Raman Wavenumber Shifts Research Articles

The role of symmetry-breaking strains on quartz inclusions in anisotropic hosts: Implications for Raman elastic geobarometry

Raman elastic geobarometry for mineral host-inclusion systems is used to determine the strains acting on an inclusion still entrapped in its host by measuring its Raman wavenumber shifts which are interpreted through the phonon-mode Grüneisen tensors of the inclusion phase. The calculated inclusion strains can then be used in an elastic model to calculate the pressure and temperature conditions of entrapment. This method is applied frequently to host inclusion systems where the host is almost elastically isotropic (e.g. garnet) and the inclusion is elastically anisotropic (e.g. quartz and zircon). In this case, when the entrapment occurs under hydrostatic conditions the host will impose isotropic strains on the inclusion which in turn will develop non-hydrostatic stress. In this scenario the symmetry of the inclusion mineral is preserved and the strains in the inclusion can be measured via Raman spectroscopy using the phonon-mode Grüneisen tensor approach. However, a more complex situation arises when the host-inclusion system is fully anisotropic, such as when a quartz inclusion is entrapped within a zircon host, because the symmetry of the inclusion can be broken due to the external anisotropic strain field imposed on the inclusion by the host, which in turn will modify the phonon modes. We therefore calculated the strain states of quartz inclusions entrapped in zircon hosts in multiple orientations and at various geologically relevant pressure and temperature conditions. We then performed ab initio Hartree-Fock/Density Functional Theory (HF/DFT) simulations on α-quartz in these strain states. These HF/DFT simulations show that the changes in the positions of the Raman modes produced by strains that are expected for symmetry broken quartz inclusions in zircon are generally similar to those that would be seen if the quartz inclusions remained truly trigonal in symmetry. Therefore, the use of the trigonal phonon-mode Grüneisen tensor to determine the inclusion strains does not lead to geologically significant errors in calculated quartz inclusion entrapment pressures in zircon. • Mineral inclusions in anisotropic hosts can be subject to symmetry-breaking strains. • Symmetry-breaking strains modify the Raman spectrum of quartz. • Applicability of the trigonal Grüneisen tensor to symmetry-broken quartz is tested. • Entrapment pressures from the isotropic elastic model are in error by <0.185 GPa. • Entrapment pressures from the anisotropic elastic model are in error by <0.034 GPa.

Polarized Raman spectroscopy-stress relationship considering shear stress effect.

This Letter uses polarized Raman spectroscopy as a "strain rosette" to quantitatively determine all the in-plane components of the stress tensor for (110) silicon. Through polarized Raman spectroscopy, Raman wavenumber shifts can be obtained at the same point with different polarization directions of the incident and/or scattered light. With at least three measured Raman shifts in different polarized directions, the three stress components of a surface that contains two non-equal normal stresses and one shear stress can be calculated accordingly. We develop an analytical and linear Raman wavenumber shift-stress relationship when shear stress is considered. The experimental results verify the theoretical predictions. It shows that the simple stress condition assumption may lead to erroneous results.

Determination of Phonon Deformation Potentials in Carbon-doped Silicon

Background and purpose Carbon-doped silicon (Si:C) is used as a stressor to the channel of n-type MOSFET [1]. However, there are few report directly evaluated the strain states of Si:C. The strain-Raman coefficient that relate Raman shift to in-plane strain has not been derived yet. In this study, we determined the strain-Raman coefficient for Si:C using water-immersion Raman spectroscopy in conjunction with X-ray diffraction (XRD) measurement. Experimental method Si:C films were grown on (001) Si substrate by molecular beam epitaxy. The film thickness were 43, 50 and 37 nm, with C concentration of 0.600%, 0.826% and 1.14% respectively. The film thickness and the C concentration were confirmed by cross section TEM and SIMS measurement, respectively. Raman peak shift was measured by water immersion Raman spectroscopy. For the Raman evaluation, the numerical aperture of the water immersion lens and the refractive index of the medium were 1.2 and 1.3, respectively. The wavelength of the excitation light source and the focal length of the spectrometer were 355 nm and 2000 mm. Here, the penetration depth is approximately 5 nm. All the Raman spectroscopy were performed under the LO-active conditions. The in-plane and out-of-plane strain were measured by XRD. Part of the XRD measurement was performed at SPring-8 using synchrotron radiation as X-ray source. Results and Discussion Figure 1 shows the Raman peak shift obtained from Si:C with various C concentration. The spectra were calibrated with the strain-free single crystalline-Si (c-Si) at 520 cm-1. From Fig. 1, the Raman shift is decreased as the C concentration increases. This reflect the tensile strain is applied to Si:C. Table 1 shows the results of the XRD, and the in-plane and out-of-plane strain in Si:C. Here, ε || and ε ⊥ are the in-plane and out-of-plane strain, respectively. The in-plane and out-of-plane lattice spacing of c-Si is 1.357525 Å. From Table 1, it is clear that the tensile strain is applied to Si:C. This is consistent with the Raman spectroscopy result. There should be a relationship such as the following equation between Raman shift and in-plane strain. ω Si:C = ω Si + ax + bε || (1) Here, ω Si:C and ω Si are the Raman shift of Si:C and Si, x is C concentration, and a and b are the alloy-disorder coefficient and strain-shift coefficient, respectively. In this study, we used the value of a coefficient to be 210 cm-1 to determine b coefficient [2]. From Eq. (1), the in-plane strain ε || can be obtained by the following equation using LO phonon Raman wavenumber shift from the strain-free Raman shift ω 0 Δω LO = ω Si:C – ω 0 = bε ||, (2) ω 0 = ω Si + ax = 520 + 210x. (3) Figure 3 shows Raman wavenumber shift Δω LO as a function of the in-plane strain ε || obtained from the XRD. The dotted line is the linear fit to the experimental data. As shown in Fig. 3, although the C concentration x range is very narrow, we confirmed that the Δω LO shows a linear dependence on the in-plane strain ε ||. Finally, we have succeeded to determine the value of strain-Raman (b) coefficient: b = -539.5 cm-1. Acknowledgements The XRD measurement of 0.600 and 1.06% Si:C was performed at SPring-8 (JASRI) with proposal number of 2015A1971, 2015B1925.

DC and AC Performance of Graphite Films Supercapacitors Prepared by Contact Glow Discharge Electrolysis

In the present work, we fabricate and characterize carbon graphite films by high-voltage cathodic and anodic contact glow discharge electrolysis (CGDE) for supercapacitor applications. Transmission electron microscopy revealed that the carbon films obtained by anodic CGDE, in which a carbon graphite is used as the positive electrode, are in the form of two-dimensional, relatively large lateral size sheets without major fractures or structural distortions. Whereas with the cathodic configuration, tiny and elongated flakes of graphite attached to larger sheets are obtained. We observed negative Raman wavenumber shifts of the G peak and the appearance of the T peak at ca. 1100 cm− 1, which are attributed to thermal-induced strains and structural damages in the graphite crystal lattice, as well as to some C-C sp3 bonds content. In addition to the aforementioned results and optical emission spectroscopy, it is proposed that both formation mechanisms by electrochemical exfoliation and material evaporation occur depending on the used polarization. All-solid-state symmetric supercapacitors using polyvinyl alcohol/H3PO4 as gel electrolyte were fabricated and tested under dc and ac frequencies. We found two different behaviors: at dc and close-to-dc, the material prepared with cathodic CGDE showed close-to-ideal behavior with higher capacitance at different charging/discharging rates, which makes it more suitable for energy storage applications, whereas at higher frequencies ( ⩾ 100 Hz), the material prepared with anodic CGDE performed better for ac filtering applications that has been verified using an inverting integrator circuit.

In-Plane Biaxial Strain Evaluation Induced in Ge1-X Sn x Films Using Oil-Immersion Raman Spectroscopy

Introduction Germanium Tin (GeSn) has a potential to supersede Si as channel material for next generation LSI. The hole mobility of GeSn with 3% Sn concentration is higher than that of pure Ge [1]. Strain or strain relaxation is certainly induced in the channel region through the device process. In addition, it is well known that carrier mobility is varied by the strain. Therefore, we believe that it is important to evaluate the precise strain states. In our previous reports, we have evaluated the anisotropic strain in Si and Si1-x Ge x using oil-immersion Raman spectroscopy, which can excite both longitudinal optical (LO) mode and transverse optical (TO) mode. In this study, we evaluated the in-plane biaxial strain induced in Ge1-x Sn x films using oil-immersion Raman spectroscopy. Experiment We evaluated the strain induced in the Ge1-x Sn x films which were epitaxially grown on (001) Ge substrate by the metal-organic chemical vapor deposition (MOCVD) [2]. Sn concentrations in Ge1-x Sn x films were 1.8, 2.2, and 3.2%, respectively, which were defined by Rutherford backscattering spectrometry. From transmission electron microscopy measurements, thicknesses of Ge1-x Sn x films were 104, 17, and 34 nm, respectively. In the oil-immersion Raman spectroscopy, the excitation light with wavelength of 532 nm irradiated the Ge1-x Sn x films under the conventional (001) backscattering configuration. The light path was immersed by the high refractive index oil. The numerical aperture (NA) of the immersion lens and refractive index of the oil were 1.4 and 1.5, respectively. In the XRD measurements, synchrotron radiation was used for the X-ray source with the energy of 10 or 12 keV. Out-of-plane strain εL in the Ge1-x Sn x films was measured from 004 diffraction. Results and discussion Fig. 1 shows the LO and TO mode Raman spectra from the GeSn0.018 film. These spectra were calibrated by the strain free bulk Ge peak at 300 cm-1. From Raman spectroscopy and XRD results, we derived phonon deformation potentials (PDPs) of the strained Ge1-x Sn x , which is indispensable to evaluate stress. The PDPs (p and q) can be derived by solving equation 1, where Δω, ω0, εL, and ε|| are Raman wavenumber shift, strain-free Raman shift, in-plane strain, and out-of-plane strain, respectively. The derived p and q were plotted in figure 2. In this figure, p and q for pure Ge (x=0) are reported by S. C. Jain et al. [3]. As shown in this figure, the p and q suggest almost constant for the Ge1-x Sn x (x < 0.032). Using the derived PDPs, we calculated the anisotropic stresses (σ xx and σ yy ) induced in Ge1-x Sn x films. As a result, we obtained σ xx = -0.40 and σ yy = -0.40 GPa for the strained GeSn0.018, σ xx = -0.47 and σ yy = -0.47 GPa for the strained GeSn0.022, and σ xx = -0.68 and σ yy = -0.68 GPa for the strained GeSn0.032. From these results, we can confirm that the stresses induced in Ge1-x Sn x films were almost isotropic states. In this work, the PDPs for Ge1-x Sn x were derived for the first time. Acknowledgements This study was partially supported by the Japan Society for the Promotion of Science through a Grant-in-Aid for Science Research B (No. 24360125). XRD measurements were performed at BL19B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Nos. 2014B1613, 2014B1892, 2015A1971, 2015B1925, and 2016A1529).

(Invited) Anisotropoic Strain Evaluation in the Finite Si Area by Surface Plasmon Enhanced Raman Spectroscopy

Introduction The strain in the channel of a transistor can enhance carrier mobility. The strain state is complicated because the channel is affected by the various components. Raman spectroscopy has been performed for the strain evaluation in Si owing to high-strain sensitivity and high-spatial resolution [1]. However, it is difficult to evaluate the complicated strain state using conventional Raman. In this study, Raman spectroscopy using z-polar light excitation was performed in order to evaluate anisotropic biaxial strain states in the finite Si area. Experiment Two types of strained Si substrates, strained Si on insulator (SSOI) as shown by the TEM image in the inset of Fig. 1, and strained-Si followed by SiGe on insulator (SGOI) as shown in the inset of Fig. 2, were used as the samples. The Si substrate with the line-and-space pattered SiN film was also used for the strain evaluation in the finite Si area. The space widths were varied from 5.0 to 0.6 mm.The excitation light component perpendicular to the surface, i.e., z-polarization, were achieved by oil immersion Raman with high-NA objective lens or surface enhanced Raman spectroscopy (SERS) with Ag particle on the sample surface. The z-polar light excitation allows the excitation of the transverse optical (TO) phonon as well as longitudinal optical (LO) phonon [2]. The relationship between the Raman wavenumber shifts Dw LO and Dw TO and biaxial stresses were expressed by the following equation (1) (The coordinate is defined: x: [110], y: [1(_)10], and z: [001]) [3].In the experiment, the 532 nm laser and the oil-immersion lens were used. The numerical aperture and refractive index of oil were 1.4 and 1.5, respectively. Results and Discussion Figure 1 shows the oil-immersion Raman spectra from SSOI in the LO and TO active conditions. Although the peak positions originating in the Si substrate are the same, the peak positions originating in the strained Si layer are different each other. This result shows the excitation of the TO phonon. Figure 2 shows the Raman spectra from the strained Si on SGOI with SERS (w/ Ag) and the oil-imersion (w/o Ag) conditions. It should be noticed that the intensity ratio of the strained Si peak around 515 cm- 1 to the Si substrate peak at 520 cm- 1 increased in the SERS condition. Furthermore, the line width of the strained Si peak in the SERS conditions was broadened. This was caused by the strong excitation of the TO phonon owing to the depolarization. The electrical field component ratios were calculated by finite-difference time-domain method [4]. From the calculation, the value of the z-polarization was the highest for the SERS conditions among the SERS, oil-immersion, and dry conditions, as shown in Table 1. Figure 3(a) shows the wavenumber shifts of TO and LO phonons from the Si substrate with the L&S pattered SiN film as a function of the space width obtained by SERS. Using the above equation, the biaxial stresses s xx and s yy were calculated, as shown in Fig. 3(b). s xx perpendicular to the pattern increased with the decrease in the space width, while s yy parallel to the pattern remained in the low value. The biaxial stress states were able to be evaluated efficiently by using the SERS technique. Acknowledgement This study was partially supported by the Semiconductor Technology Academic Research Center (STARC), the Japan Society for the Promotion of Science through a Grant-in-Aid for Scientific Research B (No. 24360125), and the Japan Science and Technology Agency through the Adaptable and Seamless Technology transfer Program (A-STEP) through target-driven R&D.

Nanoscale Probing of Thermal, Stress, and Optical Fields under Near-Field Laser Heating

Micro/nanoparticle induced near-field laser ultra-focusing and heating has been widely used in laser-assisted nanopatterning and nanolithography to pattern nanoscale features on a large-area substrate. Knowledge of the temperature and stress in the nanoscale near-field heating region is critical for process control and optimization. At present, probing of the nanoscale temperature, stress, and optical fields remains a great challenge since the heating area is very small (∼100 nm or less) and not immediately accessible for sensing. In this work, we report the first experimental study on nanoscale mapping of particle-induced thermal, stress, and optical fields by using a single laser for both near-field excitation and Raman probing. The mapping results based on Raman intensity variation, wavenumber shift, and linewidth broadening all give consistent conjugated thermal, stress, and near-field focusing effects at a 20 nm resolution (<λ/26, λ = 32 nm). Nanoscale mapping of near-field effects of particles from 1210 down to 160 nm demonstrates the strong capacity of such a technique. By developing a new strategy for physical analysis, we have de-conjugated the effects of temperature, stress, and near-field focusing from the Raman mapping. The temperature rise and stress in the nanoscale heating region is evaluated at different energy levels. High-fidelity electromagnetic and temperature field simulation is conducted to accurately interpret the experimental results.

Ultraviolet Raman scattering in ZnO nanowires: quasimode mixing and temperature effects

AbstractWe use near‐resonance Raman scattering to investigate zinc oxide (ZnO) nanowires grown by chemical vapor deposition on Si substrates. We discuss the role of quasimode mixing on the wavenumber of the longitudinal optical (LO) bands, and we perform Raman measurements with different excitation powers to investigate possible laser heating effects. We find that in the Raman spectra of as‐deposited nanowires grown along the c‐axis of wurtzite, the LO bands are located slightly below the E1(LO) mode of bulk ZnO. We perform a calculation of the expected LO wavenumber in an ensemble of randomly oriented nanowires. Our analysis shows that light refraction, together with the orientation‐dependent cross‐section of the nanowires for the incoming light, counterbalances quasimode mixing effects in the as‐grown product, giving rise to LO bands that are barely redshifted relative to the E1(LO) mode. In the case of ZnO nanowires that have been mechanically removed (scratched) and subsequently deposited onto separate Si substrates, we observe clear laser‐induced heating. Temperature effects account well for the Raman wavenumber shifts displayed by the LO bands in the Raman spectra of the scratched nanowires. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Radiation damage and uranium concentration in zircon as assessed by Raman spectroscopy and neutron irradiation

Radiation damage of natural and synthetic zircon grains is evaluated by Raman spectroscopy to understand annealing and stability of fission tracks. Analyses focus on a suite of 338 Paleozoic detrital zircon grains from metamorphosed strata in the Hellenic forearc that were variably annealed by a Miocene thermal event, as well as a suite of 97 synthetic zircon grains. The Raman wavenumber shift of ν 3 [SiO 4 ] reveals that radiation damage and damage distribution in this suite mainly depends on uranium concentration. In zircon with similar uranium concentration, the Raman wavenumber shift allows for the determination of radiation damage in different crystals, which is a function of effective accumulation time. Nine detrital zircons grains with moderate radiation damage were stepwise annealed at 1000 and 1400 °C, which resulted in progressive removal of radiation damage revealed in an increase of ν 3 [SiO 4 ] peak positions. For a partly reset sample that was brought to temperatures of ~350 °C in a geologic setting (Hellenic forearc), we use the Raman measurements and uranium determination to estimate a Zircon Damage Discrimination Factor (Z RDD ), which is our attempt to estimate only radiation damage in single grains by accounting for affects of the uranium atom in the Raman wavenumber. This discrimination allows for a separation of zircon fission track (ZFT) ages of single ages based on grains that have a low track retention (high damage, fully reset grain), thus refining the age determination of cooling in a rock that shows variable resetting.

High‐pressure Brillouin study of the elastic properties of rare‐gas solid xenon at pressures up to 45 GPa

AbstractThe pressure dependences of three adiabatic elastic constants, adiabatic bulk modulus, refractive index, and elastic anisotropy, as well as Cauchy deviation of fcc solid Xe have been determined up to 10 GPa at 296 K by high‐pressure Brillouin scattering spectroscopy. The characteristics of elastic properties at high pressure of rare‐gas solid Xe are investigated by comparison with the previous studies on Ne, Ar, and Kr. Above 10 GPa, the occurrence of splitting in the Brillouin signals and the direction dependence of acoustic velocities for solid Xe clearly show partial phase transformation to the hcp structure reported by the previous X‐ray diffraction and Raman scattering studies. The shear elastic modulus in the hcp phase of solid Xe has also been estimated at pressures up to 45 GPa by using the pressure dependence of the Raman wavenumber shift for the E2g mode. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Raman spectroscopy of a hydrated CO 2/water composite

Formation of a sinking carbon dioxide (CO 2) hydrate composite has been investigated as an alternative to direct liquid CO 2 injection and pure CO 2 hydrate formation for ocean carbon sequestration. Raman spectroscopy of the CO 2 hydrate composite was also performed to determine the presence of various components in the composite produced by the co-injection of liquid CO 2 and water. This work is focused on the formation and spectroscopy of a semi-solid sinking CO 2 hydrate composite formed using a co-flow injector in 72-liter and 0.45-liter pressurized vessels at pressure and temperature conditions equivalent to approximately 1.3-km depth in the ocean. The Raman wavenumber shifts (Δcm − 1 ) corresponding to CO 2 and water molecules as well as shifts in Raman peak positions due to different CO 2 phases were obtained. The Raman spectra of the composite showed that both liquid and hydrate phases of CO 2 are present. The dissolution rate of CO 2 hydrate composite in water was also studied. An attempt was made to calculate the hydration number for the CO 2 hydrate composite and also the percentage of liquid CO 2 and water loss during formation.

The RAMANITA © method for non-destructive and in situ semi-quantitative chemical analysis of mineral solid-solutions by multidimensional calibration of Raman wavenumber shifts

The “RAMANITA ©” method, for semi-quantitative chemical analysis of mineral solid-solutions by multidimensional calibration of Raman wavenumber shifts and mathematical calculation by simultaneous equations, is published here in detail in English for the first time. It was conceived by the present writer 20 years ago for binary and ternary pyroxene and garnet systems. The mathematical description was set out in 1989, but in an abstract in an obscure French special publication. Detailed “step-by-step” calibration of two garnet ternaries, followed by their linking, by M. Pinet and D.C. Smith in the early 1990s provided a hexary garnet database. Much later, using this garnet database, which forms part of his personal database called RAMANITA ©, the present writer began to develop the method by improving the terminology, automating the calculations, discussing problems and experimenting with different real chemical problems in archaeometry. Although this RAMANITA © method has been very briefly mentioned in two recent books, the necessary full mathematical explanation is given only here. The method will find application in any study which requires obtaining a non-destructive semi-quantitative chemical analysis from mineral solid solutions that cannot be analysed by any destructive analytical method, in particular for archaeological, geological or extraterrestrial research projects, e.g. - from gemstones or other crystalline artworks of the cultural heritage (especially by Mobile Raman Microscopy (MRM)) in situ in museums or at archaeological sites, including under water for subaquatic archaeometry; - from scientifically precious mineral microinclusions (such as garnet or pyroxene within diamond); - from minerals in rocks analysed in situ on planetary bodies by a rover (especially “at distance” by telescopy). Recently some other workers have begun deducing chemical compositions from Raman wavenumber shifts in multivariate chemical space, but the philosophical approach is quite different.

Coupled effects of bombarding ions energy on the microstructure and stress level of RFPECVD a-C:H films: correlation with Raman spectroscopy

In this work a-C:H films have been prepared in a capacitively coupled RF-PECVD device ( ν=13.56 MHz) from methane as the gas source. By the use of ERDA, IRTF and X-Ray reflectometry techniques, we have first investigated the structural evolutions of the films as a function of the ion energy. In the second part, we have measured mechanical properties (hardness and Young's modulus) by nanoindentation. Concerning the stress level, according to Stoney's equation, the magnitude of the internal stress has been determined by substrates deflection measurements: this finally leads to a quantification of the adhesion through the calculation of the interfacial fracture energy (G ic). Raman spectroscopy has been used as a probe of both film quality and mechanical properties. The position of the G band is correlated with the sp 3 carbon content and the stress level. One observes that the G peak position moves to high frequencies when the ion energy increases, indicating a graphitization of the samples. The relationship linking the Raman wavenumber shift to stress is discussed.

Physical chemistry and mechanical imaging of ceramic-fibre-reinforced ceramic- or metal-matrix composites

Raman (micro)spectrometry allows the study of the non-metallic phases of ceramic- or metal-matrix composites at the micrometer scale. The three examples that are given concern a mullite-matrix composite reinforced by the Nippon Carbon NLM-202™ SiC fibre, an alumina-matrix composite reinforced by a Saphikon™ monocrystalline α-Al 2O 3 fibre and a Textron SCS-6™ fibre-reinforced Ti6242 matrix composite. Physical and chemical evolution of the SCS-6 fibre within the matrix is discussed. A comparison is made between residual thermal stresses estimated from the thermal expansion coefficients of the fibres and matrices and the values obtained from Raman wavenumber shifts.

Cryogenic Raman spectroscopy of glycerol

In situ Raman spectra of glycerol in the spectral range 3700–300 cm−1 were obtained at 298, 223 and 77 K using a Raman microprobe. Comparative polarization Raman spectroscopy followed by band component analysis of glycerol at 298 both and 223 K were employed for band assignment. In addition to the documentary information from glycerol-related compounds, the polarization analysis (interpreted mostly from intensity changes) and the Raman wavenumber shifts registered upon cooling glycerol were the criteria used for these assignments. In the high-wavenumber region (3700–2500 cm−1) the bands at 3407, 3240, 2946, 2886 and 2763 cm−1 undergo a significant cryogenic shift to lower wavenumbers. The first two bands are assigned to antisymmetric and symmetric OH stretches, respectively, and the last three bands to CH stretching vibrations. These Raman shifts are related to intermolecular hydrogen-bond displacements upon cooling glycerol from room temperature. Below 1500 cm−1, the assignment of Raman bands is more complicated because many vibrations are coupled. Cryogenic shifts to higher wavenumbers are observed mainly for the lines attributed to the COH deformation (1342 cm−1), CCO vibration modes (1054 and 1115 cm−1) and CH2 rocks (976 and 925 cm−1). The peak at 673 cm−1 arising from a bending vibration also shifts to a higher wavenumbers on cooling. The Raman shifts are well interpreted as an effect of cooling on H-bond strengthening in glycerol. Copyright © 2000 John Wiley & Sons, Ltd.

Determination of molecular changes in soft tissues under strain using laser Raman microscopy

The paper presents a non-contact technique to examine the molecular changes in a collagen fibre subjected to in vitro axial tension. Laser Raman microscopy was employed to monitor the vibrational changes in specific assignments of the Raman spectrum of collagen. Results were presented in the form of Raman wavenumber shift as a function of applied tensile strain. Two distinct reponses were observed depending on whether the vibrations were axial to, or normal to, the collagen backbone. The former response produced a decrease in wavenumber values, indicating tension, whereas the latter produced an increase, indicating compression. The rate of wavenumber shift with applied strain was non-linear in form, with a marked increase at higher levels of applied strain, for example, a strain 4% in the case of axial vibrations. This technique can prove to be a powerful tool for examining deformation at the molecular level in collagenous tissues.

Cryogenic Raman spectroscopy of glycerol

In situ Raman spectra of glycerol in the spectral range 3700-300 cm were obtained at 298, 223 and 77 K using a Raman microprobe. Comparative polarization Raman spectroscopy followed by band component analysis of glycerol at 298 both and 223 K were employed for band assignment. In addition to the documentary information from glycerol-related compounds, the polarization analysis (interpreted mostly from intensity changes) and the Raman wavenumber shifts registered upon cooling glycerol were the criteria used for these assignments. In the high-wavenumber region (3700-2500 cm) the bands at 3407, 3240, 2946, 2886 and 2763 cm undergo a significant cryogenic shift to lower wavenumbers. The first two bands are assigned to antisymmetric and symmetric OH stretches, respectively, and the last three bands to CH stretching vibrations. These Raman shifts are related to intermolecular hydrogen-bond displacements upon cooling glycerol from room temperature. Below 1500 cm, the assignment of Raman bands is more complicated because many vibrations are coupled. Cryogenic shifts to higher wavenumbers are observed mainly for the lines attributed to the COH deformation (1342 cm), CCO vibration modes (1054 and 1115 cm) and CH rocks (976 and 925 cm). The peak at 673 cm arising from a bending vibration also shifts to a higher wavenumbers on cooling. The Raman shifts are well interpreted as an effect of cooling on H-bond strengthening in glycerol.

Relationships Among Solvent Softness Scales

Quantitative measures of solvent softness, in the sense of Pearson's hard-soft acid-base (HSAB) concept, are considered using three scales: the μ scale, based on the Gibbs energies of transfer of selected ions, the Raman wavenumber shift of HgBr2 (the Ds scale), and the difference between the IR wavenumber shift of the C-I stretch of ICN and the O-H stretch of phenol. Raman and IR band shifts have been measured for a number of solvents for the neat ones (Raman) and in CCl4 solution (IR). Good linear correlations between the three scales are obtained that permit the prediction of the softness of a wide range of solvents. A number of anomalies encountered are discussed.

New approaches in the characterization of surface-enhanced Raman scattering-active substrates

This paper develops new approaches to characterize the morphology of silver and gold colloids used as substrates underlying surface-enhanced Raman scattering (SERS). Since both electromagnetic and chemical SERS theories predict that the Raman enhancement depends strongly on surface roughness features, a better understanding of the SERS spectra and an optimization of the enhancement factor require the knowledge of the size and shape distributions of the particles and clusters of the metal sols. For this purpose, we have investigated two in situ techniques. The first deals with the mechanical vibration band (also called acoustic mode) of the metallic particles of the colloidal sols; this band can be observed at very low Raman wavenumber shifts (approximately 10 cm-1) provide it is enhanced by surface plasmon resonance excitation. The experiments on these acoustic modes were carried out on silver and gold colloids, at several laser excitation wavelengths and in the presence of various polarizable molecules (pyridine, acridine, benzoic acid) or halide ions. Since the wavenumber and the shape of these acoustic bands are related to the morphology of the colloidal particles, a previously developed model was used which permits the calculation of the acoustic mode profiles, to approach the size and shape distributions of the roughness features giving rise to the SERS enhancement. Since extinction, scattering and absorption bands of metal colloids arise from surface plasmon resonance excitation, UV–visible spectroscopy is also a powerful tool for analyzing the optical properties of colloids. From the observed extinction profiles of silver and gold colloids, aggregated with the same probe molecules as those used in the low Raman wavenumber scattering experiments, attempts were made to obtain the size and/or the shape distributions of the various aggregates. The comparison between the distributions deduced from both of the above-mentioned methods along with those obtained by transmission electron microscopy (TEM) suggests that the particles or clusters at the origin of the SERS effect are sized over several orders of magnitude. It is therefore concluded that the SERS effect arises mainly from the resonance of plasmon eigenmodes of small protrusions coupled over regions smaller than the visible wavelength. © 1998 John Wiley & Sons, Ltd.

New approaches in the characterization of surface‐enhanced Raman scattering‐active substrates

This paper develops new approaches to characterize the morphology of silver and gold colloids used as substrates underlying surface-enhanced Raman scattering (SERS). Since both electromagnetic and chemical SERS theories predict that the Raman enhancement depends strongly on surface roughness features, a better understanding of the SERS spectra and an optimization of the enhancement factor require the knowledge of the size and shape distributions of the particles and clusters of the metal sols. For this purpose, we have investigated two in situ techniques. The first deals with the mechanical vibration band (also called acoustic mode) of the metallic particles of the colloidal sols; this band can be observed at very low Raman wavenumber shifts (approximately 10 cm-1) provide it is enhanced by surface plasmon resonance excitation. The experiments on these acoustic modes were carried out on silver and gold colloids, at several laser excitation wavelengths and in the presence of various polarizable molecules (pyridine, acridine, benzoic acid) or halide ions. Since the wavenumber and the shape of these acoustic bands are related to the morphology of the colloidal particles, a previously developed model was used which permits the calculation of the acoustic mode profiles, to approach the size and shape distributions of the roughness features giving rise to the SERS enhancement. Since extinction, scattering and absorption bands of metal colloids arise from surface plasmon resonance excitation, UV–visible spectroscopy is also a powerful tool for analyzing the optical properties of colloids. From the observed extinction profiles of silver and gold colloids, aggregated with the same probe molecules as those used in the low Raman wavenumber scattering experiments, attempts were made to obtain the size and/or the shape distributions of the various aggregates. The comparison between the distributions deduced from both of the above-mentioned methods along with those obtained by transmission electron microscopy (TEM) suggests that the particles or clusters at the origin of the SERS effect are sized over several orders of magnitude. It is therefore concluded that the SERS effect arises mainly from the resonance of plasmon eigenmodes of small protrusions coupled over regions smaller than the visible wavelength. © 1998 John Wiley & Sons, Ltd.