Formation of partially reversible nanostructures in Ni40Ti60 thin films by focused electron beam irradiation

Abstract

Background: Micrometer and submicron-scale shape memory devices are typically fabricated by standard lithographic techniques or focused ion beam milling. It was previously shown that submicron-scale structures can be directly formed on metal surfaces by focused electron beam irradiation in a single fabrication step, without resist layers or etching. Aim: Our aim was to apply the method of a focused electron beam irradiation to a surface of a shape memory material to check if the fabricated structures would display any shape memory effects. Approach: Ni40Ti60 thin film, which was obtained by dual magnetron sputtering on a heated Si substrate, was irradiated by a focused electron beam in point mode. After the irradiation, thin film was heated to 100°C and irradiated points were measured by atomic force microscopy both before and after the heating. Results: After heating, the volume of the formed structures decreased by up to 88% due to their partial reversion back to a flat surface. Conclusions: These results present a new method of fabrication for shape memory devices. As only a one-way shape memory effect is achieved in our work, its immediate applications appear to be limited, but we hope that this work will open possibilities for new types of shape memory devices at the nanometer scale.