Raman scattering of non-planar graphite: arched edges, polyhedral crystals, whiskers and cones

Planar graphite has been extensively studied by Raman scattering for years. A comparative Raman study of several different and less common non-planar graphitic materials is given here. New kinds of graphite whiskers and tubular graphite cones (synthetic and natural) have been introduced. Raman spectroscopy has been applied to the characterization of natural graphite crystal edge planes, an individual graphite whisker, graphite polyhedral crystals and tubular graphite cones. Almost all of the observed Raman modes were assigned according to the selection rules and the double-resonance Raman mechanism. The polarization properties related to the structural features, the line shape of the first-order dispersive mode and its combination modes, the frequency variation of some modes in different carbon materials and other unique Raman spectral features are discussed here in detail.     

Observation of Raman scattering by cloud droplets in the atmosphere

In a recent field campaign, the NASA Goddard Space Flight Center scanning Raman lidar measured, in the water vapor channel, Raman scattering from low-level clouds well in excess of 100% relative humidity. The excess scattering has been interpreted to be spontaneous Raman scattering by liquid water in the cloud droplets. A review of research on Raman scattering by microspheres indicates that the technique may provide a remote method to observe cloud liquid water. The clouds studied appear, from Mie scattering, to have two distinct layers with only the upper layer showing significant Raman scattering from liquid water in the droplets.     

Interaction of lead selenide with reduced graphene oxide: investigation through cyclic voltammetry and spectroscopy

Interaction between reduced graphene oxide (rGO) and PbSe quantum dots (Q-PbSe) have been studied by Cyclic Voltammetry (CV), Raman and FTIR spectroscopy. For that, the composites of Q-PbSe and rGO have been prepared by a one pot synthesis method. From the TEM analysis, Q-dots decorated on graphene layer have been concluded. Cyclic Voltammetry techniques have been employed to determine the change in quasi-particle gap and band edge parameters of Q-PbSe due to the interaction with rGO. The results were corroborated with FTIR and Raman analysis where substantial change in IR bands and shift in the Raman peaks have been observed, due to the interaction between Q-PbSe and rGO.     

Managing the degree of exfoliation and number of graphene layers using probe sonication approach

We have demonstrated a fast, versatile, and scalable approach to synthesize high-quality few layer graphene sheets with low defect ratio and high crystallinity produced from exfoliation of graphite flakes in DMF by using probe sonication. The effect of sonication time on degree of exfoliation and number of graphene layers has been fully investigated. The degree of exfoliation of graphene sheets as a function of sonication time has been successfully analyzed by XRD, UV-Vis spectroscopy, TEM, and BET studies. The morphological changes at different sonication times have also been observed by SEM. A structural and defect characterization of graphene sheets has been discussed in detail by Raman spectroscopic technique. The shift in position of 2D Raman band and its de-convolution provided information about formation of multi to few layer graphene sheets with sonication. Moreover, Raman results are highly consistent with TEM studies as per number of graphene layers is concerned.     

Characterization of the growth of sol-gel derived Ba---Ti---O thin films by laser Raman spectroscopy

The isothermal growth kinetics of sol-gel derived BaTi₅O₁₁ thin films has been studied by laser Raman spectroscopy. Thin films of the precursors were spin coated on silicon wafers with platinum or gold overlayers. The films were then annealed isothermally, and Raman spectra were recorded in situ. The time-dependent intensity changes of the Raman bands could be analyzed in terms of Avrami models. The interaction of the BaTi₅O₁₁ film with the platinum or gold overlayers during heat treatment apparently increased the Raman intensity by a factor of about 100.     

Asymmetry of the Forward and Backward Raman Gain Coefficient at 1.54 mum in Methane

The threshold pump energies at 1.06 mum and Raman gain coefficients of stimulated Raman scattering (SRS) at 1.54 mum have been measured in both single-pass and half-resonator configurations at various methane pressures. In the single-pass configuration, the Raman gain coefficients of the backward and forward SRS are 0.32 and 0.23 cm/GW at 95 atm, respectively. The backward Raman gain coefficient is higher than the forward Raman gain coefficient. This gain reduction is caused by the depletion of local pump intensity, the phase-matching conditions, and the transient effect of the high amplification rate in the forward SRS process. In the half-resonator configuration, the Raman gain coefficient was 0.46 cm/GW at 75 atm of methane.     

Analysis of the fragmentation test for carbon-fibre/epoxy model composites by means of Raman spectroscopy

The interfaces between high-modulus PAN-(T50) and mesophase pitch-based (P55) carbon fibres and an epoxy matrix have been studied by using the conventional fragmentation test in conjunction with polarised-light optical microscopy. Raman spectroscopy has also been used to follow stress transfer from the matrix to the fibres for the same fragmentation geometries. The level of fibre/matrix adhesion and mechanisms by which the stress is transfered from the matrix to the fibres has been determined from both the stress birefringence patterns and strain-induced Raman band shifts in the fibres. The values of interfacial shear strength have been determined by means of both the conventional analysis and the Raman technique. It is found that the Raman method gives a much more detailed picture of stress transfer in the test specimens and that the two methods give somewhat different values of the interfacial shear strength. The values of interfacial shear stress have been discussed with respect to fibre surface energy, surface chemistry and surface morphology. It was found that the surface chemical functional groups appear to have no direct correlation with interfacial shear strength. Furthermore, it appears that mechanical interlocking due to surface roughness could contribute to the higher values of interfacial shear strength determined for the PAN-based fibre.     

Behaviors of the "raman spectroscopic signature of life" in single living fission yeast cells under different nutrient, stress, and atmospheric conditions

Time- and space-resolved Raman spectra of mitochondria in single living fission yeast cells have been measured under various nutrient, stress, and atmospheric conditions. A focus is placed on the behavior of the Raman band located at 1602 cm(-1), which sensitively reflects the metabolic activity in mitochondria and which has been called by us the "Raman spectroscopic signature of life". Addition of nutrients increases the intensity of this band by approximately 1.5 times, confirming its correlation with the metabolic activity in mitochondria. The spectra of cells cultured under 100% N(2), 100% O(2), and N(2)/O(2) (V(N2):V(O2) congruent with approximately = 4:1) atmospheres have been measured for both (16)O(2) and (18)O(2). Yeast cells have been found to lose their metabolic activity after the culture under 100% N(2) and 100% O(2) atmospheres. Cells cultured under a N(2)/(16)O(2) ((16)O(2) = 20%) atmosphere show strong "Raman spectroscopic signature of life". No (18)O isotopic shift has been found for the wavenumber 1602 cm(-1), indicating that the origin of this signature is neither O(2) nor an O-containing small molecule. Addition of H(2)O(2) causes a quick decrease of the "Raman spectroscopic signature of life", followed by the cis-trans isomerization in the unsaturated phospholipid chain. The "Raman spectroscopic signature of life" has thus been proved to be a reliable real-time and in vivo indicator for monitoring the metabolic activity in living cells.     

Strain measurement in diacetylene-containing copolymers using Raman spectroscopy

Rigid diacetylene-containing block copolymers are shown to have Raman spectra similar to those of polydiacetylene single crystals. The vibrational frequencies of certain main-chain Raman-active modes of the copolymers are sensitive to deformation which enables strain measurement to be made by following the shift in the Raman band positions. Measurements of the stress concentrations around defects in copolymer specimens during deformation have been carried out using Raman spectroscopy and they have been compared with theoretical analyses of stress concentrations. There is good agreement between the theoretical and experimental measurements and it has been demonstrated that the use of Raman spectroscopy allows the measurement of stress or strain in complex situations for which no theoretical solutions exist.     

Intensities of E. coli nucleic acid Raman spectra excited selectively from whole cells with 251-nm light

Escherichia coli bacteria in the logarithmic growth phase have been investigated by UV resonance Raman spectroscopy. Bacterial whole-cell Raman spectra excited at 251 nm reflect nearly exclusively the nucleic acid composition even though a very large fraction of the bacterial mass is composed of protein. It has been demonstrated that if bacteria are grown under controlled (logarithmic growth) conditions, which give rise to organisms of known average biochemical composition, the intensities of E. coli Raman spectra can be explained quantitatively from the knowledge of component nucleic acid base resonance Raman cross sections.     

Raman spectroscopy of graphite

We present a review of the Raman spectra of graphite from an experimental and theoretical point of view. The disorder-induced Raman bands in this material have been a puzzling Raman problem for almost 30 years. Double-resonant Raman scattering explains their origin as well as the excitation-energy dependence, the overtone spectrum and the difference between Stokes and anti-Stokes scattering. We develop the symmetry-imposed selection rules for double-resonant Raman scattering in graphite and point out misassignments in previously published works. An excellent agreement is found between the graphite phonon dispersion from double-resonant Raman scattering and other experimental methods.     

Preparation and bactericidal properties of silver nanoparticles in aqueous tea leaf extract

Ag nanoparticles 10 to 60 nm in size have been prepared by reducing silver ions in aqueous tea leaf extract. The properties of the nanoparticles have been studied by ultraviolet spectroscopy, atomic absorption, surface-enhanced Raman spectroscopy, and atomic force microscopy. According to the Raman spectroscopy results, the equilibrium of the redox reaction is displaced to an antioxidant form of flavonoids. The presence of silver nanoparticles enhances the antioxidant and bactericidal properties of tea.     

A study on adsorption of acetonitrile on gold nanorods by non-resonant Raman measurements and density functional theory calculations

Adsorption of acetonitrile (Ac) molecules on gold (Au) nanorods has been investigated by Raman spectroscopic measurements and density functional theory (DFT) calculations. DFT calculations provide a valuable insight into the underlying structure of the metal-molecule complex. From the best agreement between the observed and the calculated Raman frequencies and also from other spectroscopic observations, we propose that Ac molecules interact with Au nanorods and form an [Ac+2Au](0)-like complex on the surface of nanostructures. The environmental effect has also been taken into consideration to explain the Raman activity of the complex.     

Defects in individual semiconducting single wall carbon nanotubes: Raman spectroscopic and in situ Raman spectroelectrochemical study

Raman spectroscopy and in situ Raman spectroelectrochemistry have been used to study the influence of defects on the Raman spectra of semiconducting individual single-walled carbon nanotubes (SWCNTs). The defects were created intentionally on part of an originally defect-free individual semiconducting nanotube, which allowed us to analyze how defects influence this particular nanotube. The formation of defects was followed by Raman spectroscopy that showed D band intensity coming from the defective part and no D band intensity coming from the original part of the same nanotube. It is shown that the presence of defects also reduces the intensity of the symmetry-allowed Raman features. Furthermore, the changes to the Raman resonance window upon the introduction of defects are analyzed. It is demonstrated that defects lead to both a broadening of the Raman resonance profile and a decrease in the maximum intensity of the resonance profile. The in situ Raman spectroelectrochemical data show a doping dependence of the Raman features taken from the defective part of the tested SWCNT.     

Nanometer resolution stress measurement of the Si gate using illumination-collection-type scanning near-field Raman spectroscopy with a completely metal-inside-coated pyramidal probe

We have proposed an illumination-collection-type scanning near-field Raman spectroscopy (SNRS) with a completely gold metal-inside-coated (MIC) pyramidal probe without an optical aperture in order to detect the Raman spectra of fine Si devices for local stress measurements. The gold MIC pyramidal probe has been studied to act as a plasmon resonance near-field optical probe with high power using a finite differential time domain (FDTD) simulation and the prototyped SNRS. In the simulation, the propagated optical power can be made available for SNRS. In the experiments, it is clear that the prototyped SNRS enhanced the Si Raman peak signal by plasmon resonance and could measure the Si Raman peak shift by line scanning the Si gate region and the Si active layer. Furthermore, compressive and tensile stresses localized around the Si gate were demonstrated by the Si Raman peak shift with a resolution of about 10 nm. It is clarified that the proposed SNRS has the possibility of detecting the Raman spectra of a local area.     

Compressional behaviour of carbon fibres

Spectroscopic-mechanical studies have been conducted on a range of carbon fibres by bonding single filaments on the top surface of a cantilever beam. Such a loading configuration allows the acquisition of the Raman spectrum of carbon fibres and the derivation of the Raman frequency strain dependence in tension and compression. Strain hardening phenomena in tension and strain softening phenomena in compression were closely observed. The differences in the slopes of the Raman frequency versus applied strain curves in tension and compression respectively, have been used to obtain good estimates of the compression moduli. A method of converting the fibre Raman frequency versus strain data into stress-strain curves in both tension and compression, is demonstrated. Values of fibre stress and fibre modulus at failure in compression compare exceptionally well with corresponding estimates deduced from full composite data. The mode of failure in compression has been found to depend upon the carbon fibre structure. It is demonstrated that certain modifications in the manufacturing technology of PAN-based fibres can lead to fibres which show resistance to catastrophic compressive failure without significant losses in the fibre compressive modulus.     

分布式光纤拉曼放大器研制的进展

对分布式光纤拉曼放大器研究的历史、基本原理、优化设计以及现状和进展进行了讨论.对S波段的色散补偿型分布式光纤拉曼放大器以及采用光纤拉曼激光器作为抽运源,在前向抽运和后向抽运条件下,对5kmDCF-50kmG652光纤色散补偿型分布式光纤拉曼放大器增益光谱和噪声谱进行了研究.设计和制作了光纤光栅的增益平坦滤波器,取得了较好的增益平坦效果.FRA-1型分布式光纤拉曼放大器在校园网进行了应用试验,取得了较好的试验效果.     

Study of a new resin-based composites containing hydroxyapatite filler using Raman and infrared spectroscopy

The degree of conversion of polymeric matrix in hydroxyapatite-containing dental fillings by Raman and infrared spectroscopy has been determined. Resin-based dental composites are one of the most popular filling materials used in dentistry. These light-cured materials are characterized by the value of the degree of conversion, which depends on curing time and influences the quality of obtained dental filling. Distribution of the filler into polymeric matrix, which has a significant impact on the properties of the final product, has been determined by Raman mapping. The applied procedure also has allowed to present the changes of the degree of conversion on the examined surfaces. The results of the study demonstrate the versatility of the Raman spectroscopy as the analytical spectroscopic technique for determining chemical properties of dental fillings and providing insight into their organization at the microstructural level. The obtained degree of conversion values have been compared with data for the commercially available dental fillings characterized by other authors.     

Remote pulsed Raman spectroscopy of inorganic and organic materials to a radial distance of 100 meters

A portable pulsed remote Raman spectroscopy system has been fabricated and tested to 100 m radial distance. The remote Raman system is based on a directly coupled f/2.2 spectrograph with a small (125 mm diameter) telescope and a frequency-doubled Nd:YAG pulsed laser (20 Hz, 532 nm, 25 mJ/pulse) used as the excitation source in a co-axial geometry. The performance of the Raman system is demonstrated by measuring the gated Raman spectra of calcite, sodium phosphate, acetone, and naphthalene. Raman spectra of these materials were recorded with the 532 nm pulsed laser excitation and accumulating the spectra with 600 laser shots (30 s integration time) at 100 m with good signal-to-background ratio. The remote pulsed Raman system can be used for remotely identifying both inorganic and organic materials during daytime or nighttime. The system will be useful for terrestrial applications such as monitoring environmental pollution and for detecting minerals and organic materials such as polycyclic aromatic hydrocarbons (PAHs) on planetary surfaces such as Mars.     

Two-dimensional temperature determination in the exhaust region of a laminar flat-flame burner with linear Raman scattering

For planar temperature measurements in combusting flows, the well-established laser Raman technique has been further developed to provide two-dimensional local resolution. After excitation with a frequency-doubled Nd:YAG laser, the anti-Stokes and the Stokes Raman signals of the vibrational Q branch of molecular N(2) were detected at 473.3 and 607.3 nm, respectively. From the ratio of the two images, two-dimensional temperature distributions have been obtained by application of an analytical function, which was determined from theoretically calculated Raman spectra. Time-averaged measurements have been performed in the exhaust region of an atmospheric-pressure laminar CH(4)/air flat-flame burner for different equivalence ratios. The accuracy and precision of the results are discussed in combination with the prospects for time-resolved single-pulse measurements.