- Email: [email protected]
Dual-band plasmonic perfect absorber based on all-metal nanostructure for refractive index sensing application
Accepted Manuscript Dual-band plasmonic perfect absorber based on all-metal nanostructure for refractive index sensing application Yongzhi Cheng, Hongsen Zhang, Xue Song Mao, RongZhou Gong PII: DOI: Reference:
S0167-577X(18)30292-1 https://doi.org/10.1016/j.matlet.2018.02.078 MLBLUE 23904
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
2 January 2018 16 February 2018 19 February 2018
Please cite this article as: Y. Cheng, H. Zhang, X.S. Mao, R. Gong, Dual-band plasmonic perfect absorber based on all-metal nanostructure for refractive index sensing application, Materials Letters (2018), doi: https://doi.org/ 10.1016/j.matlet.2018.02.078
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dual-band plasmonic perfect absorber based on all-metal nanostructure for refractive index sensing application Yongzhi Cheng1, Hongsen Zhang1, Xue Song Mao1, and RongZhou Gong2 1
School of information Science and Engineering, Wuhan University of Science and
Technology, Wuhan, Hubei, 430081, China 2
School of Optical and Electronic Information, Huazhong University of Science and
Technology, Wuhan, Hubei, 430074, China
We present a simple design of a dual-band plasmonic perfect absorber (PA) based on all-metal nanostructure for ultra-sensitive refractive index (RI) sensing applications in infrared region. The proposed PA is only consisted of an assembly of vertical-split-ring (VSR) structure array adhered on a continuous gold film. The numerical simulation results show that the designed PA can achieve absorbance of 99.1% and 98.8% with quality-factor (Q-factor) of 16.4 and 19.8 at 163.6 THz and 258.8 THz, respectively. The physical origin of the observed absorption is elucidated through distributions of magnetic field and power loss density at resonances. The designed PA served as a refractive index (RI) sensor can achieve sensitivity of 1518 and 959 nm/refractive index unit (RIU), respectively. The proposed dual-band PA could be a desirable candidate for applications in the RI sensing, notch filtering and the enhanced infrared spectroscopy. Keywords: Metamaterials, plasmonic perfect absorber, all-metal nanostructure, simulation and modeling, sensors.
1. Introduction Recently, electromagnetic (EM) or optical metamaterial (MM) perfect absorbers (PAs) have been paid great attention increasingly since the perfect absorption concept was firstly demonstrated experimentally by Landy et. al [1]. Optical PAs are generally categorized into narrowband and broadband in terms of the
Corresponding author: Yongzhi Cheng ([email protected]) 1
absorption bandwidth. The narrowband PAs could be served as thermal emitters [2] and sensors [3,4], while broadband ones could be potential applications in energy harvesting and solar photovoltaic [5-8]. The typical optical PAs are composed of three layer metal-dielectric-metal (MDM) structures, and the perfect absorption is usually originated from intrinsic surface plasmon polaritons (SPPs) resonances [9-14]. The perfect absorption can be realized by optimizing the shape, size, and optical properties of the nanostructure of the PA [9-12]. These narrowband MDM structure PAs can absorb nearly all incident lights, which could be served as detector or sensor. However, for RI sensing applications, the MDM structure PAs usually account an issue that the sensing components are difficult to bond with the sensing medium. Up to date, several efforts have been made to overcome this issue. For example, Shen et. al. proposed a gold mushroom PA for RI sensing with a higher figure of merit (FOM) of about 108 [13]. Then, Li et. al. proposed a double-layered metal grating structure with triple-band responses, which could be served as a high-performance RI sensor with FOM as high as 38 [15]. More recently, some RI sensors based on all-metal nanostructures have been proposed [16-18], which can be easily filled with analyte. However, these RI sensors worked only in a single narrow-band, thus limiting potential applications. Thus, the effective design for plasmonic PA with easily filled analyte, higher sensitivity, and multispectral responses is highly desirable for sensing application. In this letter, we proposed a dual-band PA based on all-metal nanostructure for ultrasensitive RI sensing application in infrared region. Simulation results indicate that the absorbance of the PA is greater than 98% at two different resonance frequencies. Underlying perfect absorption mechanism is studied through magnetic field and power loss distributions. Compared to the previous plasmonic PAs [13-18], our design has a higher sensitive for glucose concentration for RI sensing application.
2. Structure design and simulation The design schematic of the unit-cell structure of the plasmonic PA is depicted in Figs. 1(a,b). Unlike previous MDM structures, the designed PA is only consisted of 2
all-gold vertical-split-ring (VSR) structure array periodically arranged on the surface of a continuous gold film. The thickness of the gold film used here is much larger than the skin depth in the infrared regime, thus the transmission can be neglected. The plasmonic nanostructure is placed directly on the glass substrate with a periodicity of 800 nm. The incident light is propagating along the openings plane of the VSR structure in z-direction. The optimized geometric dimensions are given as: px = py = 800 nm, r = 180 nm, w = 40 nm, h = 800 nm, g = 20 nm, and ts = 100 nm. The simulation of the designed nanostructure was carried out using the frequency domain solver with the finite integration technique (FIT) in CST Microwave Studio. The permittivity of bulk gold in the near-infrared region is described by Drude model from Ref [16]. In the simulation, we set period boundary conditions both in the x and y directions to replicate an infinite array of the VSRs, and open boundary condition along the light propagating direction. For our design, the absorbance can be calculated by A(ω) = 1 - R(ω), where R(ω) represents the reflectance as functions of frequency ω.
3. Results and Discussions Figure 2 shows the reflectance (R(ω)) and absorbance (A(ω)) spectra of the designed PA. From the Fig.2, there are two significant dips with very small values, which are labeled as f1 and f2, indicating two resonance modes. The reflectance decreases to the minimal values of 0.9% and 1.2%, and the corresponding absorbance is up to 99.1% and 98.8% at f1 = 163.6 THz and f2 = 258.8 THz, respectively. Obviously, it is polarization-insensitive under normal incident light due to the rotational symmetry of the unit-cell nanostructures. Besides, the values of the Q-factor (Q = f / FWHM, where f is the center resonance frequency, FWHM is the full width at half maximum of absorbance) of the two resonance modes are about 16.4 and 19.8, respectively. The two steep resonances with perfect absorption provide some potential applications in detectors and sensors [18-20]. To better understand physical mechanism of the observed dual-band perfect absorption, distributions of the magnetic field (Hy in y-z plane) and three-dimensional 3
(3D) power loss density of the unit-cell structure at resonances are depicted as shown in Fig. 3. It can be observed that the localized magnetic fields (Hy) are mainly concentered on the middle gap vicinity of the VSR structure at resonances, revealing the guide mode excitation with a perfect standing wave along the z-direction. From Figs. 3(a,c), at 163.6 THz and 258.8 THz, the zeroth-order and first-order mode resonances can be excited effectively, respectively. At resonances, the enhanced EM fields are located at middle gap vicinity of VSRs, which is similar to the grating structure absorber [21,22]. The incident light energy can be confined significantly in the vicinity of the middle gap of the VSRs, as shown in Figs. 3(b,d). Obviously, the distribution properties of the power loss density are consistent well with the ones of the magnetic fields. Thus, the dual-band perfect absorption mechanism is mainly attributed to the guide mode excitations with different order. For our proposed infrared dual-band plasmonic PA, the change of refractive index (RI) of a gas or liquid would be feasible in chemical or biomedical sensing application. The dual-band response of the proposed PA with different surrounding RI is studied numerically. As shown in Fig. 4(a), we used glucose solution as analyte when the proposed PA as sensor [10,16]. Fig. 4(b,c) present the simulated absorbance for the PA surrounding glucose solution with different RI values. It can be seen that the absorption peak frequencies of the PA are highly dependent on the RI values. The absorption frequencies are shifted to the lower ones with the increase of the RI values of the surrounding glucose solution. To further investigate the sensing property of PA-based sensor, the sensing capabilities can be defined by sensitivity S and figure of merit FOM [10]. The sensitivity and FOM can be expressed as S = Δλ /Δn and FOM = S / FWHM, respectively, where Δλ and Δn are the wavelength and RI value shift of the analyte, and FWHM is the full width at half maximum of absorbance. Figure 5 presents the relations between the wavelength shift Δλ of the absorption peaks and the RI variation Δn of the analyte. The slope of the fitting curve depicts the wavelength as RI values. As shown in Fig. 5, the sensitivities are about 1518 and 959 nm/RIU by linear fittings for peak1 and peak2, respectively. The sensitivity of the PA-based sensor is much remarkable compared with the MDM 4
structures MMA-based sensor [9,10,12,13,15-19]. In addition, the calculated FOM for peak1 and peak2 are about 12.79 and 16.54. Thus, the proposed dual-band PA is a highly desirable device for detecting or sensing RI changes of a tested agent [10,16].
4. Conclusions In conclusion, a dual-band plasmonic PA only consisted of the VSRs array adhered on a gold film has been demonstrated numerically in infrared region. The dual-band near perfect absorption mainly originates from the guide mode excitation with different orders. The further simulated results reveal that the dual-band PA has a highly sensitive response to the RI values change in the surrounding analyte, which can achieve sensitivities of about 1518 and 959 nm/RIU, and the FOM of about 12.79 and 16.54, respectively. In addition, the sensing components of the PA are easy to bond with the sensing medium for detecting or sensing applications. Thus, the proposed dual-band PA-based sensor is not only simpler in geometry structure but also higher sensing performance, which means great potential applications in biosensing, medical diagnostics, and detecting areas.
Acknowledgments This work was supported by the financial support from the Joint Funds of the National Natural Science Foundation of China (Grant Nos. U1435209, and 61605147) and the Natural Science Foundation of Hubei province (Grant No. 2017CFB588).
REFERENCES [1] N. I. Landy, S. Sajuyigbe, J. J. Mock, et al.,Phys. Rev. Lett. 100 (2008) 207402. [2] X. Liu, T. Tyler, T. Starr, et al., Phys. Rev. Lett. 107 (2011) 045901. [3] J. Homola, Chem. Rev. 108 (2008) 462-493. [4] T. Chen, S. Li and H. Sun, Sensors 12 (2012) 2742-2765. [5] S. E. Han, and G. Chen, Nan. Lett. 10 (2010)1012-1015. [6] C. F. Guo, T. Sun, F. Cao, Q. Liu, and Z. Ren, Light Sci. Appl. 3 (2014) e161. [7] R. Waseem, B. Angelo, Z. Pierfrancesco, et al., Sci. Rep. 6 (2016) 24539. [8] C. Wu, B. Neuner, J. John, et al., J. Opt. 14 (2012) 024005. [9] S. Luo, J. Zhao, D. Zuo, X. Wang, Opt. Exp. 24 (2016) 9288-9294. [10] N. Liu, M. Mesch, T. Weiss, et al.,Nano Lett. 10 (2010) 2342-2348. [11] J. Hao, L. Zhou, and M. Qiu, Phys. Rev. B 83 (2011) 165107. 5
[12] X. Lu, L. Zhang, and T. Zhang, Opt. Exp. 23 (2015) 20715- 20720. [13] Y. Shen, J. Zhou, T. Liu, et al., Nat. Commun. 4 (2013) 2381. [14] Y. Cheng, M. Huang, H. Chen, Z. Guo, et al., Materials 10 (2017) 591. [15] G. Li, Y. Shen, G. Xiao, et al., Opt. Exp. 23 (2015) 8995- 9003. [16] Y. Z. Cheng, X. S. Mao, C. J. Wu, et al., Opt. Materials 53 (2016) 195-200. [17] R. Li, D. Wu, Y. Liu, et al., Nano. Res. Lett. 12 (2017) 1 [18] X. Lu, L. Zhang, and T. Zhang, Opt. Exp. 23 (2015) 20715-20720. [19] Z. Yong, S. Zhang, C. Gong, et al., Sci. Rep. 6 (2016) 24063. [20] D. Wu, R. Li, Y. Liu, et al., Nano. Res. Lett. 12 (2017) 427. [21] Y. L. Liao, Y. Zhao, Opt. Commun. 334 (2015) 328-331. [22] Y. L. Liao, Y. Zhao, H. P. Lu, Mod. Phys. Lett. B 30 (2016) 1650352.
6
(a)
(b)
g
r
py
h
w
ts
px
Fig. 1 Schematic of the dual narrow-band PA: (a) the front and (b) lattice view of the unit-cell structure 1.0
f1
f2
R(ω)
0.5 y
x
z A(ω) 0.0
150
180
210
240
270
Frequency (THz)
Fig. 2 Simulated reflectance (R(ω)) and absorbance (A(ω)) of the proposed PA (a) (b) +Max
y
x
Hx
z
z
(d)
(c)
Hx
x
x
z
z
y
x
-Max
Fig. 3 The distributions of magnetic fields (Hy in y-z plane) and three-dimensional (3D) power loss density of the unit-cell structure at resonance frequencies: (a) f1 = 163.6 THz, (b) f2 = 258.8 THz
7
1.0
(b)
Peak2
Absorbance
Peak1
n=1.312 n=1.322 n=1.332 n=1.342 n=1.352
0.5
0.0 1.0
140
160
180
200
220
Peak1 Frequency (THz)
260 Peak2
Absorbance
(c) Gold
240
0.5
Analyte (a)
Glass
0.0
140
145
150
225
230
235
240
Frequency (THz)
Fig. 4 (a) The design scheme of the RI sensor based on dual-band PA array, where the designed water as reference analyte: (b,c) Absorbance spectra with different RIs of glucose solution.
Wavelength, λi/μm
2.12 2.10 S1=1518
nm/RIU Peak1(Sim.) Peak1(Fit.) Peak2(Sim.) Peak2(Fit.)
2.08 2.06 1.32
S2=959 nm/RIU
1.28 1.31
1.32
1.33
1.34
Refractive index, n
1.35
Fig. 5 Linear fit (solid line) and simulated resonance wavelengths (black squares and circulars) as a function of RI values of the surrounding analyte
8
1. A dual-band perfect absorber (PA) based on all-metal nanostructure is proposed. 2. The mechanism relies on the guide mode excitation with a perfect standing wave. 3. The dual-band PA can serve as a refractive index (RI) sensor in infrared region. 4. The PA-based RI sensor has a sensitivity of about 1518 and 959 nm/RIU, respectively.
9
S0167-577X(18)30292-1 https://doi.org/10.1016/j.matlet.2018.02.078 MLBLUE 23904
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
2 January 2018 16 February 2018 19 February 2018
Please cite this article as: Y. Cheng, H. Zhang, X.S. Mao, R. Gong, Dual-band plasmonic perfect absorber based on all-metal nanostructure for refractive index sensing application, Materials Letters (2018), doi: https://doi.org/ 10.1016/j.matlet.2018.02.078
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dual-band plasmonic perfect absorber based on all-metal nanostructure for refractive index sensing application Yongzhi Cheng1, Hongsen Zhang1, Xue Song Mao1, and RongZhou Gong2 1
School of information Science and Engineering, Wuhan University of Science and
Technology, Wuhan, Hubei, 430081, China 2
School of Optical and Electronic Information, Huazhong University of Science and
Technology, Wuhan, Hubei, 430074, China
We present a simple design of a dual-band plasmonic perfect absorber (PA) based on all-metal nanostructure for ultra-sensitive refractive index (RI) sensing applications in infrared region. The proposed PA is only consisted of an assembly of vertical-split-ring (VSR) structure array adhered on a continuous gold film. The numerical simulation results show that the designed PA can achieve absorbance of 99.1% and 98.8% with quality-factor (Q-factor) of 16.4 and 19.8 at 163.6 THz and 258.8 THz, respectively. The physical origin of the observed absorption is elucidated through distributions of magnetic field and power loss density at resonances. The designed PA served as a refractive index (RI) sensor can achieve sensitivity of 1518 and 959 nm/refractive index unit (RIU), respectively. The proposed dual-band PA could be a desirable candidate for applications in the RI sensing, notch filtering and the enhanced infrared spectroscopy. Keywords: Metamaterials, plasmonic perfect absorber, all-metal nanostructure, simulation and modeling, sensors.
1. Introduction Recently, electromagnetic (EM) or optical metamaterial (MM) perfect absorbers (PAs) have been paid great attention increasingly since the perfect absorption concept was firstly demonstrated experimentally by Landy et. al [1]. Optical PAs are generally categorized into narrowband and broadband in terms of the
Corresponding author: Yongzhi Cheng ([email protected]) 1
absorption bandwidth. The narrowband PAs could be served as thermal emitters [2] and sensors [3,4], while broadband ones could be potential applications in energy harvesting and solar photovoltaic [5-8]. The typical optical PAs are composed of three layer metal-dielectric-metal (MDM) structures, and the perfect absorption is usually originated from intrinsic surface plasmon polaritons (SPPs) resonances [9-14]. The perfect absorption can be realized by optimizing the shape, size, and optical properties of the nanostructure of the PA [9-12]. These narrowband MDM structure PAs can absorb nearly all incident lights, which could be served as detector or sensor. However, for RI sensing applications, the MDM structure PAs usually account an issue that the sensing components are difficult to bond with the sensing medium. Up to date, several efforts have been made to overcome this issue. For example, Shen et. al. proposed a gold mushroom PA for RI sensing with a higher figure of merit (FOM) of about 108 [13]. Then, Li et. al. proposed a double-layered metal grating structure with triple-band responses, which could be served as a high-performance RI sensor with FOM as high as 38 [15]. More recently, some RI sensors based on all-metal nanostructures have been proposed [16-18], which can be easily filled with analyte. However, these RI sensors worked only in a single narrow-band, thus limiting potential applications. Thus, the effective design for plasmonic PA with easily filled analyte, higher sensitivity, and multispectral responses is highly desirable for sensing application. In this letter, we proposed a dual-band PA based on all-metal nanostructure for ultrasensitive RI sensing application in infrared region. Simulation results indicate that the absorbance of the PA is greater than 98% at two different resonance frequencies. Underlying perfect absorption mechanism is studied through magnetic field and power loss distributions. Compared to the previous plasmonic PAs [13-18], our design has a higher sensitive for glucose concentration for RI sensing application.
2. Structure design and simulation The design schematic of the unit-cell structure of the plasmonic PA is depicted in Figs. 1(a,b). Unlike previous MDM structures, the designed PA is only consisted of 2
all-gold vertical-split-ring (VSR) structure array periodically arranged on the surface of a continuous gold film. The thickness of the gold film used here is much larger than the skin depth in the infrared regime, thus the transmission can be neglected. The plasmonic nanostructure is placed directly on the glass substrate with a periodicity of 800 nm. The incident light is propagating along the openings plane of the VSR structure in z-direction. The optimized geometric dimensions are given as: px = py = 800 nm, r = 180 nm, w = 40 nm, h = 800 nm, g = 20 nm, and ts = 100 nm. The simulation of the designed nanostructure was carried out using the frequency domain solver with the finite integration technique (FIT) in CST Microwave Studio. The permittivity of bulk gold in the near-infrared region is described by Drude model from Ref [16]. In the simulation, we set period boundary conditions both in the x and y directions to replicate an infinite array of the VSRs, and open boundary condition along the light propagating direction. For our design, the absorbance can be calculated by A(ω) = 1 - R(ω), where R(ω) represents the reflectance as functions of frequency ω.
3. Results and Discussions Figure 2 shows the reflectance (R(ω)) and absorbance (A(ω)) spectra of the designed PA. From the Fig.2, there are two significant dips with very small values, which are labeled as f1 and f2, indicating two resonance modes. The reflectance decreases to the minimal values of 0.9% and 1.2%, and the corresponding absorbance is up to 99.1% and 98.8% at f1 = 163.6 THz and f2 = 258.8 THz, respectively. Obviously, it is polarization-insensitive under normal incident light due to the rotational symmetry of the unit-cell nanostructures. Besides, the values of the Q-factor (Q = f / FWHM, where f is the center resonance frequency, FWHM is the full width at half maximum of absorbance) of the two resonance modes are about 16.4 and 19.8, respectively. The two steep resonances with perfect absorption provide some potential applications in detectors and sensors [18-20]. To better understand physical mechanism of the observed dual-band perfect absorption, distributions of the magnetic field (Hy in y-z plane) and three-dimensional 3
(3D) power loss density of the unit-cell structure at resonances are depicted as shown in Fig. 3. It can be observed that the localized magnetic fields (Hy) are mainly concentered on the middle gap vicinity of the VSR structure at resonances, revealing the guide mode excitation with a perfect standing wave along the z-direction. From Figs. 3(a,c), at 163.6 THz and 258.8 THz, the zeroth-order and first-order mode resonances can be excited effectively, respectively. At resonances, the enhanced EM fields are located at middle gap vicinity of VSRs, which is similar to the grating structure absorber [21,22]. The incident light energy can be confined significantly in the vicinity of the middle gap of the VSRs, as shown in Figs. 3(b,d). Obviously, the distribution properties of the power loss density are consistent well with the ones of the magnetic fields. Thus, the dual-band perfect absorption mechanism is mainly attributed to the guide mode excitations with different order. For our proposed infrared dual-band plasmonic PA, the change of refractive index (RI) of a gas or liquid would be feasible in chemical or biomedical sensing application. The dual-band response of the proposed PA with different surrounding RI is studied numerically. As shown in Fig. 4(a), we used glucose solution as analyte when the proposed PA as sensor [10,16]. Fig. 4(b,c) present the simulated absorbance for the PA surrounding glucose solution with different RI values. It can be seen that the absorption peak frequencies of the PA are highly dependent on the RI values. The absorption frequencies are shifted to the lower ones with the increase of the RI values of the surrounding glucose solution. To further investigate the sensing property of PA-based sensor, the sensing capabilities can be defined by sensitivity S and figure of merit FOM [10]. The sensitivity and FOM can be expressed as S = Δλ /Δn and FOM = S / FWHM, respectively, where Δλ and Δn are the wavelength and RI value shift of the analyte, and FWHM is the full width at half maximum of absorbance. Figure 5 presents the relations between the wavelength shift Δλ of the absorption peaks and the RI variation Δn of the analyte. The slope of the fitting curve depicts the wavelength as RI values. As shown in Fig. 5, the sensitivities are about 1518 and 959 nm/RIU by linear fittings for peak1 and peak2, respectively. The sensitivity of the PA-based sensor is much remarkable compared with the MDM 4
structures MMA-based sensor [9,10,12,13,15-19]. In addition, the calculated FOM for peak1 and peak2 are about 12.79 and 16.54. Thus, the proposed dual-band PA is a highly desirable device for detecting or sensing RI changes of a tested agent [10,16].
4. Conclusions In conclusion, a dual-band plasmonic PA only consisted of the VSRs array adhered on a gold film has been demonstrated numerically in infrared region. The dual-band near perfect absorption mainly originates from the guide mode excitation with different orders. The further simulated results reveal that the dual-band PA has a highly sensitive response to the RI values change in the surrounding analyte, which can achieve sensitivities of about 1518 and 959 nm/RIU, and the FOM of about 12.79 and 16.54, respectively. In addition, the sensing components of the PA are easy to bond with the sensing medium for detecting or sensing applications. Thus, the proposed dual-band PA-based sensor is not only simpler in geometry structure but also higher sensing performance, which means great potential applications in biosensing, medical diagnostics, and detecting areas.
Acknowledgments This work was supported by the financial support from the Joint Funds of the National Natural Science Foundation of China (Grant Nos. U1435209, and 61605147) and the Natural Science Foundation of Hubei province (Grant No. 2017CFB588).
REFERENCES [1] N. I. Landy, S. Sajuyigbe, J. J. Mock, et al.,Phys. Rev. Lett. 100 (2008) 207402. [2] X. Liu, T. Tyler, T. Starr, et al., Phys. Rev. Lett. 107 (2011) 045901. [3] J. Homola, Chem. Rev. 108 (2008) 462-493. [4] T. Chen, S. Li and H. Sun, Sensors 12 (2012) 2742-2765. [5] S. E. Han, and G. Chen, Nan. Lett. 10 (2010)1012-1015. [6] C. F. Guo, T. Sun, F. Cao, Q. Liu, and Z. Ren, Light Sci. Appl. 3 (2014) e161. [7] R. Waseem, B. Angelo, Z. Pierfrancesco, et al., Sci. Rep. 6 (2016) 24539. [8] C. Wu, B. Neuner, J. John, et al., J. Opt. 14 (2012) 024005. [9] S. Luo, J. Zhao, D. Zuo, X. Wang, Opt. Exp. 24 (2016) 9288-9294. [10] N. Liu, M. Mesch, T. Weiss, et al.,Nano Lett. 10 (2010) 2342-2348. [11] J. Hao, L. Zhou, and M. Qiu, Phys. Rev. B 83 (2011) 165107. 5
[12] X. Lu, L. Zhang, and T. Zhang, Opt. Exp. 23 (2015) 20715- 20720. [13] Y. Shen, J. Zhou, T. Liu, et al., Nat. Commun. 4 (2013) 2381. [14] Y. Cheng, M. Huang, H. Chen, Z. Guo, et al., Materials 10 (2017) 591. [15] G. Li, Y. Shen, G. Xiao, et al., Opt. Exp. 23 (2015) 8995- 9003. [16] Y. Z. Cheng, X. S. Mao, C. J. Wu, et al., Opt. Materials 53 (2016) 195-200. [17] R. Li, D. Wu, Y. Liu, et al., Nano. Res. Lett. 12 (2017) 1 [18] X. Lu, L. Zhang, and T. Zhang, Opt. Exp. 23 (2015) 20715-20720. [19] Z. Yong, S. Zhang, C. Gong, et al., Sci. Rep. 6 (2016) 24063. [20] D. Wu, R. Li, Y. Liu, et al., Nano. Res. Lett. 12 (2017) 427. [21] Y. L. Liao, Y. Zhao, Opt. Commun. 334 (2015) 328-331. [22] Y. L. Liao, Y. Zhao, H. P. Lu, Mod. Phys. Lett. B 30 (2016) 1650352.
6
(a)
(b)
g
r
py
h
w
ts
px
Fig. 1 Schematic of the dual narrow-band PA: (a) the front and (b) lattice view of the unit-cell structure 1.0
f1
f2
R(ω)
0.5 y
x
z A(ω) 0.0
150
180
210
240
270
Frequency (THz)
Fig. 2 Simulated reflectance (R(ω)) and absorbance (A(ω)) of the proposed PA (a) (b) +Max
y
x
Hx
z
z
(d)
(c)
Hx
x
x
z
z
y
x
-Max
Fig. 3 The distributions of magnetic fields (Hy in y-z plane) and three-dimensional (3D) power loss density of the unit-cell structure at resonance frequencies: (a) f1 = 163.6 THz, (b) f2 = 258.8 THz
7
1.0
(b)
Peak2
Absorbance
Peak1
n=1.312 n=1.322 n=1.332 n=1.342 n=1.352
0.5
0.0 1.0
140
160
180
200
220
Peak1 Frequency (THz)
260 Peak2
Absorbance
(c) Gold
240
0.5
Analyte (a)
Glass
0.0
140
145
150
225
230
235
240
Frequency (THz)
Fig. 4 (a) The design scheme of the RI sensor based on dual-band PA array, where the designed water as reference analyte: (b,c) Absorbance spectra with different RIs of glucose solution.
Wavelength, λi/μm
2.12 2.10 S1=1518
nm/RIU Peak1(Sim.) Peak1(Fit.) Peak2(Sim.) Peak2(Fit.)
2.08 2.06 1.32
S2=959 nm/RIU
1.28 1.31
1.32
1.33
1.34
Refractive index, n
1.35
Fig. 5 Linear fit (solid line) and simulated resonance wavelengths (black squares and circulars) as a function of RI values of the surrounding analyte
8
1. A dual-band perfect absorber (PA) based on all-metal nanostructure is proposed. 2. The mechanism relies on the guide mode excitation with a perfect standing wave. 3. The dual-band PA can serve as a refractive index (RI) sensor in infrared region. 4. The PA-based RI sensor has a sensitivity of about 1518 and 959 nm/RIU, respectively.
9