Study of surface plasmon resonance in transition metal nitride thin films

Abstract

Converting light into plasmons contributes to the extension of photonics into nano size region. Plasmonic phenomena arise from the collective oscillations of free electrons in a material when an electromagnetic ray is incident on it. Metals have abundance of free electrons, and hence metallic elements are required in plasmonic structures. Gold and silver have traditionally been used for such applications because they exhibit surface plasmon properties in the visible wavelength region. However, these metals are expensive and have some limitations that make them unsuitable for potential device applications. In current scenario of plasmonics discipline, alternatives to traditional metals are being sought primarily. Transition metal nitrides are a better alternative plasmonic material in the visible region. This thesis focuses on the development of two technologically important transition metal nitrides, titanium and zirconium nitrides, with plasmonic characteristics in visible region. One of the essential properties for plasmonic behaviour is high carrier density (of the order of 1022/cm3), which is crucial to achieve the required negative permittivity in the wavelength region of interest. Being non-stoichiometric, the opto-electronic properties of these nitrides depend mainly on their preparation routes. They can have high carrier concentrations in the above order, thereby achieving metallic behaviour in the visible region. Another important property required for efficient plasmonics is reduced dielectric loss, which necessitates correlated opto-electrical property analysis and structural confirmation in the developed films. Although transition metal nitride film properties depend on stoichiometry and deposition method, this work also aims to examine process dependence in titanium nitride films, which further tunes the material structure and plasmonic properties. Rather than using a vacuum deposition for thin film fabrication, the focus was to develop a cost-effective novel approach for the fabrication of titanium nitride plasmonic film by opting nitridation of ammonia. Initial understanding on material properties was achieved through comprehensive study on TN films developed by sputtering technique. Then, opted nitridation routes for converting titanium metal and titanium dioxide films into plasmonic TiN, of which the latter proved to be a cost-effective approach. In each case, the plasmonic properties were investigated and excited surface plasmon polariton in the optimized films using a prism base Kretschmann configuration in a wavelength interrogation method. Zirconium nitride is projected in the literature to be a better plasmonic material than titanium nitride in the visible region. In this work, the properties of DC sputtered zirconium nitride films were investigated, and the structural, optical, and electrical properties were studied in the context of plasmonics. Finally, surface plasmon polariton was successfully excited in the Kretschmann configuration, proving zirconium nitride to be an excellent alternative plasmonic material. The research findings were published in three international journals and at several conferences.