Ion Beam Induced Graphitization of Phenolformaldehyde
- PDF / 333,930 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 78 Downloads / 220 Views
D. ILA, A. L. EVELYN AND G. M. JENKINS Center for Irradiation of Materials, Alabama A&M University, P.O. Box 1447, Normal, AL 35762-1447, U.S.A. ABSTRACT We have studied MeV ion beam induced phase transformation in phenolformaldehyde cured at 170'C by both Raman microprobe spectroscopy and in situ resistance measurement of the irradiated area. Samples were irradiated using various doses of protons, alphas and nitrogen beams. Irradiated volumes in each sample were tested in situ for enhanced electrical conductivity and later on by Raman microprobe spectroscopy. The results have shown changes in the resistance as much as seven orders of magnitude by alpha particles, six orders by nitrogen bombardment and three orders by hydrogen. Raman microprobe spectroscopy of the darkened phase shows development of the D- and G-lines which are characteristic of the production of a carbonized resin. These spectra indicate that maximum carbonization was caused by the nitrogen beam. INTRODUCTION Ion bombardment and implantation have been widely used to alter the electrical properties of polymers and the results have been reviewed elsewhere [1-3]. Ion implantation produces accurate location of dopant depth and doping with ions that cannot be achieved chemically. Most workers report enhanced conductivity which saturates after high fluence. This enhancement is associated with darkening. Ion implantation causes physical damage which includes breaking covalent bonds, scissoring polymer chains, cross-linking and release of volatile species. It is also reported that conductivity enhancement by ion bombardment is a result of energy deposition and densification rather than ion doping [4]. Generally, the darkening has been attributed to beam induced carbonization, without specifying the form of carbon produced or studying the mechanism of carbonization. It has also been reported that such darkened polymers are resistant to oxidation and retain enhanced conductivity over many months [5]. This enhanced conductivity induced by ion bombardment decreases with time [6]. We have been concentrating on the effect of MeV ion bombardment which allows us to alter the polymer structure locally well below the surface; the higher the energy the deeper the damaged volume. A recent study [7] has shown that the electrical conductivity of a polyimide increases several orders of magnitude after ion beam bombardment. Surface conductivity change is accompanied by a shift to lower binding energy of all core level spectra for both normal and grazing emission. The authors ascribe these changes to the formation of a conductive phase of interconnected aromatic carbon characterized by C Is spectra which approach those of graphite. Formation of this conducting phase seems to be a common effect of inert ion beam treatment of resins and depends on ion fluence. We have studied this effect in phenolic resin using various bombarding ions because we had already studied the thermal conversion of this resin into a polymeric glassy carbon [8] and 441 Mat. Res. Soc. Symp. Proc. Vol
Data Loading...
