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Optical nonlinearity and dispersion were studied for Cu nanoparticle composite. Negative Cu− ions with 60 keV were applied for implanting into SrTiO3 at a flux of 10 μA/cm2 up to a total fluence of 1 × 1017 ions/cm2. The steady-state optical spectrum of Cu-implanted SrTiO3 showed a surface plasmon resonance resulting from the formation of nanoparticles. Transient transmission and reflection were measured by the pump–probe method with a femtosecond laser system. Optical nonlinearity originated from Cu:SrTiO3 nanoparticle composite and from SrTiO3 matrix overlap, in measured transient spectra. The nonlinear component of Cu:SrTiO3 composite was extracted from the transient spectra with the difference of time response. Nonlinear dielectric coefficient and dispersion around the surface plasmon resonance were derived from extracted transient spectra. The dispersion was compared with a local electric field factor.

Optical transmission and ion-induced photon emission of SiO 2 (silica glass), LiNbO 3 and Al 2 O 3 were measured during implantation of 60-keV Cu − or Au − ions. Conditions of stability of metal nanocomposites were determined and represented with the help of nonequilibrium phase diagrams. Formation of structures dynamically stable under ion bombardment diminished the efficiency of ion implantation for further accumulation of implants as in nanoparticles. Contributions from various radiation-induced processes (sputtering, radiation-induced diffusion, atomic collisions, electronic excitations, etc.) to formation of nanocomposites were evaluated.

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.

Linear and nonlinear optical properties of Au and Cu nanoparticle composites, fabricated by ion implantation, were studied with evaluation of applicability to all-optical switching device. Negative ions of 60 keV were implanted into amorphous SiO 2 at fluxes of about 10 μA/cm 2 to a fluence of 1 × 10 17 ions/cm 2 . The surface plasmon resonance of the Au:SiO 2 composite was enhanced stronger than that of the Cu:SiO 2 composite because of a difference of the local field in nanoparticles. Nonlinear optical constants were evaluated by the Z -scan method with a tunable femtosecond laser system. The nonlinear absorption coefficients exhibited maximal values of −4.9 × 10 1 m/GW for Cu:SiO 2 and −1.3 × 10 2 m/GW for Au:SiO 2 around the surface plasmon resonance. For application of the composites to optical switching by optical bistability, it was estimated that the reflectivity of resonators is >0.94 for the Au:SiO 2 composite and that the switching energy was approximately 10 pJ/bit.

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.

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.

Optical absorption and nonlinear optical response were studied for metal nanoparticle composites. Negative ions, Cu−, Au−, Ag−, Ta− and W− with 60 keV were applied for implanting into amorphous(a)-SiO2 The absorption spectra of various metal ion implanted a-SiO2 showed a surface plasmon peak resulting from formation of nanoparticles. The surface plasmon resonance was widely located over the infrared and the visible range. Nonlinear optical property of Cu nanoparticles was measured with a pump–probe method using a femtosecond laser system. A wavelength of the pumping laser with a pulse width of 0.2 ps was tuned over a wide visible range of 533–606 nm around the surface plasmon resonance. Transient spectra, immediately after laser pumping at various wavelengths, excellently agreed with each other. The transient changes recovered within a few femtoseconds. The nonlinearity and transient response, excited by laser with a pulse width of 0.2 ps, were independent of excited wavelengths.

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.

Linear and nonlinear optical properties were studied for Cu nanoparticle composites with high Cu concentrations. Negative Cu ions of 60 keV were implanted into amorphous SiO2 at a fixed flux of 10 μA/cm2 to fluences ranging from 3 × 1016 to 6 × 1017 ions/cm2. Implanted Cu contents were evaluated by Rutherford backscattering spectrometry with 2 MeV He+ ions. Optical absorption increased with the Cu concentration but the surface plasmon peak was maximized around a fraction of 0.10 and attenuated beyond that fraction. Nonlinear optical properties were evaluated by the z-scan method and pump-probe method with a femtosecond laser system. The nonlinear absorption constant increased with the volume fraction but deviated from linearity beyond a Cu volume fraction of 0.20. The laser-induced transient response was ∼1 ps and was independent of the Cu concentration.

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.

Metal nanoparticles fabricated by heavy-ion implantation of insulators are promising for non-linear optical applications. Spectra of optical transmission of silica glass in the visible region were measured during and after implantation of 3 MeV Cu2+ ions. Three absorption bands contribute to the spectra: transient absorption (TA) at 2.34 eV, a surface plasmon resonance (SPR) peak at 2.21 eV and a tail of residual absorption (RA), which increases when the photon energy is increased from 2.2 to 2.6 eV. The TA and a change of the SPR peak strongly contribute to the total transient absorption obtained as the difference in absorption during and after irradiation. The effect of RA shows up as a decrease of absorption after switching on the ion beam. The TA provides a means for selective electronic excitation by a laser during implantation of silica glass. The precipitation of Cu atoms and the growth of Cu nanoparticles are well distinguishable stages of nanoparticle formation. The SPR peak appears at a fluence of 3.3 × 1016 ions/cm2, corresponding to the onset of precipitation. At fluences higher than 3.4 × 1016 ions/cm2, when the growth of nanoparticles predominates, the fluence dependence of the SPR peak is linear.

The outward mass transport during implantation of 60 keV negative Cu, Ag and Au ions into LiNbO3 and Al2O3 was studied by using in situ time-resolved optical spectroscopy. Single crystals of LiNbO3 and Al2O3 were irradiated continuously or by pulses of ions. Spectra of ion-induced light emission at the wavelengths from 250 to 900 nm were in situ measured. The ratios of individual lines of the same atomic species (Li for LiNbO3 and Al for Al2O3) change with the dose. The change of energy distribution of sputtered atoms is explained by a competition between two mechanisms of sputtering: the sputtering induced by atomic collisions or electronic excitation. The result shows a strong relationship between irreversible structural change of implanted regions (formation of nanocomposite and damage) and energy distribution of sputtered atoms. r 2004 Elsevier Ltd. All rights reserved.

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.

Radioluminescence (RL) of sapphire and polycrystalline alumina (p-Al2O3) under 8 MeV proton (flux 2 � 10 12 proton/cm 2 s), 150 MeV argon (4.3 � 10 8 ion/cm 2 s) and 253 MeV krypton (4.3 � 10 8 ion/cm 2 s) ion irradiation has been measured in the UV and visible ranges. The processes causing the changes of RL of sapphire with a dose differ from those of p-Al2O3. Radiation-induced annealing of oxygen vacancies in p-Al2O3 occurs with decreasing F þ -band. Inhomogeneous distribution of traps associated with grain boundaries causes electrical charging of microscopic regions in p-Al2O3 and an increase of F-band of RL. The accumulation of charge carriers at traps increases excitation probability of F þ -center and results in growth of F þ -band of sapphire. A ratio of initial to saturation intensity of the F þ -band increases with increasing the linear energy loss of incident particles.

Optical and acoustic properties of the materials based on Al2O3, SiO2 and BN under 8 MeV proton irradiation (

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.