Confocal Raman spectroscopic study on minerals in chondrite

Abstract

Confocal Raman spectroscopy has been effective in unveiling strucutres of local area of the sample using a pinhole aperture, which removes signals from out-of-focus. Raman is also among the non-destructive probes wihch provides information from surface to depth. If the surface to be analyzed is out of focus, the spectrum appears from surrounding and/or under surface minerals. In this study, we introduce the application of confocal Raman spectroscopy on minerals in meteorite. The Raman experiments were performed at Thermo Fisher Scientific Korea with a DXR2xi equipped with a spectra physics argon ion laser and using 532 nm excitation. The laser beam was focused on the samples by a 100 X objective, leading to a ~1 μm diameter spot. The power of the laser was tuned as 9.1 mW (on the sample surface, measured out of a 10 X objective). Acquisition consisted of ~0.2 s exposer time with 600 scans. We provide well-resolved spectrum of local area of sample using confocal Raman spectroscopy without overlap with other peaks. We also probe the phase of mineral under surface using depth profiling. While the Raman spectrum of plagioclase in chondrule of Antarctic chondrite show the complex peaks including that of olivine and pyroxene without confocal analysis, that of plagioclase are only observed with confocal analysis. The depth profiling results with 0.6 μm step size show that the peak intensity of pyroxene increases with increasing depth. The phase change with depth can be determined without damage of the samples using confocal Raman spectroscopy.