Interaction of gold nanostars with neuronal cells and single negative terahertz metamaterials with barium titanate resonators
As the title implies, this dissertation covers two independent topics. The first topic is concerned with biomedical applications of nanoparticles while the second topic presents our results in developing all-dielectric single negative metamaterials at terahertz frequencies. In recent years, the interest in using nanoparticles for biomedical applications has greatly increased. Therefore, there is a need to understand the mechanism of interactions as well as any non-lethal effects nanoparticles may have on biological systems. The first part of this dissertation is focused on advancing the field of nanomedicine by developing gold nanostars with a surface plasmon resonance in the infrared that can be used for photothermal ablation. In addition it seeks to quantify the effect gold nanostars have on the firing rate of neuronal cells. The terahertz (THz) region of the electromagnetic spectrum is located between microwaves and infrared where 1 THz corresponds to wavelengths of 300 microns and energies of 3 meV. There are several emerging applications for THz technology spanning biomedical and security imaging, chemical/biological sensing and communications. However, the development of these applications has been hindered because of the lack of electrically and magnetically active natural materials at these frequencies. By designing all-dielectric resonators in which we take advantage of Mie resonances, we can construct metamaterials with effective negative permeabilities and permittivities. In the second topic of this dissertation we present our results developing all-dielectric metamaterials with single negative values. Using a commercial-grade simulator based on the finite-difference time-domain method, we obtained the scattering parameters of the resonators. From the S parameters, we calculated the effective permittivity and permeability of the metamaterials. Using realistic values for the constituent dielectric's permittivity and loss tangent we performed a systematic study of two different resonator geometries: rectangular and triangular prisms. We varied the resonator dimensions, their periodicity and the orientation of the polarization of the incident electric field and were able to obtain negative permeabilities for the rectangular prisms and negative permittivities for the triangular prisms for both orientations of the electric field. Increasing the loss tangent in the rectangular prisms has the effect of removing the region of negative permeabilities.