Optimization and design of nano/micro structures by plasmonics for sensors and biomedical applications.

Objectives
We want to optimize material and geometry of nano/micro structures in order to increase the optical response of the material. This problem is known as the design of structures.

Methods
Development of algorithms in order to optimize structure and geometry of materials.

Results and prospects
An adapted method of optimization of coated metallic nanoparticles is introduced to perform the optimal choice of material and sizes for better scattering or absorption efficiency. This design of nanoshells, involving plasmon resonance, is achieved in order to maximize the efficiency factors. The presented method is turned to tune the efficiency of nanoshells for biomedical application and an increasing of the efficiency factors by one or two order of magnitude is predicted with realistic materials.

In the same way, the efficiency of plasmon-resonance-based sensors can be greatly improved with such an accurate design of the nano-structures that constitute them. Therefore, we also focus our attention on the design of a particular kind of these nanometric structures that consists of planar multilayered systems for an accurate design of the nano-structures that constitute sensors. We show the significant influence, on the plasmon resonance conditions, of the intermediate layer used to adhere a thin film of gold to a dielectric substrate. To illustrate this effect, we consider different intermediate layers to compute the optimal geometry that vanish the reflected energy. For this, we use the S-formulation and an evolutionary method for the electromagnetic and the optimization problems, respectively.