J.M. Ramillon

Swift heavy ions on polymers: Hydrocarbon gas release ☆

Abstract In order to understand how bond cleavages occur during ion–polymer interaction, we have made quantitative measurements of the gases evolved under irradiation from the polymers polyethylene, polypropylene and polybutene. The ions used for irradiation were 10.2 MeV amu−1 13C, 2.6 MeV amu−1 14N and 6 MeV amu−1 58Ni. We conceived a new set-up using a Fourier Transform Infrared analysis of the gas mixture released from the polymer film. Observation of the recorded spectra clearly shows that molecular emission is extremely sensitive to the electronic stopping power (dE/dx)e. At low (dE/dx)e, gas yields are strongly polymer dependent and we mainly observe the scission of the tertiary bond: Polypropylene (PP) releases methane and Polybutene (PB) ethane. At high (dE/dx)e, we observe principally acetylene emission, other unsaturated molecules are also greatly favoured. Gas yields are therefore less specific of a given polymer. We show in this work, that the chemical identification of the molecules outgassing the polymer film explains how a polymer chain reacts towards clustered ionisation induced by swift heavy ions.

Electronic and structural modification of polyvinylidene fluoride under high energy oxygen ion irradiation

Stacks of polyvinylidene fluoride (PVDF) foils were exposed to an oxygen beam of 800 MeV. Electronic and structural modifications induced by the radiations were studied by X-ray photoelectron spectroscopy (XPS) using a monochromatized X-ray Al K α source, and by electron spin resonance (ESR) experiments. It was observed that i) the creation of allenes compounds produced by the dehydrofluorination of PVDF; ii) the presence of primary free radicals and peroxide radicals. The amount of the created defects is related to the electronic ion stopping power d E /d x and to the deposited dose.

Optical properties of synthetic carbon nanoparticles as model of cosmic dust

Carbon nanoparticles synthesised by laser pyrolysis of small hydrocarbons are deposited at low energy on a silicon substrate. Infrared spectroscopy of the as-formed films are studied as a function of the synthesis parameters and post-treatments, such as annealing and heavy ion irradiation. Correlation between infrared spectroscopy and multiscale organisation of the samples is made through transmission electron microscopy, including image analysis. Changes in infrared spectra are analysed in terms of the carbon network building. The relevance of the results to model the structure and spectroscopy of carbon dust in the carbon-rich circumstellar media is discussed.

Surface processes occurring on PVDF under energetic ion irradiation

Abstract Modifications induced in polyvinylidene fluoride by energetic ions (E ⩾ 1 MeV/amu) have been reported in previous papers [1–3]. It was shown by using methods such as X-ray photoemission spectroscopy (XPS), infrared absorption spectroscopy (IRAS), electron spin resonance (RPE) or differential scanning calorimetry (DSC) that light and very heavy ions lead to opposite modifications of the polymer. Superficial unsaturations characterized as cumulene compounds, and HF gas desorption were produced under oxygen ions. On the other hand, with heavy ions, the polymer surface appears not to be damaged and a rebuilding process was suggested, which involves a migration of reactives species from the bulk to the surface. In this paper, we report desorption experiments and XPS measurements which support a readdition mechanism of HF molecules on cumulene compounds. Gas desorption measurements carried out with a quadrupole mass spectrometer, during the polymer exposure to the ions, lead to a two-step desorption mechanism: migration of HF and F2, followed by desorption of these species from the surface. XPS spectra of PVDF samples irradiated at a high fluence with a focussed krypton ion beam show new structures which correspond to the readdition of reactive species (HF∗, H∗, F∗), on unsaturations produced during the first step of the modification. A PVDF sample of 50 μm thickness previously irradiated with oxygen ions which led to superficial allenic structures was irradiated again with krypton ions. The XPS measurements of the C1s and F1s photoemission lines, the shape of which is similar to that obtained for a pristine PVDF sample, clearly show that a readdition mechanism occurs on the unsaturations previously produced under energetic light ions.

Production of pulsed, mass-selected beams of metal and semiconductor clusters

We report on the development of a beam line for mass-selected metal and semiconductor clusters. The cluster source combines the principles of plasma sputtering and gas condensation. Both techniques together allow to produce clusters in a wide size range. With the aid of a time-of-flight system, small clusters (i.e., Cu(n)(+), n<100) are selected and pure beams containing only one cluster size are provided. For large clusters (containing several thousands of atoms), a beam with a narrow size distribution is obtained. A 90 degrees quadrupole deviator is used to separate charged clusters from neutral ones.

Irradiation of ethylene/styrene copolymers: evidence of sensitization of the aromatic moiety as counterpart of the radiation protection effect.

Molecules containing aromatics systems are more stable in the presence of ionizing radiations than alkanes. In the same way, introducing aromatic rings into aliphatic compounds increases their stability. The protective effect is nonlocal and likely results from the transfer of energy and species from the aliphatic moiety to the aromatic one. For years, it was commonly assumed that the aromatic moiety, which is very radiation resistant, accommodates the extra energy remaining unaffected. The use of Fourier transform infrared spectroscopy, online with high energy ion beam irradiation of ethylene/styrene random copolymers, allows us to bring experimental evidence that the benzene rings are sensitized by transfer reactions and consequently that this effect is more important in polymers with low benzene ring molar content.

Excitation of Ar16+ projectiles in intermediate velocity collisions with neutrals

Abstract Excitation cross sections 1s2 → 1snp of 13.6 MeV/u Ar16+ ions colliding with various target atoms (2 ≤ ZT ≤ 54) have been measured by looking at the projectile emission with a high-resolution X-ray spectrometer. This experimental technic allows us to distinguish all the processes involved in the collision such as, for example, the competitive capture ionization. The determination of intra-shell excitation ( 1s2s ⇎ 1s2p ) coming from the 1s2s(3S1) metastable state has also been deduced.

Recent questions about the excitation mechanism at intermediate velocity

Abstract For both fundamental reasons and potential applications, the process of K-excitation by heavy ions at intermediate velocity has been re-investigated experimentally and theoretically and the main results are described here. The nature and the origin of the so-called “saturation effect” at high exciting charge is not yet elucidated. The importance of K-excitation is outlined in connection with problems of radiation damage.

A new setup for localized implantation and live-characterization of keV energy multiply charged ions at the nanoscale

An innovative experimental setup, PELIICAEN, allowing the modification of materials and the study of the effects induced by multiply charged ion beams at the nanoscale is presented. This ultra-high vacuum (below 5 × 10-10 mbar) apparatus is equipped with a focused ion beam column using multiply charged ions and a scanning electron microscope developed by Orsay Physics, as well as a scanning probe microscope. The dual beam approach coupled to the scanning probe microscope achieves nanometer scale in situ topological analysis of the surface modifications induced by the ion beams. Preliminary results using the different on-line characterization techniques to study the formation of nano-hillocks on silicon and mica substrates are presented to illustrate the performances of the setup.

Aliphatic/aromatic systems under irradiation: influence of the irradiation temperature and of the molecular organization.

With the aim of understanding the electronic excitation, charge or reactive species transfers occurring during irradiation, we studied the role of the aromatic content on ethylene/styrene random copolymers (PES) and on cyclohexane/benzene glasses (amorphous organic solids). Radiation-induced modifications were monitored in situ, at the molecular level, using Fourier transform infrared spectroscopy (FTIR). Irradiations were performed under a vacuum, and thanks to in situ measurements, oxidation was avoided. We followed both the C═C bond creation in the aliphatic moiety and the destruction of the aromatic moiety. The influence of the irradiation temperature was investigated by irradiating samples at room temperature and at 11 K. At such a low temperature, long-range migration hardly occurs and its influence is considerably reduced or could even vanish. Therefore, low temperature irradiation gives insight on the relative influence of reactive species transport and electronic excitation and charge transport. We found that the effect of lowering the PES irradiation temperature from room temperature to 11 K is small, indicating a minor role for the reactive species transport. Moreover, the two chosen systems allow the examination of the relative magnitude of intra- and intermolecular transfers. We demonstrate that, under conditions where reactive species are almost frozen, intermolecular transfers are very efficient.