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Polarons, bipolarons, and absorption spectroscopy of PEDOT
摘要： Electronic structure and optical absorption spectra of poly(3,4-ethylenedioxythiophene) (PEDOT) for different oxidation levels were studied using density functional theory (DFT) and time-dependent DFT. It is shown that the DFT-based predictions for the polaronic and bipolaronic states and the nature of corresponding optical transitions are qualitatively different from the widely used traditional picture based on semi-empirical pre-DFT approaches that still dominate the current literature. Based on the results of our calculations, the experimental Vis/NIR absorbance spectroscopy and the electron paramagnetic resonance spectroscopy are re-examined and a new interpretation of the measured spectra and the spin signal which is qualitatively different from the traditional interpretation is provided. The findings and conclusions concerning the nature of polaronic and bipolaronic states, band structure and absorption spectra presented for PEDOT, are generic for a wide class of conducting polymers (such as polythiophenes and their derivatives) that have similar structure of monomer units.
关键词： Vis/NIR absorbance spectroscopy,PEDOT,conducting polymers,Polarons,electron paramagnetic resonance spectroscopy,bipolarons
更新于2025-09-04 15:30:14
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Deposition of Amorphous Carbon Thin Films by RF Magnetron Sputtering using Woodceramics as Target
摘要： Woodceramics, a substance based on woody materials carbonized at elevated temperatures after impregnating with phenolic resin, have been developed as a new kind of porous carbonaceous material. To expand the industrial application, we attempted to produce amorphous carbon films were RF magnetron sputtering using woodceramics as its target. As a result, typical amorphous carbon films were successfully produced using woodceramics, and the films were characterized by X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. The films produced were composed of carbon turbostratic structure or amorphous whose electron configurations consisted of sp2 and sp3. The ratio of sp3 bonding in the films were about 53% just after the sputtering, but the number increased to about 82% after etching the material using argon ions. Fundamental mechanical properties such as hardness and friction coefficient were also measured and taken into account.
关键词： magnetron sputtering,Raman spectroscopy,X-ray photoelectron spectroscopy,amorphous carbon film,woodceramics
更新于2025-09-04 15:30:14
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Raman and Surface-Enhanced Raman Scattering for Biofilm Characterization
摘要： Bio?lms are a communal way of living for microorganisms in which microorganism cells are surrounded by extracellular polymeric substances (EPS). Most microorganisms can live in bio?lm form. Since microorganisms are everywhere, understanding bio?lm structure and composition is crucial for making the world a better place to live, not only for humans but also for other living creatures. Raman spectroscopy is a nondestructive technique and provides ?ngerprint information about an analyte of interest. Surface-enhanced Raman spectroscopy is a form of this technique and provides enhanced scattering of the analyte that is in close vicinity of a nanostructured noble metal surface such as silver or gold. In this review, the applications of both techniques and their combination with other bio?lm analysis techniques for characterization of composition and structure of bio?lms are discussed.
关键词： Raman spectroscopy,surface-enhanced Raman spectroscopy,biofilm,nanoparticles,bacteria
更新于2025-09-04 15:30:14
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Effect of Annealing on the Surface Morphology, Optical and and Structural Properties of Nanodimensional Tungsten Oxide Prepared by Coprecipitation Technique
摘要： Tungsten oxide (WO3) nanoparticles with monoclinic structure have been synthesized by using an inexpensive coprecipitation process. The obtained nanoparticles were annealed at 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C for 1 h under the same physical conditions. The morphology, structure, and optical properties of the synthesized nanoparticles were studied by x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–Vis) spectrophotometry, and Raman spectroscopy. The XRD results confirmed that the synthesized nanomaterial was crystalline in nature with monoclinic phase. The crystallite size varied from 14 nm to 87 nm when changing the annealing temperature. Williamson–Hall analysis was used to investigate the change in lattice strain and crystallite size. The optical performance was investigated by using UV–visible spectroscopy. The bandgap of the prepared nanomaterials varied from 2.51 eV to 3.77 eV with the annealing temperature, due to the variation of the effect of oxygen vacancies on the electronic band structure. SEM revealed formation of uniform and irregular-sized nanoparticles. HRTEM analysis revealed that the nanoparticles grew along the [002] plane with d-spacing of 0.39 nm for the material annealed at 500°C and along the [200] plane with spacing of 0.36 nm when annealed at 800°C. The crystalline nature of the synthesized nanomaterial was confirmed by uniform and clear fringes obtained in TEM micrographs. The correlation between the peak position and width of the key band at 806 cm?1 in Raman spectroscopy band is discussed. These enhancements in the properties of WO3 nanomaterial make it an efficient material for many potential applications, e.g., in photocatalysis, electro- and photochromic devices, etc.
关键词： HRTEM,XRD,SEM,UV–Vis spectroscopy,Raman spectroscopy
更新于2025-09-04 15:30:14
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Direct Observation of Ion Pairing in Aqueous Nitric Acid Using 2D Infrared Spectroscopy
摘要： Ion-ion interactions and ion pairing play an important role in the properties of concentrated electrolyte solutions, yet remain difficult to study due to the heterogeneous and highly dynamic behavior of these systems. In concentrated acid solutions these questions take on a further level of complexity, because the structure of the aqueous proton itself is uncertain, and may be influenced by the counterion. Here, we address these questions by studying the IR spectra of nitric acid as a function of concentration in H2O, and comparing these to the spectra of several alkali nitrate salts. We show how the close proximity between cations and NO3– ions in solution at high concentration affect the IR spectra, and therefore the molecular structures. Using 2D IR spectroscopy, we demonstrate the formation of contracted ion pair configurations in nitric acid solutions between NO3– ions and H+(aq) via the observation of a distinct anisotropic intermolecular crosspeak between these species. By studying the concentration dependence of this spectral feature, we show that this ion-paired configuration exists in solution at concentrations as low as 2M, and suggests that the structure of H+(aq) solvation complex in these ion pairs differs from the structure in bulk solution.
关键词： 2D IR spectroscopy,Proton hydration,Aqueous nitric acid,Ion pairing,Vibrational spectroscopy
更新于2025-09-04 15:30:14
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Mineralogy and spectroscopy (VIS near infrared and micro-Raman) of chromite from Nidar ophiolite complex, SE Ladakh, India: Implications for future planetary exploration
摘要： To determine the chemical composition of minerals on planetary surfaces from spectroscopic data, it is required to establish the link between mineralogy, spectroscopy and chemical composition of rock forming minerals on Earth. To meet this requirement, we performed integrated mineralogical and spectroscopic (Visible-Near Infrared and micro Raman) characterisation of chromite from the chromitite layer in the mantle section of the Nidar ophiolite complex, SE Ladakh, J&K, India. Chromite commonly occurs as monominerallic chromitite layers (up to 1 meter wide) and disseminated grains within the dunites and harzburgites. The Cr2O3 content is generally high (>60 wt%) and chemically homogeneous across the grains. The X-ray Diffraction (XRD) analyses show highest peak intensity at ~36° 2θ, followed by other diagnostic peaks for chromite. Micro-Raman of chromite yields very strong diagnostic Raman active vibrational modes at 685 cm-1 (A1g), followed by 520 cm-1 (F2g(2)). The other peaks, viz. 446 cm-1 and 610 cm-1 are rather weak and correspond to Eg and F2g, respectively. VNIR (0.4μ to 2.4μ) reflectance spectroscopy of chromite suggested strong absorption near 2 μm and could be useful to quantify the chemical composition (especially Cr2O3, Al2O3 and Cr#). We found a good correlation of VNIR absorption and chemical composition of chromite (e.g. band positions versus Al2O3 and Cr# are well within 95% correlation interval). The intense Raman peak at 685 cm-1 corresponds to higher Cr content. This study, therefore, implies a significant understanding in determination of mineral chemistry (especially Chromites) by VNIR and micro Raman spectroscopy, which could be a useful tool for the future planetary exploration.
关键词： micro-Raman spectroscopy,VNIR spectroscopy,Nidar ophiolite complex,Chromite,Planetary exploration
更新于2025-09-04 15:30:14
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Structural and optical properties of sulfur passivated epitaxial step-graded GaAs <sub/>1-y</sub> Sb <sub/>y</sub> materials
摘要： The impact of bulk and surface defect states on the vibrational and optical properties of step-graded epitaxial GaAs1-ySby (0 ≤ y ≤ 1) materials with and without chemical surface treatment by (NH4)2S was investigated. Tunable antimony (Sb) composition GaAs1-ySby epitaxial layers, grown by solid source molecular beam epitaxy (MBE), were realized on GaAs and Si substrates by varying key growth parameters (e.g., Sb/Ga ?ux ratio, growth temperature). Raman and photoluminescence (PL) spectroscopic analysis of (NH4)2S-treated GaAs1-ySby epitaxial layers revealed composition-independent Raman spectral widths and enhanced PL intensity (1.3×) following (NH4)2S surface treatment, indicating bulk defect-minimal epitaxy and a reduction in the surface recombination velocity corresponding to reduced surface defect sites, respectively. Moreover, quanti?cation of the luminescence recombination mechanisms across a range of measurement temperatures and excitation intensities (i.e., varying laser power) indicate the presence of free-electron to neutral acceptor pair or Sb-defect-related recombination pathways, with detectable bulk defect recombination discernible only in binary GaSb PL spectra. In addition, PL analysis of the short- and long-term thermodynamic stability of sulfur-treated GaAs1-ySby/Al2O3 heterointerfaces revealed an absence of quanti?able atomic interdiffusion or native oxide formation. Leveraging the combined Raman and PL analysis herein, the quality of the heteroepitaxial step-graded epitaxial GaAs1-ySby materials can be optimized for optical devices.
关键词： molecular beam epitaxy,optical properties,structural properties,sulfur passivation,Raman spectroscopy,surface treatment,photoluminescence spectroscopy,GaAs1-ySby
更新于2025-09-04 15:30:14
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Ultrasonic Studies of Solid Azobenzene-Decorated Polymer Thin Films
摘要： This work investigates the effect of ultrasound on switching of cis azobenzene isomers to their trans counterparts in solid films of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)]. Ultraviolet?visible and 1H nuclear magnetic resonance spectroscopies demonstrate that 46% of the cis isomer converts to the trans form purely by ultrasonic agitation and 46% converts to the trans isomer by localized ultrasound-induced heating effects. Comparative studies of isomerization by ultrasound wave, heat, and visible irradiation show that ultrasound exposure requires a longer time to switch the cis-to-trans conformation. The estimated activation energy for the cis-to-trans conversion in solid polymer films is shown to be comparable to previous values of azobenzene isomerization, indicating that incorporation of the chromophore in a polymeric system affects the kinetics of transition but not the barriers to conformational change.
关键词： azobenzene,nuclear magnetic resonance spectroscopy,polymer thin films,ultrasound,isomerization,ultraviolet?visible spectroscopy
更新于2025-09-04 15:30:14
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Structure and Properties of Gallium-Rich Sodium Germano-Gallate Glasses
摘要： Glass compositions in the gallium-rich region of the ternary GaO3/2-GeO2-NaO1/2 vitreous system are studied as a function of the Na/Ga cationic ratio (ranging from 1.30 to 1.61) for a fixed GeO2 content. Glass structures are investigated by 71Ga MAS-NMR, infrared and Raman spectroscopies, and the thermal, optical and physical properties are characterized. Vibrational spectra are interpreted with the help of density functional theory (DFT) calculations. Gallium oxide generally enters the germania network in four-fold coordination, however for Na/Ga ratio below unity, gallium cations tend to charge balance with the formation of 5- or 6-fold coordination units. When the amount of sodium is greater than gallium, non-bridging oxygens (NBOs) are formed preferably on germanate tetrahedral units. These structural descriptions are used to understand the evolution of glass properties such as glass transition temperature, density and refractive index.
关键词： germano-gallate glasses,infrared,vibrational spectroscopy,glass structure,71Ga NMR spectroscopy
更新于2025-09-04 15:30:14
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Study of spectral and recombination characteristics of HVPE GaN grown on ammono substrates
摘要： A comprehensive study of the bulk ~400 μm thick GaN samples, grown by HVPE technology on AT-GaN seeds, and containing different carbon doping is reported. Spectroscopy of point centres has been implemented by combining several contactless/optical techniques: time resolved photoluminescence (TR-PL), microwave probed photoconductivity (MW-PC) transient and pulsed-photo-ionization spectroscopy (PPIS) techniques, together with steady-state PL (SS-PL) and transmission spectral measurements. The dynamics of the non-radiative and radiative recombination dependent on the excess carrier density and incorporated carbon concentration has been revealed. The cross-section of the photon-electron interaction and broadening factors due to electron-phonon coupling have been evaluated for various centres. Profiling of the excess carrier decay transients by scanning a wafer-edge boundary has been employed for estimation of surface recombination velocity. The asymmetry of surface recombination in heavily carbon doped samples has been corroborated by SS-PL intensity changes when comparing spectra recorded by exciting the opposite wafer surfaces using UV light. It has been inferred that the surface and bulk non-radiative recombination with 70 ns carrier lifetime is efficient only within initial stages of MW-PC and TR-PL transients. Several traps, tentatively attributed to CNON, CN, CI, VGa point defects, have been deduced from pulsed photo-ionization spectroscopy. The CN defect appeared to be the most efficient in redistribution of the radiative recombination. For these centres, the parameters such as the photon-electron interaction cross-section, broadening factor due to electron-phonon coupling, and concentration have been evaluated for GaN samples, carbon doped with different levels. The CNVGa, CICGa, CGaVN complexes have also been implied by considering TR-PL and SS-PL spectra. The conversion from absorption to emission spectra has been revealed and explained based on van Roosbroeck-Shockley approach. The long-tail photoluminescence decay with durations up to tens of ms has been explained by nearly resonant photo-ionization and photoluminescence transitions in sequence of self-sustaining processes when local excitation travels by hopping over the re-absorption lengths.
关键词： Photo-ionization spectroscopy,Microwave probed photoconductivity transients,Photoluminescence spectroscopy,Carbon doped HVPE GaN,Surface recombination
更新于2025-09-04 15:30:14