Raman scattering spectroscopy has been used for the characterization of zinc oxide nanoparticles obtained by mechanical activation in a high-energy vibro-mill and planetary ball mill. Raman modes observed in spectra of nonactivated sample are assigned to Raman spectra of the ZnO monocrystal, while the spectra of mechanically activated samples point out to the structural and stoichiometric changes, depending on the milling time and the choice of equipment. Observed redshift and peak broadening of the E 2 high and E 1 (LO) first-order Raman modes are attributed to increased disorder induced by mechanical milling, followed by the effects of phonon confinement due to correlation length decrease. The additional modes identified in Raman spectra of activated ZnO samples are related to the surface optical phonon modes, due to the intrinsic surface defects and presence of ZrO 2 as extrinsic defects introduced by milling in zirconia vials.
The conventional Raman scattering spectroscopy is one of the most used and powerful techniques for characterization of nano-sized materials and structures. By proper analysis of optical mode shift and broadening in nanomaterials based on phonon confinement model, it is possible to deduce about the influence of various effects like particle size and size distribution, strain, change of phonon dispersion, substitutional effects, defect states and nonstoichiometry, electron-phonon coupling. We have demonstrated potentials of this technique in CeO2 and TiO2 nanocrystalline systems analyzing their optical phonon properties.
The vibrational properties of CrI3 single crystals were investigated using Raman spectroscopy and were analyzed with respect to the changes of the crystal structure. All but one mode are observed for both the low-temperature R3 and the high-temperature C2/m phase. For all observed modes the energies and symmetries are in good agreement with DFT calculations. The symmetry of a single-layer was identified as p31/m. In contrast to previous studies we observe the transition from the R3 to the C2/m phase at 180 K and find no evidence for coexistence of both phases over a wide temperature range.
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