Tem Observation

During pulse laser irradiation of samples in a vacuum chamber, evaporation should proceed on the grain surface since frequent changes of pressure were observed. But it was not clear whether evaporation or recondensation is responsible for the surface alteration. In order to clarify microscopic processes and the cause of reflectance change, we observed the irradiated samples by a transmission electron microscope (TEM).

From the irradiated samples, altered surface grains were picked up. Their thin sections (about 80-100 nm thickness) were produced using an ultramicrotome and observed by 200 keV High-Resolution TEM JEOL2010 at Kobe University equipped with EDS. Some sections of the rim region of irradiated olivine grains contain a large number of nanophase particles as shown in Figure 5. The size of those particles, which have never been observed in raw olivine samples, is between several to 30 nm. According to EDS analysis, the rim region with the nanophase particles is rich in iron. Moreover, electron diffraction patterns and high resolution TEM image showed that those nanophase particles are body-centered cubit alpha-Fe [14]. These nanophase particles should be responsible for the change of optical properties such as darkening and reddening as proposed [2] and calculated [5]. These particles may be also related to SMFe in lunar soils [3, 4]. We have also confirmed that nanophase iron particles are also found in irradiated pyroxene samples (Nakamura et al., in preparation).

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