Chapter 4
Luminescence Study of Ion-Irradiated Aromatic Polymers Y. Aoki, H. Namba, F. Hosoi, and S. Nagai
Downloaded by TUFTS UNIV on February 21, 2018 | https://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1994-0579.ch004
Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, Watanuki-machi, Takasaki, Gunma 370-12, Japan
Luminescence spectra of solid polymer films such as polystyrene, poly(2-vinyl naphthalene) and poly(N-vinyl carbazole) were measured during ion irradiation with 200 keV He ions. For each polymer, the specific feature of luminescence spectrum due to the excimer of the pendant aromatic group was observed. This excimerfluorescencewas decreased in intensity with the irradiation dose over thefluencerange of 1-2 x 10 ions/cm , while a new luminescence was observed to grow at the longer wavelength, for polystyrene and poly(2-vinyl naphthalene), but not for poly(N-vinyl carbazole). The decreasing rate of the excimer fluorescence corresponded to the increasing rate of the new luminescence. Thus, a new kind of luminescent species are produced by ion irradiation, accompanied by the disappearance of the excimerfluorescence.Its formation process might be associated with the overlapping effect of ion tracks occurred in ion-irradiated polymers. +
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Ion irradiation effects on polymer materials have attracted interests of many scientists in the field of materials research, especially of polymer modification with ion beam(/). The ion irradiation effects of polymers could be roughly classified into two kinds of effects at present. One is the intra-track effect which occurs within an individual ion track and it is dependent on the distribution of energy deposition by only one ion and it is specified by the energy and the kind of the ion. The other one is the dose effect which can be observed when more than two ion tracks influence the same part of polymer. Then intra-track effects seem to occur predominantly at low dose while the dose effects are expected in a higherfluenceregion because the former is a local effect. According to previous reports(7-5), at low ionfluencethe changes in the chemical bonding, chain scission and/or crosslinking, of polymers are obtained, and at highfluencemost of polymers are decomposed nearly completely to inorganic hydrogenated carbonaceous materials which show good electric conducting property.
0097-^156/94/0579-0045$08.00/0 © 1994 American Chemical Society
Ito et al.; Polymeric Materials for Microelectronic Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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POLYMERIC MATERIALS FOR MICROELECTRONIC APPLICATIONS
However, there are few reports describing the effects, in the intermediate fluence region, on the structures of the polymers, the chemical reactions, etc. An ion pulse radiolysis study of polystyrene(^) shows excimer fluorescence and un-identifed luminescence in the luminescence spectrum. In this report, the un-identified luminescence from ion-irradiated polystyrene and poly(2-vinyl naphthalene) will be shown, which can be considered to result from overlapping of ion tracks and to give some information about ion radiolysis of polymers in the intermediate region.
Downloaded by TUFTS UNIV on February 21, 2018 | https://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1994-0579.ch004
Experimental Polystyrene (578, Scientific Polymer Products), poly(2-vinyl naphthalene)(V-284, General Science Corporation), and poly(N-vinyl carbazole)(093C, Scientific Polymer Products) were used as received. The polymer films were prepared by casting on Si wafers or quartz plates. The casting solvents were toluene for polystyrene and poly(2-vinyl naphthalene), and dichloromethane for poly(N-vinyl carbazole). Ion irradiation was done with 200 keV He beam from a 200 keV ion implanter at JAERI-TAKASAKI. The ion beam was scanned in vertical and horizontal directions on a lOmm-diameter aperture to obtain uniform ion doses. The current density was estimated from the ion current through the aperture and the aperture size. The apparatuses for luminescence measurement were composed of a monochrometer/ spectrograph (HR250, Jovin-yvon), a multichannel photodetector with image intensifier(OMH-42, ATAGO BUSSAN) and a photomultiplier tube (R2758, HAMAMATSU) in photon counting mode. Luminescence spectra were measured repeatedly during irradiation under the current density of 12.7 nA/cm . The dose for one spectrum was 3.2 χ 10 ions/cm . In the measurement of the fluence dependence of luminescence by photon counting system, the rise time of the photomultiplier output was ca. 2.7 ns and the channel advance time was set to be 500 ms. Molecular products emitted from polymer samples during ion irradiation were also detected by a quadrupole mass spectrometer (QMG-420C, Balzers) as a complemental product analysis. In this measurement, the beam current density (51.0 nA/cm ) was higher than that for luminescence measurement in order to obtain appropriate yields of emitted products. +
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Results and discussion Figure 1(a), (b) and (c) show the luminescence spectra of polystyrene, poly(2-vinyl naphthalene) and poly(N-vinyl carbazole) induced by 200 keV He irradiation. The fluorescence of sandwich-type excimer was observed around 330 nm for polystyrene(5), and around 420 nm for poly(2-vinyl naphthalene)(
