Oxidising Role of Water Vapour in the 250 Kev D + Induced Radiolysis of Polyimide Kapton-H
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OXIDISING ROLE OF WATER VAPOUR IN THE 250 keV D+ INDUCED RADIOLYSIS OF POLYIMIDE KAPTON-Ha) U.K. Chaturvedi, A. Patnaik, Ramji Pathak, R.N.Chakraborty and A.K. Nigam Van-de Graaff Laboratory, Department of Physics Banaras Hindu University, Varanasi 221005, India Residual water vapour present in the vacuum system has been observed to play a dominant oxidising role in the 250 keV D+ induced radiolysis of polyimide (Kapton-H). The partial pressure (pp) of water in the vacuum system decreases sharply as the D+ beam impinges the polymeric surface, but soon after, it recovers to its initial value as the accumulated dose increases. Emission of CO 2 is observed which has its maximum at a time when the H20 partial pressure is at a minimum. The CO 2 level also returns to its original level with time. This complementary variation of CO2 and H20 confirms that absorbed and adsorbed water molecules are radiolysed by the ion beam and initiate oxidation of the radiolytically evolved CO to yield CO2 on and within the ion implanted surface of the polyimide. Further, the small enhancement in the 28 amu peak (N2 + CO), which exhibits
no maximum/minimum over the entire implantation time, can be understood in terms of the evolution of N2 from the imide ring as a result of radiolysis of this nitrogen containing polymers. INTRODUCTION Recently, the analysis of the gaseous products coming out of the macromolecules and molecular solids when bombarded with ions of different mases and energies, has attracted attention of many scientists1, 2 ' 3 Kapton-Ha) (Polypyromellitimide; also known as polyimide) is one of the most important polymer having heat and radiation resistant property and having wide applications in space technology, 'micro-electronics fabrication, plasma fusion programmes etc.4,5 Since in most of these applications the Kapton is exposed to ionizing radiations, it is desirable to understand the basic physics and chemistry involved in its radiolysis. During last several years, many polymers including polyimides have shown laser induced ablation and smooth etching 6but no such effect has been observed by us using ion beams 9 , although the total deposited energy by ion beam irradiation much larger than those in cases of laser ablation. In addition to this, detection of CN groups in the optical emission spectra of non-nitrogenous excimer
polymers like PMMA 6 also poses an unresolved question. This points out the role of the ambient gases/vapours in the whole process. Another interesting feature a) Trade name of Du Pont Inc. Mat. Res. Soc. Symp. Proc. Vol. 100. ' 1988 Materials Research Society
750
is the evolution of substantial amount of CO 2 with CO when polyimides are thermally or laser degraded even in vacuum0.
Careful studies in case of laser abla-
tion of polyimide have shown that initially CO gets evolved which subsequently 8 gets oxidised into CO 2 before its escape from the polymer surface . This suggests the presence of some oxidising agents either in the polyimide matrix or in vacuum
in the form of residual vapou
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