Raman Scattering Spectroscopy Research Articles

Ambient Temperature–Corrected Mechanical Stress Mapping of Gallium Nitride and Aluminum Indium Gallium Phosphide Films by Raman Scattering Spectroscopy for Characterization of Light‐Emitting Diodes

Raman spectroscopy can provide a detailed analysis of mechanical stress in crystalline materials through the measurement of shifts in vibrational frequency. However, the ambient temperature drift during measurements can lead to inaccurate mechanical stress values. Herein, the 2D Raman mapping analysis of gallium nitride (GaN) and aluminum indium gallium phosphide (AlInGaP) epitaxial films within packaged light‐emitting diode (LED) devices reveals micrometer‐scale localized stress distributions. A temperature‐corrected measurement method is developed to evaluate the mechanical stress of InGaN LED dies at various LED operating conditions. The impact of die design on mechanical stress is studied for both GaN on Al2O3 (chip scale package, CSP) and GaN thin‐film flip chip (TFFC) designs. Raman mapping of AlInGaP LEDs is also demonstrated and shows comparable resolution with the GaN LED results.

Low-Frequency Raman Scattering Spectroscopy as an Accessible Approach to Understand Drug Solubilization in Milk-Based Formulations during Digestion.

Techniques enabling in situ monitoring of drug solubilization and changes in the solid-state of the drug during the digestion of milk and milk-based formulations are valuable for predicting the effectiveness of such formulations in improving the oral bioavailability of poorly water-soluble drugs. We have recently reported the use of low-frequency Raman scattering spectroscopy (region of analysis <200 cm–1) as an analytical approach to probe solubilization of drugs during digestion in milk using ferroquine (SSR97193) as the model compound. This study investigates the wider utilization of this technique to probe the solubilization behavior of other poorly water-soluble drugs (halofantrine, lumefantrine, and clofazimine) in not only milk but also infant formula in the absence or presence of bile salts during in vitro digestion. Multivariate analysis was used to interpret changes to the spectra related to the drug as a function of digestion time, through tracking changes in the principal component (PC) values characteristic to the drug signals. Characteristic low-frequency Raman bands for all of the drugs were evident after dispersing the solid drugs in suspension form in milk and infant formula. The drugs were generally solubilized during the digestion of the formulations as observed previously for ferroquine and correlated with behavior determined using small-angle X-ray scattering (SAXS). A greater extent of drug solubilization was also generally observed in the infant formula compared to milk. However, in the case of the drug clofazimine, the correlation between low-frequency Raman scattering and SAXS was not clear, which may arise due to background interference from clofazimine being an intense red dye, which highlights a potential limitation of this new approach. Overall, the in situ monitoring of drug solubilization in milk and milk-based formulations during digestion can be achieved using low-frequency Raman scattering spectroscopy, and the information obtained from studying this spectral region can provide better insights into drug solubilization compared to the mid-frequency Raman region.

Высокоэффективные воспроизводимые зонды для спектроскопии комбинационного рассеяния с усилением на острие (TERS)

The principal limitation of the use of the Tip Enhanced Raman Scattering spectroscopy (TERS) is due to the lack of reliable scanning probes. The paper presents a simple technique for the fabrication of cantilever-based TERS-probes with highly reproducible characteristics, high performance, reliable and giving sufficient enhancement. The technique is based on the modification of standard scanning probe microscope contilevers by plasma etching and the subsequent formation of a TERS-amplifying region on the tip of probe by deposition of colloidal nanoparticles by dielectrophoresis.

Pressure-induced electronic anomaly and multiband superconductivity in the doped topological insulator NbxBi2Se3

The tunability of the electronic topological transition is fundamentally important to unveil new quantum matters. Here, we report the observation of pressure-induced electronic anomaly below 12.0 GPa in Nb0.25Bi2Se3 using a combination of electrical transport, synchrotron x-ray diffraction, Raman-scattering spectroscopy measurements, and first-principles calculations. At ambient pressure, the band-structure calculations demonstrate the Nb0.25Bi2Se3 is a heavily electron-doped semiconductor with multiple band structure. With applying pressure, it is shown that the pressure can induce Fermi-surface reconstruction at a time-reversal invariant point. We further present evidence of multiband superconductivity characterized by an upward curvature in the upper critical field in the pressurized Nb0.25Bi2Se3 crystal. The superconducting critical parameters of pressurized Nb0.25Bi2Se3 crystal are obtained. Furthermore, the superconducting phase diagram under high pressure is discussed within BCS theory. These findings highlight the critical role of the multiple-band structure induced by strong hybridization between the Nb-4d and Bi/Se-p orbitals in accessing quantum states.

Synthesis, Characterization, Photocatalytic and Sensing Properties of Mn-Doped ZnO Nanoparticles.

In this paper, Mn-doped ZnO nanoparticles (0 to 10 mol% Mn) were synthesized by facile low-temperature aqueous solution process and characterized by several techniques such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible and Raman-scattering spectroscopy. The SEM studies confirmed that the synthesized nanoparticles are grown in high density and increase in Mn content was found to have a significant effect on the morphologies of ZnO nanoparticles. The XPS studies established the structural variation of the samples with the change in dopant concentration and its oxidation state. XPS probe the existence of impurity phases in the as-synthesized samples. The results indicate further that hexagonal wurtzite structure of ZnO undergoes distortion with the increase in the dopant concentration. Also, with the increase in the dopant concentration, the blue-shift was observed in the UV-vis. spectra. Photocatalytic and chemicals sensing performances of these nanomaterials have been investigated by subjecting them to photocatalytic degradation of methyl orange (MO) under UV irradiation and for the detection of picric acid (PA) in aqueous solutions. Mn doped ZnO samples were found to be more efficient in catalyzing the MO degradation than pure ZnO. 5 mol% Mn doped ZnO nanomaterials were studied to use as fluorescence sensor for the detection of PA and the observed detection limit was found to be 2.5 μM.

Multiwavelength Raman Scattering Spectroscopy Study of Graphene Synthesized on Si(100) and SiO2 by Microwave Plasma‐Enhanced Chemical Vapor Deposition

Herein, multiwavelength Raman spectroscopy studies of graphene samples synthesized directly on SiO2 and Si(100) substrates by microwave plasma‐enhanced chemical vapor deposition (MW PECVD), using five different excitation wavelengths in ultraviolet (UV), visible light, and near‐infrared (NIR) ranges, are presented paying attention to the peculiarities of the spectra. Raman spectra parameters are analyzed to reveal effects of the excitation wavelength. Structural features of graphene directly synthesized on SiO2 and Si(100) are discussed. Analysis of the interdependences of various Raman spectra parameters reveals that the most informative spectra are recorded using 532 nm wavelength excitation. Examination of the full width at half maximum values of G band (FWHM(G)) reveals that the graphene layers synthesized on Si(100) substrate consist of smaller crystallites comparing with SiO2 substrate.

Vibrational coupling effects in the energy redistribution of alkylbenzenes

Ultrafast time- and frequency-resolved coherent anti-Stokes Raman Scattering spectroscopy (CARS) was used to detect vibrational energy redistribution in liquid alkylbenzenes at ambient-temperature. The C–H stretching vibrational modes (vibrational frequencies near ∼3000 cm−1) on substituents were selectively excited, the substituents were CH3 (toluene), (CH3)2CH (isopropylbenzene) and (CH3)3C (t-butylbenzene), vibrational energy flow from the substitution modes to the phenyl modes was observed in the electronic ground state of alkylbenzenes. According to the selective excitation CARS experimental results, beats among these relevant modes were observed and vibrational coupling information was extracted via Fourier analysis. Vibrational coupling and substitution structure that effect energy redistribution processes were discussed.

Ytterbium-Doped ZnO Flowers Based Phenyl Hydrazine Chemical Sensor.

Herein, we report the fabrication and characterization of phenyl hydrazine sensor based on ytterbium (Yb) doped ZnO flowers composed of nanorods prepared by simple hydrothermal process. The as-synthesized nanomaterial was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) attached with energy dispersive spectroscopy (EDS), Fourier transformation infrared (FTIR) and Raman-scattering spectroscopy which revealed the large-quantity synthesis, well-crystallinity and wurtzite hexagonal crystal structure of Yb-doped ZnO flowers. The fabricated phenyl hydrazine chemical sensor, by employing Yb-doped ZnO flowers as an electron mediator, exhibited sensitivity of ∼34.2 µA·mM-1 ·cm-2, detection limit of 24 mM and linear dynamic range of 0.25-4.0 mM. The presented work demonstrates that the Yb-doped ZnO nanomaterials are promising electron mediator which can be used for the fabrication of chemical sensors to detect various hazardous and toxic chemicals as phenyl hydrazine.

Study of Diluted Meldonium Solutions by Surface Enhanced Raman Scattering Spectroscopy

Silvered porous silicon was utilized as an active substrate for a detection of small amounts of meldonium by surface enhanced Raman scattering (SERS) spectroscopy. We were able to detect the meldonium in its water solutions at the concentrations of 10[Formula: see text]–10[Formula: see text][Formula: see text]M. Immersion of the silvered porous silicon in the meldonium solutions at the 10[Formula: see text][Formula: see text]M concentration and lower led to the dimers’ formation. At the concentrations larger than 10[Formula: see text][Formula: see text]M, a greater contribution to the enhancement of the Raman intensity was caused by a chemical mechanism while the smaller amounts were detected mostly due to an electromagnetic mechanism.

Resonance Raman Scattering Spectroscopy of Four-Monolayer Thick MoS2 Films

We studied the Raman scattering in bulk and four-monolayer thick MoS2 films under the resonance laser excitation of A, B, and C excitons. We demonstrate the fine structure agility of a phonon mode associated with out-of-plane vibration of sulfur atoms (A1g) when passing from bulk to atomically thin film. The C exciton resonance excitation allows us to register the line corresponding to optical-phonon (E1g) scattering and the set of peaks with a 660 – 740 cm−1 Stokes shift associated with resonance scattering by two optical (Eu) phonons.

Application of Low-Frequency Raman Scattering Spectroscopy to Probe in Situ Drug Solubilization in Milk during Digestion.

We have recently shown that real-time monitoring of drug solubilization and changes to solid state of the drug during digestion of milk can be achieved using synchrotron small-angle X-ray scattering. A complementary laboratory-based method to explore such changes is low-frequency Raman spectroscopy, which has been increasingly used to characterize crystalline drugs and their polymorphs in powders and suspensions. This study investigates the use of this technique to monitor in situ drug solubilization in milk during the process of digestion, using a lipolysis model/flow-through configuration identical to that used previously for in situ synchrotron small-angle X-ray scattering studies. An antimalarial drug, ferroquine (SSR97193), was used as the model drug for this study. The Raman spectra were processed using multivariate analysis to extract the drug signals from the milk digestion background. The results showed disappearance of the ferroquine peaks in the low-frequency Raman region (<200 cm–1) after approximately 15–20 min of digestion when milk fat was present in the system, which indicated drug solubilization and was in good agreement with the in situ small-angle X-ray scattering measurements. This proof-of-concept study therefore suggests that low-frequency Raman spectroscopy can be used to monitor drug solubilization in a complex digesting milk medium because of the unique vibrational modes of the drug crystal lattices.

Study of LaFeO3 perovskite material by high-pressure Raman scattering

We use high-pressure Raman-scattering spectroscopy to study LaFeO3 synthesized by using the sol-gel method. The structural evolution of the samples under high pressure and at room temperature is monitored via the Raman-scattering spectrum in the pressure range of 0.50 to 22.1 GPa. When the pressure surpasses 12 GPa, the Raman spectra change significantly around 180 cm−1, which indicates a structural phase transition. However, the Raman spectrum remains constant under 5.0 GPa, which indicates that the LaFeO3 structure is preserved at these pressures.

Evolution of dielectric properties of thermally reduced graphene oxide as a function of pyrolisis temperature

Reduced grapheneoxide (rGO) is a derivative of graphene and its properties allow several applications, such as supercapacitors, sensors, filters, among others. The rGO was obtained at 400 °C and 1000 °C. These materials were analysed using Scanning Electron Microscopy, Transmission Electron Microscopy, Thermogravimetric Analysis, Differential Exploratory Calorimetry, X-Ray Diffraction, Raman Scattering Spectroscopy, Fourier Transform Infrared Spectroscopy and Vector Network Analyzer. The sample treated at 400 °C resulted in a more exfoliated material, presenting six sheets in the interlayer, with well-distributed aromatic symmetry and more electroactive groups. Thus, it showed higher electric permittivity in agreement with Raman G symmetry results, implying an increase of CC aromatic ring quantities, enabling this material to be used in electronic devices and nanocomposites with electromagnetic properties. This article aims to study the influence of structural and consequent changes in the dielectric properties of rGO samples as a function of pyrolysis temperature.

Surface and optical properties of indium-rich InGaN layers grown on sapphire by migration-enhanced plasma assisted metal organic chemical vapor deposition

In-rich InGaN nanoscale thin films grown on (0001) sapphire (Al2O3) using migration enhanced plasma-assisted metal-organic chemical vapor deposition (MEPA-MOCVD) method are characterized by high-resolution x-ray diffraction (HR-XRD), x-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy (RSS), as well as variable angle spectroscopic ellipsometry (VASE). Theoretical calculations were performed to acquire the optical constants and vibrational properties of the films. The indium composition x (In) values determined by HR-XRD and from the surface area calculated by XPS are in good agreement with each other. The valence band maxima of InxGa1−xN films (x = 0.65–0.80) were observed to shift to lower binding energy with the increase of indium concentration. The RSS results confirmed the one-phonon behavior for the A1(LO) and E2(high) modes with x (In)—independent of phonon frequencies of the substrate. The simulated refractive index n was found to increase with In composition, the band gap (Eg) shifted, however, towards the lower energy side. For a given In composition and by increasing the measurement temperature from 30 °C to 600 °C, the variations of optical constants (n and Eg) showed similar trends as in samples with increasing In composition.

Investigation of high indium-composition InGaN/GaN heterostructures on ZnO grown by metallic organic chemical vapor deposition

The optical properties and film quality for a series of high-In composition InGaN films grown on ZnO substrate by metal-organic chemical vapor deposition (MOCVD) are characterized by using high resolution X-ray diffraction (HRXRD), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman scattering spectroscopy (RSS). The In composition is evaluated by analyzing the RBS and PL emission spectra. The XPS measurements revealed the diffusion of Zn atoms from the substrate into InGaN films. All the analyses of experimental measurements have shown that the growth temperature played an important role in indium composition as well as of film quality. An optimum growth temperature is a necessary condition for obtaining high-quality films.

Germanium isotope effect induced guest rattling and cage distortion in clathrates

Intermetallic clathrates are materials characterized by a large cage structure where guest atoms can move anharmonically, providing these materials exotic thermoelectric properties. Unfortunately, the dynamical and atomic nature of the rattling phonons, and their interactions with the electronic structure, are not fully understood. Here, we report that a germanium isotope effect can trigger an inherent guest rattling and cage distortion in clathrate Ba8Ga16Ge30 (BGG). Raman-scattering spectroscopy and advanced electron microscopy demonstrate that the atomic germanium isotope effect induces an off-centre rattling at the 6d sites as well as a tetrakaidecahedron deformation which is anisotropic for n-type BGG but isotropic for p-type BGG. The present findings indicate that the large n-type germanium isotope effect arises from the strong electron-phonon coupling, which opens up a novel avenue for manipulating dynamical motions of phonons via atomic isotope engineering.

The synovial fluid analysis by using Raman Scattering spectroscopy in order to educe the synovial joint pathology

In this paper, we present the results of experimental studies by using Raman-scattering spectroscopy method of synovial fluid that was obtained from the joint cavity during the surgery. Analyzing the composition of synovial fluid, it was identified that with the progress of degenerative-dystrophic process in synovial fluid of the affected joint, the gross amount of components increases at wave numbers: 1155 cm-1 (hyaluronic acid (C-O, C-C )) and 1250cm-1(Amide III). The entered optical numbers allow us to characterize synovial fluid (SF) in osteoarthrosis (OA). This specific Raman-scattering spectroscopy method may become a new diagnostic screening in order to educe the synovial joint pathology.

Comparative spectral analysis of the extra-cell matrixes surface of heart valves before and during the process of their decullularization

There are presented the results of the application of Raman-scattering spectroscopy method (RS) for the qualitative analysis of rams' heart valves surfaces before and during their decellularization. While analyzing RS spectra, it was found that basic differences appear at wave numbers 812 cm-1, 1062 cm-1, 1340 cm-1 and 1440 cm-1, corresponding to phosphodiester linkage of RNA; OSO-3 corresponds to symmetrical stretching of glycosaminoglycans and chondroitin-6-sulfate; corresponds to deformation mode of proteins and nucleic acids (DNA); proteins, lipids. Optical analysis has shown that while analyzing decellularization on the valves surfaces, the content of glycosaminoglycans, proteins and lipids decreases; retains a high DNA content. It was found that with the aid of entered optical numbers it is possible to control the process efficiency of decellularization of the heart valves.

Template-free hydrothermal synthesis of Flower-like hierarchical zinc oxide nanostructures

Flower-like hierarchical zinc oxide nanostructures have been successfully synthesized by a facile and template-free hydrothermal method from zinc acetate (Zn(AC)2) and potassium hydroxide (KOH) only. Furthermore, the effects of alkaline mineralizer type on product synthesis by hydrothermal processing have been studied. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscope, UV–vis spectrophotometry and Raman-scattering spectroscopy. When the type of mineralizer was KOH, the shape of ZnO sample has presented flower-like hierarchical nanostructures with diameters of 2–4 μm. Photocatalytic activity of the hierarchical ZnO nanostructures was evaluated by the degradation of methylene blue (MB) under UV light illumination. The as-prepared ZnO nanostructures exhibited a significantly enhanced photocatalytic activity than commercial ZnO. This was mainly attributed to the unique morphology and higher surface area.

Hydroquinone Sensor Based on Neodymium (Nd) Doped ZnO Hexagonal Nanorods

Herein, we report a simple hydrothermal synthesis and detailed characterizations of Nd-doped ZnO pointed hexagonal nanorods by various techniques such as field emission scanning electron microscopy (FESEM) attached with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), UV-visible, Fourier transform infrared (FTIR) and Raman-scattering spectroscopy. The morphological studies revealed pointed hexagonal nanorods arranged in flower-shaped morphologies and well-crystalline with the wurtzite hexagonal phase. The Nd-doped ZnO nanorods were used as potential scaffold to fabricate high sensitivity hydroquinone sensor which exhibited sensitivity of ∼7.43 μA·mM–1cm–2 with a linear dynamic range of (LDR) of 0.313 mM–2.5 mM and correlation coefficient (R2) of 0.99671. The detection limit of Nd-doped ZnO pointed hexagonal nanorods based hydroquinone sensor was found to be 0.313 mM.