Shoko Odake

Factors Determining the Stability, Resolution, and Precision of a Conventional Raman Spectrometer

We verified the performance of a conventional Raman spectrometer, which is composed of a 30 cm single polychromator, a Si based charge-coupled device (CCD) camera, and a holographic supernotch filter. For that purpose, the time change of the peak positions of Raman spectra of naphthalene and fluorescence spectra of ruby (Cr-doped Al2O3) were monitored continually. A time-dependent deviation composed of two components was observed: a monotonous drift up to 0.4 cm−1 and a periodic oscillation with a range of 0.15 cm−1. The former component was stabilized at approximately 2000 s after the CCD detector was cooled, indicating that incomplete refrigeration of the CCD detector induced the drift. The latter component synchronized with the periodic oscillation of the room temperature, indicating that thermal expansion or contraction of the whole apparatus induced this oscillation. The implemental deviation is reduced when measurements are conducted using a sufficiently cooled CCD detector at a constant room temperature. Moreover, the effect of the room temperature oscillation is lowered in a spectrum acquired over a duration that is longer than one cycle of this oscillation. Applying the least squares fitting method to carefully measured spectra enhanced the precision of the determination of the peak position to 0.05 cm−1 using the spectrometer with pixel resolution of 1.5 cm−1.

Plastic deformation of lower mantle diamonds by inclusion phase transformations

The changes in pressure ( P ) and temperature ( T ) conditions experienced by a natural diamond, as it rises to shallower depths and is eventually erupted at the Earth’s surface, give rise to stresses between the diamond and any inclusions it contains as a consequence of their differing changes in volume cell parameters in response to P and T . In the case of diamonds with lower-mantle silicate inclusions such effects will be markedly enhanced by phase transformations by which MgSi-perovskite and CaSi-perovskite transform to pyroxene, pyroxenoid and other phases. Using micro-Raman and SEM-EBSD techniques, we have carried out investigations of the diamond immediately adjacent to inclusions with lower mantle perovskite chemical compositions, and compared them with studies of lower-mantle ferropericlase and upper-mantle inclusions. In the Raman studies evidence of shifts in frequency and width in the diamond Raman spectral band at 1333 cm−1 were sought and found to be greater for perovskite than ferropericlase. However, even for MgSi-perovskite the effects only indicated stored residual pressures of ca 0.35 GPa, which have also been found for typical upper mantle inclusions. The EBSD studies showed a marked contrast between diamond adjacent to former perovskite (now transformed to pyroxene and other phases) and ferropericlase. EBSD mapping shows lattice distortions in diamond adjacent to former MgSi-perovskite and CaSi-perovskite of 4 to 7°; but adjacent to ferropericlase the distortion was only 1–2°. The results show that the large strain changes accompanying decompression and phase transformation of the perovskite inclusions were largely accommodated by plastic strain within the diamonds at high temperatures, and only small residual pressures were retained in the diamonds.

3 – Diamond and Other Possible Ultradeep Evidence Discovered in the Orogenic Spinel-Garnet Peridotite from the Moldanubian Zone of the Bohemian Massif, Czech Republic

Publisher Summary In the Plesovice peridotite, several lines of evidence suggesting an ultradeep condition are found. All of these facts suggest that the Plesovice peridotite once resided in the diamond-stability field, which could not be identified by the previous geothermobarometric studies. This suggests that diamond was stable in the rock before Stage I (high-temperature spinel6garnet peridotite stage), which is the oldest generation of mineral assemblage previously recognized in the Plesovice peridotite. Furthermore, the presence of pyroxene exsolution lamellae in the earlier generation of spinel (Stage I) implies the preexisting high-pressure stage before Stage I. If graphite in MS inclusions were originally crystallized as diamond, parental fluids responsible for MS inclusion was most likely entrapped in the host mineral before Stage I, and they should have crystallized daughter minerals during the cooling/exhumation trajectory from the diamond-stability field, through Stage I, to the chlorite peridotite stage. For MS inclusions within Spinel-I, there is a good possibility original fluid/melt was entrapped in the diamond-stability field, if host Spinel-I was originally its high-pressure polymorph, Ca-ferrite, or Ca-titanite. On the other hand, one could not find the typical pyroxene exsolution texture in garnet. This probably suggests that most garnet was secondary formed at the expense of Spinel-I at relatively low-pressure condition. Therefore, if graphite in garnet was originally diamond, it is most likely that the diamond was graphitized before the entrapment within garnet crystal.

Optical Characteristics of Nano-Polycrystalline Diamond Synthesized Directly from Graphite under High Pressure and High Temperature

Optical properties of nano-polycrystalline diamond (NPD) synthesized by direct conversion from high-purity graphite under high pressure and temperature were investigated by infrared (IR), ultraviolet (UV), and photoluminescence (PL) spectroscopy. IR spectroscopy revealed that NPD has no large lattice strain and very few impurities, but possesses an absorption band attributed to a trace of hexagonal diamond. UV spectra displayed a continuous absorption wing due to structural defects and secondary absorption edge attributed to electron transitions from aggregated nitrogen. PL spectra exhibited peaks of N3 centers and broad bands related to dislocations.

High Precision in Raman Frequency Achieved Using Real-Time Calibration with a Neon Emission Line: Application to Three-Dimensional Stress Mapping Observations

A three-dimensional (3D) Raman mapping system with a real-time calibration function was developed for detecting stress distributions in solid materials from subtle frequency shifts in Raman spectra. An atomic emission line of neon at 918.3 cm−1 when excited at 514.5 nm was used as a wavenumber standard. An emission spectrum of neon and a Raman spectrum from a sample were introduced into a single polychromator using a bifurcated optical fiber. These two spectra were recorded simultaneously on a charge-coupled device (CCD) detector using double-track mode. Energy deviation induced by the fluctuation of laboratory temperature, etc., was removed effectively using the neon emission line. High stability during long measurements was achieved. By applying curve fitting, positions of the Raman line were determined with precision of about 0.05 cm−1. The present system was applied to measurements of residual pressure around mineral inclusions in a natural diamond: 3D stress mapping was achieved.

Large-volume static compression using nano-polycrystalline diamond for opposed anvils in compact cells

In order to extend the pressure regime of intrinsically low-sensitivity methods of measurement, such as neutron scattering and NMR, sample volume to be compressed in compact opposed-anvil cells is desired to be significantly increased. We hereby conducted a series of experiments using two types of compact cells equipped with enforced loading mechanisms. Super-hard nano-polycrystalline diamond (NPD) anvils were carefully prepared for large-volume compression in these cells. These anvils are harder, larger and stronger than single crystal diamond anvils, so that they could play an ideal role to accept the larger forces. Supported and unsupported anvil geometries were separately tested to evaluate this expectation. In spite of insufficient support to the anvils, pressures to 14 GPa were generated for the sample volume of > 0.1 mm3, without damaging the NPD anvils. These results demonstrate a large future potential of compact cells equipped with NPD anvils and enforced loading mechanism.