Light Scattering From Periodic, Conducting Nanostructures

Author

Wesley Kenneth Mills, Utah State University

Date of Award

5-2023

Degree Type

Thesis

Degree Name

Departmental Honors

Department

Physics

Abstract

A material with broadband light absorbing capabilities has the potential for much usefulness in devices such as photovoltaics and thermoelectrics. By energy conservation, a non-transparent material with low reflectance will be highly absorbing. Thus, much research has been devoted to understanding what makes material having low reflectance across a wide wavelength spectrum.

The importance of a material’s electronic structure in determining reflectance is well-established. Current research is revealing the additional importance of surface architecture in the reflective properties of a material. A metasurface is a two-dimentional material with physical features at or smaller than the wavelength of light considered. These wavelength-scale features allow metasurfaces to exhibit uncommon light-matter interactions, such as having a negative index of refraction or generating light beams with orbital angular momentum. Natural or man-made metasurfaces with periodic or quasi-periodic surface features have been found to have extremely low reflectance, but the underlying mechanism has not been clearly established.

Here, mode matching at the boundaries is used to solve a plane wave of light scattering from an array of apertures in a perfectly conducting metal. This approach provides numerical solutions of Maxwell’s equations, instead of the commonly used finite-difference-time-domain simulations which provide solutions but can vary with the setup parameters involved in the simulation. My results indicate that interference effects are the primary cause behind the dark nature of periodic meta surfaces. These results provide guidelines to design subwavelength structures that can achieve low reflectance over a broader range of wavelengths.

Furthermore, this technique can be extended to quasi-periodic surfaces. Similar to Fourier analysis, the surface structure could be represented by a distribution of periodic structures where reflectance from each periodic structure can be solved as detailed in this study. These quasi-periodic structures are closer to many ultra-dark surfaces found in nature, such as the dark patches on the wings of some butterfly species. Thus, being able to analyze aperiodic structures could further advance our design of broadband absorbers.

Recommended Citation

Mills, Wesley Kenneth, "Light Scattering From Periodic, Conducting Nanostructures" (2023). Undergraduate Honors Capstone Projects. 955.
https://digitalcommons.usu.edu/honors/955