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In situ Raman spectroscopic evidence for oxygen reduction reaction intermediates at platinum single-crystal surfaces
摘要： Developing an understanding of structure–activity relationships and reaction mechanisms of catalytic processes is critical to the successful design of highly efficient catalysts. As a fundamental reaction in fuel cells, elucidation of the oxygen reduction reaction (ORR) mechanism at Pt(hkl) surfaces has remained a significant challenge for researchers. Here, we employ in situ electrochemical surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) calculation techniques to examine the ORR process at Pt(hkl) surfaces. Direct spectroscopic evidence for ORR intermediates indicates that, under acidic conditions, the pathway of ORR at Pt(111) occurs through the formation of HO2*, whereas at Pt(110) and Pt(100) it occurs via the generation of OH*. However, we propose that the pathway of the ORR under alkaline conditions at Pt(hkl) surfaces mainly occurs through the formation of O2?. Notably, these results demonstrate that the SERS technique offers an effective and reliable way for real-time investigation of catalytic processes at atomically flat surfaces not normally amenable to study with Raman spectroscopy.
关键词： density functional theory,in situ Raman spectroscopy,electrochemical surface-enhanced Raman spectroscopy,oxygen reduction reaction,platinum single-crystal surfaces
更新于2025-09-10 09:29:36
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Bulk and surface characterisation of micrometer-thick cobalt ferrite films grown by IR PLD
摘要： We have studied micrometer-thick cobalt ferrite films deposited on Si (100) single crystal substrates by nanosecond pulsed laser deposition at 1064 nm.The thickness of the deposited films (1.3 μm) was monitored by AFM. The chemical and structural characterisation of the films was carried out by Raman spectroscopy and transmission M?ssbauer spectroscopy at 300 and 26 K. For comparison purposes, transmission M?ssbauer data at these two temperatures were also recorded from a commercial cobalt ferrite powder and the home-made target used to grow the films. The surface characterisation was performed by X-Ray Photoelectron Spectroscopy (XPS) and Integral Low Energy Electron Spectroscopy (ILEEMS). XPS showed Co and Fe to be present as Co2+ and Fe3+, as expected for cobalt ferrite. The Raman spectra showed the lines characteristic of cobalt ferrite. The M?ssbauer spectra, both in the transmission and backscattering modes, were fitted to two sextets whose hyperfine parameters are in good agreement with those expected from Fe3+ cations occupying the tetrahedral and octahedral sites in the spinel-related structure. No significant differences were observed in the relative areas of the two sextets in the transmission and ILEEMS spectra, suggesting that the cation distribution at the surface and the bulk are not too different. However, the relative areas of the two components changed drastically with temperature both in the spectra of the films as in those recorded from the cobalt ferrite standards. We discuss the possible origin of the evolution with temperature of those relative areas.
关键词： X-ray photoelectron spectroscopy,Raman spectroscopy,Cobalt ferrite,M?ssbauer spectroscopy,Pulsed laser deposition
更新于2025-09-10 09:29:36
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Effect of hydrogen concentration on graphene synthesis using microwave-driven plasma-mediated methane cracking
摘要： Gas phase graphene forms as an aerosol in a microwave plasma among other carbon forms. Consisting of 2-6 sheets per stack with dimensions between 100 – 500 nm, it is referred to as nanographene (NG). Surprisingly, increasing H/C ratio in the feedstock increases the relative graphitic content of the product. Dependence of the different carbon forms upon H/C ratio of the gas feed mixture is shown across multiple analytical characterizations. Attributes of (a) phase quality (pristine nature of NG) and (b) phase quantity (how much NG forms relative to other carbon sp2 phases) are addressed. Phase identification of the forms is performed via transmission electron microscopy with quantification by thermogravimetric analysis, assessing their respective oxidative reactivity benchmarked to commercially available similar carbon products applied as standards. X-ray diffraction differentiates these forms based on varied extent of graphitic structure. Electron energy loss spectroscopy assesses graphitic content by the ratio of sp2/sp3 bonding. Raman spectroscopy supports the observed shift in relative proportions of the carbon forms towards preferential graphitic content with increasing H/C. Selected area diffraction illustrates this for NG. Fringe analyses of nanostructure quantifies this shift for carbon particles. Infra-red spectroscopy reveals complementary C-H bonding as a measure of graphitic quality.
关键词： electron energy loss spectroscopy,thermogravimetric analysis,hydrogen concentration,methane cracking,graphene synthesis,X-ray diffraction,nanographene,microwave-driven plasma,Raman spectroscopy,infra-red spectroscopy
更新于2025-09-10 09:29:36
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Reference Module in Materials Science and Materials Engineering || Tip-Enhanced Raman Microscopy: Instrumentation, Techniques and Applications in Practice
摘要： The idea of optical microscopy is to use a set of lenses to magnify the object to see. Scientists changed the idea of this conventional optical microscopy since the scanning probe microscope (SPM) came out in 1980s. Inouye and Kawata proposed to use a sharp metal probe to create an optical image [1]. They scanned the metal tip on a sample surface while recording the optical near-field signals scattered by the tip [1,2]. The spatial resolution is not determined by the numerical aperture (N.A.) of the objective lens but by the tip radius that is typically a few tens of nanometers. The use of a metal tip provides not only high spatial resolution but also an enhancement of optical signals as a result of excitation of surface plasmons at the sharp metal tip. With the tip-enhancement effect, it becomes possible to detect even a very weak optical signal scattered from an extremely tiny volume. One such process is Raman scattering. The application of tip-enhancement to Raman spectroscopy was reported in the year of 2000 by three independent groups led by Kawata, Zenobi, and Anderson, respectively [3–6]. Using TERS, distribution of molecules [7–11] and electronic [12] and chemical properties within nanoscale materials [13–18] have been successfully visualized through Raman signatures with a nanoscale spatial resolution. There are a number of review articles for TERS microscopy and spectroscopy available in literatures [14,19–22]. During the past 20 years, the development of TERS has been mostly driven by research labs having research-grade apparatus operated by skillful researchers. The situation has been changing in the recent years, some companies have started to sell commercial products of TERS microscopes in the market. However, in order to realize TERS microscope as an analytical tool for the routine use of research and industry, challenges in TERS probes, reproducibility issues remain such as stable implementation of atomic force microscopes (AFMs), and peripheral operational techniques.
关键词： Raman spectroscopy,nanoscale imaging,plasmonic enhancement,Tip-Enhanced Raman Microscopy,TERS
更新于2025-09-10 09:29:36
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Raman scattering of impact diamonds
摘要： We report the results of a study of the polycrystalline powder of the diamond-lonsdaleite from the Popigai crater (Siberia) using UV micro-Raman spectroscopy and high-resolution synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond-lonsdaleite samples with close amounts of diamond and lonsdaleite, we were able to identify the polytypic composition of impact diamonds in contrast to the method of X-ray diffraction. We have managed to get for the first time the spectrum of "pure" lonsdaleite. Its deconvolution has allowed us to identify all the three Raman - active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.
关键词： Raman scattering,polytypic composition,impact diamonds,synchrotron X-ray diffraction,lonsdaleite,UV micro-Raman spectroscopy
更新于2025-09-10 09:29:36
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Effective Raman spectra identification with tree-based methods
摘要： Treatment of spectral information is an essential tool for the examination of various cultural heritage materials. Raman spectroscopy has become an everyday practice for compound identification due to its non-intrusive nature, but often it can be a complex operation. Spectral identification and analysis on artists’ materials is being done with the aid of already existing spectral databases and spectrum matching algorithms. We demonstrate that with a machine learning method called Extremely Randomised Trees, we can learn a model in a supervised learning fashion, able to accurately match an entire-spectrum range into its respective mineral. Our approach was tested and was found to outperform the state-of-the-art methods on the corrected RRUFF dataset, while maintaining low computational complexity and inherently supporting parallelisation.
关键词： Randomised trees,Random forest,Mineral identification,Raman spectroscopy,Machine learning,Classification,Raman spectra identification
更新于2025-09-10 09:29:36
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[ACS Symposium Series] Raman Spectroscopy in the Undergraduate Curriculum Volume 1305 || Research with Undergraduates at the Intersection of Chemistry and Art: Surface-Enhanced Raman Scattering Studies of Oil Paintings
摘要： Undergraduate students are provided increasingly the opportunity to explore Raman spectroscopy as a part of their physical and analytical chemistry courses. Here, we describe a new approach for engaging undergraduate students with Raman spectroscopy in the research lab setting. In particular, Wustholz at William & Mary and Svoboda at Colonial Williamsburg engage in productive collaboration wherein develop surface-enhanced Raman scattering (SERS)-based methods to identify fugitive pigments in art. In this chapter, we present several case studies that highlight the pedagogical journeys of student researchers working at the intersection of chemistry and art. We describe how this collaborative SERS research has led to discovery, innovation, and the professional development of undergraduates.
关键词： surface-enhanced Raman scattering,SERS,chemistry and art,undergraduate research,Raman spectroscopy,fugitive pigments
更新于2025-09-10 09:29:36
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Cross-Section Analysis of the Composition of Sprayed Cu <sub/>2</sub> ZnSnS <sub/>4</sub> Thin Films by XPS, EDS, and Multi-Wavelength Raman Spectroscopy
摘要： A detailed cross-section analysis of the chemical composition of sprayed Cu2ZnSnS4 thin films is presented. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy (with near-IR, visible, and UV-lasers) are used to demonstrate that while CZTS effectively forms within the bulk of the film, there is some degree of element segregation, formation of undesirable secondary phases, and the presence of a disordered kesterite structure across the film. Different penetration depths of the excitation signals correspond to the many different surface sensitive techniques employed in this work. XPS results reveal that the surface of Cu4ZnSnS4 (CZTS) films presents a high concentration of tin and zinc and a low sulfur concentration, while being highly depleted in copper. EDS, XRD, and infrared Raman spectroscopy confirm that the composition of as-sprayed and sulfurized films is close to stoichiometric Cu2ZnSnS4. Resonant UV-Raman spectroscopy helps to identify secondary phases located at the external surface of sprayed and sulfurized CZTS films (mainly ZnS, ZnO), while VIS-Raman spectroscopy helps to identify a disordered kesterite structure close to the surface. Secondary phases need to be chemically etched when aiming at incorporating kesterite films obtained by spray pyrolysis into photovoltaic devices.
关键词： multi-wavelength Raman spectroscopy,X-ray photoelectron spectroscopy,spray pyrolysis,thin films,kesterite
更新于2025-09-10 09:29:36
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Oxidation of Epitaxial Silicene on Ag(111)
摘要： The high chemical reactivity of epitaxial silicene on Ag(111) still remains a debated subject in the literature. In particular results on the oxidation of epitaxial silicene and its related lifetime under ambient conditions are controversially discussed. Here, a detailed investigation of the oxygen exposure to epitaxial silicene layers investigated by means of X-ray photoemission and in situ Raman spectroscopy is reported. The results should clearly cease the discussion on the stability of epitaxial silicene against oxygen as it becomes completely oxidized after an exposure to only 100 L of oxygen. Such a small dose sets strict limits for ex situ studies of epitaxial silicene. Besides the formation of silicon oxide also the silver substrate surface oxidizes, suggesting that the silicene layer can hardly protect it, probably owing to the high number of domain boundaries within the silicene layer.
关键词： epitaxial silicene,2D materials,oxidation,in situ Raman spectroscopy,photoemission spectroscopy
更新于2025-09-10 09:29:36
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Correlated Materials Characterization via Multimodal Chemical and Functional Imaging
摘要： Multimodal chemical imaging simultaneously offers high resolution chemical and physical information with nanoscale, and in select cases atomic resolution. By coupling modalities that collect physical and chemical information, we can address scientific problems in biological systems, battery and fuel cell research, catalysis, pharmaceuticals, photovoltaics, medicine and many others. The combined systems enable local correlation of material properties with chemical makeup, making fundamental questions in how chemistry and structure drive functionality approachable. In this review we present recent progress and offer a perspective for chemical imaging used to characterize a variety of samples by a number of platforms. Specifically, we present cases in infrared and Raman spectroscopies combined with scanning probe microscopy; optical microscopy and mass spectrometry; nonlinear optical microscopy; and finally, ion, electron and probe microscopies with mass spectrometry. We also discuss the challenges associated with the use of data originated by the combinatorial hardware, analysis, and machine learning as well as processing tools necessary for interpretation of multidimensional data acquired from multimodal studies.
关键词： raman spectroscopy,ion microscopy,nonlinear optical microscopy,mass spectrometry,electron microscopy,infrared spectroscopy,chemical imaging,scanning probe microscopy,data analytics,optical microscopy
更新于2025-09-10 09:29:36