Plasmonic characteristics of niobium nitride thin films modulated by assisting ions

NbN_x films were prepared by dual ion beam sputter deposition. Different assisting ion current density J_a and assisting ion energy E_a were used to modulate the structural and dielectric properties of the films. All the films are of fcc structure, and assisting ions can improve their crystallinity. Higher J_a and E_a can reduce the screened plasma frequency and the optical energy loss of the films. Importantly, with appropriate experimental parameters, the NbN_x films exhibit tunable dual epsilon-near-zero behavior. The assisting ions cause the variation of the carrier concentration in the films, and then modulate the dielectric properties of the films. Our results show that NbN_x films can be applied in different fields by tailoring their plasmonic properties by assisting ions.