R.L. Zimmerman

Nano-cluster engineering: A combined ion implantation/co-deposition and ionizing radiation

We have used the energy deposited due to the electronic excitation by post-implantation irradiation to induce the nucleation of nano-clusters of Au in silica. We have produced the Au/silica by two methods. (A) MeV Au implantation into silica, (B) producing thin films of a combined Au and silica on a silica substrate, using co-deposition of gold and silica. The process of ion beam assisted nucleation of nano-clusters was used to reduce the threshold implantation dose, or the Au concentration in the silica host, required to produce Au nano-crystals by at least two orders of magnitude. In this presentation, we applied a similar technique, post-irradiation electronic excitation, to films produced by both ion implantation of Au into silica as well as to films produced using co-deposition of gold and silica. By a co-deposition technique, gold and silica (co-deposited at various concentrations) are grown, then post-irradiated. The resultant Au nano-cluster formation was observed and studied using optical spectroscopy, X-ray diffraction, RBS and TEM.

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.

Radiation Induced Nucleation of Nanoparticles in Silica

Abstract There is a threshold implantation dose, after which some of the implanted species will tend to spontaneously form nanoclusters, over-dose-implantation . Similarly, there is a threshold implantation dose for the implanted species in a layer of the host material, such that after high temperature annealing the nanoclusters can nucleate before the implanted material can dissolve in the host material (during such heat treatments). In this paper, we present the results of our investigation of producing nanoclusters of gold in silica at fluences of two orders of magnitude less than what is traditionally used. This is accomplished by implanting 2.0 MeV Au into silica followed by MeV bombardment by MeV Si ions. This process was used to reduce the threshold implantation dose by at least two orders of magnitude. To follow the formation of nanoclusters, we used both indirect measurement methods such as optical absorption spectrophotometry (non-destructive), and direct methods such as transmission electron microscopy (destructive). The size of the nanoclusters, ranging from 1 to 10 nm, are controlled by the implantation dose and by the total electronic energy deposited by each post-bombarding ion in the implanted layer. We will show how and at what concentrations species such as gold nucleates to form nanoclusters, either by induced strain or by radiation-enhanced nucleation at a dose below that needed for spontaneous nanocluster formation.

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.

Ion beam promoted lithium absorption in glassy polymeric carbon

Abstract Glassy Polymeric Carbon (GPC) samples prepared from a precursor possess accessible pore volume that depends on the heat treatment temperature [G.M. Jenkins and K. Kawamura, Polymeric Carbons - Carbon Fiber, Glass and Char (Cambridge University Press, Cambridge, 1976) p. 140]. We have shown that lithium percolates without diffusion into the accessible pores of GPC samples immersed in a molten lithium salt bath at 700°C [D. Ila, G.M. Jenkins, L.R. Holland, A.L. Evelyn and H. Jena, Vacuum 45 (1994) 451]. Ion bombardment with 10 MeV Au atoms increases the total pore volume available for lithium occupation even for samples normally impermeable to lithium. The lithium concentration depth profile is measured using Li 7 (p,2α) nuclear reaction analysis. We will report on lithium percolation into GPC prepared at temperatures between 500°C and 1000°C and activated by a 10 MeV gold ion bombardment.

Determining the shortest production time for glassy carbon ware

Abstract Because of the high production rate of gaseous reaction products in critical temperature ranges where out-diffusion is relatively slow, glassy carbon ware is difficult to make in thick section by pyrolysis of phenolic resin, without causing kilning faults. Using wedge shapes of cured phenolic resin we found the greatest thickness possible for a fixed heating rate during postcuring (400–500 K) and precarbonization (500–875 K), the stages in which failures occur. In postcuring, the critical heating rate varies inversely as the fifth power of critical thickness; in precarbonization, it varies inversely as the third power. Heating rate can be raised much faster at other stages of pyrolysis, leading to fully carbonized ware at 1500 K. Mass spectrometry shows the main gas product is steam; carboniferous gases are also evolved during precarbonization. We discuss diffusion models applicable to any firing process in which volatiles need to diffuse from solids.

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.

Enhanced tissue adhesion by increased porosity and surface roughness of carbon based biomaterials

Abstract We present recent results using ions of C, O, Si, Fe, Zn and Au at energies between 100 keV and 10 MeV to increase the roughness and porosity of the partially and fully cured precursor phenolic resins. The fully cured phenolic resin is called glassy polymeric carbon (GPC). GPC is chemically inert, biocompatible and useful for medical applications, such as heart valves and other prosthetic devices. Ion implantation enhances biological cell/tissue growth on, and tissue adhesion to, prosthetic devices made from GPC. We have previously shown that increased porosity of GPC is also useful for drug delivery devices. The porosity of the ion implanted partially and fully cured precursor phenolic resins was measured by introducing lithium from a molten LiCl salt into each sample. By using Li(p,2α) nuclear reaction analysis (NRA) we measured the concentration of Li retention in the pre- and post-implanted samples. The surface roughness was measured using optical microscopy. The curing process was monitored using micro-Raman microscopy. We have correlated the NRA measurements of increased pore availability with the observations of increased surface roughness.