Secondary molecular ion emission from aliphatic polymers bombarded with low energy ions: Effects of the molecular structure and the ion beam induced surface degradation (original) (raw)
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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Thin poly(ethylene terephthalate) (PET) ®lms were bombarded by In ions with dierent primary beam conditions, and the positive secondary ions were mass-and energy-analysed by means of a Time-of-Flight Secondary Ion Mass Spectrometer. In the context of a wider study devoted to the emission processes of molecular ions sputtered from polymers, the aim of this work was to check the in¯uence of two of these parameters (primary impact energy and incidence angle) on the kinetic energy distributions (KED) of the observed ions. In general, the shape of the measured kinetic energy distributions is almost independent on the primary ion energy, as shown by the similar spectra observed with 7±22 keV In primaries. Nevertheless, the energy spectra of the ®ngerprint fragment ions obtained at 2 keV with an impact angle of 65°are broader than those observed for higher energy and lower impact angle (7±22 keV; $40°). Indeed, the KEDs measured in the (2 keV; 65°) bombardment conditions show an additional contribution centred around 5±6 eV, i.e. in the high energy tail of the distributions. The relative intensity of this contribution increases with the fragment size, up to 15% of the total ion intensity for C 17 H 12 O 5. The results are discussed in terms of collision cascade propagation in the surface region of the target, by comparing the experimental observations to simulations realised with the TRIM code.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1991
The keV-MeV ion irradiation of polymers produces deep changes in their physical and chemical properties associated with the breaking and rearrangement of original bonds. The modification of chain structure occurs within a well defined ion fluence range which depends on the ion linear energy transfer as well as on the target parameters. At low ion fluences (≈1014 ions/cm2) crosslinks between chains and chain-scissions are detected with a chemical yield in the range 0.05–0.3, depending on the ion mass. With increasing ion fluence (1015 ions/cm 2) the original polymer structure is heavily modified and the irradiated films exhibit properties close to those of hydrogenated amorphous carbon. At very high fluences (≈1016 ions/cm 2) graphitization of the material occurs.
Ion bombardment of polyethylene—influence of polymer structure
Vacuum, 2007
Polyethylenes of various macromolecular and supermolecular structures were studied from the point of view of their susceptibility to an ion beam treatment. An influence of molecular weight (M w ), molecular weight distribution (M w /M n ) and the degree of branching were compared within the set of low-density polyethylenes (LDPE) studied. An influence of the length of branches was compared between LDPE, linear low-density (LLDPE) and high-density (HDPE) polyethylenes. An influence of the degree of crystallinity and the morphology of a crystalline phase were compared for HDPE samples solidified under various thermal conditions and ultra-high molecular weight polyethylene (UHMWPE). Plate polymer targets $2 mm were bombarded with 100 keV He + or 130 keV Ar + ions (dose of 10 14 -10 16 ions/cm 2 ; ion energy stream density o0.1 mA/cm 2 ), micromechanical properties of their surface layer (hardness, mechanical modulus and elastic recovery) determined and compared to the virgin materials.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1998
The secondary ions sputtered from thin polymer ®lms under 15 keV, Ga bombardment were mass-and energy-analysed by means of a Time-of-Flight Secondary Ion Mass Spectrometer. The comparison between aliphatic (polyisobutylene) and aromatic polyole®ns (polystyrene) allows to propose a process of ion emission in which the mean kinetic energy of the secondary ions is related the degree of fragmentation with respect to the polymer target structure. The important yield decrease and the broadening of the kinetic energy distributions (KEDs) observed for the C x H 2x ions sputtered from pre-bombarded polyisobutylene (10 12 ±10 15 ions/cm 2) are explained in terms of physico-chemical mod-i®cation of the surface. The fast metastable decay of molecular ions in the acceleration section of the spectrometer is also investigated. Ó 1998 Elsevier Science B.V.
Chemical Changes Created by High Energy Ions in Polyethylene
IEEE Transactions on Electrical Insulation, 1987
Argon and oxygen ions were accelerated with energies of 50 to 150 keV and rastered across high density polyethylene. The free radicals formed in the ion-implanted polyethylene were studied using an electron spin resonance spectrometer. The free radicals formed were stable in air and even survived solvent separation of the undamaged polymer from the ion damaged polymer. Chemical characterizations indicated that pregraphitic or graphitic-like particles are formed with defect sites which are, in effect, free radicals stabilized by a polyaromatic system.
Structural modification of polymer films by ion irradiation
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1992
The atomic and electronic structure of polymer films undergoes deep modifications during high energy (keV-MeV) ion irradiation, from molecular solid to amorphous material. At low energy density (1022–1024) typical effects include chain scissions, crosslinks, molecular emission and double bonds formation. In hydrocarbon polymer (polystyrene, polyethylene) the main effect of irradiation is the formation of new bonds as detected by molecular weight distribution, solubility and optical measurements. Moreover the concentration of trigonal carbon (sp2) in the polymer changes with ion fluence (1011–1014) and stabilizes to a value of 20% independently on the initial chemical structure of the irradiated sample. Photoemission spectroscopy shows an evolution of valence band states from localized to extended states. At high energy density (1024–1026) the irradiated polymer continues to evolve showing spectroscopic characteristics close to those of hydrogenated amorphous carbon. Trigonal carbon concentration changes with ion fluence (1014–1016) reaching the steady state value of 60% and the hydrogen concentration decreases to 20%. Moreover the values of the optical gap (2.5–0.5 eV) suggest the presence of medium range order in the obtained hydrogenated amorphous carbon. These values are consistent with the formation of graphitic clusters, whose size goes from 5 Å to 20 Å by changing the ion fluence (or energy density).
Polymer modifications due to absorption of different ionizating radiations
In the last years, an useful collaboration developed between the material engineers and the physicians of Messina University. The study of the intimate structure of a material, before and after its modification induced by an external ionizing radiation source (electrons, ions, gamma) requires the simultaneous presence of specialist in Chemistry, Physics and Engineering in order to define the best modification conditions and the consequent features of the new synthesized material. In particular the polyethylene, employed in different fields, such as microelectronics and biomedicine, was chosen as an important target to modify its properties through ions and electron beam irradiations. Ion beams, with energy of the order of some hundred keV and doses of the order of 10 14 /cm 2 , are able to improve the polyethylene surface properties without change the pristine bulk. Instead, electron beams with energy of about 5 MeV and high dose, improve significantly bulk properties of the polymer. The effects of the ion and electron modifications were investigated with several physics characterization methods, as will be discussed in the following.
Examination of ion beam induced damage on polymer surface using Ar clusters
Surface and Interface Analysis, 2016
The damage of polymer surfaces caused by the high energy primary ion beams of TOF-SIMS was examined using Ar cluster ions. Polymer damage, the damage of secondary ions detected from the polystyrene surface and the damage layer formed by the Bi 3 primary ion beam have previously been studied. In this study, the damage observed in the secondary ions was studied by using Ar cluster primary ions. The secondary ions were mainly classified into two types, ions reflecting the polystyrene structure and cyclized ions, generated by excessive energy, which are not useful for qualitative analysis. The layer damaged by irradiation of the Bi 3 primary ion regarding PS samples was confirmed using Ar cluster sputtering beams. The depth of the layer that has chemical damage in the PS main chain caused by 30 kV Bi 3 ++ (ion dose: 5 × 10 12 ions/cm 2) irradiation was approximately 50-60 nm. The Ar cluster ion sputter rate in PS decreases with the Bi 3 ion irradiation. Micro PS particles that are not able to be detected by a conventional TOF-SIMS measurement can be effectively analyzed by accumulating the secondary ions over the static limit using Ar cluster sputtering.
Ion irradiation induced chemical changes of polymers used for optical applications
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1997
Polymers are a class of materials widely used in different fields of applications. In the field of optical telecommunication, polymers are discussed as a new class of materials for the fabrication of passive optical devices. Ion irradiation is a promising method to generate structures with a modified index of refraction, which is necessary for the guidance of light with different wavelengths in an optical device. The behaviour of different polymers which fulfil the requirements of high transparency has been studied during and after ion irradiation. Mass spectroscopy measurements of the reaction products outgassing during ion irradiation were performed as well as infrared (IR) measurements after irradiation. Ion induced chemical changes will be discussed in relation to modified macroscopic properties such as the index of refraction.