# Color-Adjustable Devices Based on the Surface Plasmons Effect
## 3 Results and Discussion  
Considering that the template was composed of an array of circle holes, we first studied the EOT effect of the template. As shown in Figure 2a, we altered the radius of the circle hole. The parameters were set as follows: the period \(P_{x}=P_{y}=200\) nm; the thicknesses of the substrate and the metal thin film were unchanged, \(h_{1}=50\) nm and \(h_{2}=100\) nm, respectively; the radii \(R\) of the circle hole were 60 nm to 90 nm, and the step was 10 nm. It can be seen from the figure that a transmission peak is generated at 355 nm. As the radius increases, the transmission peak basically does not shift. For square hole arrays with \(P_{x}=P_{y}=P\), when the light source is incident perpendicularly to the metal film, the position \(\lambda_{max}\) of the EOT peak generated by the SPPs mode is mainly determined by the arrays period \(P\)[1,31]. However, the peak value increases. This is due to the increase in the hole's space, so that more incident light can pass through. This means that there is almost no significant effect in the visible light regions for the device when the hole's radius and structural period are constant. In order to allow the nanoparticles in the hole to have more space, we chose a radius of 90 nm for the circle hole. As shown in Figure 1c, we designed five kinds of nanoparticles: sphere, cross, torus, cylinder, and cube. In the simulations, we gave transmission spectrums for each type of nanoparticle, which had six different geometric parameters. The geometric parameters of the five nanoparticles were set as follows: (1) Sphere: the radii \(R_{1}\) of the sphere were 45 nm to 70 nm and the step was 5 nm. (2) Cross: the widths \(W_{2}\) of the rectangle of the cross remained unchanged at 20 nm, and we only changed the lengths of the rectangle. The lengths \(L_{2}\) were 80 nm to 130 nm, the step was 10 nm, and the nanoparticle thickness \(H_{2}\) was 50 nm. (3) Torus: the radii \(R_{3\text{-}1\text{(3-2)}}\) of the torus were 15(35) to 40(60) nm, the step was 5 nm, and the nanoparticle thickness \(H_{3}\) was 50 nm. (4) Cylinder: the radii \(R_{4}\) of the cylinder were 40 nm to 65 nm, the step was 5 nm, and the nanoparticle thickness \(H_{4}\) was 50 nm. (5) Cube: the side lengths \(L_{5}\) of the cube were 60 nm to 110 nm, the step was 10 nm, and the nanoparticle thickness \(H_{5}\) was 50 nm. In order to understand more clearly how nanoparticles were filled into the template, the schematic diagram of the structures of five kinds of nanoparticles filled into the template is given in Figure 1d. As shown in Figure 2b-f, as the size of the metal nanoparticles increases, red-shift happensto the transmission peaks. Apparently, the positions of the transmission peaks, which cover the entire visible light regions, have played an extremely important role in constructing a coloring device for the surface plasmon's structure from the six sets of simulation data. Considering the influence of isolated nanoparticles on the template, we directly placed nanoparticles on the quartz substrate to explore the effect of enhanced light transmission. The geometric parameters of nanoparticles are consistent with those of the front, and only the aluminum film is removed. Figure 3 shows the transmittance of nanoparticles with different geometry. It can be seen that with the increase in the size of nanoparticles, the transmission peak gradually red-shifts and the transmittance decreases. Generally speaking, plasmonic nanostructures with resonant excitation allow, to the extreme limit, the incident light in nanoscale space, so as to form an enhanced electromagnetic (EM) field. As we all know, the narrower the width of the slit is, the stronger the coupling of the charge densities on the two walls of the slit could be in the metallic nano-structure. The effective refractive index \(n_{\textit{eff}}\) increases with decreasing the width of the nano-slits. It leads to the red-shift of the transmission peak to appear [32; 33].