The great potential of nanoporous membranes for water filtration and chemical separation has been challenged by the trade-off between selectivity and permeability. Here we report on nanoporous polymer membranes with an excellent balance between selectivity and permeability of ions. Our membranes are fabricated by irradiating 2-μm-thick polyethylene terephthalate Lumirror® films with GeV heavy ions followed by ultraviolet exposure. These membranes show a high transport rate of K⁺ ions of up to 14 mol h⁻¹ m⁻² and a selectivity of alkali metal ions over heavy metal ions of >500. Combining transport experiments and molecular dynamics simulations with a polymeric nanopore model, we demonstrate that the high permeability is attributable to the presence of nanopores with a radius of ~0.5 nm and a density of up to 5 × 10¹⁰ cm⁻², and the selectivity is ascribed to the interaction between the partially dehydrated ions and the negatively charged nanopore wall.

We report on the observation of a fine structure in ion tracks in amorphous ${\mathrm{SiO}}_2$ using small angle x-ray scattering measurements. Tracks were generated by high energy ion irradiation with Au and Xe between 27 MeV and 1.43 GeV. In agreement with molecular dynamics simulations, the tracks consist of a core characterized by a significant density deficit compared to unirradiated material, surrounded by a high density shell. The structure is consistent with a frozen-in pressure wave originating from the center of the ion track as a result of a thermal spike.

Structural modification of vitreous SiO2 by Au ion irradiation is investigated over an energy regime ($\sim${}0.3\char21{}15~MeV) in which the decrease of the nuclear energy loss with increasing energy is compensated by the increase of the electronic energy loss, leading to a nearly constant total energy loss of $\sim${}4 keV/nm. The radii of damaged zones resulting from the ion impact, deduced from changes in infrared bands as a function of ion fluence, decrease from 4.9 nm at 0.3 MeV to 2.5 and 2.6 nm at 9.8 and 14.8 MeV, respectively. Based on previous data where vitreous SiO2 was irradiated with much higher energy Au ions, the damage zone radius increases from 2.4 nm at 22.7 MeV to 5.4 nm at 168 MeV, and a U-shaped dependence on energy is observed is observed in the energy region from 0.3 to 168 MeV. The current results demonstrate that large damage radii at low and high ion energy can be explained by the elastic or inelastic thermal spike model, respectively. In the transition regime where both nuclear and electronic energy loss are significant, a unified thermal spike model consisting of a coherent synergy of the elastic collision spike model with the inelastic thermal spike model is suggested to interpret and describe the radius evolution from the nuclear to the electronic energy regime.

The melting behavior of Ge nanocrystals embedded within ${\mathrm{SiO}}_2$ is evaluated using in situ transmission electron microscopy. The observed melting-point hysteresis is large ($\pm 17\%$) and nearly symmetric about the bulk melting point. This hysteresis is modeled successfully using classical nucleation theory without the need to invoke epitaxy.

Swift heavy-ion irradiation of elemental metal nanoparticles (NPs) embedded in amorphous SiO2 induces a spherical to rodlike shape transformation with the direction of NP elongation aligned to that of the incident ion. Large, once-spherical NPs become progressively more rodlike while small NPs below a critical diameter do not elongate but dissolve in the matrix. We examine this shape transformation for ten metals under a common irradiation condition to achieve mechanistic insight into the transformation process. Subtle differences are apparent including the saturation of the elongated NP width at a minimum sustainable, metal-specific value. Elongated NPs of lesser width are unstable and subject to vaporization. Furthermore, we demonstrate the elongation process is governed by the formation of a molten ion-track in amorphous SiO2 such that upon saturation the elongated NP width never exceeds the molten ion-track diameter.