Pulsed ion beam irradiation effects on surfaces of polymeric materials

Various polymers were irradiated with high energy ( keV) carbon and hydrogen ion beams obtained from a high intensity pulsed power source. Energy deposition was in the range of 0.1–5 J/cm² during each pulse, and ion penetration was limited to a few microns. The rapid energy deposition (<500 ns) corresponded to a dose rate of approximately 10¹² Gy/s and resulted in a considerable temperature rise in the surface material accompanied by the formation of gaseous radiolysis products in amounts as high as the volume of the surface layer in which they were formed. Analysis by scanning electron microscopy revealed that dramatic changes to the polymer surface had occurred in some (but not all) of the materials, which took the form of extensive porosity or roughening. © 1998 John Wiley & Sons, Ltd.     

An investigation on focused electron/ion beam induced degradation mechanisms of conjugated polymers

Irradiation damage, caused by the use of beams in the electron microscopes, leads to undesired physical/chemical material property changes or uncontrollable modification of structures that are being processed. Particularly, soft matter such as polymers or biological materials is highly susceptible and very much prone to react on irradiation by electron and ion beams. The effect is even higher when materials are subjected to energetic species such as ions that possess high momentum and relatively low mean path due to their mass. Especially when Ga(+) ions (used as the ion source in Focused Ion Beam (FIB) instruments) are considered, the end-effect might even be the total loss of the material's properties. This paper will discuss the possible types of degradation mechanisms and defect formations that can take place during ion and electron beam irradiation of the conjugated polymers: e.g. polyfluorene (PF) and poly-3-hexylthiophene (P3HT) thin films. For the investigation of the irradiation induced degradation mechanisms in this study, complementary analytical techniques such as Raman Spectroscopy (RS), Infrared Spectroscopy (IR), Electron Energy Loss Spectroscopy (EELS), Atomic Force Microscopy (AFM), and Fluorescence Microscopy including Photoluminescence (PL) and Electroluminescence (EL) Microscopy were applied.     

Orientation-dependent nanostructuring of titanium surfaces by low-energy ion beam erosion

Regular nanoscopic ripple and dot patterns are fabricated on poly-crystalline titanium samples by irradiation with 1.5 keV argon ions at normal incidence. The morphology of the nanostructures is investigated by scanning electron microscopy and scanning force microscopy. The ripple structures exhibit a saw-tooth cross-section profile. Electron backscatter diffraction experiments are performed to analyze the local grain structure. The study suggests a distinct correlation of the nanostructure morphology to the crystallographic orientation of the titanium surface.     

Study on the radiation degradation of polyether-polyurethane induced by electron beam

Polyether-urethane samples were irradiated at the dose range from 10 to 2000 kGy by 2 MeV electron beams. Volatile species from the polymer degradation were analyzed quantitatively and qualitatively with GC/MS. Thermal properties and micro-phase separation of the samples were examined by TG and the morphology was studied by TEM and SEM. The results show that the irradiated polyether-polyurethane evolves CO₂, H₂, CH₄ and C₂H₆, etc. The thermal stabilities between the hard and soft segments in the irradiated samples are different. At high doses, the phase separation in the sample is predominant and the hard segment of sample is more stable. The dose rate affects the soft segment of the irradiated sample much more.     

Image reversal for direct electron beam patterning of protein coated surfaces

Electron beam lithography (EBL) is used to create surfaces with protein patterns, which are characterized by immunofluorescence and atomic force microscopies. Both negative and positive image processes are realized by electron beam irradiation of proteins absorbed on a silicon surface, where image reversal is achieved by selectively binding a second species of protein to the electron beam exposed areas on the first protein layer. Biofunctionality at the cellular level was established by culturing cortical cells on patterned lines of fibronectin adsorbed on a bovine serum albumin background for 7 days in culture.     

Cationic concentration effects on electron beam cured of carbon-epoxy composites

Electron beam (e-beam) curing is a technology that offers advantages over the thermal curing process, that usually requires high temperature and are time-consuming. E-beam curing is faster and occurs at low temperatures that help reduce residual mechanical stresses in a thermoset composite. The aim of the present study is to analyze the effects of cationic initiator (diaryliodonium hexafluoroantimonate) ranged from 1 to 3 wt% in DGEBA (diglycidyl ether of bisphenol A) epoxy resin when cured by a 1.5 MeV electron beam. The specimens were cured to a total dose of 200.4 kGy for 40 min. Analyses by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) show that the e-beam irradiated samples with 2 wt% cationic initiator were 96% cured obtained a glass transition temperature (tan δ) of 167 °C. The same epoxy resin, thermally cured for 16 h with an anhydride hardener, reached a T_g (tan δ) of 136 °C. So, the irradiated sample had its T_g increased approximately 20% and the curing process was much less time consuming.     

Investigation of copper patinas using ion beam analysis and scanning electron microscopy

Ion beam analysis (IBA) techniques were applied successfully to the investigation of non‐corroded and artificially corroded patina layers grown on copper substrates in order to explore their potential use in the study of degradation phenomena of copper and copper alloys subjected to chemical treatment and exposed to selected environmental conditions. Rutherford backscattering spectroscopy (RBS) with deuterons as projectiles and the nuclear reactions ¹⁶O(d,p)¹⁷O and ³²S(p,p′γ)³²S were applied to the investigation of the depth distribution of oxygen and sulphur in near‐surface layers of synthetic patina consisting of mineral phases corresponding to chalcanthite as well as to cuprite + chalcanthite and antlerite + brochantite + chalcanthite. Electrochemical techniques (potentiodynamic polarization and cyclic voltammetry in 0.5 M Na₂SO₄) were used for artificial acceleration and study of the corrosion processes, and scanning electron microscopy (SEM/EDS) was used for examination of the surface morphology of the samples. A patinated roof sample from the Vienna Hofburg also was investigated using the same techniques. The measurement showed that IBA can provide valuable information for the study of patina near‐surface layers of thickness up to a few micrometres and indicated that cuprite was the mineral phase primarily formed on the copper substrates and the main component of the interface between the patina layer and the metallic substrate. The investigated copper patinas looked rather heterogeneous and were characterized by high porosity. Mixed patinas exhibited considerable stability to further corrosive attack. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of degradation effects induced by gamma radiation and electron beam radiation in two cable jacketing materials

The radiation degradation behavior of commercial low density polyethylene (LDPE) and ethylene–vinylacetate (EVA) cable materials has been investigated. The changes of mechanical properties, thermooxidative stability and density exhibit different radiation stability towards ⁶⁰Co-gamma radiation and 160 keV electron beam radiation. This difference reflects much higher penetration of the gamma radiation through the polymeric material as a function of sample thickness. These results are discussed with respect to the role of beta radiation during design basis events in a nuclear power plants. In case when total accidental design basis event (DBE) dose (involving about 80% soft beta radiation) is simulated by ⁶⁰Co-gamma radiation the conservatism is reached.     

Combined use of ion beam slope cutting and scanning electron microscopy for the investigation of the 3-dimensional micro-structure of alterated mediaeval glass

Ion beam slope cutting (IBSC) has been developed as a preparation method for SEM and TEM to avoid the problems which occur using the common mechanical preparation techniques. IBSC has been practised on metals, plastic composites ceramics and alterated mediaeval glass, too. For the investigation of the 3-dimensional microstructure of the glass samples, IBSC has been the only method, which will enable a small cut without destroying the valuable cultural heritage. By SEM investigations of the ion beam cut, the alteration process of mediaeval glass has been observed starting on the surface and spreading into deeper zones of glass. Vertical and lateral cracks are only developing and spreading in the surroundings of crater erosions. The cracks cause splitting of parts near the surface of glass. Inside the cracks, harmful atmospheric gases, like SO₂ and CO₂, are reacting with the main glass components to alterations salts, which will build up a white and black crust on the surface and in zones near the surface.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Investigation of resonant inner-shell processes with an electron beam ion trap

The collision processes of highly charged ions with electrons have been studied with an electron beam ion trap. Resonant inner-shell processes such as dielectronic recombination and resonant excitation double autoionization were investigated by observing the number ratio of extracted ions with adjacent charge states.     

Bombardment induced ion transport--part II. Experimental potassium ion conductivities in borosilicate glass

A new experimental approach for measuring the ionic conductivity of solid materials is proposed. The experiment is based on bombarding an ion conducting sample with an alkali ion beam. This generates a well defined surface potential which in turn causes ion transport in the material. The ion transport is measured at the back side of the sample. The viability of the concept is demonstrated by measuring the temperature dependence of the potassium ion conductivity of a potassium borosilicate glass. The activation energy for the potassium transport is 1.04 eV ± 0.06 eV. For comparison, conductivity data obtained by impedance spectroscopy are presented, which support the bombardment induced data.     

Advanced curing technologies using photo- and electron beam induced cationic polymerization

Diaryliodonium and triarylsulfonium salts mediate photo-, γ-ray and e-beam induced cationic polymerizations. Examples of these three types of polymerizations are described. The potential use of this new methodology for the rapid fabrication of carbon fiber reinforced composites is detailed.     

Ion beam induced effects in thin-film analysis

Summary Quantitative thin film and in-depth analysis is often complicated or even prevented by interfering effects which are induced by the ion bombardment used for sputter removal of the sample. From these effects, sputter induced surface microtopography and bombardment induced stoichiometry changes are discussed on the basis of recent experimental and theoretical results. A method for establishing extremely plane bombarding craters at low bombarding energies is mentioned.

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Ionenstrahlinduzierte Effekte bei der Dünnschichtanalytik

Zusammenfassung Quantitative Dünnschicht-oder Tiefenprofilanalysen werden häufig durch Störeffekte erschwert oder verhindert, die durch den zum Probenabtrag benutzten Ionenbeschuß induziert werden. Von diesen Effekten werden die beschußinduzierte Oberflächen-Mikrotopographie und die durch den Ionenbeschuß verursachten Stöchiometrieän-derungen an der Probenoberfläche anhand neuer theoretischer und experimenteller Ergebnisse diskutiert. Weiter wird ein Verfahren zur Erzeugung extrem ebener Beschußkrater bei niedrigen Ionenbeschußenergien besprochen.

     

4He+ ion beam irradiation induced modification of poly(dimethylsiloxane). Characterization by infrared spectroscopy and ion beam analytical techniques

In this study we investigated the chemical and surface wettability changes of poly(dimethylsiloxane) (PDMS) induced by a 2.0 MeV He(+) beam irradiation. The chemical changes created in PDMS were characterized by universal attenuated total reflectance infrared (UATR-FTIR) spectroscopy, while the changes of the wettability were determined by contact angle measurements. In a separate analysis, hydrogen depletion was also investigated with a 1.6 MeV He(+) beam by applying the elastic recoil detection analysis (ERDA) and Rutherford backscattering spectrometry techniques simultaneously. The ERDA results showed that the hydrogen content of PDMS decreased irreversibly, which means that volatile products were formed under radiolysis, such as hydrogen or methane. The results were completed with UATR-FTIR measurements. We propose a complete reaction mechanism for the processes taking place in PDMS. These ion beam induced processes, such as chain scissions, cross-linking, and depletion of small molecular weight fragments, lead to the formation of a silica-like final product (SiO(x)). The significant chemical changes at the surface influence the wettability of PDMS, making it considerably more hydrophilic. The penetration depth of the 2.0 MeV He(+) ions is significantly higher compared to that of other surface modification techniques, which makes the modified layer thick and homogeneous; on the other hand, it is easily controllable by the energy of the incident ions.     

Secondary hydrogen-deuterium isotope effects on electron impact induced fragmentations

Secondary hydrogen-deuterium isotope effects have been observed in the mass spectra of cis-4-t-butylcyclohexyl iodide, 5-iodononane and 2-iodopropane. Under conditions which suppress competing and second generation fragmentations, β-deuterium substitution decreases the intensity ratio \documentclass{article}\pagestyle{empty}\begin{document}$ ([{\rm M} - {\rm I]}^{\rm + } /[{\rm M]}^{\mathop + \limits_ \cdot } ) $\end{document}, a result analogous to a normal isotope effect. The decrease is larger in the spectrum of cis-4-t-butylcyclohexyl iodide-trans-2-d than in the spectrum of the cis-2-d derivative. Since these effects parallel those in the better understood solvolysis reaction, both effects may have a common origin. In contrast, deuteration of more remote positions in cis-4-t-butylcyclohexyl iodide and 5-iodononane increases the indicated intensity ratio, an apparent inverse isotope effect. Although similar effects have been observed in solvolysis reactions, the mass spectral effect may be attributable to an increase in the nonfixed energy available for fragmentation. These results suggest that secondary isotope effects can be readily measured in certain cases, and that they may eventually become useful probes into the mechanisms of mass spectral fragmentations.     

Investigation of the electron beam induced transformation of Cu3 N-films

Homogeneous films of metastable Cu₃N were deposited on Si-<100> wafers at 90°?C by means of reactive magnetron sputtering ion plating. Under electron bombardment with a focused beam at high current (> 700 nA, 15 keV) these films transform into metallic Cu and N₂. The depletion of N was measured quantitatively by EPMA. Structures with a lateral size of 2 μm consisting of metallic copper were written into the Cu₃N films. AFM surface scans revealed a vertical growth of the columnar grains of the Cu₃N film due to the electron bombardment.     

Laser desorption-ionization of polycyclic aromatic hydrocarbons from glass surfaces with ion mobility spectrometry analysis

Polycyclic aromatic hydrocarbons (PAHs) were analyzed as adsorbates on borosilicate glass at levels from 40 pg (5.5 pg mm⁻²) to 7 μg (1 μg mm⁻²) using laser desorption-ionization (LDI) in air at ambient pressure and 100 °C with ion characterization by mobility spectrometry. Gas-phase positive ions with distinctive mobilities were produced from six PAHs using an unfocused beam at 266 nm, 6 mJ pulse⁻¹ and 10 Hz from a Nd-YAG laser. The ions produced were identified as M⁺ using mass spectrometry (MS) with a LDI source at atmospheric pressure. The mobility spectrometry drift tube provided low memory effects and allowed observation of time-resolved intensity profiles for ion signals, and changes in this behavior with loading level suggested intermolecular interactions from multilayer formation. Mobility peaks were broader than those seen in gas-phase reactions, and this was attributed to Coulombic repulsion caused by the small volume near the surface where ionization would take place. An ion shutter in the drift tube could be synchronized with the laser pulse to offer additional specificity using tandem mobility separation; further, resolution was improved in mixtures of PAHs with similar mobilities. Negative ions were also detected, though these were mass-identified as ions formed from air through the capture of electrons released from the PAHs; no M⁻-ions were observed in air. Limits of detection ranged from sub-pg to low-ng for individual PAHs.     

Homogeneous liquid crystal orientation on ion beam exposure TiO2 surfaces depending on an anisotropic dipole field

We studied homogeneous liquid crystal (LC) alignment properties on ion-beam (IB) irradiated TiO₂ films deposited by the electron beam evaporation method. Stable homogeneous LC alignment on a TiO₂ surface resulted from IB irradiation energy over 1800 eV. X-ray photoelectron spectroscopy analyses showed that Ti⁴⁺ 2p_3/2 and Ti⁴⁺ 2p_1/2 peaks were increased with increasing IB energy. Assuming that the increased peaks produced anisotropy dipole fields in the direction of the IB exposure process, we confirmed that the increasing IB energy induced strengthened the surface energy for entirely clear and stable LC molecule orientation. The voltage-transmittance characteristics of the twisted-nematic cell on the TiO₂ surface indicate that the TiO₂ film has potential for use as the LC alignment layer.