Optical characterization and emission properties of periodic arrays of titanium nitride nanoparticles

Abstract

Various metallic nanostructures have been proposed to effectively utilize surface plasmon polaritons (SPPs) to improve the performance of optical devices such as solar cells, antennas, sensors, and light emission devices. With the progress in the research on SPP-based devices, the requirements for better materials have been increasing. Conventional SPP materials such as silver and gold have problems in processing; they are incompatible with reactive ion etching and they cannot be processed at high temperatures. Transition metal nitrides are promising candidates for the complementary material for noble metals. Especially, titanium nitride (TiN) attracts attention because of the compatibility with nanofabrication processes and the plasmonic properties in the visible and the near-infrared regions. So far, the plasmonic properties of TiN have been investigated mainly in the near-infrared region. In this study, we have fabricated the periodic arrays of TiN nanoparticles by using nanoimprint lithography and reactive ion etching processes to investigate the optical response in the visible. The periodic arrays allow the simultaneous excitation of SPPs of TiN nanoparticles and the optical diffraction in the plane of the arrays, resulting in the collective plasmonic mode where the SPPs radiatively coupled via diffraction. Combining fluorescent dye with the TiN arrays, we demonstrate the directionally-enhanced emission in the visible as large as 3 times in intensity by coupling the emission to the collective mode.