D. Ila

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.

Application of MeV ion implantation in the formation of nano-metallic clusters in silica

The implantation of metal ions into photorefractive materials followed by thermal annealing leads to an increase in resonance optical absorption as well as an enhancement of the nonlinear optical properties. The authors have implanted ions of Au (3.6 MeV), Ag (1.5 MeV) and Cu (2.0 MeV) into pure silica followed by careful heat treatment. Using optical absorption spectrophotometry and Rutherford backscattering spectrometry the authors have measured the cluster size for each heat treatment temperature and determined the activation energies for their formation. The third order electric susceptibility for silica with 2 nm gold clusters has been determined by Z-scan to be 6.5 {times} 10{sup {minus}8} esu.

ION BEAM MODIFICATION OF PES, PS AND PVC POLYMERS

Abstract MeV ions passing through polymer films modify their electrical and optical properties and these changes are related to changes in the chemical structures of the polymers. The effects of certain cross linking enhancers, such as sulfur and other pendant molecules, on the ion beam modification process were investigated. Stacked, thin films of polyethersulfone, polyvinyl chloride and polystyrene were bombarded with MeV helium ions and the induced changes in the chemical structure of the polymers were studied with Raman microprobe analysis and RBS combined with in situ residual gas analysis. FTIR spectroscopy was used to categorize the changes in the optical properties. The results were then compared with those from previously studied polyethylene and polyvinylidene chloride polymers.

EFFECTS OF MEV IONS ON PE AND PVDC

Abstract We studied the effects of 3.5 and 5.0 MeV alpha bombardment on polyethylene and polyvinylidene chloride, both of which have simple chemical structures. Using a thin polymer film stacking technique, we were able to map the effects of the MeV alpha particles in their track. The first layer of the thin polymer film stack experienced mostly the effects of the electronic energy deposited, and the last layer received mostly effects of the nuclear stopping. Using Raman microprobe analysis and by measuring the ratio of the formation of graphene structures (G-line) to the disordered (amorphous) carbon line (D-line), we were able to separate the severed bond effects at the end of the alpha particle tracks in the last polymer film layers from the effects of the electronic energy deposited in the first polymer film layers. The results are in agreement with our other measurements of each polymer film using FTIR, RBS and resistance measurements.

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.

Effects of MeV Ion Beam on Polymers

The electronic ({var_epsilon}{sub c}) and nuclear ({var_epsilon}{sub n}) stopping effects produced by 3.5 MeV and 5.0 MeV ion bombardment in polyvinylidine chloride (PVDC), polyethylene (PE) and polyethylene sulfide were studied and compared. To separate these effects the authors chose two bombardment energies and a thin film polymer stacking technique developed in house. The resulting stacked layered system consisting of each polymer was bombarded with 3.5 MeV and 5.0 MeV alpha particles. The layered system was selected such that the first few layers experience most of the effects of the electronic energy deposited and the last layer receives the effects of the nuclear stopping. The electrical conductance and the changes in the chemical structure were measured by direct resistivity measurements, Raman microprobe analysis, RBS, and FTIR. The post-irradiation characterization resolved the effects of the stopping powers on the polymer films.

Formation of Silver Metal Nanoclusters in MgO by MeV Ag Implantation

Nanoclusters of Ag metal in MgO(100) single crystals was formed by implantation of 1.5 MeV silver ions at fluences of 6 {times} 10{sup 16} ion/cm{sup 2} and at 1.2 {times} 10{sup 17} ion/cm{sup 2}, and subsequent annealing at temperatures between 600 C to 1,100 C. The formation of the Ag metallic clusters was confirmed using optical absorption spectrophotometry by the absorption band at 430 nm. This is in agreement with the theoretical prediction using Mie`s theory, with calculated average nanocluster size about 3 nm. Using ion channeling the authors confirmed that the orientation of the Ag nanoclusters was in the same direction of the host crystal. Using Z-scan they found the nonlinear refractive index of Ag implanted MgO to be 4.9 {times} 10{sup {minus}8} esu.

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.

Structural Changes in Polymer Films by Fast Ion Implantation

In applications from food wrapping to solar sails, polymers films can be subjected to intense charged panicle bombardment and implantation. ETFE (ethylenetetrafluoroethylene) with high impact resistance is used for pumps, valves, tie wraps, and electrical components. PFA (tetrafluoroethylene‐per‐fluoromethoxyethylene) and FEP (tetrafluoroethylene‐hexa‐fluoropropylene) are sufficiently biocompatible to be used as transcutaneous implants since they resist damage from the ionizing space radiation, they can be used in aerospace engineering applications. PVDC (polyvinyllidene‐chloride) is used for food packaging, and combined with others plastics, improves the oxygen barrier responsible for the food preservation. Fluoropolymers are also known for their radiation dosimetry applications, dependent on the type and energy of the radiation, as well as of the beam intensity.In this work ETFE, PFA, FEP and PVDC were irradiated with ions of keV and MeV energies at several fluences and were analyzed through techniques ...