Distinct Raman Spectra Research Articles

Confocal Raman Microscopy – Shedding Light on the Ionomer Properties of PFSA Membranes

Perfluorinated sulfonic acid (PFSA) polymers are the state-of-the-art material for the proton exchange membrane (PEM) in various electrochemical energy conversion devices, e.g., PEM fuel cells, PEM water electrolyzers, or redox flow batteries, combining chemical and mechanical durability with high proton conductivity.The most prominent example of a PFSA material is NafionTM, which is a so-called long side chain (LSC) ionomer due to its comparably long side chain between the polymer backbone and the charged sulfonyl end group. On the other hand, short side chain (SSC) ionomers like Aquivion® and 3M Ionomer or composite membranes are promising approaches to improve performance in harsh conditions, such as low humidity or high operating temperatures.1 SSC PEMs feature increased water uptake, proton conductivity,2 and crystallinity3 compared to LSC PEMs. Composite PEMs can be specifically tailored to the required operating conditions by carefully designing the interlayers or additives. As the performance and longevity of electrochemical cells are a delicate convolution of various (composite) membrane properties and parameters, a method for evaluating ionomer membrane properties is crucial for rationally engineering optimized PEMs.Here, we use confocal Raman microscopy (CRM) to investigate application-relevant properties of PFSA PEMs and for high-resolution imaging of composite membranes.4 Thus, the high spatial resolution of confocal optical microscopy and the chemical sensitivity of Raman scattering are combined in a single measurement approach. NafionTM, 3M Ionomer, and Aquivion® at varying equivalent weights (EW) feature distinctive Raman spectra (Fig. 1) that show characteristic spectral changes depending on the ionomer’s side chain structure and EW. We show that the EW of these PFSA types can be reliably measured using Raman spectroscopy. Further, parameters such as swelling, ionizable group content, and water uptake can be quantified by CRM non-destructively and contact-free. The diffraction-limited resolution of CRM of less than 2 µm enables a view of the local distribution of these properties and, therefore, allows to image and analyze composite membranes. In summary, we comprehensively study ionomer properties of (composite) membranes and establish CRM as a powerful platform for characterizing advanced PEMs for electrochemical energy deviceReferences A. S. Aricò, A. Di Blasi, G. Brunaccini, F. Sergi, G. Dispenza, L. Andaloro, M. Ferraro, V. Antonucci, P. Asher, S. Buche, D. Fongalland, G. A. Hards, J. D. B. Sharman, A. Bayer, G. Heinz, N. Zandonà, R. Zuber, M. Gebert, M. Corasaniti, A. Ghielmi and D. J. Jones, Fuel Cells, 10(6), 1013–1023 (2010).Y.-C. Park, K. Kakinuma, H. Uchida, M. Watanabe and M. Uchida, Journal of Power Sources, 275, 384–391 (2015).K. D. Kreuer, M. Schuster, B. Obliers, O. Diat, U. Traub, A. Fuchs, U. Klock, S. J. Paddison and J. Maier, Journal of Power Sources, 178(2), 499–509 (2008).M. Maier, D. Abbas, M. Komma, M. S. Mu'min, S. Thiele and T. Böhm, Journal of Membrane Science, 669, 121244 (2023). Figure 1

Single-cell Raman spectroscopy identifies Escherichia coli persisters and reveals their enhanced metabolic activities.

Microbial persisters are the featured tiny sub-population of microorganisms that are highly tolerant to multiple antimicrobials. Currently, studies on persisters remain a considerable challenge owing to technical limitations. Here, we explored the application of single-cell Raman spectroscopy (SCRS) in the investigation of persisters. Escherichia coli (ATCC 25922) cells were treated with a lethal dosage of ampicillin (100 μg/mL, 32 × MIC, 4 h) for the formation of persisters. The biochemical characters of E. coli and its persisters were assessed by SCRS, and their metabolic activities were labeled and measured with D2O-based single-cell Raman spectroscopy (D2O-Ramanometry). Notable differences in the intensity of Raman bands related to major cellular components and metabolites were observed between E. coli and its ampicillin-treated persisters. Based on their distinct Raman spectra, E. coli and its persister cells were classified into different projective zones through the principal component analysis and t-distributed stochastic neighbor embedding. According to the D2O absorption rate, E. coli persisters exhibited higher metabolic activities than those of untreated E. coli. Importantly, after the termination of ampicillin exposure, these persister cells showed a temporal pattern of D2O intake that was distinct from non-persister cells. To our knowledge, this is the first report on identifying E. coli persisters and assessing their metabolic activities through the integrated SCRS and D2O-Ramanometry approach. These novel findings enhance our understanding of the phenotypes and functionalities of microbial persister cells. Further investigations could be extended to other pathogens by disclosing microbial pathogenicity mechanisms for developing novel therapeutic strategies and approaches.

Classification of Preeclamptic Placental Extracellular Vesicles Using Femtosecond Laser Fabricated Nanoplasmonic Sensors.

Placental extracellular vesicles (EVs) play an essential role in pregnancy by protecting and transporting diverse biomolecules that aid in fetomaternal communication. However, in preeclampsia, they have also been implicated in contributing to disease progression. Despite their potential clinical value, current technologies cannot provide a rapid and effective means of differentiating between healthy and diseased placental EVs. To address this, a fabrication process called laser-induced nanostructuring of SERS-active thin films (LINST) was developed to produce scalable nanoplasmonic substrates that provide exceptional Raman signal enhancement and allow the biochemical fingerprinting of EVs. After validating the performance of LINST substrates with chemical standards, placental EVs from tissue explant cultures were characterized, demonstrating that preeclamptic and normotensive placental EVs have classifiably distinct Raman spectra following the application of advanced machine learning algorithms. Given the abundance of placental EVs in maternal circulation, these findings encourage immediate exploration of surface-enhanced Raman spectroscopy (SERS) of EVs as a promising method for preeclampsia liquid biopsies, while this novel fabrication process will provide a versatile and scalable substrate for many other SERS applications.

Visualizing surface marker expression and intratumoral heterogeneity with SERRS-NPs imaging.

Cell surface marker expression in tumors dictates the selection of therapeutics, therapy response, and survival. However, biopsies are invasive, sample only a small area of the tumor landscape and may miss significant areas of heterogeneous expression. Here, we investigated the potential of antibody-conjugated surface-enhanced resonance Raman scattering nanoparticles (SERRS-NPs) to depict and quantify high and low tumoral surface marker expression, focusing on the surface markers epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) in an intracerebral and peripheral setting with an inter- and intratumoral comparison of Raman signal intensities.Methods: ICR-Prkdc <scid> mice were injected with glioblastoma, epidermoid carcinoma, or breast tumor cell lines intracerebrally and peripherally. SERRS-NPs were functionalized with cetuximab or trastuzumab and administered via tail vein injection. Raman imaging was performed 18 hours post-injection in excised tumors and in vivo through the skull. Tumors were then fixed and processed for immunohistochemical evaluation.Results: Confirmed by MRI and immunohistochemistry for EGFR and HER2, our results demonstrate that antibody-conjugated SERRS-NPs go beyond the delineation of a tumor and offer clear and distinct Raman spectra that reflect the distribution of the targeted surface marker. The intensity of the SERRS-NP signal accurately discriminated high- versus low-expressing surface markers between tumors, and between different areas within tumors.Conclusion: Biopsies can be highly invasive procedures and provide a limited sample of molecular expression within a tumor. Our nanoparticle-based Raman imaging approach offers the potential to provide non-invasive and more comprehensive molecular imaging and an alternative to the current clinical gold standard of immunohistochemistry.

Asymmetric, mixed-valence molecules for spectroscopic readout of quantum-dot cellular automata

Mixed-valence compounds may provide molecular devices for an energy-efficient, low-power, general-purpose computing paradigm known as quantum-dot cellular automata (QCA). Multiple redox centers on mixed-valence molecules provide a system of coupled quantum dots. The configuration of mobile charge on a double-quantum-dot (DQD) molecule encodes a bit of classical information robust at room temperature. When arranged in non-homogeneous patterns (circuits) on a substrate, local Coulomb coupling between molecules enables information processing. While single-electron transistors and single-electron boxes could provide low-temperature solutions for reading the state of a ∼1 nm scale molecule, we propose a room-temperature read-out scheme. Here, DQD molecules are designed with slightly dissimilar quantum dots. Ab initio calculations show that the binary device states of an asymmetric molecule have distinct Raman spectra. Additionally, the dots are similar enough that mobile charge is not trapped on either dot, allowing device switching driven by the charge configuration of a neighbor molecule. A technique such as tip-enhanced Raman spectroscopy could be used to detect the state of a circuit comprised of several QCA molecules.

Ferrous hydroxychlorides hibbingite [γ-Fe2(OH)3Cl] and parahibbingite [β-Fe2(OH)3Cl] as a concealed sink of Cl and H2O in ultrabasic and granitic systems

Abstract Ferrous hydroxychlorides are geochemically important but less recognized mineral species due to their extreme sensitivity to oxidation and hydration in contact with air {typically they convert to akaganéite [Fe3+(O,OH,Cl)]}. Only the γ-form was previously known as the orthorhombic mineral hibbingite, associated with altered mafic intrusive rocks. In this study, we describe the β-polymorph of Fe2(OH)3Cl as a new mineral parahibbingite that was found in pyroxenite from the Karee platinum mine in the Bushveld Complex, South Africa. The two minerals were distinguished by a combination of Raman spectroscopy and FIB-SEM-TEM analytical techniques (TEM-EDX and TEM-SAED). They can be easily recognized by their distinct Raman spectra. Parahibbingite has two very strong vibration bands at ~3550 and 3560 cm–1, accompanied by much weaker bands at ~124 and 160 cm−1, while the Raman spectrum of hibbingite has a sharp, strong band at 3450 cm−1 and two moderate bands at 199 and 385 cm−1. Parahibbingite was found as fine-grained reaction rims at the contact of orthopyroxene phenocrysts and talc inside a drill core. It has a trigonal space group [R3m, a = 6.94(5) Å; c = 14.5(2) Å], with an empirical formula (Fe1.982+Mn0.012+Ca0.01)(OH)3.08Cl0.92. The origin of this mineral in the Bushveld Complex is most likely related to a late hydrothermal alteration of pyroxenite. Hibbingite forms as an abundant daughter mineral hosted by fluid inclusions and salt melt inclusions in hydrothermal quartz associated with granitic systems during cooling under reducing conditions. Such inclusions are common in Au-porphyry mineralization worldwide, such as the Biely Vrch (Slovakia) deposit studied in detail in this work. The lattice parameters obtained by TEM-SAED are a = 6.30 Å, b = 7.12 Å, and c = 9.89 Å. Hibbingite was recognized as the only phase that carries “water” (as a hydroxyl group) in otherwise water-free, salt melt inclusions. Furthermore, both hibbingite and parahibbingite should be considered as reservoirs for Cl and H2O in large volumes of altered basic and ultrabasic rocks. They can transport volatiles to shallow levels of subduction zones. Alternatively, their dissolution can fuel remobilization, transport, and deposition of sulfidic ores in saline fluids. Their detection, however, is difficult because of their sensitivity to oxidizing atmospheres. For example, in natural outcrops exposed to air, they may vanish, thus distorting estimates of their abundance and role in many processes that involve mineral-derived volatiles.

Confocal Raman spectroscopic study of melt inclusions in olivine of mantle xenoliths from the Bultfontein kimberlite pipe (Kimberley cluster, South Africa): Evidence for alkali‐rich carbonate melt in the mantle beneath Kaapvaal Craton

AbstractIdentifying the composition of primary/primitive mantle melts is crucial for understanding the mantle's evolution and mantle‐derived magmatism. Melt inclusions in mantle xenoliths provide key information about such melts. This study used confocal Raman spectroscopy to characterize mineral assemblage of unexposed crystallized secondary melt inclusions in the olivine from the xenoliths of the sheared garnet peridotites from the Bultfontein kimberlite pipe (Kimberley cluster, Kaapvaal Craton, South Africa). The studied peridotites originated from 112‐ to 146‐km mantle depths. In total, 16 minerals were identified among daughter crysatls, which include carbonates (calcite, magnesite, dolomite), alkali carbonates (eitelite, nyerereite, gregoryite/natrite, K–Na–Ca–carbonate (K,Na)2Ca(CO3)2 (K analogue of nyerereite), alkali carbonates with additional anions (northupite, bradleyite, burkeite), alkali sulfates (glauberite, thenardite, aphthitalite), apatite, tetraferriphlogopite, and magnetite. Several more daughter minerals gave distinct Raman spectra, but they were not determined due to the lack of similar spectra in the databases. Carbonates are predominant among the daughter minerals in the melt inclusions. Many daughter minerals are rich in alkalis. These facts indicate that melt(s), parental for the inclusions, is alkali‐rich carbonate in composition. Two possible models were suggested for the origin of these melt inclusions: (1) in situ fracturing of olivine and the mantle melt infiltration shortly before the sheared peridotites were entrained by the ascending kimberlitic magma; (2) infiltration of the transporting kimberlite melt into xenoliths during ascent. Both models imply that the alkali‐rich carbonate melt(s) that interacted with peridotites originated at a greater depth than the entrapment level of studied xenoliths (&gt;150 km), that is, at the base of the lithosphere or in the asthenosphere. This melt is genetically related to the kimberlite magmatism that formed the Bultfontein pipe and points at the alkali‐rich carbonate composition of primary kimberlite melt.

Optical analysis of homocysteine metabolites using vibrational spectroscopy

Homocysteine (HCy) is a sulphur-containing amino acid that correlates with several maladaptive health conditions, including an enhanced risk of cardiovascular and neurodegenerative diseases. Detection of HCy and its potentially pathogenic metabolites are studied here for the first time, to the first of our knowledge, using Raman spectroscopy. This study shows that different HCy metabolites have distinct Raman spectra and that the limits of detection reach the sub-mM level for these compounds. This investigation paves the way for photonics–based approaches for detection of HCy–related fluids as predictive biomarkers of disease in blood, which would assist in early intervention for improved clinical outcomes.

Multiplex fatty acid imaging inside cells by Raman microscopy.

Visualizing intracellular fatty acids (including free and esterified form) is very useful for understanding how and where such molecules are incorporated, stored, and metabolized within cells. However, techniques of imaging multiple intracellular fatty acids have been limited by their small size, making it difficult to label and track without changing their biological and biophysical characteristics. Here, we present a new method for simultaneously visualizing up to five atomically labeled intracellular fatty acid species. For this, we utilized the distinctive Raman spectra depending on the labeling patterns and created a new, extensible opensource software to perform by-pixel analysis of extracting original spectra from mixed ones. Our multiplex imaging method revealed that fatty acids with more double bonds tend to concentrate more efficiently at lipid droplets. This novel approach contributes to reveal not only the spatial dynamics of fatty acids, but also of any other metabolites inside cells.

Raman spectroscopic identification of cookeite in the crystal-rich inclusions in spodumene from the Jiajika lithium pegmatite deposit, China, and its geological implications

Abstract. Cookeite usually occurs as a late alteration product in lithium–cesium–tantalum-type granitic pegmatite. Consequently, cookeite-bearing crystal-rich inclusions (CIs) in pegmatite are considered to be of secondary origin, which constrains our understanding of pegmatite formation. Thus far, no reported cookeite has produced a distinct Raman spectrum. However, the CIs hosted in spodumene in the Jiajika pegmatite deposit, China, contain a cookeite-like hydrous lithium–aluminum–silicate phase, yielding a distinct Raman spectrum. In electron microprobe analysis, focused ion beam scanning electron microscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS), the average composition of this hydrous phase was determined as Li1.005(Al3.997Fe0.018)(Si3.086Al0.914)O10.076OH7.902F0.098, close to the International Mineralogical Association (IMA) formula of cookeite, (Al, Li)3Al2(Si, Al)4O10(OH)8. The distinct Raman peaks at 98, 167, 219, 266, 342, 382, 457, 592, 710, and 3640 cm−1 were consistent with those of natural cookeite recrystallized in a hydrothermal diamond-anvil cell. The peaks were ascribed to the crystallization of cookeite from the liquid trapped in the closed space during the spodumene crystallization, which occurred at relatively high temperature and pressure without incorporating the minor elements commonly present during alteration processes. These minor elements often obscure the Raman signals, primarily by fluorescence effects. This type of cookeite in CIs with distinct Raman signals is unusual and can indicate whether the cookeite crystallized from fluid trapped within the closed space of a primary inclusion. In such a case, the fluid can be considered a flux-rich hydrous melt in pegmatite formation models.

High accuracy detection of malignant pleural effusion based on label-free surface-enhanced Raman spectroscopy and multivariate statistical analysis.

The present study aims to diagnose malignant pleural effusion (MPE) based on the identification of distinctive Raman spectra bands. The tests on 83 pleural effusion (PE) samples including 32 benign PE (BPE) and 51 MPE were performed based on rapid and label-free surface-enhanced Raman spectroscopy (SERS). The TiO2 photo-catalyzed Ag NPs were used as SERS substrate. And the SERS spectra of BPE and MPE were compared and diagnosed through orthogonal partial least squares discriminant analysis (OPLS-DA). The diagnosis results showed that the sensitivity and specificity can reach 92.2% and 93.8%, respectively, based on leave-one-out cross validation. And the area under curve values of MPE was 0.985. This study demonstrated an accurate way of combining Raman spectra of PE with OPLS-DA to identify MPE and BPE.

Solubility Measurement Study on a Metastable Polymorph of β-2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane by Raman Spectroscopy

Raman spectroscopy was used to measure the solubility of the metastable form of β-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (β-HNIW) in organic binary solvent mixtures. The distinct Raman spectra peaks of the solid, solute, solution, and solvent were investigated. Peaks that were not overlapping each other were used to develop a calibration curve. Then, linear relationships between solution concentration and Raman intensity were used to measure the solubility of β-HNIW in binary solvent mixtures during the dissolving process. The solubility of β-HNIW in binary solvent mixtures (ethyl acetate + n-hetpane, ethyl acetate + 1,1,2-trichloroethane, ethyl acetate + cyclohexane, ethyl acetate + toluene, ethyl acetate + diethyl ether, and ethyl acetate + petroleum ether) was investigated. The temperature ranged from 283.15 K to 333.15 K at atmospheric pressure. The solubility of β-HNIW in binary solvent mixtures decreases with increasing temperature. In order to correlate the solubility of β-HNIW,...

Raman spectroscopic vibrational analysis of the complex iron sulfates clairite, metavoltine, and voltaite from the burning coal dump Anna I, Alsdorf, Germany

AbstractVibrational spectroscopy has been used to characterize the three uncommon complex iron sulfates clairite, (NH4)2Fe3(SO4)4(OH)3 3H2O, metavoltine, Na6K2Fe2+Fe3+6(SO4)12O2·18H2O, and voltaite, K2Fe2+5Fe3+3Al(SO4)12 18H2O. The investigated specimens were formed at the burning coal dump Anna I (Alsdorf, Germany) due to alteration processes connected with the subsurface thermal activity. It is found that all three minerals display complex Raman spectra with an extensive proliferation of bands attributed to the sulfate vibrational modes. Both clairite and metavoltine show extraordinary strong Raman bands in the low‐wavenumber region, which can be attributed to the FeO stretching modes. Clairite and metavoltine show a very similar spectral shape; it can be concluded that both minerals can exhibit a similar crystal structure. In comparison, voltaite represents a different structural type; therefore, a distinct Raman spectrum is observed.

Stacking-dependent interlayer phonons in 3R and 2H MoS2

We have investigated the interlayer shear and breathing phonon modes in MoS2 with pure 3R and 2H stacking order by using polarization-dependent ultralow-frequency Raman spectroscopy. We observe up to three shear branches and four breathing branches in MoS2 with thickness from 2 to 13 layers. The breathing modes show the same Raman activity behavior for both polytypes, but the 2H breathing frequencies are consistently several wavenumbers higher than the 3R breathing frequencies, signifying that 2H MoS2 has slightly stronger interlayer lattice coupling than 3R MoS2. In contrast, the shear-mode Raman spectra are strikingly different for 2H and 3R MoS2. While the strongest shear mode corresponds to the highest-frequency branch in the 2H structure, it corresponds to the lowest-frequency branch in the 3R structure. Such distinct and complementary Raman spectra of the 3R and 2H polytypes allow us to survey a broad range of shear modes in MoS2, from the highest to lowest branch. By combining the linear chain model, group theory, effective bond polarizability model and first-principles calculations, we can account for all the major observations in our experiment.

Non-invasive In Vivo Imaging of Cancer Using Surface-Enhanced Spatially Offset Raman Spectroscopy (SESORS).

Rationale: The goal of imaging tumors at depth with high sensitivity and specificity represents a significant challenge in the field of biomedical optical imaging. 'Surface enhanced Raman scattering' (SERS) nanoparticles (NPs) have been employed as image contrast agents and can be used to specifically target cells in vivo. By tracking their unique “fingerprint” spectra, it becomes possible to determine their precise location. However, while the detection of SERS NPs is very sensitive and specific, conventional Raman spectroscopy imaging devices are limited in their inability to probe through tissue depths of more than a few millimetres, due to scattering and absorption of photons by biological tissues. Here, we combine the use of "Spatially Offset Raman spectroscopy" (SORS) with that of "surface-enhanced resonance Raman spectroscopy" (SERRS) in a technique known as "surface enhanced spatially offset resonance Raman spectroscopy" (SESO(R)RS) to image deep-seated glioblastoma multiforme (GBM) tumors in vivo in mice through the intact skull.Methods: A SORS imaging system was built in-house. Proof of concept SORS imaging was achieved using a PTFE-skull-tissue phantom. Imaging of GBMs in the RCAS-PDGF/N-tva transgenic mouse model was achieved through the use of gold nanostars functionalized with a resonant Raman reporter to create SERRS nanostars. These were then encapsulated in a thin silica shell and functionalized with a cyclic-RGDyK peptide to yield integrin-targeting SERRS nanostars. Non-invasive in vivo SORS image acquisition of the integrin-targeted nanostars was then performed in living mice under general anesthesia. Conventional non-SORS imaging was used as a direct comparison.Results: Using a low power density laser, GBMs were imaged via SESORRS in mice (n = 5) and confirmed using MRI and histopathology. The results demonstrate that via utilization of the SORS approach, it is possible to acquire clear and distinct Raman spectra from deep-seated GBMs in mice in vivo through the skull. SESORRS images generated using classical least squares outlined the tumors with high precision as confirmed via MRI and histology. Unlike SESORRS, conventional Raman imaging of the same areas did not provide a clear delineation of the tumor.Conclusion: To the best of our knowledge this is the first report of in vivo SESO(R)RS imaging. In a relevant brain tumor mouse model we demonstrate that this technique can overcome the limitations of conventional Raman imaging with regards to penetration depth. This work therefore represents a significant step forward in the potential clinical translation of SERRS nanoparticles for high precision cancer imaging.

Quantifying alkyl chain disorder in crystalline models of lipid bilayers using Raman spectroscopy

AbstractCrystalline bis‐N‐alkyl‐chlorotriazines 2–6 can be considered multilayers of lipid bilayers comprising a rigid hydrogen‐bonded tape in the polar layer separated by a lipid region of small to medium‐length alkyl chains. The persistent ordering of these tapes acts as a scaffold in the solid state enabling measurement of temperature‐induced conformational changes in the “lipid phase” using X‐ray crystallography. The alkyl chains in these structures are loosely packed but generally ordered at low temperature, undergoing a slow transition to a disordered structure clearly observed in the Raman spectrum. The longer‐chain derivatives 4–6 show a distinct Raman spectrum for the ordered and disordered crystallographic phases enabling a least squares fitting at each temperature point. Calibration of the Raman fit values for 5 and 6 using powder X‐ray diffraction allows a quantification of each phase and highlights the unique response of each derivative with temperature. This approach for quantifying the onset of disorder and structural phase transitions should be relevant to a wide range of lipid‐based systems.

Epitaxial growth and electrical properties of VO2 on [LaAlO3]0.3[Sr2AlTaO6]0.7 (111) substrate

The authors report the epitaxial growth and the electrical properties, especially the metal-to-insulator transition, of vanadium dioxide (VO2) thin films synthesized on [LaAlO3]0.3[Sr2AlTaO6]0.7 (LSAT) (111) (LSAT) substrates by pulsed laser deposition. X-ray diffraction studies show that the epitaxial relationship between the VO2 thin films and LSAT substrate is given as VO2(020)||LSAT(111) and VO2[001]||LSAT[112¯]. The authors observed a sharp 4 orders of magnitude change in the longitudinal resistance for the VO2 thin films around the transition temperature. The authors also measured distinct Raman spectra below and above the transition point indicating a concomitant structural transition between the insulator and metallic phases, in agreement with past investigations.

Raman spectroscopic study of six synthetic anhydrous sulfates relevant to the mineralogy of fumaroles

AbstractFumaroles, vents that emit hot gases and vapor, are an accompanying phenomenon of volcanic activity. Such phenomena are also observed within the framework of self‐ignited burning coal seams and coal heap fires, if less commonly. The high temperatures and chemical reactions between the gas and solid phases are responsible for extensive alteration of surrounding rocks, resulting in mineral encrustations of unusual compositions. Rare anhydrous sulfates (millosevichite, mikasaite, efremovite, godovikovite, sabieite, and steklite) are signature minerals of fumarole encrustations. Comprehensive Raman data for these anhydrous phases are required for the successful identification of natural samples by Raman spectroscopy. Six synthetic equivalents of the natural anhydrous sulfates were prepared by heating of the hydrated analogues and were investigated using both a bench‐top Raman microspectrometer and a portable Raman spectrometer. This comparative approach can help further steps for the successful deployments of miniature Raman tools in situ under field conditions. The studied anhydrous sulfates displayed distinctive Raman spectra of their crystalline phases. Compared with their fully hydrated counterparts, a shifting of bands of the ν1 symmetric stretching mode was observed in the Raman spectra of all samples. Isostructural millosevichite and mikasaite have very distinctive Raman spectra; however, structurally related godovikovite, sabieite, and steklite show very similar spectral shapes. For ammonium‐bearing phases (efremovite, godovikovite, sabieite), the Raman signatures of the NH4 group were observable at &gt;2,800 cm−1 and in the 1,400–1,800 cm−1 region. Our measurements show that the performance of a light‐weight portable Raman spectrometer with near infrared excitation was sufficient for the unambiguous discrimination of the investigated sulfates.

In-situ studies on the micro-structure evolution of A2W2O7 (A = Li, Na, K) during melting by high temperature Raman spectroscopy and density functional theory

In-situ high temperature Raman spectroscopic (HTRS) technique in combination with density functional theory (DFT) analysis has been adopted to investigate the micro-structure of solid and molten A2W2O7 (A=Li, Na, K). The [WO6] octahedra were found to be connected to each other by corner and edge sharing in the crystalline Li2W2O7 and K2W2O7 compounds. In the crystal lattice of Na2W2O7, on the other hand, the [WO4] tetrahedra and [WO6] octahedra were found to coexist and paired by corner sharing. Although the structural diversity has clearly led to distinct Raman spectra of the crystalline A2W2O7 compounds, the spectra of their melts tended to be analogous, showing the typical vibration modes of (W2O7)2− dimer. A mechanism was then proposed to explain the structure evolution occurring during the melting process of A2W2O7. The effect of A+ cation on the Raman bands of (W2O7)2− dimer in molten A2W2O7 has also been investigated. Both the wavenumber and full width at half-height (FWHH) of the characteristic band assigned to the symmetrical stretching vibration mode of WOnb (non-bridging oxygen) in (W2O7)2− were found to decrease in the sequence of Li+, Na+ and K+, indicating the cation effect on the mean bond length and its distribution range of WOnb. In addition, the relative intensity of this band was also influenced by the cation and it was increased in the order of Li2W2O7, Na2W2O7 and K2W2O7, which has been explained by the charge transfer process and confirmed by Mulliken overlap population analysis.

Physicochemical and surface properties of acrylic intraocular lenses and their clinical significance

To analyze and compare several commercially available acrylic intraocular lenses (IOLs) with particular regard to their clinical significance, we examined the physicochemical and surface properties of four currently available acrylic IOLs using static water contact angle, atomic force microscopy (AFM), Raman spectroscopy, and differential scanning calorimetry (DSC) measurements. The hydrophobic acrylic IOLs, ZA9003, and MA60BM, had contact angles ranging from 77.9° ± 0.65° to 84.4° ± 0.09°. The contact angles in the hydrophilic acrylic (970C) and heparin-surface-modified (HSM) hydrophilic acrylic IOLs (BioVue) were 61.8° ± 0.45° and 69.7° ± 0.76°, respectively. The roughness of the IOL optic surface differed depending on the type of IOL (p < 0.001). The surface roughness of BioVue had the lowest value: 5.87 ± 1.26 nm. This suggests that the BioVue IOL may lead to reduced cellular adhesion compared to the unmodified IOLs. All IOLs including those composed of acrylic optic materials from different manufacturers showed distinct Raman spectra peaks. The glass transition temperatures (Tg) for the hydrophobic acrylic IOLs were between 12.5 and 13.8 °C. These results suggest that the intraoperative and postoperative behavior of an IOL can be predicted. This information is also expected to contribute greatly to the industrial production of reliable biocompatible IOLs.