a b s t r a c tThe morphology of swift heavy ion tracks in the Gd 2 Zr 2Àx Ti x O 7 pyrochlore system has been investigated as a function of the variation in chemical composition and electronic energy loss, dE/dx, over a range of energetic ions: 58 Ni, 101 Ru, 129 Xe, 181 Ta, 197 Au, 208 Pb, and 238 U of 11.1 MeV/u specific energy. Bright-field transmission electron microscopy, synchrotron X-ray diffraction, and Raman spectroscopy reveal an increasing degree of amorphization with increasing Ti-content and dE/dx. The size and morphology of individual ion tracks in Gd 2 Ti 2 O 7 were characterized by high-resolution transmission electron microscopy revealing a core-shell structure with an outer defect-fluorite dominated shell at low dE/dx to predominantly amorphous tracks at high dE/dx. Inelastic thermal-spike calculations have been used together with atomic-scale characterization of ion tracks in Gd 2 Ti 2 O 7 by high resolution transmission electron microscopy to deduce critical energy densities for the complex core-shell morphologies induced by ions of different dE/dx.

We have investigated the deterioration of field effect transistors based on twodimensional materials due to irradiation with swift heavy ions. Devices were prepared with exfoliated single layers of MoS 2 and graphene, respectively. They were characterized before and after irradiation with 1.14 GeV U 28+ ions using three different fluences. By electrical characterization, atomic force microscopy and Raman spectroscopy we show that the irradiation leads to significant changes of structural and electrical properties. At the highest fluence of 4 × 10 11 ions/cm 2 , the MoS 2 transistor is destroyed, while the graphene based device remains operational, albeit with an inferior performance. * electronic address: marika.schleberger@uni-due.de

Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance in fission-based energy systems. As advanced nuclear fuels and wasteforms are developed, fundamental understanding of the processes controlling radiation damage accumulation is necessary. Here we report oxidation state reduction of actinide and analogue elements caused by high-energy, heavy ion irradiation and demonstrate coupling of this redox behaviour with structural modifications. ThO 2 , in which thorium is stable only in a tetravalent state, exhibits damage accumulation processes distinct from those of multivalent cation compounds CeO 2 (Ce 3 þ and Ce 4 þ ) and UO 3 (U 4 þ , U 5 þ and U 6 þ ). The radiation tolerance of these materials depends on the efficiency of this redox reaction, such that damage can be inhibited by altering grain size and cation valence variability. Thus, the redox behaviour of actinide materials is important for the design of nuclear fuels and the prediction of their performance.

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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.

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Nanochannels and nanowires with diameters ranging from 30 to 400 nm were produced by etching ion tracks in thin polyarylate and polycarbonate foils. The shape and the size distribution of dry and wet nanochannels, as well as of nanowires grown therein, were examined by small-angle x-ray scattering. The x-ray intensity as a function of the scattering vector exhibits pronounced oscillations showing that both the channels and the wires have a highly cylindrical geometry and a very narrow size distribution. UV exposure before chemical etching significantly improves the monodispersity of the nanopores. For fixed etching conditions, the scattering patterns provide evidence that the diameter of dry and water-filled channels as well as for embedded nanowires are identical, demonstrating that the pores in the polymer are completely filled.