We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into ...layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40 nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model.
Modifications of the structure and mechanical properties in LiF crystals irradiated with MeV-energy Au ions have been studied using nanoindentation, atomic force microscopy and optical spectroscopy. ...The nanostructuring of crystals under a high-fluence irradiation (above 10
13
ions/cm
2
) was observed. Nanoindentation tests show a strong ion-induced increase of hardness (up to 150–200%), which is related to the high volume concentration of complex color centers, defect aggregates, dislocation loops and grain boundaries acting as strong barriers for dislocations. From the depth profiling of the hardness and energy loss it follows that both nuclear and electronic stopping mechanisms of MeV Au ions contribute to the creation of damage and hardening. Whereas the electronic stopping is dominating in the near-surface region, the effect of elastic displacements prevails in deeper layers close to the projectile range.
Creation of color centers in LiF under irradiation with 3–12-MeV Au ions was studied. Comparison of experimental data of color center creation with computer simulation of the energy deposition and ...elastic atomic displacements reveals the role of elastic collisions in defect creation by these ions, which have comparable magnitudes of electronic and elastic stopping. The experimentally measured efficiency of color center creation and that predicted by the simulation of elastic displacements have a similar dependence on the projectile energy. Thus, the color center creation is mainly associated with the elastic collisions, despite the relatively large values of the electronic stopping power for these ions.
Modification of the polymer PETG by 16 MeV Au ions da Rocha, M.S.; Valente, C.A.; de Lima, M.H.L. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
July 2024, 2024-07-00, Letnik:
552
Journal Article
Recenzirano
Commercial poly(ethylene glycol-co-1,4 cyclohexanedimethanol terephthalate) (PETG) foils were irradiated with 16 MeV Au7+ ions and the resulting modifications in the polymer chemical structure, ...optical properties, and surface hydrophobicity were analyzed. Under irradiation, PETG displays a redshift in the optical absorbance edge, accompanied by a decrease in the optical gap from 3.8 eV to 2.4 eV. An overall decrease of characteristic functional groups is observed with damage cross sections varying from (1–2) × 10-13 cm2. New bands are formed linked mainly to oxidation and formation of conjugated carbon–carbon double bonds. The hydrophilicity of the irradiated surfaces increases possibly due to surface oxidation.
Thin films of poly(methyl methacrylate) and poly(vinyl chloride) of different thickness are used to investigate the effect of spatial confinement on the efficiency of bond breaking induced by 2 MeV ...H^{+} and 2.1 GeV Bi ions. Effective cross sections for oxygen and chlorine loss are extracted for films down to a thickness of about 5 nm and are compared to theoretical estimations based on radial energy density profiles simulated with geant-dna. The cross sections are to a large extent thickness independent, indicating that bond breaking is dominated by short-range processes. This is in contrast to the strongly reduced efficiencies found recently for cratering induced by high-energy ions in similar ultrathin polymer films Phys. Rev. Lett. 114, 118302 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.118302.
The purpose of this in vitro study is to evaluate the effect of the incorporation of silanized and non-silanized silica nanoparticles (~ 160 nm) in mechanical properties and surface roughness of ...self-cured acrylic resins. Five groups of samples were produced (with six specimens each), following the ISO 20795-1:2013 specifications. In the control group (Ctrl), no particles were added in the resin composition. Non-silanized silica nanoparticles were added either into the polymer (0.7 wt%, group G1) or into the monomer (0.27 wt%, G2). Two equivalent groups were formed for composite resins with silanized nanoparticles (groups G3 with 0.7 wt% incorporated into the polymer and G4 with 0.27 wt% added into the monomer). Data were submitted to Shapiro-Wilk (
α
= 0.05) and ANOVA/Tukey (
α
= 0.05). Nanoparticle-loaded resins showed similar microhardness as the control and a reduced flexural strength (20–27%) which was neither dependent on the amount of filler added nor in the method of nanoparticle incorporation. Surface silanization caused no major improvement in the mechanical behavior of the nanoresins but appears to improve dispersibility, as indicated by a smaller surface roughness.
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•Nanocrystals are emitted during electronic sputtering of calcium fluoride.•Jet-like component of sputtering is related to the particle emission.•Particle size distributions do not ...follow a simple power law.•Larger off-normal angles of ion incidence enhances the particle contribution.
Material sputtered from CaF2 single crystals by 180 MeV Au ions impinging at different incidence angles were collected on high-purity amorphous C-coated Cu grids and Si100 wafer catcher surfaces over a broad angular range. These catcher surfaces were characterized complementary by transmission electron microscopy, atomic force microscopy and medium energy ion scattering, revealing the presence of a distribution of partially buried CaF2 nanoparticles in conjunction to a thin layer of deposited CaF2 material. Particle size distributions do not follow simple power laws and depend on the angles of ion incidence and particle detection. It is shown that the particle ejection is directly related to the jet-like component of sputtering, previously observed in ionic crystals, contributing significantly to the total yield. This contribution enhances as the impinging ions approach grazing incidence. Possible scenarios for the emission of particles are discussed in light of these observations.
We report on the effect of different coatings (dextran, chitosan, polyethylene glycol, carboxy-silane, and silica) in the toxicity elicited by superparamagnetic iron oxide nanoparticles (SPIONs) in ...the developing zebrafish (
Danio rerio
). Animals were exposed to nanoparticle concentrations ranging from 0.125 to 8.0 mM of Fe during the first 5 days after fertilization. Embryotoxicity parameters (survival, hatching rate, and the incidence of anatomical malformations) and behavioral patterns (locomotion during the exploration of a new environment, thigmotaxis, and the escape response to an aversive stimulus) were evaluated. Exposed embryos hatched between 48 and 72 hpf, as expected for the species, but tendencies of either acceleration or delay were observed, depending on the nanoparticle coating. Malformations in exposed and control groups were similar, independent of the coating. Mortality rates were also not significantly affected by exposure to most of the coated SPIONs, except for animals treated with chitosan-coated nanoparticles, which induced 100% mortality at concentrations higher than 2 mM. A similar trend was observed in the behavioral parameters, in which significant adverse effects were mostly caused by chitosan-coated nanoparticles even at low concentrations. The higher toxicity observed for chitosan-coated particles raises concern and deserves further mechanistic investigations, considering the ample use of this compound in pharmaceutical and biomedical applications.
Studies on tunable electronically anisotropic material on semiconductor, “TEAMS”, with a polysilane layer spin-coated onto a silicon wafer and then contacted on both top and rear sides, are reported ...in the present paper. This structure was irradiated with swift heavy ions, and its electrical characteristics were studied both during and after irradiation. It was found that the current/voltage characteristics depend on the ion fluence, the time of voltage application, the gating voltage, the ambient pressure, light, and the post-annealing temperature of the samples. Under specific conditions, a negative differential resistance was also exhibited. The observations are indicative of a peculiar conduction mechanism.
We report on surface modification of poly(methyl methacrylate) (PMMA) thin films deposited onto silicon wafers induced by fast ions in a wide range of electronic stopping powers 14 keV/nm (2.1 GeV ...Bi), 2.2 keV/nm (17 MeV Au) and 0.019 keV/nm (2 MeV H). Marked differences were observed on surface morphology induced by low and high dE/dx ions. The effect of the 2 MeV H beam on the PMMA surface was a weak smoothing, whilst for the heavier Bi and Au ions, pronounced roughening occurs with development of porosity and other surface features in a broad range of spatial frequencies. For the heavy ions, surface changes develop in basically two regimes. At the single ion regime at low fluences, most of the changes can be attributed to sputtering and flow of material in individual ion impacts. At the track overlap regime, porosity emerge in a pattern of holes, with an areal density not directly related to the ion fluence, but still spread uniformly across the film. A good correlation between the input of energy and the changes in surface morphology was obtained when (dE/dx)1.85 was used as the scaling factor.
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