Journal of Raman Spectroscopy最新文献

Lapis lazuli is a semiprecious stone that falls under the category of blue-colored minerals that played a vital role in the cultural historic artwork throughout the world. Finding the provenance of lapis lazuli is a slightly challenging task. The sources of lapis lazuli pigments used at Ajanta Caves and its provenance have been a subject of interest and a research question. Six samples of lapis lazuli pigment of murals of 2nd century bce Ajanta Caves were examined using micro-Raman spectroscopy, Fourier transform infrared spectrophotometry (FTIR), X-ray fluorescence spectroscopy, spectrophotometry, X-ray diffractometry (XRD), and stereomicroscopy to find out the possible provenance raw materials through the mineralogical compositions. This study will be very helpful to tailor future conservation strategies. The results showed that these pigment samples are similar based on their composition, presenting diopside and specific trace element proportions as provenance markers. The results revealed that these raw materials for the lapis lazuli pigments used at Ajanta Caves may have been imported from lapis lazuli mines located at Badakhshan in Afghanistan, as the mines have been actively mined for over 6000 years, making them a significant source of lapis lazuli for ancient civilizations.

Graphite is a common mineral occurring in different metamorphic rocks, including high/ultrahigh-temperature and high/ultrahigh-pressure rocks. Raman spectroscopic studies combined with carbon isotope composition may highlight the carbon source (crustal or mantle) and PT conditions of graphite crystallization. In the present study, seven graphite-bearing samples of felsic granulite xenoliths from the “Eclogitovaya” pipe (the Eastern Pamir, Tajikistan) have been studied by Raman spectroscopy and analyzed its carbon isotope composition. Graphite crystals occur in the matrix as well as inclusions in rock-forming minerals (e.g., garnet and kyanite), indicating their simultaneous crystallization. The graphite formed as a result of the metamorphic transformation of carbonaceous material (δ¹³С ranges from −14.5‰ to −20.1‰) originally present in the rocks during subduction. Structural analysis of intact graphite inclusions in garnet revealed rims of disordered graphite surrounding well-ordered graphite cores. Composite inclusions consisting of disordered graphite, well-ordered graphite, and CO₂ were also observed. However, any evidence for precipitation of disordered graphite from fluid has not been found. It is likely that the origin of disordered graphite in the Eastern Pamir granulite xenoliths is attributed to the stress at the graphite–garnet interface during the rapid exhumation of the xenoliths.

Density functional theory (DFT) at the PBE0-D₃ hybrid functional and 6-311G + (d,p) basis set levels was employed to optimize the ground state of malachite green (MG). The optimized MG molecule has a nonplanar structure. The electrical properties and densities were calculated for MG by the natural population analysis (NPA) method at the same level. GaussView and Multiwfn software were used to draw a Fukui function electron density isosurface coloring map and an electrostatic potential coloring map of the MG molecular surface. We found that the region near the two N atoms in MG was most susceptible to an electrophilic reaction. Time-dependent density functional theory (TD-DFT) was used to calculate the electronic excitation data of MG and draw the UV–Vis spectrum of MG at the same level. By comparing the experimental UV–Vis spectrum with the calculated UV–Vis spectrum, it was found that the UV–Vis spectrum of MG has three peaks, of which the maximum peak is 616 nm (calculated as 586 nm). The structure of the MG-Ag₄ complex was optimized by using DFT. The resonance surface-enhanced Raman scattering (SERS) spectrum excited with 633-nm laser light was calculated and compared with the experimental results, and there was a high similarity in the characteristic peak positions between them. Further analysis showed that MG combined with the silver plane by the adsorption orientation of one of the N,N-dimethylaniline skeleton planes was almost perpendicular to the silver plane in SERS detection. One of the N atoms in N,N-dimethylaniline is combined with Ag and then adsorbed onto the silver substrate to form a special surface-bound compound.

Surface-enhanced Raman spectroscopy (SERS) is often considered as a versatile tool for high-sensitive detection of low concentrations of analytes. Typically, gold or silver patterned surfaces, namely the SERS substrates, are utilized to amplify Raman signal. However, most SERS substrates require microfabrication processes based on costly infrastructures. In this paper, we propose a simple yet effective scheme for fabricating SERS substrates on thermoplastics. The process involves ultrasonically stacking nanopowders on thermoplastic substrate via a stencil. We showed that gold surfaces on polymethly methacrylate (PMMA) substrates could be fabricated by ultrasonic means in less than 10 s by using a benchtop ultrasonic welder. We investigated the effect of process parameters, namely the pressure and the vibration time, on the surface topography and SERS performance. The results show that the process is mainly controlled by the vibration time, such that at moderate vibration times (~ 5 s), uniformly rough surfaces could be repeatably achieved. Fabricated samples were tested for SERS performance using 5,5′-ditiobis (2-nitrobenzoic acid) (DTNB) as the Raman reporter. We showed that the substrates fabricated under 2.7 MPa pressure and 5 s vibration time yielded comparatively low relative standard deviations (RSD) of SERS intensity—6.12% for point-to-point variation and 6.73% for batch-to-batch variation—along with an enhancement factor (EF) of 1.28 × 10⁵. The performance of the SERS substrates, considering RSD and EF, indicates that the proposed fabrication method could be a promising alternative for SERS based sensing applications.

The Raman Laser Spectrometer (RLS), part of the Pasteur analytical suite onboard the ExoMars 2028 Rosalind Franklin rover, is designed to perform structural and compositional analyses of powdered subsurface samples on Mars. Its fully autonomous operation within the constraints of the Pasteur Analytical Laboratory-limited by time, energy, and sample availability-requires an efficient balance between scientific performance and operational viability. This study presents a qualitative analysis of RLS operations under mission-representative conditions using the Flight Spare (FS) model, focusing on the impact of key parameters-number of accumulations, autofocus frequency, and analyzed spots per sample-on the system's detection capabilities. Experimental campaigns were conducted using ESA-selected analog samples representative of Oxia Planum geology. Performance was evaluated using both the RLS FS and the ExoMars Simulator. Results show high consistency (90-95%) in mineral detection between systems, confirming the robustness of the RLS FS under representative scenarios. The instrument demonstrated its ability to identify key phases, including oxides, silicates, carbonates, hydrated sulfates, and amorphous carbon, highlighting its relevance to geological and astrobiological investigations. Operational tests confirmed that reducing the number of accumulations or autofocus activations-under appropriate sample conditions-does not compromise spectral quality. These findings support a flexible strategy that adapts operational parameters to the scientific context, optimizing resource use and preserving long-term instrument reliability. The results will contribute to the refinement of nominal activity plans for ExoMars and reinforce the use of the RLS FS as a critical asset for validating future configurations of the flight model.