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Abstract: Thermal annealing effects on Zn+ ion-implanted silica glass (a-SiO2) have been studied in order to control void formation. Void formation in a-SiO2 with Zn+ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn+ ions of 60keV were implanted into a-SiO2 to a fluence of 1.0×1017 ions/cm2. After the implantation, thermal annealing at 600 or 700°C for 1h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10–15nm 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 1h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO2 substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10–25nm in diameter inside the a-SiO2. These results indicate that the oxidation at 700°C for 1h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids. [Copyright &y& Elsevier]

Abstract: Silica glasses (SiO2) were implanted with Zn+ ions of 60keV to a fluence of 1.0×1017 ions/cm2, and were annealed in oxygen gas flow at 700°C for 1h, to form ZnO nanoparticles (NPs). In as-implanted state, metallic Zn NPs of 10–15nm in diameter are formed between 10 and 50nm in depth. NPs are not observed on the surface and down to 10nm in depth. After the annealing at 700°C for 1h in oxygen gas, ZnO NPs of ∼10nm in diameter are observed around 50nm in depth. Moreover, droplet-like ZnO NPs larger than 30nm in diameter grow on the surface of SiO2 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. [Copyright &y& Elsevier]

Abstract: Formation processes of nickel oxide (NiO) nanoparticles (NPs) in silica glass (SiO2) by implantation of 60keV 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 ∼80nm thick. The mean depth 〈z〉 and the standard deviation 〈(Δz)2〉1/2 of Ni atom distribution determined by XTEM were 43 and 15nm, respectively. After the oxidation at 800°C for 1h, 〈z〉 and 〈(Δz)2〉1/2 became 47nm and 20nm, 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 43nm3, 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. [Copyright &y& Elsevier]

Implantation of Cu negative ions of 60 keV induces frequency shifts of infrared (IR) vibration modes of SiO2. 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 SiO2. Ion-flux dependence was examined in the flux range of 0.95–100 μA/cm2 with keeping the total fluence 3×1016 ions/cm2. 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 SiO2. [Copyright &y& Elsevier]

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/cm2 up to a total dose of 1.5 × 1017 ions/cm2. 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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Silica glass implanted with Zn ions of 60 keV to 1.0×1017 ions/cm2 was annealed in oxygen gas to form ZnO nanoparticles (NPs). In as-implanted state, the implanted Zn atoms form Zn metallic NPs inside of the silica. After annealing at 600 °C, ZnO NPs form on the surface, while Zn metallic NPs still remain in the deep region. At 700 °C, most of Zn atoms move to the surface to form the droplet-shaped ZnO NPs which show two photoluminescence bands, i.e., an exciton band at 375 nm and a defect band at ∼500 nm. The defect band almost disappears in the samples annealed at 600 °C, which include both ZnO NPs and Zn NPs. [ABSTRACT FROM AUTHOR]

Abstract: 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 60keV 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 ∼27nm with increasing the fluence up to 1×1017 ions/cm2, and very high-concentration (∼20at%) 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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: 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. Micro-indentation effects on surface plasmon resonance (SPR) in optical absorption have been studied to control nanoparticle formation in Cu ion-implanted SiO2 substrate. The SiO2 was firstly implanted with 2MeV Cu2+ ions at an ion flux of 4μA/cm2, up to a fluence of 6×1016 ions/cm2. 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 1h. 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 2.2eV 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. [Copyright &y& Elsevier]

Abstract: 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-SiO2 substrate by periodic heavy-ion irradiation technique. The pitch of these gratings was 2μm and 3μm, respectively. The flux and fluence were at the range of 6–10μA/cm2 and 6×1016–1×1017 ions/cm2, 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. [Copyright &y& Elsevier]

Abstract: 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 2MeV Cu2+ ions, at an ion flux of 4μA/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 1h. 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 2.2eV, 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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Kinetic behaviors of nanoparticle formation in LiNbO3 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 LiNbO3 disks at fluxes up to 50 μA/cm2. 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/cm2, LiNbO3 showed spontaneous formation of Cu nanocrystals of ∼10 nm, including nonspherical shape. Crystallinity of the LiNbO3 lattice implanted was sustained up to 3 × 1016 ions/cm2. The Cu nanoparticles in LiNbO3 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/cm2, significant coarsening of Cu particles and amorphization of the LiNbO3 lattice occurred. The results indicate that metal nanoparticle formation in LiNbO3 is sensitive to the ion flux and that the optimization is requisite to fabricate well-defined nanocomposites. [Copyright &y& Elsevier]

Abstract: Spectra of the optical transmission of Al2O3 were measured during implantation of 60keV Cu− ions at ion fluxes from 5 to 50μA/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 50μA/cm2. Intrinsic size effects have little influence on the linear and non-linear optical absorption of nanocomposites. [Copyright &y& Elsevier]