Y. Matsushima

The Phase Transition Pressures of Zincsulfoselenide Single Crystals

The static phase transition points of ZnSe and ZnSexS1-x(0.40 ≤ x ≤ 1) single crystals in the high pressure region are determined based on the transformation pressures of Bi I-II, Bi III-V, and ZnS using the cubic anvil method where the pressure-induced variation of resistance is measured. The transition pressures of the samples vary almost linearly with the composition of ZnS in ZnSexS1-x.

Strong environmental tolerance of Artemia under very high pressure

It was shown by the present authors group that a tardigrade in its tun-state can survive after exposed to 7.5 GPa for 13 hours. We have extended this experiment to other tiny animals searching for lives under extreme conditions of high hydrostatic pressure. Artemia, a kind of planktons, in its dried egg-state have strong environmental tolerance. Dozens of Artemia eggs were sealed in a small Teflon capsule together with a liquid pressure medium, and exposed to the high hydrostatic pressure of 7.5 GPa. After the pressure was released, they were soaked in seawater to observe hatching rate. It was proved that 80-90% of the Artemia eggs were alive and hatched into Nauplii after exposed to the maximum pressure of 7.5 GPa for up to 48 hours. Comparing with Tardigrades, Artemia are four-times stronger against high pressure.

Effect of very high pressure on life of plants and animals

We studied the tolerance of living organisms, such as a small animal (Milnesium tardigradum), a small crustacean (Artemia), non-vascular plants or moss (Ptichomitrium and Venturiella), and a vascular plant (Trifolium) to the extremely high hydrostatic pressure of 7.5 GPa. It turned out that most of the high pressure exposed seeds of white clover were alive. Those exposed to 7.5 GPa for up to 1 day and seeded on agar germinated roots. Those exposed for up to 1 hour and seeded on soil germinated stems and leaves. Considering the fact that proteins begins to unfold around 0.3 GPa, it seems difficult to understand that all the living samples which have been investigated can survive after exposure to 7.5 GPa.

Strong environmental tolerance of moss Venturiella under very high pressure

It was shown by the present authors group that tardigrade can survive under high pressure of 7.5 GPa. In the case of land plants, however, no result of such experiment has been reported. We have extended our experiments to moss searching for lives under very high pressure. Spore placentas of moss Venturiella were sealed in a small Teflon capsule together with a liquid pressure medium. The capsule was put in the center of a pyrophillite cube, and the maximum pressure of 7.5 GPa was applied using a two-stage cubic anvil press. The pressure was kept constant at the maximum pressure for12, 24, 72 and 144 hours. After the pressure was released, the spores were seeded on a ager medium, and incubated for one week and more longer at 25°C with white light of 2000 lux. It was proved that 70-90% of the spores were alive and germinated after exposed to the maximum pressure of 7.5 GPa for up to 72 hours. However, after exposed to 7.5 GPa for 6 days, only 4 individuals in a hundred were germinated. The pressure tolerance of moss Venturiella is found to be stronger than a small animal, tardigrade.

Impurity Levels of Alkaline Metals in Zincselenide Single Crystals Examined by Photoluminescence.

Zincselenide (ZnSe) single crystals doped with alkaline metals (Li, Na, K, Rb and Cs) were grown by sublimation method. In order to obtain the impurity levels of alkaline metals in ZnSe, we measured the temperature as well as excitation intensity dependences of the photoluminescence spectra. To further verify our results, we also measured the selective photoluminecence spectra of the aforementioned doped ZnSe. The values of the acceptor binding energy (E A) of Li, Na, K, Rb and Cs were 118 ±2, 98 ±2, 94 ±2, 89 ±2 and 74 ±2 meV, respectively. The acceptor binding energy level is found to increase as the atomic number of the dopant decreases.

Distortion of spores of moss Venturiella under ultra high pressure

In our previous studies on the tolerance of living organisms such as planktons and spores of mosses to the high hydrostatic pressure of 7.5 GPa, we showed that all the samples could be borne at this high pressure. These studies have been extended to the extreme high pressure of 20 GPa by using a Kawai-type octahedral anvil press. It was found that the average diameter of the spores of Venturiella exposed to 20 GPa for 30 min was 25.5 μm, which is 16.5% smaller (40.0% smaller in volume) than that of the control group which was not exposed to high pressure. The inner organisms showed a further extent of plastic deformation. As a result, a gap appeared between the outer cover and the cytoplasm. A relationship has been obtained between the survival ratio and plastic deformation of spores of moss Venturiella caused by the application of ultra high pressure.

Maintaining viability of white clover under very high pressure

The high pressure technique developed in physics may give a new possibility if it is applied to a biological study. We have been studying the tolerance of small living samples such as planktons and mosses, and found that all of them were alive after exposed to extremely high hydrostatic pressure of 7.5 GPa. This technique has been extended to a higher plant Trifolium lepens L. (white clover). A few seeds of white clover were exposed to 7.5 GPa for up to 6 days. After the pressure was released, they were seeded on agar, or directly on sowing soil. Seventeen out of the total 22 seeds exposed to the high pressure were found to be alive. Those exposed for up to 1 day and seeded on agar germinated roots. Those exposed for up to 1 h and seeded on soil germinated stems and leaves. The present technique has the possibility of being applied to improve breed of plants and to discover a very strong species that stands against very severe environmental conditions.

Temperature dependence of luminescence in ZnSe

Abstract As-grown ZnSe and RbCl- and CsCl-doped ZnSe single crystals are grown by a sublimination method. The temperature dependence of the photoluminescence (PL) spectra in the blue emission region is measured from 4.2 K to 300 K. The emission band is observed in RbCl- and CsCl-doped ZnSe from 4.2 K to 300 K. In as-grown and Zn-annealed ZnSe, the emission band undergoes considerable attenuation at 100 K. However, the emission band is clearly observed in Se-annealed ZnSe up to near room temperature. These results prove that the disappearance of Se vacancies enhances room temperature PL.

Effect of ultra-high pressure on small animals, tardigrades and Artemia

Abstract This research shows that small animals, tardigrades (Milnesium tardigradum) in tun (dehydrated) state and Artemia salina cists (dried eggs) can tolerate the very high hydrostatic pressure of 7.5 GPa. It was really surprising that living organisms can survive after exposure to such a high pressure. We extended these studies to the extremely high pressure of 20 GPa by using a Kawai-type octahedral anvil press. After exposure to this pressure for 30 min, the tardigrades were soaked in pure water and investigated under a microscope. Their bodies regained metabolic state and no serious injury could be seen. But they were not alive. A few of Artemia eggs went part of the way to hatching after soaked in sea water, but they never grew any further. Comparing with the case of blue-green alga, these animals are weaker under ultra-high pressure.

The band profile of zinc sulfoselenide single crystals grown by sublimation method

Abstract ZnSe x S 1− x single crystals which can be used in blue luminescent devices have been prepared from the vapor phase by sublimation method. Their photoluminescence and reflection spectra were measured. Typically, there was a very weak free exciton luminescence; but, the bound exciton emissions were very pronounced, indicating the presence of substitutional impurities in the form of neutral donors and acceptors. The energy band profile was been obtained within the wide composition range of bulk ZnSe x S 1− x single crystals.