Journal of Raman Spectroscopy最新文献

In this study, the resonance Raman spectra of hydrothermally produced 2H-MoS₂ nanoflakes excited by a 633-nm laser were examined. Spectral observations include both fundamental MoS₂ modes and additional Raman lines, which arise from alterations in the energy states of the semiconductor owing to the incidence of laser radiation. Phonon softening and alterations in the phonon lifetime were computed for different laser powers. The Fano resonance, which causes asymmetry in the Raman spectral lines, was analyzed at different laser powers. The Fano line-shape function is used to fit the asymmetry in the in-plane vibrational mode whereas multi-peak fitting using the Fano-Lorentzian function is used to fit the out-of-the-plane fundamental mode, which is coupled with “b” mode. A direct study of the electron–phonon interaction was carried out with the “b” mode. The shift in laser wavenumber was then investigated using the 2LA(M) modes observed in the resonance Raman spectra. These findings provide new optoelectronic device designers with an understanding of the intricate electron–phonon interactions in transition metal dichalcogenides.

The nature of the nonequilibrium states of materials upon rapid compression/decompression processes in the intermediate regime, between static and shock compression, is an emerging field of high pressure research. Rapid compression experiments were performed to examine the structural response of silicon (Si) up to 11 GPa and over compression rates ranging from 0.011 to 0.325 GPa/s, using a piezo-driven dynamic diamond anvil cell (dDAC) coupled with time-resolved Raman spectroscopy. The observed structural stability and the remarkable consistency in the pressure-dependent Raman shift of the diamond cubic Si (Si-I) showed its high potential as a Raman pressure scale for compression rate below 0.325 GPa/s. The validity of the derived Si scale was verified by in situ continuously monitoring pressure of two rapid compressed samples, that is, gypsum and ZnO. Results indicated that pressures determined using Si were in good agreement with those estimated from the ruby scale. Success in pressure calibration with Si, during time-resolved Raman spectroscopy measurements of material under rapid compression using a dDAC, will greatly simplify the required hardware system in home-laboratory and may also help in reaching a higher signal-to-noise in Raman measurement on a short time scale.

We prepared two types of trench-test metal-oxide semiconductor field-effect transistor (MOSFET) structures on m- and a-faces in 4H silicon carbide (4H-SiC) and investigated the anisotropic stress distribution of small trenches with a depth of 1 μm using a scanning near-field optical Raman microscope (SNOM) that we developed. The stress distributions of σ₁₁ (a-axis) under the bottom of the trench for m-face were approximately 100 MPa larger than those for a-face, and the stress distributions of σ₃₃ (c-axis) under the bottom of the trench for m-face were almost the same as those for a-face. The experimental result agrees well with that calculated by the finite element method (FEM). These results indicate that the anisotropic stress distributions of σ₁₁ components around the apex of the trenches of 4H-SiC trench-test MOSFET occur in m- and a-faces. Thus, it is possible that the differences in mobilities for m- and a-faces might be caused by the anisotropic stresses.

This paper addresses the challenge posed by the size of certain objects that do not conform to the constraints of microscope-coupled Raman spectrometers, making sample collection impossible due to their inherent value or nature. Specifically, materials like hydroxyapatite-based substances used in artistic and ornamental carvings, such as bone or ivory, fall within this problematic category. The focus of this study is the enhancement of analytical capabilities in the context of large objects using a Raman microscope system. The study details the innovation involving a remote probe integrated with fiber optics, elaborating on the design and performance aspects, and emphasizing the appropriateness of chosen components in the analysis of ivory artifacts belonging to private collectors. In order to assess the robustness of our discriminative approaches, an archaeological bone and the exposed dentine in a human tooth were also evaluated and compared. Results showed that using an 805-nm longpass dichroic mirror successfully directed the near-infrared laser onto the samples and significantly suppressed the Rayleigh scattering contribution to the spectrum. Regarding the preprocessing methods to spectra evaluation essayed, the most promising approach was the use of principal component analysis for dimension reduction followed by k-means cluster analysis. By leveraging the complementary strengths of PCA and k-means clustering, the robustness and interpretability of clustering analyses are enhanced.

Brillouin light scattering (BLS) is the inelastic scattering of light from elementary excitations with periodic density modulation. The characteristics of non-contact, high sensitivity, and high resolution in energy, wavevector, time, space, and phase make the BLS spectrometer widely used in investigating many intriguing physical phenomena, including the acoustic phonon confinement effects, Bose-Einstein condensation (BEC), supercurrent, and soliton formation. Generally, the quick and correct assignment of the signals in the BLS spectra is a prerequisite for further investigations. Herein, we experimentally identify the high-order spurious signals in the BLS spectra, which make the interpretation of the spectra difficult. The additional signals are demonstrated to originate from the laser and the temperature-controlled laser filter used for laser filtering. Our results would contribute to the rapid assignment of the signals from the sample after excluding the spurious signals reported here. Moreover, the series of high-order modes spaced by the free spectral range can serve as a weak broadband light source, which has great potential for investigating the optical responses of materials.

Vanadium dioxide (VO₂) undergoes a reversible first-order metal-to-insulator transition (MIT) from a high-temperature metallic phase to a low-temperature insulating phase at a critical temperature T_c of 68°C. The MIT is accompanied by a structural phase transition. In addition to the metallic high-temperature rutile phase, several insulating phases may be involved depending on doping, interfacial stress, or external stimuli. Unambiguously identifying the crystal phases involved in the phase transition is of key interest from the point of view of application as well as fundamental science. We study the impact of Ti doping of VO₂ thin films on (110) rutile TiO₂ substrates. We conduct a careful analysis of structural properties by combining results of x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The transition temperature T_c of the deposited thin films decreases with increasing Ti-content. All our thin film samples undergo a structural phase transition from the monoclinic M₁-phase to the rutile R-phase with increasing temperature without passing the intermediate monoclinic M₂-phase. A careful analysis of polarization and angle-dependent Raman data reveals that, above T_c, the unit cell of the high-temperature rutile Ti_xV_1-xO₂ phase is aligned with that of the rutile TiO₂ substrate whereas, below T_c, 180°-domains of the M₁-phase of Ti_xV_1-xO₂ are observed. The structural relationship between TiO₂ substrate and the high respective low-temperature phase of the Ti_xV_1-xO₂ determined by Raman spectroscopy is in excellent agreement with TEM results on these samples. Raman spectroscopy is a powerful tool for studying structural changes of VO₂-based samples in the vicinity of MIT.

East Asian inks are a major component of calligraphy, paintings, and prints in China, Japan, and Korea and are historically made from either pine soot or oil-lamp soot mixed with a proteinaceous binder. Although the inks from the two different soot sources have different properties in East Asian works of art, no non-destructive methods to differentiate them scientifically currently exist. Raman spectroscopy (RS) of carbonaceous materials is commonly used to extract information about their properties and has been applied here to East Asian inks. Soots used in making modern inks were collected from 10 sources in China and Japan and analyzed using RS. RS using 405-, 633-, and 785-nm excitation has been able to differentiate pine soot from oil-lamp soot, also called lampblack. In addition, principal component analysis (PCA) of only 785-nm Raman spectra has been able to discriminate between two different soots used in a 19th-century Japanese woodblock printing of Kaishien Gaden. In addition to allowing discrimination between inks on East Asian works of art, these results may be of use to other fields using carbonaceous materials.

Ecstasy tablets, a type of common street drug originally consisting of 3,4-methylenedioxymethamphetamine (MDMA), provide stimulant and hallucinogen psychoactive effects. They are frequently found in nightclubs, musical festivals or other recreational events believed to create a relaxing experience for the users. From a forensic perspective, when the drug of abuse is suspected in such scenarios, the law enforcement personnel would then require an easy-to-perform, quick and accurate method to detect the existence of such controlled substance prior to the seizure and subsequent forensic examination. In this study, we assessed the performance of a portable Raman spectroscopy as the primary aid in determining ecstasy tablets at the point of use. A total of 130 ecstasy tablet samples were analysed by Raman spectroscopy and characterised by gas chromatography–mass spectrometry (GC–MS). Active chemical substances and cutting agents detected by the two instrumentations were then compared. The performance of Raman spectroscopy was further assessed in terms of its accuracy, sensitivity and specificity, corresponding to the analysis results obtained from GC–MS analysis. Overall, portable Raman Spectroscopy used in this study shows an accuracy of 85.4% in analysing ecstasy tablets obtained from case samples, while the sensitivity and specificity were determined as 85.2% and 100%, respectively. No false positives for MDMA or other drugs were reported. Our results show that portable Raman spectroscopy is a suitable technique for targeted determination of the presence of ecstasy tablets, especially in forensic cases that require non-destructive, rapid and mass screening during on-site testing by law enforcement personnel.

Drug resistance plays a vital role in both cancer treatment and prognosis. Especially, early insights into such drug-induced resistance in acute myeloid leukemia (AML) can help to improve treatment plans, reduce costs, and bring overall positive outcomes for patients. Raman spectroscopy provides precise biomolecular information and can provide all these necessities effectively. In this study, we employed machine learning (ML) discrimination of Raman micro-spectroscopic data of myelocytic leukemia cell line HL-60 from its drug-resistant counterpart HL-60/MX2. Principal component analysis (PCA), linear discriminant analysis (LDA), and logistic regression (LR) methods were evaluated for their ability to identify and discriminate drug resistance in AML cells. Our study demonstrates the power of ML to classify drug-induced resistance in AML cells utilizing subtle variations in biomolecular information contained in molecular spectroscopic data by obtaining 94.11% and 97.05% classification accuracies by LDA and LR models, respectively. We also showed that the ML methods are discernable. Our findings depict the importance of automation and its optimal usage in cancer study and diagnosis. The results of our study are expected to take ML-assisted Raman spectroscopy one step closer to making it a generalized tool in medical diagnosis in the future.

Mn₂(C₂H₆N₆)₄(NO₃)₄·2H₂O (Mn) as one of the energetic coordination complexes was chosen for high-pressure research. In this work, Mn was analyzed by in situ Raman scattering, infrared absorption, and synchrotron angle-dispersive X-ray diffraction (ADXRD) technologies up to ~20 GPa at room temperature. The vibrational modes of Mn at ambient pressure were comprehensively resolved based on the experimental results. Detailed spectral analyses revealed that Mn underwent three pressure-induced phase transitions at 0.5, 2.5, and 5.7 GPa, respectively. ADXRD experiments confirmed the existence of these three phase transitions in Raman and infrared spectra analyses. Based on the analysis of the vibrational spectra and the changes of lattice parameters under pressure, it can be considered that the deformation of the 3-hydrazino-4-amino-1, 2, 4-triazole (HATr) ligand led to the first phase transition, and the distortion of the triazole ring induced the second phase transition, and the rearrangement of the hydrogen bonds resulted in the third phase transition. In addition, it can be inferred from Raman spectra and ADXRD data that Mn may have experienced the abnormal expansion during the first phase transition. This work may lay the foundation for further investigating the structure and properties of energetic coordination complexes under pressure.