Plasmonic materials display high local field enhancements and enable the sub-wavelength confinement of light. This has applications in next-generation nanoscale photonic and optoelectronic devices, chemical and biological sensing, and efficient energy harvesting amongst others. However, the typical plasmonic materials, gold and silver, have intrinsic material limitations that prohibit their widespread use in practical plasmonic devices. These limitations include poor thermal stability, limited spectral tunability, and incompatibility with existing complementary metal-oxide-semiconductor (CMOS) device fabrication processes, in addition to their high cost. Accordingly, alternative plasmonic materials are desired that can overcome these limitations. One class of materials which has been suggested to achieve this are transition metal nitrides.
This thesis presents research into the viability of some transition metal nitrides as alternative plasmonic materials. It outlines an investigation of the spectral tunability and CMOS compatibility of binary, ternary, and layered transition metal nitride and oxynitride thin films of niobium and titanium. Comprehensive characterisation of the optical, structural, and morphological properties of these films is reported and fabrication methodologies to achieve high-quality plasmonic thin films are compared. Mechanisms of spectral tunability are discussed and an explanation for the occurrence of tuneable double-epsilon-near-zero behaviour within niobium oxynitride and titanium oxynitride is provided.
This thesis also reports the nanofabrication and characterisation of titanium nitride and niobium nitride features and arrays. Firstly, the plasmonic response of individual titanium nitride nano-discs patterned via electron beam lithography (EBL) and characterised using cathodoluminescence is reported. The thermal stability of these sub micron TiN features is then compared with similar features of gold. Secondly, the successful patterning of niobium nitride via colloidal lithography is reported and the merits and limitations of this scalable nanofabrication technique are considered when applied to transition metal nitrides.