Tadaki Miyoshi

Study of Crystal Growth Mechanism for Poly-Si Film Prepared by Excimer Laser Annealing

Recrystallization of polycrystalline silicon (poly-Si) film by excimer laser annealing (ELA) is discussed by considering the experimental results that the three stages of nucleation, textured grain growth and secondary grain growth were observed. Although the phenomenon of nucleation in the amorphous silicon (a-Si) is understood by considering crystallization from the super cooled liquid, the growth mechanisms of the textured grain and secondary grain are not understood by this, because the melting point of poly-Si which has already been formed on the entire surface during these growth stages is higher than that of a-Si. The recrystallization mechanism considering the dislocation movement is introduced to investigate the present phenomenon. It also clarifies the reason why secondary grain growth occurs under the critical conditions of laser irradiation energy and shot number. The feasibility of nucleation through the super cooled liquid is also discussed.

Laser-Induced Fluorescence of Oil Colours and Its Application to the Identification of Pigments in Oil Paintings

We have investigated the spectra and decay characteristics of the fluorescence produced in oil colours under pulsed laser excitation. It was found possible to identify prigments in paintings by measuring the fluorescence, and it is suggested that the laser-induced fluorescence method can be used to detect forgeries in oil paintings.

Fluorescence from Pearls and Shells of Black Lip Oyster, Pinctada Margaritifera, and Its Contribution to the Distinction of Mother Oysters Used in Pearl Culture

The fluoresence of pearls and shells of Pinctada margaritifera (black lip oyster) has been measured in order to distinguish the species of mother oysters which produce those pearls. A distinction is possible for pearls of P. margaritifera from those of Pinctada fucata and Pinctada maxima using a difference in the fluoresence spectra; this difference is caused by the presence or absence of porphyrin in pearls, respectively. However, the distinction between P. margaritifera and Pteria penguin, both of which have porphyrin in nacre, is difficult by measuring the fluorescence spectra. It is achieved by measuring the optical reflection spectra, since P. margaritifera shows a peculiar dip at 700 nm.

Fluorescence from Varnishes for Oil Paintings under N2 Laser Excitation

The fluorescence spectra of varnish films have been measured as a function of the storage time. The varnishes used were made from natural resins (copal, mastic and dammar), synthetic resin and beeswax. Peak wavelengths of the fluorescence shifted to longer wavelengths with long-time storage. The effect of light on the fluorescence spectrum was found to be small.

Grain Enlargement of Polycrystalline Silicon by Multipulse Excimer Laser Annealing: Role of Hydrogen

The role of hydrogen introduced into melt-Si during excimer laser annealing (ELA) is examined from the viewpoint of grain enlargement. An amorphous silicon (a-Si)/SiN/quartz glass structure is successfully prepared by a catalytic chemical vapor deposition (Cat-CVD) method for a SiN film, in which the hydrogen concentration of the SiN film is controlled. The grain size increases as the hydrogen concentration decreases, and it partially exceeds 2 µm when the hydrogen concentration of the SiN film is fixed at 2.3 at. %. The relationship between defects at grain boundary and hydrogen is also considered.

Influence of Microcrystallite Size on Photodarkening Effects in CdS-Doped Glasses

Size dependence of photodarkening effects in CdS-doped glasses was investigated using luminescence and electron spin resonance (ESR). As the microcrystallite size decreases, the ESR signal associated with the photodarkening effects increases. This result indicates that the photoinduced centers responsible for the photodarkening effects are created in the interface region between CdS microcrystals and glass matrix.

Time-Resolved Luminescence Spectra of Porous Si

Time-resolved luminescence spectra of porous Si were measured under an N2 laser excitation. The luminescence shows a nonexponential decay with an initial time constant of less than 5 ns and more than 200 ns for the secondary decay. The luminescence is considered to be associated with localized states, which are probably conduction and valence sublevels in Si microstructures.

Effects of γ-Ray Irradiation on Colour and Fluorescence of Pearls

The colour of cultured pears of P. fucata can be changed by γ-ray irradiation, which has been applied to pearl processing. The effect of γ-ray irradiation on the colour and fluorescence of pearls was investigated experimentally. The experimental results show that a colour change of pearls to bluish-grey is mainly responsible for a decrease in the reflection factor of the nuclei. Furthermore, a significant change in the fluorescence spectra has been observed for pearls and nuclei. These changes are considered to be caused by the degradation of conchiolin contained in the nacre. Fluorescence from pearls is not affected by the nuclei, but the colour of pears is affected. Thus, the fluorescence method is suitable for investigating the effect of γ-ray irradiation on the nacre.

Effect of photodarkening on photoluminescence dynamics in CdS-doped glass

We have studied the effect of photodarkening on photoluminescence dynamics in CdS nanocrystals in glass. We have found that the commonly observed increase in the decay rate during photodarkening is spectrally selective, being limited only to the photoluminescence spectral region generally related with carriers in nanocrystal interior states or in shallow traps. On the contrary, the photoluminescence decay rate is exponentially dependent on photon energy (exponential constant of 0.8 eV for the fresh sample) in the spectral interval covering the whole photoluminescence spectrum.

Laser-Induced Reversion of Photodarkening in CdS-Doped Glass

The effect of laser irradiation on photodarkened CdS-doped glass has been investigated as a function of the wavelength of laser light, using electron spin resonance (ESR) and time-resolved luminescence. When the wavelength of laser light is tuned to 500 nm, the intensity of the ESR signal associated with photodarkening decreases, as does the decay rate of luminescence. This indicates laser-induced reversion of photodarkening.