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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.

We have investigated direct nanomachining of inorganic materials using laser plasma soft X-rays. Soft X-rays (X) were generated by irradiation of Ta targets (Ta) with 532 nm Nd:YAG laser light(Y) with a pulse duration of 7 ns, at an energy density of about 10/sup 4/ J/cm/sup 2/. Under the condition, Ta plasma emit soft X-rays at around 10 nm. The soft X-rays were focused on samples (Q) with a spot size of 150 /spl mu/m, using an ellipsoidal mirror (M) that we designed so as to focus soft X-rays at around 10 nm efficiently. It was confirmed that SiO/sub 2/ has optical absorption at around 10 nm. We found that synthetic quartz glass, fused silica, Pyrex, HF, CaF/sub 2/, Al/sub 2/O/sub 3/ and LiNbO/sub 3/ can be machined smoothly by irradiation with laser plasma soft X-rays. Typically, quartz glass is ablated at 40 nm/shot, and has a surface roughness less than 10 nm after 10 shots. In order to investigate lateral resolution, we fabricated a WSi contact mask with 200-nm-pitch line-and-space patterns on quartz glass. We found that quarts glass plates can be machined at a resolution less than 100 nm. In conclusion, we have established a technique for nanomachining a wide variety of inorganic materials using laser plasma soft X-rays at a precision less than 100 nm.

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.

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 demonstrate an electron excitation effect in silicon nanocrystals (SiNCs) embedded in a SiO2 layer treated with hydrogen atoms for passivation of interface defects. Using electron spin resonance (ESR) measurements of quasi-conduction electrons (QCE) excited at lower temperatures, we observed the enhancement of the number of QCE in SiNCs by light irradiation. The electron excitation effect is retained at temperatures lower than 250 K after stopping the light irradiation. The dependence on the size of SiNCs and on excitation laser wavelength suggest that the main memory process is caused by photo-induced electron charging induced through electron excitation of interface states between SiNCs and SiO2.

We found a new filtering effect of hydrogen (H) and deuterium (D) isotope atoms 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. It was determined from H and D mixed-atom treatment of Si wafer with the native oxide and the systematic measurements of Raman scattering of hydrogen molecules (H2, HD, or D2) and secondary ion mass spectrometry. 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.

Si nanocrystals (SiNCs) embedded in formed amorphous SiO2 layer and P nanoscale doping have been investigated by electron spin resonance (ESR) measurements at low temperatures. Hydrogen atom treatment is found to be required to determine the proper doping effects and electronic states of doped donors and quasi-conduction electrons in SiNCs. The dependences of microwave power and temperature for the ESR hyperfine structure of isolated P donors indicate that the spin–lattice relaxation time T1 becomes longer with decreasing size of SiNCs. From the experimental results of donor concentration and temperature dependence, we propose a novel model that the spin property of SiNCs of approximately 5.8 nm size is strongly dependent on the number of donors doped in a SiNC, i.e., odd or even. Using this model, we also estimate the numbers of P donors included in each SiNC to be 1 to at most 6, which are less than 1/10 of the average P doping concentrations.

We have studied three different H2 molecules in crystalline silicon using Raman scattering. The vibrational line at 3601 cm-1 attributable to H2 in Td site is observed both in n-type and p-type crystalline silicon. It is suggested from the hydrogenation-temperature dependence that the charge states and the sites of atomic hydrogen affects the formation of this type of H2. H2 in platelet observed at 4158 cm-1 decreased in its intensity in Si+-implanted silicon. A new vibrational line is detected at 3822 cm-1, and attributed to H2 trapped by hydrogen-related defects such as multivacancies produced by ion implantation.

We have developed a method for synthesizing SiOx films with visible light emission, applying a laser ablation technique. The films were formed by depositing laser-ablated silicon particles in oxygen gas diluted with helium gas. Soft X-ray absorption spectroscopy revealed that the composition of the film is controlled by the total pressure of the gas. Films with particular composition exhibit intense red photoluminescence with a peak below 1.5 eV after annealing in argon gas at 1000°C. In addition to this, most of the films exhibit 2.2-eV photoluminescence after annealing at 500°C. On the basis of these results, the origin of the photoluminescence is discussed.

Luminescent nanometer-sized silicon particles are fabricated by laser ablation of a silicon target in helium gas. The formation of products is found to be governed by the dynamics of the laser-ablated silicon particles in the gas. The products deposited on silicon substrates exhibit light emission with a peak at 1.6 eV in the air, while 2.1 eV after annealing for 20 min at 800°C in oxygen gas. Applying the laser ablation technique, we demonstrate a novel technique for fabricating silicon particles embedded in a silicon dioxide film. The particles also exhibit visible light emission.

We have investigated hydrogen molecules ( H2) formed in heavily doped n-type silicon by remote hydrogen atom treatment. We measure the Raman lines of H2 as a function of the substrate temperature during hydrogen atom treatment. A broad vibrational Raman line of H2 can be clearly observed at around 4158 cm-1 for substrate temperatures between 250 and 500° C, indicating that hydrogen exists in molecular form in crystalline silicon. The vibrational Raman line of H2 has a maximum intensity for a substrate temperature of 400° C. An isotope shift is also detected at around 2990 cm-1 in silicon treated with deuterium atoms at 400° C.

We have studied hydrogen passivation of phosphorus (P) donors and hydrogen states in heavily doped n-type silicon by electron spin resonance (ESR) of P donors and conduction electrons. A remote-treatment method of atomic hydrogen was used for the introduction of H atoms. The hydrogen passivation fraction measured in the P-doped Si samples shows strong dependence on donor concentration. The most effective substrate temperature for hydrogen passivation is between 100 and 120° C. It is found, from the reactivation of hydrogen-passivated P donors by isochronal annealing, that the recovery stage of P donors shifts to higher temperatures with decreasing donor concentration. These results suggest that the binding of the P–Si–H complex due partially to the Coulomb interaction decreases with increasing P concentration. Hydrogen-induced platelets are also discussed.

We have investigated the dynamic behavior of laser-ablated Si particles by means of time-resolved X-ray absorption spectroscopy. Laser-ablated Si particles are found to induce sputtering of an Al plate which is located near the Si target. Moreover, it is suggested that Si cluster formation is enhanced by collisions between laser-ablated Si particles and Si particles backscattered by a Si wafer located near the Si target. We tentatively assign unidentified X-ray absorption peaks appearing near 120 eV to small Si clusters.

Electronic states of a shallow donor in InP are investigated as functions of donor concentration (N D–N A) from 4.0×1015 to 5.5×1016/cm3 by electron spin resonance (ESR) at low temperatures. The Overhauser shift, nuclear spin-lattice relaxation time T 1N, and g-value are found to strongly depend on N D–N A; i.e., T 1N has a maximum at around 7×1015/cm3, while the g-value increases with increasing donor concentration, ranging from 1.2024 to 1.2143. Sweeping the magnetic field at appropriate speeds yields significantly inhomogeneous broadening of the ESR line, indicating that the ESR comes from bound donor electrons at least below N D–N A of 1.5×1016/cm3. A model of donor clusters is proposed to interpret the obtained results. The donor-concentration dependence of the g-values indicates that the donor states are significantly changed with the average donor-cluster size.

A time-resolved X-ray absorption spectroscopy apparatus in the laboratory scale has been set-up which utilizes laser plasmas as a soft X-ray source. One of the major objectives using this apparatus is to observe X-ray absorption fine structures (XAFS) of various materials during materials processing in an energy region between 100eV and 3keV. For this purpose, we have provided two sets of optical and detecting systems, i.e., a toroidal mirror, grazing incidence flat-field grating and MCP for lower energy region (100-1000eV), and a toroidal mirror, curved KAP crystal and MCP for higher energy region (1-3keV). The most intense X-rays are generated from Au plasma and the intensity reaches as high as 1016 photons/pulse in 2π steradian in the energy region below 300eV. In this case, the conversion efficiency of the laser energy to X-rays is 4.6%. The energy resolution of the spectrometer ΔE/E has been found to be 5×10-3. We show some examples of XAFS measurements on carbon during laser ablation.

In addition to the two groups of radiative fragments which have previously been described, two groups of nonradiative fragments are first observed in laser-ablated fragments of YBa2Cu3O y , using a space/time-resolved optical transmittance measurement. The average velocities of the nonradiative fragments (2×105 cm/s and 2×104 cm/s) are much lower than those of the radiative fragments (5×106 cm/s and 1×106 cm/s). The yield of the nonradiative fragments increases with increasing laser wavelength, while that of the radiative fragments is nearly wavelength independent.

We find from an electron spin resonance (ESR) study that the efficiency of hydrogen passivation of phosphorus donors in silicon decreases from 35 to 0 percent as the donor concentration increases. The measurement of the depth profile of deuterium by secondary ion mass spectrometry (SIMS) shows that deuterium concentration becomes smaller at a P peak region with donor concentrations higher than a critical value (∼1×1019/cm3). These results indicate that hydrogen becomes inactive for H-P complex formation in heavily donor-doped, metallic silicon.

Improvement in the characteristics of YBa2Cu3O y superconducting thin films was performed by a second laser irradiation method. Particles in the laser ablated plume were decomposed and/or excited by the second laser irradiation. By controlling a time delay of the second laser from the ablation laser, ablated particles with average velocities of 1×106 cm/s and 2×105 cm/s were irradiated with the second laser. Notable improvement was observed when the slower ablated particles were irradiated with the second laser.

Paramagnetic defects have been studied over a wide dose range. At doses>6×1014 P+/cm2, only one isotropic spectrum of g=2.0062±0.0004 which characterizes a continuous amorphous layer is observed. At doses between 0.1 and 6.0×1014 P+/cm2, four types of paramagnetic defect centers coexist. One is a new center that shows motional effect at around 200 K and has a very short spin-lattice relaxation time. The others are the isotropic center with g\fallingdotseq2.006 which originates from isolated amorphous regions, the Si-B2 and -P3 centers and the spin-lattice relaxation time of these centers increases in this order. The spin-lattice relaxation time of the new center is between that of the isotropic center (~10-6 sec) and the Si-B2. Among the isolated defect centers, the new and Si-B2 centers become dominant instead of the Si-P3 center with increasing dose to ~1014 P+/cm2. Three types of motional effects are considered from the observed ESR spectra.

It is demonstrated that a deep level of a paramagnetic off-center substitutional N can be determined by electron spin resonance (ESR) measurements of the peak-to-peak derivative linewidth Δ H msl over a wide temperature region from 150 to 550 K. The temperature dependence of Δ H msl observed above ∼330 K is interpreted in terms of one type of motional broadening. According to this model, we obtain an energy level of 0.33±0.02 eV below the conduction band and the electron capture cross section σ0 of 1.0×10-15 cm2, which are in agreement with one of the levels obtained by deep-level transient spectroscopy (DLTS).

Atomic migration of metallic atoms in the interfaces of Au-Si and Ni-Si is investigated with emphasis on the difference among c-Si, a-Si:H/c-Si and a-Si:F:H/c-Si. 40 MeV-O5+ ion backscattering spectra of the Au-Si system heat-treated at 350°C for 30 min indicate that Au atoms of more than 1020cm-3 were distributed in Si up to a depth of about 1 µm and 3 µm for a-Si:F:H/c-Si and a-Si:H/c-Si, respectively. Because the thickness of a-Si is about 5000 Å, this means that a large amount of Au migrated not only in the a-Si film but also into the substrate of c-Si even below the eutectic point, while Au-migration was not observed in the case of direct contact interface between Au and c-Si.

We have investigated energy beam irradiation of high-T c superconductors which were treated in various ways. It is found for the first time that infrared-light irradiation and cw-laser irradiation for short periods are useful to get an orthorhombic phase with T c of about 90 K at local regions from a tetragonal phase or a quenched amorphous-like phase, including mixed tetragonal and orthorhombic phases. It is likely that an amorphous phase produced by ion implantation of 400 keV O+ up to a dose of 1×1017/cm2 is transformed to the superconducting orthorhombic phase by thermal annealing at 900 and 950°C.

For the formation of Y-Ba-Cu oxide films by pulsed-laser sputtering, the dependence on laser energy density was first investigated over a wide range from 0.6 to 3 J/cm2 at 1.064 µm. Rutherford backscattering spectrometry proved that the composition of deposited films strongly depends on the energy density. Films formed at a narrow window of laser energy density from the sputtering threshold of 0.6 J/cm2 to 0.8 J/cm2 showed superconductivity with a T c onset at 81 K and zero resistance at 79 K in spite of an excess of Cu and Ba atoms after annealing in oxygen. The X-ray diffraction patterns showed that these films have highly preferred orientation of the c-axis, and scanning electron microscopy exhibited the texture of highly dense grains with large sizes of about 5 µm at the surface.

By analyzing the electrons emitted at 180° with respect to the ion-beam direction, we have carried out an improved measurement of the energy-degradation spectra of Si K-shell Auger electrons induced by 18- and 24-MeV He++. The ions were incident on a silicon single crystal under shadowing and random conditions. From the analysis of the degradation-spectrum width for the shadowing conditions, the stopping power for 1.6-keV electrons in a silicon crystal was determined as 1.50±0.08 eV/Å, close to the theoretical value of 1.6 eV/Å obtained by Tung et al. The present results are almost consistent with a previous work by Kudo et al. carried out under different experimental conditions.

The electrical properties of laser-annealed glow-discharge amorphous silicon (GD a-Si) layers have been studied. The principal results obtained are as follows: (1) electrical measurements show that the resistivity of the GD a-Si layer is decreased by four to five orders of magnitude by the laser annealing; (2) Rutherford back-scattering measurements show that the hydrogen content in the GD a-Si layer deposited at room temperature is about 35 atomic percent, and this H2 is not effused from the sample by the laser annealing when the power is near the threshold energy density; (3) reflection electron diffraction measurements show that the GD a-Si layer is transformed into a polycrystalline silicon layer by laser annealing.

The Si lattice temperature during pulsed-laser annealing has been measured by an interference method, namely a time-dependent optical reflectivity measurement on SOS. This method utilizes optical interference effects between the light reflected from the Si surface and that from the Si-sapphire interface. It was found that the Si lattice temperature increased to at least approximately 1000°C during pulsed-laser annealing. Additionally, this work clarifies the temperature dependence of the refractive index n(T) of Si for a wavelength of 6328 Å, i.e. n(T)=3.98+4.7×10-4 T(°C).

By using single-crystal targets of MgO and GaP, we have measured the energy-degradation spectra of K-shell Auger electrons induced from Mg and P by twenty-MeV He++ ions. The spectra measured under ion-beam shadowing conditions were interpreted through a modified model in which multiple angular deflection of Auger electrons is taken into account. From the analysis, the stopping power for 1.18-keV electrons in MgO was determined to be 2.10±0.21 eV/Å, and that for 1.86-keV electrons in GaP was determined to be 1.60±0.15 eV/Å.

Hg loss from the near-surface region of Hg1-x Cd x Te with and without anodic oxide caps by a 60-min heat-treatment has been estimated for x≃0.2 and x≃0.3 from 40-MeV-O5+ backscattering spectra. The Hg loss rate for various heat-treatment temperatures T was compared with the T-dependence of the Hg content of the oxide films. For x≃0.2, the Hg loss of a sample with 1000 Å oxide film exceeded 1×1017 Hg/cm2 at T>300°C, while that of the uncapped sample reached the same level around T=250°C. For x≃0.3, the Hg loss was not appreciable up to 320°C, even for an uncapped sample; however, it exceeded 1×1017 Hg/cm2 around T=340°C, even for a capped sample. Furthermore, the Hg content of anodic oxide films rapidly decreased in the temperature range 250∼290°C for both x≃0.2 and x≃0.3. These behaviours suggest that protective effect of the oxide cap against Hg loss decreases with decreasing Hg-content of the films.