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Plasmonic crystals with sharp optical transmission behaviors
Materials Letters 185 (2016) 519–522
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Plasmonic crystals with sharp optical transmission behaviors ⁎
Zhengqi Liu , Guolan Fu, Zhenping Huang, Jian Chen
crossmark
Jiangxi Key Laboratory of Nanomaterials and Sensors, School of Physics, Communication and Electronics, Jiangxi Normal University, Nanchang 330022, Jiangxi, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Optical materials and properties Microstructure Plasmonic crystal
In this work, we for the first time propose and demonstrate a feasible strategy for multi-band ultra-narrow optical transmission of the plasmonic crystals by introducing a high-index dielectric (HID) cavity, which can be acted as an efficient optical field coupling and hybridization component. Five sharp transmission bands with the maximal bandwidth of 6.5 nm are achieved. High spectral Q-factor of 327 with the corresponding bandwidth of 2.8 nm is observed in the optical region. These features pave a simple and universal way for multispectral narrowband optical transmission based on the typical plasmonic crystals.
1. Introduction
2. Materials and method
Surface plasmons are the oscillations of the electrons in the metallic nanostructures or nanoparticles, which can support strong optical field coupling and confinement with the illumination [1–4]. Extremely enhanced electric field distribution of the localized plasmon particles and the resonant spectral responses in the metallic array or plasmonic crystals have shown numerous applications in the optical sensing and detection [5,6], propagation manipulation such as optical filtering [7]. The optical spectrum is usually broad [8] due to the excitation of the surface plasmons within vicinity of the metallic structures. The spectral full-width at half-maximum bandwidth is typically of 100–200 nm in the optical spectrum regime [3]. The broadband spectrum directly leads to a low Q-factor of the lineshape, which inevitably hampers the applications in many applications such as sub-diffraction filtering, displaying, sensing and detection. Recently, great efforts [9–13] have been made to improve the bandwidth at the cost of the need of highprecise design and fabrication techniques for achieving narrowband spectrum. These structural features eventually limit their further applications. In this work, we propose and demonstrate a new strategy for multispectral sharp optical transmission spectrum based on a conventional metal/dielectric platform, which consists of a silver (Ag) disk array and a high-index dielectric (HID) cavity sandwiched by a thin low-index dielectric (LID) spacer. Spectral Q-factor is up to 327 with the corresponding bandwidth down to 2.8 nm in the optical region.
Fig. 1(a) shows the schematic of the proposed structure consisting of a Ag disk array on a thin LID spacer coupled with a HID cavity with n of 3.5. Plasmonic crystal is with a period (P) of 350 nm and the diameter (D) of the disk is 300 nm. The height of the disk is 50 nm. Silica with the refractive index n of 1.45 is used as the LID spacer. The thickness of the LID is 30 nm. HID dielectrics such as the semiconductors of silicon have been demonstrated to produce multiple optical resonances for optical field coupling [9,11,14]. The thickness of the HID cavity is depicted as tHID (tHID=500 nm). Three-dimensional finite-domain time-difference method [15] was employed to calculate the optical properties. The complex dielectric constants of Ag are taken from measured data and described by the Drude model..
⁎
3. Results and discussion Transmission spectrum with five sharp peaks (λ1–λ5) is obtained in Fig. 1(b). At λ1, spectral bandwidth is 5 nm, which leads to a Q-factor of 122 as tens of times larger than that of the conventional plasmonic crystal [3]. For the peak at λ2, a bandwidth of 6.5 nm and the spectral Q-factor of 107 are observed. At λ3, the transmittance (T) is up to 91% and the bandwidth is down to 5 nm. An extremely narrow peak at λ4 (917.5 nm) is observed, where the bandwidth is down to 2.8 nm and the Q-factor is up to 327. For the peak at λ5, spectral bandwidth is also down to 3.6 nm and the Q-factor is of 282. Overall, multispectral transmission with the bandwidth down to sub-10 nm is achieved. Schematic of the conventional plasmonic crystal on a silica substrate and the transmission spectrum with two broad transmission bands
Corresponding author. E-mail addresses: [email protected], [email protected] (Z. Liu).
http://dx.doi.org/10.1016/j.matlet.2016.09.056 Received 19 May 2016; Received in revised form 16 August 2016; Accepted 17 September 2016 Available online 17 September 2016 0167-577X/ © 2016 Elsevier B.V. All rights reserved.
Materials Letters 185 (2016) 519–522
Z. Liu et al.
Fig. 1. (a) Schematic of the structure with the parameters depicted as P, D, tHID. (b) Transmission spectrum of structure with the five sharp peaks. (c) Schematic of the conventional plasmonic crystal on the silica. (d) Transmission spectrum of the conventional plasmonic crystal on the silica and the corresponding HID cavity.
Fig. 2. (a–d) Normalized electric field intensity distributions of the transmission peaks of λ1–λ5, respectively.
responses indicate the great contribution for the sharp transmission spectrum by the HID cavity. Calculated electric field intensity distributions for the peaks of λ1–λ5 are shown in Fig. 2. For these patterns, two main features can be observed. One is the strong electric field distributed at the corner areas
adjacent to the dip centered at 603.7 nm are shown in Fig. 1(c) and (d), respectively. For the HID cavity, multiple transmission bands are observed in the spectral range due to the cavity resonances [9–14]. Nevertheless, transmission peaks are with broad bandwidths for the Ag disk array without HID cavity and the single HID cavity. These distinct 520
Materials Letters 185 (2016) 519–522
Z. Liu et al.
distributions in the HID cavity show the excitation of the 4th, 3th, 2th and 1th cavity mode as shown in Fig. 2(b–e), respectively. These distribution patterns confirm that the obtained multiple narrowband transmission results from the hybridization coupling between the plasmonic resonances of the Ag disk array and the optical modes of the HID cavity.. Fig. 3 presents the spectra of the structure with different HID cavity under a tuning nHID. With a low nHID, only two or three transmission peaks with relative weak intensity are observed as shown in Fig. 3(a). Increasing nHID, the transmission is enhanced and the spectral curves show obvious red-shifts as shown in Fig. 3(b). Moreover, multispectral sharp transmission with larger number of bands is obtained. For instance, in comparison with the spectrum of the system with a nHID of 2.5, four sharp transmission peaks are observed for the system with a nHID of 3.0. In addition, strong spectral red-shift for the transmission curve is observed. These features are the main results of the multiple optical modes supported by a higher nHID cavity since it can provide more and stronger optical cavity modes.. For the structure with a 50-nm-thick HID cavity, only one transmission band with the T < 40% is observed in Fig. 4(a). Increasing tHID to 100 nm, a strong transmission peak with T above 80% is observed at 680.9 nm. The corresponding electric field intensity distribution pattern for the peak is shown as the inset picture in Fig. 4(a). It is observed that only one node is found in the HID cavity, which indicates the excitation of the 1th cavity mode of the 100-nmthick HID cavity. Based on the classical optical cavity resonant theory, the wavelength of the cavity mode (λj) is defined by jλj=2nHID×tHID (j, the order of the cavity mode). The 1th cavity mode can be predicted to occur at the wavelength of 700 nm. This calculated resonant wavelength is very close to the obtained transmission peak at 680.9 nm. The slight spectral shift mainly results from the plasmon resonance and the coupling between the plasmon mode and the cavity resonance. Increasing tHID to 150 nm, dual-band transmission is observed due to the 2th and 1th cavity modes supported by the thicker HID cavity. Fig. 4(b) shows the optical transmission spectra of the structure with a thicker HID cavity. More and stronger sharp transmission peaks can be obtained for the system with a much thicker cavity. These features not only confirm the great contribution for the high transmission spectrum by the HID cavity but also indicate a way for tuning the enhanced optical transmission for the conventional plasmonic crystal by utilizing dielectric cavity coupler. For the system formed by a lossy Si HID cavity (Fig. 4(c)), the optical properties including the five sharp transmission peaks are retained in general except the slight reduction for the transmission intensity. The optical response can be further tuned by the thickness of the LID since it can modify the coupling between the plasmonic resonance and the optical cavity modes..
Fig. 3. (a) and (b) Transmission spectrum of the structure under different refractive index of the HID cavity (nHID). The structural parameters of P, D, and tHID are 350 nm, 300 nm, and 500 nm, respectively.
of the top Ag disk and the field coupling occurred at the gap area between the top disk and the bottom HID cavity. The other is the obvious optical cavity resonant mode distributions in the HID cavity. In contrast to the usually formal cavity modes with almost paralleling patterns [14], the reconfiguration patterns confirm the hybridization coupling between the top plasmonic dipolar resonances and the bottom optical cavity modes [11,14]. For instance, at λ1, besides the strong electric field distributed in the Ag disk corner and the spacer areas, the electric field distribution in the bottom HID cavity shows a pattern with five nodes (zero intensity point) along z-direction (Fig. 2(a)), which directly verifies the excitation of the 5th cavity mode of the HID cavity [11]. Similarly, for the transmission peaks at λ2–λ5, the electric field
Fig. 4. (a) and (b) Transmission spectrum of the structure under different tHID cavity. The inset pattern shows the corresponding electric field distribution for the peak at 680.9 nm of the structure with a 100-nm-thick HID spacer. (c) Transmission spectra of the system formed by the lossy Si HID cavity under a 30 nm and 15 nm LID buffer layer.
521
Materials Letters 185 (2016) 519–522
Z. Liu et al.
References
4. Conclusion We have proposed and demonstrated a feasible way for multi-band ultra-narrow optical transmission for the plasmonic crystal by introducing a HID cavity. The introduced HID cavity provides multiple optical modes, which interacts with the plasmon resonances of the metallic nanoparticles array and thus produces multi-band sharp high transmission spectrum. Spectral bandwidth down to single-digit level and the Q-factor up to 327 are achieved. These findings pave a new way for manipulating the optical transmission of the conventional plasmonic structures by utilizing a HID dielectric cavity.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Acknowledgements The work supported from National Natural Science Foundation of China (Grants 11464019, 11564017, and 11264017).
522
J.A. Schuller, et al., Nat. Mater. 9 (2010) 193–204. H.A. Atwater, A. Polman, Nat. Mater. 9 (2010) 205–213. K.A. Willets, R.P. Van Duyne, Annu. Rev. Phys. Chem. 58 (2007) 267–297. Y. Yu, S. Fan, X. Wang, Z. Ma, H. Dai, J. Han, Mater. Lett. 134 (2014) 233–236. L. Chen, et al., J. Phys. Chem. C 117 (2013) 20146–20153. Y. Shen, et al., Nat. Commun. 4 (2013) 2381. J.H. Shi, H.F. Ma, W.X. Jiang, T.J. Cui, Phys. Rev. B 86 (2012) 035103. T.W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio, P.A. Wolff, Nature 391 (1998) 667–669. A. Vázquez-Guardado, A. Safaei, S. Modak, D. Franklin, D. Chanda, Phys. Rev. Lett. 113 (2014) 263902. Z. Li, S. Butun, K. Aydin, ACS Nano 8 (2014) 8242–8248. D. Chanda, et al., Nat. Commun. 2 (2011) 479. J. Chen, et al., Mater. Lett. 136 (2014) 205–208. J. Chen, et al., Opt. Express 23 (2015) 16238–16245. Z. Liu, et al., Mater. Lett. 160 (2015) 518–521. G. Liu, et al., Phys. Chem. Chem. Phys. 16 (2014) 4320–4328.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Plasmonic crystals with sharp optical transmission behaviors ⁎
Zhengqi Liu , Guolan Fu, Zhenping Huang, Jian Chen
crossmark
Jiangxi Key Laboratory of Nanomaterials and Sensors, School of Physics, Communication and Electronics, Jiangxi Normal University, Nanchang 330022, Jiangxi, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Optical materials and properties Microstructure Plasmonic crystal
In this work, we for the first time propose and demonstrate a feasible strategy for multi-band ultra-narrow optical transmission of the plasmonic crystals by introducing a high-index dielectric (HID) cavity, which can be acted as an efficient optical field coupling and hybridization component. Five sharp transmission bands with the maximal bandwidth of 6.5 nm are achieved. High spectral Q-factor of 327 with the corresponding bandwidth of 2.8 nm is observed in the optical region. These features pave a simple and universal way for multispectral narrowband optical transmission based on the typical plasmonic crystals.
1. Introduction
2. Materials and method
Surface plasmons are the oscillations of the electrons in the metallic nanostructures or nanoparticles, which can support strong optical field coupling and confinement with the illumination [1–4]. Extremely enhanced electric field distribution of the localized plasmon particles and the resonant spectral responses in the metallic array or plasmonic crystals have shown numerous applications in the optical sensing and detection [5,6], propagation manipulation such as optical filtering [7]. The optical spectrum is usually broad [8] due to the excitation of the surface plasmons within vicinity of the metallic structures. The spectral full-width at half-maximum bandwidth is typically of 100–200 nm in the optical spectrum regime [3]. The broadband spectrum directly leads to a low Q-factor of the lineshape, which inevitably hampers the applications in many applications such as sub-diffraction filtering, displaying, sensing and detection. Recently, great efforts [9–13] have been made to improve the bandwidth at the cost of the need of highprecise design and fabrication techniques for achieving narrowband spectrum. These structural features eventually limit their further applications. In this work, we propose and demonstrate a new strategy for multispectral sharp optical transmission spectrum based on a conventional metal/dielectric platform, which consists of a silver (Ag) disk array and a high-index dielectric (HID) cavity sandwiched by a thin low-index dielectric (LID) spacer. Spectral Q-factor is up to 327 with the corresponding bandwidth down to 2.8 nm in the optical region.
Fig. 1(a) shows the schematic of the proposed structure consisting of a Ag disk array on a thin LID spacer coupled with a HID cavity with n of 3.5. Plasmonic crystal is with a period (P) of 350 nm and the diameter (D) of the disk is 300 nm. The height of the disk is 50 nm. Silica with the refractive index n of 1.45 is used as the LID spacer. The thickness of the LID is 30 nm. HID dielectrics such as the semiconductors of silicon have been demonstrated to produce multiple optical resonances for optical field coupling [9,11,14]. The thickness of the HID cavity is depicted as tHID (tHID=500 nm). Three-dimensional finite-domain time-difference method [15] was employed to calculate the optical properties. The complex dielectric constants of Ag are taken from measured data and described by the Drude model..
⁎
3. Results and discussion Transmission spectrum with five sharp peaks (λ1–λ5) is obtained in Fig. 1(b). At λ1, spectral bandwidth is 5 nm, which leads to a Q-factor of 122 as tens of times larger than that of the conventional plasmonic crystal [3]. For the peak at λ2, a bandwidth of 6.5 nm and the spectral Q-factor of 107 are observed. At λ3, the transmittance (T) is up to 91% and the bandwidth is down to 5 nm. An extremely narrow peak at λ4 (917.5 nm) is observed, where the bandwidth is down to 2.8 nm and the Q-factor is up to 327. For the peak at λ5, spectral bandwidth is also down to 3.6 nm and the Q-factor is of 282. Overall, multispectral transmission with the bandwidth down to sub-10 nm is achieved. Schematic of the conventional plasmonic crystal on a silica substrate and the transmission spectrum with two broad transmission bands
Corresponding author. E-mail addresses: [email protected], [email protected] (Z. Liu).
http://dx.doi.org/10.1016/j.matlet.2016.09.056 Received 19 May 2016; Received in revised form 16 August 2016; Accepted 17 September 2016 Available online 17 September 2016 0167-577X/ © 2016 Elsevier B.V. All rights reserved.
Materials Letters 185 (2016) 519–522
Z. Liu et al.
Fig. 1. (a) Schematic of the structure with the parameters depicted as P, D, tHID. (b) Transmission spectrum of structure with the five sharp peaks. (c) Schematic of the conventional plasmonic crystal on the silica. (d) Transmission spectrum of the conventional plasmonic crystal on the silica and the corresponding HID cavity.
Fig. 2. (a–d) Normalized electric field intensity distributions of the transmission peaks of λ1–λ5, respectively.
responses indicate the great contribution for the sharp transmission spectrum by the HID cavity. Calculated electric field intensity distributions for the peaks of λ1–λ5 are shown in Fig. 2. For these patterns, two main features can be observed. One is the strong electric field distributed at the corner areas
adjacent to the dip centered at 603.7 nm are shown in Fig. 1(c) and (d), respectively. For the HID cavity, multiple transmission bands are observed in the spectral range due to the cavity resonances [9–14]. Nevertheless, transmission peaks are with broad bandwidths for the Ag disk array without HID cavity and the single HID cavity. These distinct 520
Materials Letters 185 (2016) 519–522
Z. Liu et al.
distributions in the HID cavity show the excitation of the 4th, 3th, 2th and 1th cavity mode as shown in Fig. 2(b–e), respectively. These distribution patterns confirm that the obtained multiple narrowband transmission results from the hybridization coupling between the plasmonic resonances of the Ag disk array and the optical modes of the HID cavity.. Fig. 3 presents the spectra of the structure with different HID cavity under a tuning nHID. With a low nHID, only two or three transmission peaks with relative weak intensity are observed as shown in Fig. 3(a). Increasing nHID, the transmission is enhanced and the spectral curves show obvious red-shifts as shown in Fig. 3(b). Moreover, multispectral sharp transmission with larger number of bands is obtained. For instance, in comparison with the spectrum of the system with a nHID of 2.5, four sharp transmission peaks are observed for the system with a nHID of 3.0. In addition, strong spectral red-shift for the transmission curve is observed. These features are the main results of the multiple optical modes supported by a higher nHID cavity since it can provide more and stronger optical cavity modes.. For the structure with a 50-nm-thick HID cavity, only one transmission band with the T < 40% is observed in Fig. 4(a). Increasing tHID to 100 nm, a strong transmission peak with T above 80% is observed at 680.9 nm. The corresponding electric field intensity distribution pattern for the peak is shown as the inset picture in Fig. 4(a). It is observed that only one node is found in the HID cavity, which indicates the excitation of the 1th cavity mode of the 100-nmthick HID cavity. Based on the classical optical cavity resonant theory, the wavelength of the cavity mode (λj) is defined by jλj=2nHID×tHID (j, the order of the cavity mode). The 1th cavity mode can be predicted to occur at the wavelength of 700 nm. This calculated resonant wavelength is very close to the obtained transmission peak at 680.9 nm. The slight spectral shift mainly results from the plasmon resonance and the coupling between the plasmon mode and the cavity resonance. Increasing tHID to 150 nm, dual-band transmission is observed due to the 2th and 1th cavity modes supported by the thicker HID cavity. Fig. 4(b) shows the optical transmission spectra of the structure with a thicker HID cavity. More and stronger sharp transmission peaks can be obtained for the system with a much thicker cavity. These features not only confirm the great contribution for the high transmission spectrum by the HID cavity but also indicate a way for tuning the enhanced optical transmission for the conventional plasmonic crystal by utilizing dielectric cavity coupler. For the system formed by a lossy Si HID cavity (Fig. 4(c)), the optical properties including the five sharp transmission peaks are retained in general except the slight reduction for the transmission intensity. The optical response can be further tuned by the thickness of the LID since it can modify the coupling between the plasmonic resonance and the optical cavity modes..
Fig. 3. (a) and (b) Transmission spectrum of the structure under different refractive index of the HID cavity (nHID). The structural parameters of P, D, and tHID are 350 nm, 300 nm, and 500 nm, respectively.
of the top Ag disk and the field coupling occurred at the gap area between the top disk and the bottom HID cavity. The other is the obvious optical cavity resonant mode distributions in the HID cavity. In contrast to the usually formal cavity modes with almost paralleling patterns [14], the reconfiguration patterns confirm the hybridization coupling between the top plasmonic dipolar resonances and the bottom optical cavity modes [11,14]. For instance, at λ1, besides the strong electric field distributed in the Ag disk corner and the spacer areas, the electric field distribution in the bottom HID cavity shows a pattern with five nodes (zero intensity point) along z-direction (Fig. 2(a)), which directly verifies the excitation of the 5th cavity mode of the HID cavity [11]. Similarly, for the transmission peaks at λ2–λ5, the electric field
Fig. 4. (a) and (b) Transmission spectrum of the structure under different tHID cavity. The inset pattern shows the corresponding electric field distribution for the peak at 680.9 nm of the structure with a 100-nm-thick HID spacer. (c) Transmission spectra of the system formed by the lossy Si HID cavity under a 30 nm and 15 nm LID buffer layer.
521
Materials Letters 185 (2016) 519–522
Z. Liu et al.
References
4. Conclusion We have proposed and demonstrated a feasible way for multi-band ultra-narrow optical transmission for the plasmonic crystal by introducing a HID cavity. The introduced HID cavity provides multiple optical modes, which interacts with the plasmon resonances of the metallic nanoparticles array and thus produces multi-band sharp high transmission spectrum. Spectral bandwidth down to single-digit level and the Q-factor up to 327 are achieved. These findings pave a new way for manipulating the optical transmission of the conventional plasmonic structures by utilizing a HID dielectric cavity.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
Acknowledgements The work supported from National Natural Science Foundation of China (Grants 11464019, 11564017, and 11264017).
522
J.A. Schuller, et al., Nat. Mater. 9 (2010) 193–204. H.A. Atwater, A. Polman, Nat. Mater. 9 (2010) 205–213. K.A. Willets, R.P. Van Duyne, Annu. Rev. Phys. Chem. 58 (2007) 267–297. Y. Yu, S. Fan, X. Wang, Z. Ma, H. Dai, J. Han, Mater. Lett. 134 (2014) 233–236. L. Chen, et al., J. Phys. Chem. C 117 (2013) 20146–20153. Y. Shen, et al., Nat. Commun. 4 (2013) 2381. J.H. Shi, H.F. Ma, W.X. Jiang, T.J. Cui, Phys. Rev. B 86 (2012) 035103. T.W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio, P.A. Wolff, Nature 391 (1998) 667–669. A. Vázquez-Guardado, A. Safaei, S. Modak, D. Franklin, D. Chanda, Phys. Rev. Lett. 113 (2014) 263902. Z. Li, S. Butun, K. Aydin, ACS Nano 8 (2014) 8242–8248. D. Chanda, et al., Nat. Commun. 2 (2011) 479. J. Chen, et al., Mater. Lett. 136 (2014) 205–208. J. Chen, et al., Opt. Express 23 (2015) 16238–16245. Z. Liu, et al., Mater. Lett. 160 (2015) 518–521. G. Liu, et al., Phys. Chem. Chem. Phys. 16 (2014) 4320–4328.