Raman Spectroscopy Research Articles

Carbon Nanotubes Decorated with Nickel or Copper as Anti-Wear and Extreme-Pressure Additives for Greases

To increase the anti-wear (AW) and anti-scuffing possibilities of commercially available lithium grease, this paper proposed enriching the original composition with functionalised carbon nanotubes (CNTs) at a concentration of 0.1% (w/w). The CNTs were modified by decorating them with nanoparticles of two metals with established tribological potential: copper and nickel. The AW and extreme-pressure properties were determined using the customised ISO-20623 test on a four-ball apparatus. The AW properties were determined using the standardised parameter MWSD (mean wear scar diameter) and the anti-scuffing properties using the last non-seizing load. The greases enriched with nanoadditives showed better AW properties compared to the reference grease at higher loads (1–1.2 kN). Particularly favourable results were observed for grease with the addition of Cu-decorated CNTs, for which the MWSD values were more than 50% lower than the reference. Optical microscopy, SEM and TEM microscopy with EDS analysis, and Raman spectroscopy were used to identify the wear mechanisms and characterise the role of nanoadditives in the lubrication process.

Porous Carbon Fabricated by Microbial Pretreatment of Brewer’s Grain for the Improvement of Toluene Adsorption Performance

Porous activated carbons (AC-AN and AC-AO) for toluene adsorption were prepared starting from brewer’s grain biomass pretreated with microorganisms (Aspergillus niger van Tieghem for AC-AN and Aspergillus oryzae RIB40 for AC-AO). The structures and chemical properties of the three activated carbon materials (AC-AN, AC-AO, and AC that was not pretreated with microorganisms) were characterized by N2 adsorption–desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The adsorption behavior of the three activated carbons for toluene was studied and correlated with the physical and chemical properties of these materials. The results suggested that the activated carbons prepared by microbial pretreatment had a rougher morphology, higher specific surface area, richer pore structure, fewer oxygen-containing functional groups on the surface, and better adsorption performance for toluene (increased by 31.5% and 18.3% with AC-AN and AC-AO, respectively) compared with the untreated activated carbon (AC). The Thomas model was used to fit the toluene adsorption data, indicating that the rich pore structure accelerated the kinetic process of toluene adsorption. Therefore, appropriate microbial pretreatment of the feedstock that is used to prepare activated carbon can effectively improve its adsorption capacity towards toluene.

Role of BPO4 flux in BaBPO5 crystal growth characterized through high-temperature Raman spectroscopy

In this study, we explored the growth of incongruently melting crystals in a starting solution with flux to better understand the role of flux in crystal growth mechanisms. We recorded the spectrum of BaBPO5 crystals across a 200-1400 cm−1 range for detailed Raman spectroscopic analysis. The observed Raman bands corresponded to the vibrations of PO4 and BO4 units. These units link with B-O-P bonds via common corners to form PBO7 groups that serve as basic structural units of the crystal. Notably, these PBO7 structures remain stable at high temperatures up to the crystal melting point, at which the isolated PO4 groups predominantly exist in the melt, as revealed by high-temperature Raman spectroscopy. Further investigations into the Raman spectra of the starting solution enriched with BPO4 self-flux indicate that PBO7 groups are crucial for crystal growth. The addition of PBO4 flux aids in the formation of these PBO7 units. This research paves the way for expanding our understanding to other systems, which will help elucidate the mechanisms behind crystal growth.

Assessing the combined effects of chemical and mechanical parameters on silar-grown nanostructured ZnO thin films

In the literature, a comprehensive assessment of the combined impacts of chemical and mechanical parameters on the properties of thin films grown by SILAR is missing. In this work, ZnO film formation is investigated under variable precursor concentration, pH, withdrawal speed and number of cycles. Interestingly, the produced ZnO films displayed remarkable aspect ratio and morphological variability, ranging from the commonly obtained nanograins shape towards hexagonal nanorods, flower- like rods and nanoneedles, which to our knowledge have not yet been achieved by using single step SILAR process. More particularly, low concentration and intermediate pH and withdrawal rates were favorable for nanorods formation. In addition, increasing the withdrawal speed from 26 to 30 cm·min-1 resulted in a thinner film with improved rod uniformity and reduced crystallite size. This is the first study on the impact of substrate withdrawal speed on SILAR films. Among all studied parameters, the number of cycles was particularly useful for tuning film thickness, while preserving its target shape. In addition, the films grown under a higher number of cycles showed improved film crystallinity and rod orientation with reduced dislocation density, microstrain and bandgap energy. In our conditions, the most suitable combination of parameters required for exhibiting optimized nanorod-shaped coating are: a concentration of 0.07 M, pH of 10.5, speed of 30 cm·min-1 and 40 cycles. In this case, XRD, XPS, Raman and FTIR spectra displayed typical features of hexagonal Wurtzite structure of ZnO with no impurities within the film surface, whereas AFM measured a thickness of 1.4 μm with 243 nm surface roughness.

Efficient and Stable Red‐Orange Emission from Polaronic Magnetic Excitons in Mn (II)‐Doped 0D All‐Inorganic Rb4CdCl6

AbstractThe impact of magnetic coupling effects on the luminescence of 0D (zero‐dimensional) perovskite materials doped with TM (transition metal) ions remains underexplored. This study synthesizes Mn2+‐doped 0D Rb4CdCl6 halide structures using a solvent‐based method, with Rb+ ions systematically arranged around isolated [CdCl6]4− octahedra. The resulting Rb4Cd1‐xMnxCl6 powder exhibits stable orange‐red luminescence under UV (ultraviolet) excitation, achieving a PLQY (photoluminescence quantum yield) of 88.96%. The parent Rb4CdCl6 is non‐luminescent, but doping with Mn2+ induces strong luminescence due to combined emissions from d‐d transitions of Mn2+, weakly ferromagnetically coupled Mn2+ pairs, and STEs (self‐trapped excitons). Characterization via XRD (X‐ray diffraction) and DFT (density functional theory) reveals that Mn2+ doping occurs through both substitutional and interstitial processes, facilitating magnetic coupling. Raman spectroscopy identifies strong electron‐phonon coupling at a phonon mode of 112 cm−1, supporting STEs generation. Magnetic property analysis shows significant ferromagnetic coupling between Mn2+ pairs and paramagnetic single Mn2+ ions, enhancing luminescence. The material demonstrates remarkable structural and thermal stability, positioning Rb4Cd1‐xMnxCl6 as a promising candidate for optoelectronic applications.

Gold Tetrahedral Nanoframes with Mono-Rim or Dual-Rim Morphologies for Enhanced Near-Field Focusing in SERS.

This study presents a synthesis method for Au tetrahedral nanoframes (Td NFs) through a rationally designed multiple-step process, followed by an investigation of their distinctively ordered self-assembly for enhanced performance in surface-enhanced Raman spectroscopy (SERS). Two distinct Au Td NF building blocks are synthesized, exhibiting mono-rim or dual-rim morphologies. The mono-rim structure lacks intra-nanogaps, whereas the dual-rim configuration features well-defined intra-nanogaps. The non-centrosymmetric Td NFs self-assemble into a distinctive antiparallel arrangement that alternates between the tip-up and face-up orientations of the Au Td NFs. This configuration results in the formation of both triply tip-to-tip and face-to-face nanogaps. The unique zigzag pattern exhibited strong electromagnetic field enhancement and extensive spatial hot zones, significantly amplifying near-field focusing and, consequently, the SERS effect. The near-field enhancement of Au Td NF assemblies is confirmed through finite element method simulations and experimentally validated by comparing bulk SERS measurements with those of Au octahedron NF assemblies, which tend to adopt a parallel face-to-tip alignment during assembly. Owing to the complex arrangement of multiple intra-nanogaps between the internal rim-to-rim interfaces and the four exposed facets, dual-rim Td NFs exhibited single-particle SERS activity, a capability not observed in analogous Td NFs with single rims.

Vibrational and DFT Studies and Anticancer Activity of Novel Pd(II) and Pt(II) Complexes with Chloro Derivatives of 7-Azaindole-3-Carbaldehyde

This study investigates the structural, vibrational, and biological properties of novel palladium(II) and platinum(II) complexes with 5-chloro-7-azaindole-3-carbaldehyde (5ClL) and 4-chloro-7-azaindole-3-carbaldehyde (4ClL) ligands. Infrared and Raman spectroscopy, combined with DFT (ωB97X-D) calculations, provided valuable information about metal–ligand interactions, the cis or trans conformation of the aldehyde group in the ligands, and the presence of trans isomers in the metal complexes obtained in the solid state. In vitro tests were used to evaluate the antiproliferative activity of the novel complexes against several cancer cell lines, including ovarian cancer (A2780), cisplatin-resistant ovarian cancer (A2780cis), colon cancer (HT-29), and triple-negative breast cancer (MDA-MB-231), as well as normal mouse fibroblasts (BALB/3T3). The platinum complex, trans-[PtCl2(5ClL)2], exhibited superior activity against A2780cis (IC50 = 4.96 ± 0.49 µM) and MDA-MB-231 (IC50 = 4.83 ± 0.38 µM) compared to cisplatin, while the palladium complexes (trans-[PdCl2(4ClL)2] and trans-[PdCl2(5ClL)2]) demonstrated enhanced selectivity with reduced toxicity to normal fibroblasts (IC50 = 11.29 ± 6.65 µM and 14.98 ± 5.59 µM, respectively).

Topographic Evaluation of the Remineralizing Potential of Biomimetic Scaffolds on Enamel White Spot Lesions: An InVitro Study.

The modern approach to managing noncavitated white spot lesions (WSLs) emphasizes noninvasive strategies and biomimetic remineralization. Biomimetic scaffolds are designed to regenerate dental tissues rather than simply repair them. This study aimed to assess lesion depth, enamel structure, and the elemental composition of artificially induced WSLs after treatment with biomimetic remineralization techniques. Ninety-six freshly extracted anterior teeth, free from caries or enamel defects and extracted due to periodontal disease, were used. White spot lesions were induced on the labial surfaces, and the samples were divided into three groups based on the remineralizing agent: Group I, treated with casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), which served as the positive control; Group II, treated with self-assembling peptide P11-4 (SAP-P11-4); and Group III, treated with phosphorylated nano-chitosan (Pchi-ACP). Enamel topography was analyzed at baseline and after treatment using polarized light microscopy, micro-Raman spectroscopy, and scanning electron microscopy. Statistical analysis was conducted using one-way ANOVA, Kruskal-Wallis, and Dunn's post hoc test (p = 0.05). The Kruskal-Wallis test indicated a significant difference in remineralization potential among the groups. Pchi-ACP showed the greatest reduction in lesion depth (62.65%), demonstrating significant subsurface enamel remineralization. This group also exhibited a smooth, regular enamel surface with shallow linear depressions. Elemental analysis confirmed successful calcium phosphate precipitation in Pchi-ACP, indicating a trend toward enamel regeneration. Pchi-ACP represents a promising biomimetic and minimally invasive approach for treating early WSLs, signifying a transition toward regenerative dentistry. (SAP-P11-4), while effective, was less successful than phosphorylated nano-chitosan but outperformed (CPP-ACP). Pchi-ACP demonstrates significant potential for minimally invasive treatment of early noncavitated carious lesions. By preserving natural tooth structure, this approach could greatly enhance oral health outcomes in the long term.

Antibiotic SERS spectral analysis based on data augmentation and attention mechanism strategy.

The analysis of Raman spectrum data has gradually transitioned into the era of machine learning. However, it is still constrained by the challenge of acquiring large volumes of raw data and the issue of losing characteristic information from spectral data. In this paper, we propose a strategy that combines data amplification and attention mechanisms for analyzing antibiotic spectral data. Firstly, a Generative Adversarial Network was employed to amplify the SERS spectrum of eight antibiotics by 10 times, to augment the dataset to fulfill the requirements of the neural network. Then, the amplified data is input into a one-dimensional convolutional neural network with an attentional mechanism module, which enables a more accurate capture of spectral feature information. The one-dimensional convolutional neural network achieved a 97.5% accuracy in classifying eight antibiotics. The accuracy of the four mixtures within the same class was 89.4%.

Spatially Quantitative Imaging of Enzyme Activity in a Living Cell.

Enzyme activity plays a key role in cell heterogeneity. Its spatially quantitative imaging in a living cell not only directly displays but also helps people to understand cell heterogeneity. Current methods are hard to achieve due to the short intracellular retention or lack of internal reference of the imaging probes. Herein, we rationally designed a self-referenced Raman probe Val-Cit-Cys(StBu)-Pra-Gly-CBT (Yne-CBT) which takes an intracellular cathepsin B (CTSB)-initiated CBT-Cys click reaction to yield a long-retained cyclic dimer in cell. In the meantime, Raman signal changes of its two chemical bonds (C≡C and C≡N) after the reaction are used for self-referencing and quantitative Raman imaging of CTSB activity. In vitro experiments demonstrated that, with shell-isolated nanoparticle-enhanced Raman spectroscopy technique, 20 μM Yne-CBT was able to quantitatively detect CTSB activity with a limit of detection of 61.4 U L-1. Under a homemade microfluidic channel, Yne-CBT was successfully applied for spatially quantitative imaging CTSB activity in a living cell. Our strategy provides people with a facile method to directly and quantitatively display cell heterogeneity.

Semi-coherent Interface and Vacancy Engineering for Constructing NiTe/FeTe/Fe3O4/FF to Boost Electrochemical Overall Water Splitting.

Transition metal-based tellurides (TMTs) with excellent electrical conductivity are expected to be ideal electrocatalysts for overall water splitting. However, compared to transition metal sulfides and selenides, the reported applications of TMTs in overall water splitting are fewer. Herein, the NiTe/FeTe/Fe3O4/FF carnation flower-like with a semi-coherent interface is successfully constructed to enhance the electrochemical overall water splitting performance. Specifically, it achieves low overpotentials of 54 and 176 mV at 10 mA cm-2 forthe hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. What's more, the electrolyzer requires a cell voltage of 1.5 V to sustain a current density of 10 mA cm-2 and maintains remarkable stability for an extensive duration of 450 h even at a current density of 100 mA cm-2. Semi-coherent interface engineering and vacancy engineering not only improve the OH⁻ adsorption capacity of catalysts but also promote the desorption of adsorbed hydrogen (Hads). In situ Raman spectroscopy reveals that FeOOH and NiOOH formed by NiTe/FeTe/Fe3O4/FF during the OER are the genuine active sites. This study provides a promising approach for the electrochemical water splitting of TMTs by combining semi-coherent interface engineering and vacancy engineering.

Rapid diagnosis of bacterial vaginosis using machine-learning-assisted surface-enhanced Raman spectroscopy of human vaginal fluids.

The accurate and rapid diagnosis of bacterial vaginosis (BV) is crucial due to its high prevalence and association with serious health complications, including increased risk of sexually transmitted infections and adverse pregnancy outcomes. Although widely used, traditional diagnostic methods have significant limitations in subjectivity, complexity, and cost. The development of a novel diagnostic approach that integrates SERS with ML offers a promising solution. The CNN model's high prediction accuracy, cost-effectiveness, and extraordinary rapidity underscore its significant potential to enhance the diagnosis of BV in clinical settings. This method not only addresses the limitations of current diagnostic tools but also provides a more accessible and reliable option for healthcare providers, ultimately enhancing patient care and health outcomes.

Disulfide-Containing Nitrosoarenes: Synthesis and Insights into Their Self-Polymerization on a Gold Surface.

Disulfide-containing nitrosoarenes with [bis(4-nitrosobenzyl) disulfide, NOBnDS (1)] or without [4-nitrosophenyl disulfide, NOPDS (2), and 1,2-bis(4'-nitroso-[1,1'-biphenyl]-4-yl)disulfane, NOBPDS (3)] an alkyl spacer between the sulfur headgroup and the aromatic moiety (phenyl in NOPDS (2) or biphenyl in NOBPDS (3)) were synthesized and used as precursors to form azodioxy thiolate films on Au(111) substrates. Due to the incorporated disulfide functionalities, these specifically designed nitrosoarenes are enabled to self-polymerize through azodioxy bonds on a gold surface. Thin films of NOBnDS (1), NOPDS (2), and NOBPDS (3) were prepared at different adsorption times via the solution-phase self-assembly of molecules onto the Au(111) surface and characterized by Raman spectroscopy, ellipsometry, water contact angle measurements, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). For comparison, films of structurally analogous disulfide-containing nitro derivatives on Au(111), which can form only monolayer films, thus serving as a reference, were also fabricated and characterized. Raman spectra of NOBnDS (1), NOPDS (2), and NOBPDS (3) films on the Au(111) substrates revealed the presence of a N═N stretching band of the E-azodioxy group. Ellipsometry showed that nitrosoarenes form thicker films compared with their nitro counterparts, indicating the formation of azodioxy oligomer films. AFM revealed an island-like morphology of the nitrosoarene films, in contrast to the rather homogeneous one observed for the monolayer films of nitro derivatives. STM images of nitrosoarene films indicated the formation of poorly organized surface structures in which oligomer chains are possibly interdigitated and substantially tilted relative to the surface normal, which agrees with the relatively low values of the ellipsometry-derived thicknesses. The obtained results emphasized the influence of the substituent electronic effects on the on-surface formation of azodioxides and could be used for the future design of azodioxy thiolate films on gold surfaces.

The crystal structures of methyl prop-2-ynoate, dimethyl fumarate and their protonated species.

Methyl prop-2-ynoate (C4H4O2) was investigated in the binary superacidic system HF/MF5 (M = Sb or As) and dimethyl fumarate (C6H8O4) in the superacidic system HF/SbF5, as well as HF/BF3. The starting materials methyl prop-2-ynoate and dimethyl fumarate were crystallized, the former for the first time. The protonated species of these esters, namely, (1-methoxyprop-2-yn-1-ylidene)oxidanium hexafluoroarsenate, C4H5O2+ AsF6-, 1,4-dimethoxy-4-oxobut-2-en-1-ylidene]oxidanium tetrafluoroborate bis(hydrogen fluoride), C6H9O4+ BF4- 2HF, and hemi{[1,4-dimethoxy-4-oxidaniumylidenebut-2-en-1-ylidene]oxidanium} undecafluorodiantimonate, 0.5C6H10O42+ Sb2F11-, were characterized by single-crystal X-ray diffraction and Raman spectroscopy. The protonated species were recrystallized from anhydrous hydrogen fluoride. In the solid state of the monoprotonated species of methyl prop-2-ynoate and the diprotonated species of dimethyl fumarate, strong intramolecular O-H...F hydrogen bonds build a three-dimensional network. The monoprotonated species of dimethyl fumarate builds chains by strong O-H...O hydrogen bonds between the cations.

Research Progress on Evaluating the Effectiveness and Safety of Transdermal Absorption of Cosmetics

This review systematically summarizes research progress in the evaluation of the effectiveness and safety of the transdermal absorption of cosmetics, focusing on the classification, applicability, and relevant regulations of different evaluation methods. Transdermal absorption refers to the process in which active ingredients enter the epidermis, dermis, and other parts of the skin through the skin barrier and exert their effects. The article first classifies the in vitro and in vivo evaluation methods of transdermal absorption. It also provides a detailed overview of the regulations and standards for in vitro transdermal absorption, compares the standards of different institutions, and highlights the diffusion cell method, developed by scientists at Procter & Gamble, which is the mainstream method for in vitro testing. In addition, the paper summarizes the utilization of modern testing techniques such as high-throughput screening technology, mass spectrometry imaging, Raman spectroscopy, and confocal microscopy in the study of transdermal absorption and introduces the working principles of various instruments and their specific application cases in transdermal absorption studies.

High-Temperature Polymorphism and Band-Gap Evolution in BaZrS3.

Barium zirconium trisulfide (BZS) is a three-dimensional (3D) perovskite with optoelectronic properties suitable for photovoltaic (PV) and light-emitting diode (LED) applications that is conventionally reported in the orthorhombic Pnma (62) symmetry. Synchrotron X-ray diffraction, thermal analysis, and Raman and absorption spectroscopy revealed three high-temperature polymorphs that appear when BZS is heated in air prior to complete oxidation (BaZrS3 + 5O2 → BaSO4 + ZrO2 + 2SO2↑) at 700 °C with the approximate stability ranges: BaZrS3 IVPnma (62)T < 400 °CBaZrS3 IIICmcm (63)400 °C ≤ T ≤ 500 °CBaZrS3 II14/mcm (140)500 °C ≤ T ≤ 700 °CDifferential scanning calorimetry (DSC) revealed exothermic features accompanying the IV → III and III → II phase changes. Furthermore, the direct band gap varied inversely with temperature with distinct energies for each polymorph (1.84 eV ≤ IV ≤ 1.65 eV; 1.65 eV ≤ III ≤ 1.54 eV; 1.54 eV ≤ II ≤ 1.52 eV). Raman spectroscopy found that polymorphic changes up to 600 °C were reversible with bands characteristic of BaZrS3 IV entirely restored upon cooling to room temperature (RT). This more complete understanding of BSZ polymorphism provides a basis for producing crystallochemical variants with enhanced optoelectronic properties under ambient conditions.

Triplet Network for One-Shot Raman Spectrum Recognition.

Raman spectroscopy is widely used for material detection due to its specificity, but its application to spectral recognition often faces limitations due to insufficient training data, unlike fields such as image recognition. Traditional machine learning or basic neural networks are commonly used, but they have limited ability to achieve high precision. We have proposed a novel approach that combines the Triplet network (TN) and K-nearest neighbor (KNN) techniques to address this issue. TN maps the Raman spectral sequences to a 128-dimensional Euclidean space to extract features, enabling the features in the new space to more accurately represent the similarities or differences between spectra, and then utilizes the KNN algorithm to perform classification tasks in this feature space. Our method exhibits superior performance in recognizing unknown Raman spectra with minimal training samples per class. We employed a handheld Raman spectrometer with an excitation wavelength of 785 nm to collect the Raman spectra of 36 samples, including 28 safe materials and eight hazardous materials. Using only one spectrum as a support set for each category, the hazardous samples were successfully distinguished from the safe samples with an accuracy of 99.6%. Additionally, our model offers adaptability without requiring exhaustive retraining when adding new prediction classes. In situations with high background fluorescence, the TN performs better in measuring the distance between spectra of the same class than traditional distance measurement methods.

Performance of CaO-Promoted Ni Catalysts over Nanostructured CeO2 in Dry Reforming of Methane

Ni (20 wt.%) catalysts supported on CeO2 were synthesized using the incipient wetness impregnation method and promoted with varying amounts of CaO (0, 5, 10, 15, 20 wt.%). The catalysts were evaluated in dry reforming of methane (DRM) at 650 °C for 24 h. Fresh catalysts were characterized by XRD, WD-XRF, H2-TPR, N2 physisorption, HDP, SEM, and FT-IR spectroscopy (DRIFT and ATR), while spent catalysts were characterized by XRD, Raman spectroscopy, and SEM. The incorporation of 5–15 wt.% CaO on CeO2 significantly improved its catalytic performance. FT-IR analysis confirmed the presence of CaCO3 bands, indicating carbonate formation. The Ni/CeO2 catalyst with 15 wt.% CaO exhibited the highest catalytic activity. The promoted catalysts demonstrated high stability, attributed to strong interactions between CeO2, CaO, and CaCO3. However, when CaO promotion reached 20 wt.%, catalytic activity decreased. Despite large carbon formations, the catalysts maintained their stability with no significant deactivation due to sintering or coke accumulation.

Raman spectroscopy with a microfluidic device embedded with plasmonic metasurface

Raman spectroscopy with a microfluidic device embedded with plasmonic metasurface

Charge transport mechanism in [GeOx](z)[SiO2](1-z) based MIS structures

The mechanisms of conductivity in metal–insulator–semiconductor (MIS) structures based on [GeOx](z)[SiO2](1-z) films (0.25 ≤ z ≤ 1) fabricated by co-evaporation of germanium oxide and silicon oxide powders in vacuum and deposition on a p+-type silicon substrate are studied. Indium tin oxide deposited by magnetron method is used as the top electrode. According to IR spectroscopy, Ge–O, Si–O, and Ge–O–Si bonds are detected in the films, while no features related to the presence of germanium clusters are found in the Raman spectra. The current–voltage characteristics (I–V curves) are measured at different temperatures and analyzed by applying the eight most common models of charge transport in MIS structures. It is found that the experimental I–V curves are most accurately approximated in the space charge limited current model, and the parameters of the charge traps are determined within this model.