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Raman scattering spectra in single crystals of lithium tantalate at 180-degree scattering geometry in a wide spectral frequency range (50 ÷ 2800 cm−1) were studied. Raman peaks were found in 1300 ÷ 2000 cm−1 region with frequencies exceeding doubled frequencies of LiTaO3 crystal lattice fundamental vibrations of A1 and E-type. The conditions for the manifestation of bound polar phonons in lithium tantalate Raman spectra were analyzed. The spectral intensity of Raman scattering in the overtone region of the spectrum of lithium tantalate was calculated taking into account the presence of a biphonon, and a satisfactory agreement between theory and experiment was obtained. [ABSTRACT FROM AUTHOR]

A study of a new ferroelastic phase transition in Pb(Zr0.53Ti0.47)O3:Gd detected at 144 °C, induced by Gd doping is presented. The existence of such phase transition is barely detectable in the permittivity vs. temperature curve; however, it is made evident through the analyses of the temperature coefficient of the resonant frequency Tkf dependence with temperature in the radial mode resonance spectrum. This coefficient has a sharp discontinuity at around 144 °C. Micro Raman spectra show that the Raman modes associated to Pb/Gd and (Zr/Ti)O6 positioned at 93.6 cm-1 E(1TO) and 144 cm-1 E(1LO) have a minimum in intensity around 140 °C. Besides the modes of the tetragonal structure, there are the modes at 67.3 and 77.8 cm-1 corresponding to a rhombohedral structure, appearing at all temperatures. The Raman intensity vs. temperature plots of the different modes shows a minimum around 140 °C that confirms the ferroelastic transition detected in the resonance spectrum. [ABSTRACT FROM AUTHOR]

Raman spectra of the delafossite CuGa1‐xCrxO2 (0 ≤ x ≤ 1) solid solution films have been measured in the temperature range from 80 to 823 K. Raman phonon modes are observed at 224 (Ag), 328 (A2u), 396 (Eg), and 757 (A1g) cm−1 for the CuGaO2 film, and phonon modes of the CuCrO2 film are around 211 (Ag), 324 (A2u), 458 (Eg), and 712 (A1g) cm−1, respectively. The A1g phonon mode has a distinct redshift with increasing Cr composition, which indicates that the interatomic potential becomes weaker between Cu and O atoms. Except Raman modes at the Brillouin zone center, the additional phonon modes in the spectral range of 500−670 cm−1 were observed due to Raman selection rules being relaxed by the crystal defects. With increasing temperature, the A1g phonon mode undergoes a larger phonon softening but a smaller line broadening relative to that of the Eg phonon mode, which indicated the anisotropic behavior for the delafossite CuGa1‐xCrxO2 films. The nonlinear temperature dependence of the phonon frequency and linewidth is an indication of nonharmonic lattice dynamics. The Raman shift and the linewidth of the Eg and A1g optical modes as a function of temperature were studied as an experimental evidence of the combined effect of lattice expansion and anharmonic phonon–phonon interaction. And the three‐phonon anharmonic coupling plays the dominant role in the anharmonicity behavior. The phonon anharmonicity behavior of the CuGaO2 and CuCrO2 films is slightly different. The larger Γ0 is intrinsic for the A1g mode of the CuGa0.8Cr0.2O2 film due to the broadening by the crystalline defects, which perturb the translation symmetry of the harmonic crystal, making the momentum conservation rule for phonon scattering partially relaxed. [ABSTRACT FROM AUTHOR]

The optical properties of KIO3 photonic structures of various types were studied in this article. The composite photonic materials used were based on opal photonic crystals, monodisperse silica nanoparticles, and diamond microparticles, respectively. The size effect of the Raman intensity in these structures was investigated. At a certain size of globules or particles, the Raman intensity of ferroelectric photonic structures was greater than the initial Raman spectral intensity of KIO3. [ABSTRACT FROM AUTHOR]

[Display omitted] • Raman spectra and X-ray diffraction patterns of MgP 2 O 6 were collected up to 1073 K. • No temperature-induced phase transition occurs for MgP 2 O 6. • The effect of temperature on the Raman active vibrations of MgP 2 O 6 was analyzed. • The thermal expansion coefficients and isobaric mode Grüneisen parameters of MgP 2 O 6 were determined. The Raman spectra and thermal expansion of MgP 2 O 6 metaphosphate were investigated at various temperatures up to 1073 K at ambient pressure. No temperature-induced phase transition was observed in this study. The effect of temperature on the Raman active vibrations and unit cell parameters was determined. All the observed Raman active bands of MgP 2 O 6 showed linear temperature dependences in the range of −2.61 × 10−2 ∼ −0.49 × 10−2 cm−1 K−1. The thermal expansion coefficient of MgP 2 O 6 was estimated to be 3.21(2) × 10−5 K−1. An axial anisotropic thermal expansion exists and the c -axis shows the smallest thermal expansion. The isobaric mode Grüneisen parameters of MgP 2 O 6 were calculated. The obtained results were compared with other compounds in the MgO-P 2 O 5 system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two phase transitions were observed in the pressures of near 49 GPa and 51 GPa. • The thermal expansion Raman redshift effect was studied based on the EOS. • The changes in vibrational modes of the phase transition region were studied. Currently, only one crystal structure of LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) (P2 1 /n) has been discovered, and there are still debates on its phase transition point and phase diagram. Based on previous work, we performed crystal structure, Raman spectra, and vibrational properties calculations on LLM-105 crystal. Our results indicate that the crystal structure of LLM-105 remains stable until compressed to 49 GPa, beyond which it may undergo two phase transitions at pressure intervals of 49.0–49.1 GPa and 51.4–51.5 GPa, respectively. Analysis of Raman shift results suggests that these two phase transitions may be reversible, with an intermediate phase possibly acting as a transition phase. Additionally, based on the quasi-harmonic approximation, we fitted the experimental data of LLM-105 lattice expansion state, obtaining the volume at zero pressure and using it for Raman spectra calculations. The results demonstrated the accuracy of this quasi-harmonic approximation method in describing the redshift of Raman peaks during the heating process and the excitation ratio of Raman peaks in different wavenumber ranges. [ABSTRACT FROM AUTHOR]

• The program TROVE computes variationally rovibrational states of smaller molecules. • We have extended it to simulate nonresonant Raman spectra. • Input for the simulations are ab initio potential and polarizability surfaces. • Simulations for CH 3 are in good agreement with available experimental data. • The extended program provides new support for remote-sensing experiments. We report first-principles variational simulation of the non-resonant Raman spectrum for the methyl radical (12CH 3) in the electronic ground state. Calculations are based on a high level ab initio potential energy and dipole moment surfaces of CH 3 and employ the accurate variational treatment of the ro-vibrational dynamics implemented in the general code TROVE [S. N. Yurchenko, W. Thiel, and P. Jensen, J. Mol. Spectrosc. 245, 126–140 (2007); A. Yachmenev and S. N. Yurchenko, J. Chem. Phys. 143, 014105 (2015)]. TROVE can be applied to arbitrary molecules of moderate size and we extend here its capabilities towards simulations of Raman spectra. The simulations for CH 3 are found to be in a good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

Abstract In this work, we present the structural, electronic, vibrational and optical properties of FeGe monolayer structure within the framework of generalized gradient approximation (GGA-PBE) and DFT + U implementation of density functional theory (DFT). We have observed a small indirect band gap of 90 meV in FeGe monolayer by GGA method, which yields semiconducting behaviour and while introducing coulomb potential (U), shows metallic nature with a finite density of states at Fermi level. The study of the effective mass of electron and hole reveals that electron is heavier than hole in FeGe monolayer. The density of states shows that both valance and conduction bands are mainly dominated by Fe-3d states, while the contribution of Ge-4p states is having small contribution at the Fermi level. We have also studied extensively the vibration frequencies of atoms in Raman spectra at ambient condition. The dielectric properties of FeGe, plasmon frequency and reflectivity edge are also analyzed. The GGA and GGA + U methods show the reflectivity edge lies in the UV region. Highlights • Optimizing metal-semiconductor alloy FeGe monolayer having pentagonal structure. • FeGe showed semiconducting behavior with small band gap of 90 meV by DFT method. • Metallic behavior with quantum conductance of 2G o calculated by DFT + U method. • The transfer rate of charge carrier is dominated by hole in FeGe monolayer. • Raman spectra due to different vibration modes are studied. • Plasmon frequency and reflectance edge for the both monolayers have been analyzed. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) method was used to grow large area and layer controllable WS 2 film. Our results show that the as grown WS 2 film is an excellent substrate for surface enhanced Raman scattering (SERS). The Raman enhancement effect depends crucially on the layer number of WS 2 film: monolayer WS 2 offers the strongest Raman signal, and the Raman enhancement effect gradually decreases with the increase in the layer number of WS 2 . Further analysis indicates that this transition originates from the charge transfer yield between the R6G molecules and the underlying WS 2 substrate. [ABSTRACT FROM AUTHOR]

Within density-functional theory, perturbation theory (PT) is the state-of-the-art formalism for assessing the response to homogeneous electric fields and the associated material properties, e.g., polarizabilities, dielectric constants, and Raman intensities. Here, we derive a real-space formulation of PT and present an implementation within the all-electron, numeric atom-centered orbitals electronic structure code FHI-aims that allows for massively parallel calculations. As demonstrated by extensive validation, we achieve a rapid computation of accurate response properties of molecules and solids. As an application showcase, we present harmonic and anharmonic Raman spectra, the latter obtained by combining hundreds of thousands of PT calculations with ab initio molecular dynamics. By using the PBE exchange-correlation functional with many-body van der Waals corrections, we obtain spectra in good agreement with experiment especially with respect to lineshapes for the isolated paracetamol molecule and two polymorphs of the paracetamol crystal. [ABSTRACT FROM AUTHOR]

Tellurite and borotellurite glasses containing Bi 2 O 3 and TiO 2 were prepared and structure-property correlations were carried out by density measurements, X-ray diffraction, Differential Scanning Calorimetry (DSC), Raman, FTIR, UV–visible and 11 B MAS-NMR studies. Titanium-tellurite and titanium bismuth tellurite glasses require high melt-cooling rates and were prepared by splat quenching. On adding B 2 O 3 , the glass forming ability (GFA) enhances considerably and bulk glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV–visible studies were used to determine the optical band gap and refractive index. Raman studies found that the co-ordination number of tellurium ions with oxygen (N Te O ) remains constant with variation in TiO 2 molar content, while the incorporation of B 2 O 3 and Bi 2 O 3 decreases N Te O . DSC studies show that the glass transition temperature (T g ) increases with B 2 O 3 and TiO 2 concentrations and that T g correlates well with bond enthalpy of the metal oxides. 11 B MAS-NMR studies found that the co-ordination number of boron with oxygen (N B O ) decreases with increase in B 2 O 3 content while increasing TiO 2 and Bi 2 O 3 concentration does not significantly modify N B O . [ABSTRACT FROM AUTHOR]

Characterizing two-dimensional (2D) layered materials in the monolayer limit is key to discovering their new phenomena and unusual properties. We theoretically predict the electric field modulated Raman spectra of 2D MoSi 2 N 4 , TiSi 2 N 4 and MoGe 2 As 4 monolayers, with two kinds of laser lines (532 and 633 nm). Based on the Raman tensor, we have calculated the angle-dependent Raman intensities of the major Raman peak ( A 1 ′ 1) in MoSi 2 N 4 , TiSi 2 N 4 and MoGe 2 As 4 monolayers, locating at 1029 cm−1, 993 cm−1 and 317 cm−1, respectively. Applying the external electric field to MoSi 2 N 4 monolayer, the symmetry of D 3 h reduces to C 3 v , which results in more peaks of Raman-active modes found in the Raman spectra. As a result, besides E ′ and A 1 ′ modes, three other major Raman peaks ( A 1 ′ 1 , A 1 ′ 2 and A 1 ′ 3) are found in MoSi 2 N 4 , TiSi 2 N 4 and MoGe 2 As 4 monolayers, which can help us to distinguish the 2D MA 2 Z 4 materials. We find that the enhancement factor by external electric field can be up to 10 times. Moreover, the non-resonant Raman spectra peaks of doubly degenerate mode (E ′) and one-dimensional modes A 1 ′ and A 2 ″ in MoSi 2 N 4 , TiSi 2 N 4 and MoGe 2 As 4 monolayer are calculated. These theoretical results of Raman spectra of MoSi 2 N 4 monolayer may provide theoretical guidelines for its utilization in crystal structure characterizations and optoelectric devices. • Angle-dependent Raman intensities in MoSi 2 N 4 (1029 cm−1), TiSi 2 N 4 (993 cm−1) and MoGe 2 As 4 (317 cm−1) monolayers. • New Raman peaks induced by external electric field. • The enhancement factor by external electric field can be up to 10. [ABSTRACT FROM AUTHOR]

The polarized Raman spectra of SrBO (SBO) single crystals are studied in detail in the temperature range of 300-1273 K. The TO, LO, and IO phonon lines of A, A, B, and B symmetries of rhombic SBO at 300 K are identified. The behavior of the Raman spectra of SBO crystals is studied upon heating up to their melting. The relation of Raman spectra with the structure of boron-oxygen fragments, as well as the transformation of spectra in the process of melting of SBO crystals, is discussed. [ABSTRACT FROM AUTHOR]

The behavior of the Raman spectra of SrBO (SBO) and LiBO crystals upon melting and glass formation is studied by high-temperature Raman spectroscopy (HTRS). The character of formation of boron-oxygen fragments in different aggregate states of SBO is discussed based on an analysis of the Raman spectra in the crystalline, glassy, and molten states. [ABSTRACT FROM AUTHOR]

Pure and Cr (1, 3, 5, 7 and 10 at.%) doped SnO nanoparticles were synthesized in aqueous solution by a low cost chemical co-precipitation method without using any stabilizing agent. The effects of Cr doping on Raman, optical band gap and magnetic properties of SnO nanoparticles were investigated. Particle size is found to decrease with Cr doping into the SnO matrix which was confirmed by TEM. Besides of the fundamental mode of vibration, two additional peaks are also observed in Raman spectra which are correlated to Cr. The absorption spectra showed two peaks at 340 and 454 nm. The absorbance peak at 340 nm is assigned to the transition from valence band (VB) to conduction band (CB) and the peak at 454 nm was due to the transition from VB to mid gap energy level introduced by Cr. The optical band gap of undoped SnO nanoparticles is calculated to be 3 eV. With the doping of Cr in SnO, band gap increases due to the decrease in particle size. The emission intensity is found to decrease with the increase in Cr doping due to the emission from CB to mid gap energy levels introduced by Cr between CB and VB. Undoped SnO nanoparticles show room temperature ferromagnetism due to the presence of defects and oxygen vacancies. The heavily doped SnO nanoparticles show paramagnetic nature due to the antiferromagnetic coupling between Cr and its nearest neighbour. [ABSTRACT FROM AUTHOR]

Background: In recent years, high throughput and non-invasive Raman spectrometry technique has matured as an effective approach to identification of individual cells by species, even in complex, mixed populations. Raman profiling is an appealing optical microscopic method to achieve this. To fully utilize Raman proling for single-cell analysis, an extensive understanding of Raman spectra is necessary to answer questions such as which filtering methodologies are effective for pre-processing of Raman spectra, what strains can be distinguished by Raman spectra, and what features serve best as Raman-based biomarkers for single-cells, etc. Results: In this work, we have proposed an approach called rDisc to discretize the original Raman spectrum into only a few (usually less than 20) representative peaks (Raman shifts). The approach has advantages in removing noises, and condensing the original spectrum. In particular, effective signal processing procedures were designed to eliminate noise, utilising wavelet transform denoising, baseline correction, and signal normalization. In the discretizing process, representative peaks were selected to signicantly decrease the Raman data size. More importantly, the selected peaks are chosen as suitable to serve as key biological markers to differentiate species and other cellular features. Additionally, the classication performance of discretized spectra was found to be comparable to full spectrum having more than 1000 Raman shifts. Overall, the discretized spectrum needs about 5storage space of a full spectrum and the processing speed is considerably faster. This makes rDisc clearly superior to other methods for single-cell classication. [ABSTRACT FROM AUTHOR]