J.C. Cheang-Wong

Optical properties of Ir2+-implanted silica glass

Abstract High-purity silica samples (OH content less than 1 ppm, impurity content less than 20 ppm) were implanted with 2 MeV Ir2+ ions at doses ranging from 0.6 to 7×10 16 ions/cm 2 , and annealed in air at 300°C, 600°C and 900°C for 1 h. An optical absorption band at 248 nm, associated with the presence of B2 defects, appears in the spectra of all the Ir-implanted samples before the annealing, but these B2 defects disappear for heat treatments at T⩾600°C. It is important to stress that no surface plasmon resonance associated with Ir ions was observed in the optical absorption spectra of the Ir-implanted silica samples. Photoluminescence (PL) spectra show emission bands at 310, 415 and 620 nm, which can be associated with oxygen vacancies (B2 defects), O–O weak bonds and non-bridging oxygen hole centers (NBOHC), respectively. In this work we present the first optical studies on Ir-implanted silica glass and discuss the effect of the ion-induced structural defects on the absorption and emission spectra after heat treatments in air.

Metallic nanoparticle formation in ion-implanted silica after thermal annealing in reducing or oxidizing atmospheres

Abstract High-purity silica samples with OH content less than 1 ppm, were implanted with 2 MeV Cu + , Ag + and Au 2+ ions at fluences of 0.7, 3 and 6×10 16 ions/cm 2 , and annealed in either reducing (70%N 2 +30%H 2 ) or oxidizing (air) atmosphere at 300, 600, 900 and 1100 °C for 1 h. For the three implanted species, after annealing at 900 °C in the reducing atmosphere, the absorption spectra present a broad band at 250 nm (4.9 eV), even for samples in which there are no nanoparticles formed. The nanoparticle formation in both atmospheres is quite different for the three implanted ions.

Optical absorption and emission studies of 2 MeV Cu-implanted silica glass

It has been found that the chemical state of implanted ions in SiO2 depends on local concentration and on the transport process of the implanted element. In this work we report the optical properties of high-energy Cu-implanted silica glass. 2MeV Cu+ ions were implanted at room temperature (RT) in silica glass at fluences of 0.7, 3.0 and 5.0×1016 ions/cm2. The absorption spectra of the as-implanted samples indicated the formation of B2 centers, but no Cu nanoparticles were formed. The photoluminescence (PL) spectra for excitation at 280 nm exhibited broad bands at 410 and 550 nm, associated with the presence of Cu+ ions in the as-implanted samples. We discuss the effect of thermal annealing in air on the absorption and the emission spectra of these Cu-implanted samples, as well as the formation of copper nanoclusters from original Cu+ ions.

Ultrafast optical phase modulation with metallic nanoparticles in ion-implanted bilayer silica

The nonlinear optical response of metallic-nanoparticle-containing composites was studied with picosecond and femtosecond pulses. Two different types of nanocomposites were prepared by an ion-implantation process, one containing Au nanoparticles (NPs) and the other Ag NPs. In order to measure the optical nonlinearities, we used a picosecond self-diffraction experiment and the femtosecond time-resolved optical Kerr gate technique. In both cases, electronic polarization and saturated absorption were identified as the physical mechanisms responsible for the picosecond third-order nonlinear response for a near-resonant 532 nm excitation. In contrast, a purely electronic nonlinearity was detected at 830 nm with non-resonant 80 fs pulses. Regarding the nonlinear optical refractive behavior, the Au nanocomposite presented a self-defocusing effect, while the Ag one presented the opposite, that is, a self-focusing response. But, when evaluating the simultaneous contributions when the samples are tested as a multilayer sample (silica-Au NPs-silica-Ag NPs-silica), we were able to obtain optical phase modulation of ultra-short laser pulses, as a result of a significant optical Kerr effect present in these nanocomposites. This allowed us to implement an ultrafast all-optical phase modulator device by using a combination of two different metallic ion-implanted silica samples. This control of the optical phase is a consequence of the separate excitation of the nonlinear refracting phenomena exhibited by the separate Au and Ag nanocomposites.

Relationship between the Ag depth profiles and nanoparticle formation in Ag-implanted silica

Ion implantation has attracted considerable interest as a method to modify the optical properties of insulators in order to produce materials with nonlinear optical properties. In this work, high-purity silica samples were implanted at room temperature with 2 MeV Ag ions at various fluences (0.5, 2.4 and 5.3 × 1016 ions/cm2). The samples were then annealed in either a reducing or an oxidizing atmosphere at temperatures ranging from 300 °C to 1100 °C. The samples were characterized by optical absorption and Rutherford backscattering measurements. Changes in the optical properties of the samples arise from nanometre-sized metallic clusters produced as a result of implantation and/or annealing. The Ag nanoclusters strongly absorb optical radiation at the surface plasmon resonance wavelength (~400 nm). The Rutherford backscattering spectrometry results indicate that the Ag concentration in the samples decreases with increasing annealing temperatures and then influences the optical properties. Indeed, it seems that at relatively high temperatures the Ag nanoclusters can melt and become atomically dispersed silver within the glass. As the mobility of these Ag atoms increases, they migrate not to the sample surface, but mainly laterally through the sample, and eventually the Ag material is lost by the borders of the sample. A correlation was found between the Ag depth profiles and the formation of the surface plasmon resonance as a function of the annealing temperature. The implications and the possible mechanisms concerning this behaviour are discussed in this paper.

Absorptive and refractive nonlinearities by four-wave mixing for Au nanoparticles in ion-implanted silica

We report a theoretical and experimental study on the real and imaginary part of the third-order nonlinear optical susceptibility at 532 nm and 7 ns pulse for high-purity silica samples containing Au nanoparticles prepared by ion implantation. We present a method for measuring the magnitude and sign of refractive and absorptive nonlinearities based on four-wave mixing (FWM). This method is derived from a comparison of the light intensities of incident and self-diffracted polarized waves. In the nanosecond regime the samples exhibit saturable absorption and it seems that a thermal effect is the mechanism responsible of nonlinearity of index.

Influence of indium concentration and substrate temperature on the physical characteristics of chemically sprayed ZnO:In thin films deposited from zinc pentanedionate and indium sulfate

Chemically sprayed indium-doped zinc oxide thin films (ZnO:In) were deposited on glass substrates starting from zinc pentanedionate and indium sulfate. The influence of both the dopant concentration in the starting solution an dt he substrate temperature on the transport, morphology, composition, linear and nonlinear optical (NLO) properties o ft he ZnO:Inthin films were studied. The structure of all the ZnO:In thin films was polycrystalline, and variation in the preferential growth with the indium content in the solution was observed: fro ma ni nitial (002) growth in films with low In content, switching to a predominance of (101) planes for intermediate dopant regime, and finally turning to a (100) growth for heavily doped films. The crystallite size was found to decrease with doping concentration and range from 36 to 23 nm. The fil mc omposition and the dopant concentration were determined by Rutherford backscattering spectrometry; these results showed that the films are almost stoichiometric ZnO. The optimum deposition conditions leading to conductive an dt ransparent ZnO:In thin films were also found. In this way a resistivity of 4 × 10 −3 � cm an da na verage transmittance in the visible spectra of 85%, with a( 101) preferential growth, were obtained in optimized ZnO:In thin films. (Some figures in this article are in colour only in the electronic version)

Tuning the aspect ratio of silver nanospheroids embedded in silica

A method is proposed to control the aspect ratio (epsilon) of elongated nanoparticles obtained by ion implantation in a transparent matrix. The procedure was tested for Ag spheroids in silica and we could accurately change epsilon in the range from the maximum value obtained by the ion implantation (around 3.0 in this case) to 1.0 (spherical shape). The values of epsilon were determined in several steps from optical extinction spectroscopy measurements, by fitting the modification and splitting of the surface plasmon resonance peak, using the T-matrix method. In the initial (maximum deformation) and final (undeformed) states, transmission electron microscopy images were obtained, showing a good agreement with the T-matrix results in both cases.

Nonlinear optical spectroscopy of isotropic and anisotropic metallic nanocomposites

In this work, we studied the nonlinear absorption and refraction of isotropic and anisotropic metallic nanocomposites, which consist of Au and Ag nanoparticles (NPs) embedded in matrices of SiO2. We performed this study at different wavelengths using the Z-scan technique in the picosecond regime. The wavelengths were selected accordingly to the absorption spectra of the nanocomposites, choosing wavelengths into the inter- and intra-band transitions regions, including the surface plasmon (SP) resonance, as well as in the transparent region. For the anisotropic nanocomposites, the polarization and the incident angle were varied in order to evaluate the different components of the third order susceptibility tensor, χ(3). We observed dramatic changes of sign for both, nonlinear refraction and absorption, when passing from Au to Ag and/or varying the wave length. The results accentuate the importance of the hot-electrons contribution to the nonlinear optical response at this temporal regime, when compared to inter-band and intra-band transitions contributions.

GISAXS Size Distribution Characterization of Cu Nanoparticles Embedded in silica

Cu nanoparticles embedded in high purity silica produced by deep ion implantation at 2 MeV and located around 0.8u2009μm underneath the surface were analyzed by GISAXS and TEM. Same results were obtained by both techniques, indicating that GISAXS is a reliable method for shape and size characterization of metallic nanoclusters underneath the surface of a silica matrix. The Cu nanoparticles presented a nearly‐spherical shape with a mean radius around 3±1.2u2009nm.