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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 and far-field radiation patterns withH = 20 nm. Near-field intensities and far-field radiation patterns for the structure with dielectric layer thickness 20 nm at λ = 671 nm. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 671 nm and H = 20 nm in Figure 5. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a) and (b) are 104.30, 104.56, times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction. (c) The corresponding far-field radiation pattern which is excited by placing an x-polarized electric dipole source at the feed gap of the dipole antenna.
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Fig6: Near-field intensities and far-field radiation patterns withH = 20 nm. Near-field intensities and far-field radiation patterns for the structure with dielectric layer thickness 20 nm at λ = 671 nm. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 671 nm and H = 20 nm in Figure 5. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a) and (b) are 104.30, 104.56, times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction. (c) The corresponding far-field radiation pattern which is excited by placing an x-polarized electric dipole source at the feed gap of the dipole antenna.

Mentions: The maximum electric field at the center of the gap appears at λ = 671 nm in the case of H = 20 nm in Figure 5 and its near-field electric field distributions are shown in Figure 6a,b. The electric field is concentrated in the center region of the hole. The maximum electric field intensity is located at the nanoantenna upper-surface corners, and its enhancement factor is 104.6. Compared to the results in Figure 3c, it is found that the electric field is more concentrated in the nanoantenna in Figure 6a. This is because the dielectric layer thickness is optimized in Figure 6; however, it should be noted that the illuminated light wavelengths are different between the cases in Figures 3 and6. This phenomena can also be observed in the top view shown in Figure 6b and Figure 3d. It is also found that the light field intensities around the rings in Figure 6b are not as strong as the case in Figure 3d. The far-field radiation for the case of H = 20 nm at λ = 671 nm by exciting an x-polarized electric dipole source which is placed at the feed gap of the dipole antenna is shown in Figure 6c. It has a narrow light beam radiating to the far field. The narrow-beam radiation effect can be explained by an exponentially decaying leaky plasmon wave[19]. Our structure with concentric rings can be viewed as a structure which can support the leaky wave in the outward directions of the nanoantenna. Thus, the narrower beams are observed in Figure 6c and Figure 4b as compared to Figure 4a.Figure 6


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 and far-field radiation patterns withH = 20 nm. Near-field intensities and far-field radiation patterns for the structure with dielectric layer thickness 20 nm at λ = 671 nm. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 671 nm and H = 20 nm in Figure 5. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a) and (b) are 104.30, 104.56, times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction. (c) The corresponding far-field radiation pattern which is excited by placing an x-polarized electric dipole source at the feed gap of the dipole antenna.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig6: Near-field intensities and far-field radiation patterns withH = 20 nm. Near-field intensities and far-field radiation patterns for the structure with dielectric layer thickness 20 nm at λ = 671 nm. (a) The cross-section view and (b) the top view of the electric field distribution of DESR structure at λ = 671 nm and H = 20 nm in Figure 5. The scale bars are in logarithmic scale and limited to 0 to 3. The maximum field intensity of (a) and (b) are 104.30, 104.56, times of the incident light intensity. The illuminated light is the plane wave propagated from the top to bottom; i.e., in - z direction. (c) The corresponding far-field radiation pattern which is excited by placing an x-polarized electric dipole source at the feed gap of the dipole antenna.
Mentions: The maximum electric field at the center of the gap appears at λ = 671 nm in the case of H = 20 nm in Figure 5 and its near-field electric field distributions are shown in Figure 6a,b. The electric field is concentrated in the center region of the hole. The maximum electric field intensity is located at the nanoantenna upper-surface corners, and its enhancement factor is 104.6. Compared to the results in Figure 3c, it is found that the electric field is more concentrated in the nanoantenna in Figure 6a. This is because the dielectric layer thickness is optimized in Figure 6; however, it should be noted that the illuminated light wavelengths are different between the cases in Figures 3 and6. This phenomena can also be observed in the top view shown in Figure 6b and Figure 3d. It is also found that the light field intensities around the rings in Figure 6b are not as strong as the case in Figure 3d. The far-field radiation for the case of H = 20 nm at λ = 671 nm by exciting an x-polarized electric dipole source which is placed at the feed gap of the dipole antenna is shown in Figure 6c. It has a narrow light beam radiating to the far field. The narrow-beam radiation effect can be explained by an exponentially decaying leaky plasmon wave[19]. Our structure with concentric rings can be viewed as a structure which can support the leaky wave in the outward directions of the nanoantenna. Thus, the narrower beams are observed in Figure 6c and Figure 4b as compared to Figure 4a.Figure 6

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.