A.L. Evelyn

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.

RBS and Raman spectroscopy study of heat-treatment effect on phenolformaldehyde resin☆

Abstract Phenolformaldehyde resin, which is used to make items of glassy carbon hollow ware, contains residual alkaline catalyst and other impurities. Pyrolysis reduces the concentrations of hydrogen and oxygen during condensation and dehydrogenation reactions, which occur between 150 and 1000°C as the resin is converted to a polymeric glassy carbon. Molded samples heat-treated from 150 to 600°C and sprayed samples heat-treated to 1000 and 2500°C were studied using Rutherford backscattering spectrometry (RBS) and Raman spectroscopy. Raman spectroscopy was used to study the structural changes induced by heat treatment. Raman spectroscopy showed that most carbonization occurred at 500 to 600°C while the RBS data from resin samples at each temperature showed that oxygen and sodium concentrations were reduced at higher temperatures.

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.

High Porosity Polymeric Carbon Ware for Controlled Release of Drugs

Polymeric carbon ware prepared at various temperatures with variable accessible pore volume was filled with lithium by submerging in molten LiCl at 700°C. Using Li(p,α) nuclear reaction analysis the concentration profile and the volume density of Li were measured. It was found that they were highest for polymeric carbon samples prepared at 650°C.

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].

Radiation Enhanced Porosity and Roughness of Biomaterials

Glassy Polymeric Carbon (GPC), made from cured phenolic resins, is sufficiently chemically inert and biocompatible that it is suitable for medical applications, such as heart valves and other prosthetic devices. We have used energetic ion bombardment of the partially and fully cured precursor phenolic resins to enhance biological cell/tissue growth on, and to increase tissue adhesion to, prosthetic devices made from GPC. GPC samples were bombarded with energetic ions to 10 MeV. The surface topography and increased surface roughness was observed using optical microscopy and atomic force microscopy (AFM). The increased porosity was measured by introducing lithium from a molten LiCl salt into the GPC and using (p, α) nuclear reaction analysis (NRA) to measure the concentration of Li retention in the modified GPC. The NRA measurements of increased pore availability were correlated with the observations of increased surface roughness.

Ion Beam Enhanced Electrical Conductivity in Polymers

We have used proton, alpha, nitrogen and oxygen particles at energies between 1 to 8.5 MeV to modify the conductance of various polymers with linear molecular chain structure and polymers with two dimensional networks of chemical bonds, specifically benzene ring. The beam energy and the beam current, 100 pA to 30 nA, for each species were selected to deliver maximum electronic stopping power in a predetermined depth and area. The electrical conductance of the bombarded volume in each polymer was measured in situ and changes were recorded to be between 10- 13 Siemens before bombardment to 0.1 Siemens after bombardment depending on the total energy deposited in a given volume of the polymers. The carbonized volumes were analyzed by Raman microprobe spectroscopy which showed that the strongest graphitic (G-line) and distorted (D-line) Raman signals observed were from the volume with the highest conductance.