Raman scattering of NiS2

Raman scattering measurements of NiS₂ is done and five optical phonon peaks are found. These peaks are assigned to A_g, E_g and 3T_g phonons which are all of the Raman active optical phonons in pyrite-type crystal. The results are compared with those of FeS₂ and MnS₂.     

Raman scattering of LiGaO2

The Raman spectrum of LiGaO₂ is reported together with a preliminary identification of the optical modes and their temperature dependence between 6 and 700 K. The observed temperature dependence of the lines gave no indication for second order processes. However, at low temperatures additional lines have been observed indicating a phase transition at approximately 65 K.     

Raman scattering in Ag-intercalated TiS2

Ag-intercalated TiS₂ has been investigated using electron diffraction and Raman scattering. The energies of the E_g-1 and A_1g modes in 1T-TiS₂ at 300 K were found to be 232 and 336 cm^-1, respectively. In Ag_0.3TiS₂, at an ambient temperature of 4.2 K, modes were observed at 207, 239, 277, 311, and 347 cm^-1. Three of these modes have been associated with the formation of a superlattice at low temperatures. The superlattice formation was observed by electron diffraction and is attributed to an ordering of the silver atoms at interlayer interstices.     

Magnon Raman scattering in CoBr2

The one-magnon Raman spectrum of CoBr₂ has been investigated as a function of temperature, and peak frequency, integrated intensity and width parameters obtained. The results obtained for the band energy at low temperature (22.2 ± 0.2 cm^-1 at 5.7.K) are in good agreement with AFMR and neutron scattering results. The one-magnon energy renormalises relatively slowly with increasing temperature and is about 15 cm^-1 at T_N = 19 K, whereas the integrated intensity approaches zero like the magnetization at T_N and the width diverges. A low intensity band at 26.8 ± 1 cm^-1 (7.6K) may be due to two-magnon scattering from spin waves along the c-axis.     

Raman scattering from magnons in CoCl2 and FeCl2

One-magnon Raman scattering has been observed in the metamagnets CoCl₂ and FeCl₂. The k = 0 magnon energies are 16 ± 1 cm^-1 at 21 K and 16.4 ± 0.4 cm^-1 at 12 K, respectively and these values are in good agreement with previous AFMR and neutron scattering results. A search for two-magnon scattering in both compounds was unsuccessful, largely because of masking from nearby first-order phonons and a weak temperature dependent broad band at 140 cm^-1 in CoCl₂, which is assigned to two-phonon scattering from acoustic phonons.     

Raman scattering from 1T-TaS2

Raman measurements on the 1T-polytype of TaS₂ are reported. In the commensurate charge density wave state, a large number of Raman-active peaks are observed below 400 cm^-1. Most of these peaks are attributed to k = 0 optic phonons resulting from superlattice formation.     

Enhanced Raman scattering from nano-SnO2 grains

We present the Raman spectra of nano-SnO_{2} grains with sizes from 4nm to 80nm excited by 532nm and 1.06μm lines. The enhanced Raman scattering of the nanograins is observed for both exciting lines when the grain size is less than 8nm. The less the grain size is, the more intensely the Raman scattering is enhanced. According to our results, the enhancements of the Raman intensity are a few tenfolds and different for different exciting lines when the grain size is 4nm. It can be attributed to enhanced Raman scattering by electron－hole pair excitations in the nanograins that originate from sub-microscopic (10nm) size and other defect- and surface-related features. A critical size that divides respective predominance of bulk properties and the defect-, surface-, and size-related features can be determined to be about 8nm.     

Raman scattering in CeB6

Raman spectra of phonons in CeB₆ were measured. The observed three peaks were assigned to the A_1g, E_g and F_2g phonon modes. The frequencies of the modes suggest that the Ce ion is in the trivalent state.     

The Raman scattering of Zn3As2

The Raman scattering of Zn₃As₂ crystal is presented within 50–420 cm⁻¹ energy range. The group theory method are used to determine symmetry of the allowed lattice modes, and further to discuss the results obtained.     

Raman scattering in FeF3

Peaks in the FeF₃ phonon Raman spectrum are assigned to the A_1g(312 cm^-1) and E_g(105, 187, 450 cm^-1) representations of the D⁶_3d group. Anomalous temperature dependence of the frequency, intensity and line width of the 187 cm^-1 line has been observed.     

Raman scattering in 3RNbS2

Raman scattering spectra on a layer type compound 3RNbS₂ were measured at 300 and 77 K, and three peaks were observed at 382, 325 and 281 cm^?1 at 300 K. The vibration modes were analyzed in terms of Bromley's nearest neighbour model, and a good agreement with the experiment was obtained.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.     

Resonant Raman scattering of CdCr2Se4

The scattering cross section of the Raman-active phonons at 156 cm^?1 (Eg) and 169 cm^?1 (F2g) in the ferromagnetic semiconductor CdCr₂Se₄ (T_c=130 K) has been measured as a function of incident photon energy between 1.55 and 2.81 eV, both in the ferromagnetic and paramagnetic phases. The resonance curve peaks sharply near 2 eV and shows a broadening for temperatures below the Curie point. The relative line intensities change significantly with photon energy. The results show that the concept of spin-dependent Raman scattering in the ferromagnetic spinels has to be revised in terms of exchange-splitting-induced resonant Raman scattering.     

Raman scattering of the MoS2 and WS2 single nanotubes

We report here the results of the first resonance Raman study on single MoS₂ and WS₂ nanotubes and microtubes synthesized by chemical transport reaction. These multiwall tubes represent the longest known inorganic nanotubes grown up to several millimetre lengths with diameters ranging from less than ten nanometers to several micrometers. The nanotubes grown at nearly equilibrium conditions contain extremely low density of structural defects. The selected area diffraction on the thick-wall nanotubes revealing the rhombohedral (3R) stacking, otherwise stable at elevated pressure above 4 GPa, provides indirect evidence of the presence of strain incorporated into the nanotube wall. Results are compared with phonon spectra of plate-like crystals of the same compound. The observed up-shift of Raman peaks in the tubes spectra is explained by the presence of strain. Well preserved crystal structure of tubes is confirmed by comparison with phonon spectra of nanostructured materials from literature.     

Resonance Raman scattering from amorphous As2S3

Resonance Raman scattering from amorphous As₂S₃, obtained by temperature tuning the band edge through the He-Ne 6328 Å laser line, is reported.     

Indirect exciton luminescense and Raman scattering in CdI2

Intrinsic luminescence and Raman scattering in 4HCdI₂ have been investigated at 2 K. Weak emission bands observed near the absorption edge are attributed to the phonon-assistes indirect exciton luminescence. Several new Raman lines are observed under resonant excitation in addition to known lines. The symmetry of the phonon modes associated with the indirect transitions as well as with Raman scattering is discussed.     

Raman scattering in monodomain RbCoF3

Polarized Raman spectra are reported for scattering from a single oriented antiferromagnetic domain in RbCoF₃. Monodomain samples were achieved by the application of a small [100] uniaxial stress. Spectra were recorded at 2 K using non-absorbed, orange laser light. The D_4h symmetry assignments for the principal features are: 34(Γ⁺₅), 335 (Γ⁺₁ and Γ⁺₁), 420 (Γ⁺₁), 950 (Γ⁺₃) and 1050 cm^-1 (Γ⁺₁). These results are not consistent with the prediction of previous models for magnetic exciton scattering.     

Raman scattering in low-dimensional HfTe5

Nine long-wavelength phonons have been observed by Raman scattering in the quasi-one-dimensional crystal HfTe₅. The assignment of these phonon modes is made on the basis of symmetry arguments using the correlation method. The similarity between the HfTe₅ and the ZrTe₃ chain-like crystal structures instigates the attribution of the most characteristic modes like the high-frequency chalcogen diatomic-mode and the low frequency rigid-chain mode. Although no new line appears even at 14 K, the irregular temperature dependence of the spectra suggests the possibility of a structural instability connected with a large peak in the electrical resistivity and with the X-ray diffraction anomalies.     

Raman scattering in magnetic US3

A Raman scattering investigation of magnetic US₃ has been made from 7 to 300 K. Comparison of room temperature spectra with those of the non magnetic isostructural sulfide HfS₃ allowed the assignment of most of the lines to $\textcolor{red}{}\text{=}\text{0}$ optical phonons. Drastic changes take place in the 10?150 cm^?1 range when lowering the temperature down to 7 K : four equally spaced lines appear at 54, 72.5, 91 and 109.5 cm^?1. Three of them broaden significantly with increasing temperature and disappear near 50 K, at which previous measurements indicate a maximum in the magnetic susceptibility and suggest a magnetic phase transition. The stronger fourth line is still observed at 100 K and merges into a phonon line at higher temperature. These four lines are attributed to electronic transitions within the 5f² configuration of U⁴⁺. Their temperature dependences appear to involve a spin-dependent scattering mechanism and are consistent with antiferromagnetic ordering.     

Raman scattering in quasi-one-dimensional ZrTe5

Raman scattering experiments on the compound ZrTe₅ isostructural with HfTe₅ have been performed at temperatures between 300–313 K. The Raman spectra of ZrTe₅ resemble those of HfTe₅ excepting two high frequency modes which should include the most characteristic diatomic mode. In spite of structural similarity with the transition-metal trichalcogenides, the Raman scattering activity cannot be directly compared. These unexpected results and the unusual temperature dependence of the Raman intensities suggest the possibility of a structural instability in HfTe₅ and/or ZrTe₅ in relation with the anomalies in the transport properties and in the X-ray forbidden reflections.