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DEPTH PROFILING OF HYDROGEN IN ION-IMPLANTED POLYMERS

J. DAVID CARLSON Lord Corporation Research Center, P.O.

Box 1107, Cary, NC 27511

PETER P. PRONKO and DAVID C. INGRAM Universal Energy Systems, 4401 Dayton-Xenia Road,

USA

Dayton, OH 45432

USA

ABSTRACT Depth profiling of hydrogen in polymeric materials Backscattering methods are ruled poses special problems. because of kinematics. Nuclear reaction methods out are undesirable because small reaction cross sections necessitate large fluences of high mass projectiles and We result in unacceptable levels of radiation damage. have used a helium-induced proton-recoil technique with 3 MeV 4He particles to measure the hydrogen distribution in pristine and ion-implanted polyvinylidene fluoride The incident 4He particles stopped in (PVDF) films. the 25 micron PVDF films while the recoiling protons were detected after passing through the polymer film. Large changes in the hydrogen content of PVDF films implanted with modest fluences of 6 MeV carbon, oxygen and nickel ions were observed.

INTRODUCTION Ion implantation has become a well established and powerful technique Recently, interest has for modifying metals and semiconductors [1-4]. developed in the application of ion-implantation and ion-irradiation to the Implantation and irradiation effects in modification of polymers [5-9]. polymers present a number of contrasts to those in semiconductors and metals. Not only can the presence of an implanted species affect the chemistry of the implanted polymer, but the transferred energy alone may drastically alter the entire character of the polymer through a variety of processes. These include crosslinking, chain scission, free radical formation, and chemical decomposition into small organic molecules. The evolution of molecular species during the course of ion irradiation of polymer films [10] and the eventual formation of residual carbonaceous films [9,11] indicate that large changes in the elemental composition of We polymers are induced by implantation or irradiation with MeV heavy ions. have found that, with care, Rutherford backscattering (RBS) can be used to quantify changes in the carbon and heavier element composition of polymers. Depth profiling of hydrogen, however, poses special problems and conventional analytical tools are found to be undesirable. Nuclear Backscattering methods are ruled out because of kinematics. reaction analysis (NRA), on the other hand, which works quite well for profiling hydrogen in metals is ruled out because the relatively small reaction cross sections necessitate large fluences of heavy ions and result Heavy in unacceptable levels of damage in radiation sensitive polymers. ion fluences sufficient for NRA of hydrogen in organic polymers are 2 typically in the range of 1014 to 1016 ions/cm . These are significantly 13 2 larger than the 5 x 10 /cm fluences of similar mass ions we have found sufficient to cause changes of nearly a factor of two in polymer elemental NRA defeats its own purpose by causing changes composition (see below). l