Tailoring the Conductivity of Polypyrrole Films Using Low-Energy Platinum Ion Implantation

Low-energy platinum ions were implanted with 15 keV under normal incidence into synthesized conducting polymer films with the aim to improve film conductivity and to demonstrate the use of implanted platinum in a simple sensing design. Conductivity measurements, cyclic voltammetry, and Raman spectroscopy were performed on samples both before and following ion implantation. Results display an optimum fluence of ion implantation for which polypyrrole films implanted with 2 × 10¹⁶ at. cm^–2 display and retain enhanced conductivity compared with nonimplanted samples. X-ray photoelectron spectroscopy (XPS) and scanning electron microscope–energy-dispersive X-ray spectroscopy (SEM-EDS) confirmed that implanted platinum is present mainly as Pt⁰ and indicated that the depth and amount of ion implantation are in agreement with a simulated implantation profile. Raman spectroscopy showed a surface-enhanced Raman spectroscopy (SERS) effect with platinum’s presence. The advantageous increase in conductivity can be rationalized by two chemical modifications to the polymer upon high-fluence implantation: (1) an increase in the number of charge carriers (dications) within the polymer and (2) the presence of elemental platinum metal and its synergistic effect on conductivity. A simple DNA sensor was constructed on the basis of polypyrrole/Pt⁰ films where Pt⁰ was able to serve as anchoring points for DNA attachment as well as an enhancer of the film’s conductivity. This enabled a DNA sensor capable of successful detection of cDNA, and a good discrimination of noncDNA, thus opening a way to direct electrochemical biosensing on the basis of ion implanted highly conducting polymer films

Nucleation and Growth of Fe Nanoparticles in SiO₂: A TEM, XPS, and Fe L-Edge XANES Investigation

Magnetic iron nanoparticles embedded in insulating oxides matrices are prized targets for “on chip” magnetic sensors, nano fluxgates and nano hard magnets. In this study, the nucleation and growth of iron nanoparticles in the near surface region of 400 nm silica thin films (on silicon substrates) during ion implantation and post- implantation electron beam annealing was systematically investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fe L-edge X-ray absorption near edge spectroscopy (XANES). Results show the presence of Fe oxides after low-fluence low-energy ion implantation in SiO₂, suggesting that initially Fe substitutes for Si in the silica matrix. Larger Fe fluences lead to the formation of sub-2 nm metallic Fe nuclei. Postimplantation annealing transformed the dispersed cationic Fe species into metallic Fe nanoclusters (diameter 1–10 nm) that are stabilized by a thin passivating surface oxide film. The versatility of ion implantation and electron beam annealing for the synthesis iron nanoparticles in silica matrices is demonstrated