Formation of singlet oxygen in solution by using Si nanocrystals as photosensitizers has been demonstrated. It has been shown that the absorption band of 1,3-diphenylisobenzofuran ͑DPBF͒ in benzene centered at 416 nm decreases by irradiating green ͑514.5 nm͒ or red ͑632.8 nm͒ light if fresh porous Si powder is dispersed in the solution. The decomposition of DPBF was observed only when fresh porous Si was irradiated by light, i.e., without light irradiation no effects were observed. Furthermore, the effect was drastically suppressed if porous Si powder was annealed and a monolayer of oxide was formed on the surface of nanocrystals. The rate of the decomposition of DPBF was accelerated when the solution was bubbled by oxygen gas. These results indicate that electronic excitation of Si nanocrystals is transferred to molecular oxygen dissolved in solution, resulting in the formation of singlet oxygen. Generated singlet oxygen reacts with DPBF ͑1,4-cycloaddition reaction͒, forming endoperoxides, which in turn decompose to yield irreversible products. In addition to the singlet-oxygen-mediated decomposition of DPBF, the possibility of direct reaction between triplet excited states of Si nanocrystals and DPBF is discussed.

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Photoluminescence (PL) from singlet oxygen generated by energy transfer from porous Si is observed at room temperature in an organic solvent. The evidence of the indirect excitation by energy transfer is obtained from PL excitation spectroscopy. The excitation spectrum indicates that by using porous Si as a photosensitizer, light of the entire visible range can be utilized for singlet oxygen generation at room temperature.

Singlet oxygen formation by porous Si in solution has been demonstrated. It has been shown that the absorption band of 1,3-diphenylisobenzofuran (DPBF) in benzene becomes smaller, i.e., DPBF is degraded, by irradiating green or red light if the powder of fresh porous Si is dispersed in the solution. The effect was drastically suppressed by the formation of a monolayer of backbonded oxide at the surface of nanocrystals. The degradation was accelerated when the solution was bubbled with oxygen gas. These results indicate that electronic excitation of Si nanocrystals is transferred to molecular oxygen dissolved in solution, resulting in the formation of singlet oxygen. Generated singlet oxygen reacts with DPBF, forming endoperoxides, which in turn decompose to yield irreversible products.

Space structures encounter various special environments in space. One of these environments is severe thermal condition. Difference of temperature of space structures during day-time and night-time is about 200 kelvin. These severe thermal conditions cause thermal deformation of the structures. In fact, we observed the signal level of radio wave from the LDR (Large Deployable Reflector) of the ETS-VIII (Engineering Test Satellite -VIII) changing during the Earth eclipse. This phenomenon may be caused by thermal deformation of the LDR. This thermal deformation is a key issue to maintain the accuracy of communication beams reflected by the space antenna. Analysis of thermal deformation of the LDR is carried out, and a new suppression scheme for thermal deformation is proposed in this paper.