Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si.

Gaining an understanding the dynamic behaviors of dopant atoms in silicon nanowires (SiNWs) is the key to achieving low-power and high-speed transistor devices using SiNWs. The segregation behavior of boron (B) and phosphorus (P) atoms in B- and P-doped SiNWs during thermal oxidation was closely observed using B local vibrational peaks and Fano broadening in optical phonon peaks of B-doped SiNWs by micro-Raman scattering. Electron spin resonance (ESR) signals from conduction electrons were used for P-doped SiNWs. Our results showed that B atoms preferentially segregate in the surface oxide layer, whereas P atoms tend to accumulate in the Si region around the interface of SiNWs. The radial distribution of P atoms in SiNWs was also investigated to prove the difference segregation behaviors between of P and B atoms.

Local vibrational modes of boron ͑B͒ in silicon nanowires ͑SiNWs͒ synthesized by laser ablation were observed at about 618 and 640 cm −1 by Raman scattering measurements. Boron doping was performed during the growth of SiNWs. Fano ͓Phys. Rev. 124, 1866 ͑1961͔͒ broadening was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs. Hydrogen ͑H͒ passivation of B acceptors in the SiNWs was also investigated. A broad peak was observed at around 650-680 cm −1 after hydrogenation, demonstrating that B dopants were passivated by the formation of the well-known H-B passivation centers.

A gradual downshift and asymmetric broadening of the Si optical phonon peak were observed by Raman scattering measurements of continuously thermally oxidized silicon nanowires ͑SiNWs͒ synthesized by laser ablation. This downshift and broadening can be interpreted by the phonon confinement effect. Further thermal oxidation produced a reverse change; namely, an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.

We report the first observation of the vibrational Raman spectrum of hydrogen molecules H 2 in crystalline silicon treated with hydrogen atoms at 400 ± C. The Raman spectrum of H 2 in silicon observed at room temperature exhibits a frequency shift of around 4158 cm 21 and a very broad half-width of approximately 34 cm 21. An isotope shift was also detected at around 2990 cm 21 in silicon treated with deuterium atoms at 400 ± C. The frequency shifts of the observed lines are in close agreement with those reported for H 2 and D 2 in the gas, liquid, and solid phases.

The microscopic mechanisms behind the very high mobility in rubrene single-crystal transistors achieved by interface treatments with self-assembled monolayers (SAMs) have been clarified by using field-induced electron spin resonance (FI-ESR). Clearly observed FI-ESR signals exhibit extremely narrow linewidths owing to the very high carrier mobility. The precise angular dependence of FI-ESR g values shows that crystallinity in the semiconductor channel is unchanged by the SAM treatments. The trapping time of charge carriers at the interface directly evaluated from the ESR linewidth greatly decreases from ∼700 to ∼60 ps concomitant with the remarkable improvement in mobility because of the SAM treatments.

Phosphorus ͑P͒ doping was performed during the synthesis of silicon nanowires ͑SiNWs͒ by laser ablation. At least three types of signals were observed by electron spin resonance ͑ESR͒ at 4.2 K. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by the detection of an ESR signal with a g value of 1.998, which corresponds to conduction electrons in crystalline Si, and by an energy-dispersive x-ray spectroscopy spectrum of the P K␣ line. The ESR results also revealed the presence of defects. These defects were partially passivated by hydrogen and oxygen atoms.

The phonon confinement and self-limiting oxidation effects of silicon nanowires ͑SiNWs͒ synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs' surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.