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Electric field enhancement and far-field radiation pattern of the nanoantenna with concentric rings.

Chen SW, Huang YH, Chao BK, Hsueh CH, Li JH - Nanoscale Res Lett (2014)

Bottom Line: The directivity of a dipole antenna can be improved by directivity-enhanced Raman scattering structure, which is a combination of a dipole antenna and a ring reflector layer on a ground plane.The measured results show that the structure with concentric rings can have stronger SERS signals.The proposed structure can be useful for several nanoantenna applications, such as sensing or detecting.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Science and Ocean Engineering, National Taiwan University, Taipei, 10617, Taiwan, shihwenc@gmail.com.

ABSTRACT
The optical antennas have the potential in various applications because of their field enhancement and directivity control. The directivity of a dipole antenna can be improved by directivity-enhanced Raman scattering structure, which is a combination of a dipole antenna and a ring reflector layer on a ground plane. The concentric rings can collect the light into the center hole. Depending upon the geometry of the antenna inside the hole, different electric field enhancements can be achieved. In this paper, we propose to combine the concentric rings with the directivity-enhanced Raman scattering structure in order to study its electric field enhancement and the far-field radiation pattern by finite-difference time-domain simulations. Compared with the structure without the concentric rings over the ground plane, it is found that our proposed structure can obtain stronger electric field enhancements and narrower radiation beams because the gold rings can help to couple the light into the nanoantenna and they also scatter light into the far field and modify the far-field radiation pattern. The designed structures were fabricated and the chemical molecules of thiophenol were attached on the structures for surface-enhanced Raman scattering (SERS) measurements. The measured results show that the structure with concentric rings can have stronger SERS signals. The effects of the dielectric layer thickness in our proposed structure on the near-field enhancements and far-field radiation are also investigated. The proposed structure can be useful for several nanoantenna applications, such as sensing or detecting.

No MeSH data available.


Electric field intensity verse wavelength for the structures with and without the concentric rings. The field intensities at the middle of the gap of the DERS structure with and without the concentric rings, where the black, blue, red, and light blue lines represent the structure with and without concentric rings with periodicity of ring P = 600 nm, P = 650 nm, and P = 700 nm, respectively.
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Fig2: Electric field intensity verse wavelength for the structures with and without the concentric rings. The field intensities at the middle of the gap of the DERS structure with and without the concentric rings, where the black, blue, red, and light blue lines represent the structure with and without concentric rings with periodicity of ring P = 600 nm, P = 650 nm, and P = 700 nm, respectively.

Mentions: For the applications in detecting molecules, the strong localized electric field can be helpful for Raman signals. Usually, the strongest electric field is near the corner of metal; however, the selected point at the middle of the gap can be treated as a fair reference. Figure 2 shows the electric field intensities /E/2 at the middle of the gap for the structures shown in Figure 1. The black line in Figure 2 represents the normalized electric field intensities /E/2 at the middle of the gap of the DERS structure in Figure 1a, and it has two peaks at λ = 617 nm and λ = 880 nm, respectively. The blue, red, and light blue lines indicate the normalized electric field intensities /E/2 at the middle of the gap of the dipole antenna with concentric rings structure for periodicity of the ring P = 600 nm, P = 650 nm, and P = 700 nm, respectively. It shows that the maximum intensity occurs for the case of P = 700 nm. However, if the excitation laser wavelength is 785 nm and detected molecule causes the Stokes shifted scattered radiation at wavelength of 880 nm, the better choice of electric field intensity enhancement from λ = 785 nm to λ = 880 nm is for the case with periodicity of P = 650 nm in Figure 2. For the case without concentric rings structure, the two peaks for the black line in Figure 2 occur at λ = 617 nm and λ = 880 nm. They are the resonant points when the interaction of the dipole antenna and the ground plane has the localized maximum field intensity; i.e., the transmission light reflects back by the ground plane rising the localized surface plasmons of the dipole antenna. At the maximum peaks around λ = 880 nm, the black line of the DERS structure has 550 times enhanced field intensity and the red line with concentric rings of periodicity P = 650 nm has 7,254 times enhanced electric field intensity. This is because the resonances of concentric rings structure and the DERS structure appear at the nearby wavelengths. The surface wave generated by the concentrated rings coupling into the dipole antenna which interacts with the ground plane produces the strong electric field at the center of the dipole antenna. The peaks of the red line with concentric rings of periodicity P = 650 nm occur around λ = 550 to 750 nm in Figure 2. They are the resonance peaks of the concentric rings structure, and they shift to longer wavelength when the periodicity of ring increases. According to the previous research without the ground plane[20], the maximum transmission was predicted to occur around a wavelength slightly larger than the period, P = 650 nm, of the concentric rings structure. Although these peaks enhance the electric field intensity in the gap of the dipole antenna, they do not overlap the resonant peaks of the DERS structure. As a result, their intensities are less than the intensity at λ = 880 nm.Figure 2


Electric field enhancement and far-field radiation pattern of the nanoantenna with concentric rings.

Chen SW, Huang YH, Chao BK, Hsueh CH, Li JH - Nanoscale Res Lett (2014)

Electric field intensity verse wavelength for the structures with and without the concentric rings. The field intensities at the middle of the gap of the DERS structure with and without the concentric rings, where the black, blue, red, and light blue lines represent the structure with and without concentric rings with periodicity of ring P = 600 nm, P = 650 nm, and P = 700 nm, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494036&req=5

Fig2: Electric field intensity verse wavelength for the structures with and without the concentric rings. The field intensities at the middle of the gap of the DERS structure with and without the concentric rings, where the black, blue, red, and light blue lines represent the structure with and without concentric rings with periodicity of ring P = 600 nm, P = 650 nm, and P = 700 nm, respectively.
Mentions: For the applications in detecting molecules, the strong localized electric field can be helpful for Raman signals. Usually, the strongest electric field is near the corner of metal; however, the selected point at the middle of the gap can be treated as a fair reference. Figure 2 shows the electric field intensities /E/2 at the middle of the gap for the structures shown in Figure 1. The black line in Figure 2 represents the normalized electric field intensities /E/2 at the middle of the gap of the DERS structure in Figure 1a, and it has two peaks at λ = 617 nm and λ = 880 nm, respectively. The blue, red, and light blue lines indicate the normalized electric field intensities /E/2 at the middle of the gap of the dipole antenna with concentric rings structure for periodicity of the ring P = 600 nm, P = 650 nm, and P = 700 nm, respectively. It shows that the maximum intensity occurs for the case of P = 700 nm. However, if the excitation laser wavelength is 785 nm and detected molecule causes the Stokes shifted scattered radiation at wavelength of 880 nm, the better choice of electric field intensity enhancement from λ = 785 nm to λ = 880 nm is for the case with periodicity of P = 650 nm in Figure 2. For the case without concentric rings structure, the two peaks for the black line in Figure 2 occur at λ = 617 nm and λ = 880 nm. They are the resonant points when the interaction of the dipole antenna and the ground plane has the localized maximum field intensity; i.e., the transmission light reflects back by the ground plane rising the localized surface plasmons of the dipole antenna. At the maximum peaks around λ = 880 nm, the black line of the DERS structure has 550 times enhanced field intensity and the red line with concentric rings of periodicity P = 650 nm has 7,254 times enhanced electric field intensity. This is because the resonances of concentric rings structure and the DERS structure appear at the nearby wavelengths. The surface wave generated by the concentrated rings coupling into the dipole antenna which interacts with the ground plane produces the strong electric field at the center of the dipole antenna. The peaks of the red line with concentric rings of periodicity P = 650 nm occur around λ = 550 to 750 nm in Figure 2. They are the resonance peaks of the concentric rings structure, and they shift to longer wavelength when the periodicity of ring increases. According to the previous research without the ground plane[20], the maximum transmission was predicted to occur around a wavelength slightly larger than the period, P = 650 nm, of the concentric rings structure. Although these peaks enhance the electric field intensity in the gap of the dipole antenna, they do not overlap the resonant peaks of the DERS structure. As a result, their intensities are less than the intensity at λ = 880 nm.Figure 2

Bottom Line: The directivity of a dipole antenna can be improved by directivity-enhanced Raman scattering structure, which is a combination of a dipole antenna and a ring reflector layer on a ground plane.The measured results show that the structure with concentric rings can have stronger SERS signals.The proposed structure can be useful for several nanoantenna applications, such as sensing or detecting.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Science and Ocean Engineering, National Taiwan University, Taipei, 10617, Taiwan, shihwenc@gmail.com.

ABSTRACT
The optical antennas have the potential in various applications because of their field enhancement and directivity control. The directivity of a dipole antenna can be improved by directivity-enhanced Raman scattering structure, which is a combination of a dipole antenna and a ring reflector layer on a ground plane. The concentric rings can collect the light into the center hole. Depending upon the geometry of the antenna inside the hole, different electric field enhancements can be achieved. In this paper, we propose to combine the concentric rings with the directivity-enhanced Raman scattering structure in order to study its electric field enhancement and the far-field radiation pattern by finite-difference time-domain simulations. Compared with the structure without the concentric rings over the ground plane, it is found that our proposed structure can obtain stronger electric field enhancements and narrower radiation beams because the gold rings can help to couple the light into the nanoantenna and they also scatter light into the far field and modify the far-field radiation pattern. The designed structures were fabricated and the chemical molecules of thiophenol were attached on the structures for surface-enhanced Raman scattering (SERS) measurements. The measured results show that the structure with concentric rings can have stronger SERS signals. The effects of the dielectric layer thickness in our proposed structure on the near-field enhancements and far-field radiation are also investigated. The proposed structure can be useful for several nanoantenna applications, such as sensing or detecting.

No MeSH data available.