Plasmonics and Metamaterials

2.1 Plasmonics

It is defined as how the use of light to manipulate the movement of free electrons in metal/metamaterials. Let's take gold or silver as an example; each gold or silver atoms have one free electron. But a gold crystal or silver crystals have many free electrons, used light to many free electrons. The light used to excite the collective pattern movement of free electrons in metamaterials.

Figure 1.

Metal and dielectric

Wood, Pendry, & Tsai, 2006.

Once we have a periodic pattern formed regarding electron movement, then we shall start to have a wave type of interaction between photon and electron wave.

But in this case, this electron wave is not precisely an electron wave that discussed in quantum mechanics but the circular electron wave is basically an electron start to accumulate some localized area, e.g., in Figure 1 it's been shown that in some area there accumulate a lot of electrons, but the side effect is that have some areas short of electrons to become a positive charge equivalently. Thus, a positive/negative charge region forms a periodic structure on the surface of the metal and dielectric materials.

So, we can use light to create that kind of electron wave. Once we have a stream like this, imagine that this wave can propagate along this interface between metal and dielectric materials.

To manipulate electrons in the materials, this is probably where people can use the external free space propagation wave or light wave. If extend that idea by adding some more materials to this plasmonic as if here there is only one metal. But by making this metal-dielectric composite in a nanoscale then can create artificial materials that not exist in nature. That is meta-materials.

The name for the metamaterials, the “Meta” means that this is not true this is a virtual material, this is not the material that can be found in nature, this is something that can be seen in the environment, this is something that created by engineering methods.

2.2 Metamaterial

It is a composite structure made of metals and dielectrics. So, this is not a homogeneous material; basically, these are inhomogeneous artificial materials made of metal and dielectric materials.

Because those metals or dielectric structures in this metamaterials are very small, they are much smaller than the wavelength. On a wavelength scale efficiently can assume that homogenous material but with very different physical properties in comparison to either metal or dielectric. Thus, now are creating artificial materials made of or blending the metal and dielectric materials in a way that they have desired property.

In Figure 2 given below, showing that whenever have a dielectric metal surface, possibly can excite this, collective electron movement that follows the frequency of excitation light wave. The property of the metal to be controlled by the wavelength as well as the structure of the metal.

Here it is something that is called the SPP “Surface Plasmon Polariton” which is transverse EM wave, in this case, a transverse wave that is E-field is inside the plane, and H-field is perpendicular to this plane. This wave in a free space than coupled to this plasma and interface a metal and dielectrics and, the wave of charges on the metal-dielectric interface and this is called Surface Plasmon Polariton. Basically, it is coupling effect between the EM wave and the free electron movement on the metal surface. This probably in a very smooth surface, on this axis can assume that its infinite extended surface so could imagine could have this propagation wave along this interface. Thus, it is coupling effect between the EM wave and the free electron movement on the metal surface.

Figure 2.

(a) Nano-wires and (b) nano-dots structure

This probably is a very smooth surface, on this axis can assume that its infinite long surface so could imagine could have this propagation wave along this interface.