R.M. Papaléo

Modifications in the chemical bonding and optical absorption of PPS by ion bombardment

Abstract Commercial-grade thin poly(p-phenylene sulphide) (PPS) foils, 2 μm thick, have been bombarded with 1H+ (380 keV), and with 0.61 MeV/amu 4He+, 12C2+, 16O3+, 32S3+, 79Br9+ and 127I14+ ions. The completely modified foils have been analyzed by Fourier transform infrared absorption spectroscopy (FTIR) and by ultraviolet-visible absorption spectroscopy (UV-VIS). The bond breaking and rearrangement processes were followed by using the FTIR results. The absorbance of bands related to CS, SS, CH and most of the ring carbon bonds show an exponential decrease as a function of fluence. The absorption bands most sensitive to the ion bombardment are those assigned to CS and SS bonds. The CC and CH bonds are less sensitive and certain absorption band changes indicate carbon-carbon aliphatic and or aromatic conjugation, due to their increasing intensity as a function of the ion fluence. Damage cross sections have been extracted from the plots of IR absorbance versus fluence. The values of the damage cross sections obtained scale roughly with the square of d E d x (independent of the nature of the chemical bond). The optical absorption coefficient has also been followed as a function of the ion fluence.

Radiation damage features on mica and L-valine probed by scanning force microscopy

The radiation damage tracks on the surface of muscovite mica due to single 78.2 MeV 127I ions from the Uppsala EN tandem accelerator have been studied using tapping mode scanning force microscopy (TM-SFM). Conically-shaped hillocks having nearly circular bases were observed on a sample irradiated at normal incidence. Samples irradiated at grazing angles of incidence displayed wider and taller hillocks, and each hillock was accompanied by a raised tail over the bulk ion track. First SFM results are also presented from a study of radiation damage features on mica and single crystals of L-valine induced by single 23 MeV C60 ions from the Orsay tandem accelerator. Brief comments are made on the scaling laws that could link results obtained with atomic and cluster ions.

HEAVY-ION-INDUCED SPUTTERING AND CRATERING OF BIOMOLECULAR SURFACES

We measured the electronic-stopping-power dependences of mega-electronvolt atomic-ion-induced sputtering and cratering of bio-organic targets. We employed a collector method to study relative total ...

Damaging of C60 films by MeV heavy ions

Abstract Thin films of C60 (99.99% purity) have been irradiated with 55 MeV 127I10+ ions in a fluence range from 2.5 × 109 to 3 × 1012 ions/cm2. Two methods have been employed to assess the modifications induced by the MeV ion irradiation: in situ plasma desorption mass spectrometry analysis and off-line micro-Raman spectroscopy. The yields of secondary low mass carbon cluster ions and intact C60 ions have been determined at different fluences. Damage cross-sections for the C60 molecules have been extracted from the ion yield curves as a function of MeV ion fluence. The secondary ion spectra of the C60 targets also show peaks corresponding to larger fullerenes with masses at least up to 2500 u. The evolution of the ion yields of these higher mass carbon clusters gives an evidence that they are not originally present in the target. They may be formed by coalescence reactions of C60 molecules as a result of an individual MeV ion impact.

MeV ion sputtering of polymers: correlation between secondary ion radial velocity distributions and heavy ion track structure

Abstract Systematic investigations of the initial radial velocity distributions of low mass positive and negative secondary ions, sputtered electronically from thin films of polyvinylidene fluoride and polystyrene, are reported. 72.3 MeV 127 I 13+ primary ions bombard the targets at 45° angle of incidence. Sputtered secondary ions in an individual MeV ion impact are analysed in a high resolution time-of-flight mass spectrometer. The accurate mass measurements of all ion peaks in the range from 1 to 100 m/z provide unequivocal determination of the chemical composition of these ions, forming homologous series, C n H ± m and C n H m F ± p . Plots of both the initial mean radial velocity (〈 v x 〉) and kinetic energy (α 〈 v 2 x 〉) as a function of the ion m / z results in a periodic pattern. Ions with lower hydrogen content exhibit wider velocity distributions (i.e. higher 〈 v 2 x 〉) and (〈 v x 〉) directed towards the primary ion trajectory. Ions with higher hydrogen content have lower mean kinetic energies and 〈 v x 〉 directed away from the incident ion trajectory. We argue that the 〈 v x 〉 and 〈 v 2 x 〉 periodic behaviour, connected to the chemical constitution of the ions, reflects the radial profile of the deposited energy density in the heavy ion track.

Damage cross sections and surface track dimensions of biomolecular surfaces bombarded by swift heavy ions

Damage cross sections and surface track dimensions of biomolecular surfaces bombarded by swift heavy ions

Swift atomic ion irradiation of C60 films: dependence of the damage cross section on the primary ion stopping power

Abstract Vacuum-sublimated C60 films (around 1 μm thick) are bombarded with fast atomic ions (4He, 12C, 16O, 32S, 79Br, 127I) in the range from 2 to 80 MeV. The initial velocity of the primary ions is kept constant at 1.1 cm/ns, in order to maintain the same ion track size for all impacting ions. Under these conditions the deposited energy density in the ion tracks is varied only due to changes in the stopping power, d E d x , of the projectiles. Atomic force microscopy (AFM) and Fourier transform infrared absorption spectroscopy (FTIR) were used to characterise the targets. AFM images indicate no major changes in topography and roughness of the irradiated samples. FTIR analyses of the irradiated samples give information on the changes in concentration of intact C60 molecules as a function of primary ion fluence. From plots of the intensity of the C60-specific IR absorption bands versus fluence, damage cross sections (σ) for the C60 molecules are extracted. For all analysed bands, the values of σ scale with the square of d E d x , i.e. the deposited energy density in the ion tracks.

Ion desorption from organic and inorganic targets induced by 100 keV gold cluster ions

Abstract The emission of different secondary ions from inorganic (CsBr) and organic (103 u peptide — valinomycin) targets is monitored as a function of the number of atoms of impacting Au−n cluster ions (n = 1 to 5) at constant energy of 100 keV. A method for determination of the multiplicities (defined here as the number of ions of the same type emitted per impact event) is described. The multiplicity is a measure of the ion emission probability in a single impact event and thus may provide evidence for “cooperative” effects in polyatomic ion impact induced sputtering.

Plasma desorption mass spectrometry in studies of formation and sputtering of fullerenes by MeV atomic ions

Abstract An account is presented on plasma desorption mass spectrometry (PDMS) studies of different carbon-containing organic solids utilizing megaelectronvolt (MeV) atomic ions from the Uppsvala EN-tandem accelerator. Positive ions of even-numbered carbon clusters (C+n, n = 40 to > 200) are ejected as a result of the interaction of the fast MeV ions with the target. The distribution of cluster sizes suggests that stable, closed carbon-cage structures — fullerenes - are formed. Among the investigated materials that produce carbon clusters are poly(vinylidenefluoride) and fluorinated fullerenes — C60F2m. For comparison purposes data from C60 targets have been also collected and analyzed. PDMS has been used for the in situ assessment of the damaging of C60 films by MeV heavy ions. Results on delayed electron emission from C−60 sputtered by MeV ions from C60 fullerene targets are also presented. A model of fullerene formation as a result of MeV ion interactions with the organic solid, including the yield dependence on primary ion charge state, is summarized. Both the data and the model suggest that fullerenes are formed as a result of a single primary ion impact and that they are ejected from an axially expanding infratrack plasma region. Results on different types of coalescence reactions in synthetic C60 fullerene targets and in blends of pure (synthetic) C60 with polystyrene leading to ejection of higher mass positive fullerene ions (C+k, k from 60 to more than 200) are also reported. The coalescence reactions are induced by the interaction of a single MeV ion with the solid. We argue that our data contribute to elucidating some general patterns of the fullerene formation mechanism.

Electronic sputtering of carbon clusters from ion beam irradiated organic films

Abstract Positive ions of even numbered carbon clusters C+2n (n > 20) are ejected as a result of the interaction of fast MeV ions with poly(vinylidene fluoride) (PVDF). Experiments provide circumstantial evidence that these ejected carbon clusters have a three-dimentional structure, consisting of pentagons and hexagons, i.e. they are fullerenes. We have studied the effect of macroscopic carbonisation induced by ion bombardment on the ejection of carbon cluster ions (C+n, n = 1–33; C+2nn = 21–50) from PVDF. Damage cross-section values are extracted from the fluence dependence of the secondary ion yields. The yield of fullerene ions from PVDF decreases as a function of MeV ion fluence. Accordingly, macroscopic carbonisation of the polymer is detrimental and is not a prerequisite to fullerene emission, confirming earlier findings that these carbon clusters are formed and ejected in a single MeV ion impact basis. For comparison, the sputtering of carbon cluster ions originating from films of poly(tetrafluorethylene), poly(styrene), poly(ethylene terephthalate) and fluorinated fullerene have also been studied.