Polyimide degradation induced by irradiation with N + ions
- PDF / 145,037 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 46 Downloads / 196 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Polyimide degradation induced by irradiation with N+ ions ˇ c´ık, I. Miˇcek, and V. Rybka V. Svorˇ Department of Solid State Engineering, Institute of Chemical Technology, 166 28 Prague, Czech Republic
V. Hnatowicz ˇ z, Czech Republic Institute of Nuclear Physics, Czech Academy of Science, 250 68 Reˇ
ˇ y F. Cern´ Department of Physics, Czech Technical University, 166 07 Prague, Czech Republic (Received 6 June 1996; accepted 4 February 1997)
The samples of Upilex R polyimide (PI) were irradiated with 90 keV N+ ions to the fluences from 5 3 1014 to 2 3 1017 cm–2 , and sheet resistance (Rs ) and thermoelectric power (TEP) were measured in dependence on the ion fluence and the sample temperature. The Rs achieves its minimum for the ion fluence of 13 1017 cm–2 , and from the measured temperature dependence of Rs it may be concluded that the ion beam modified PI exhibits semiconductor properties with charge transport governed by the variable range hopping mechanism. The measured TEP of the PI samples irradiated to the fluences above 1 3 1016 cm–2 is low (the order of mVyK). Such properties are typical for metals, and the conclusion is that the charge transport in the irradiated PI samples is contributed by the mechanisms which are characteristic for both semiconductors and metals. The role of conjugated double bonds was examined by measuring absorption UV-VIS spectra. The number of the conjugated double bonds correlates with observed Rs , and the width of the forbidden band, determined from UV-VIS spectra, is a decreasing function of the ion fluence.
I. INTRODUCTION
The irradiation of polymers with heavy ions leads to a significant increase of their electrical conductivity.1–5 In some cases, the conductivity of the radiationmodified layer is comparable with that of inorganic semiconductors.6 In polymers the ion irradiation leads to chemical bond splitting by free radicals, to polymer oxidation, and eventually to cross-linking.7 For polymers irradiated to lower fluences, the conductivity increase is mainly related to additional conjugated double bonds created by polymer dehydrogenation.8 At higher ion fluences, another conductivity increase is mainly due to polymer carbonization9 and creation of carbon clusters.10,11 In the polyimide (PI) case, the ion irradiation results in rather strong changes in the chemical structure of the PI macromolecular chain. The imide groups transform into amide ones,12 the aromatic rings are split down,13 and the polymer is deoxygenated.14 The production of carbon clusters in PI irradiated to fluences above 1 3 1014 cm–2 was reported.13–15 The conductivity increase in radiation-modified PI is due to the dehydrogenation of the PI macromolecular chain, to the production of conjugated double bonds via opening of aromatic rings, and to polymer carbonization.13,16 In this study the temperature dependence of the Rs (sheet resistance) and TEP (thermoelectric power) J. Mater. Res., Vol. 12, No. 6, Jun 1997
http://journals.cambridge.org
Downloaded: 2
Data Loading...
