Raman Peak Intensity Research Articles

Near‐infrared Raman spectroscopy for gastric precancer diagnosis

AbstractRaman spectroscopy is a molecular vibrational spectroscopic technique that is capable of optically probing the biomolecular changes associated with neoplastic transformation. The purpose of this study was to apply near‐infrared (NIR) Raman spectroscopy for differentiating dysplasia from normal gastric mucosa tissue. A total of 65 gastric mucosa tissues (44 normal and 21 dysplasia) were obtained from 35 patients who underwent endoscopy investigation or gastrectomy operation for this study. A rapid NIR Raman system was utilized for tissue Raman spectroscopic measurements at 785‐nm laser excitation. High‐quality Raman spectra in the range of 800–1800 cm−1 can be acquired from gastric mucosa tissue within 5 s. Raman spectra showed significant differences between normal and dysplastic tissue, particularly in the spectral ranges of 850–1150, 1200–1500 and 1600–1750 cm−1, which contained signals related to proteins, nucleic acids and lipids. The diagnostic decision algorithm based on the combination of Raman peak intensity ratios of I875/I1450 and I1208/I1655 and the logistic regression analysis yielded a diagnostic sensitivity of 90.5% and specificity of 90.9% for identification of gastric dysplasia tissue. This work demonstrates that NIR Raman spectroscopy in conjunction with intensity ratio algorithms has the potential for the noninvasive diagnosis and detection of precancer in the stomach at the molecular level. Copyright © 2009 John Wiley & Sons, Ltd.

Promotion of nano-anatase TiO 2 on the spectral responses and photochemical activities of D1/D2/Cyt b559 complex of spinach

Previous researches approved that photocatalysis activity of nano-TiO 2 could obviously increase photosynthetic effects of spinach, but the mechanism of improving light energy transfer and conversion is still unclear. In the present we investigated effects of nano-anatase TiO 2 on the spectral responses and photochemical activities of D1/D2/Cyt b559 complex of spinach. Several effects of nano-anatase TiO 2 were observed: (1) UV–vis spectrum was blue shifted in both Soret and Q bands, and the absorption intensity was obviously increased; (2) resonance Raman spectrum showed four main peaks, which are ascribed to carotene, and the Raman peak intensity was as 6.98 times as that of the control; (3) the fluorescence emission peak was blue shifted and the intensity was decreased by 23.59%; (4) the DCPIP photoreduction activity showed 129.24% enhancement; (5) the oxygen-evolving rate of PS II was elevated by 51.89%. Taken together, the studies of the experiments showed that nano-anatase TiO 2 had bound to D1/D2/Cyt b559 complex, promoted the spectral responses, leading to the improvement of primary electron separation, electron transfer and light energy conversion of D1/D2/Cyt b559 complex.

Formula omitted] band Raman spectra of single, double and triple layer graphene

We have measured the Raman spectra of one to three layer graphene as a function of laser excitation energy. The observed G ′ band Raman peak (∼2650 cm −1) intensity decreases with increasing numbers of graphene layers. The electronic energy band structure calculated by the extended tight binding model shows that there are four and nine possible optical processes in double resonance theory for the Raman G ′ band of double and triple layers graphene, respectively. Raman intensity calculations show that each peak position depends on its wavevector, and then the G ′ band of double and triple layer graphene has three and five components, respectively.

One-Pot Assembly of Cu2O Chain-Like Hollow Structures

Novel Cu2O chain-like network was assembled via a facile one-pot solution process with the assistance of poly(vinylpyrrolidone) (PVP). TEM observations showed that the chain-like structures were aggregated by hollow spheres approximately 70 nm in diameter. To be worth mentioning, HRTEM image recorded from the coherent interfacial region demonstrated that the lattice fringes penetrate from one sphere into the adjacent one smoothly without apparent diffraction contrast, which indicated that the hollow spheres experienced lattice fusion and grew into each other. Based on the systematic studies, an oriented aggregation mechanism was proposed, i.e., Cu2O nanoparticles into hollow spheres and subsequently the hollow spheres into the chain-like structures. The Raman spectra of the Cu2O chain-like hollow nanostructures were also investigated. It was found that the Raman peak intensity is different from that in the previous reports, which might be originated from the structure defect resulted from the oriented attachment.

Preparation of Carbon Nanowall by Hot-Wire Chemical Vapor Deposition and Effects of Substrate Heating Temperature and Filament Temperature

The preparation of carbon nanowalls (CNWs) by hot-wire chemical vapor deposition (HWCVD) and the effects of substrate heating temperature Th and filament temperature Tf in this method have been investigated. The CNWs can be prepared by HWCVD using CH4 without H2 dilution. The wall size obtained from the scanning electron microscope image and the Raman peak intensity ratio of the G peak to the D peak of the sample changed with Th and Tf. However, both were maxima at a substrate surface temperature Ts of 730–740 °C, which was not the same as Th, and this result was independent of Tf. The CNWs did not grow at Tf of 1850 °C, because the Tf of 1850 °C was insufficient for the decomposition of CH4. On the basis of these results, we show that Th, i.e., Ts is a more important parameter than Tf in the preparation of CNWs by HWCVD.

Revisiting the separation dependent surface enhanced Raman scattering

Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role.

Fluidized bed chemical vapor deposition of pyrolytic carbon – II. Effect of deposition conditions on anisotropy

Pyrolytic carbon coatings were deposited on top of alumina particles at deposition temperatures from 1250 °C to 1450 °C and with acetylene and acetylene/propylene mixtures at concentrations between 25% and 70%, v/v. The anisotropy of pyrolytic carbon coatings was quantified using electron diffraction and Raman peak intensities, and related to the deposition conditions and microstructure. In correlation with the TEM images, it was found that the value of orientation angle (OA) measured from selected area electron diffraction patterns, increased with increasing deposition temperature and precursor concentration corresponding to a reduction in texture. The effect of temperature was more pronounced for the acetylene/propylene mixture and at low temperatures highly anisotropic material was obtained on a local scale. However, the use of larger TEM selecting apertures showed that the majority of coatings were isotropic overall. A correlation was found between OA and Raman D band intensity which allows quick classification of pyrolytic carbon texture.

Femtosecond stimulated Raman spectroscopy of methanol and acetone in a noncollinear geometry using a supercontinuum probe

The design of a femtosecond stimulated Raman spectroscopy (FSRS) setup capable of recording high contrast Raman spectra is presented. The Raman transition is stimulated by a supercontinuum pulse and pumped by the second-harmonic of a Ti:sapphire amplifier system fundamental wavelength. This scheme alleviates rapid amplitude modulation near 800 nm using the smooth amplitude region in the continuum near the 400 nm pump. Raman spectra of acetone and methanol are presented in which the Raman peak intensity is the most pronounced feature of the spectrum. A mechanism limiting the resolution and peak intensity based on the nonlinear index of refraction effects is suggested.

Theory of resonant multiphonon Raman scattering in graphene

We present a detailed calculation of intensities of two-phonon and four-phonon Raman peaks in graphene. Writing the low-energy Hamiltonian of the interaction of electrons with the crystal vibrations and the electromagnetic field from pure symmetry considerations, we describe the system in terms of just a few independent coupling constants, considered to be parameters of the theory. The electron-scattering rate is introduced phenomenologically as another parameter. The results of the calculation are used to extract information about these parameters from the experimentally measured Raman peak intensities. In particular, the Raman intensities are sensitive to the electron-scattering rate, which is not easy to measure by other techniques. Also, the Raman intensities depend on electron-phonon coupling constants; to reproduce the experimental results, one has to take into account renormalization of these coupling constants by electron-electron interaction.

Resonant Raman scattering probe of alloying effect in ZnMgO thin films

We have presented a detailed resonant Raman scattering investigation for the alloying effect in hexagonal Zn1−xMgxO (x⩽0.323) thin films grown by pulsed laser deposition. Alloy-induced longitudinal optical (LO) phonon resonance effect has been achieved from the Raman peak shift, lineshape, and intensity through changing the Mg composition and temperature to tune the ZnMgO bandgap. By the aid of theoretical analysis combining with the extrinsic Fröhlich interaction mediated via a localized exciton, we demonstrate the pronounced outgoing resonance behavior for the LO phonons in ZnMgO, where the localized exciton due to alloy disorder dominates the resonance processes.

Study of acoustical phonon modes in superlattices with SiGe QDs

Multilayers with SiGe nanoislands (QD's) grown in a broad temperature range are studied using Raman spectroscopy, HRXRD and compared with similar multilayers without islands. As the growth temperature increases, Si content in the islands increases, partially relieving strain. These structural transformations manifest themselves in both the intensity and frequency of the low‐frequency Raman peaks. Due to composition‐ and strain‐induced changes in the island band structure, excitation conditions come out of resonance, reducing Raman peak intensity. We have shown that at the interpretation of the Raman scattering by folded acoustic phonons for structures with nanoislands the real morphology of the island layer should be considered. The observed series of the low‐frequency Raman peaks, for the multilayered structures with the number of QD layers below ten, is due to the acoustic phonon modes within the islands. The enhancement of the scattering intensity due to resonance of the excitation light with the electronic transitions within the islands plays a significant role. Theoretical analysis was fulfilled in the framework of microscopic approach with using Green function method and taking into account the real structure of QD's and their interaction with surrounding matrix.

Double resonant Raman scattering in nanographite films

Experimental results are presented on Raman scattering in graphite films produced by DC plasmaenhanced chemical vapor deposition from a methane-hydrogen gas mixture. Scanning electron and probe microscopy data show that, depending on substrate material and deposition time, the deposited film is either a mesoporous material consisting of graphite nanocrystallites with basal planes oriented perpendicular to the substrate surface or an atomically flat, nanometer-thick stack of graphene layers parallel to the substrate. A comparative Raman spectroscopy analysis is performed for film samples deposited on nickel and silicon substrates for 5 and 60 min, as well as for highly ordered graphite samples. The Raman spectra of the examined samples correspond to the double resonant scattering mechanism. The behavior of Raman peak position and intensity as functions of excitation wavelength suggests a high degree of structural order in the graphite films deposited on nickel for 5 min. The results obtained are used to show that the thickness of these films is 1.5 ± 0.5 nm.

Vibrational properties of -AlOOH under pressure

We have performed first-principles calculations to investigate the behavior of the hydrogen bond in δ-AlOOH under pressure. The highest OH-stretching A1 and B2 mode frequencies decrease under pressure leading to hydrogen bond symmetrization. After hydrogen bond symmetrization, the corresponding frequencies gradually increase. This softening and subsequent hardening of the OH bonds is a good spectroscopic indicator of hydrogen bond symmetrization and is observed in our GGA static calculations at ~30 GPa without considering tunneling effects. We have also carried out calculations of Raman peak intensities in several supercells with various hydrogen orderings to investigate the potential effect of H-disorder on the Raman spectrum of δ-AlOOH. Our results suggest that the four broad Raman bands observed experimentally in the range of OH-stretching mode frequencies could originate in H-disorder in this phase.

Tribological properties of diamond-like carbon films deposited by pulsed laser arc deposition

A novel method, pulsed laser arc deposition combining the advantages of pulsed laser deposition and cathode vacuum arc techniques, was used to deposit the diamond-like carbon (DLC) nanofilms with different thicknesses. Spectroscopic ellipsometer, Auger electron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and multi-functional friction and wear tester were employed to investigate the physical and tribological properties of the deposited films. The results show that the deposited films are amorphous and the sp2, sp3 and C-O bonds at the top surface of the films are identified. The Raman peak intensity and surface roughness increase with increasing film thickness. Friction coefficients are about 0.1, 0.15, 0.18, when the film thicknesses are in the range of 17-21 nm, 30-57 nm, 67-123 nm, respectively. This is attributed to the united effects of substrate and surface roughness. The wear mechanism of DLC films is mainly abrasive wear when film thickness is in the range of 17-41 nm, while it transforms to abrasive and adhesive wear, when the film thickness lies between 72 and 123 nm.

Photocatalytic properties of visible-light enabling layered titanium oxide/tin indium oxide films

Visible-light enabling titanium oxide/tin indium oxide (TiO2/ITO) thin films deposited on unheated glass slides with prolonged deposition duration were investigated in this study. Structural properties characterized by X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) showed typical polycrystalline structure with primary anatase phase along with elongated pyramid-like grains lying on the film surface and densely packed columnar structure from cross-sectional profile. The XRD preferential peak of (211) and the Raman peak intensity at ∼640cm−1 dramatically increased without noticeable broadening and shift as the deposition time was prolonged beyond 2h. This implies that more perfectly crystalline structure, less internal stress, and comparatively larger grains were obtained by this technique. The Ti2p3/2 and O1s XPS peaks shifted toward higher binding energy suggest that the local chemical state was influenced by the prolonged deposition duration in the film, which resulted in red shift of absorption threshold into visible-light region. Under ultra-violet (UV) and visible-light illumination, the visible-light enabling film exhibited the best photocatalytic activity on MB degradation with the rate-constant of about 0.231h−1. Hydrophilic conversion rate was estimated to be 8.14×10−3deg−1min−1 and long-term UV-induced hydrophilicity of ∼10° in the dark storage up to 72h was observed. In addition to its inherent characteristics of the layered TiO2/ITO structure on hole/electron separation, all these could be attributed to more perfectly formed crystalline structure, densely packed columnar crystals and the surface roughness along with its enlarged surface area.

Raman microspectroscopic mapping or thermal system used to investigate milling‐induced solid‐state conversion of famotidine polymorphs

AbstractConfocal Raman microspectroscopy was used to nondestructively determine the polymorphic conversion of famotidine in the course of the milling process. A mapping system was applied to assess the blending uniformity of each polymorphic component in the milled mixture. Raman microspectroscopy combined with a thermal analyzer was also used to investigate the synergistic co‐effects of milling and heating on the polymorphic conversion of famotidine polymorphs. Famotidine has two polymorphs, forms A and B, the raw material of famotidine used was proved to be of form B. The Raman peak intensity ratio of the 2920 cm−1 band for form A and 2897 cm−1 band for form B was used to act as an indicator to evaluate the polymorphic conversion of famotidine form B to form A after different milling courses. The results indicate that the peak intensity at 2897 cm−1 gradually decreased with the milling time, whereas the peak intensity at 2920 cm−1 slowly enlarged, suggesting the polymorphic conversion of famotidine from form B to form A. The longer milling process might strongly induce and promote this polymorphic conversion of famotidine. Both polymorphic forms of famotidine were found to be well uniformly distributed within the milled samples due to their smaller varieties by using the Raman microscopic mapping system. The temperature effect could synergistically accelerate the polymorphic conversion of famotidine from form B to form A in the milled sample. The thermal‐dependent critical temperature for sharply enhancing the content of famotidine form A in each milled sample was also identified. Copyright © 2007 John Wiley & Sons, Ltd.

Low-temperature Al-induced crystallization of hydrogenated amorphous Si 1− xGe x (0.2 ≤ x ≤ 1) thin films

Low-temperature Al-induced crystallization of hydrogenated amorphous silicon–germanium thin films has been investigated by X-ray diffraction, Raman spectra and scanning electron microscopy measurements. It was shown that the Al-induced layer exchange significantly promotes the crystallization of the films. The influence of the annealing temperature and the Ge fraction on X-ray diffraction patterns and Raman spectra was analyzed. The increase in Raman peak intensity was observed with the increase of the annealing temperature, and the high-frequency shifts of Ge–Ge and Si–Ge peaks were found with the increase of the Ge fraction. There is an enhancement in film crystallinity and grain size with the increase of the Ge fraction and annealing temperature.

Fiber optic Raman sensor to monitor the concentration ratio of nitrogen and oxygen in a cryogenic mixture

A spontaneous Raman scattering optical fiber sensor was developed for a specific need of the National Aeronautics and Space Administration (NASA) for long-term detection and monitoring of the purity of liquid oxygen (LO(2)) in the oxidizer feed line during ground testing of rocket engines. The Raman peak intensity ratios for liquid nitrogen (LN(2)) and LO(2) with varied weight ratios (LN(2)/LO(2)) were analyzed for their applicability to impurity sensing. The study of the sensor performance with different excitation light sources has helped to design a miniaturized, cost-effective system for this application. The optimal system response time of this miniaturized sensor for LN(2)/LO(2) measurement was found to be in the range of a few seconds. It will need to be further reduced to the millisecond range for real-time, quantitative monitoring of the quality of cryogenic fluids in a harsh environment.

Micro-Raman study on the improvement of luminescence efficiency of GaAsN alloys

We have used in situ micro-Raman spectroscopy to clarify the mechanism of the luminescence efficiency improvement of GaAsN alloys by laser irradiation. Raman peak intensity of GaAs-like longitudinal optical (LO) mode phonon was observed to increase with the laser irradiation time. With increasing laser power density, the Raman intensity of GaAs-like LO mode phonon was found to increase more rapidly and to be saturated in a shorter time. Changes in the Raman intensity can be expressed by the same equation used for the luminescence efficiency improvement. Time constants of changes in the Raman intensity were almost in agreement with those of the luminescence efficiency improvement. This indicates that the increase in Raman intensity of GaAs-like LO phonon is closely related to the luminescence efficiency improvement.

The influence of composition on optical properties of ferroelectric potassium lithium niobate single crystals

Homogeneous crack-free Potassium Lithium Niobate (KLN) single crystals with different Li content were grown up by the TSSG technique. Lattice vibration spectra of these samples were investigated using Raman spectroscopy. The results showed that characteristic Raman spectra of the [NbO6]7− octahedral ions were strikingly influenced by the Li ions. Thus, the symmetric bend vibration mode ν5 of the KLN sample with higher Li content was split into three Raman peaks, while the sample with lower Li content displayed a single peak, supporting that the bend vibration modes of the [NbO6]7− octahedrons were obviously perturbed by Li ions occupying C-sites. Enhanced Raman peak intensities of the KLN sample post-annealed at 900°C for 24h evidenced that content of defects in KLN crystal might be reduced. The transmittance spectra showed that the crystal with higher Li content had better transmittance intensity.