O.A. Plaksin

Zn and ZnO nanoparticles fabricated by ion implantation combined with thermal oxidation, and the defect-free luminescence

Silica glass implanted with Zn ions of 60keV to 1.0×1017ions∕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 375nm and a defect band at ∼500nm. The defect band almost disappears in the samples annealed at 600°C, which include both ZnO NPs and Zn NPs.

Dispersion of nonlinear dielectric function of Au nanoparticles in silica glass

We have investigated wavelength dispersion of photo-induced nonlinear dielectric function of Au nanoparticle materials. Transient transmission and reflection spectra were sequentially measured by the pump-probe method with a femtosecond laser system. The dispersion of real and imaginary parts of the nonlinear dielectric function of Au:SiO(2) nanoparticle material in the vicinity of the surface plasmon resonance was evaluated from these transient spectra with total differential. A local electromagnetic field factor and interband transition in Au nanoparticles directly dominate the dispersion.

Atomic force microscopy and x-ray photoelectron spectroscopy studies of ZnO nanoparticles on SiO2 fabricated by ion implantation and thermal oxidation

The morphology and chemical composition of the surface of SiO2 that had been implanted with Zn ions of 60keV and annealed in two different atmospheres, i.e., oxygen gas and a vacuum, were compared. In the as-implanted state, the surface mainly consisted of SiO2 with low roughness due to radiation-induced smoothing. A large number of domelike structures of ZnO appeared on the surface of the SiO2 after annealing in oxygen gas at 600°C for 1h, and the size increased with the annealing temperature up to 800°C. After annealing at 900°C, the surface roughness steeply decreased and the composition changed to Zn2SiO4.

Electronic excitation and optical responses of metal-nanoparticle composites under heavy-ion implantation

Measurements of optical transmission and ion-induced photon emission (IIPE) during implantation of copper ions into silica glass (a-SiO2) have been combined in order to study formation of Cu nanoparticles. It has been shown that in situ measurements are more advantageous than conventional experimental approaches of examining the properties of ion-implanted nanocomposites solely after implantation. Series of experiments have been done to prove that the band of IIPE at 545–550 nm originates from Cu+ solutes in a-SiO2. The combination of in situ optical techniques provides means of monitoring Cu nanoparticles and Cu solutes via the optical absorption in the range of the surface-plasmon resonance (SPR) of nanoparticles and the IIPE of Cu+ solutes. It has been shown that a simple linear approximation can be used to separate optical bands of defects, Cu solutes, and nanoparticles. Ion-induced transient optical absorption has been found in the ranges of SPR and defect bands. The transient optical response in the...

Radiation-induced differential optical absorption of metal nanoparticles

A method of measuring the temperature of metal nanoparticles under ion bombardment is proposed. Optical absorption in the range of the surface plasmon resonance of metal nanoparticles was measured during implantation of 3MeV Cu2+ ions into silica glass to derive a difference in optical absorption between beam on and off regimes. The radiation-induced differential (RD) spectra were similar to the spectra of thermomodulation (TM) and quite different from the spectra of nonlinear optical response measured by the pump-probe method. Increasing amplitude of RD and TM spectra was assigned to an increase of lattice temperature of Cu nanoparticles.

Saturation of nonlinear optical absorption of metal-nanoparticle composites

Metal-nanoparticle composites consisting of copper and gold nanoparticles embedded in insulators (Cu:SiO2, Au:SiO2, and Cu:Al2O3) have been fabricated by metal-ion implantation. Nonlinear optical (NLO) absorption of the nanocomposites has been examined by the Z-scan method with a tunable femtosecond laser. We have measured (a) NLO absorption spectra near the surface-plasmon resonance and (b) laser-intensity dependence of NLO absorption, α(I). The results are compared to the data reported on NLO response for various laser pulse durations. By analyzing the laser-intensity dependence of Z-scan signals, the saturation intensity of light, IS, the coefficient of NLO absorption, β, and the radius of the beam waist, w0, are derived. This approach takes into account the saturation of optical absorption, whereas the conventional approach using the linear approximation α(I)≈α0+βI cannot do it. The analysis shows that transient optical absorption, |α(I)−α0|, decreases with shortening the laser pulse duration. The dec...

Production of Cu2O nanoparticles in SiO2 by ion implantation and two-step annealing at different oxygen pressures

Two different methods were applied to fabricate cuprous-oxide (Cu2O) nanoparticles (NPs) in silica glasses (SiO2), namely (i) low oxygen-pressure (LOP) oxidation of Cu NPs, which had previously been formed in SiO2by implantation of Cu ions and (ii) two-step annealing of Cu NPs in atmospheric-pressure oxygen gas (to convert Cu NPs to CuO) and in LOP-Ar gas (to convert CuO to Cu2O). The LOP oxidation at 800 °C converts a small portion of Cu NPs to the Cu2O phase, but most of the Cu NPs survive in the metallic state. By increasing the oxidation temperature to 900 °C, the Cu2O phase dissolves. On the other hand, the two-step annealing at different oxygen pressures converts all the Cu species to Cu2O NPs. Any diffraction peaks due to Cu NPs or CuO NPs, except Cu2O NPs, were not observed.

Radioluminescence of alumina during proton and heavy ion irradiation

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 electrical phenomena in dielectric materials under irradiation

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

Implantation-induced nonequilibrium reaction between Zn ions of 60keV and SiO2 target

Silica glass (SiO2) was implanted with 60keV Zn+ ions to a fluence of 1.0×1017ions∕cm2, and the chemical states were investigated along the depth in as-implanted state by x-ray excited Auger electron spectroscopy and x-ray photoelectron spectroscopy. The metallic Zn and Zn2SiO4 phases were found to have, respectively, formed in the shallow and deep regions of the SiO2, whereas thermodynamics predicts the Zn phase only. Oxygen atoms in SiO2 are preferentially displaced to the deeper region because of the lighter mass. The excess oxygen in the deep region and athermal energy from the implantation drive the formation of Zn2SiO4.