MeV Ion Beam Fabrication of Nanopores
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1020-GG03-06
MeV Ion Beam Fabrication of Nanopores Renato Amaral Minamisawa, Robert Lee Zimmerman, Claudiu Muntele, and Daryush ILA Physics, Center for Irradiation of Materials, Alabama A&M University, PO box 1447, Normal, AL, 35762
ABSTRACT We have used MeV ion beams to fabricate nanopores in Poly(tetrafluorethylene-coperfluoro-(propyl vinyl ether)) (PFA) fluoropolymer membranes. We have developed an in house system to produce nanopores. Using MeV ion beams we developed a method to produce pores from nanometers to one-micron diameter. A thin film of the PFA polymer was mounted to cover a window to a gas filled chamber and then exposed to a uniformly scanned MeV ion beam masked to define the exposed area. The gas leak rate through the fabricated pores was monitored by an in situ RGA system both during and after each bombardment to correlate the leakage with the total area of the pores produced. In this project we used MeV light and heavy ions to best define the pore diameter through each hole and the pore entrance and exit dimensions in the membranes. INTRODUCTION Porous membranes using synthetic polymers have been applied in several research methods and devices such as hydrophobic filters for removal of microorganisms and particles from air and other gases, chromatography gases detection [1], biologic detectors etc. PFA, which is a fully fluorinated something with oxygen cross links between chains expressed by the molecular formula [(CF2CF2)nCF2C(OR)F]n, proved suitable for a large range of these porous membrane applications because it is chemically inert, with high chemical resistance to solvents and has a melting point around 304 oC [2]. The controlled fabrication of pores in PFA in different length scales may provide a material with high quality performance for membranes applications. Attempting to produce micropores in PFA, Caplan et al. [3] have developed in 1997 a method using thermally induced phase separation. However the process is time consuming and makes it difficult to control the size of the fabricated pores. In 2003 Apel et al. [4] reported the fabrication of nanometer (~500 nm) holes in poly(ethylene terephthalate) (PET) polymer films using MeV to GeV energy ion track etch technique. However, although the spatial resolution is efficient for biologic membrane transport studies, it is limited to only several applications. To overcome these problems, Li et al. and Stein et al. [5, 6] have recently proposed a successful ionsculpted method using a keV focused ion beam (FIB) apparatus to produce pores in the nanometer length scale in thin, isolating silicon nitride solid-state membranes. Although the Si3N4 is easier to be manipulated, the high chemical inertness of synthetic polymers is still a desired property.
We report in this article recent studies of pores fabrication at micro and nano scale in PFA thin films using a homemade feedback controlled ion beam system adapted to a MeV Pelletron accelerator. Structural chemical changes in the PFA thin films bombarded with MeV ions will be reported as well
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