Study of polycarbonate degradation induced by irradiation with He + ions
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Vladimir Hnatowicz and Jifi Kvitek Institute of Nuclear Research, Czech Academy of Sciences, 250 68 Rei, Czech Republic (Received 12 April 1994; accepted 19 September 1994)
A stack of five polycarbonate foils, each 1.4 fim thick, was irradiated with 1.3 MeV 4 He + ions to the dose of 1.1 X 1014 cm" 2 . Ion beam induced polymer degradation, as a function of the particle energy, was studied by UV-VIS and IR spectroscopy of individual foils. In the irradiated foils, a significant reduction of characteristic absorption bands is observed, indicating polymer degradation. Significant increase of the surface polarity, characterized by a polar component of the surface free energy, is also found. Both the degree of the polymer degradation and the surface polarity correlate with the total energy deposited by 4 He + ions in the foils.
I. INTRODUCTION Ion irradiation of polymeric materials leads to irreversible changes of their macromolecular structure, and it can be used for changing, in a controllable manner, the physical properties of the polymer surface.1'2 Soon after the implantation of the doses as low as 1012 cm, - 2 observable modifications of the polymer structure take place. Scission of the polymeric chain and the breaking of another chemical bond are the major processes leading to the creation of free radicals, which may later recombine. The primary degradation processes are followed by polymer oxidation, creation of conjugated double bonds,3 and chain aggregation.1 Volatile degradation products were observed to escape from the polymer during the ion implantation.4 The role of these phenomena depends on the polymer properties (gross composition, molecular structure, density, etc.), as well as on the implantation regime (ion mass and energy, beam intensity, sample temperature, etc.). If the implanted ion dose is increased above 1014 cm" 2 , significant carbonization of the material appears, and its final structure is not similar to the original chain structure of the polymer any longer.1'5 Ion implantation is a suitable tool for the modification of electrical, optical, and mechanical properties of polymer surface layers to depths, depending on the ion range.6 In the present work, the degradation of polycarbonate induced by 4 He + ions was studied for the ion dose of 1.1 X 1014 cm" 2 and as a function of the ion energy.
bardment was studied. The stack of five PC foils, each 1.4 /mm thick, was irradiated with 1.3 MeV 4 He + ions in an electrostatic accelerator to the dose of 1.1 X 1014 cm" 2 . The irradiated area was 0.7 cm2, and the beam spot homogeneity was controlled visually on a screen which could be inserted in front of the target. The ion total dose was measured by the charge collected on the target. The ion current was kept below 20 nA to avoid thermal degradation of the foils. After the irradiation, the foil stack was disassembled and each foil was investigated separately. The IR and UV-VIS spectra from unirradiated (pristine) and irradiated foils were obtained by means of standard spectrophotometers. The IR
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