Epsilon-near-zero nanoparticles

Abstract

Epsilon-near-zero (ENZ) materials are a part of optical materials studied in plasmonics. As the techniques of nanofabrication and nanotechnology have developed, interest in materials such as ENZ has increased. Studies on the topic have usually been carried out using planar multilayered structures, which consist of dielectric and metallic materials. With that in mind, the aim of this thesis is to investigate the multilayered structure in a spherical form. This is to find a more precise and diverse method to tune the ENZ properties. The spherical nanostructures are often called nanoparticles, and some potentially useful applications could include optical sensors and hydrogen generation. The fabrication could be done by making use of chemical synthesis. The bachelor’s thesis is divided into three parts. The first theoretical section explores the background of ENZ research and metamaterials. In the second theoretical section, the chosen structure is explained, and its effective permittivity is derived. Effective permittivity can be utilized to simplify the structure and to determine its ENZ wavelength. The simulations chapter is further divided into four parts. These include optimisation of structures, comparison of ENZ and resonance behaviour, customisation of properties, and calculations for similar experimental nanoparticles from literature. The simulations also include the verification and applicability of the theory and a comparison of the used software. The simulations were performed with STRATIFY; an open-source code developed directly in MATLAB. It calculates the electromagnetic properties of multilayered nanoparticles, by solving Maxwell’s equations at the nanoscale. For this, it utilizes the Transfer-matrix method (TMM). The main research topics of the simulations were the electric near-field enhancements, and absorption and scattering cross-sections, of the particles placed in a vacuum. Ansys Lumerical FDTD was used for the software comparison. The work provides a preliminary basis for research on ENZ nanoparticles. It indicates the existence of a modifiable ENZ region, ranging from visible light to infrared radiation. The spectral shift can be realised by changing the ratio of adjacent radii and the composition of the layers. Multiple approaches were used in the process. Another important result was to demonstrate the functionality and applicability of effective permittivity when defining the ENZ nanoparticles. The results are in favor of further research, both theoretical and experimental.