Recrystallization of amorphous nano-tracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate.

The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×1011 cm−2 and 1012 cm−2. The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼1014 cm−2. Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed

Nanodesign of superhydrophobic surfaces

International audienceWhen deposited on a hydrophobic rough surface, a small water drop looks like a small pearl. In this study we investigate the conditions to observe such a phenomenon when the roughness of the substrate, of fractal nature, consists of nanofeatures obtained by the ion track etching technique. The surface roughness was characterized by two parameters: the fractal dimension Df and the aspect ratio AR. Both were extracted from the analysis of atomic force microscopy images and were directly correlated with the etching time. Df is found in the interval of 2.46–2.69, while AR varies from 0.5 to ~15. We show that for the highest Df values the water contact angles on these surfaces can exceed 150°, while the hysteresis—the difference between the advancing and receding contact angles—is reduced to 4–5°. Superhydrophobic surfaces can thus be obtained and this property seems well controlled by the fractal dimension, which is itself controlled by the ion track etching process. Furthermore, the experimental results are well described by the wetting theory, and it is shown that superhydrophobicity of these surfaces results from a single-scale roughness of nanometric size

Superoleophobic Behavior Induced by Nanofeatures on Oleophilic Surfaces

International audienceThe control of surface wetting properties to produce robust and strong hydrophobic and oleophobic effects on intrinsically oleophilic surfaces is at the heart of many technological applications. In this paper, we explore the conditions to observe such effects when the roughness of the substrate is of fractal nature and consists of nanofeatures obtained by the ion track etching technique. The wetting properties were investigated using eight different liquids with surface tensions γ varying from 18 to 72 mN m-1.While it is observed that all the tested oils readily wet the flat substrates, it is found that the contact angles are systematically exalted on the rough surfaces even for the liquids with very low surface tension. For liquids with γ ≥ 25 mN m-1 an oleophobic behavior is clearly induced by the nanostructuration. For liquids with γ < 25 mN m-1, although the contact angle is enhanced on the nanorough surfaces, it conserves its oleophilic character (θ* lower than 90°). Moreover, our experiments show that even in the case of hexane, liquid having the lowest surface tension, the homogeneous wetting (Wenzel state) is never reached. This high resistance to liquid impregnation is discussed within the framework of recent approaches explaining the wetting properties of superoleophobic surfaces

Latent tracks formation in silicon single crystals irradiated with fullerenes in the electronic regime

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Adhesion enhancement of thin gold films on sapphire by electronic processes using atomic and fullerene ions

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Damage creation in alpha-Al2O3 by MeV fullerene impacts

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Damage creation in alpha-Al2O3 by MeV fullerene impacts

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