Raman Spectroscopy Research Articles

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.

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.

OPTICAL PROPERTIES OF THE AgBiP2Se6 SINGLE CRYSTAL

The AgBiP2Se6 compound has emerged as one of the most studied hexachalcohypodiphosphates in recent years. This is interest is driven by its distinctive layered structure, which implies the possibility of obtaining monolayers and the observation of various of quantum effects. Most studies to date, however, have focused on first-principles calculations, while experimental investigations have primarily been limited to structural analysis and stoichiometric composition determination. This work partially addresses the gap in research by exploring the optical properties of AgBiP2Se6. Transmission spectra within the optical range of 220-1400 nm, as well as Raman spectra, were obtained from single crystalline AgBiP2Se6 samples. The band gap, determined from the transmission spectra using the graphical Tauc method, was found to be 1.44 eV. This value aligns closely with the DFT band-structure calculations using the Perdue-Burke-Erzenhorf (PBE) model without a Hubbard correction parameter (1.384 eV). The Raman spectrum of the AgBiP2Se6 crystal reveals five distinct peaks at approximately 68, 125, 169, 436, and 462 cm-1. The peak at 68 cm-1 can be attributed to the vibrational mode of the cationic centers; the peaks at 125 and 169 cm-1 can correspond to deformations within the Se-P-P and Se-P-Se bonding systems involving changes in bond angles; and the peaks at 436 and 462 cm-1 reflect bond length changes within the anionic (P2Se6)4-group.

Crystallographic symmetry increasing in the pressure-induced phase transition of the hydrogen-bonded organic crystal 1-methylhydantoin.

In situ high-pressure Raman spectroscopy and synchrotron angular dispersive x-ray diffraction techniques, combined with first-principles calculations, have been performed to investigate the 1-methylhydantoin (C4H6N2O2, 1-MH) molecular crystal. High-pressure experiments have shown that phase I (monoclinic system) begins to transform into phase II (orthorhombic system) at pressures above 4.0GPa, and the transformation range is from 4.0 to 14.2GPa. It is proposed that the mechanism of phase transition is the interlayer contraction and rearrangement of the hydrogen-bonding network due to the enhanced strong hydrogen-bonded interactions at high pressures. This study provides some theoretical basis for this rare pressure-induced phase transition from low symmetry to high symmetry in organic supramolecular polymorphism.

Rhenium Iodide Cluster Re&lt;sub&gt;3&lt;/sub&gt;I&lt;sub&gt;9&lt;/sub&gt; as a Precursor in the Synthesis of [Re(CO)&lt;sub&gt;5&lt;/sub&gt;I] and ((н-C&lt;sub&gt;4&lt;/sub&gt;H&lt;sub&gt;9&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;N)2[Re&lt;sub&gt;2&lt;/sub&gt;Cl&lt;sub&gt;8&lt;/sub&gt;

The reduction of rhenium iodide cluster Re3I9 to [Re(CO)5I] (55% yield) was observed in the presence of concentrated HCl and HCOOH at 130°C. In a dimethylammonium chloride [(CH3)2NH2]Cl melt, the triangular cluster polymer Re3I9 is transformed into the dianionic binuclear cluster complex [Re2Cl8]2–, which was isolated as the tetrabutylammonium salt ((n-C4H9)4N)2[Re2Cl8] in 46% yield. The structure of the complex [Re(CO)5I] was confirmed by powder X-ray diffraction, energy dispersive spectroscopy, IR spectroscopy, and Raman spectroscopy. ((n-C4H9)4N)2[Re2Cl8] was identified using elemental analysis, energy dispersive spectroscopy, and IR and Raman spectroscopy. An acetonitrile solution of ((n-C4H9)4N)2[Re2Cl8] was characterized by the mass spectrum and characteristic UV-Vis spectrum.

Spectroscopic Signatures of Ultra-Thin Amorphous Carbon with the Tuned Disorder Directly Grown on a Dielectric Substrate.

The reduced structural complexity of atomically thin amorphous carbons makes it suitable for semiconductor technology. Inherent challenges arise from transfer processes subsequent to growth on metallic substrates, posing significant challenges to the accurate characterization of amorphous materials, thereby compromising the reliability of spectroscopic analysis. Here this work presents a novel approach: direct growth of ultra-thin amorphous carbon with tuned disorder on a dielectric substrate (SiO2/Si) using photochemical reaction and thermal annealing process with a solid precursor. This work characterizes the amorphous carbon films' disorder using spectroscopic techniques, such as X-ray photoelectron spectroscopy, Electron energy loss spectroscopy, and Raman spectroscopy, which offer greater convenience compared to microscopy-based studies. This method, rooted in comprehensive spectroscopic characterization, elucidates characteristic signatures inherent to the amorphous carbon films. These findings reveal that Raman spectroscopy is particularly effective in identifying the amorphous phase of atomically-thin carbon. Additionally, I-V characterization and high-frequency dielectric measurements showcase the potential application of directly grown amorphous carbon films in the semiconductor industry, where nanometer-level thin conductors and dielectrics are commonly utilized. This transfer-free characterization method provides a useful tool to find the correlation between atomic structure and electrical/optical properties, giving valuable insights into comprehensive crystallographic fundamental research.

Lithium Storage Mechanisms and Electrochemical Behavior of a Molybdenum Disulfide Nanoparticle Anode

This study investigates the electrochemical behavior of molybdenum disulfide (MoS2) as an anode in Li‐ion batteries, focusing on the extra capacity phenomenon. Employing advanced characterization methods such as in situ and ex situ X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, and transmission electron microscopy, the research unravels the complex structural and chemical evolution of MoS2 throughout its cycling. A key discovery is the identification of a unique Li intercalation mechanism in MoS2, leading to the formation of reversible LixMoS2 phases that contribute to the extra capacity of the MoS2 electrode. Density function theory calculations suggest the potential for overlithiation in MoS2, predicting Li5MoS2 as the most energetically favorable phase within the lithiation–delithiation process. Additionally, the formation of a Li‐rich phase on the surface of Li4MoS2 is considered energetically advantageous. After the first discharge, the battery system engages in two main reactions. One involves operation as a Li‐sulfur battery within the carbonate electrolyte, and the other is the reversible intercalation and deintercalation of Li in LixMoS2. The latter reaction contributes to the extra capacity of the battery. The incorporation of reduced graphene oxide as a conductive additive in MoS2 electrodes notably improves their rate capability and cycling stability.

Advancements in Detection Methods for Salmonella in Food: A Comprehensive Review

Non-typhoidal Salmonella species are one of the leading causes of gastrointestinal disease in North America, leading to a significant burden on the healthcare system resulting in a huge economic impact. Consequently, early detection of Salmonella species in the food supply, in accordance with food safety regulations, is crucial for protecting public health, preventing outbreaks, and avoiding serious economic losses. A variety of techniques have been employed to detect the presence of this pathogen in the food supply, including culture-based, immunological, and molecular methods. The present review summarizes these methods and highlights recent updates on promising emerging technologies, including aptasensors, Surface Plasmon Resonance (SPR), and Surface Enhanced Raman Spectroscopy (SERS).

Ti3AlC2 single crystal growth via controlling horizontal temperature gradient

ABSTRACTGrowth of single‐crystal MAX phases is crucial for studying their intrinsic physical properties. Although Ti3AlC2 is one of the most popular MAX phases for the study of high‐temperature structural materials as well as a precursor for MXene, the growth of Ti3AlC2 single crystals remains a challenge owing to the limited solubility of graphite in the Ti melt via the self‐flux method. In this study, a horizontal temperature gradient was used to resolve the dissolution of graphite in the melt and its diffusion rate. Ti3AlC2 single crystals with an area of 9 mm2 were successfully produced under horizontal temperature gradients. It was tentatively proposed that the crystallinity of Ti3AlC2 single crystals could be reflected by the intensity ratio of the in‐plane and c‐axial phonon vibration modes in the Raman spectra of the MAX phase.

N- to p-Type Conductivity Transition of Lu3N@C80 Due to Anisotropic Deformation of Fullerene and Pyramidalization of Endohedral Clusters.

The endohedral fullerene Lu3N@C80 was examined using in situ high-pressure measurements, which included electrical transport, Fourier-transform infrared spectroscopy, and Raman spectroscopy, in combination with theoretical calculations. Lu3N@C80 was found to undergo a reversible n- to p-type conversion at ∼8.9 GPa. This p-type semiconductor remains stable up to 25 GPa. The fullerene cage collapses at ∼29 GPa, resulting in an irreversible p- to n-type conversion. Raman, infrared, and X-ray absorption spectroscopy reveal that an anisotropic distortion of the carbon cage and a pyramidalization of the planar Lu3N clusters occur during compression. Density functional theory simulations indicate that the p orbitals of C atoms in the fullerene cage primarily contribute to the density of states (DOS). Pressure-induced deformation of the fullerene cage dominates the DOS changes in the conduction and valence bands close to the Fermi level. The findings elucidate the relationship between the conductivity and structural changes in the endohedral clusters.