Bending of nanoporous thin films under ion radiation

Highlights: • Radiation-induced coarsening/sintering leads to negative swelling. • Inhomogeneous radiation-induced coarsening of nanoporous structure results in bending. • Nanoporous materials are unsuitable for coatings in nuclear applications. -- Abstract: In general, fundamental understanding of radiation resistance of high surface density nanoporous materials and nanoporous coatings is severely lacking. In this contribution ion-induced bending phenomena are studied in free-standing nanoporous Au cantilevers with thickness in the range of 100 to 200 nm. Experiments were performed in a Tescan Lyra dual beam system with Ga⁺ ion irradiation normal to the sample surface up to a maximum fluence of ~3 × 10¹⁹ m⁻². Cantilevers bend towards the incident ion beam. It was found that the sensitivity of nanoporous Au samples to radiation-induced bending is substantially higher in comparison to the solid bulk counterparts. The process is described in terms of ion-induced coarsening of the structure top layers, which generates a volume contraction responsible for the bending moment. Therefore it is concluded that radiation-induced coarsening/sintering leads to negative swelling. Radiation-modified effective Young's modulus of the top layers was shown to influence essentially the fluence dependence of bending curvature. Model predictions agree well with our experimental findings showing that inhomogeneous radiation-induced coarsening of nanoporous structure results in bending and that nanoporous materials are less suitable for coatings in nuclear applications under the test conditions.