J. Eriksson

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

MeV-atomic-ion-induced surface tracks in Langmuir-Blodgett films and L-valine crystals studied by scanning force microscopy

To acquire new information about the electronic sputtering of organic samples, we have obtained tapping mode scanning force microscopy images of craters induced by individual surface-grazing 48.6 MeV 79Br ions incident on Langmuir-Blodgett (LB) and l-valine surfaces. Crater sizes depended somewhat on the parameters of the tapping mode. For LB films, crater widths were 24–34 nm, while depths ranged from 5 to 8 nm. For l-valine crystals, crater widths ranged from 33 to 39 nm, and depths ranged from 4–7 nm. We discuss the observations in the framework of pressure pulse and evaporative thermal spike sputtering models.

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.

MeV atomic ion sputtering of fullerenes: a radial velocity distribution study

We report swift heavy-ion-induced sputtering of carbon cluster ions from fullerene-containing and polymer thin films (pure C60, fluorinated C60(C60Fm, 24 < m < 48), blends of pure C60 with polystyrene (PS/C60), and poly(vinylidene fluoride) (PVDF)). Intact C60 molecular ions and their fragments (C60-2n, 1 < n < 5), together with a series of higher mass carbon cluster ions (C60+2n, n from 1 to at least 100) are ejected as a result of the interaction of an individual MeV ion with the various targets. The intensity patterns of the higher mass carbon cluster ion series depend on the type of bombarded target. For pure C60 targets the high mass clusters have higher yields around multiples of 60 (C120 and C180). In the case of PS/C60, C60Fm and PVDF targets, the cluster intensity decreases continuously with increasing cluster size. Measurements of the initial radial velocity distributions of such cluster ions have been performed in a reflectron time-of-flight mass spectrometer, using 72.3 MeV 127I13+ as primary ions. The radial velocity distributions of the sputtered ions are indicative of the processes of their formation: condensation of hot carbon atom “gas” in the core of the ion tracks versus coalescence of C60 molecules, most probably in the gas phase.