Optical engineering of titanium nitride thin films for nanoplasmonic biosensing

Official URL: https://risc01.sabanciuniv.edu/record=b2708508_(Table of contents)

Over the last years, promising concepts and practical approaches of miniaturized devices with remarkable features in the field of plasmonics have drawn a lot of attention. Generally, noble metals have been used in this field due to their high electrical conductivity, tunable plasmon frequencies, and chemical stability. However, they have a barrier for high volume production and for high-performance applications because of their high costs and loss mechanism in visible and near infrared region. Noble metals, like gold and silver, does not allow tunability in their optical properties. Therefore, research has begun to find and improve alternative plasmonic materials to replace noble metals. The transition metal nitrides (TMNs) have been suggested as an alternative for their low cost, chemical stability, and compatibility with biological mediums when compared in the literature for nanoplasmonic biosensing applications. Especially, their plasmonic response can be tuned with nanostructural and stoichiometrical change. This thesis provides brief introduction for detection methods for nanoplasmonic sensing. A lithography approach, nanosphere lithography, is explained for future work in this research due to its simplicity and cost-effectiveness in patterning surfaces towards biosensing applications. Noble metals and TMNs will be compared, particularly suggested titanium nitride (TiN) thin films belonging to the 4B transition metal group in the periodic table. Thin-film fabrication was done under reactive radio-frequency sputtering. This study offers a route for optimization of TiN film fabrication and demonstrates several ways to reduce oxygen contaminant concentration in sputtering. Produced thin films’ characterizations were done with energy-dispersive spectroscopy, X-ray diffraction, Raman spectroscopy, four-point probe measurement, variable angle spectroscopic ellipsometry to evaluate the compositional, electrical, morphological, and optical properties. Room temperature, purging with argon gas, overnight vacuum, and substrate heating sputtering are compared. All three approaches towards decreasing oxygen presence during deposition and enhancing crystollographic structure showed improvement in the conductivity and crystallinity of the thin films.