we identified (0,2), (0,0), (2,2) and (1,0) modes.