Journal of Raman Spectroscopy最新文献

We carried out a detailed study of the texture, mineralogy, and spectroscopic properties of the Slobodka ordinary chondrite meteorite. Previous descriptions differ on the classification of this meteorite, so we re-evaluated its petrologic type and shock stage. The observed texture and mineral chemistry are most consistent with the L4 chondrites. It records features of strong shock metamorphism mostly consistent with shock stage S4, including irregular and planar fractures, undulatory extinction, and mosaicism in olivine, pyroxene, and plagioclase. The distribution of shock damage was further evaluated at the mesoscale, revealing significant heterogeneity: regions of shock stage S4 are located near shock melt veins, a few selected areas indicate shock stage S3, and areas farther away from shock melt veins exhibit shock stage S2. The application of a range of in-situ analytical techniques, including Raman spectroscopy and electron back-scatter diffraction as well as microprobe, revealed the presence of five preserved high-pressure phases within the investigated sample of Slobodka, namely albitic jadeite, tuite, majorite, wadsleyite, and xieite. Together, these findings demonstrate that Slobodka preserves textural and mineralogical characteristics indicative of the highly energetic impact that likely fragmented the parent body of the L-chondrites.

The formation of amyloid fibrils by different proteins and peptides is a well-studied topic. In the last decade, it has been reported that metabolites can also self-assemble into amyloid-like fibrils. The aggregation of single amino acids such as phenylalanine, tyrosine, and tryptophan has also been linked to tyrosinemia type II, hypertryptophanemia, and Hartnup diseases. It is a challenge to monitor the intermolecular interactions involved in the supramolecular self-assembling of metabolites in a time-dependent manner. Here, the surface-enhanced Raman scattering (SERS) technique was used to directly probe the changes in the molecular interactions during the self-assembling of tryptophan into amyloid-like structures, particularly in the initial stages. We showed that this simple and label-free nanoplasmonic-based methodology can be used to examine at the molecular level the formation of amyloid-like aggregates as a function of time. Specifically, the technique was shown to be sensitive and provide insights into the formation of hydrogen bonding, π-stacking interactions, and hydrophobicity changes during the self-assembling of tryptophan. Thus, this work can open new possibilities for the applications of SERS to describe in more detail the mechanisms of formation of other metabolites assembled structures, which may be valuable for understanding several related diseases.

Manganese oxides (MnOx) are primary components of marine polymetallic deposits, which represent strategic reservoirs for critical metals essential for the transition to sustainable energy (including lithium, cobalt, and tellurium). Due to their nature (intergrown micro- to nano-sized and often poorly crystalline minerals), MnOx are challenging to investigate. Consequently, the application of methods for fast, highly-resolved and possibly remote and non-destructive identification of MnOx is critical in several disciplines, from ore geology to materials science. Micro-Raman spectroscopy is commonly used for this purpose. However, MnOx are sensitive to laser irradiation and, therefore, can undergo significant modification during analysis. For this reason, it is essential to establish a proper analytical protocol for their identification. In this study, we present our results on the behavior of the most common MnOx with layer structures under irradiation by a 532-nm laser, with intensity ranging from 23 μW/μm² to 36.8 mW/μm², continuing our recent work on dense and channel MnOx. Our results show that birnessite, ranciéite, chalcophanite, vernadite, and asbolane are stable up to 391 mW/μm², while lithiophorite endures up to 2.5 mW/μm²; however, its stability is significantly reduced when other metal cations substitute Mn and Al. Under higher laser power, all MnOx transform into a spinel-type phase such as hausmannite, jacobsite, Mn-rich hetaerolite, or galaxite, depending on the chemical composition of the starting material. Based on our data, we propose an innovative analytical protocol for robust phase identification by analyzing Raman scattering at varying laser power, from the starting material to its final degradation product.

Tourmalines, a complex borosilicate mineral supergroup, are significant in geological studies due to their chemical and mechanical stability across various temperature and pressure conditions, making them useful as source rock indicators. A major issue in the characterization of tourmaline composition is the consideration of the iron oxidation state, which can significantly influence the distribution of elements at each site. This study reports the enhancement of a previous model that correlates Raman spectral parameters of dravite–schorl tourmalines with their composition, taking into account the Fe valence state in Y and Z sites measured through micro-x-ray absorption near edge structure (μXANES) spectroscopy. Raman spectroscopy was employed in a prior study on these two tourmaline species by correlating peak positions and intensities with differences in the magnesium–iron ratio. However, it was assumed that all iron was in the ferrous oxidation state (Fe²⁺), which led to a misrepresentation of the Fe³⁺ content in certain samples. The model has been thus implemented in this work by using μXANES, enabling the accurate quantification of Fe²⁺ and Fe³⁺ in dravite–schorl minerals, hence refining Mg/(Mg + Fe²⁺) ratios for Raman spectral analysis. Results demonstrate the validity of the correlation between Raman peaks in both the fingerprint and OH stretching regions and the magnesium–ferrous iron ratio. Our research confirms that Raman spectrum analysis is an effective method for recognizing tourmalines from the dravite–schorl series and evaluating their composition, including now the evaluation of the Fe²⁺ and Fe³⁺ occupancy. By integrating μRaman and μXANES techniques, one can acquire insights into the oxidation state of iron in tourmalines from the dravite–schorl series, thereby enhancing the accuracy of the Mg/(Mg + Fe²⁺) ratio. The observed linear correlations for P₂ peak position, P₁/P₂ relative intensities, and ^WOH(3) peak position in the Raman spectrum enable the rapid identification of dravite and schorl tourmalines, as well as the retrieval of relative Mg and Fe²⁺ contents.

This paper suggests the use of high-resolution Raman scattering bands of MgCa carbonates as posteriori thermometer minerals in archaeometric studies. Therefore, the thermal behavior of two dolomite samples and the hydration and carbonation reaction in air of the decomposition products were investigated by Raman microspectroscopy. The increase in the calcination temperature resulted in the formation of – Raman silent MgO and – inert Mg calcite at 700°C–750°C. In contrast, the decarbonation, hydration, and recarbonation of sample material exposed to 750°C–900°C in a muffle furnace led to the appearance of Mg-free calcite. High spectral resolution Raman spectroscopy enabled a spectral distinction between these two groups due to differences in the band parameters (peak position, bandwidth) of the vibrational (v₁, v₄, L) modes of calcite. In combination with Raman microspectroscopic mapping, this spectral information represents a new approach for the estimation of burning temperatures of medieval high-fired gypsum mortars via natural dolomite impurities. Thus, the results of this work highlight the importance and potential of Raman microspectroscopy as a thermometric tool for elucidating the thermal history of anthropogenic fired materials, with potential applications for archaeometry and art technology, as well as for quality controls in the frame of the production of mineral mortar binders and ceramics or bricks, respectively.