Search

Thermal annealing effects on Zn + ion-implanted silica glass (a-SiO 2 ) have been studied in order to control void formation. Void formation in a-SiO 2 with Zn + ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn + ions of 60 keV were implanted into a-SiO 2 to a fluence of 1.0 × 10 17 ions/cm 2 . After the implantation, thermal annealing at 600 or 700 °C for 1 h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10–15 nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600 °C in oxygen gas. Annealing in oxygen gas at 700 °C for 1 h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO 2 substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10–25 nm in diameter inside the a-SiO 2 . These results indicate that the oxidation at 700 °C for 1 h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids.

Enhancement of surface plasmon resonance (SPR) in optical absorption has been found on Cu ion-implanted SiO 2 substrate modified by micro-indentation and post-annealing. Micro-indentation effects on surface plasmon resonance (SPR) in optical absorption have been studied to control nanoparticle formation in Cu ion-implanted SiO 2 substrate. The SiO 2 was firstly implanted with 2 MeV Cu 2+ ions at an ion flux of 4 μA/cm 2 , up to a fluence of 6 × 10 16 ions/cm 2 . After the ion implantation, dot-array patterns of micro-indents were made by a micro-Vickers hardness tester, and followed by annealing at 600 °C in vacuum for 1 h. The optical absorption spectra of the indented region and the non-indented flat region were measured and compared with each other. After post-annealing at 600 °C, the indented area showed higher absorbance of SPR at 2.2 eV than that of the flat region annealed under the same annealing conditions. The TEM study shows larger and denser Cu precipitates inside the indentation than those in the flat area. The results indicate that the defects produced by indentation enhance the atomic migration in the plastic zone during thermal relaxation process, resulting in promoting the enhanced precipitation of Cu nanoparticles.

The optical propagation property of a planar waveguide with a periodic nanoparticle grating layer is characterized by using sliding prism method. Here, Cu nanoparticle grating was fabricated on a-SiO 2 substrate by periodic heavy-ion irradiation technique. The pitch of these gratings was 2 μm and 3 μm, respectively. The flux and fluence were at the range of 6–10 μA/cm 2 and 6 × 10 16 –1 × 10 17 ions/cm 2 , respectively. The grating effect, mainly including the mode selection effect, is observed. The effect depends on the pitch of the grating and the morphology of nanoparticles. The propagation loss of the waveguide induced by nanoparticle layer is evaluated.

Nanoscopic network structure of N -isopropylacrylamide (NIPAM) gel cross-linked with N , N ′-methelenbisacrylamide (BIS) was replicated in sol–gel derived silica matrix. As a result of that, the silica became a nanoporous solid with a high-porosity, which reaches 60–80%. The porosity was totally due to mesopores whose size was within 10 nm. Electron microscope observation revealed that the nanoscale network structure were replicated in the silica matrix as considered to be constituted from the main polymer chains and their interconnecting cross-linkers. The mesh size observed in the TEM micrograph matches the span length estimated from the molar ratio (∼80) of the main chain moiety (NIPAM) to that of cross-linker (BIS). When the weight ratio of NIPAM to silica matrix is smaller than unity, the pore size distribution measured by nitrogen adsorption/desorption has a sharp peak at 2 nm indicating that the worm-like nanopore is formed as a replica of an individual NIPAM chain. The peak position in the pore size distribution shifts to a larger value as the weight ratio of NIPAM was increased, suggesting the nanoscale segregation of NIPAM chains in the silica matrix. Therefore, the resultant size of the nanopores are considered to be determined at the moment of the structural freezing caused by the completion of the cross-linking in NIPAM gel. The completion of cross-linking (gellation) eliminates the mobility both of silica and NIPAM/BIS moiety. The TEM micrograph of a sample prepared at a large weight ratio also shows that larger nanopores tend to be generated when the template NIPAM moiety is more abundant.

Enhancement of surface plasmon resonance (SPR) in optical absorption has been found on Cu ion-implanted SiO2 substrate modified by micro-indentation and post annealing. The SiO2was firstly implanted with 2 MeV Cu2+ ions, at an ion flux of 4 μA/cm2, up to a fluence of 6 × 1016 ions/cm2 at room temperature. After the ion implantation, dot-array patterns of micro-indents were made by a micro-Vickers machine, and annealed at 600 °C, 700 °C and 800 °C in vacuum for 1 h. The optical absorption spectra of the indented region and the non-indented flat region were measured by a dual beam spectrometer. After post annealing at different temperatures, all the indented areas showed higher absorbance of SPR at 2.2 eV, comparing to the flat region annealed under the same annealing conditions. In particular, the SPR enhancement reached maximum after 600 °C annealing, and decreases with further increasing annealing temperature. The result of SPR enhancement by the micro-indentation suggests that the indentation-induced deformation enhances the atomic migration, resulting in promoting the precipitation under thermal annealing.

A new method for nanoparticle planar control has been proposed based on optical laser-lithography technique. With this method, the planar spatial resolution of the lithography is improved. Combining the lithography with subsequent ion-irradiation technique, a two-dimensionally (2D) patterned structure of Cu nanoparticles in a silica substrate is obtained with a sub-micrometer spatial resolution. The size of each “spot” is 500 × 500 nm 2 , and the pitch is 2 μm. Planar TEM image and the result of scanning near-field optical microscopy (SNOM) verify the nanoparticle 2D-patterned distribution. Further improvement of the processing may enable 2D nanoparticle patterning with a pitch on a sub-micrometer scale.

Surface recession due to sputtering under low-energy and high-fluence heavy-ion implantation makes shallower and broader depth profile of implanted ions than those calculated by conventional ion-range simulation-codes such as SRIM. Depth profiles of Zn atoms in silica glasses (SiO2) implanted with Zn+ ions of 60 keV up to 1.0×1017 ions/cm2 were evaluated using both experimental methods as Rutherford backscattering spectrometry (RBS), sputtering depth-profiling by X-ray photoelectron spectroscopy (XPS), and an advanced numerical simulation code TRIDYN, which includes the sputtering loss effects. The TRIDYN code predicts the shallowing of the projectile range from ∼46 to ∼27 nm with increasing the fluence up to 1×1017 ions/cm2, and very high-concentration (∼20 at%) of Zn atoms close to the surface. However, RBS and XPS results exclude such high concentration close to the surface. These results suggest remarkable redistribution of Zn atoms from the nearer surface to the deeper region during the implantation. In fact, Zn-atom concentration near the surface and that near the projectile range are, respectively, lower and higher than those by the SRIM code predictions.

Silica glasses (SiO 2 ) were implanted with Zn + ions of 60 keV to a fluence of 1.0 x 10 17 ions/cm 2 , and were annealed in oxygen gas flow at 700 °C for 1 h, to form ZnO nanoparticles (NPs). In as-implanted state, metallic Zn NPs of 10-15 nm in diameter are formed between 10 and 50 nm in depth. NPs are not observed on the surface and down to 10 nm in depth. After the annealing at 700 C for 1 h in oxygen gas, ZnO NPs of ∼ 10 nm in diameter are observed around 50 nm in depth. Moreover, droplet-like ZnO NPs larger than 30 nm in diameter grow on the surface of SiO 2 substrate. Migration of Zn atoms toward the surface, i.e., shallowing of the depth profile, is observed under the oxygen annealing, while vacuum annealing at the same temperature 700°C does not induce any prominent migration of Zn atoms. Mechanisms of the shallowing and the formation of ZnO NPs are discussed.

Kinetic processes of nanoparticle formation by ion implantation was studied for the insulators of a-SiO 2 , LiNbO 3 , MgO · 2.4(Al 2 O 3 ) and PMMA, either by changing ion flux or by using a co-irradiation technique of ions and photons. Under Cu-implantation of 60 keV Cu − , nanoparticles spontaneously formed without thermal annealing, indicating radiation-induced diffusion of implants. The high-flux implantation caused instable behaviors of nanoparticle morphology in a-SiO 2 , LiNbO 3 and PMMA, i.e. enhanced atomic rearrangement or loss of nanoparticles. The spinel MgO · 2.4(Al 2 O 3 ) also showed nanoparticle precipitation at 60 keV, but the precipitation tendency is less than the others. Combined irradiation of 3 MeV Cu ions and photons of 2.3 eV or 3.5 eV indicates that the electronic excitation during ion implantation significantly enhances nanoparticle precipitation, greatly depending on photon energy and fluence. The selectivity for photons can be applied to control nanoparticle precipitation.

In the negative ion based neutral beam injector (N-NBI) for JT-60U, an extension of the pulse duration up to 30 s has been intended to study quasi-steady state plasmas, where the NBI pulse duration is significantly longer than the plasma current diffusion time. Achieving long pulse injection requires a reduction of the heat load on the grids of the ion source. The ion source was modified to reduce the pressure within the grid structure by increasing the vacuum conductance of the acceleration grids. The acceleration efficiency was improved from 0.74 to 0.79. The heat load of the grounded grid, which was the main heat load of the acceleration grids, decreased from 9.2 to 7.0% at a constant arc chamber pressure of 0.3 Pa. These improvements seemed to be caused by the reduction of beam ion stripping loss. Up to now, a long pulse injection of 17 s at the power of 1.6 MW with beam energy of 366 keV was obtained by using one ion source. The temperature rise of the cooling water from the grounded grid saturated at less than 35 °C during operation, so the heat load of the grid is significantly reduced for steady state operation at this power level.

Implantation of 60 keV Cu − ions into LiNbO 3 resulted in formation of complex nanocomposites consisting of metal Cu nanoparticles distributed among nanodomains of the host medium. The nanodomains of the host medium correspond to regions of a few hundred naometers in diameter with a constant refractive index. Distributions of the Cu nanoparticles and nanodomains in the implanted region do not correlate with each other. Variations of linear and non-linear optical absorption of the nanocomposites are mainly determined by the change of chemical composition and structure of implanted regions of LiNbO 3 .

Negative ion implantation has been applied to polymers in order to modify the surface and to fabricate nanoparticles. Metal nanoparticles in the vicinity of a polymeric surface are promising for biomedical applications as well as nonlinear optical applications. Substrates of polymethyl methacrylate (PMMA) were implanted with Ag− and Cu− of 60 keV at 3 μA/cm2 up to 3×1017 ions/cm2. Optical absorption spectra of the implanted PMMA were measured in a photon range from 0.5 to 4.5 eV. A peak of surface plasmon resonance (SPR) emerges in the absorption spectra above about 1×1017 ions/cm2, both for the Ag− and Cu− cases. A coexisting absorption slope, due mostly to defects, increases but tends to saturate with ion fluence. The SPR peak of Ag-implanted PMMA is much broader than that of the Cu-implanted one. Corresponding to the SPR spectra, metal nanoparticles are observed by cross-sectional TEM. With increasing ion fluence, the Ag nanoparticles spread out towards the surface, in contrast to the localized Cu nanoparticles. The results demonstrate that metal nanoparticle fabrication in polymers is capable by using appropriate low-energy ions and provides a variety of spatial distributions dependent on ion species and fluence. In particular, Ag− ion implantation fabricates surface-exposed/gradient nanoparticles, which are suitable for biomedical applications such as anti-microbial effects.

Spectra of the optical transmission and ion-induced photon emission (IIPE) of silica glass were measured during implantation of 60 keV Cu − ions at ion fluxes from 1 to 75 μA/cm 2 up to a fluence of 2 × 10 17 ions/cm 2 , aimed at monitoring the formation of Cu nanoparticles. The precipitation threshold of Cu atoms is flux-dependent. At fluxes from 1 to 10 μA/cm 2 , the formation of nanoparticles is efficient up to fluences of 2 × 10 17 ions/cm 2 . The efficiency of IIPE of Cu + solutes in silica glass (band at 2.25 eV) is proportional to a total concentration of Cu solutes. In a single-phase region (solid solution of Cu atoms), the efficiency of IIPE of Cu + solutes is flux-independent. In a two-phase region (solid solution and Cu nanoparticles), the dynamic balance between the nanoparticles and Cu solutes determines the flux-dependent behavior of the efficiency of IIPE.

Silica glass was implanted with negative 60 keV Cu ions at an ion flux from 5 to 75 μA/cm2 up to a fluence of 1 × 1017 ions/cm2 at initial sample temperatures of 300, 573 and 773 K. Spectra of ion-induced photon emission (IIPE) were collected in situ in the range from 250 to 850 nm. Optical absorption spectra of implanted specimens were ex situ measured in the range from 190 to 2500 nm. IIPE spectra showed a broad band centered around 560 nm (2.2 eV) that was assigned to Cu+ solutes. The band appeared at the onset of irradiation, increased in intensity up to a fluence of about 5 × 1015 ions/cm2 and then gradually decreased indicating three stage of the ion beam synthesis of nanoclusters: accumulation of implants, nucleation and growth nanoclusters. The IIPE intensity normalized on the ion flux is independent on the ion flux below 20 μA/cm2 at higher fluences. The intensity of the band increased with increasing samples temperature, when optical absorption spectra reveal the increase of Cu nanoparticles size.

Formation processes of nickel oxide (NiO) nanoparticles (NPs) in silica glass (SiO2) by implantation of 60 keV Ni− ions combined with thermal oxidation are studied using cross-sectional transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry. In as-implanted state, Ni metallic NPs form within the surface layer of ∼80 nm thick. The mean depth 〈z〉 and the standard deviation 〈(Δz)2〉1/2 of Ni atom distribution determined by XTEM were 43 and 15 nm, respectively. After the oxidation at 800 °C for 1 h, 〈z〉 and 〈(Δz)2〉1/2 became 47 nm and 20 nm, respectively, i.e. the distribution was almost the same except a small diffusional shift to the deeper region. Mean volume of Ni- and NiO-NPs after heat treatments at 800 °C were 27 and 43 nm3, respectively. The larger mean volume of NiO-NPs is explained from the fact that NiO-NPs include both Ni and O atoms, i.e. approximately 2N atoms, while Ni-NPs include Ni atoms only, i.e. N atoms. Both the Ni- and NiO-NPs include 2.4 × 103 Ni atoms per NP in average. These results indicate that NiO-NPs are formed by oxidation of Ni-NPs without pronounced redistribution of Ni atoms.

Spectra of ion-induced photon emissions (IIPE) of silica glass were measured during implantation of 3 MeV Cu ions at a constant flux of 3–10 μA/cm2 up to a fluence of 9×1016 ions/cm2. Three bands compose the IIPE spectra: a tail of the oxygen-deficient center band, the band of Cu+ ions at 2.27 eV and the band of non-bridging oxygen hole center at 1.89 eV. Intrinsic defects of silica glass contribute to the IIPE at the onset of irradiation only. At fluences higher than 5×1014 ions/cm2, the fluence dependence of the Cu+-band of IIPE represents (a) the accumulation of Cu solutes preceding the nanoparticle formation and (b) no change of Cu solute concentration during nanoparticle growth. The intensity of the Cu+-band is proportional to the total concentration of Cu solutes. The balance of Cu solutes and Cu nanoparticles is sensitive to the ion flux. The concentration of Cu solutes necessary for nanoparticle formation cannot be attained at fluxes higher than 10 μA/cm2.

Magnetic nanoparticles are fabricated in silica glass (SiO2) using high-flux implantation of 60 keV negative nickel ions Ni−. Photo-absorption measurements and cross-sectional transmission electron microscopy (XTEM) observation confirm the formation of metallic Ni nanoparticles in SiO2, and exclude the possible formation of Ni silicides (Ni3Si, Ni2Si, NiSi) and oxides (NiO) as major products. The mean diameter of the nanoparticles was ∼2.9 nm, and the observed depth distribution was similar to a prediction from the TRIDYN code when sputtering was accounted for. Temperature- and field-dependences of magnetization show that the nanoparticles are in the superparamagnetic state at T>∼50 K. From the peak temperature of the zero-field cooling (ZFC) magnetization, which is ∼27 K, and the mean diameter determined from XTEM, it is suggested that the magnetic anisotropy constant K of the nanoparticles is enhanced by ∼8 times as compared to the bulk value.

Negative ion implantation has been applied to fabricate metal nanocomposites of metals and polymers which are promising for nonlinear electronic, optical and biomedical applications. We have studied nanoparticle formation processes of Ag and their effects on surface properties of polymers, in comparison with those of Cu. Polycarbonate (PC) substrates were irradiated by negative Ag and Cu ions of 60 keV to various doses up to 3 × 1017 ions/cm2. Optical absorption spectra of the irradiated PC were measured in the range from 0.5 to 4.5 eV. Surface- and nanoparticle morphology of the PC were studied by AFM and cross-sectional TEM. Depth profiles of implant concentrations were evaluated by RBS. A surface-plasmon-resonance peak of Ag around 2 eV appears in the optical spectra of PC implanted to a dose of 1 × 1017 ions/cm2, whereas their defect absorption is not significant. The TEM and RBS measurements show that well-defined implantation is capable at this fairly low energy, though surface recession takes place because of ion sputtering. The structure of PC is stable enough for formation of Ag nanocomposites. Depth distribution of Ag nanoparticles significantly shifts towards the surface, differently from the case of Cu nanoparticles. Negative ion implantation provides nanoparticle formation for surface modification of polymers, with understanding the ion-induced precipitation processes in the polymers.

Kinetic behaviors of nanoparticle formation in LiNbO 3 have been studied with negative Cu ion implantation and the effects on nonlinear optical properties have been discussed. Negative Cu ions of 60 keV are implanted into LiNbO 3 disks at fluxes up to 50 μA/cm 2 . Ion-induced photon spectroscopy was applied to monitor the ion-substrate interactions and the nanoparticle morphology was studied by cross-sectional TEM. Metal precipitation behaviors as well as the matrix stability significantly depended on ion flux. In a flux range of 3–10 μA/cm 2 , LiNbO 3 showed spontaneous formation of Cu nanocrystals of ∼10 nm, including nonspherical shape. Crystallinity of the LiNbO 3 lattice implanted was sustained up to 3 × 10 16 ions/cm 2 . The Cu nanoparticles in LiNbO 3 showed a sub-picosec nonlinear optical response. However, significant Li-atom release to the vacuum was detected by ion-induced photon spectroscopy, indicating formation of a Li-depleted zone. Particularly above a flux of 30 μA/cm 2 , significant coarsening of Cu particles and amorphization of the LiNbO 3 lattice occurred. The results indicate that metal nanoparticle formation in LiNbO 3 is sensitive to the ion flux and that the optimization is requisite to fabricate well-defined nanocomposites.

Implantation of Cu negative ions of 60 keV induces frequency shifts of infrared (IR) vibration modes of SiO 2 . Since the penetration depth of IR light is much larger than the projectile range of Cu − ions, conventional IR reflection spectroscopy detects little shifts. To evaluate the true shifts induced by the implantation, the near-surface sensitive IR reflection spectroscopy (NSS-IRRS) was applied using a suitable sample structure. Distinct shifts of −5, +6 and −44 cm −1 , respectively, are observed in rocking, bending and stretching modes of Si–O–Si bonding of SiO 2 . Ion-flux dependence was examined in the flux range of 0.95–100 μA/cm 2 with keeping the total fluence 3×10 16 ions/cm 2 . Almost no ion-flux dependence is observed in the shifts of these modes, which is in contrast with the strong flux dependences of size- and depth-distributions of Cu nanoparticles in SiO 2 .

Although ion implantation has a unique merit in fabricating immiscible metal–insulator composites being promising for non-linear optical applications, high-flux implantation especially is subject to pronounced atomic transports, either inside or outside the solid. Negative Cu ions of 60 keV irradiated substrates of a-SiO 2 and MgO · 2.4(Al 2 O 3 ) at fluxes up to 100 μA/cm 2 . Atomic redistribution of Cu nanoparticles inside the substrate was observed by cross-sectional TEM. Atomic release of Cu implants out of the substrate was detected by ion-induced photon spectroscopy, with fast-response CCD cameras. Spontaneous metal precipitation in insulators is attained at high flux. The ion-induced photon spectra of a-SiO 2 consist of sharp line spectra and a broad luminescence. The presence of line spectra demonstrated the outward transport into vacuum and loss of Cu atoms via the surface to the vacuum. Cations in MgO · 2.4(Al 2 O 3 ) are also significantly released to the vacuum via the surface. The outward mass transport results from ion-induced sputtering/sublimation of implants, concurrently with radiation-induced diffusion towards the surface.

High energy accelerator and high current ion source development have been carried out at JAERI for negative-ion based neutral beam (N-NB) systems of JT-60U and ITER. One of R&D issues on the ITER prototype 5-staged electrostatic accelerator was voltage holding capability of the accelerator insulator column. By installing a stress ring, which reduces electric field concentration at the triple junction (interface of metal flange, insulator, and vacuum), 300 kV is held at each stage instead of rated voltage of 200 kV. At present the accelerator insulator column sustains 900 kV stably with the rings in all five stages. In the JT-60U N-NB system, a beamlet deflection by distorted electric field was found at the bottom of the extractor. Correcting the distorted field, reduction in beam divergence was confirmed for the overall beam. As the result, the heat load on the NB port limiter of JT-60U, located about 20 m away from the accelerator, was reduced to less than a half of the previous value before the correction. Consequently, we have succeeded in 10 s continuous injection of H 0 beam with the NB power of 2.6 MW at 355 keV.

Metal nanoparticle formation and radiation resistance of polymers with heavy ion implantation have been studied to develop modification process of the optical properties of polymers. Negative Cu ions of 60 keV were implanted into high-density polyethylene (HDPE), polystyrene (PS) and polycarbonate (PC) at 1 μA/cm 2 up to a total dose of 1.5 × 10 17 ions/cm 2 . Optical absorption spectra at high total doses show surface plasmon resonance, indicating formation of Cu nanoparticles for all the polymers. The onset dose at which the plasmon peak appears depends on the polymer species. The metal nanoparticle formation in polymers is confirmed by cross-sectional TEM. Depth profiles of Cu atoms evaluated by RBS do not indicate distinct ion-induced diffusion. The FTIR-ATR spectra show fairly good resistance against radiation damage in the order of PC, PS and HDPE. These results indicate that low energy Cu − irradiation at appropriate doses does not cause serious damage on the polymer matrices, and that Cu atoms implanted into the polymers cause nanoparticle precipitation to be promising for optical application.

Metal nanoparticles embedded in insulators exhibit a strong surface resonance and have been studied for optical switching. In this study, negative Cu ions of 60 keV were implanted into a-SiO2, MgO · 2.4(Al2O3) and LiNbO3 at 10–50 μA/cm2 to 1 × 1017 ions/cm2. The resultant nanoparticle morphology was studied by cross-sectional TEM and shown to depend on the substrate species. The a-SiO2 showed the formation of spherical Cu nanocrystals of ∼10 nm. The MgO · 2.4(Al2O3) suppressed particle coarsening even at high dose rates, sustaining crystallinity of the lattice. On the other hand, the LiNbO3 exhibited non-spherical Cu nanocrystals of ∼10 nm. Ion-induced photon spectroscopy was applied to monitor the ion–substrate interactions from outside of the substrates. The non-linear optical properties were evaluated by a pump–probe method around the plasmon energy of about 2 eV. Although LiNbO3 exhibited a sub-picosec non-linear response, ion-induced photon spectroscopy revealed Li-atom release to the vacuum under ion implantation, influencing the Cu nanoparticle formation.

Ion irradiation induces a frequency shift of Si–O–Si stretching vibration (ω4 mode, ∼1100 cm−1) in SiO2. Since the penetration depth of IR light is much larger than the projectile range of low-energy heavy ions (∼200 keV or less), conventional IR reflection spectroscopy detects a smaller shift than the true one. The near-surface sensitive reflection spectroscopy (NSSRS) was applied using a suitable sample structure, and obtained the true shift of ∼44 cm−1. The coherent two-layer reflection model, with the true shift value, well reproduces the spectra of the irradiated SiO2, and indicates that the ion-induced ω4 peak shift obtained with NSSRS has the same origin with the ion-induced 1040 cm−1 shoulder obtained with conventional spectroscopy. The present results indicate that the ω4 peak shift is ascribed not to the compaction, but to the Si–O–Si bond-breaking.

Amorphous (a-) SiO2 substrates were irradiated with 30 keV Au−, 60 keV Au− and Au2− ions up to total dose 1 × 1017 atoms/cm2. The growth of metal nanoparticles in the implanted layer was observed by cross-sectional transmission electron microscopy. Optical absorbance spectra of all implanted specimens exhibited a distinctive peak associated with a surface plasmon resonance of Au nanoparticles. The resonance energy and spectral shape of the absorbance spectra are similar in case of monoatomic and diatomic Au ion bombardment. The spectral similarity in the low-energy implanted samples reflects the importance of post-collision processes, such as diffusion and thermodynamic processes in metal nanoparticle formation.

Simultaneous laser irradiation under ion irradiation is conducted to control nanoparticle precipitation in amorphous (a-)SiO 2 . Copper ions of 3 MeV and photons of 532 nm by Nd:YAG laser are irradiated to substrates of a-SiO 2 . The ion dose rate and total dose are set at 2–10 μA/cm 2 and 3.0 × 10 16 –3.0 × 10 17 ions/cm 2 , respectively, and the laser power density is 0.05–0.2 J/cm 2 pulse at 10 Hz. The laser is simultaneously irradiated with ions in the co-irradiation mode, and the result is compared to that in the sequential and ion-only irradiation. Cross-sectional TEM of the irradiated specimens is conducted after measuring optical absorption spectra. In the case of co-irradiation of intense laser power and high dose (0.2 J/cm 2 pulse and 3.0 × 10 17 ions/cm 2 ), Cu nanoparticles precipitate much more extensively than in the sequential irradiation, increasing both the particle diameter and the total Cu atoms in the nanoparticles. The optical absorption spectra show a surface plasmon peak of the nanoparticles. The precipitation enhancement in the co-irradiation mode suggests that the electronic energy is absorbed by the dynamic electronic states and promotes the Cu precipitation via enhancing the atomic migration.

Metal-ion implantation is well established as a suitable technique for fabrication of nanoparticles embedded in insulators. Photon emission induced by 60 keV Cu − incident ion was in situ measured over a wavelength range from 200 to 900 nm. Special attention was paid to the behavior of the Cu I atomic line emission related to the mass transport of implants. Based on comparison of experimental results for the wide band gap materials (SiO 2 and MgAl 2 O 4 ) with those for metals (W, Mo, Al), it is concluded that, at the beginning of ion bombardment, the radiation is mostly emitted by backscattered atoms. The causes of this are different for the different groups of materials: the high backscattering yield in the case of metals and the high survival probability of the excited backscattered atoms in the case of insulators, when the excitation levels lie below the conduction band edge and the radiative decay is only the available channel for deexcitation. Significant contribution in the Cu I line intensity was observed with increasing dose due to sputtered Cu atoms.

Ion-induced surface modification processes of polystyrene (PS) and high-density polyethylene (HDPE) have been studied by either in situ photon-emission spectroscopy or ex situ surface analyses. Heavy Cuions of 60 keV irradiated the polymers at a dose rate of 1 lA/cm 2 and ion-induced photon emission was in situ measured in a spectral region of 250-850 nm. Ion-induced chemical reactions of the surface layers were ex situ evaluated by X-ray photoelectron spectroscopy (XPS). Intensity, spectral shape and dose dependence of the photon emission were significantly different between aromatic-containing polymers (PS) and linear polymers (HDPE) in the same irradiation condition. The emission spectrum of HDPE represented a broad band with a maximum at about 595 nm, while that of PS showed a sharp peak around 656 nm. The total emission yield observed for PS was much lower than that of HDPE, and the decay rates of emission intensity for PS were different from that of HDPE in a dose region less than 10 14 ions/cm 2 . The XPS analyses showed chemical change of the surface bonding. These results suggested that ion-induced processes caused hydrogen extraction, crosslinking and bond scission of the matrix. 2002 Elsevier Science B.V. All rights reserved.

Ion-induced photon emission under heavy-ion bombardment has been studied over an energy range from near-infrared to vacuum-ultraviolet. Time-resolved optical devices with fast-response CCD cameras detected photons from a-SiO2 under implantation with negative Cu ions of 60 keV, up to a dose rate of 100 μA/cm2. The ion-induced photon spectra consisted of sharp line spectra due to isolated atoms of Si, Cu and a broad band of visible light. The line spectra resulted from an ion-induced glow above the surface and indicated pronounced outward transport of Cu atoms to the vacuum. Intensity of the line spectra and the broad band varied non-linearly with dose and dose rate. The in-situ spectroscopy provided diagnostic information of surface- and intra-solid processes associated with nanoparticle formation at high dose rates. The Cu sublimation reflected from presence of a Cu-depleted zone beneath the surface, which is one of the important factors to form a two-dimensional arrangement of nanoparticles.

Photon irradiation effects during heavy-ion implantation have been studied to distinguish and control electronic excitation effects on surface modification of insulators, particularly on nanoparticle formation in insulators. Photons of a sub-gap energy (2.3 eV) and high-energy Cu ions were applied to substrates of a-SiO 2 (KU-1). The Cu 2+ ions of 3 MeV irradiated the specimens at 10 μA/cm 2 to 3×10 17 ions/cm 2 , and the 532 nm-YAG laser, either simultaneously or sequentially, irradiated them at 0.2 J/cm 2 · pulse , 10 Hz, for a period corresponding to the ion dose. Atomic-force microscopy and cross-sectional transmission electron microscopy were conducted to study the surface- and bulk morphology, respectively. The ion-alone irradiation smoothed the surface, up to the high dose. Intense photon irradiation under ion implantation significantly roughened the surface and concurrently promoted nanoparticle formation. Optical absorption spectra showed that simultaneous irradiation decreased radiation-induced defects for the low dose and enhanced surface plasmon of nanoparticles for the high dose. The results indicate that intense photon irradiation, coexistent with heavy-ion irradiation, excites transient electronic states and/or implanted atoms and result in surface desorption, defect annihilation and nanoparticle formation. The in-beam photon irradiation is suitable for optical material processing, both for the matrix and nanoparticles.

Ion-induced photon emission under 60 keV Cu − implantation into the insulators of MgAl 2 O 4 and LiNbO 3 was in situ measured over a wide wavelength range from 200 to 900 nm. The formation of the Mg and Li deficient layers for the respective insulator was detected based on the dose dependence of the Al, Mg and Li atomic line intensities. The Al I and Mg I line intensities from spinel exhibit different behaviors depending on irradiation temperatures: they gradually decrease while the (Al I)/(Mg I) ratio increases up to dose of 3×10 17 ions/cm 2 at room temperature or exhibits a steady-state tendency at high temperature. Sharp decrease of Li I line intensity from LiNbO 3 under high dose rate bombardment indicates drastic changes of surface layer that may alter the phase stability and optical performance of insulators.

The 500 keV negative-ion based neutral beam injector for JT-60U has been operated since 1996 and has injected so far a neutral beam power of 5.2 MW at 350 keV for 0.7 s. In order to further increase the beam power and extend the beam pulse duration time, a few issues concerning the negative ion source have to be solved. The most serious issue of them is non-uniformity of source plasma in the arc chamber. Two out of some countermeasures for improving the non-uniformity have been tried. The first is changing the spatial distribution of the arc discharge through regulating arc current resistors which connect in series to each of eight filament groups. The second is masking both ends of the plasma grid with thin molybdenum plates to block beam extraction at the edges. Owing to these countermeasures, the acceleration efficiency of the deuterium negative ion beams in the accelerator has improved by more than 30% from 0.55 to 0.74.

Steady-state optical absorption and nonlinear transient resonance have been studied for Cu nanoparticle composites, fabricated in magnesium aluminate spinel by high-current negative ion implantation. The implantation was conducted at high ion fluxes of 60 keV up to a total dose of 3×1016 ions/cm2. Optical absorption strongly depended on dose rate, ranging from 1 to 100 μA/cm2. The dose rate dependence of the absorption spectra around the surface plasmon resonance behaved analogously to that of a-SiO2, though the radiation-induced absorption band depended on stoichiometry of the spinel. The spectral shape of transient absorption at various dose rates is similar but the bleached plasmon band shifts is in parallel with the steady-state surface plasmon resonance. The dose rate chiefly influences dielectric properties of a spinel matrix but not that of particles.

Silicon-thermal-oxide (a-SiO2) films of 115 nm thick on Si wafers are implanted by high-flux Cu negative-ions of 60 keV. Optical reflectivity measurements show that the Si substrates are transformed into an amorphous-like state after the implantation. The “amorphization” is ascribed to recoil atoms, not directly to the incident Cu ions. The crystallinity is recovered after a heat treatment at 900°C for 1 h in Ar gas. The interference fringes in the reflectivity spectra shift to high energy side at 60 μA / cm 2 and the higher fluxes, indicating decrease of the oxide thickness. At the same fluxes, AFM observation shows a prominent change of surface morphology and a large increase of step-height at implanted–unimplanted area boundaries, indicating enhanced sputtering under high-flux implantation.

Co-irradiation effects of ions and photons on insulators have been studied to explore electronic excitation effects on surface modification. Ion implantation of MeV–Cu ions and green-laser irradiation was conducted to a-SiO2 (820 ppm OH − ) and spinel MgO·2.4(Al2O3). The dose rate varied from 2 to 10 μA/cm 2 for Cu ions of 3 MeV and from 0.05 to 0.2 J/cm 2 · pulse at 10 Hz for YAG–SHG laser, for a period corresponding to 3×10 16 ions/cm 2 . Atomic-force microscopy (AFM) was conducted to evaluate the surface morphology. Optical absorption was measured in a photon energy range from 0.5 to 6.5 eV. Single irradiation, either Cu ion-alone or laser-alone, caused few discernible changes of surface morphology. Co-irradiation of ions and photons at high power densities caused significant changes in the surface texture with an increase in surface roughness. Optical absorbance of the co-irradiated specimens also showed a change larger than that of sequentially irradiated ones. The results indicate that nonlinear synergistic effects are induced by the co-irradiation and may develop to a new modification method.

In fabricating metal nanoparticles in insulators, high-current negative ions have been shown to cause efficient and spontaneous growth of nanospheres. The in-beam growth is inevitably subjected to rearrangement of implanted atoms, departing from initially deposited positions. For high-current techniques for insulators, we discuss important experimental factors and explore possible mechanisms of the in-beam growth and atomic rearrangement of nanoparticles. Experimental data of interest are for negative Cu ion implantation at 60 keV into insulators, amorphous(a-), crystalline (c-) SiO 2 and a spinel oxide, MgAl 2 O 4 . Dose rates ranged up to 260 μA/cm 2 , with a total dose of 3.0×10 16 ions/cm 2 . Nanoparticle morphology and surface morphology by AFM were significantly dependent not only on dose rate but also on the boundary conditions. With increasing dose rate, the in-beam growth of nanoparticles became pronounced and the atomic profile shifted toward the surface. Since beam heating, especially in vacuum, is of concern, thermal analysis was carried out with a one-dimensional simulation code. Candidate mechanisms are depth-oriented gradients of deposited nuclear/electronic energy, chemical/elastic potentials and thermal effects. The relevant mechanisms are explored among these candidates.

Intense Cu− ions of 60 keV spontaneously grow nanospheres embedded within a shallow depth in insulators, which exhibit optical nonlinearity. The in-beam growth of nanoparticles is preferred but subjected to phase instability. Spinel oxides may be a candidate substrate to realize the phase stability, because of good radiation resistance and sufficient transparency. Spinel of MgAl2O4 and amorphous(a-) SiO2 were irradiated with Cu− at dose rates up to 100 μA/cm2, at a total dose of 3.0 × 1016 ions/cm2. Nanocrystal morphology and optical absorption (hν=0.5 – 5 eV) varied depending on dose rate. At high dose rates, a-SiO2 showed a strong tendency of depth-dependent rearrangement and particle coarsening. The MgAl2O4 also showed spontaneous precipitation of nanoparticles but, in contrast, neither long-range rearrangement of implants nor particle coarsening, up to high dose rates. Therefore, the MgAl2O4 spinel is a promising substrate to realize fine and stable nanostructures.

Thermal stability of nanoparticles, fabricated by high-current negative ions, has been studied focusing on optical applications. Negative Cu ions of 60 keV were irradiated to silica glasses at high dose rates up to 50 μA/cm2, to a total dose of 3×10 16 ions/cm 2 . The high-current implantation caused a bimodal distribution of Cu nanoparticles. Thermal annealing at 773–1273 K for 1 h was applied to the specimens. For each step, optical absorption was measured in an energy range from 0.5 to 6.5 eV and nanoparticle morphology was evaluated by cross-sectional TEM. Depth profiles of Cu atoms were compared to those by RBS. Thermal annealing below 873 K gave no discernible changes in either nanoparticle morphology or absorption spectra. Above 1073 K, pronounced coarsening of Cu particles occurred, with enhancing the bimodal distribution. Around 1273 K, all the Cu particles disappeared, suggesting evaporation of Cu implants from the surface. The result indicates that the nanoparticle structure is thermally stable below about 873 K, and becomes unstable at higher temperatures.

Optical properties of negative Cu ion-implanted silica glasses were measured over a photon energy range 0.5–6.5 eV. The implantation was conducted at high beam fluxes of 60 keV energy up to a total fluence of 3.0 × 1016 ions/cm2. From the transmission and reflection data, dielectric constants, eeff for the Cu implanted layer and em for the Cu nanoparticles, were self-consistently determined. In the dielectric spectra, bands due to the Cu particles were evidently present below 4.2 eV. An absorption band of the irradiated silica screened that of the Cu particles in the higher photon region. In the imaginary em spectrum, the intraband contribution disappeared owing to the nano-size effect and the interband contribution at 3.8 eV became smaller than that of bulk Cu. Third-order susceptibility χm(3) was also evaluated with the degenerate four-wave mixing and was of the order of 10−8–10−9 esu.

Head-attached interface device (HIDE) has been developed as a new type of human interface device in an actual work environment. The HIDE has flexible integrated functions which consist of speech recognition and view direction detection as hand-free input channels, direct presentation of audio/visual information as output channels, and mobile system configuration. In this paper, the design concept of the HIDE was first introduced, and individual functions to configure the design concept were developed by their separate testing. An integrated prototype system HIDE was then produced, and its functional evaluation test was made to examine the individual functions as the whole system. It was confirmed that the HIDE would be feasible enough to introduce in practical use.

Spectra of the optical transmission of Al2O3 were measured during implantation of 60 keV Cu− ions at ion fluxes from 5 to 50 μA/cm2, to monitor formation of Cu nanoparticles. The precipitation threshold is flux-dependent. The formation of nanoparticles is (a) efficient up to a fluences of 2 × 1017 ions/cm2 and (b) most efficient for a flux of 50 μA/cm2. Intrinsic size effects have little influence on the linear and non-linear optical absorption of nanocomposites.

A new ellipsometric technique, made possible by the use of an orthogonally polarized two-frequency laser, is described, and results of measurement of small birefringence of laser mirrors with the new technique are reported.