Journal of Raman Spectroscopy最新文献

The IR and Raman spectra of five AVF₃ compounds (A = Li, Na, K, Rb, and Cs) is computed by using an all electron Gaussian type basis set, the hybrid B3LYP functional, and the CRYSTAL code. For the Cs and Rb compounds, only the cubic ($�P�m�\overline{�3�}�m$) spectra are generated, corresponding to the most stable structure. Also for KVF₃, NaVF₃, and LiVF₃, the cubic spectra are computed, for comparison with the Rb and Cs compounds. The spectra corresponding to a minimum of the total energy along the group-subgroup chain cubic-tetragonal $�\left(�P�\frac{�4�}{�m�}�b�m�\right)$-orthorhombic(Pnma) are also generated for the three lighter compounds. The role of the A cation varies along the series, as expected from the very large mass and ionic radius differences. The deformation of the VF₆ octahedra becomes very large for the Li and Na compounds, as documented by the spectra of the Pnma phase, which are very different from the cubic ones.

For the first time, the Raman spectra in a range of 50–2850 cm⁻¹ from different areas of the gradient crystal LiNbO₃:Er³⁺ (congruent in the main components, Er gradient of 0.55 at%/cm) grown by the Czochralski method were investigated. The compositionally homogeneous, nominally pure, congruent LiNbO_3cong (R = [Li]/[Nb] = 0.946) and the single-crystal LiNbO₃:Er³⁺ (3.1 wt%), also grown by the Czochralski method, were used as reference samples. It was found that in the gradient crystal LiNbO₃:Er³⁺ (congruent in the main components, Er gradient of 0.55 at%/cm), the intensity of the second-order Raman lines is significantly higher than the intensity of fundamental vibrations, which is due to the high microheterogeneity of the gradient crystal. A coincidence of the type of Raman spectra in scattering geometries $�z�\left(\mathrm{xx},\mathrm{yy},\mathrm{xy}\right)�\overline{z}$ and $�x�\left(\mathrm{zz},\mathrm{zy}\right)�\overline{x}$ has been established, for which no explanation has been found at the moment. It has been shown that second-order Raman spectra can be a powerful tool for studying the compositional and structural perfection of materials based on LiNbO₃ crystals, including doped crystalline and ceramic materials and materials with an artificially specified composition gradient.

Mechanochemical (MC) methods have emerged as an alternative approach to induce chemical reactions in various systems offering promising opportunities for innovative energy-efficient synthesis methods of polycrystalline materials. MC reactions can proceed via the pathways different to those in the conventional solid-state synthesis methods, through new metastable intermediate and often amorphous phases. Fundamental understanding of reactivity of solids during this process is required for knowledge-guided synthesis procedures. In this study, we have investigated the structural changes in SrCO₃ + V₂O₅ mixtures upon ball-milling and the feasibility or MC synthesis of the tertiary vanadium oxide, SrV₂O₆ that is conventionally prepared by solid-state synthesis above 600°C. We varied the milling speed, duration, and ball diameter to examine the effects of the milling parameters on the reaction intermediates and outcomes. The phase composition of the intermediate and final mixtures was characterized using X-ray diffraction, thermogravimetry combined with differential scanning calorimetry (TGA-DSC), and Raman spectroscopy. Although powder X-ray diffraction was used to identify the evolution of the crystalline phases, the intermediate milling products and the final phase obtained in the milling were mostly amorphous, and the Raman and TGA-DSC analyses provided indispensable evidence of the presence of amorphous SrV₂O₆ in the mixtures as the main phase. The polycrystalline vanadate product was obtained after a short thermal treatment of the ball-milled powders at 420°C with the average particle size smaller than that of the sample synthesized via the solid-state method.

Researchers have long been interested in nucleic acid detection technology. Surface-enhanced Raman spectroscopy (SERS) is distinguished by its high sensitivity, minimal sample volume, resistance to fluorescence interference, cost-effectiveness, and rapidity compared to conventional nucleic acid analysis methods. The clustered regularly interspaced short palindromic repeats/CRISPR-associated protein (CRISPR/Cas), a novel gene editing tool, has garnered significant interest in nucleic acid analysis due to its precise identification and isothermal advantages. Integrating the CRISPR/Cas system's specific identification capabilities with the high-sensitivity fingerprinting properties of SERS offers a sensitive, ultra-low volume, rapid, and straightforward method for detecting new nucleic acid modalities. This review delineates the components and characteristics of the CRISPR/Cas system, encompassing three Cas proteins (Cas9, Cas12, and Cas13) and detection technologies derived from CRISPR/Cas, namely, high-sensitivity enzymatic reporter unlocking (SHERLOCK) and DNA endonuclease-targeted CRISPR trans reporters (DETECTR). Advancements in SERS and CRISPR/Cas-SERS-based nucleic acid assays were emphasized, encompassing traditional SERS and CRISPR/Cas-SERS-based nucleic acid and non-nucleic acid tests. Examples encompass microfluidics/microdroplet-based CRISPR/Cas-SERS and non-amplified detection based on CRISPR/Cas-SERS, and so on.

Three paintings of Symeon Savvidis, one of Francesco Pige and one from Andreas Kriezis belonging to the permanent collection of the National Gallery-Alexandros Soutsos Museum located in Athens, Greece, were analysed in situ, during the museum's opening hours, by Raman spectroscopy, handheld x-ray fluorescence (hXRF) and hyperspectral imaging (UV-Vis-NIR HSI). Raman spectroscopy point analysis, performed on multiple points on the surface of the paintings, revealed the materials used by the artists. Additionally, micro-Raman maps were obtained from selected areas, for the distribution of the pigments to be revealed. This is one of the first testimonies of in situ Raman mapping of easel paintings, performed in a museum, during opening hours. Challenges on maintaining the focusing during the acquisition of the Raman maps are also underlined. Materials frequently identified via Raman spectroscopy were lead white (2PbCO₃·Pb (OH)₂), vermillion (HgS), ultramarine blue (Na_6-10Al₆Si₆O₂₄S_2-4), Prussian blue (KFe^III[Fe^II (CN)₆]·xH₂O or Fe₄ ^III[Fe^II (CN)₆]₃·xH₂O) with other components found complementing the palette of the artists (e.g., chrome yellow (PbCrO₄), chrome orange (PbCrO₄·Pb(OH)₂, carbon-based black (C)). Sporadically and in different paintings, haematite (α-Fe₂O₃), strontium yellow (SrCrO₄) and barium sulfate (BaSO₄) were characterized. hXRF and UV-Vis-NIR HSI supported the information retrieved by both Raman instruments.

Raman spectroscopy basically probes the changes in polarizability induced by lattice vibration, popularly known as Raman tensor which is highly sensitive to the interatomic distances. The question is how precisely this can be probed. Can Raman spectroscopy sense very small atomic displacement, say femtometer displacement? The answer is yes; now, it is a reality, thanks to the light polarization dependence of the Raman scattering. In this review, we discuss the working principles of the atomic displacement detection protocol using angle resolved polarized Raman spectroscopy and theoretical formulation of the relation between the directional atomic displacement (strain) and spectral parameters along with some experimental results on different classes of materials like multiferroic and ferroelectric. The very high detection capability of this technique enables one to unearth the microscopic mechanism of the electric polarization in Type II multiferroic material CuO and resolve the long-standing debate on crystal symmetry of the popularly used substrate material NdGaO₃ and detection of Ti displacement in classical ferroelectric BaTiO₃. Remarkably, the required apparatus is very simple; it includes a polarization analysis capable Raman spectrometer to probe a specific Raman tensor element, a sample rotation stage to adjust the polarization of the incident and scattered light with respect to crystallographic orientations, and of course sample should be single crystals or epitaxial thin film. The simple instrumental requirements, straightforward direct method of atomic displacement detection, high sensitivity for the low atomic number elements, and microscopic special resolution make it highly useful in future applications where small atomic displacement (particularly from the center of symmetry) to external factors like temperature, pressure, and electric or magnetic field plays pivotal in shaping physical properties.

Raman spectroscopy, especially Raman imaging, has become a popular technique for fluid inclusion studies. Raman imaging is particularly useful for the study of tiny inclusions appearing in high or ultrahigh pressure (UHP) metamorphic minerals. The small size of daughter phases, as well as the presence of liquid or gas phases, precludes the application of microprobe analysis for unexposed inclusions. Nontransparent inclusions, usually assigned as “opaque”, “ore,” or “black” accessory minerals, are rarely studied by Raman spectroscopy due to the high absorbance of laser energy by black materials, their unstable behavior at the laser beam, and low Raman signal. Despite these difficulties, a number of documented examples show that multiphase inclusions in these metamorphic rocks may persist. These inclusions provide valuable information on the composition of fluids in deeply subducted environments. For the first time, we demonstrate that “opaque” or “black” inclusions in UHP rocks are multiphase. They contain CO₂ + CH₄ gas bubbles ± calcite and graphite with different degrees of crystallinity. These multiphase fluid inclusions coexist side by side with “classical” inclusions which also contain CO₂ and CH₄ gases, as well as liquid water, but no graphite. Our findings demonstrate that Raman imaging of “classical” and “black” fluid inclusions and subsequent data treatment by different techniques may bring important information about their composition.