Confocal μ-Raman Spectroscopy Research Articles

Million Microfiber Releases: Comparing Washable and Disposable Face Masks.

The extensive use of single-use or disposable face masks has raised environmental concerns related to microfiber contamination. In contrast, research on the potential release and ecological impact of microfibers from washable masks (WMs), suggested as an eco-friendly alternative, is currently lacking. Here, we comprehensively investigated the release of microfibers from disposable and WMs of different types in simulated aquatic environments and real-life scenarios, including shaking, disinfection, hand washing, and machine washing. Using a combination of wide-field fluorescence microscopy, He-ion microscopy, and confocal μ-Raman spectroscopy, we revealed that disposable masks (DMs) released microfibers ranging from 18 to 3042 microfiber/piece, whereas WMs released 6.1 × 104-6.7 × 106 microfibers/piece depending on the simulated conditions above. Another noteworthy finding was the observed negative correlation between microfiber release and the proportion of reinforcement (embossing) on the DM surfaces. Microfibers from tested DMs primarily comprised polypropylene (PP), while WMs predominantly released poly(ethylene terephthalate) (PET) and cellulose microfibers. Furthermore, acute toxicological analyses unveiled that PP microfibers (0.01-50 mg/L) from DMs impacted zebrafish larval swimming behavior, while PET microfibers from WMs delayed early-stage zebrafish hatching. This study offers new insights into the source of microfiber contamination and raises concerns about the environmental implications linked to the use of washable face masks.

Solid-state reaction synthesis of amorphous/nanostructured Si@SiOx-Cu3Si composites by mechanical milling for lithium-ion anodes

In present study we developed an effective way to obtain amorphous/nanocrystalline Si in high-capacity Si-based composites for improving their cycle stability as lithium-ion anodes. Amorphous/nanostructured Si@SiOx-Cu3Si composites were synthesized via solid-state reactions using mechanical milling with bulk Si and CuO as starting materials. The microstructural characterization of Si@SiOx-Cu3Si composites demonstrated the phase transformation during the synthesis process of mechanical milling. The ratio and fine-scale distribution of amorphous Si in Si@SiOx-Cu3Si composites were quantitatively analyzed by confocal μ-Raman spectroscopy. The electrochemical properties indicated that Si@SiOx-Cu3Si composites exhibited enhanced cyclability due to containing a highly disordered amorphous Si. Calculated in a full-cell stack model, the lithium-ion cell using Si@SiOx-Cu3Si anodes could provide higher energy density over commercial graphite.

Nitrate Removal by Donnan Dialysis and Anion-Exchange Membrane Bioreactor Using Upcycled End-of-Life Reverse Osmosis Membranes.

This work explores the application of Reverse Osmosis (RO) upcycled membranes, as Anion Exchange Membranes (AEMs) in Donnan Dialysis (DD) and related processes, such as the Ion Exchange Membrane Bioreactor (IEMB), for the removal of nitrate from contaminated water, to meet drinking water standards. Such upcycled membranes might be manufactured at a lower price than commercial AEMs, while their utilization reinforces the commitment to a circular economy transition. In an effort to gain a better understanding of such AEMs, confocal µ-Raman spectroscopy was employed, to assess the distribution of the ion-exchange sites through the thickness of the prepared membranes, and 2D fluorescence spectroscopy, to evaluate alterations in the membranes caused by fouling and chemical cleaning The best performing membrane reached a 56% average nitrate removal within 24 h in the DD and IEMB systems, with the latter furthermore allowing for simultaneous elimination of the pollutant by biological denitrification, thus avoiding its discharge into the environment. Overall, this work validates the technical feasibility of using RO upcycled AEMs in DD and IEMB processes for nitrate removal. This membrane recycling concept might also find applications for the removal and/or recovery of other target negatively charged species.

Tuning Inactive Phases in Si-Ti-B Ternary Alloy Anodes to Achieve Stable Cycling for High-Energy-Density Lithium-Ion Batteries.

Cycle stability improvement of a high-capacity Si anode is a challenge for its wide application in high-energy-density lithium-ion batteries. Active amorphous/nanosized Si embedded in an inactive matrix is a strategy to improve the cycle stability of Si anodes. Ternary Si100-x-yTixBy (5 ≤ y ≤ x ≤ 20) alloys are designed and prepared by ball milling using elemental Si, Ti, and B as starting materials. The formation sequence of inactive phases during mechanical alloying is predicted by an effective heat-of-formation model and verified by microstructural characterization. The local-fine distribution of free amorphous and nanocrystalline Si in the Si100-x-yTixBy is analyzed by confocal μ-Raman spectroscopy. When used as lithium-ion anodes, the capacity and voltage affected by Si and inactive compounds in the Si100-x-yTixBy are concerned to assess their high energy density. Furthermore, the impact of free active Si, the inactive phase, and amorphous Si on the cyclability of Si100-x-yTixBy is studied. The results show that the Si100-x-yTixBy material is a potential anode for high-energy-density Li-ion batteries and could be used to guide the design of multi-component Si-alloy anodes.

Field-induced transformation of ferroelectric domain states in KTN crystal

We report an interesting study of electric-field-induced transformation from a single domain ferroelectric state to the multiple domain ferroelectric state in a KTa1−xNbxO3 (KTN) crystal. Experimental results obtained using the confocal μ-Raman spectroscopy confirm the dynamic change of lattice structures induced by an external electric field. Furthermore, the dependence of relative permittivity on the applied voltage also indicates the transformation of ferroelectric states involving the processes of splintering, inversion, and re-formation of ferroelectric domains.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

Surface Properties of Laser-Treated Molybdenum Disulfide Nanosheets for Optoelectronic Applications

Transition metal dichalcogenide two-dimensional materials have attracted significant attention due to their unique optical, mechanical, and electronic properties. For example, molybdenum disulfide (MoS2) exhibits a tunable band gap that strongly depends on the numbers of layers, which makes it an attractive material for optoelectronic applications. In addition, recent reports have shown that laser thinning can be used to engineer an MoS2 monolayer with specific shapes and dimensions. Here, we study laser-thinned MoS2 in both ambient and vacuum conditions via confocal μ-Raman spectroscopy, imaging X-ray photoelectron spectroscopy (i-XPS), and atomic force microscopy (AFM). For low laser powers in ambient environments, there is insufficient energy to oxidize MoS2, which leads to etching and redeposition of amorphous MoS2 on the nanosheet as confirmed by AFM. At high powers in ambient, the laser energy and oxygen environment enable both MoS2 nanoparticle formation and nanosheet oxidation as revealed in AFM and i-XPS. At comparable laser power densities in vacuum, MoS2 oxidation is suppressed and the particle density is reduced as compared to ambient. The extent of nanoparticle formation and nanosheet oxidation in each of these regimes is found to be dependent on the number of layers and laser treatment time. Our results can shed some light on the underlying mechanism of which atomically thin MoS2 nanosheets exhibit under high incident laser power for future optoelectronic applications.

New evidence about the use of serpentinite in the Minoan architecture. A μ-Raman based study of the “House of the High Priest” drain in Knossos

Serpentinites have been widely used as a raw material in a huge repertoire of shapes during the Minoan period, for the construction of artifacts both for domestic use as well as for religious purposes. However, the utilization of serpentinites is extremely limited in the Minoan palatial architecture. In all the cases where the use of serpentinite is documented, it has been for the construction of column bases. The aim of this study is the investigation of the material used for the construction of the drain located under the stair leading to the adyton (sanctuary) of the “House of the High Priest” one of the peripheral monuments of the Palace of Knossos.Despite the fact that Sir A. Evans documented the stone drain and described the raw material as stone, no further comments were made regarding the exact type of stone used by the Minoans. Furthermore, the fact that a rather unusual material was used for the construction of a drain instead of a more typical material such as limestone or sandstone, enhances the ill-defined and controversial character of the “House of the High Priest”.The initial mineralogical characterization of the drain material was carried out by means of X-ray powder Diffraction leading to the identification of several minerals and polymorphs. Further examination of the sample in terms of microstructural and chemical analysis of the different inclusions was implemented by means of confocal μ-Raman spectroscopy. Within the concept of this study emphasis is given to the application of this nondestructive and noninvasive technique that can be applied in situ for the analysis and characterization of objects of archaeological significance made out of serpentinite minerals, where often sample acquisition is not possible.The choice of Raman spectroscopy as the main non-destructive analytical tool consists a strategic decision for two main reasons: (a) There are several other architectural elements implemented in the Minoan palatial architecture allegedly made out of serpentinite that macroscopically bear different characteristics and have to be examined, and (b) the majority of the Minoan stone vases corpus is consisted of artifacts made out of serpentinite but in both cases sampling is not possible. Lastly, the correlation of the data acquired from the analysis of the serpentinite outcrops on the island of Crete, with those from the archaeological objects might augment the development of knowledge regarding the cultural networks among the agricultural areas, where the serpentinite sources are located towards the centers of the Minoan civilization.

Characterization and Local Structure Analysis of Carbon Coated SiOx Using Confocal μ-Raman Microscope

High energy-density battery with reasonable cycle life is essential for large scale application. For this purpose, Si has attracted attention as a promising anode material. it has the highest theoretical capacity (Li22Si5, 4200mAh/g) and a low operating voltage compared to that of commercialized graphite anode material (LiC6, 372mAh/g).Unfortunately, in Si-based compounds a large volumetric change up to ~400% drastically decreases the specific capacity during charge/discharge. To address the severe volumetric change, an alternative material, silicon monoxide (SiO x , x~1) has attracted a lot of attention because its unique microstructures can accommodate large volume change while maintaining a reasonable capacity. However, large 1st cycle irreversible capacity and still short cycle life are remained task. Though many researchers have studied reaction mechanism of SiOx to improve efficiency and cycle life, it is still challengeable. It is because SiOx has various structure models and is thermodynamically unstable at all temperatures. The structural complexity in metastable compounds draws various electrochemical properties even in the similar chemical formula. We easily analyzed SiOx structures related with electrochemical properties, utilizing confocal μ-Raman spectroscopy. Two types of SiOx sample, SiOx and carbon(C)-coated SiOx were prepared to understand local microstructure of SiOx and its effects on electrochemical reactions. The bare SiOx showed inhomogeneous distribution of a-Si and c-Si in particles; some particles mainly had a-Si phase but other particles mainly consist of micro-sized Si phase. In contrast, C-coated SiOx is composed of a particle that had uniform microstructure such as nano-sized crystalline Si embedded in small amount of a-Si and a-SiO2 matrix. Even though the two samples had similar composition, quite different electrochemical properties were found out due to different local microstructure in SiOx. The C-coated SiOx achieved higher initial coulombic efficiency (ICE) and capacity retention compared to the bare SiOx. Therefore, the confocal μ-Raman spectroscopy helps to characterize local microstructure of the samples with amorphous and crystalline phases and relate the structures and its electrochemical behaviors.

Characterizing local structure of SiOx using confocal μ-Raman spectroscopy and its effects on electrochemical property

We use confocal μ-Raman spectroscopy to characterize the local microstructure of SiOx particles that are composed of amorphous and crystalline phase and to understand its effects on electrochemical reactions. Particles of bare SiOx (x∼1) consist of an inhomogeneous mixture of a-Si and c-Si; some particles mainly have a-Si phase but others consist mainly of micro-sized crystalline Si phase. In contrast, particles of C-coated SiOx are composed of uniform nano-sized crystalline Si embedded in a-SiO2 matrix with small amounts of a-Si. The two samples had different electrochemical properties due to this difference in microstructure. Initial coulombic efficiency (ICE) and capacity retention were higher in the C-coated SiOx than in the bare SiOx. The findings demonstrate that confocal μ-Raman spectroscopy is very useful tool for characterizing the microstructure of SiOx and the understanding of local microstructures of SiOx is very important for understanding electrochemical reactions.

In situ monitoring of Joule heating effects in germanium nanowires by μ-Raman spectroscopy

We explored a noninvasive optical method to determine the Joule heating of individual germanium nanowires. Using confocal μ-Raman spectroscopy, variations in the optical phonon frequency, in detail the downshifting of the first-order Stokes Raman band, are correlated to the temperature increase of vapor–liquid–solid grown germanium nanowires under an applied electrical bias. The germanium nanowires were found to handle high threshold current densities of more than 106 A cm−2 before sustaining immediate deterioration. Failure of single crystalline germanium nanowires was directly observed when the applied electric field reached the breakdown point of 1.25 × 105 V cm−1.

3 In situ and operando determination of the water content distribution in proton conducting membranes for fuel cells: a critical review

Proton exchange membrane fuel cells have been recognized as a promising zero-emission power source for portable, mobile and stationary applications. The information of water content distribution in the different components of the cell during operation, particularly the proton conducting membrane, is a critical issue for the validation of mass transfer models, the definition of optimized operating conditions and the development of efficient systems with innovative designs for efficient water management. In order to fully understand the way a fuel cell performs, water transport and distribution have to be investigated in situ and operando. In this review, we critically examine the state-of-the-art of operando diagnostics sensitive to the membrane water content, particularly those techniques able (in principle) to give insights into water transport occurring along both the in- and through-plane directions. Particular attention is devoted to experimental results obtained across the membrane thickness i.e. to the determination of water concentration profiles originating from the water activity and electrical gradients occurring through the working fuel cell. Different operando techniques have been developed for this purpose, from the early 1990s up to the last few years: internal resistance measurements, magnetic resonance and neutron imaging, neutron and X-ray scattering, confocal μ-Raman spectroscopy. These techniques can be roughly separated as either direct (i.e. the water amount can be directly derived from the detected signal, avoiding sometimes arbitrary assumptions during data processing) but intrusive (i.e. they require significant modification of the fuel cell, compared to the current design and materials) or indirect but with a significantly lower intrusiveness. It appears that operando measurements of the membrane water distribution allow a unique picture of how the internal part of the fuel cell works, thus certainly contributing to the development of more effective cell designs and materials in the near future. Nevertheless, improvement in the fundamental understanding of the actual fuel cell requires further efforts to increase spatial and, more particularly, temporal resolution of current operando techniques. Also, the comparison of limitations arising from the basic principles of the different operando approaches suggests that ultimate progress will arise from the combination of complementary techniques for simultaneous measurements.

Lift-off of mesoporous layers by electrochemical etching on Si (100) substrates with miscut of 6° off towards (111)

Uniform mesoporous Si double layers are formed on 4 inch p-type < 100> wafers with an off orientation of 6º towards < 111> by means of electrochemical etching in ethanoic-based HF electrolytes. These substrates are of interest for the epitaxial growth of III–V compound semiconductor stacks on their top for the production of multi-junction solar cells and very thin electronic devices. We demonstrate transfer of porous layers after an annealing process in hydrogen atmosphere. Electron Back-Scatter Diffraction analysis confirms that the substrate orientation is conserved during the etching and annealing steps. Confocal μ-Raman spectroscopy analysis shows a decrease in the Raman signal intensity after etching and a subsequent increase after annealing while no shift is observed. By means of Atomic Force Microscopy, analysis the surface appearance after the etching and annealing steps can be visualized. The mean surface roughness varies during the process from 0.55 nm for the unprocessed wafers to 0.27 nm after etching and 0.78 nm after annealing. The decrease of average roughness after etching is caused by an electropolishing step prior to porous formation. Despite of slight increase of mean surface roughness after annealing the samples are still appropriate for high quality epitaxial growth and subsequent lift-off.

μ-XRF/μ-RS vs. SR μ-XRD for pigment identification in illuminated manuscripts

For the non-destructive identification of pigments and colorants in works of art, in archaeological and in forensic materials, a wide range of analytical techniques can be used. Bearing in mind that every method holds particular limitations, two complementary spectroscopic techniques, namely confocal μ-Raman spectroscopy (μ-RS) and μ-X-ray fluorescence spectroscopy (μ-XRF), were joined in one instrument. The combined μ-XRF and μ-RS device, called PRAXIS unites both complementary techniques in one mobile setup, which allows μ- and in situ analysis. μ-XRF allows one to collect elemental and spatially-resolved information in a non-destructive way on major and minor constituents of a variety of materials. However, the main disadvantages of μ-XRF are the penetration depth of the X-rays and the fact that only elements and not specific molecular combinations of elements can be detected. As a result μ-XRF is often not specific enough to identify the pigments within complex mixtures. Confocal Raman microscopy (μ-RS) can offer a surplus as molecular information can be obtained from single pigment grains. However, in some cases the presence of a strong fluorescence background limits the applicability. In this paper, the concrete analytical possibilities of the combined PRAXIS device are evaluated by comparing the results on an illuminated sheet of parchment with the analytical information supplied by synchrotron radiation μ-X-ray diffraction (SR μ-XRD), a highly specific technique.

Cross-polarization imaging and micro-raman detection of defects in the epitaxy of 4H-SiC

Cross-polarized imaging with an optical scanner and confocal μ-Raman spectroscopy have been used to reveal and to study structural defects in n-4H-SiC. We introduce a new method of polarized imaging that uses a combination of linear and circular polarization, which enhances contrast in images of defect regions. Regions that show intensity contrast have been observed to have characteristics of either low-angle grain boundaries or sharp lines of delineation between low and high strain areas. Different types of polytype inclusions have also been observed, and the material within the inclusions has been shown to be either 3C-SiC or 6H-SiC. Polytype inclusions occur as isolated features or form cores of holes, and they can form at any point of the growth.