V. Hnatowicz

Surface properties and biocompatibility of ion-implanted polymers

The surface properties of the polyethylene (PE), polypropylene (PP) and polystyrene (PS) samples doped with 150 keV F+ ions with doses of 1 × 1012-1 × 1015 cm–2 have been characterized by different techniques and their biocompatibility to vascular smooth muscle cells was examined. The concentration and the conjugation length of the double bonds produced by ion impact, the conductivity and the surface polarity increased with the level of doping. The cell density was measured on the PP and PS samples doped with doses below 1 × 1013 cm–2. The cells cultured on the ion-doped PS and PP exhibited better homogeneity and the resulting density was several times higher than that on the undoped polymers. No such effects were observed on the doped PE. The enhanced cell proliferation correlates with the increased surface polarity of the doped polymers.

Early stages of growth of gold layers sputter deposited on glass and silicon substrates

Extremely thin gold layers were sputter deposited on glass and silicon substrates, and their thickness and morphology were studied by Rutherford backscattering (RBS) and atomic force microscopy (AFM) methods. The deposited layers change from discontinuous to continuous ones for longer deposition times. While the deposition rate on the silicon substrate is constant, nearly independent on the layer thickness, the rate on the glass substrate increases with increasing layer thickness. The observed dependence can be explained by a simple kinetic model, taking into account different sticking probabilities of gold atoms on a bare glass substrate and regions with gold coverage. Detailed analysis of the shape of the RBS gold signal shows that in the initial stages of the deposition, the gold layers on the glass substrate consist of gold islands with significantly different thicknesses. These findings were confirmed by AFM measurements, too. Gold coverage of the silicon substrate is rather homogeneous, consisting of tiny gold grains, but a pronounced worm-like structure is formed for the layer thickness at electrical continuity threshold. On the glass substrate, the gold clusters of different sizes are clearly observed. For later deposition stages, a clear tendency of the gold atoms to aggregate into larger clusters of approximately the same size is observed. At later deposition stages, gold clusters of up to 100 nm in diameter are formed.

Cell adhesion on modified polyethylene

Polyethylene (PE) was irradiated with 10 and 63 keV Ar+ ions to fluences of 1 × 1017 to 3 × 1019 m−2 and then it was grafted with aminoacid (alanine). The changes of surface polarity, electrical conductivity, and oxygen concentration were examined on pristine, as-irradiated, and irradiated-grafted PE. The in vitro adhesion of mice fibroblasts on the modified PE was evaluated 24 hours after inoculation. It was proved that for the PE irradiated at 10 keV ion energy, the presence of chemically bound alanine increases cell adhesion and its homogenity. For PE irradiated with 63 keV ions, however, the alanine grafting leads to a reduction of the number of adhering cells. It was found that a rising surface polarity increases cell adhesion, but when its value is too high the cell adhesion starts to decrease. No correlation between electrical conductivity and cell adhesion was observed. In general, higher cell adhesion is observed on modified PE in comparison with pristine one.

On the redistribution of6Li+ ions implanted into polypropylene foils

Abstract6Li+ (150 keV) was implanted into thin polypropylene foils at fluences of 1 x 1013 to 1 x 1014 cm−2. Subsequent neutron depth profiling measurements of the Li distributions revealed considerable deviations from the expected ballistic range profiles. This Li redistribution was simulated by a numerical computer calculation. The best fit between measurements and simulations was obtained by assuming that (i) Li redistributes immediately after its ballistic slowing-down, (ii) the Li mobility is enhanced in the radiation-damaged polymer region, the local diffusion enhancement being controlled by the targets electronic damage, (iii) mobile Li is readily trapped at radiation-induced defects, their density being proportional to the targets electronic damage, (iv) these traps are saturable ones, and (v) Li migration is not restricted to the ion track region, but proceeds also through the neighboring unirradiated bulk, though with slower speed.

Oxidation of polyethylene implanted with As ions to different extents

Polyethylene (PE) samples implanted with 150 keV As+ ions to the extents of 5 × 1013−1 × 1015 cm−2 were studied using a standard RBS (Rutherford Back Scattering) technique. The measured projected range of As+ ions (Rp = 120 ± 20 nm) is significantly lower than theoretical range of 170 nm calculated using TRIM code for pristine PE, the difference probably being due to structural changes in PE resulting from the ion implantation. The measured range straggling ΔRP = 60 ± 10 nm also exceeds the theoretical TRIM value of 33 nm. The profile broadening might be due to the diffusion of the As atoms through the damaged surface layer of PE. Noticeable oxidation of the implanted samples was also observed, with most of the oxygen atoms trapped in the region of maximum radiation defects. The total oxygen content in the sample surface layer and its depth concentration profile depend on the extent of implanted ions. For the highest implanted dose of 1 × 1015 cm−2, the oxygen depth profile exhibits two distinct concentration maxima, the first on the sample surface and the second at a depth close to the expected range of 150 keV As+ ions.

POLYIMIDE DEGRADATION INDUCED BY IRRADIATION WITH N+ IONS

The samples of Upilex R polyimide (PI) were irradiated with 90 keV N{sup +} ions to the fluences from 5{times}10{sup 14} to 2{times}10{sup 17}cm{sup {minus}2} and sheet resistance (R{sub s}) and thermoelectric power (TEP) were measured in dependence on the ion fluence and the sample temperature. The R{sub s} achieves its minimum for the ion fluence of 1{times}10{sup 17}cm{sup {minus}2} and from the measured temperature dependence of R{sub s} it may be concluded that the ion be a 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{times}10{sup 16}cm{sup {minus}2} is low (the order of {mu}V/K). 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 of absorption UV-VIS spectra. The number of the conjugated double bonds correlated with observed R{sub s}, and the width of forbidden band, determined from UV-VIS spectra, is a decreasing function of the ion fluence. {copyright} {ital 1997 Materials Research Society.}

Ion Implantation into Polypropylene

The effects of F+ ion implantation on the composition and the structure of oriented polypropylene were studied by optical methods and the Rutherford backscattering (RBS) technique. From the measurement of the contact angle, it was found that the polar component of the surface energy increases with increasing ion fluence. The spectroscopic measurements confirmed the formation of conjugated double bonds and C=O groups in the implanted polypropylene, but not the presence of C-F groups. The oxygen contamination of the polypropylene surface layer was observed in RBS measurements.

Variable surface properties of PTFE foils

Abstract Surface properties of commercially available polytetrafluoroethylene (PTFE) foils of different thicknesses were examined using three different methods: AFM, study of a electrokinetical ζ-potential and measurement of a contact angle by goniometry. It was found that the front and back sides of the foils exhibit different surface morphology and roughness, different values of the ζ-potential and contact angle. The contact angle and the ζ-potential are decreasing functions of the foil thickness.

Electrical resistivity and thermoelectric power of carbon black loaded polyethylene modified by GeV ion irradiation

Abstract Polyethylene films (PE), 75 μm thick, doped with carbon black (CB) to different concentrations under and above the percolation threshold (PT), were irradiated with 2.6 GeV Au 24+ ions to give final doses between 1 × 10 8 and 1 × 10 11 cm −2 . On virgin and ion irradiated samples, temperature dependences of the resistivity and the thermoelectric power (TEP) were measured and the melting process was followed using differential scanning calorimetry. The ion irradiation causes R S to decrease for the samples under PT. All samples exhibit negative TEP which is a decreasing function of the sample temperatures and an increasing function of R S . The ion irradiation leads to significant TEP increase. From the measured temperature dependencies of R S and TEP it may be concluded that metallic-like conductivity takes place in the temperature range up to the melting point of the PE crystalline phase and that above the PT, thermal generation of the charge carriers is low and the variable hopping mechanism of the electrical conductivity contributed to the charge transport.

Modifications of polypropylene induced by the implantation of iodine ions

The polypropylene (PP) samples implanted with I+ ions at the implantation energies of 50, 100 and 150 keV to the fluence of 1×1015 cm-2 were studied using standard RBS (Rutherford backscattering) technique. The surface of the implanted PP samples is heavily damaged and enriched in carbon. The measured projected ranges of iodine atoms are by 10 to 30% lower than the theoretical ones calculated using Monte-Carlo simulation code TRIM (transport of ions in matter) code for pristine PP. The differences may be due to structural changes of polymer during the ion implantation. The range stragglings exceed the theoretical TRIM estimations about twice. The profile broadening is probably due to the diffusion of the iodine atoms through the damaged PP surface layer. In repeated RBS measurements, the iodine diffusion was confirmed with diffusion coefficient of 2.7×10-18 cm2s-1. Noticeable oxidation of the implanted samples was observed, with majority of the oxygen atoms being trapped in the region of maximum radiation defects. The bulk oxygen concentration profile resembles that of iodine but it is shifted inward by 200-350A. The relative oxygen content in the bulk is an increasing function of the implantation energy and it exceeds considerably the stoichiometric value for common iodine oxides.