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Raman spectroscopy plays a pivotal role in spectroscopic investigations. The small Raman scattering cross-section of numerous analytes, however, requires enhancement of the signal through specific structuring of the electromagnetic and morphological properties of the underlying surface. This enhancement technique is known as surface-enhanced Raman spectroscopy (SERS). Despite the existence of various proposed alternatives, the approach involving Fabry–Pérot cavities, which constitutes a straightforward method to enhance the electromagnetic field around the analyte, has not been extensively utilized. This is because, for the analyte to experience the maximum electric field, it needs to be embedded within the cavity. Consequently, the top mirror of the cavity will eventually shield it from the external laser source. Recently, an open-cavity configuration has been demonstrated to exhibit properties similar to the classic Fabry–Pérot configuration, with the added advantage of maintaining direct accessibility for the laser source. This paper showcases how such a simple yet innovative configuration can be effectively utilized to achieve remarkable Raman enhancement. The simple structure, coupled with its inexpensive nature and versatility in material selection and scalability, makes it an ideal choice for various analytes and integration into diverse Raman apparatus setups. [ABSTRACT FROM AUTHOR]

Raman and infrared measurements of the same locations were conducted on a northwest African (NWA) 10580 CO3 meteorite sample, before and after three proton irradiations (1 keV ion energy using 1011, 1014, and 1017 ion/cm2 fluent values), to simulate space weathering effects. In the case of Raman spectroscopy, both FWHM and peak positions of the major olivine and pyroxene bands changed after the irradiation, and the minor bands disappeared. In the FTIR spectra, the minor bands of olivine and pyroxene also disappeared; meanwhile, major IR bands of pyroxene remained visible, demonstrating both positive and negative peak shifts, and the olivines were characterised only by negative peak shifts. The olivines were characterised by negative FWHM changes for major bands, but positive FWHM changes for minor bands. The pyroxenes were characterised by elevated FWHM changes for minor bands after the irradiation. The disappearance of minor bands both of IR and Raman spectra indicates the amorphization of minerals. The negative peak shift in IR spectra indicates Mg loss for olivine and pyroxene, in agreement with the literature. The Raman spectra are characterised by positive peak shift and positive FWHM changes; the IR spectra are characterised by a negative peak shift. The Mg loss, which was detected by negative peak shifts of FTIR bands, may be caused by distortion of the crystal structure, which could be detected by a positive peak shift in Raman spectra. This joint observation and interpretation has not been formulated in the literature, but indicates further possibilities in the confirmation of mineral changes by different instruments. Shock alteration-based observations by other researchers could be used as a reference for irradiation experiments as irradiation makes a similar structural alteration, like a low-grade shock metamorphism. [ABSTRACT FROM AUTHOR]

A new type of poly-diamond plate without a catalyst was produced via the high-pressure high-temperature (HPHT) compression of diamond powders. The densification of diamond powders and sp3 to sp2 carbon on the surface under HPHT compression was investigated through the characterization of the microstructure, Raman spectroscopy analysis and electrical resistance measurement. The densification and sp3-sp2 transformation on the surface are mainly affected by the pressure, temperature and particle size. The quantitative analysis of the diamond sp3 and sp2 carbon amount was performed through the peak fitting of Raman spectra. It was found that finer diamond particles under a higher temperature and a lower pressure tend to produce more sp2 carbon; otherwise, they produce less. In addition, it is interesting to note that the local residual stresses measured using Raman spectra increase with the diamond particle size. The suspected reason is that the increased particle size reduces the number of contact points, resulting in a higher localized pressure at each contact point. The hypothesis was supported by finite element calculation. This study provides detailed and quantitative data about the densification of diamond powders and sp3 to sp2 transformation on the surface under HPHT treatment, which is valuable for the sintering of polycrystalline diamonds (PCDs) and the HPHT treatment of diamonds. [ABSTRACT FROM AUTHOR]

In addition to graphene, the transition metal dichalcogenides, black phosphorus and multiple other layered materials have undergone immense investigations. Among them, metal thiophosphates (MPSx) have emerged as a promising material for various applications. While several layered metal thiophosphates with general-formula MPSx have been scrutinized extensively, van der Waals (vdW) CdPS3 has been overlooked in the literature. Here we report on the extensive Raman scattering of layered CdPS3, showing structural phase transition at a low temperature. The emergence of multiple new peaks at low frequency and a significant shift in peak position with temperature implied a probable change in crystal symmetry from trigonal D3d to triclinic Ci below the phase transition temperature, TK~180 K. In addition, we also showed a p-type performance of CdPS3 FET fabricated using Au electrodes. This work adds CdPS3 to the list of potential layered materials for energy application. [ABSTRACT FROM AUTHOR]

In the present study, the influence of disperse systems on Raman scattering was investigated. How an increasing particle concentration weakens the quantitative signal of the Raman spectrum is shown. Furthermore, the change in the position of the optimal measurement point in the fluid was considered in detail. Additional transmission measurements can be used to derive a simple and robust correction method that allows the actual concentration of the continuous phase to be determined with a standard deviation of 2.6%. [ABSTRACT FROM AUTHOR]

This study demonstrated the capability of two readily available optical spectroscopy tools, namely UV-Vis absorption spectrophotometry and Raman/surface-enhanced Raman spectroscopy, to select in a rapid and noninvasive manner the most homogenous gold nanoparticle (AuNP) models and to identify their chemical binding mechanism to 2-thiouracil (2-TU). 2-TU is an anticancer drug of great promise in the antiproliferative and photothermal therapies of cancer. The citrate-capped AuNPs emerged as the most stable as well as time- and cost-effective AuNP model out of the three widely used colloidal nanocores (citrate-, borohydride-citrate-, and sodium dodecyl sulfate (SDS)-capped AuNPs) that were examined. 2-TU chemically attached to the relatively monodispersed AuNPs via a chemisorption mechanism. The 2-TU-AuNPs complex formed through the covalent bonding of the S atom of 2-TU to the nanosurface in a vertical orientation. The spectroscopic results were then confirmed with the help of density functional theory (DFT) calculations and other physicochemical characterization tools for nanomaterials such as transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. Overall, the purified 2-TU-AuNPs were found to be spherical, had an average diameter of 25 ± 2 nm, a narrow size distribution (1–30 nm), a sharp localized surface plasmon resonance (LSPR) peak at 525 nm, and a negative surface charge (−14 mV). [ABSTRACT FROM AUTHOR]