Raman Spectrum Intensity Research Articles

Effects of silver nanoparticles on Raman spectrum and fluorescence enhancement of nano-diamond

The nano-diamond has been a hot topic in the field of nano-science and nanotechnology for its optical properties. Much effort has been devoted to improving the fluorescence and Raman scattering intensity of nitrogen-vacancy (NV) center in nano-diamond by using plasmon resonance effect in sensing area. A combination of Ag nanoparticle and diamond can not only take advantage of the stability and biocompatibility of diamond, but also enhance the local electric field around NV center through the Ag nanoparticles, thereby speeding up the radiation of the fluorescent near the surface of the substrate, improving the strength and stability of the fluorescence, and greatly broadening the application areas of Raman spectroscopy. In this paper, we mix the nano-diamonds with Ag nanoparticles to improve the fluorescence and Raman scattering intensity on the basis of the localized surface plasmon resonance effect. The influences of Ag mass concentration on the Raman spectrum and fluorescence intensity are investigated. The results show that when the concentration of nano-Ag nanoparticles reaches up to 5 wt%, the light intensity becomes saturated, but the concentration further increases up to a value more than 7 wt% the light intensity begins to decline. Then the corresponding radiative transition rate and the fluorescence quantum efficiency are investigated, and based on these researches, influences and mechanism of surface plasmon resonance (SPR) enhancement are discussed thoroughly. We deduced that the fluorescence enhancement is mainly due to the enhanced surface plasmon field caused by transfer of surface plasmon resonance energy and the energy transfer between surface plasmon and excited state of NV centers. When the concentration of Ag nanoparticles reaches an appropriate value, a suitable distance between metal nanoparticles and diamond is obtained, thereby ensuring the strong local electric field forming on the metal surface, accelerating the emitting photons of diamond in the excited state, and also suppressing the transfer of non-radiative energy, eventually leading to the increase of diamond fluorescence emission intensity.

Raman analysis of bilayer graphene film prepared on commercial Cu(0.5 at% Ni) foil

This study reports the Raman analysis of bilayer graphene films prepared on commercial dilute Cu(0.5 at% Ni) foils using atmospheric pressure chemical vapor deposition. A bilayer graphene film obtained on Cu foil is known to have small areas of bilayer (islands) with a significant fraction of non‐Bernal stacking, while that obtained on Cu/Ni is known to grow over a large area with Bernal stacking. In the Raman optical microscope images, a wafer‐scale monolayer and large‐area bilayer graphene films were distinguished and confirmed with Raman spectra intensities ratios of 2D to G peaks. The large‐area part of bilayer graphene film obtained was assisted by Ni surface segregation because Ni has higher methane decomposition rate and carbon solubility compared with Cu. The Raman data suggest a Bernal stacking order in the prepared bilayer graphene film. A four‐point probe sheet resistance of graphene films confirmed a bilayer graphene film sheet resistance distinguished from that of monolayer graphene. A relatively higher Ni surface concentration in Cu(0.5 at% Ni) foil was confirmed with time‐of‐flight secondary ion mass spectrometry. The inhomogeneous distribution of Ni in a foil and the diverse crystallographic surface of a foil (confirmed with proton‐induced X‐ray emission and electron backscatter diffraction, respectively) could be a reason for incomplete wafer‐scale bilayer graphene film. The Ni surface segregation in dilute Cu(0.5 at% Ni) foil has a potential to impact on atmospheric pressure chemical vapor deposition growth of large‐area bilayer graphene film. Copyright © 2015 John Wiley & Sons, Ltd.

Comparative research on the optical properties of three surface patterning ZnO ordered arrays

We fabricate three surface patterning zinc oxide (ZnO) ordered arrays on glass substrates by using nanosphere lithography technique and dc magnetron sputtering technique. The crescent, tube and honeycomb surface morphologies of the samples are observed by scanning electron microscopy. The transmittance, fluorescence and confocal Raman spectra of the sample are measured. Obviously, when the angle between the plume and the substrate is 90°, the honeycomb arrays have a better transmission. Additionally, the PL intensity of honeycomb arrays is superior. With the increasing of the angle between the substrate and the sputtering plume, the fluorescence peak shows blue shift. The Raman peak located at 438 cm− 1 belongs to ZnO E2 (high) mode, which corresponds to the characteristic band of the hexagonal wurtzite phase. The tube arrays have the best Raman spectrum intensity.

Characterization of Breast Cancer Tissue From a Rat Model With and Without Cancer: The Use of Raman Spectroscopy

Micro-Raman spectroscopy was performed on normal and tumor breast tissue of rats. Our results have shown that the strength of the Raman spectra intensity can be useful to differentiate between normal and breast tumor tissues. Also, the Raman fingerprint of the biochemical markers of the tissue makes possible the automatic discrimination and classification between normal and abnormal tissue. For this evaluation, principal component analysis and the generalized linear discriminate analysis were used. From our results, we believe that rat model of breast cancer can be helpful to the understanding of the molecular changes of breast cancer and its early detection.

First Order Raman Scattering in Bulk Bi2S3 and Quantum Dots: Reconsidering Controversial Interpretations

In the present work, the nonresonance and resonance Raman scattering by Bi2S3 quantum dots, with an average size of 2.3 nm and standard deviation of 0.4 nm, is studied. The Raman spectra of a bulk sample, used as reference, also helped to identify recurrent misleading interpretations present in the literature. A blue-shift of 0.58 eV was observed in the band gap of the quantum dots with respect to the bulk value. In nonresonance conditions, the Raman bands of the Bi2S3 quantum dots (those at 186, 236, and 259 cm–1) are asymmetrically broadened, and the intensity of the peak at 259 cm–1 is enhanced, when compared to the bulk reference. In resonance condition, the Raman spectrum intensity of the Bi2S3 nanostructures is enhanced by a factor of ∼26 at 237 cm–1 with respect to the nonresonance case and ∼18 times with respect to that corresponding to its bulk counterpart. The observed results are qualitatively explained in the framework of the microscopic Raman scattering theory of spherical quantum dots.

Significant enhancement of thermoelectric properties and metallization of Al-doped Mg2Si under pressure

We report results of investigations of electronic transport properties and lattice dynamics of Al-doped magnesium silicide (Mg2Si) thermoelectrics at ambient and high pressures to and beyond 15 GPa. High-quality samples of Mg2Si doped with 1 at. % of Al were prepared by spark plasma sintering technique. The samples were extensively examined at ambient pressure conditions by X-ray diffraction studies, Raman spectroscopy, electrical resistivity, magnetoresistance, Hall effect, thermoelectric power (Seebeck effect), and thermal conductivity. A Kondo-like feature in the electrical resistivity curves at low temperatures indicates a possible magnetism in the samples. The absolute values of the thermopower and electrical resistivity, and Raman spectra intensity of Mg2Si:Al dramatically diminished upon room-temperature compression. The calculated thermoelectric power factor of Mg2Si:Al raised with pressure to 2–3 GPa peaking in the maximum the values as high as about 8 × 10−3 W/(K2m) and then gradually decreased with further compression. Raman spectroscopy studies indicated the crossovers near ∼5–7 and ∼11–12 GPa that are likely related to phase transitions. The data gathered suggest that Mg2Si:Al is metallized under moderate pressures between ∼5 and 12 GPa.

Temperature induced changes in resonance Raman spectra intensity of all-trans-β-carotene: Changes in the fundamental, combination and overtone modes

The resonance Raman spectra of the fundamental, combination and overtone modes around the CC and CC stretches of all-trans-β-carotene in 1,2-dichloroethane solution are obtained from the 293K to 83K temperature range. The results indicate that the intensity of the fundamentals in the liquid and solid phases generally increases as the temperature decreases, except for the liquid–solid phase transition, which exhibits a decreasing trend. The Raman intensities ratio between the fundamentals υ1 and υ2, combinations (overtones) and the fundamentals both increases with decreasing temperature. The Raman bandwidths of the CC bonds gradually become narrow as the temperature decreases. These varieties of relative intensity are analyzed using the coherent weakly damped electron–lattice vibration mode, the effective conjugation length mode as well as the theory of electron–phonon interaction in this work.

Raman spectroscopic study of the mineral qingheiite Na2(Mn2+,Mg,Fe2+)2(Al,Fe3+)(PO4)3, a pegmatite phosphate mineral from Santa Ana pegmatite, Argentina

The pegmatite mineral qingheiite Na2(Mn2+,Mg,Fe2+)2(Al,Fe3+)(PO4)3 has been studied by a combination of SEM and EMP, Raman and infrared spectroscopy. The studied sample was collected from the Santa Ana pegmatite, Argentina. The mineral occurs as a primary mineral in lithium bearing pegmatite, in association with beausite and lithiophilite. The Raman spectrum is characterized by a very sharp intense Raman band at 980cm−1 assigned to the PO43- symmetric stretching mode.Multiple Raman bands are observed in the PO43- antisymmetric stretching region, providing evidence for the existence of more than one phosphate unit in the structure of qingheiite and evidence for the reduction in symmetry of the phosphate units. This concept is affirmed by the number of bands in the ν4 and ν2 bending regions. No intensity was observed in the OH stretching region in the Raman spectrum but significant intensity is found in the infrared spectrum. Infrared bands are observed at 2917, 3195, 3414 and 3498cm−1 are assigned to water stretching vibrations. It is suggested that some water is coordinating the metal cations in the structure of qingheiite.

Raman spectrum method for characterization of pull-in voltages of graphene capacitive shunt switches

An approach using Raman spectrum method is reported to measure pull-in voltages of graphene capacitive shunt switches. When the bias excesses the pull-in voltage, the Raman spectrum's intensity largely decreases. Two factors that contribute to the intensity reduction are investigated. Moreover, by monitoring the frequency shift of G peak and 2D band, we are able to detect the pull-in voltage and measure the strain change in graphene beams during switching.

Label-free quantitative detection using porous silicon as optical biosensor

The single-layer porous silicon is prepared by electrochemistry etching method, which is used as an immunosensor for determining recombinant mouse zona pellucida 3 fusion protein (r-mZP3) by Raman spectroscopy analysis at room temperature. The molecule binding increases the effective optical thickness (EOT), and thus the Raman spectrum intensity decreases. The concentration and variation of Raman intensity show a good linear quantitative relation. The excellent sensing performance could open the way to a new family of optical sensors for biological standardization.

Functional mapping of carious enamel in human teeth with Raman microspectroscopy

AbstractWe employed Raman microspectroscopy to measure the Raman spectra of phosphate in sound and carious tooth substance. The peak intensity at 960 cm−1 of the phosphate (PO43−) symmetric stretching vibrational mode (υ1) in sound enamel was stronger than that of sound dentin, which indicated that sound enamel contained more phosphate than sound dentin. Furthermore, the element analysis of phosphate in sound teeth substance, measured using a scanning electron microscope (SEM) equipped with an energy dispersive X‐ray spectroscope (EDX), gave similar results to those of the Raman measurement. In addition, the border between sound enamel and dentin was clearly demonstrated by mapping the image of the Raman spectrum of phosphate. The mapping image of phosphate in the carious enamel region revealed a heterogeneous low Raman spectrum intensity of phosphate in the area surrounding carious enamel; this finding indicates that phosphate had dissolved from the tooth substance in such areas. In contrast with the decrease in the Raman spectrum intensity of phosphate, the intensity of amide I increased mainly in the low‐phosphate area. Although it remains very difficult to clinically identify the accurate border between sound and carious tooth substance, this distinction may be enabled by using the Raman spectrum of carious tooth substance. Copyright © 2008 John Wiley & Sons, Ltd.

Molecular theory of low-frequency Raman spectrum of water in the translational-band region

The depolarized low-frequency Raman spectrum (RS) arising in water in the translational-band (T-band) region, viz. near the frequency ν about 180 cm − 1 , is calculated using an analytical representation of the dipolar autocorrelation function. The proposed model comprises the dimer of H 2O or D 2O molecules, connected by the hydrogen bond (HB) and suffering elastic vibrations along the HB direction. The HB polarizability is assumed to be proportional to the square of the elastic dipole moment and varies in time due to HB longitudinal vibration. The correct frequency of the RS-peak intensity is obtained due to parameterization of the HB force constant k. A contribution to RS due to elastic reorientation of the H-bonded polar molecule is also accounted for. An interplay of these two molecular mechanisms generates, in agreement with the experimental data, two overlapping bands located in the 180 cm − 1 region. The presented calculation also explains the effect of temperature on the Raman spectra in the T-band. The frequency dependence of the RS intensity correlates with the absorption νε″ ( ν) and loss ε″ ( ν) spectra calculated in the T-band region for the same model parameters.

Ab initio MO Calculations on the Structure and Raman and Infrared Spectra of [Al4O2Cl10]2– Oxide in Chloroaluminate Melts

The oxide complexation chemistry in molten tetrachloroaluminate salts and ionic liquids is discussed with respect to what possible structures may be formed in addition to [AlCl4]−: [Al2OCl6]2−, [Al3OCl8]−, [Al2O2Cl4]2−, [Al3O2Cl6]− and [Al4O2Cl10]2−. Ab initio molecular orbital calculations are carried out on these various aluminium chloride and oxochloride ions, in assumed isolated gaseous free ionic state, by use of the Gaussian 03W program at the restricted Hartree-Fock (HF) level and with the 6-31+G(d,p) basis set.Without any pre-assumed symmetries and with tight optimization convergence criteria and by using the modified GDIIS algorithm, the model calculations generally converge. The structures and their binding energies are presented. The expected geometries are supported, with one exception perhaps being the [Al2OCl6]2− ion, that gave a linear Al-O-Al bonding system of staggered AlCl3-groups (approximate D3d symmetry), in analogy to the linear Al-O-Al geometry of the analogous [Al2OF6]2− ion, found previously. The calculations include determination of the vibrational harmonic normal modes and the infrared and Raman spectra (vibrational band wavenumbers and intensities), without any empiric adjustments of the harmonic force constants, using constants directly predicted from the Gaussian 03W program. Previously obtained IR absorption and Raman scattering spectra of melts are assigned, by comparing to the ab initio quantum mechanical vibrational analysis results. It is concluded that the small oxide content commonly found in basic and neutral tetrachloroaluminate melts, most probably consists of [Al4O2Cl10]2− ions, and the vibrational spectra are given.

Influence of a magnetic field on the electronic Raman response in high- Tc cuprates

The effect of a magnetic field parallel to the CuO 2 plane on the Raman spectra is investigated based on the Slave–Boson approach to the t − t′ − J model with a Zeeman field and the random-phase approximation. We find that the Raman spectra intensities in the superconducting (SC) state are suppressed for both the B 1g and the B 2g channels with a slight shift of the peaks position toward lower frequency in the B 1g channel and a negligible shift in the B 2g channel due to the Zeeman splitting. There is a field-induced peak and dip structure at low energy response in the B 2g channel at very low temperature. While rising temperature has a similar effect in reducing the Raman response peak in the superconducting (SC) state, it smears out the field-induced peak and dip structure in the B 2g channel. We compare these results with experiments and give explanations based on the field-induced changes of the density of the superconducting condensate, the momentum distribution of the quasiparticle energy and the scattering rate.

In-situ observation on domain switching of PLZT via Raman spectroscopy

An in-situ and nondestructive technique was proposed and established for the study of domain switching in PLZT ceramics via observation of Raman spectrum changes based on the Raman light scattering principle and the soft mode theory. A Vickers indent was introduced into the polarized PLZT specimen so that the Raman spectrum change associated with the domain switching as induced either by an applied electric field or by a stress field surrounding the tip of the Vickers indent crack was in-situ measured and studied using this established technique. The relation between the domain switching and the measured Raman spectrum was discussed. It is well demonstrated that this technique can sensitively detect and measure the domain switching via the observation of Raman spectrum changes. The results confirm that Raman spectrum intensity is directly attributed to the change of the polarization direction of the incidence and scattered lights with respect to the direction of the average polarization direction of the domain in the polarized specimen. When the two directions are parallel, the induced polarizability tensor of the specimen would be enhanced and give rise to a higher intensity for Raman scattering light.

Amorphization of natrolite and edingtonite at high pressure

Amorphization of natrolite Na 2 [Al 2 Si 3 O 10 ]2H 2 O (Khibiny, Kola Peninsula, Russia) and edingtonite Ba[Al 2 Si 3 O 10 ]4H 2 O (Bohlet, Sweden) was investigated at high pressures up to 11 GPa, using Raman spectroscopy. Natrolite compressed in a non-penetrating medium of methanol-ethanol shows one apparent crystal-to-crystal transition at approximately 3.7 GPa before amorphization. Amorphization, reflected by decrease of Raman spectrum intensity, starts in the pressure range of 6–7 GPa and is completed by ~9 GPa. Amorphized Na 2 [Al 2 Si 3 O 10 ]2H 2 O exhibits partial reversibility to crystalline natrolite after amorphization at ~7-8 GPa and partially recovers its Raman spectrum after release of pressure. It was shown that amorphization of natrolite begins in soft structural units (water sublattice) and finishes in rigid units (T-O bonds). Comparison of natrolite and edingtonite behaviour at high pressures shows that amorphization of both zeolites begins at similar pressures but differ in their crystalline phase transitions. Edingtonite compressed in methanol-ethanol has no crystalline transition at high pressure. Ba[Al 2 Si 3 O 10 ]4H 2 O amorphized after compression up to higher pressure of ~11 GPa also exhibits partial reversibility to edingtonite crystal structure on release of pressure.

A study on Raman scattering cross section of carbon tetrachloride at low concentrations

Using the technique of the liquid-core optical fiber (LCOF), we measured the Raman spectra intensities of CCl4 in CS2 at concentrations ranging from 90 to 0.8% in volume. According to the relative peak area ratios and peak height ratios, two kinds of RSCS values of the 459 cm−1 CCl4 band for each concentration, σR A and σR H, were obtained by using Onsager’s model and the internal standard method. The two kinds of RSCS values and their changing tendencies are in agreement with each other. It is also found that both σR A and σR H increase with decreasing solution concentration. When the concentration is higher than 4%, both of them are flat and linear with the volume concentration of CCl4 in CS2. When the concentration is lower than 4%, they increase rapidly with decreasing concentration. At 0.8% both RSCS values increase to ten times that of the 459 cm−1 band of CCl4 in pure liquid. A tentative theory exploration for the experimental results is given, which introduces dispersion forces into Onsager’s model. Additionally, some likely influencing factors on experimental results, such as numerical aperture (NA) of LCOF and baseline subtraction, were researched.

Application of liquid-core optical fiber in the measurements of Fourier transform Raman spectra

The application of liquid-core optical fiber (LCOF) in the measurement of Fourier transform Raman spectra (FTRS) can enhance the Raman spectra intensity 10 2–10 3 times, and the minimal length of the optical fiber for yielding maximal Raman spectra intensity is the reciprocal of the optical fiber loss coefficient. By using LCOF, β-carotene's 1520 cm −1 Raman line and rhodamine's 1524 cm −1 Raman line were observed in their CS 2 solutions. These two Raman lines come from the π– π ∗ transition of the CC vibration. As β-carotene and rhodamine's concentrations decrease, their Raman lines move to long wavelength (red shift), their linewidths narrow and their molar gain coefficients increase.

NANOVIBR: Parallel codes for semiempirical quantum chemical and harmonic vibration large‐scale calculations

AbstractPackage NANOVIBR is a further development of the NANOPACK software (Int J Quantum Chem 2002, 88, 449) and is dedicated to both semiempirical quantum chemical (QCh) calculations of nano‐sized systems and harmonic vibrational problem solution for several hundred atom systems, with a particular stress on the latter. Sequential codes CLUSTER‐Z1 and CLUSTER‐Z2 form the ground of the package and provide extended QCh calculations of structural and electronic characteristics in the sp‐ and spd‐basis, as well as of force fields, harmonic vibrational frequencies, infrared, and Raman spectra intensities. The combination of fine‐grained (self‐consistent field calculation) and coarse‐grained (Hessian and spectra intensities) regimes of the parallel codes implementation results in a considerable enhancement of the calculation speed‐up. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Impedance study on electrochemical characteristics of sputtered DLC films

Diamond-like carbon (DLC) films with different structure were deposited on highly electrically conductive silicon substrates (SiO 2/Si), using d.c. magnetron sputtering deposition process. Their structure and electrochemical behavior in a 0.5 M H 2SO 4 solution were studied with micro-Raman spectroscopy, electrochemical impedance spectroscopic analysis and film impedance spectroscopy. The combined polarization resistance of silicon coated with DLC film increased to approximately 10 6–10 8 Ω cm 2, while the combined capacitance decreased to 10 −7–10 −8 F cm −2. The double layer capacitance on the DLC films was approximately 0.571–3.91×10 −6 F cm −2, which was smaller than that of popular electrode materials (graphite, platinum and mercury) and comparable with that of diamond. The double layer capacitance increased with the increased Raman spectrum intensity ratio I D/ I G and accelerated at approximately I D/ I G=2.25. These results suggest that the DLC films be good insulating and corrosion protection coatings in sulfuric acid and potential electrode materials for electrochemical analysis.