E. K. Williams

Third Order Optical Nonlinearity of Colloidal Metal Nanoclusters Formed by MeV Ion Implantation

We report the results of characterization of nonlinear refractive index of the composite material produced by MeV Ag ion implantation of LiNbO{sub 3} crystal (z-cut). The material after implantation exhibited a linear optical absorption spectrum with the surface plasmon peak near 430 nm attributed to the colloidal silver nanoclusters. Heat treatment of the material at 500 deg C caused a shift of the absorption peak to 550 nm. The nonlinear refractive index of the sample after heat treatment was measured in the region of the absorption peak with the Z-scan technique using a tunable picosecond laser source (4.5 ps pulse width).The experimental data were compared against the reference sample made of MeV Cu implanted silica with the absorption peak in the same region. The nonlinear index of the Ag implanted LiNbO{sub 3} sample produced at five times less fluence is on average two times greater than that of the reference.

Fabrication of copper and gold nanoclusters in MgO (100) by MeV ion implantation

Abstract MeV ions of Au and Cu were implanted into single crystals of MgO (100) and the formation of metallic nanoclusters was observed by an indirect method of optical absorption spectrophotometry. Using Mies theory we related the observed optical absorption band to the formation of nanoclusters and using Doyles theory, as well as Rutherford Backscattering Spectrometry (RBS), we correlated the full width half maximum (FWHM) of the absorption bands to the estimated size of the metallic nanoclusters between 1 and 10 nm. These clusters were formed by implantation above the threshold fluence for cluster formation and by a combination of threshold fluence of the implanted species and thermal annealing. The changes in the estimated size of the nanoclusters, after annealing at temperatures ranging from 500°C to 1000°C, were observed using optical absorption spectrophotometry and calculated using Doyles theory.

Gold, silver and copper nanocrystal formation in SiC by MeV implantation

Abstract Nanoclusters gold, silver and copper are produced in 6H-SiC by implanting 1.0 MeV Au, 2.0 MeV Ag and 2.0 MeV Cu into the Si face of SiC at room or elevated temperature followed by annealing at various temperatures. The absorption bands for each type of metal nanoclusters in SiC were determined using optical absorption spectrophotometry. Elevated temperature implantation reduces optical absorption due to ion implantation induced defects. Using the Mie theory, we determined the index of refraction in the implanted volume.

Change in yhe Optical Properties of Sapphire Induced by Ion Implantation

We have studied the formation of nano-crystals, after implantation of 2.0 MeV gold, 1.5 MeV silver, 160 keV copper and 160 keV tin into single crystal of A1 2 O 3 . We also studied the change in the linear optical properties of the implanted Al 2 O 3 before and after subsequent annealing by measuring the increase in resonance optical absorption. Applying Doyles theory and the results obtained from Rutherford backscattering spectrometry (RBS) as well as the full width half maximum of the absorption band from Optical Absorption Photospectrometry (OAP), we measured the average size of the metallic clusters for each sample after heat treatment. The formation and crystallinity of the nanoclusters were also confirmed using transmission electron microscopy (TEM) technique.

Improved Sensitivity SiC Hydrogen Sensor

We have produced silicon carbide sensors by two techniques: palladium coating and low energy palladium implantation, The palladium implantation was done at 550°C into the Si face of 6H, n-type Sic at various energies and at various fluences. The sensitivity of each sensor was measured at temperatures between 20°C to 4OOOC. The response of the Sic sensors produced by Pd implantation has revealed a completely different behavior than the Sic sensors produced by Pd deposition In the Pd deposited Sic sensors, as well as in the ones reported in the literature [ 1, 21, the current rises in the presence of hydrogen at room temperature as well as at elevated temperatures. In the case of Pd implanted Sic sensors, the current decreases in the presence of hydrogen whenever the temperature is raised above 100°C [3].

Nonlinear optical waveguides produced by MeV metal ion-beam implantation of lithium niobate

We report linear and nonlinear optical properties of planar waveguides produced by implantation of MeV Ag ions into LiBnO3. The linear optical properties include spectrum of propagation modes and optical extinction spectrum. The nonlinear properties include optical spectrum of nonlinear refractive index and nonlinear absorption. Light guiding in the implanted crystal is associated with the modification of the linear refractive index. The modification is a result of two concurrent processes such as crystal is damage in the nuclear stopping region producing a low index optical barrier between the top light guiding layer and the bulk crystal and the diffusion of the implanted ions into the implanted ions into the top layer causing its index increase. Relatively high nonlinear refractive index is a result of enhancement of intrinsic third order nonlinearity of the implant by the mechanism of surface plasmon resonance. The intrinsic nonlinearity is associated primarily with intraband and interband electron transitions. The spectrum of the nonlinear index correlates with the spectrum of optical extinction featuring prominent peak due to surface plasmon resonance. Possible applications of the waveguides include ultrafast photonic switches and modulators.

Nonlinear optical waveguides based on metal nanocluster composites produced by ion beam implantation

We present the results of analysis of microstructural and optical properties of composite nonlinear optical waveguides made by ion implantation of LiNbO3 with MeV ions of silver. Light guiding properties were studied by the prism coupling method, and nonlinear optical susceptibility was characterized using the Z-scan method. Special attention was paid to the influence of a host material and heat treatment on light guiding, optical absorption, and third order susceptibility.

Optical composite nanostructures produced by silver ion implantation of lithium niobate

We analyze microstructure and optical properties of thin light-guiding nanocompositte planar structures produced by implantation of MeV Ag into LiNbO3. The structures demonstrate such prominent features as change of color from yellow to pink accompanied by the appearance of light guiding after heat treatment of the implanted sample at 500 degree(s)C for one hour in open air. TEM analysis shows that before heat treatment the implanted region consists of amorphous and porous lithium niobate and nanoclusters of metallic silver localized near the edge of the nuclear stopping region. The surface plasmon resonance peak attributed to the nanoclusters is located near 430 nm giving yellow color to the sample. After heat treatment the implanted region re-crystallizes in the form of randomly oriented sub-micron grains of lithium niobate doped with enlarged and dispersed silver nanoclusters. Optical prism coupling analysis shows that the implanted region performs as a planar light guide with the refractive index apparently higher than the nuclear stopping region beneath it. In addition, the surface plasmon resonance peak of the nanoclusters moves to 550 nm giving pink color to the sample. Using computer simulations based on the Mie model, we explain such significant red frequency shift of the plasmon resonance by the increase of the effective refractive index of the host material after recrystallization and elimination of porosity caused by heat treatment. Theoretical data are in good agreement with experimental spectra of the optical extinction of the sample before and after heat treatment. This is also in agreement with the fact that the implanted planar structure becomes a light guide with substantially increased effective refractive index. Fabricated nanostructure can find application in ultra-fast photonic switches where light guiding is combined with the optical nonlinearity of the third order enhanced by the plasmon resonance.

Fabrication of nonlinear light-guiding nanocomposite structures by metal ion implantation

We analyze microstructure, linear and nonlinear optical properties of planar waveguides produced by implantation of MeV Ag ions into LiNbO3. The linear optical properties include spectrum of propagation modes, and optical absorption spectrum. The nonlinear properties include optical spectrum of nonlinear refractive index. Operation of the implanted crystal as an optical waveguide is due to modification of the linear refractive index of the implanted region. The samples as implanted do not show any light guiding. Heat treatment of the implanted samples makes planar light guides on the implanted surface. High- resolution electron microscopy reveals recrystallization of the host between the surface and the nuclear stopping region in the form of randomly oriented micro crystals. They make up a light guiding layer isolated from the bulk crystal by the low index nuclear stopping layer. Optical absorption has a peak at 430 nm. This peak is due to the surface plasmon resonance in metal nanoclusters formed in the host after implantation. Heat treatment of the silver implanted samples shifts the absorption peak to 550 nm. Relatively strong third order nonlinearity of the samples is due to the three orders of magnitude enhancement of the intrinsic intraband and interband electron component of polarizability in the vicinity of the surface plasmon resonance. The nonlinear refractive index of the samples (of the order of 10-10 cm2/W) was measured with the Z-scan technique using a picosecond laser source. Possible applications of the waveguides include ultra-fast photonic switches and modulators.

Visibility of fabricating an electro-optic sensor using LiNbO3 crystal implanted Mn ions

The effect of the ion implantation of Fe, Mn on LiNbO3, as well as the dispersion of Ag colloids in LiNbO3 were studied using electron paramagnetic resonance (EPR). EPR measurements on these crystals were performed as a function of fluence at room temperature. The fluence was 1 X 1014 and 1 X 1016 ions/cm2 for Fe and 2 X 1016 ions/cm2 for Ag. The unpaired carrier concentration increases with increasing fluence. The photosensitivity of these crystals was determined by observing in situ the effect of the laser illumination on the EPR signal and measuring the decay and growth of the EPR signal. EPR and optical absorption showed significant differences in the dispersion of the colloids with implant temperature and implant order.