Focused-ion-beam-based nano-kirigami: from art to photonics

Kirigami, i.e. the cutting and folding of flat objects to create versatile shapes, is one of the most traditional Chinese arts that has been widely used in window decorations, gift cards, festivals, and various ceremonies, and has recently found intriguing applications in modern sciences and technologies. In this article, we review the newly developed focused-ion-beam-based nanoscale kirigami, named nano-kirigami, as a powerful three-dimensional (3D) nanofabrication technique. By utilizing the topography-guided stress equilibrium induced by ion-beam irradiation on a free-standing gold nanofilm, versatile 3D shape transformations such as upward buckling, downward bending, complex rotation, and twisting of nanostructures are precisely achieved. It is shown that the generated 3D nanostructures possess exceptional geometries and promising photonic functionalities, including strongly interacting multiple Fano resonances, giant optical chirality, clear photonic spin Hall effects, and diffractive phase/polarization effects. The studies of such structures can build up novel platforms for versatile manufacturing techniques and be helpful to establish new areas in plasmonics, nanophotonics, optomechanics, MEMS/NEMS, etc., with the generation of exotic but functional nanostructures.