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Boron (B) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B in SiNWs were observed by micro-Raman scattering measurements at room temperature. Broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak. This is called Fano broadening. These results prove that B atoms were doped in substitutional sites of crystalline Si core of SiNWs during laser ablation.

Hydrogen passivation effect on the enhancement of photoluminescence (PL) of Er ions in SiO2films contained Si nanocrystallites (nc-Si) has been investigated. Er-doped SiO2films were fabricated by laser ablation of Er-deposited Si substrate in oxygen gas atmosphere. The PL intensity of Er ions and nc-Si were increased by hydrogen gas treatments, while ESR signal intensity of residual defects located at the interfaces between nc-Si and SiO2was decreased. These results indicate that hydrogen passivation of residual defects is useful for the enhancement of the Er PL.

Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) as catalysts were investigated. The diameter of SiNWs decreased with decreasing synthesis temperature and content of Ni catalyst. Gradual down shift and asymmetric broadening of Si optical phonon peak depending on the diameter of SiNWs were observed for continuously, thermally oxidized SiNWs and SiNWs with smaller diameters formed at lower temperature. This can be interpreted by the phonon confinement effect. On the other hand, further thermal oxidation produced an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the surface oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.

Utilizing laser ablation of Si targets, nanoparticles can be cleanly formed in rare gas. In order to fabricate nanoparticles with well-defined structures such as those whose surfaces are chemically modified, it is important to investigate the formation process of the nanoparticles. We have developed a decomposition method for measuring time-resolved spatial distributions of nanoparticles in rare gas. Applying this method, we have investigated formation processes of silicon nanoparticles in 2-Torr argon gas. The nanoparticles are found to grow from 300 Ais to 1 ms after the ablation.

Hydrogen molecules have been formed in crystalline silicon at various temperatures by a hydrogen-atom remote treatment. The Raman spectrum of the vibrational lines of hydrogen molecules in crystalline silicon is detected for silicon samples treated at temperatures between 250 and 500° C. The maximum production is obtained at 400° C. The Raman spectrum of hydrogen molecules in silicon observed at room temperature exhibits a frequency shift of around 4158 cm−1 and a very broad half-width of approximately 34 cm−1. Isotope shift also can be observed at around 2990 cm−1 in silicon treated with deuterium atoms at 400° C. The frequency shifts of the observed lines are in close agreement with those reported for molecular hydrogen and deuterium in gas, liquid, and solid phases. We discuss a model for the hydrogen molecule configuration and rule out the possibility of high-pressure hydrogen molecular gas in microvoids in crystalline silicon. These results indicate that hydrogen molecules exist at the tetrahedral interstitial sites in crystalline silicon.

Applying laser ablation technique, we have synthesized two types of SiO2 films that include nanometer-sized Si particles. One is synthesized by alternative deposition of Si nanoparticles layers and SiO2 layers. The synthesized film exhibits red photoluminescence (PL) with a peak energy below 1.5 eV. The other is synthesized by annealing at 1000°C of SiOx films, which are formed by laser ablation in diluted O2 gas. We find that there is a narrow range of composition for efficient red PL. Based on the experimental results, we tentatively discuss a possible model for the origin of the red PL.

Time-resolved Si lattice-temperature measurement has been developed on wide time scale from 10−9 to 100 sec during laser annealing, by utilizing the time-dependent optical interference in Si on sappire. This interference is due to small changes in Si refractive index induced by temporal changes in Si lattice-temperature. For ns–pulsed laser annealing, part of the absorbed photon energy is found to be transferred into lattice (phonons) in a time much shorter than 40-ns pulse duration. A new method using a microscope is demonstrated for time- and space-resolved Si latticetemperature measurements during cw laser annealing.

We report time-resolved X-ray absorption and extended X-ray absorption fine structure (EXAFS) measurements on amorphous silicon under nanosecond pulsed-laser irradiation. Each measurement was performed with one laser shot in the X-ray energy range from 90 to 300 eV. An X-ray absorption spectrum for induced liquid Si (liq*Si) was first observed above an energy density of 0.17 J/cm2. It differs significantly from the spectrum for amorphous Si and characteristically shows the disappearance of the Si-L(II,III) edge structure at around 100 eV. This phenomenon is interpreted in terms of a significant reduction in the 3s-like character of the unfilled part of the conduction band of liq*Si compared to that of amorphous Si. This is the first direct evidence that liq*Si has a metallic-like electronic structure. Timeresolved EXAFS results are also discussed briefly.