Laser Raman Microscopy Research Articles

From black-and-white to colour in the Silurian

Ironstones and iron-rich limestones regularly occur as components of time-specific intervals of the Palaeozoic as well as in younger times (Brett et al., 2012--this issue). Silurian sediments deposited at high latitudes along the peri-Gondwana border are characterized by black and white limestone and graptolitic shale sequences. Those in the Carnic Alps (southern Austria) additionally contain colourful pink to red limestones and ironstones. Laminated structures such as the (ferruginous)-coatings around skeletal fragments (mostly trilobites and some cephalopods and echinoderms) and stromatolitic features along discontinuity surfaces display dark red, green, white and brownish colours due to the presence of goethite, magnetite, hematite, chamosite, calcite and subordinate apatite. Confocal laser Raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceous matter associated with fossilized microbial structures in the form of stromatolites, filaments and coccoids, suggesting a microbial role in the colouring of the Silurian world of the Carnic Alps. Iron concentrations up to 30× that of matrix and surrounding non-ferruginous rocks suggest blooms of iron microbe activity in response to the time-specific occurrence of chemically charged sea water during global biotic events.

Effect of laser irradiation on the stability of a photo-sensitive active pharmaceutical ingredient by Raman microscopy

This study was conducted to investigate the effect of laser beam irradiation from a novel non-confocal laser Raman microscope on the stability of a photo-sensitive drug. The non-confocal Raman microscopy, which irradiates a low-power unfocused laser beam on the surface of the samples by controlling of optical system, was applied to characterize the stability of nifedipine as a photo-sensitive drug model. The time-dependent changes in the Raman spectra of nifedipine were monitored in order to evaluate the degradation of nifedipine during laser irradiation. The results were compared with the Raman spectra measured by using the confocal laser Raman microscopy which irradiates a low-power focused laser beam. The intensity of some peaks in the confocal Raman spectra significantly decreased depending on the irradiation-time length, compared to the non-confocal Raman macroscopic analysis. The photodegradation of nifedipine caused by the laser irradiation followed the first-order kinetics. The degradation rate constants of nifedipine with the non-confocal analysis were lower than those of nifedipine with the confocal analysis. Thus, the novel non-confocal laser Raman microscopy can be applied to reduce the degradation of the photo-sensitive drug during laser irradiation, and the results suggest that the non-confocal laser Raman microscopy will be a useful technique for the measuring of Raman spectra of photo-sensitive materials with a long-term exposure.

In situ investigation of the microstructure of KGd(WO4)2 crystal growth boundary layer by confocal laser Raman microscopy

The microstructure of the solution near the crystal–solution interface is important for understanding the crystal growth mechanism. The microstructure of KGd(WO4)2 crystal growth boundary layer was studied in situ by confocal laser Raman microscopy. The experimental results show that a free WO4 tetrahedron is the basic structural unit in KGd(WO4)2–K2W2O7 high temperature solution, and distorted WO6 octahedron, WOW and WOOW oxygen bridge bonds begin to appear and increase in concentration with the positions moving towards the crystal–solution interface. Meanwhile, a quasi-ordered boundary layer with the thickness of 50–70 μm was found near the interface. A growth mechanism of structural evolution was proposed in the boundary layer, where free WO4 tetrahedra are transformed into distorted WO6 octahedral long chain structures by forming the WOW and WOOW oxygen bridge bonds. According to the growth mechanism, the KGd(WO4)2 crystal growth behaviour can be understood very well.

Confocal volume in laser Raman microscopy depth profiling

To clarify the degradation of confocality in laser Raman microscopy depth profiling (optical sectioning) and the influence of pinhole filtering on it, we investigate the confocal volume in detail based on Gaussian beam optics and scalar wave optics. Theoretical depth profiles of a homogeneous transparent sample for four different pinhole sizes, which are computed using the measured incident beam waist radius w0 and only a few optical system specific parameters such as a numerical aperture (NA) and a focal length, show a good agreement with the corresponding measured depth profiles. The computed confocal volume demonstrates that the pinhole size affects the actual probe depth as well as the axial resolution and the total intensity loss.

The Nondestructive Identification of Printing Pigments in Bank Notes Issued by Yantai XiGongshun, the Republic of China

Two kinds of bank note issued by YanTai XiGongShun, the Republic of China, are collected by Laboratory of Printing History, School of Printing and Packaging Engineering, Beijing Institute of Graphic Communication. The colors on these bank notes are bright and the patterns and signs can be easily recognized. All bank notes are of the elongated shape, and are printed with bank name, par value, circulation area, anti-counterfeiting characters and decorative pictures in the front of the bank notes. The two colors on these bank notes were analyzed using laser Raman microscopy, and the results showed that the red, blue and green pigments are cinnabar, Lapis lazuli, respectively.

Analysis of the surface structure of DNA/polycation/hyaluronic acid ternary complex by Raman microscopy

We have developed a new type of ternary gene transfection system comprising plasmid, polyethyleneimine, and hyaluronic acid (HA). HA recharged the positively charged DNA complexes into negative, and diminished the adverse interactions with bio-components. HA also improved the transcription efficiency, stabilized the dispersion, and protected the particles against lyophilizing induced inactivation. It enabled the preparation of very small complex particles, which showed high in vivo gene expression. In spite of the many attractive properties of the ternary complex systems, their detailed structure is still not clear. In this study, surface structures of the complexes were analyzed by non-confocal laser Raman microscopy. The correlation between the ζ-potential and the Raman spectrum is discussed. The DNA complex that showed the highest gene-expression level was prepared at the mixing ratio of COOH/NH = 0.5. At this ratio, all the amino groups were just protonated, and the surface was completely covered by HA attributed to the reduced nonspecific interaction of the complex in which all the amino groups have already interacted with carboxyls of HA, but not too much HA on the surface taken up by the cells.

Effect of fatigue on the interface integrity of unidirectional C f-reinforced epoxy resin composites

The current study reports on the fatigue behaviour, micromechanics of reinforcement and stress transfer efficiency of the interface of an autoclave-processed C f-epoxy laminate. Throughout fatigue loading at a maximum strain below the critical fatigue limit of the matrix material, testing was interrupted at discrete fatigue levels of 10 0, 10 3, 10 4 and 10 5 cycles to allow for laser Raman microscopy measurements of the axial stresses developing along natural and induced discontinuities on fibres in the composite. The established axial stress profiles were regressed to establish the corresponding interfacial shear stress (ISS) profiles at each fatigue level. The effect of fatigue on the stress transfer efficiency of the interface was calculated through the evolution of three interfacial performance parameters (maximum ISS, length required for its attainment and transfer length) as a function of loading cycles. Additional measurements on “random” locations helped identify the main damage mechanisms developing at the microscale.

Combined use of confocal laser scanning microscopy (CLSM) and Raman microscopy (RM): Investigations on EPS – Matrix

Confocal laser scanning microscopy (CLSM) was applied in combination with Raman microscopy (RM) for the characterization of heterotrophic biofilms. Compared to CLSM, RM allows for a deeper insight into the chemical structure of extracellular polymeric substances (EPS) of the biofilm matrix. A low load of glucose (2 g m −2 d −1) was applied as substrate to ensure small growth rates of the heterotrophic biofilm. To investigate the influence of hydrodynamic conditions on the chemical composition of EPS, a three funnel flow system was used, wherein biofilms were grown at Reynolds numbers of 1000, 2500 and 4000, respectively. 31 and 92 days after inoculation with activated sludge supernatant RM was applied as an additional technique to standard CLSM measurements for a more detailed analysis of the biofilm matrix. Polysaccharide-related Raman bands are in good agreement with the lectin binding analysis from CLSM. For the older biofilm, lectin binding analysis showed no change in the composition of EPS, whereas Raman spectra pointed out a change of EPS composition from predominantly polysaccharides to predominantly (glyco) proteins. For the applied substrate condition no significant influence of the Reynolds number on the chemical properties was observed.

Influence of Yttrium Ion-Implantation on the Growth Kinetics and Micro-Structure of NiO Oxide Film

Isothermal and cyclic oxidation behaviours of pure and yttrium-implanted nickel were studied at 1000°C in air. Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the micro-morphology and structure of oxide scales formed on the nickel substrate. It was found that Y-implantation significantly improved the anti-oxidation ability of nickel in both isothermal and cyclic oxidizing experiments. Laser Raman microscopy was also used to study the stress status of oxide scales formed on nickel with and without yttrium. The main reason for the improvement in anti-oxidation of nickel was that Y-implantation greatly reduced the growing speed and grain size of NiO. This fine-grained NiO oxide film might have better high temperature plasticity and could relieve parts of compressive stress by means of creeping, and maintained a ridge character and a relatively low internal stress level. Hence yttrium ion-implantation remarkably enhanced the adhesion of protective NiO oxide scale formed on the nickel substrate.

Lithiated MoO3 Nanobelts with Greatly Improved Performance for Lithium Batteries

Recently, nanostructured materials have attracted great interest in the field of lithium-ion batteries, essentially because of their substantial advantages, such as short transport path lengths for both electrons and Li ions, a large amount of contact surface area between the electrode and electrolyte, and large flexibility and toughness for accommodating strain introduced by Li insertion/extraction. Among the transition-metal oxides, nanostructured MoO3 has been extensively investigated as a key material for fundamental research and technological applications in optical devices, smart windows, catalysts, sensors, lubricants, and electrochemical storage. There are two basic polytypes of MoO3: orthorhombic MoO3 (a-type) being a thermodynamically stable phase, and the metastable monoclinic MoO3 (b-type) with a ReO3-type structure. The most important structural characteristic of a-MoO3 is its structural anisotropy, which can be considered as a layered structure parallel to (010) (See the inset of Fig. S1, Supporting Information). Each layer is composed of two sub-layers, each of which is formed by corner-sharing octahedra along [001] and [100]; the two sub-layers stack together by sharing the edges of the octahedra along [001]. An alternate stack of these layered sheets along [010] would lead to the formation of a-MoO3, where a van der Waals interaction would be the major binding force between the piled sheets. One might take advantage of the intrinsic structural anisotropy of a-MoO3 for tuning its properties by interlayer structural modification, annealing, and lithiation. In this Communication, we report the electroactivity of a-MoO3 nanobelts after lithiation that show superior performance to nonlithiated a-MoO3 nanobelts. An X-ray diffraction (XRD) measurement was performed using a D/MAX-III X-ray diffractometer. Fourier-transformed infrared (FTIR) absorption spectra were recorded using the 60-SXB IR spectrometer. Raman spectra were taken using a Renishaw RM-1000 laser Raman microscopy system. Scanning electron microscopy (SEM) images were collected with a JSM-5610 and FES-EM LEO 1530. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) were recorded by using a JEOL JEM2010 FEF microscope. The electrochemical properties were studied with a multichannel battery testing system. Batteries were fabricated using a lithium pellet as the negative electrode; 1 M solution of LiPF6 in ethylene carbon (EC)/dimethyl carbonate (DMC) as the electrolyte; and a pellet made of the nanobelts, acetylene black and PTFE in a 10:7:1 ratio as the positive electrode. The fabrication of a single nanobelt-based device has been described in detail elsewhere. XRD measurement was first used to study the phase and lattice modification of the nanobelts before and after lithiation (Fig. 1A). The diffraction peaks of the XRD pattern for both samples can be readily indexed to be orthorhombic with lattice constants of a = 3.962 A, b = 13.85 A, c = 3.697 A (International Centre for Diffraction Data (ICDD) No. 050508). No peaks of any other phases were detected, indicating the high purity of the MoO3 nanobelts. For the non-lithiated MoO3 nanobelts, the stronger intensities of (020), (040), and (060) peaks than those for the bulk MoO3 (Fig. S1, Supporting Information) indicates the anisotropic growth of the nanostructure as well as the preferred orientation of the nanobelts on the substrate. Importantly, in comparison to the nonlithiated sample, there is a small shift of the (020) peak toward a lower diffraction angle for the lithiated sample. This is direct evidence of an expanded b-plane interlayer distance for 0.065 A after lithiation, possibly due to the introduction of Li interstitials between the layers. The morphology and microstructure of the products were observed by using SEM and TEM. Before lithiation (Fig. 1B), C O M M U N IC A TI O N

The luminescent carbon-bearing microinclusion enigma in the Kimi Unit, Rhodope, Greece: Raman microscopic point analyses and mapping with different lasers

The Kimi Unit of the Rhodope Metamorphic Province (RMP), NE Greece, experienced ultrahigh-pressure metamorphism (UHPM), as documented by the unequivocal presence of diamond microinclusions in metapelitic garnet porphyroblasts. Certain peculiar lozenge-shaped 2–8 μm sized inclusions in diamond-bearing garnets reveal a broad composite and asymmetric triplet band (phase XXX) at ∼1331 cm −1 in their Raman spectra acquired with a 632.8 nm He–Ne laser, initially attributed to an sp 3-hybridized C-polymorph. These have been meticulously re-investigated by means of combined 2-wavelength (514.5 nm/632.8 nm laser) Raman microscopy. Raman mapping has been extensively employed in order to examine the spatial distribution of phase XXX and of other phases in these polyphase inclusions and to explore for additional Raman bands. The triplet band at ∼1331 cm −1 measured with the 632.8 nm laser shifts to much higher wavenumbers (∼4966 cm −1) when excited with a 514.5 nm Ar + laser, proving that the XXX triplet is not a real Raman band but a luminescence one at ∼691.1 nm. Numerous hypotheses on the nature of the mysterious phase XXX (e.g. Cr 3+-bearing mineral, carbonate, C polymorph, gas, organic phase) are explored and discussed but all are shown to be unsatisfactory. It is suggested that XXX occurs as nanocrystals that luminesce strongly giving the appearance (in Raman maps) of being larger.

Deposition and deformation of late Archaean sediments and preservation of microfossils in the Harris Greenstone Domain, Gawler Craton, South Australia

Late Archaean sediments, felsic, mafic and ultramafic volcanics in the Harris Greenstone Domain, central Gawler Craton, South Australia are interpreted to have been deposited at ∼2520 Ma in back arc settings and were metamorphosed at ∼2440 Ma. Sedimentary evidence suggests that the metasediments in the Domain might have been deposited in fluvial/estuarine to deltaic-shelf environments and deformed by intermediate amphibolite facies metamorphism accompanying the Sleafordian Orogeny at ∼2440 Ma. Microfossils are preserved in metachert layers that had been boudinaged into lenses. These microfossils, including spinose acritarchs, are organic-walled as evidenced by Laser-Raman microscopy. Fossil-bearing off-cuts were then treated by HF and similar microfossils, degraded organic matter and acid-resistant minerals, such as zircon, were exposed in situ on the etched surface. Their morphologically complex forms and detailed wall structures suggest that these microfossils are of primary biological origin. The microfossils in foliated metachert lenses, either from original deposition or from post-depositional quartz veins, are older than the ∼2440 Ma age of the Sleafordian Orogeny, which provides a minimum age for the host rocks. In either case, these spinose acritarchs are the oldest protists known to date.

Direct measurement of fiber bridging in notched glass-ceramic-matrix composites

A novel, high-resolution remote Raman microscope was used for the direct in situ assessment of deformation on bridging fibers in a double-edge-notched SiC-Nicalon reinforced ceramic-glass matrix composite at various stages of monotonic tensile loading. The effect of notch length on the bridging strain profiles obtained by individually probing a large number of fibers across the bridged ligament of the composite was investigated. Bridging strain measurements in the microscale are used to identify the role and sequence of the failure micromechanisms developing within the bridging zone and are compared with their macromechanically derived counterparts. The difference of 25% in failure strain between the as-received fiber and the maximum value obtained on composite-fibers through laser Raman microscopy (LRM), is attributed to the different patterns of fiber failure in composites as compared to the techniques used for fibers characterization such as monofilament and bundle testing in air. This article demonstrates how the LRM-strain data can be utilized to obtain a direct, microscale measure of the interfacial-shear strength of the composite. The obtained interfacial shear strength (ISS) value of 7 MPa compares well with the macromechanically predicted value and offers a much higher precision compared to other experimental techniques.

Purification of Multiwalled Carbon Nanotubes by Annealing and Extraction Based on the Difference in van der Waals Potential

The potential energies of van der Waals interactions between two multiwalled carbon nanotubes (MWNTs) as well as two carbon nanoparticles (CNPs) were calculated and compared on the basis of the continuum Lennard-Jones model. The well depth of the potential is 1 order of magnitude higher for MWNTs than for CNPs, indicating that MWNTs and CNPs can be separated from each other through polymer-induced steric stabilization. On the basis of this prediction, a novel method for the purification of MWNTs was proposed. The method involves a high-temperature annealing (2600 degrees C, 1 h) followed by an extraction treatment with a selected dispersing agent. While the annealing process evaporates the metal particles, the extraction treatment removes CNPs. The quality of the nanotubes obtained after purification was examined by laser Raman, thermogravimetric analysis, and electron microscopy observations.

Microscopic Orientational Order of Polymer Chains in Helical Polyacetylene Thin Films Studied by Confocal Laser Raman Microscopy

In order to study the internal structure of fibrils in helical polyacetylene thin films, we observed such films by confocal laser Raman microscopy (CLRM). The intensity of Raman signals depended greatly (∼15-fold at the most) on the polarization configuration of CLRM. We confirmed that fibrils in the films are composed of polyacetylene chains aligned along the long axes of the fibrils. We estimated the maximum value of the microscopic orientational order parameter, <P2>, to be 0.62. CLRM is a powerful tool for evaluating the microscopic orientation of conductive polymers with minimal sample preparation and high examination speed.

In situ cryogenic Raman spectroscopic studies on the synthetic fluid inclusions in the systems H2O and NaCl-H2O

Salt-hydrates have diagnostic cryogenic Raman spectra, which can reflect the composition of the parent solutions. As analogue to the natural fluid inclusions, the synthetic inclusions can be used to validate numerous assumptions related to fluid inclusion research. They can also be used to test the feasibility of application of laser Raman spectroscopy to individual fluid inclusion analysis. Using the technique proposed by Sterner and Bodnar(1984), synthetic inclusions of the systems H2O and NaCl-H2O (with NaCl as 5.12 wt%, 9.06 wt%, 16.6 wt% and 25 wt%) were formed under the pressures from 50Mpa to 100Mpa and at the temperatures from 500°C? to 600°C. In situ cryogenic Raman spectra were collected at about −180°C by combined use of freezing-heating stage and Laser Raman Microscopy. It is shown that hydrohalite (NaCl·2H2O), the salt-hydrate of NaCl in the fluid inclusions has the specific Raman spectrum and can be used as the standard to verify the existence of NaCl in the aqueous inclusions. The crystalline ice other than amorphous ice (glasses) formed from the aqueous phase whthin the synthetic inclusions during the initial freezing, but hydrohalite did not form. Subsequent warming of these inclusions induced a phase change, typically between approximately −40 and −22°C, that represents the hydrohalite crystallization event but not a eutectic melting event. So, for fluid inclusions in the system NaCl-H2O, interpretation of phase behavior below the eutectic temperature (−20.8?) should be made with caution. The ratios of the relative intensity and the area of Raman spectra between 3423 cm−1 peak of hydrohalite and 3098 cm−1 peak of ice show positive correlations to the salinities in aqueous inclusions, which can be used to determine the salinity of NaCl-H2O system inclusions.

An experimental and theoretical study of the stress transfer problem in fibrous composites

The problem of efficient stress transfer in two-phase composites is very intriguing as it is a prerequisite for the attainment of satisfactory mechanical performance in these materials. Many micromechanical models are now available for the prediction of the stress distribution on either phase or at the interface. Some of the existing models are based on poor assumptions while others are too complex to be applied directly without prior knowledge of all the elastic constants of the constituent materials and their inter-dispersion in the composite. In this paper, an attempt is made to revisit the shear-lag type of model applying it to a specific class of two-phase materials, that of long-fiber polymer composites. The experimental tool used to verify the theoretical stress distributions is the technique of laser Raman microscopy (LRM). By introducing, a local fiber discontinuity in a composite of high volume fraction we could determine both the axial fiber build-up and the corresponding interfacial shear-stress distribution at all strain levels using LRM. The results are compared to the theoretical shear-lag curves (elastic region) and useful conclusions are drawn for the universality of these models and their applicability to high volume fraction polymer composites.

Determination of interface integrity in high volume fraction polymer composites at all strain levels

In fiber-reinforced composites, the mechanical performance is strongly dependent upon the quality of fiber/matrix interface. In the present work, a novel technique is presented whereby all important interface parameters of high volume fraction composites are determined in situ on standard tensile coupons. The method involves the introduction of a small surgical cut to the upper ply of a unidirectional aramid/epoxy laminate prior to vacuum bagging. During the curing procedure and subsequent consolidation in an autoclave, the resin penetrates the area of the cut and thus no effect to the integrity of the composite is observed. The stress transfer profiles during mechanical loading emanating from the fiber break(s) can be obtained by means of the technique of laser Raman microscopy. The technique allows the determination of the maximum interfacial shear stress at all far-field strain levels and therefore presents the only alternative for the accurate estimation of interface integrity in high volume fraction polymer composites.

Preparation of titania–zirconia composite aerogel material by sol–gel combined with supercritical fluid drying

Ultra-fine titania–zirconia composite aerogel materials have been prepared by supercritical drying of alcogels formed in sol–gel process by using cheap and convenient Ti(SO 4) 2 and ZrOCl 2 as the Ti and Zr sources, respectively. The effect of zirconia content on the textual and structural properties of the resulting materials was investigated by means of nitrogen adsorption–desorption, X-ray diffraction (XRD), TGA, laser Raman and transmission electron microscopy (TEM). The experiments indicated that the titania–zirconia composite calcined at 673 K demonstrated high specific surface area (387 m 2/g) and mesoporous texture in the case where the percentage of each component in the specimen is 50%. Moreover, the XRD and Raman analysis showed that the Zr-containing compound is TiZrO 4 when the temperature is increased to 1073 K. However, the surface area still remained as high as 95 m 2/g. Therefore, we would conclude that doping of zirconia into titania structure with the formation of TiZrO 4 could increase the mesoporosity, and would lead to the composite materials with high textual and thermal stability.

Unprecedented oxo-titanium citrate complex precipitated from aqueous citrate solutions, exhibiting a novel bilayered Ti8O10 structural core.

Aqueous titanium citrate solutions were prepared from the reaction of citric acid with titanium 2-propoxide in a range of molar ratios. Solutions containing two or fewer citrates per titanium resulted in the slow crystallization of an insoluble titanium oxo-citrate complex. Single-crystal X-ray analysis identified the species as Ti(8)O(10)(citrate)(4)(H(2)O)(12).14H(2)O.3HOPr(i)(), crystallized in the tetragonal space group I4(1)/a, with a = 30.775(7) A, c = 14.528(7) A, V = 13 759(8) A(3), and Z = 8. The trianionic citrate ligands supply both carboxylate and alkoxide coordination and stabilize the structure using simultaneous chelating and bridging modes of attachment. The compound is a neutral species, exhibiting titanium in three contrasting environments. Laser Raman microscopy and (13)C CPMAS solid-state NMR data were consistent with those of the X-ray crystal structure. When exposed to air, the crystals rapidly lost water and became a powder. The dehydrated powder was noncrystalline to X-rays and insoluble, but (13)C NMR results demonstrated retention of the carboxylate linkages.