Charging effects in the ion beam analysis of insulating polymers (original) (raw)
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Electret behaviour of ion irradiated polycarbonate and kapton-H polyimide films
Vacuum, 1997
Vacuum/volume 48/number 12lpages 995 to 99711997 The electret state of a polymer arises from the induced polarization owing to the frozen in phenomenon of electric charges. The study of electret nature using thermally stimulated discharge current (TSDC) technique reveals the nature of various relaxation processes in a polymer. When a polymer is irradiated with high energy ions their dielectric relaxations get affected which can be investigated using above mentioned technique. Reported here are the results of TSD current spectra of films of polycarbonate (PC) (irradiated with 700 MeV Ag+, flux; 7 x IO" and lx IO9 ions/cm') and kapton-H polyimide (irradiated with 700 Mel/O++, flux; 1 x IO5 ions/cm'). The as-received and irradiated samples of PC were polarised at 720°C using a 200 kV/cm electric field while those of kapton-H were polarised at 90°C, field; 733 kV/cm and 18O"C, field; 266 kV/cm. With PC it is observed that the irradiation does not affect the location of TSDCpeak occurring at 144°C (activation energy; 0.6eV); however, the peak magnitude changes with irradiation dose. The peak being associated with dipolar relaxation the ion-irradiation seems to have changed the number of dipoles. The high temperature TSDC spectra is however largely affected by irradiation giving evidence of the presence of new traps. With kapton-H, it is observed that TSD current changes its direction (anomalous TSDC) in irradiated samples in the high temperature region. Such behaviour has not been observed in the thermoelectrets of as-received samples. Only the corona charged electrets were observed to give such anomalous TSDC behaviour. This suggests the creation of new energy traps from irradiation. The bulk nature of this relaxation is confirmed by the TSDC of repoled samples. The irradiation induced shallow energy traps along with dipolar relaxation are also observed from the TSDC spectra in the low temperature region. 0 1998 Elsevier Science. All rights reserved
Charge dynamics in electron-irradiated polymers
Brazilian Journal of Physics, 1999
Recent studies of charge trapping and charge transport in polymer lms irradiated and charged with monoenergetic electrons of range smaller than the sample thickness and thereafter stored or annealed under various conditions are discussed. An analytical model used to describe the phenomena takes the following parameters into consideration: Charge and energy deposition pro les, charge drift due to a shallow-trap-modulated mobility, deep trapping without release, trap lling due to a nite trap density, and ohmic relaxation due to a radiation-induced conductivity during irradiation and its delayed component after irradiation. The model calculations show the e ect of various parameters on the shape of the initial charge distribution and on its evolution with annealing time.-Experiments with the laser-induced pressure-pulse LIPP method on 12 and 25 m thick uorocarbon and polyimide lms, charged with 10 or 20 keV electron beams, respectively, yield the charge distributions after irradiation and the changes of the distributions due to annealing of the samples at 120 C for various times. A comparison of experimental and analytical results reveals the trapping kinetics and permits to estimate the deep-trap density and the-product, where is the trap-modulated mobility and is the trapping time.
Ion beam effects in polymer films: Structure evolution of the implanted layer
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997
Thin films of polyethylene, polyamide-6 and cellulose implanted with 100 keV B+, Nf and Sb+ ions to the fluences of 10'3-10'7 cmv2 were investigated using RBS and NDP techniques as well as IR, UV-visible and EPR spectroscopies. The peculiarities of the depth distribution of implanted species and the origin of the processes responsible for modification of the structural, optical and paramagnetic properties of polymers are discussed with consideration for two major reactions occurring in the implanted layer: (i) oxidation of the radiation-damaged polymer that predominates at moderate doses; (ii) clusterization of radiation defects with the formation of carbon-enriched domains ("drops") which can overlap at high ion fluences yielding the network of conjugated carbon structures.
Radiation-Induced Conductivity of Space Used Polymers Under High Energy Electron Irradiation
IEEE Transactions on Plasma Science, 2015
Polymers are widely used on spacecraft for different specific functions such as thermal and electrical insulation, mechanical support, and adhesion. These polymers are highly sensitive to radiation encountered in space. Their electric properties are especially significantly altered leading to a very specific behavior in terms of charge transport and discharge processes. Different dedicated facilities have been developed at ONERA, with Centre National d'Etudes Spatiales support, for the characterization of space used materials in representative conditions. Thanks to the use of these different facilities, it has indeed been demonstrated that radiation-induced conductivity of space polymers strongly affects the charging surface potential and depends on several parameters (radiation dose rate, total radiation dose, temperature, and on the induced electric field) through complex physical mechanisms that are described in this paper. The sensitivity of polymers on these different parameters strongly depends on the polymer trap distribution and molecular configuration. Experimental and numerical results are presented in this paper, coupled with the different experimental techniques developed and applied to this work.
Onset and growth of conduction in polyimide Kapton induced by swift heavy-ion irradiation
Physical Review B, 1997
In order to follow the insulator to conductor transition in a polymer when it is subject to a progressive degradation process, we have irradiated about 50 samples of poly͑imide͒ Kapton with heavy ions and measured their conductivities as functions of temperature, electric field, and frequency. Electron spin resonance measurements gave the spin susceptibility, linewidth, g factor, and relaxation times along each step of transforming the conductivity of the material. We defined a single damage parameter that characterizes a unique damage scale for the four different ions and the different irradiation energies that we used. From the point of view of the electronic properties, the degradation process consists mainly of the nucleation and growth of carbon disordered clusters which are rich in-conjugated bonds. During the transformation, the conductivity reflects the competition between two contributions, one of which is related to an initial disordered irradiation-doped polymeric substrate and the second to a hopping network progressively built from the merging of the clusters. The initial substrate contribution, visible in the first stage of irradiation, corresponds to a simple temperatureactivated behavior and to a clear Poole-Frenkel dependence with the electric field, while the latter shows all the features of nonadiabatic hopping in a granular system. Adiabatic hopping within the clusters invades progressively all the sample in the final stage. ͓S0163-1829͑97͒07309-8͔
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1991
The keV-MeV ion irradiation of polymers produces deep changes in their physical and chemical properties associated with the breaking and rearrangement of original bonds. The modification of chain structure occurs within a well defined ion fluence range which depends on the ion linear energy transfer as well as on the target parameters. At low ion fluences (≈1014 ions/cm2) crosslinks between chains and chain-scissions are detected with a chemical yield in the range 0.05–0.3, depending on the ion mass. With increasing ion fluence (1015 ions/cm 2) the original polymer structure is heavily modified and the irradiated films exhibit properties close to those of hydrogenated amorphous carbon. At very high fluences (≈1016 ions/cm 2) graphitization of the material occurs.
1984
During heavy ion irradiation of polymer and condensed gas films large fluxes of ions, excited neutrals and ultraviolet radiation are liberated. Because the fluxes are so large, they can contribute secondary currents comparable to (or even larger than) the current of incident ions unless they are carefully suppressed. For polymer films the secondary fluxes vary with the polymers used and with the primary ion dose. While films like HPR-204, and polyimides like PIQ show a gradual decrease of the ionic species emission, poly(methy1 methacrylate), PMMA, shows a peak in the ionic species emission with increasing dose. These observations suggest that for typical ion implantations through polymer masks, the error in the charge integration at the target may be a function of the polymer as well as the dose if proper care is not exercised in the suppression of secondaries. For condensed gas solids, efficient ultraviolet emission can produce photoelectron currents which are a strong function of film thickness. Argon is a particularly striking example. We comment on secondary suppression techniques that can be used to minimize or eliminate beam integration errors in these cases or that alternatively can provide info~atioR about the secondary fluxes and the processes which produce them.
Space charge and conduction measurements in gamma-irradiated polyethylene terephthalate
2018
We report on the impact of irradiation on the dielectric properties of Poly(Ethylene Terephthalate)(PET).Thin films of PET were irradiated in air at room temperature by means of a 60 Co gamma source at a dose rate of approximately 31 Gy/min. Total doses of 30 kGy and 150 kGy were adopted in this work. The space charge profiles and residual electric field of virgin material and material exposed to these representative doses, obtained after 30 min of depolarization following field application in the range 40-200 kV/mm, have been examined by Laser-Intensity Modulation Method (LIMM). The dependence of space charge density with electric field values and irradiation dose is analysed. Under high DC voltages and after irradiation, the space charge stored in PET tends to be less than in reference PET. The charging and discharging currents tend to increase with the irradiation, considering both the transient contribution to the current and the conductivity contribution. Space charge and conduction measurements exhibit good agreement in the fact that higher conductivity would prevent charge accumulation.
Polymer modifications due to absorption of different ionizating radiations
In the last years, an useful collaboration developed between the material engineers and the physicians of Messina University. The study of the intimate structure of a material, before and after its modification induced by an external ionizing radiation source (electrons, ions, gamma) requires the simultaneous presence of specialist in Chemistry, Physics and Engineering in order to define the best modification conditions and the consequent features of the new synthesized material. In particular the polyethylene, employed in different fields, such as microelectronics and biomedicine, was chosen as an important target to modify its properties through ions and electron beam irradiations. Ion beams, with energy of the order of some hundred keV and doses of the order of 10 14 /cm 2 , are able to improve the polyethylene surface properties without change the pristine bulk. Instead, electron beams with energy of about 5 MeV and high dose, improve significantly bulk properties of the polymer. The effects of the ion and electron modifications were investigated with several physics characterization methods, as will be discussed in the following.
Conductivity Modulation in Polymer Electrolytes and their Composites by Ion Beam Irradiation
Polymers are a class of materials widely used in different fields of applications. With imminent applications of polymers, the study of radiation induced changes in polymers has become an obvious scientific demand. The bombardment by ion beam radiations has become one of the most promising techniques in present day polymer research. When the polymers are irradiated, a variety of physical and chemical changes takes place due to energy deposition of the radiation in the polymer matrix. Scissoring, cross-linking, recombination, radical decomposition, etc. are some of the interesting changes that are obvious in polymers. The modification in polymer properties by irradiation depends mainly on the nature of radiation and the type of polymer used. Polymer electrolytes are obtained by modifying polymers by doping, complexing, or other chemical processes. In general, they suffer from low conductivity due to high crystallinity of the matrix. The effect of radiation on polymer electrolyte is expected to alter their crystalline nature vis-a-vis electrical properties. This review article shall elaborate modifications in the physical and chemical properties of polymer electrolytes and their composites. The variations in properties have been explored on PEO based polymer electrolyte and correlated with the parameters responsible for such changes. Also a comparison with different types of the polymers irradiated with a wide range of ion beams has been established.