Journal of Raman Spectroscopy最新文献

Raman spectra of zircon have recently been used as a pressure scale for studies of geological fluids at high temperatures and high pressures using diamond anvil cells (DACs). The zircon scale is advantageous in high chemical stability and the large pressure response of the B_1g mode. Despite its excellent applicability, the calibration of the scale has been carried out only in a narrow pressure–temperature range, especially under limited high-temperature and high-pressure conditions. In this study, the pressure and temperature dependence of the Raman modes of synthetic zircon was investigated up to 9.5 GPa and from room temperature to 776 K using an externally heated diamond anvil cell. Ruby and gold were used as the reference pressure scales. The Raman shift of the B_1g mode for the antisymmetric stretching of the SiO₄ structure in zircon showed a linear pressure dependence of 5.48(4) cm⁻¹/GPa up to 8 GPa at room temperature, in agreement with the previous studies. Measurements under high-pressure and high-temperature conditions confirmed that the pressure dependence up to 9.5 GPa along the isotherms from 373 to 675 K was consistent with the room-temperature value; the wavenumbers can be well deduced from the sum of the individual effects of pressure and temperature, obtained at ambient temperature and pressure, respectively. A comparison of the zircon scale with the c-BN Raman spectroscopic scale confirmed that the pressures determined with these scales were in reasonable agreement. The present results provide a confident use of the zircon Raman spectroscopic scale in a wider pressure–temperature range than previous studies for the internally consistent pressure determination.

We report the results of polarization-dependent Raman spectroscopy of phonon states in single-crystalline quasi-one-dimensional NbTe₄ and TaTe₄ van der Waals materials. The measurements were conducted in the wide temperature range from 80 to 560 K. Our results show that although both materials have identical crystal structures and symmetries, there is a drastic difference in the intensity of their Raman spectra. While TaTe₄ exhibits well-defined peaks through the examined wavenumber and temperature ranges, NbTe₄ reveals extremely weak Raman signatures. The measured spectral positions of the phonon peaks agree with the phonon band structure calculated using the density-functional theory. We offer possible reasons for the intensity differences between the two van der Waals materials. Our results provide insights into the phonon properties of NbTe₄ and TaTe₄ van der Waals materials and indicate the potential of Raman spectroscopy for studying charge-density-wave quantum condensate phases.

The cover image is based on the Special Issue – Research Article Raman identification of pigments and opacifiers: Interest and limitation of multivariate analysis by comparison with solid state spectroscopical approach—I. Lead-tin and Naples Yellow by Jacques Burlot et al., https://doi.org/10.1002/jrs.6600.

Semiconductors have attracted great attention for surface-enhanced Raman scattering (SERS) applications due to their rich variety, adjustable band structure, good chemical stability, and biocompatibility. However, their intrinsic weak SERS activity limited the further development of semiconductor substrates. Here, the α-Fe₂O₃ films with high {$�1�\overline{1}�0$} and {$�110$} facet exposure ratios were fabricated through an electrodeposition method with the existence of NH₄Cl and CH₃COONa. The α-Fe₂O₃{$�1�\overline{1}�0$} and α-Fe₂O₃{$�110$} films show excellent SERS properties with enhancement factor of 4.155×10³ and 5.481×10³, as well as the relatively low limit of detection down to 2 × 10⁻⁷ M for 4-nitrobenzenethiol. Meanwhile, the lower relative standard deviation values (<10%) confirm the well uniformity of as-prepared substrates. Ultraviolet photoelectron spectroscopy analysis reveals that the α-Fe₂O₃{$�110$} possesses the lower work function, which could guarantee the efficient interfacial charge transfer between substrates and probe molecules. Moreover, first principles calculations further indicates that the charge transfer efficiency on {$�110$} facet can be effectively improved, and thus significantly enhance the SERS activity of α-Fe₂O₃. The current study provides a strategy for the fabrication and application of semiconductor-based SERS substrates.

Raman spectra of (As_1–xBi_x)₂S₃ glass samples with x ≤ 0.2 measured at the excitation with above-bandgap (532 nm) laser light at a relatively low power density (P_exc = 4 kW/cm²) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As_1–xBi_x)₂S₃ glass previously known (x ≤ 0.06). Spectra measured at an increased P_exc (40 kW/cm²) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage-type As₄S₄ units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm⁻¹, which emerge in the Raman spectra of the (As_1–xBi_x)₂S₃ glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As_1–xBi_x)₂S₃ glass surface with formation of units containing arsenate AsO₄³⁻ and sulphate SO₄²⁻ ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.

Uranium dioxide (UO₂) is a widely studied material due to its use as fuel in pressurised water reactors (PWR), and Raman spectroscopy is a technique of choice to characterise the evolution of its microstructure. UO₂ crystallises in a fluorite CaF₂ (space group Fm-3m) structure that gives rise to a unique Raman signature, the T_2g band. However, several other bands are often detected whose attribution remains unclear. The present study gives new insights on the Raman spectrum of UO₂ thanks to the combination of isotopic labelling with ¹⁸O and Raman imaging. In addition to the expected T_2g, U₂ (LO), 2LO and U₃ bands, we have detected a doublet at 885 and 925 cm⁻¹, a U* band at 555 cm⁻¹ in some specific areas and two bands located at 367 and 1196 cm⁻¹. All Raman bands shift under the effect of the replacement of ¹⁶O by ¹⁸O, excepting for the U* band that could not be detected anymore. The isotopic shift ratio could be determined for 20% and 30% ¹⁸O labelling. No discrepancy in band position is observed between grains and grain boundaries, except for the U₂(LO) band. We also evidence a difference between the U defect bands and the 885 and 925 cm⁻¹ doublet bands evolution under labelling, although the latter also seems to be connected to the presence of defects in the material.

The examination and identification of silicate minerals are critical for advancing our understanding of the evolutionary journey of Earth-like bodies. To facilitate an efficient and productive process, it is imperative that these minerals be detected swiftly and accurately. This study is designed to explore the relationship between varying concentrations of cations and their corresponding Raman shifts. The focus is on primary silicate minerals in Earth-like bodies, specifically olivine, pyroxene, and feldspar, utilizing data from the RRUFF database. Employing a fitting formula, we identify distinct Raman peak ranges associated with different silicate minerals. Our research covers a wide array of mineral types, including five varieties of olivine (forsterite [Mg₂SiO₄], fayalite [Fe²⁺₂SiO₄], tephroite [Mn²⁺₂SiO₄], monticellite [CaMgSiO₄], and kirschsteinite [CaFe²⁺SiO₄]), four types of pyroxene (ferrosilite [Fe²⁺₂Si₂O₆], enstatite [Mg₂Si₂O₆], hedenbergite [CaFe²⁺Si₂O₆], and diopside [CaMgSi₂O₆]), and three varieties of feldspar (alkali feldspar [KAlSi₃O₈], albite [NaAlSi₃O₈], and anorthite [CaAl₂Si₂O₈]). The accuracy of matching Raman characteristics is exceptionally high for all olivine and pyroxene types (100%) and an impressive 86% for feldspar. The findings from this study highlight the crucial role of Raman spectroscopy in the field of silicate mineralogy and suggest significant implications for enhancing future exploration missions to Earth-like bodies.

Transition metal complexes, such as the low-spin bis (phenylterpyridine) (A) and bis (pyridylterpyrazine)iron (II) (B) complexes, provide didactic chromophore species for demonstrating the Raman, resonance Raman, and the surface-enhanced Raman scattering (SERS) behavior in coordination chemistry, as well as for elucidating the nature of inner-sphere and outer-sphere association with plasmonic nanoparticles. Their electrostatically stabilized ion pairs with citrate–gold nanoparticles have been studied in an aqueous solution, from the pronounced changes in the plasmonic band at 540 nm. Complex A, lacking any coordinating site, can only generate outer-sphere complexes with citrate–gold nanoparticles, but they are stable enough to give a strong SERS response, even at 10⁻⁸ M. At 10⁻⁶ M, agglomeration accompanies the decrease of the electrostatic repulsion, resulting in a sharp decay of the plasmon resonance band at 540 nm. This is followed by the rise of a plasmon coupling band above 700 nm. However, at 10⁻⁴ M, the excess of the complex in the adsorption layer produces a reverse effect, decreasing agglomeration. The observed Raman spectra are essentially similar for the several concentrations employed because the outer-sphere interaction implies a SERS electromagnetic mechanism. In contrast, complex B exhibits several pyridine and pyrazine N-atoms available to form inner-sphere-associated species. A selective enhancement of the SERS signals is observed at 10⁻⁸ M, clearly indicating a chemical mechanism, consistent with a bridging mode. At 10⁻⁶ M and above, the agglomeration leads to a plasmon coupling band at 800 nm, while the SERS response indicates a change in the binding modes dictated by the excess of the complexing molecules.

Raman hyperspectral imaging (RHSI) is a valuable tool for gaining crucial information about the chemical composition of materials. However, obtaining clear Raman signals is not always a trivial task. Raw Raman signals can be susceptible to photoluminescence interference and noise. Hence, the preprocessing of RHSI is a required step for an effective and reliable chemical analysis. The main challenge is splitting the measured RHSI into separate Raman photoluminescence signals. Since no golden-standard exists, it is non-trivial to validate the correctness of the separated signals. While current state-of-the-art preprocessing methods are effective, they require expert knowledge and involve unintuitive hyperparameters. Current approaches also lack generalizability, requiring extensive hyperparameter tuning on a case-by-case basis, while even then results are not always as expected. To this end, this work proposes a novel iterative RHSI preprocessing pipeline for splitting raw Raman signals and noise removal based on linear spline and radial basis function regression (IlsaRBF). The proposed method involves hyperparameters based on the physical properties of Raman spectroscopy, making them intuitive to use. This leads to more robust and stable hyperparameters, reducing the necessity for extensive hyperparameter tuning. A thorough evaluation shows that the proposed method outperforms the current state-of-the-art. Additionally, a cosmic ray identification and removal algorithm (CRIR) and dynamic PCA for noise reduction are introduced. A standalone tool containing our proposed methods is provided, making RHSI preprocessing available to a broader audience, aiding further research and advancements in the field of Raman spectroscopy.

Microporous materials containing hydrated silanol groups Si–OH as well as hydrated proton complexes, H_2n+1O_n⁺, including hydronium (n = 1), Zundel (n = 2), and Eigen (n = 4) cations, are of practical importance as potential ion exchangers and ion conductors. In this paper, we provide data on crystal-chemical features, hydrogen bonding and Raman spectra of alkaline microporous titano-, niobo-, zircono-, and aluminosilicate minerals belonging to the labuntsovite, lovozerite, eudialyte, and sodalite groups in which a part of sodium was substituted by hydrated proton complexes under low-temperature hydrothermal or supergene conditions. Most minerals studied in this work do not have synthetic analogues and are considered as possible natural prototypes of microporous materials with technologically important properties. The obtained experimental data and their comparison with the results of ab initio theoretical calculations published elsewhere show that Raman spectroscopy is an effective tool for the precise identification of hydrated proton complexes with extremely strong hydrogen bonds and estimation of corresponding O···O distances in the range of 2.37–2.68 Å. The presence of hydrated proton complexes in microporous silicates is a clear and sensitive geological indicator showing that a rock underwent the low-temperature alteration.