Insight mechanisms involved in the evolution of surface morphology and wettability of 100 MeV Ag-ion-treated Ag thin films have been studied using thermal spike and fractal analysis. The results of nanostructuring and wettability are correlated on the basis of atomic force microscopy (AFM), scanning electron microscopy (SEM), and contact angle (CA) measurements. The SEM images show ion-induced evolution of Ag nanostructures and reduction in the surface coverage area of Ag. The AFM images reveal the formation of nanostructures. The autocorrelation and power spectral density (PSD) functions are used to characterize the surface profile, and these confirm the formation of nanostructures. Fractal analysis is performed on pristine and ion beam tailored surfaces to explore the mechanism involved in nanostructuring. It is observed that interface width, lateral correlation length, and roughness exponent depend on ion doses. The variation in the wettability of surfaces is well correlated with interface width and compositional variation. Thermal spike simulations have been performed to understand the development of the surface morphology after ion treatment. The formation of nanostructures and reduction in surface coverage area are consequences of competition among the mechanisms of sputtering, dewetting, and diffusion processes.
An investigation was carried out to understand the phase evolution and study the structural, morphological, optical and electrical properties of Co-Sb alloys fabricated by two different approaches: (a) thermal annealing and (b) ion-beam mixing followed by post annealing. The as-deposited and 100 MeV Ag ion beam irradiated Co/Sb bilayer thin films were subjected to thermal annealing from 200 to 400 °C for 1 hour. The Rutherford backscattering spectrometry (RBS) results showed partial mixing for the thermally annealed films and complete mixing for the irradiated and post annealed films at 400 °C. The XRD and RAMAN measurements indicated the formation of Co-Sb alloy, with ∼70% concentration of CoSb3 phase in the irradiated post annealed sample at 400 °C. The band gaps of the annealed and post irradiated annealed Co-Sb alloys were determined using UV-visible spectroscopy. Electrical and thermoelectric power measurements were performed in the temperature range of 300-420 K. It was observed that the alloys formed by ion-beam induced mixing exhibited higher electrical conductivity and thermoelectric power than the as-deposited and thermally annealed Co/Sb bilayer thin films.
In this letter, we report radiation stability of graphene under extreme condition of high energy density generated by 150 MeV Au ion irradiation. The experiment reveals that graphene is radiation resistant for irradiation at 1014 ions/cm2 of 150 MeV Au ions. It is significant to note that annealing effects are observed at lower fluences whereas defect production occurs at higher fluences but significant crystallinity is retained. Our results demonstrate applicability of graphene based devices in radiation environment and space applications.
Detailed experiments and theoretical calculations on electronic sputtering of Au thin films (5-200 nm) on a quartz substrate are performed, revealing unusually large electronic sputtering, dependent on the thickness of the films. The dependence of electronic thermal conductivity (κe), electron-phonon coupling factor (g), and lattice thermal conductivity (κa) on the effective electron mean free path is taken into account in the thermal spike calculation for nanodimensional systems to elucidate the combined effect of the thickness and grain size on the electronic sputtering yield. The thermal spike simulation with refined parameters for nanodimensional systems gives a better explanation of the electronic sputtering process with a very good correlation between the experimental and theoretical yields than that of the thermal spike model with bulk parameters.
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