We report on synthesis of spherical Au nanoparticles at the surface and embedded in carbonaceous matrix by 150 keV Ar ion irradiation of thin Au film on polyethyleneterepthlate (PET). The pristine and irradiated samples are characterized by Rutherford backscattering spectrometry (RBS), atomic force microscopy, scanning electron microscopy and transmission electron microscopy (TEM) techniques. RBS spectra reveal the sputtering of Au film and interface mixing, increasing with increasing fluence. Surface morphology shows that at the fluence of 5 × 1015 ions cm−2, dewetting of thin Au film begins and partially connected nanostructures are formed whereas, at the higher fluence of 5 × 1016 ions cm−2, isolated spherical Au nanoparticles (45 ± 20 nm) are formed at the surface. Cross-sectional TEM observations also evidence the Au nanoparticles at the surface and mixed metal–polymer region indicating the formation of nanocomposites with small Au nanoparticles. The results are explained by the crater formation, sputtering followed by dewetting of the thin Au film and interdiffusion at the interface, through molten zones due to thermal spike induced by Ar ions.
The direct measurement of reaction cross sections at astrophysical energies often requires the use of solid targets of known thickness, isotopic composition, and stoichiometry that are able to withstand high beam currents for extended periods of time. Here, we report on the production and characterisation of isotopically enriched Ta2O5 targets for the study of proton-induced reactions at the Laboratory for Underground Nuclear Astrophysics facility of the Laboratori Nazionali del Gran Sasso. The targets were prepared by anodisation of tantalum backings in enriched water (up to 66% in 17 O and up to 96% in 18 O). Special care was devoted to minimising the presence of any contaminants that could induce unwanted background reactions with the beam in the energy region of astrophysical interest. Results from target characterisation measurements are reported, and the conclusions for proton capture measurements with these targets are drawn.
PACS. 26.20.Cd Stellar hydrogen burning -25.40.-h Proton-nucleus reactions -06.60.Ei Sample preparation -25.40.Lw Proton radiative captureRecently, the LUNA collaboration has undertaken the study of proton-induced reactions on 17 O and 18 O, important nucleosynthesis processes in several stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae [5,6]. In particular, the ratio between the rates of the 17 O(p,α) 14 N reaction (Q = 1191.8 keV) and the 17 O(p,γ) 18 F reaction (Q = 5606.5 keV) affects the galactic abundance of 17 O, the stellar production of the radioactive 18 F nuclide, and the predicted arXiv:1210.0327v1 [nucl-ex]
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