Symbiotic plasmonic nanomaterials: Synthesis and properties

Metal particles of the dimensions of the order of 1 to 100's of nanometers show unique properties that are not clearly evident in their bulk state. These nanoparticles are highly reactive and sensitive to the changes in the vicinity of the particle surface and hence find applications in the field of sensing of chemical and biological agents, catalysis, energy harvesting, data storage and many more. By synthesizing bimetallic nanoparticles, a single nanoparticle can show multifunctional characteristics. The focus of this thesis is to detail the synthesis and understand the properties of bimetallic nanomaterial systems that show interesting optical, chemical, and magnetic behaviors, some of which fall into the category of a symbiotic behavior. Symbiosis is the mutual sharing of resources between two individual organisms. The potential design considerations in the synthesis of such symbiotic nanomaterials include their position in the electrochemical series, thermodynamic immiscibility, and vastly contrasting properties, such as plasmonic (Ag) and ferromagnetic (Co). In addition to these aspects, nanostructure size, shape, and composition can also play an important role in the ensuing optical, magnetic and chemical behaviors. For this work, two different synthesis routes were utilized to make nanostructures of various shapes, size, composition and spacing. The second part of the thesis focused on to understand the relationship between the role of intrinsic and extrinsic factors on the optical and chemical properties of these bimetallic nanostructures. From measurements of the plasmonic resonance energy and bandwidth, we developed a quantitative picture of the dependence of oxidation stability, plasmon quality factor and the radiative quantum efficiency on size and energy. These results showed that the bimetal nanoparticles could have comparable or better quality factor and quantum efficiency than pure Ag.

We also discovered a new class of thin film amorphous transparent semiconducting material. The semiconductor was made from a ternary oxide comprising of the metals Fe, Tb, and Dy. The combination of high visible light transparency, high conductivity and extraordinarily high mobility makes this material a potential candidate for use in thin film transistor and transparent conductor applications, and is a possible replacement for In-based materials.