Search Results (70)

Low-frequency (LF, ν ≤ 200 cm⁻¹) vibrational modes of crystalline organic semiconductors are of particular interest because they significantly affect charge transport in these materials. Herein, we study LF vibrations of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) substituted by phenyls, (per)fluorophenyls or pyridyls using the synergy of Raman spectroscopy and (periodic) DFT calculations. The LF spectra for the compounds with electron-withdrawing (fluorine or nitrogen) atoms differ significantly in the band positions and intensities from those for diphenyl-substituted BTBT, whereas the high-frequency (HF, ν > 200 cm⁻¹) spectra are quite similar for all the compounds studied, excluding the perfluorophenyl-substituted BTBT. We found that Ph-BTBT-Ph counterparts containing one electron-withdrawing atom per aryl ring show significantly lower LF Raman intensity compared to the parent compound. The LF intensity decrease is attributed to the suppression of intermolecular motions by the stronger electrostatic interactions. The unexpected LF intensity increase for the perfluorophenyl-substituted BTBT can be ascribed to strong dynamic disorder induced by easier torsion of phenyls with respect to the BTBT core, which also results in the deterioration of the π-conjugation revealed in the HF Raman spectra. We anticipate that the established structure–property relationships will contribute to the rational design of crystalline organic semiconductors towards controlled dynamic disorder and high charge mobility. Full article

KTaO₃ (KTO) is a quantum paraelectric perovskite oxide which belongs to the cubic space group Pm$\overline{3}$m in a large temperature range. Polar optical modes with a T_1u symmetry of KTO are infrared-active and Raman-inactive according to the centrosymmetric exclusion principle of the selection rule. In general, the soft modes responsible for ferroelectric instability are infrared-active and Raman-inactive in the paraelectric phase. Therefore, there are still not enough studies on Raman-inactive soft modes and related phonon polaritons. In the present study, Raman-inactive polar modes and related polaritons of KTO crystals are studied by Terahertz Time-Domain spectroscopy (THz-TDS) and FTIR. The real and imaginary parts of a dielectric constant along the [100] axis are uniquely determined by transmission and reflection THz-TDS without any fitting in the low-frequency range between 6 and 225 cm⁻¹, which covers the two lowest-frequency polar modes. The reflectivity is determined by reflection FTIR in the range between 50 and 1200 cm⁻¹, and the complex dielectric constant is also estimated by the fitting in the range between 6 and 1200 cm⁻¹. The phonon–polariton dispersion relations of the real and imaginary parts of the polariton wavevector are also studied in the range between 6 and 1200 cm⁻¹. The crossover from photon-like to phonon-like polaritons and related polariton decay are observed, while no anomaly related to polariton scattering and coupling to other elementary excitations is observed in the polariton dispersion. Full article

Chagas disease remains a major neglected parasitic illness in Latin America and other endemic regions, and benznidazole (BZN) is still the primary trypanosomacidal drug despite its incompletely understood mechanism of action. This work provides a detailed biophysical characterization of the conformational behavior and vibrational properties of benznidazole (BZN), a first-line trypanocidal drug still widely used for the treatment of Chagas disease. Using density functional theory combined with relaxed potential energy surface scans in vacuum and implicit water, two low-energy conformers (BZN1 and BZN2) were identified, separated by moderate rotational barriers and a small energy difference, indicating that both are intrinsically accessible at room temperature. For each conformer, infrared and Raman spectra were calculated and assigned via vibrational mode analysis, then compared with FT-IR and FT-Raman spectra recorded for pharmaceutical-grade polycrystalline BZN. The theoretical and experimental spectra show excellent agreement, with a Raman band in the 1350–1400 $\mathrm{c}{\mathrm{m}}^{-1}$ region emerging as a sensitive conformational marker: the experimental maximum at $1359\mathrm{c}{\mathrm{m}}^{-1}$ matches the most intense BZN1 mode, whereas the corresponding BZN2 band appears about $13\mathrm{c}{\mathrm{m}}^{-1}$ higher in frequency. This clear spectroscopic fingerprint demonstrates that the solid drug is overwhelmingly composed of the BZN1 conformer, despite the theoretical accessibility of BZN2. Overall, the study links the conformational landscape of benznidazole to its vibrational signatures and highlights Raman spectroscopy, supported by quantum chemical calculations, as a powerful tool for conformational and potential polymorphic control of this clinically important nitroimidazole. Full article

Coherent Raman scattering (CRS) techniques such as coherent anti-Stokes Raman scattering (CARS) provide chemically specific vibrational contrast with signal levels far exceeding spontaneous Raman scattering (SpRS). Extending these to broadband excitation enables multiplex detection across wide spectral regions, including the fingerprint region, CH-stretch bands and high-frequency vibrational modes. This review provides a structured overview of excitation architecture for broadband CRS, ranging from low-energy oscillator schemes to energy-scalable platforms. The discussion is organized along key design parameters, including spectral bandwidth, excitation intensity, and probe delay, which jointly determine the accessible operating regimes. Rather than representing competing methods, the reviewed architectures are presented as a complementary toolbox for application-driven spectroscopy in chemically reactive environments and complex biological systems. In addition, a representative OPCPA-based implementation is presented as a platform demonstration to illustrate accessible operating regimes, single-shot stability, and multiplex detection capability under realistic experimental conditions. Full article

The constant growth of IP data traffic, driven by sustained annual increases surpassing 26%, is pushing current optical transport infrastructures towards their capacity limits. Since the deployment of new fiber cables is economically demanding, ultra-wideband transmission is emerging as a promising cost-effective solution, enabled by multi-band amplifiers and transceivers spanning the entire low-loss window of standard single-mode fibers. In this scenario, an accurate modeling of the frequency-dependent fiber parameters is essential to reliably model optical signal propagation. In particular, the combined impact of attenuation variations with frequency and inter-channel stimulated Raman scattering (SRS) fundamentally shapes the power evolution of wide wavelength division multiplexing (WDM) combs and directly affects nonlinear interference (NLI) generation, as well as the amount of ASE noise. In this work, we review a set of analytical approximations, based on phenomenological approaches, for frequency-dependent attenuation and Raman scattering gain, and analyze their impact on achieving an effective balance between computational efficiency and physical fidelity. Through extensive analyses performed with the open-source software GNPy (version 2.12, Telecom Infra Project) on an optical line system exploring multi-band scenarios spanning C+L+S, C+L+E, and U-to-E transmission, we demonstrate that the proposed approximations reproduce the reference SRS power evolution and NLI profiles with root mean square errors (RMSEs) consistently below 0.03 dB, and down to the 10⁻³–10⁻² dB range for the most accurate configurations. Although the current implementation does not yet provide a direct reduction in computational time, the proposed framework lays the groundwork for future developments toward closed-form or semi-analytical solutions, enabling more efficient modeling and optimization of ultra-wideband optical transmission. Full article

The significant disparity between the size and electronegativity of N and group-V (P, As, Sb) atoms in dilute III–V-Ns remains a cornerstone for developing the next-generation electronics. Variations in the structural, optical, and phonon properties of the quaternary GaAs_1−x−ySb_yN_x alloys are being used for improving the high-performance photovoltaic energy and optoelectronic technologies. Bandgap ${\mathrm{E}}_{\mathrm{g}}$ tunability has assisted efficient light emission/detection to cover the crucial optical fiber wavelengths for the low-cost integrated chips in data communications and sensing devices. The lattice dynamical properties of these materials are critical for assessing the reliability to evaluate the performance of long-wavelength lasers, photodetectors, and multi-junction solar cells. Our systematic Raman measurements on high-quality MBE grown $\mathrm{G}\mathrm{a}{\mathrm{A}\mathrm{s}}_{0.946}{\mathrm{S}\mathrm{b}}_{0.032}{\mathrm{N}}_{0.022}$/GaAs samples have detected ${\mathsf{\omega }}_{\mathrm{T}\mathrm{O}\left(\mathsf{\Gamma }\right)}^{\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}}$ and ${\mathsf{\omega }}_{\mathrm{T}\mathrm{O}\left(\mathsf{\Gamma }\right)}^{\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}}$ phonons along with a high frequency N_As local mode near ~476 cm⁻¹. Weak phonon structures on both sides of the broad 476 cm⁻¹ band are interpreted forming a complex N_As–Ga–Sb_As defect center. Using a realistic rigid-ion model in the Green’s function framework, the simulations of impurity modes for isolated and complex defects have provided corroboration to the experimental data. Full article

This study presents a comprehensive Raman spectroscopic and mechanical investigation of Gd₃Ga₅O₁₂ (GGG) single crystals irradiated with 231 MeV ¹³¹Xe ions at fluences ranging from 1 × 10¹¹ to 3.3 × 10¹³ ions/cm². Raman analysis reveals that all fundamental vibrational modes of the garnet structure remain observable up to the highest fluence, with the preservation of garnet crystalline topology/absence of secondary crystalline phases. However, significant line broadening (FWHM increase by 20–100%) and low-frequency shifts indicate progressive lattice disorder and phonon-defect scattering. High-frequency Ga-O stretching modes (A_1g, T_2g ~740 cm⁻¹) remain the most resistant to irradiation, while low-energy translational modes involving Gd³⁺ ions exhibit pronounced degradation and partial disappearance at high fluence. Complementary nanoindentation measurements show radiation-induced softening: hardness decreases by up to ≈60% at 3.3 × 10¹³ ions/cm², consistent with amorphization and overlapping ion tracks (~10–12 μm deep). Raman spectroscopy shows that the garnet lattice remains as the only crystalline phase up to 3.3 × 10¹³ ions/cm², while significant line broadening, mode suppression and a strong hardness decrease indicate progressive structural disorder and partial amorphization of the near-surface region. These results demonstrate that GGG maintains crystalline integrity below the track-overlap threshold (~6 keV/nm) but undergoes strong structural relaxation and mechanical weakening once this limit is exceeded. A new analytical methodology has been developed to quantify radiation-induced structural degradation. Full article

Laser slicing has emerged as a promising low-kerf and low-damage technique for SiC wafer fabrication; however, its effects on the crystal integrity, near-surface modification, and charge-transport properties require further clarification. Here, a heavily N-doped 4° off-axis 4H-SiC wafer was sliced using an ultraviolet (UV) picosecond laser, and both laser-irradiated and laser-sliced surfaces were comprehensively characterized. X-ray diffraction and pole figure measurements confirmed that the 4H stacking sequence and macroscopic crystal orientation were preserved after slicing. Raman spectroscopy, including analysis of the folded transverse-optical and longitudinal-optical phonon–plasmon coupled modes, enabled dielectric function fitting and determination of the plasmon frequency, yielding a free-carrier concentration of ~3.1 × 10¹⁸ cm⁻³. Hall measurements provided consistent carrier density, mobility, and resistivity, demonstrating that the laser slicing process did not degrade bulk electrical properties. Multi-scale Atomic Force Microscopy (AFM), Angle-Resolved X-Ray Photoelectron Spectroscopy (ARXPS), Secondary Ion Mass Spectrometry (SIMS), and Transmission Electron Microscopy (TEM)/Selected Area Electron Diffraction (SAED) analyses revealed the formation of a near-surface thin amorphous/polycrystalline modified layer and an oxygen-rich region, with significantly increased roughness and thicker modified layers on the hilly regions of the sliced surface. These results indicate that UV laser slicing maintains the intrinsic crystalline and electrical properties of 4H-SiC while introducing localized nanoscale surface damage that must be minimized by optimizing the slicing parameters and the subsequent surface-finishing processes. Full article

Phonons, the quantized lattice vibrations, are fundamental for a wide range of phenomena in condensed matter systems. In particular, low-frequency phonons significantly influence electrical conductivity, thermal transport, and the optical properties of solid-state materials. Although there is considerable literature on cadmium sulfide (CdS) phonons—studied, for example, using resonance Raman spectroscopy—up-to-date information on the low-frequency phonons of this important semiconductor is still lacking. In this study, Raman spectroscopy under off- and near-resonance conditions is employed to investigate the low-frequency phonon in wurtzite CdS single crystals. Under off-resonance conditions, the spectrum exhibits multiple low-intensity peaks, which were analyzed through curve fitting. In contrast, the near-resonance spectrum shows an intense, broad band that was deconvoluted into its constituent components, including an antiresonance feature that was mathematically modeled for the first time in CdS. The results demonstrate that Raman scattering intensity in both regimes provides valuable insights into the low-frequency phonon modes of CdS. These findings enhance our understanding of the material’s vibrational properties and may facilitate the development of more efficient CdS-based optoelectronic devices. Full article

The pressure response and structural stability of fluoranthene crystals up to 8 GPa are investigated using Raman spectroscopy. The vast majority of the Raman peaks upshift with pressure, either sublinearly (intermolecular modes) or quasilinearly (intramolecular modes), reflecting the bond hardening upon volume contraction. The frequency shifts, accompanied by intensity redistribution among the Raman peaks, are by far larger for the former than those for the latter vibrations, compatible with their nature: weak intermolecular van der Waals interactions and strong intramolecular covalent bonds. For pressures higher than 2 GPa, changes in the linear pressure coefficients of the Raman peak frequencies, mainly towards lower values, are observed. These are more pronounced for intermolecular and C–H stretching vibrations. For P > 4.7 GPa, the pressure coefficients are further reduced, while all the observed pressure-induced changes are fully reversible upon pressure release. These changes may be interpreted either as two structural transitions at ~2 and ~4.7 GPa or as a single, but sluggish, structural phase transition in the pressure range 2–4.7 GPa, featuring the reorientation and different stacking of the molecules. From the high-pressure Raman data in the low-pressure phase, a bulk modulus of ~7 GPa at ambient pressure is estimated for solid fluoranthene. Full article

The narrow bandgap InN material, with exceptional physical properties, has recently gained considerable attention, encouraging many scientists/engineers to design infrared photodetectors, light-emitting diodes, laser diodes, solar cells, and high-power electronic devices. The InN/Sapphire samples of different film thicknesses that we have used in our methodical experimental and theoretical studies are grown by plasma-assisted molecular-beam epitaxy. Hall effect measurements on these samples have revealed high-electron-charge carrier concentration, η. The preparation of InN epifilms is quite sensitive to the growth temperature T, plasma power, N/In ratio, and pressure, P. Due to the reduced distance between N atoms at a higher P, one expects the N-flow kinetics, diffusion, surface components, and scattering rates to change in the growth chamber which might impact the quality of InN films. We believe that the ionized N, rather than molecular, or neutral species are responsible for controlling the growth of InN/Sapphire epifilms. Temperature- and power-dependent photoluminescence measurements are performed, validating the bandgap variation (~0.60–0.80 eV) of all the samples. High-resolution X-ray diffraction studies have indicated that the increase in growth temperature caused the perceived narrow peaks in the X-ray-rocking curves, leading to better-quality films with well-ordered crystalline structures. Careful simulations of the infrared reflectivity spectra provided values of η and mobility μ, in good accordance with the Hall measurements. Our first-order Raman scattering spectroscopy study has not only identified the accurate phonon values of InN samples but also revealed the low-frequency longitudinal optical phonon plasmon-coupled mode in excellent agreement with theoretical calculations. Full article

The pressure response of crystalline 9,9′-spirobifluorene up to 8 GPa was studied by means of Raman spectroscopy using a diamond anvil cell as a pressure chamber. With increasing pressure, the observed Raman peaks shifted to higher frequencies, reflecting the bond hardening upon volume reduction, which was much more pronounced for the initially weaker intermolecular interactions than for the stronger intramolecular covalent bonds. The significant changes in the Raman spectrum and the pressure evolution of the frequencies at ~1.3 GPa for both the intermolecular and the intramolecular Raman peaks signaled a pressure-induced structural and molecular conformation transition with a little hysteretic behavior (~0.5 GPa) upon pressure release. For P > 4 GPa, the reversible decrease of the pressure coefficients of the majority of the intermolecular and some intramolecular peak frequencies indicated another structural modification of the studied molecular crystal. A value of ~9 GPa for the bulk modulus of the system at zero pressure was estimated from the logarithmic pressure coefficients of the frequencies of the intermolecular modes in the low-pressure phase. These coefficients were reduced by ~6 times at 4.2 GPa, indicating that the considerable stiffening of the material in the high-pressure phase emanated from the selective strengthening of the intermolecular interactions. Full article

Low-frequency peaks in the Raman spectra of amorphous poly(ether ether ketone) (PEEK) were investigated. An amorphous sample with zero crystallinity, as confirmed by wide-angle X-ray diffraction, was used in this study. In a previous study, two peaks were observed in the low-frequency Raman spectra of the crystallized samples. Among these, the peaks at 135 cm⁻¹ disappeared for the amorphous sample. Meanwhile, for the first time, the peak at 50 cm⁻¹ was observed in the crystallized sample. Similar to the peak at 135 cm⁻¹, the peak at 50 cm⁻¹ disappeared in the amorphous state, and its intensity increased with increasing crystallinity. The origins of the two peaks were associated with the Ph-CO-Ph-type intermolecular vibrational modes in the simulation. This suggests that the Ph-CO-Ph vibrational mode observed in the low-frequency region of PEEK was strongly influenced by the intermolecular order. Full article

Carbon-based novel low-dimensional XC/YC (with X, Y ≡ Si, Ge, and Sn) heterostructures have recently gained considerable scientific and technological interest in the design of electronic devices for energy transport use in extreme environments. Despite many efforts made to understand the structural, electronic, and vibrational properties of XC and X_xY_1−xC alloys, no measurements exist for identifying the phonon characteristics of superlattices (SLs) by employing either an infrared and/or Raman scattering spectroscopy. In this work, we report the results of a systematic study to investigate the lattice dynamics of the ideal ${\left(\mathrm{X}\mathrm{C}\right)}_{\mathrm{m}}$/${\left(\mathrm{Y}\mathrm{C}\right)}_{\mathrm{n}}$ as well as graded ${\left(\mathrm{X}\mathrm{C}\right)}_{10-∆}/{\left({\mathrm{X}}_{0.5}{\mathrm{Y}}_{0.5}\mathrm{C}\right)}_{∆}/{\left(\mathrm{Y}\mathrm{C}\right)}_{10-∆}/{\left({\mathrm{X}}_{0.5}{\mathrm{Y}}_{0.5}\mathrm{C}\right)}_{∆}$ SLs by meticulously including the interfacial layer thickness $∆$ (≡1–3 monolayers). While the folded acoustic phonons (FAPs) are calculated using a Rytov model, the confined optical modes (COMs) and FAPs are described by adopting a modified linear-chain model. Although the simulations of low-energy dispersions for the FAPs indicated no significant changes by increasing $∆$, the results revealed, however, considerable “downward” shifts of high frequency COMs and “upward” shifts for the low energy optical modes. In the framework of a bond polarizability model, the calculated results of Raman scattering spectra for graded SLs are presented as a function of $∆.$ Special attention is paid to those modes in the middle of the frequency region, which offer strong contributions for enhancing the Raman intensity profiles. These simulated changes are linked to the localization of atomic displacements constrained either by the XC/YC or YC/XC unabrupt interfaces. We strongly feel that this study will encourage spectroscopists to perform Raman scattering measurements to check our theoretical conjectures. Full article

We present a Raman spectroscopy study of the vibrational properties of free-base meso-tetra(4-pyridyl) porphyrin polycrystals under various temperature and hydrostatic pressure conditions. The combination of experimental results and Density Functional Theory (DFT) calculations allows us to assign most of the observed Raman bands. The modifications in the Raman spectra when excited with $488 \mathrm{n}\mathrm{m}$ and $532 \mathrm{n}\mathrm{m}$ laser lights indicate that a resonance effect in the ${\mathrm{Q}}_{\mathrm{y}}$ band is taking place. The pressure-dependent results show that the resonance conditions change with increasing pressure, probably due to the shift of the electronic transitions. The temperature-dependent results show that the relative intensities of the Raman modes change at low temperatures, while no frequency shifts are observed. The experimental and theoretical analysis presented here suggest that these molecules are well represented by the ${\mathrm{C}}_{2\mathrm{v}}$ point symmetry group. Full article