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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.


Near-field intensities for the structures with and without the concentric rings. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 880 nm and (c) the cross-section view and (d) the top view of the electric field distribution of DESR structure with concentric rings at λ = 880 nm. The white lines are stream lines of the Poynting vectors. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a), (b), (c), and (d) are 103.37, 102.94, 104.50, and 104.08 times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction.
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Fig3: Near-field intensities for the structures with and without the concentric rings. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 880 nm and (c) the cross-section view and (d) the top view of the electric field distribution of DESR structure with concentric rings at λ = 880 nm. The white lines are stream lines of the Poynting vectors. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a), (b), (c), and (d) are 103.37, 102.94, 104.50, and 104.08 times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction.

Mentions: The near-field distributions of DERS structure with and without the concentric rings at λ = 880 nm are shown in Figure 3 with a logarithmic scale. For the easy reading of the electric field intensities, the logarithmic scale bar in Figure 3 is limited to 0 to 3. Figure 3a,b shows the electric field intensities of the cross-section view and top view, respectively, for the DERS structure without concentric rings, while Figure 3c,d is for the DERS structure with concentric rings. The white lines in Figure 3a,c shows the stream slices of the Poynting vectors. The electric fields are confined in the dipole gap and the strongest electric field intensity appears at the bottom corner of the dipole antenna, where the TiO2 spacer is connected. Special rotational power flows are found at the most red regions with strong electric field intensity. The concentric rings can help to couple more light into the nanoantenna for some specific wavelength, such as λ = 880 nm in our case. The more stream slices flow into the gap of the dipole antenna in Figure 3c as compared to the case in Figure 3a where the stream slices flow backward of the dipole antenna and then goes under the top gold layer. The inner diameter of the first gold ring in Figure 3c,d should be chosen carefully because it can affect the coupling efficiency for the electric field from the concentric rings into the nanoantenna. It is also found that there are some strong field intensities around the rings. This is because of the light coupling between the gold rings, and it can help the field coupling efficiency to the nanoantenna but it can also affect the far-field radiation pattern.Figure 3


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)

Near-field intensities for the structures with and without the concentric rings. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 880 nm and (c) the cross-section view and (d) the top view of the electric field distribution of DESR structure with concentric rings at λ = 880 nm. The white lines are stream lines of the Poynting vectors. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a), (b), (c), and (d) are 103.37, 102.94, 104.50, and 104.08 times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Near-field intensities for the structures with and without the concentric rings. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 880 nm and (c) the cross-section view and (d) the top view of the electric field distribution of DESR structure with concentric rings at λ = 880 nm. The white lines are stream lines of the Poynting vectors. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a), (b), (c), and (d) are 103.37, 102.94, 104.50, and 104.08 times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction.
Mentions: The near-field distributions of DERS structure with and without the concentric rings at λ = 880 nm are shown in Figure 3 with a logarithmic scale. For the easy reading of the electric field intensities, the logarithmic scale bar in Figure 3 is limited to 0 to 3. Figure 3a,b shows the electric field intensities of the cross-section view and top view, respectively, for the DERS structure without concentric rings, while Figure 3c,d is for the DERS structure with concentric rings. The white lines in Figure 3a,c shows the stream slices of the Poynting vectors. The electric fields are confined in the dipole gap and the strongest electric field intensity appears at the bottom corner of the dipole antenna, where the TiO2 spacer is connected. Special rotational power flows are found at the most red regions with strong electric field intensity. The concentric rings can help to couple more light into the nanoantenna for some specific wavelength, such as λ = 880 nm in our case. The more stream slices flow into the gap of the dipole antenna in Figure 3c as compared to the case in Figure 3a where the stream slices flow backward of the dipole antenna and then goes under the top gold layer. The inner diameter of the first gold ring in Figure 3c,d should be chosen carefully because it can affect the coupling efficiency for the electric field from the concentric rings into the nanoantenna. It is also found that there are some strong field intensities around the rings. This is because of the light coupling between the gold rings, and it can help the field coupling efficiency to the nanoantenna but it can also affect the far-field radiation pattern.Figure 3

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.