AVS 52nd International Symposium
    Applied Surface Science Wednesday Sessions
       Session AS-WeA

Paper AS-WeA2
Formation and Volatilization of Small Molecules From a PTFE Matrix Upon MeV Alpha Particle Irradiation Examined by ToF-SIMS, SEM, and RGA

Wednesday, November 2, 2005, 2:20 pm, Room 206

Session: SIMS Cluster Probe Beams and General Topics
Presenter: G.L. Fisher, Los Alamos National Laboratory
Authors: G.L. Fisher, Los Alamos National Laboratory
R.E. Lakis, Los Alamos National Laboratory
C.C. Davis, Los Alamos National Laboratory
C.J. Wetteland, Los Alamos National Laboratory
C.W. Szakal, Pennsylvania State University
N. Winograd, Pennsylvania State University
Correspondent: Click to Email
The chemical structure and morphology at the surface of @alpha@-irradiated polytetrafluoroethylene (PTFE) has been examined and compared to unirradiated PTFE. The samples were irradiated to doses of 10@super 7@ to 10@super 11@ Rad using 5.5 MeV [@super 4@He]@super 2+@ from a tandem accelerator beam line. Static time-of-flight SIMS (ToF-SIMS), using a 20 keV C@sub 60@@super +@ source, was employed to probe chemical changes versus irradiation. Chemical images and high resolution spectra in both positive and negative polarity were collected and analyzed to reveal the effects of @alpha@ particle radiation on the chemical structure. Where appropriate, comparison is made to static ToF-SIMS data collected using a 15 keV Ga@super +@ primary ion source. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Secondary electron microscopy (SEM) was used to observe the morphological variation of samples with increasing @alpha@ particle dose. The data show that PTFE nominally retains its chemical structure and morphology at @alpha@ doses @<=@10@super 9@ Rad; however, at @alpha@ doses @>=@10@super 10@ Rad the PTFE matrix suffers severe chemical degradation, morphological roughening, and material loss. Chemical degradation is evidenced in the ToF-SIMS spectra by fragmentation, unsaturation, and speciation of molecules in the PTFE matrix. ToF-SIMS images support the assertion that chemical degradation is the result of @alpha@ particle irradiation and show morphological roughening of the sample with increased @alpha@ dose. High resolution SEM images more clearly illustrate morphological roughening and the mass loss that accompanies high doses of @alpha@ particles. Finally, RGA confirms the supposition that the product of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss.