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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.


SEM images and Raman shift spectrum for the structures with and without the concentric rings. SEM images of (a) the DERS structure and (b) the structure with concentric rings. (c) The Raman shift spectrum of the thiophenol molecule with three different structures, multi-layer film without pattern, structure without concentric rings, and structure with concentric rings.
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Fig7: SEM images and Raman shift spectrum for the structures with and without the concentric rings. SEM images of (a) the DERS structure and (b) the structure with concentric rings. (c) The Raman shift spectrum of the thiophenol molecule with three different structures, multi-layer film without pattern, structure without concentric rings, and structure with concentric rings.

Mentions: A 3-nm titanium adhesion layer and a 150-nm gold layer were first deposited onto the SiO2 substrate by electron-beam dual gun evaporation. Then, a 40-nm TiO2 layer was deposited and a 50-nm gold layer was deposited onto TiO2 layer. The patterns with and without concentric rings on the gold layer are melt by FEI Nova 600i dual beam focused ion beam (FEI, Hillsboro, OR, USA). The period of the concentric rings was designed as 650 nm. To cut the 50-nm thickness of gold film, the smallest current 1.5 pA and 30-KV accelerating voltage were applied. Figure 7a,b shows the SEM images of fabricated structures without and with the concentric rings. The gaps between the nanoantennas are about 40.6 nm in both structures. The self-assemble thiophenol was prepared as the target molecule, and the samples were immersed in the thiophenol solution with a concentration of 10-3 M for 48 h. A laser beam with λ = 785 nm is focused onto the patterns in the microscope with the magnification of objective lens as 50× and numerical aperture as 0.9. Figure 7c is the measured Raman shift spectra of the thiophenol molecule for the structures with and without concentric rings. For comparisons, the Raman shift spectrum for the multi-layer film without any pattern is also shown in Figure 7c. The Raman shifts for the thiophenol molecule are 1,000.1, 1,022.7, and 1,071.4 cm-1. The results show that the structure with the concentric rings has stronger Raman signal than the structure without the concentric rings.Figure 7


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)

SEM images and Raman shift spectrum for the structures with and without the concentric rings. SEM images of (a) the DERS structure and (b) the structure with concentric rings. (c) The Raman shift spectrum of the thiophenol molecule with three different structures, multi-layer film without pattern, structure without concentric rings, and structure with concentric rings.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Fig7: SEM images and Raman shift spectrum for the structures with and without the concentric rings. SEM images of (a) the DERS structure and (b) the structure with concentric rings. (c) The Raman shift spectrum of the thiophenol molecule with three different structures, multi-layer film without pattern, structure without concentric rings, and structure with concentric rings.
Mentions: A 3-nm titanium adhesion layer and a 150-nm gold layer were first deposited onto the SiO2 substrate by electron-beam dual gun evaporation. Then, a 40-nm TiO2 layer was deposited and a 50-nm gold layer was deposited onto TiO2 layer. The patterns with and without concentric rings on the gold layer are melt by FEI Nova 600i dual beam focused ion beam (FEI, Hillsboro, OR, USA). The period of the concentric rings was designed as 650 nm. To cut the 50-nm thickness of gold film, the smallest current 1.5 pA and 30-KV accelerating voltage were applied. Figure 7a,b shows the SEM images of fabricated structures without and with the concentric rings. The gaps between the nanoantennas are about 40.6 nm in both structures. The self-assemble thiophenol was prepared as the target molecule, and the samples were immersed in the thiophenol solution with a concentration of 10-3 M for 48 h. A laser beam with λ = 785 nm is focused onto the patterns in the microscope with the magnification of objective lens as 50× and numerical aperture as 0.9. Figure 7c is the measured Raman shift spectra of the thiophenol molecule for the structures with and without concentric rings. For comparisons, the Raman shift spectrum for the multi-layer film without any pattern is also shown in Figure 7c. The Raman shifts for the thiophenol molecule are 1,000.1, 1,022.7, and 1,071.4 cm-1. The results show that the structure with the concentric rings has stronger Raman signal than the structure without the concentric rings.Figure 7

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.