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Two probable causes of variability in the Raman spectrum of unpolished pyrite are well recognized, in principle, but not always in practice, namely: (1) downshifting of band positions due to laser heating; and (2) variations in the ratios of band intensities due to crystallographic orientation of the sample with respect to the laser’s dominant polarization plane. The aims of this paper are to determine whether these variations can be used to acquire additional information about pyrites. Here, using laser Raman microprobe analysis of natural, unpolished pyrite samples, we investigate the magnitude of downshifting of band positions associated with laser heating of different sizes of pyrite grains. We demonstrate that the magnitude of this effect can be large (up to ∼10 cm−1), negatively proportional to grain size, of greater magnitude than the effect typically attributable to natural intersample differences in trace element (TE) solid solution, and of similar magnitude among bands. Through Raman analysis of naturally occurring faces on pyrite samples at various angles of rotation, we also demonstrate that the three most common faces on pyrite can be distinguished by the ratio of the intensities of the dominant bands. We conclude that for unpolished samples, laser Raman microprobe analysis is most effective as a means of identifying pyrite, and the presence of solid solution therein, when laser power is low enough to avoid substantial heating. Once pyrite has been identified, higher laser powers can be used to produce spectra whose ratios of band intensities indicate the face or crystallographic plane being irradiated.

This paper demonstrates the sensitivity of the Raman spectra of electrospray-deposited iron-oxide nanoparticle films to their grain size. The grain size in the films was controlled using the temperature of annealing. The position and width of the bands at ∼ 225, 612, 660, and 1317 Δcm−1 were investigated for their sensitivity to both grain size and laser-induced heating, using 532 nm excitation. The parameter most sensitive to grain size was found to be the difference between the band position of the 660 Δcm−1 LO and 225 Δcm−1 TO bands (X660 - X225). The distance between the two bands narrowed with increasing annealing temperature of the films, suggesting that, as grain size increases, these two bands become closer. The 660 Δcm−1 band position was very stable regardless of variation in laser power and, thus, laser-induced heating effects. The films were prepared by electrospray deposition of a commercial maghemite (γ-Fe2O3) nanoparticle suspension onto a silicon wafer followed by post-annealing in a temperature range of 600–1000 °C for 15 min in an air atmosphere.

We applied Raman spectroscopy to monitor the distribution of mineral and the degree of mineralization across the tendon-bone insertion site in the shoulders of five rats. We acquired Raman spectra from 100 to 4,000 Deltacm(-1) on individual 1 microm points across the 120 microm wide transition zone of each tissue sample and identified all the peaks detected in pure tendon and in pure bone, as well as in the transition zone. The intensity of the 960 Deltacm(-1) P-O stretch for apatite (normalized to either the 2,940 Deltacm(-1) C-H stretch or the 1,003 Deltacm(-1) C-C stretch for collagen) was used as an indicator of the abundance of mineral. We relate the observed histological morphology in the tissue thin section with the observed Raman peaks for both the organic component (mostly collagen) and the inorganic component (a carbonated form of the mineral apatite) and discuss spectroscopic issues related to peak deconvolution and quantification of overlapping Raman peaks. We show that the mineral-to-collagen ratio at the insertion site increases linearly (R(2) = 0.8 for five samples) over the distance of 120 microm from tendon to bone, rather than abruptly, as previously inferred from histological observations. In addition, narrowing of the 960 Deltacm(-1) band across the traverse indicates that the crystalline ordering within the apatite increases concomitantly with the degree of mineralization. This finding of mineral gradation has important clinical implications and may explain why the uninjured tendon-to-bone connection of the rotator cuff can sustain very high loads without failure. Our finding is also consistent with recent mechanical models and calculations developed to better understand the materials properties of this unusually strong interface.

The theoretical parameters underlying quantitative Raman spectroscopy [relative normalized differential Raman scattering (RNDRS) cross sections] are discussed. A method is described [based on Placzek's polarizability theory (see text for reference)] by which relative abundances of species of geological interest (e.g., CO2, CH4, SO2) in individual fluid inclusions are analyzed in practice. Whereas the precision of the analysis is determined by “practical limitations” (which include counting statistics and instrumental reproducibility), its accuracy depends on “practical” as well as “theoretical limitations.” The latter are due to uncertainties in the available RNDRS cross sections. These uncertainties are so large (or even unknown to date, e.g., for liquid or high-pressure gas phases) that it becomes very difficult to estimate the accuracy of the final result. By making the (not very realistic) assumption that the RNDRS cross sections available in the literature apply to the individual fluid inclusion under analysis as well as to the instrumental configuration, we determined the mean composition of a set of synthetic fluid inclusions to be 14.8 ± 2.0 mole % CH4 and 85.2 ± 2.0 mole % CO2.