R. L. Zimmerman

Resolving the electronic and nuclear effects of MeV ions in polymers

Abstract The electronic and nuclear stopping effects produced by MeV ion bombardment in polyvinylidene chloride (PVDC) and polyethylene (PE) were separated by stacking thin films of the polymers. The resulting layered system consisting of each polymer was bombarded with 3.5 and 5.0 MeV alpha particles. A layered system was selected such that the first layers experienced most of the effects of the electronic energy deposited and the last layers received most of 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 and FTIR. Post-irradiation analyses of the films indicated differences in these properties in the various film layers which are attributed to the individual effects of the stopping powers in the polymer films.

MeV silver ion implantation induced changes in optical properties of MgO (100)

Abstract The implantation of 1.5 MeV Ag ions at 1.2 × 10 17 ion/cm 2 into MgO(100) single crystals produces optical absorption color centers which can be reduced by heat treatment at temperatures above 1000°C. We observed the formation of both F-centers and V-centers. We observed optical absorption due to the formation of silver nanoclusters at heat treatment temperatures above 550°C and due to F-center aggregates at heat treatment above 800°C. Upon further heat treatment, the color centers diminish while absorption due to the Ag nanoclusters is enhanced. Using Mies theory we confirmed that Ag is in the form of nanoclusters and by using Rutherford backscattering spectrometry (RBS) and ion channeling, we confirmed that these Ag metallic clusters have, in fact, orientations similar to that of the host substrate, MgO. The measured optical absorption due to Ag nanocrystals, 430 nm, is in agreement with the theoretical prediction.

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.

Improvement on Thermoelectric Characteristics of Layered Nanostructure by Ion Beam Bombardment

We made p-type nanoscale super lattice thermoelectric cooling devices which consist of multiple periodic layers of Si 1−x Ge x / Si, The thickness of each layer ranges between 10 and 50 nm. The super lattice was bombarded by 5 MeV Si ion with different fluencies aiming to form nano-cluster quantum dot structures. We estimated the thermo-electric efficiency of the so fabricated devices, measuring the thin film cross plane thermal conductivity by the 3rd harmonic method, measuring the cross plane Seebeck coefficient, and finally measuring the cross plane electric conductivity before and after ion bombardment. As predicted, the thermo-electric Figure of Merit of the films increases with increasing Si ion fluencies. In addition to the effect of quantum well confinement of the phonon transmission, the nano-scale crystal quantum dots produced by the incident Si beam further adversely affects the thermal conductivity by absorbing and dissipating phonon along the lattice, and therefore further reduces the cross plane thermal conductivity, This process increases the electron density of state therefore increasing Seebeck coefficient, and the electric conductivity.

PERMEABILITY CONTROL OF GPC DRUG DELIVERY SYSTEM

Abstract Glassy Polymeric Carbon (GPC), a biocompatible material, has been proposed for drug encapsulation and delivery. We have shown that a wide range of available porosity in the bulk material can be obtained by careful attention to the method of production and heat treatment of GPC. In addition, ion bombardment is shown to modify the available surface porosity and permeability. These surface characteristics are determined by choice of specie, fluence and energy of the bombarding ions. Together with appropriate drug concentration gradients within the capsule, the capsule can be made to deliver an initial dose rate either higher or lower than the steady state value. The effective surface area, as well as the availability of the pores, can be modified by oxygen or gold ion bombardment either to increase or decrease.

RBS and PIXE Ion Beam Methods for Characterizing Ni‐Co Alloys

Various electroplating/electroforming processes have been used for years to produce nickel‐cobalt components for applications from space industry to tool refurbishing. The mechanical properties (hardness, strength, etc.) are drastically affected by the nickel to cobalt ratio of the alloy, as well as the amount of organic additives and trace contaminants present in the plating tank. Traditionally, chemical or optical methods were used for characterizing the constituents of the resulting deposit. In this paper we present the usefulness of nuclear methods of analysis based on accelerated ion beams for performing both qualitative and quantitative compositional characterization of such alloys. Samples of electroformed materials were prepared in a nickel sulfamate bath with nickel‐cobalt ratios ranging between 70:30 (or 2.33:1) and 80:20 (or 4:1) atomic percent. The samples were analyzed using PIXE (Proton Induced X‐Ray Emission) with proton beam of 1 MeV and RBS (Rutherford Backscattering Spectrometry) with 6 ...

Fabrication of Optical Channel Waveguides in the GaAs/AlGaAs System by MeV Ion Beam Bombardment

We have fabricated optical channel waveguides in planar GaAs/AlGaAs waveguides using 10 MeV oxygen ions at a fluence of 3 {times} l0{sup 13} and 3 {times} l0{sup 14} ions/cm{sup 2}. Although disordering o GaAs/AlGaAs quantum well structures has previously been reported, to the best of the authors` knowledge the fabrication of channel waveguides using high energy oxygen bombardment has not been demonstrated in this material system. This technique may provide a totally new concept of localized material modifications in GaAs/AlGaAs waveguides by creating compositional disordered regions that act as optical confinement channels. The masking technique used to provide selective disordering of the planar waveguide structures will be presented. Optical measurements were performed on the channel waveguides at a wavelength of 1.3 {mu}m.

Application of MeV ion bombardment to create micro-scale annealing of Silica-Gold films

This project studies the production of nanoscale annealing using MeV Si ion beams. To test the technique we produced thin films of Au‐Silica by sequential deposition of Au and SiO2 on Suprasil substrates. We measured the thickness of the deposited films with an interferometer and by using Rutherford backscattering spectrometry (RBS). Using the measured thickness we calculated the concentration of Au in each film. TRIM simulation was used to confirm our results. Since the localized annealing causes the formation of gold nano‐clusters, we performed optical absorption photospectrometry (OAP) on all slides, before deposition, after deposition, and after bombardment by MeV Si beams. Optical index changes are apparent in the sequentially deposited multilayer samples that were not seen in Au‐silica co‐deposited samples with the same volume fraction of gold.

New optical properties of MgO after MeV metal ion implantation

The implantation of metal ions into single crystals of MgO(100) followed by thermal annealing leads to an increase in absorption of ultra violet and visible light. Metal ions of Au, Sn, Ag, Cu and Ti were implanted at a depth of a few thousand Angstroms followed by thermal annealing. MgO samples implanted with He and Si ions at greater depths were used to study the optical effects and thermal annealing of radiation damage. The influence of bombardment fluence and heat treatment on the size of the metal clusters and on the fraction of atoms in clusters were measured using absorption photospectrometry.

Low Energy Palladium Implantation in Silicon Carbide: Solid State Gas Sensors

Silicon carbide is used in developing gas sensors for elevated temperature applications (400∼ 800 °C), in oxidizing environments. The option for this material was based on the cumulus of attractive properties that it offers, such as stability up to 2700 °C, oxidation resistance up to 800 °C, and wide bandgap, which practically eliminates other semiconductor materials. When hydrogen detection is desired, the most suitable combination appears to be palladium either implanted into [1, 2] or deposited on the silicon carbide substrate [3, 4]. Here we present the methodology that we developed for gas sensor fabrication using low energy palladium implantation followed by controlled surface sputtering. The in‐house built sensor testing facility is also described. Sensor parameters and performances, as well as behavior in the presence of small concentrations of hydrogen into an inert gas (Ar) are also presented here.