Raman scattering on nanomaterials and nanostructures

Abstract

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.

Comparative study for low temperature water-gas shift reaction on Pt/ceria catalysts: Role of different ceria supports

“…XPS results indicate the non-stoichiometric characteristics of C1/Pt and C3/Pt due to the presence of Ce 3+ and Ce 4+ peaks [78]. Raman spectroscopy results in this work also indicate that the ceria in C1/Pt and C3/Pt is non-stoichiometric as evident from the weak and broad peaks at the Raman shift at 600 cm −1 [64]. The 600 cm -1 peak intensity is greater in C1/Pt than C3/Pt and C2/Pt.…”

“…A peak is seen in C1/Pt near 260 cm -1 which can be assigned to the 2TA or doubly degenerated TO mode [72][73] which is present only in ceria lattice with high defect concentration. A weak and broad peak at about 600 cm −1 can be seen in C1/Pt and C3/Pt which can be assigned to the intrinsic oxygen vacancies due to the non-stoichiometry of the sample [64]. Non-stoichiometric ceria (CeO2-x where x0.28 [74]) possesses a high concentration of defects, reduced grain boundary impedance and heat of reduction around 2.4 eV lower per oxygen vacancy compared to stoichiometric ceria [52].…”

“…Instrument alignment was optimized using a 520 cm -1 signal of a silicon wafer. Raman spectroscopy measurements were performed since this technique is well known to provide the concentration of active oxygen species and nonstoichiometry of the oxide supports [64][65]. The spectra were obtained at room temperature in vol% Ar and 6 vol% water vapor at 25 °C.…”

Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity

“…A red-shift of the F 2g mode occurs, together with an asymmetric broadening of its line shape and an intensity decrease, when the samples are heated. This phenomenon has been observed for several materials [27][28][29] as well as for ceria nanocrystals [30,31], and has been explained considering two different contributions: thermal expansion and lattice anharmonicity [29]. While the former only influences the peak position, both Raman shift and linewidth variations are consequences of the phonons anharmonic decay at higher temperatures, which may involve three-or four-phonon interactions [31].…”

Effects of annealing temperature variation on the evolution of structural and magnetic properties of NiFe2O4 nanoparticles synthesized by starch-assisted sol–gel auto-combustion method

“…It is important to notice that the Raman modes of the NiFe 2 O 4 nanoparticles annealed at lower temperature 200 o C are very broad and shift to low frequency as compared to that of nanoparticles annealed at higher temperature. This feature is related to a consequence of phonon confinement effect in nanocrystals [42][43].…”