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In doped Si nanowires (SiNWs) boron (B) atoms segregate to the surface oxide layers during thermal oxidation, while phosphorus (P) atoms preferentially pile up in Si crystalline regions close to the Si/SiO2 interface. Here we report on micro-Raman scattering and electron spin resonance (ESR) measurements showing that B atoms can be stabilized at the crystalline Si core region in codped SiNWs with average diameters of 20–30 nm because of the strong interaction between B and P atoms during thermal oxidation below 800 °C. Theoretical calculation clearly demonstrated the effect of B–P pairing, which can stabilize the B atoms in the Si side. In the B–P pairing configuration, dopant passivation—beyond simple compensation—occurs, making the impurities electrically inactive.

Recrystallization of silicon nanowires (SiNWs) after ion implantation strongly depends on the ion doses and species. Full amorphization by high-dose implantation induces polycrystal structures in SiNWs even after high-temperature annealing, with this tendency more pronounced for heavy ions. Hot-implantation techniques dramatically suppress polycrystallization in SiNWs, resulting in reversion to the original single-crystal structures and consequently high reactivation rate of dopant atoms. In this study, the chemical bonding states and electrical activities of implanted boron and phosphorus atoms were evaluated by Raman scattering and electron spin resonance, demonstrating the formation of p- and n-type SiNWs.

本研究では，pH刺激応答性ポリマーの1つとして，pH 6.5付近で相変化を示す性質を持つPoly{4-[2-(vinyloxy)-ethoxy]-benzoic acid} : Poly(VEBA)sを用いて，各種金属イオンに対する分離挙動を検討した．その結果，いくつかの特異的な金属捕集特性が確認された．その中で特に希土類元素（レアアース）について特徴的な結果が得られ，pH変化とろ過操作を用いて，レアアースを分離・回収できるシステムを開発した．回収率は検討した16種類のレアアースについてすべて90～100％ であった．また，水酸化ナトリウム水溶液を用いてPoly(VEBA)sを再溶解させることで，フィルター上で回収したPoly(VEBA)sと金属の分離が可能であった．Poly(VEBA)sを再び回収することでPoly(VEBA)sのリサイクルも可能である．本システムは，有機溶媒を使用しない全水系システムであるため環境や生体に対する安全性も高いと言える．

We review recent works on 1) an isotope effect of penetration of Hydrogen(H) and Deuterium(D) into Silicon through Si/SiO2 interface and 2) H effects for Si nanostructures, as well as summary of hydrogen states in crystal Si. In particular, a new filtering effect of H and D isotope atoms was found for penetration process into crystal silicon (Si) through the interface between a Si and SiO2 native oxide layer. More H atoms are introduced into Si than D for mixing gases. This phenomenon can be tentatively explained in terms of an isotope filtering model of H and D via an intermediate cluster state formed at the interface between the native SiO2 layer and crystal Si. Hydrogen passivation of interface defects is shown to be needed for knowing proper impurity doping effects, and electronic, optical, and magnetic properties in Si nanostructures.

Boron (B) or phosphorus (P) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B were observed in B-doped SiNWs by micro-Raman scattering measurements at room temperature. Fano 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 for B-doped SiNWs. An electron spin resonance signal due to conduction electrons was observed only for P-doped SiNWs. These results prove that B and P atoms were doped in substitutional sites of the crystalline Si core of SiNWs during laser ablation and electrically activated in the sites.

The formation and annihilation of hydrogen (H)-related complexes were investigated in boron (B)- or phosphorus (P)-doped Si treated with high concentration of atomic H. The passivation and reactivation process of dopant carriers were significantly different between the p-type and n-type specimens. The differences are explained by the stable sites of the H atoms in the p-type and n-type specimens and, in turn, by the formation of H-related defects: i.e., H multiple trapping centers are formed by bond-breaking due to H atoms only in p-type B-doped Si. The formation of such defects retards the reactivation of B dopants by annealing.

Hydrogen passivation of phosphorus (P) donors and defects in P-doped silicon nanowires (SiNWs) were investigated by electron spin resonance (ESR) at 4.2 K. P doping was performed during the synthesis of SiNWs by laser ablation. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by detection of an ESR signal with a g-value of 1.998, which corresponds to conduction electrons in crystalline Si. ESR signals related to defects in surface oxide layer and at interface between surface oxide and crystalline Si core were observed. These P donors and the defects were partially passivated by hydrogen and oxygen atoms as seen in bulk Si.

The effect of phonon confinement and impurity doping in silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The diameter 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. Boron doping was also performed during the growth of SiNWs. Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640 cm–1 by Raman scattering measurements. Fano broadening due to coupling between discrete optical phonons and the continuum of interband hole excitations was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs.

The formation of hydrogen (H)-related complexes was investigated in boron (B)-doped Si treated with high concentration of H. The isotope shifts of H-related Raman peaks by replacement of H to deuterium and 10B to 11B clearly showed the formation of the B–H complexes in which H directly bonds to B in Si. The results of the resistivity measurements suggested that the B acceptors are passivated via the formation of the B–H complexes, as well as the well-known passivation center in B-doped Si, namely, H–B passivation center.

The phonon confinement effect was investigated by Raman measurements for Si nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) catalyst and for SiNWs thermally oxidized at 700–1000 °C. The Si optical phonon peak for SiNWs, unlike that for bulk Si, showed a downshift and an asymmetric broadening. Thermal oxidation caused a further downshift and broadening. These phenomena can be explained by the phonon confinement effect due to the decrease in the diameter of the Si core of the SiNWs. It was additionally found that excess oxidation caused an upshift of the optical phonon peak due to compressive stress.

Recent experiments have shown that Si nanostructures can be formed in a matrix Of SiO2 by laser-pulse irradiation, with appealing applications in nanotechnology. We hereby present first principles simulations that provide a microscopic insight into the underlying mechanism, showing how electron excitations weaken Si-O bonds in SiO2, dislodging O atoms and allowing the formation of stable Si-Si structures below the melting temperature. (c) 2006 Elsevier B.V. All rights reserved.

Deep lamellar diffraction gratings fabricated by etching a transparent quartz plate are studied using spectroscopic ellipsometry. The rigorous coupled-wave analysis is used to calculate the optical response of the gratings. Three parameters of the rectangular profile are determined by utilizing the least-square method. Detailed investigation of the spectral dependences demonstrates the uniqueness of the solution. Observing the spectral dependences of Wood anomalies suggests that even complicated profiles can be fitted with high authenticity.

Expression of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) was compared between leiomyoma and myometrium. Cytosolic fractions from leiomyoma homogenate displayed 5-fold higher activity (estrone to estradiol), compared with surrounding myometrium (n = 6, P0.05), whereas microsomal fractions showed no difference. Oxidative activity (estradiol to estrone) did not differ between leiomyoma and myometrium. Levels of mRNA for 17beta-HSDs were then measured using real-time PCR techniques. Among the eight different types of 17beta-HSDs (types 1-5, 7, 8, and 10), type 1 was the only enzyme displaying differential expression between leiomyoma and myometrium. Mean concentration of type 1 17beta-HSD mRNA was 4-fold higher in leiomyoma than in surrounding myometrium (n = 20, P0.05). Type 1 transcript levels correlated significantly with reductive activity in individual samples (n = 6, P0.05). Northern blot analysis of leiomyoma and myometrium tissues detected 2.3- and 1.0-kb transcripts of type 1 enzyme, whereas the major 1.3-kb transcript for 17beta-HSD in placenta-derived JEG-3 cells was not detected. None of the factors increasing mRNA levels for type 1 enzyme in placenta increased mRNA levels in leiomyoma. These results indicate that leiomyoma tissues overexpress type 1 17beta-HSD, resulting in high conversion of estrone to estradiol. In situ expression of type 1 17beta-HSD may play a role in self-supported growth of leiomyoma cells.

The formation mechanism of interstitial H2 in crystalline silicon was investigated by varying the dopant concentration and hydrogenation temperature. At low temperatures such as 125°C, the Raman peak of the interstitial H2 is observed only in heavily doped n-type silicon, suggesting that the formation of H2 includes a metastable donor-hydrogen complex as the precursor and that H2 formation out of two isolated hydrogen atoms is hindered by the Coulombic repulsion between two equally charged atoms at this temperature. At moderate temperatures such as 235°C, the interstitial H2 is formed also for intrinsic and p-type silicon. The absence of the dopant-concentration dependence in p-type silicon indicates that the H2 is created from two hydrogen atoms, at least one of which is neutralized by capturing a thermally excited electron. The formation of the interstitial H2 competes with that of extended planar defects (platelets) at high temperatures such as 305°C.

Er-doped SiO2 thin films including Si nanocrystallites were fabricated by laser ablation of Si targets covered with Er thin films in O2 gas and subsequent thermal annealing. Photoluminescence measurements were performed at temperatures from 10 K to 295 K. The optimum condition was found to be an O2 gas pressure range of 40–50 mTorr. We found that the temperature dependence of Er photoluminescence intensity is governed by power density of excitation laser light. Furthermore, Er photoluminescence is more intense at 295 K than that at 10 K at power densities higher than 480 mW/cm2. These results confirm that Er atoms are excited by energy transfer from photo-excited Si nanocrystallites. On the other hand, photoluminescence intensity of Er-doped Si nanoparticles grown in gas phase gradually decreases with increasing temperature.

We have investigated the chemical reaction of Si nanoparticles with H2 and O2 gases in gas phase after laser ablation of Si targets in Ar and Ne gases. First, we observed time-resolved photoluminescence (PL) from Si nanoparticles in pure Ar gas. The formation of Si nanoparticles begins after the thermalization of Si plasma on a time scale of 1 ms. The energy dissipation of electronic system govern the formation of Si nanoparticles. It was clearly observed that Si nanoparticles grow up to 1.8 ms. Based on the formation dynamics, we observed chemically modified Si nanoparticles using the time-resolved PL method. We found that Si nanoparticles react with hydrogen and oxygen atoms dissociated in the laser plasma. The hydrogenation results in PL at 550 nm and vibronic lines in the wavelength range of 650–800 nm disappear. Oxidation results in PL quenching when O2 partial pressure is higher than 1 Pa. Thus, we have demonstrated chemical modification of Si nanoparticles.

Droplet-free deposition of Si nanoparticle films has been studied applying time-resolved imaging of Si nanoparticles formed by laser ablation of Si targets in Ar gas. We found that Si nanoparticles can be deposited not only on substrates facing to the targets but also on substrates placed beside the target. We further confirmed using a scanning tunneling microscope (STM), Si nanoparticles with sizes of 5–8 nm are deposited on substrates placed beside the target and using a scanning electron microscope (SEM) on the substrates, no droplets are observed.

We fabricated P-doped Si nanocrystallites embedded in SiO 2 films and have investigated by photoluminescence (PL) spectroscopy and electron spin resonance (ESR) spectroscopy. The films were fabricated by annealing of P-doped SiO x films that were deposited by laser ablation of P 2 O 5 -coated Si targets in O 2 gas. Visible PL from nanocrystallites is enhanced at room temperature by 10 times as intense as undoped ones. ESR spectroscopy revealed that deposition at high energy density is effective for defect-free deposition. Furthermore, P atoms are found to be doped in the crystallites and electron–hole pairs bound to the P atoms are suggested to be responsible for the enhanced PL. In addition, we found a P-related center located at interface region between P-doped films of Si nanocrystallites and Si substrates, with a large hyperfine splitting of ∼80 G observed at 20 and 40 K.

We report a systematic investigation on the Fermi-level dependence of the formation of two different types of hydrogen molecules in silicon. Hydrogen molecule at the tetrahedral (T) site (H 2 (T)) is formed only in heavily doped n-type below 200°C, but is observed both in the n- and p-type above 200°C. The temperature dependence is due to the increase of the thermally activated carrier concentration. The possible precursors of the H 2 (T) are H + (BC) and H 0 (BC) in the p-type, and H − (T) and H 0 in the n-type. The Fermi level dependence of the formation of the hydrogen molecule trapped in platelets (H 2 (p)) above 250°C is very different from that below 250°C. The result suggests that platelets are formed from hydrogen-complexes other than the H 2 * above 250°C.

Wehaveinvestigatedthethermalbehaviorofhydrogenmoleculestrappedbymultivacanciesincrystallinesiliconbyperformingthermalannealing.ThehydrogenmoleculeshadtwoRamancomponentswithdifferentannealingstages.Theiractivationenergiesforannihilationwere0.7 0.3and0.5 0.2eVforthemaincomponentandtheshoulder,respectively.Theformerwasattributedtothepotentialbarrierforahydrogenmoleculetoescapefromamultivacancytrap,andthelattertomovefromametastablesitearoundthemultivacancytraptothemoststablesite.Annealingat6108CsuggestedthatrelativelylargemultivacanciessuchasV 6 andV 10 arepossibletrappingcentersofthehydrogenmolecules.# 2001ElsevierScienceB.V.Allrightsreserved. PACS: 61.72.JiKeywords: Hydrogenmolecule;Multivacancy;Annealingbehavior;Activationenergy 1. IntroductionHydrogenisanimportantimpurityinsemicon-ductorsbecauseofitsabilitytochangeelectricalpropertiesofhostmaterialsdrastically[1].Theo-retical calculations predicted that a hydrogenmoleculeisoneofthefavorableconfigurationsincrystalline silicon. Three different configurationsof hydrogen molecules have been found experi-mentally by means of vibrational spectroscopysuchasRamanscatteringandinfraredabsorption.Murakamietal.revealedtheexistenceofhydro-genmoleculesincrystallinesiliconin1996.TheyobserveditsvibrationalRamanlineat4158cm

We have investigated the formation of silicon nanoparticles after pulsed-laser ablation of a silicon target into argon gas at pressures of 2-10 Torr. Growing process of silicon nanoparticles was observed by measuring light emission resulting from decomposition of the nanoparticles by using a second pulsed-laser. It was directly observed that the nanoparticles are formed on the time scale of 1 ms, depending on the ambient gas pressure. This information is expected to be quite helpful for growth control and for chemical surface-modification by using pulsed-laser light or by exposure to a pulsed reactive-gas jet. The nanoparticles exhibit visible photoluminescence after deposition. Effect of chemical modification to photoluminescence have been investigated. Brighter luminescence have been observed from silicon nanocrystallites precipitated in SiO2 films during annealing of SiOx films deposited using a laser ablation technique.

The Raman line of a new hydrogen molecule at approximately 3820 cm −1 has been observed for the first time in silicon after Si + ion implantation with proper doses, followed by hydrogen atom treatment. The assignment was confirmed by isotope shifts to 2770 cm −1 for D 2 molecule and to 3353 cm −1 for HD molecule. Both the ion-dose dependence and hydrogenation-temperature dependence of the Raman intensity of the H 2 molecules correlate with those of the intensity of peaks of Si–H stretching observed at 1957±1.8 cm −1 and at approximately 2185 and 2210 cm −1 . We propose a model where the hydrogen molecule corresponding to the 3820 cm −1 vibrational line is trapped in or adjacent to small H-terminated multivacancies.

We report a Raman study on the hydrogenation–temperature dependence on the formation of hydrogen molecules in crystalline silicon. The 3601 cm −1 vibrational line for H 2 , which has been attributed to hydrogen molecule in T d site, is observed in p-type as well as in n-type crystalline silicon. This H 2 molecule exhibits significantly different temperature dependence in n- and p-type Si. It is suggested from the hydrogenation–temperature dependence that the charge states and the sites of atomic hydrogen affect the formation of this type of H 2 . From the experiments using H+D atom treatments, there may be a significant isotope effect on the formation of the H 2 molecule.

We have investigated quantitatively the effect of crystal disorder on the formation of hydrogen molecule in crystalline silicon. Disordered crystalline silicon was obtained by implanting crystalline silicon with 200 keV Si + with doses ranging from 10 13 to 10 16 Si cm −2 . The optical phonon line broadened and downshifted with increasing ion dose, corresponding to an increase in crystal disorder and decrease in phonon correlation length. The implanted samples were then treated with a remote downstream hydrogen plasma at 250°C. The vibrational Raman line of hydrogen molecule at around 4160 cm −1 decreased monotonically in its intensity with decreasing phonon correlation length. The results suggest that hydrogen molecules are formed preferably in well-ordered parts of Si lattice.

The time-and spatially-resolved properties of laser ablated carbon, boron and silicon particles were measured by LAPXAS (Laser Plasma Soft X-ray Absorption Spectroscopy). The maximum speed of positively charged ions is higher than those of neutral atoms and negatively charged ions. The spatial distributions of the laser-ablated particles in the localized rare gas environment were measured. In helium gas environment, by the helium cloud generated on the top of ablation plume depressed the ablation plume. There is no formation of silicon clusters till 15μs after laser ablation in the argon gas environment.

The interface between metallic materials, especially titanium, and living cells (osteogenic cell) was investigated using a high-resolution transmission electron microscope, in order to establish the mechanism of the bio-compatibility for metals. At the titanium/cell interface there is an intermediate layer whose thickness is several ten nm involving not only metallic elements but also cell original elements. The intermediate layer does not have long/short range order or is rather complex structure. It is concluded that this intermediate layer is a mixture of titanium oxide and organic materials, which precipitates during cell culture. This precipitation of mixture is one of the advantages for titanium's biocompatibility. It is not cleared that calciumphosphate, one of the main composition of bone, precipitation on the surface on the material has any responsibility for bio-compatibility.

application/pdf, We have performed electron spin resonance (ESR) measurements on Er-doped GaAs grown with oxygen codoping by metal organic chemical vapor deposition. An isotropic line (an effective g value, g = 5.95) which had been already reported was observed in samples without oxygen codoping. On the other hand, for samples with oxygen codoping other strong anisotropic ESR lines originated from four kinds of Er3 + (4f11) centers (A, B, C, and D) were newly observed in addition to the weaker isotropic line. The anisotropic g tensors obtained by analyzing the angular dependence of the ESR lines indicate that B and C centers are of orthorhombic C2v symmetry, A center has lower symmetry than orthorhombic symmetry, and D center is of trigonal C3i symmetry. The ESR intensities of A, B, and C centers were approximately two orders of magnitude higher than that of the isotropic line with g = 5.95. The ESR intensity of D center was one order of magnitude lower than those of A, B, and C. The Er concentration dependence of the relative ESR intensities of these centers was investigated, which indicates (i) the ESR intensities of A and D increase with increasing Er concentration, and (ii) those of B and C are saturated above the Er concentration [Er] >= 1018 cm – 3. The ESR measurement under light illumination, as well as the Er concentration dependence, suggests that the B center with C2v symmetry corresponds to the dominant Er luminescent center under host photoexcitation.

Hydrogen molecule has been observed in the hydrogen-atom-treated silicon crystal using Raman spectroscopy. Trapping site and the vibrational frequency of H2 in the silicon crystal have been studied with theoretical calculations. The ab initio molecular orbital theory and the density-functional-theory calculations have been performed with a Si10H16 cluster model. The calculations show that the trapping site of H2 in the silicon crystal is the tetrahedral interstitial site and the calculated vibrational frequency agrees reasonably with the experiment.

We have performed (1) time-resolved soft X-ray absorption measurements on a time scale up to 15 μs after pulsed-laser ablation of silicon (Si) in an ambient Ar gas with a transient pressure of about 10 Torr and (2) investigation of the correlation between 1.6-eV photoluminescence (PL) from Si nanocluster-based films and the surface oxidation. No soft X-ray absorption lines corresponding to Si clusters were observed, indicating that it is likely that after 15 μs, significant clustering takes place and then Si nanoclusters can grow. From experiments involving hydrogen termination and hydrogen atom treatment in addition to natural oxidation, it is found that the 1.6-eV PL originates from the interface of a Si nanocluster core and a surface oxide layer and occurs without hydrogen atoms.

Applying laser ablation technique, we have synthesized two types of SiO 2 films that included nanometer-sized Si particles. One is synthesized by alternative deposition of Si nanoparticle layers and SiO 2 layers. The synthesized film exhibits red photoluminescence (PL) with a peak energy below 1.5 eV. The other is a SiO 2 film in which Si nanocrystallites precipitate. The films were synthesized by annealing at 1000°C of SiO x films which are formed by laser ablation in diluted O 2 gas. The films exhibit PL with peak energies of 1.5 eV, 2.2 eV and 2.7 eV. We find that there is a narrow range of composition for efficient 1.5-eV PL.

application/pdf, We have performed electron spin resonance (ESR) measurements on Yb-doped n-type and p-type InP layers epitaxially grown by metalorganic chemical vapor deposition. ESR spectra of Yb3 + (4f13) were observed in both n-type and p-type samples. However, the ESR intensity of Yb3 + (4f13) for n-type samples was found to be much lower than that for p-type samples. This suggests that most Yb ions in Yb-doped n-type InP are in the Yb2 + (4f14) state rather than in the Yb3 + (4f13) state. Thus an electron captured by the trap level formed by Yb in the band gap of InP is not located outside the Yb 4f shell as reported previously, but accommodated in the Yb 4f shell.

We have found that hydrogen exists in molecular form in crystalline silicon treated with hydrogen atoms in the downstream of a hydrogen plasma. The vibrational Raman line of hydrogen molecules is observed at $4158{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for silicon samples hydrogenated between 180 and 500 \ifmmode^\circ\else\textdegree\fi{}C. The assignment of the Raman line is confirmed by its isotope shift to $2990{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for silicon treated with deuterium atoms. The Raman intensity has a maximum for hydrogenation at 400 \ifmmode^\circ\else\textdegree\fi{}C. The vibrational Raman line of the hydrogen molecules is broad and asymmetric. It consists of at least two components, possibly arising from hydrogen molecules in different occupation sites in crystalline silicon. The rotational Raman line of hydrogen molecules is observed at $590{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}.$ The Raman band of Si-H stretching is observed for hydrogenation temperatures between 100 and 500 \ifmmode^\circ\else\textdegree\fi{}C and the intensity has a maximum for hydrogenation at 250 \ifmmode^\circ\else\textdegree\fi{}C.

We have investigated the Raman spectra of hydrogen molecules in heavily doped n-type crystalline silicon exposed to hydrogen atoms at various substrate temperatures. A significant hydrogenation-temperature dependence has been observed in the intensity and the shape of the vibrational Raman line of hydrogen molecules. The vibrational Raman line of hydrogen molecules is as broad when measured at 90 K as at 300 K. The results indicate that hydrogen molecules are formed effectively at higher temperature than the temperature appropriate for the platelet formation, and trapped in various interstitial sites in crystalline silicon.

We have calculated potentials of hydrogen molecules in the silicon clusters (Si 10 H 16 ) by the ab initio Hartree-Fock method. A tetrahedral site for the hydrogen molecule is a stable trapping site and the calculated vibrational frequency of the hydrogen molecule is 4470 cm −1 , which agrees resonably with the experimentally obtained frequency of H 2 in silicon crystal.

Hydrogen molecules are formed in the crystalline silicon treated with hydrogen atoms at substrate temperatures between 180 and 500°C. The vibrational Raman line (Q1) of hydrogen molecule in the hydrogenated crystalline silicon is observed at around 4160 cm-1. The line shape changes with hydrogenation temperature, and is composed of at least two components. The two components are ascribed to hydrogen molecule in two different interstitial sites in crystalline silicon. Each component is much broader than that of hydrogen molecules in gas phase. The line broadening can not be explained by collisional or motional broadening, but is attributed due to the configurations of hydrogen molecule with different orientations in the crystalline silicon.

application/pdf, We report the first observation of the vibrational Raman spectrum of hydrogen molecules H2 in crystalline silicon treated with hydrogen atoms at 400 °C. The Raman spectrum of H2 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. An isotope shift was also detected 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 H2 and D2 in the gas, liquid, and solid phases.

Chemical reaction of laser-ablated silicon particles with oxygen gas diluted with a helium buffer gas is found by means of soft X-ray absorption spectroscopy. In order to make clear the dynamics of silicon laser plume and the mechanism of the chemical reaction, we measured time-resolved spatial distribution of light emission from the laser-ablated particles as well as time- and space-resolved emission spectra.

Time- and space-resolved characteristics of laser-ablated carbon particles were studied by x-ray absorption spectroscopy. Absorption peaks from the 1s→2p transition of neutral carbon atom ( C 0), C −, C +, and C 2+ ions were observed, An absorption peak from 1s→π* and a broad absorption maximum from the 1s→σ* transition of small clusters were also observed. Neutral carbon, C −, C +, and small carbon clusters were emitted from the sample long after laser irradiation. Spatial distributions of laser-ablated carbon particles in the localized helium-gas environment were measured. In the helium-gas environment, the ablation plume was depressed by the helium cloud generated on the top of the ablation plume.

We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in Hegas environment. It is found that the spatial distributions of laser-ablated particles are very different between the two cases. This suggests that a higher-density region of helium gas is formed at the top of the plume of the ablated particles, and free expansion of particles is restrained by this helium cloud. Moreover, the spectrum obtained at 260 ns indicates that it takes more than 260 ns to form Si clusters. It is also demonstrated that Al particles can be sputtered in vacuum by laser-ablated Si particles if an Al plate is placed in front of the plume.

We have studied dynamical mechanism of laser ablation using combined time- and spatially-resolved measurements of laser plasma soft x-ray absorption spectroscopy and visible light emission imaging/spectroscopy. The obtained results indicate that there are no significant formation of silicon clustres and no growth of silicon nanoclusters till 2.55 ms after laser ablation. We have fabricated nanocluster-based silicon films by laser ablation in ambient gases and investigated photoluminescence at room temperature from the films. It is found that the growth of silicon nanocluster-based films with visible light emission can be well controlled by means of novel laser ablation methods.

Spectra of light transmitted through SiO2 specimens were measured during irradiation of amplified 800 nm ultrashort (400 fs) laser with a repetition rate of 100 kHz. The spectra exhibit a broad dispersion including a peak at around 450 nm, and the peak wavelength and the intensity are found to significantly depend on the irradiation time. Positively charged oxygen vacancies (E′ center) and oxygen-deficiency centers (ODCs) with neutral charge were observed by electron spin resonance (ESR) and photoluminescence (PL), respectively, after irradiation. The formation of the E′ center and the subsequent transformation to ODCs significantly depend on the laser power density. The correlation between the intensity of the peak at around 450 nm and the ESR signal intensity of the E′ center, and also the observation of PL spectrum due to ODCs suggest that self-trapped excitons exhibiting the peak at around 450 nm are created through multi-photon absorption, followed by the formation of the E′ center, and this finally leads to the formation of ODCs.

We have developed a technique to detect Si nanoparticles selectively and to measure size in situ. Applying the technique, we have investigated formation process of Si nanoparticles after pulsed laser ablation of Si targets in Ar gas. Time-resolved photoluminescence (PL) spectroscopy revealed that PL only from Si nanoparticles is observed below 2.4 eV while PL from Si nanoparticles as well as defects in SiO2 is observed above 2.4 eV. Therefore, Si nanoparticles can be detected selectively by excitation light with a photon energy below 2.4 eV. It is found that the onset of the PL from Si nanoparticles is delayed by approximately 0.3 ms from that of the defects and smaller Si nanoparticles. A size can be estimated by a band gap, which is roughly equal to the lowest photon energy at which Si nanoparticles can be excited. Thus, we estimated the sizes of growing Si nanoparticles.

We measured real-time spectra of light transmitted through SiO2 specimens during irradiation of amplified ultrashort laser with a fluence of 540 mJ/cm2. The real-time spectra exhibit a peak at around 400 nm, which significantly depends on the irradiation time. The observation and identification of defects were performed by measurements of electron spin resonance (ESR). Both dependences of the peak at around 400 nm on irradiation time and laser power are in good agreement with those of the ESR signal intensity of positively charged oxygen vacancies (E′ center). This strong correlation shows that self-trapped excitons are created followed by the formation of the E′ center and finally that of ESR inactive centers, namely, oxygen-deficiency centers.

We have performed time-and-space resolved X-ray absorption spectroscopy with a time resolution of 10 ns to study laser-ablated Si particles in a time scale ranging from 0 ns to 120 ns. Neutral and charged particles produced by laser ablation are observed through X-ray absorption spectra. Assignments of transitions from 2s and 2p initial states to higher Rydberg states of Si atom and ions are achieved, and we experimentally determine the LI \kern-1ptI,I \kern-1ptI \kern-1ptI absorption edges of neutral Si atom ( Si0) and Si ions such as Si+, Si2+, Si3+ and Si4+. The main ablated particles are found to be Si atom and Si ions in the initial stage of 0 ns to 120 ns. The relative amounts depend strongly on times and laser energy densities. We find that the spatial distributions of particles produced by laser ablation are changed with supersonic helium gas bombardment, but no cluster formation takes place. This suggests that a higher-density region of helium gas is formed at the top of the plume of ablated particles, and free expansion of particles is restrained by this helium cloud, and that it takes more than 120 ns to form Si clusters.

Two kinds of Er-doped Si-based films have been fabricated by laser ablation. One was grown in solid phase and the other was done in gas phase. For the solid-phase growth, we deposited Er-dispersed SiOx films by laser ablation and annealed them at 1000 °C for forming SiO2 films including Er-doped silicon nanocrystallites. Photoluminescence (PL) measurements were performed at temperature from 6 to 300 K. We successfully fabricated Er-doped films with intense 1.5 μm PL and without thermal quenching by the solid-phase growth. For the gas-phase growth, Er atoms were probably doped in Si nanoparticles during they are growing in Ar gas. The PL intensity gradually decreases with increase in temperature, suggesting that the sites of Er are an important factor for restraining thermal quenching.

We have investigated the formation dynamics of silicon nanoparticles after laser ablation of silicon targets in H 2 gas and O 2 gas diluted with Ar gas by 2D imaging of time-resolved photoluminescence (PL). PL intensity from silicon nanoparticles is found to be enhanced in H 2 gas with partial pressures up to 400 Pa. In O 2 gas, the PL intensity drastically decreases with increasing partial pressures. A broad band green PL indicates that hydrogenated Si nanoparticles are formed in the H 2 gas.

We found a route for synthesizing hydrogenated Si nanoparticles with 550 nm photoluminescence. The hydrogenated Si nanoparticles were synthesized by laser ablation of Si targets in H2 gas diluted with 5 Torr Ne gas. The photoluminescence, which was measured at 90 ms after laser ablation, is most enhanced in H2 gas at a partial pressure of 1 Torr under pulsed-laser excitation at 355 nm. The enhanced photoluminescence is ascribed to hydrogenated Si nanoparticles. The time-resolved photoluminescence spectroscopy revealed that the hydrogenated Si nanoparticles are stable against photoexcitation, while photodesorption of Si2 from Si nanoparticles was observed in Ne gas without H2 gas.

We have investigated responses of PDMS, PMMA and acrylic block copolymers (BCP) to EUV light from laserproduced plasma beyond ablation thresholds and micromachining. We generated wide band EUV light around 100 eV by irradiation of Ta targets with Nd:YAG laser light. In addition, narrow band EUV light at 11 and 13 nm were generated by irradiation of solid Xe and Sn targets, respectively, with pulsed CO2 laser light. The generated EUV light was condensed onto samples, using an ellipsoidal mirror. The EUV light was incident through windows of contact masks on the samples. We found that through-holes with a diameter of 1 μm can be fabricated in PDMS sheets with thicknesses of 10 μm. PDMS sheets are ablated if they are irradiated with EUV light beyond a threshold power density, while PDMS surfaces were modified by irradiation with the narrow band EUV light at lower power densities. Effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals using the practical apparatus. Furthermore, BCP sheets were ablated to have micro-structures. Thus, we have developed a practical technique for microma chining of PMMA, PDMS and BCP sheets in a micrometer scale.

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.