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Abstract
Making the chemical or biological sensors simpler and more compatible with other measurements is a key enabling technology for commercial application. In this work, we propose a plasmonic refractive-index sensor only based on gold/silicon Schottky junction to simultaneously perform optical and electrical read-out responses. Via exciting surface plasmon resonance (SPR), the designed device shows a few characteristic reflection valleys and greatly enhances the narrowband light absorption. Calculated results indicate that the SPR resonance wavelength can be tuned in the wavelength range of 1100–2000 nm by manipulating the period, width of the Si nanochannel and the incident angle of light. When the analyte is changed, the SPR resonance wavelength generated at the bottom surface of the Au layer barely shifts, while the one at the top surface shows a significant linear shift. The optimally designed system shows an optical response with a refractive index sensitivity of over 1000 nm per refractive index unit (nm/RIU). Moreover, the electrodynamic calculation of the hot electrons predicts the electrical response can be up to 14.5 mA/(W·RIU) for an example of detecting trichloromethane, where the employed light can be a monochromatic light and the sensing operation can be much simpler relative to the conventional spectral work mode.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Currently, with the booming development of biological and information sciences, biological/chemical sensors have attracted a great deal of attention in various fields, e.g., environmental monitoring, food testing, biopharmaceutical analysis, etc. According to the working principle, these sensors are mainly divided into bioelectrode sensors, semiconductor biosensors, optical biosensors, thermal biosensors, piezoelectric crystal biosensors, etc. For instance, Kannan et al. have developed a novel microbial-bioelectrochemical sensor for detecting n-cyclohexyl-2-pyrrolidone in wastewater [1]. However, due to the progress of micro-processing technology and nanotechnology, the traditional biological/chemical sensors have shown deficiencies in sensitivity, miniaturization and integration.
Recently, the optical phenomenon of surface plasmon resonances (SPRs) [2–5] has been extensively used in sensing technology, e.g., surface enhanced Raman scattering [6], surface enhanced fluorescence [7], solar cells [8], new-type photodetector [9], ultra-fast all-light switches [10], etc. Due to its narrowband resonance in spectral response and high correlation with the refractive index of background materials [11–14], SPR is widely used in biological/chemical sensors with high sensitivity and high figure of merit [15,16], but electronic readout responses are rarely reported or realized. SPR is usually subdivided into surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) [17,18]. The conventional ways to excite SPP include prism coupling method, grating diffraction method, near-field optical excitation, etc. Currently, the Kretschmann-Raether prism method is commonly used in commercial SPR sensors, where the refractive index sensitivity obtained in the near infrared band is generally between 103 and 104 nm/RIU (RIU: refractive index unit). However, this type of sensor must be equipped with a series of complicated accessories (e.g., stepper motor and rotary controller), which makes the overall volume of the sensing system too large and expensive, and it is very difficult to achieve multifunctional image transfer [19]. Photonic crystal structures have been proved to have unique advantages in miniaturized detection devices and integrated sensing systems, which is mainly attributed to the fact that the micro-nano optical characteristics can effectively simplify spectral equipment. By coupling LSPR with optical resonance of other mechanisms to form Fano resonance [20] or hybrid SPR [21], high sensitivity (S) and high quality resonance factor (Q, $Q = \lambda /\textrm{FWHM}$, where FWHM is full width at half-maximum) can be simultaneously achieved, along with high figure of merit ($\textrm{FOM}, \,\textrm{FOM} = S/\textrm{FWHM}$). Based on hyperbolic dispersion metamaterials, Kravets et al. obtained super-high-performance (i.e., FOM = 590) SPR sensors [22]. Nevertheless, a spectrophotometer or spectrograph is required in the measurement or application of the above-mentioned systems.
Here we employ the Schottky junction, which has been investigated for the hot-electron applications [23,24], with gold/silicon (Au/Si) nanochannel arrays to realize the spectral response of the background materials, furthermore, the sensing application of electrical readout under monochromatic light is also achieved based on the internal photon emission process. In the proposed configuration, metallic nanostructures work as optical absorbers, optical filters and electrodes, so the volume of the sensing system can be relatively small. Based on the change of output electrical signals, sensing applications without spectrophotometer or spectrograph can also be realized. We demonstrate that the SPR wavelength can be tuned by manipulating the period, width of the nanochannel and the incident angle. Via exciting the diffraction coupled SPP at the top surface of the Au layer, a sensing sensitivity of > 1000 nm/RIU can be achieved. Meanwhile, the electrical response is predicted to be 14.5 mA/(W·RIU).
2. Device and method
The schematic diagrams of three-dimensional (3D) and side views of the proposed plasmonic sensor are shown in Figs. 1(a) and 1(b), respectively. The core of the sensing system is a Schottky junction, which is composed of one-dimensional periodic Si nanochannels (with the period of P, the interval width of W and the depth of D) and the Au film (with the thickness of T, T = 30 nm) vertically located on the silicon surface. In addition, it includes the rear electrode at the bottom of the Si substrate and the front grid electrode connecting these discrete Au layers. When the incident light excites SPR, the reflection spectrum of the device is expected to show a significant reflection valley centering on some specific wavelengths. Besides, the electric wire connecting the front and the rear electrodes is anticipated to perform an observable photocurrent.
Fig. 1. Schematic diagram of (a) 3D and (b) side views of the proposed plasmonic sensor based on Au/Si nanochannel arrays.
The spectral response of the device is carried out by finite-different time-domain numerically calculation (FDTD Solutions, Lumerical Co., Ltd.). The spatial distribution of electromagnetic field and the spatial generation rate of hot electrons are obtained by the finite-element method (COMSOL Multiphysics software). The optical constants of n-type lightly doped Si and Au are dispersive and employed from Palik [25]. For simplicity, we set the refractive index of water (i.e., the referenced background material) and trichloromethane (CHCl3, as an example of analyte) to be 1.33 and 1.45 respectively. The light is incident from the topside of the device (i.e., along –y direction). The incident angle θ is 0° unless indicated. The polarization of the electric field is in the x-y plane. The optical absorption (Abs) of the device is calculated by unit subtracting the sum of reflectance and transmittance. Besides, the photocurrent of the device is obtained by electrodynamic calculation of the hot electrons generated in Au [26]. Detailed electric calculations are given in our previous works [27–29].
3. Results and discussion
We first investigate the influence of the height of the nanochannel. Figure 2(a) illustrates the optical absorption spectra when P = 600 nm and W = 400 nm, with varying D from 40 nm to 100 nm with a step of 10 nm. With the increasing D, one can see that: (1) each absorption spectrum has only one absorption peak in the wavelength range of interest, and the value of the absorption peak first increases and then decreases, reaching the maximum absorption peak (∼93%) when D = 50 nm; (2) the FWHM of the absorption peak gradually increases; (3) the slight shift of peak positions is not related to the increase of D. In order to achieve the high sensitivity and narrowband response, the depth of nanochannel needs to be optimized for different periods and widths, which is also indicated by other reports [10,23].
Fig. 2. (a) Optical absorption spectra for varying D; normalized spatial distribution of magnetic field (Hz) at the optical absorption peak with D = 50 nm (b) and 90 nm (c).
To reveal the primary reason for the light absorption peak, we examine the electromagnetic field distribution. Figures 2(b) and 2(c) shows the normalized magnetic field (Hz) spatial distribution at the wavelength of absorption peak for the cases of D = 50 nm and D = 90 nm, respectively. By comparing these electromagnetic field distributions, we can ascribe each absorption peak in Fig. 2(a) to the same mechanism, i.e., second-order diffraction coupled SPP at the Au/Si interface. Note that the localized energy intensity and radiation loss at the Au/Si interface for different D are different. The localized intensity of magnetic field around the Au/Si interface for D = 50 nm is substantially stronger than that for D = 90 nm (since the red and blue spots of the former are brighter); meanwhile the magnetic field extends significantly farther into silicon for the case of D = 50 nm relative to the case of D = 90 nm (i.e., much lower radiation loss for the former case). The differences at the two aspects can explain that the absorption peak for the case of D = 50 nm is higher than the case of D = 90 nm, while the FWHM is smaller.
Considering that the phase matching condition of SPR excitation can be realized by grating diffraction, we change the period to regulate the SPR wavelength. Figure 3 compares the reflectance spectra at different periods. As the P increases, more and more reflection valleys gradually appear in the wavelength range of interest. In addition, the position of the reflection valley from the same optical resonance mode shows a significant red shift with the increasing P (e.g., indicated by the dashed lines in Fig. 3). The increase of reflection valleys and the red shift of the resonance wavelength can be explained by the wave vector matching condition (i.e., the following equation) [30].
Figure 4 shows the normalized magnetic-field spatial distribution at the wavelengths of these reflection valleys (i.e., λspp = 1100 nm, 1235 nm and 1715 nm, respectively) for the case of P = 900 nm, W = 700 nm and D = 50 nm. When λspp = 1715 nm, most of the incident light energy is localized around the Au/Si interface, which can be attributed to the second-order diffraction coupled SPP on the bottom surface of the Au layer. When λspp = 1235 nm, the localized intensity of the magnetic field around the Au/Si interface is obviously stronger than that of λspp = 1715 nm, and the diffraction order increases to three order. Furthermore, there is near-field energy enhancement effect on the top surface of the Au layer (i.e., around the H2O/Au interface). When λspp = 1100 nm, although the third-order diffraction coupled SPP around the Au/Si interface is retained, the intensity of the magnetic field localized around the H2O/Au interface (i.e., the first-order diffraction coupled SPP on the top surface of Au) is obviously dominant. Therefore, the calculated reflection valley can be caused by a single optical resonance mode or a combination of multiple optical resonance modes.
Fig. 4. (a–c) corresponds to the spatial distribution of the normalized magnetic field (Hz) at λspp = 1.1 µm, 1.235 µm and 1.715 µm, respectively. The main parameters involve P = 900 nm, W = 700 nm and D = 50 nm.
Next, we investigate the influences of the interval width of nanochannel on the reflection spectrum and resonance mode for P = 900 nm and D = 70 nm. Four reflective-valley zones are shown in Fig. 5. For the convenience of description, the optical resonance modes corresponding to these valleys are named Mode 1 to 4 respectively (as indicated in Fig. 5). Each reflective-valley zone shows a slow red shift with an increase of W. By analyzing the magnetic field distribution at the center of each reflection valley with various W (Figs. are not shown), the following 4 points can be summarized: (1) Mode 1 is mainly derived from the second-order diffraction coupled SPP at the bottom surface of the Au layer; (2) Mode 2 mainly comes from the first-order diffraction coupled SPP at the top surface of the Au layer; (3) when W < 500 nm, Mode 3 is mainly derived from the third-order diffraction coupled SPP at the bottom surface of the Au layer, while W > 500 nm, it comes from the hybridization of the first-order diffraction coupled SPP at the top surface of the Au layer and the third-order diffraction coupled SPP at the bottom surface of the Au layer; (4) Mode 4 is mainly derived from the third-order diffraction coupled SPP at the bottom surface of the Au layer. It should be noted that with a continuous increase of W, the width of the Au layer inside of the nanochannel or in the interval space of the neighboring nanochannels will change significantly. Although the order of the diffraction coupled SPP around the Au/Si interface may be the same for a specified P, the number of the magnetic field bright spots inside of the nanochannel is different for various W. Therefore, it can be used to explained that Mode 3 (when W < 500 nm) and Mode 4 show the same order of diffraction coupled SPP, while the resonance wavelength and intensity are different.
Then we would like to evaluate on the angular performance of the proposed plasmonic sensing system. Figure 6 shows the reflection spectra with varying θ and fixed structure parameters (P = 900 nm, W = 500 nm and D = 70 nm). Within the spectral range of interest, the number of reflection valleys gradually increases with the increase of θ, while the valley positions from the same optical resonance mode show an obvious red shift. Moreover, the intensive optical resonance (corresponding to a sharp reflection dip) with a substantial shift (indicated by the dashed line in Fig. 6) is caused by the first-order diffraction coupled SPP at the top surface of the Au layer. These characteristics are consistent with the predicted results from the grating equation, which further indicates that the reflection valley of the device comes from the SPP coupled with the nanochannel diffraction.
Based on the above-discussed optical properties, the sensor performanceis further studied. The sensing sensitivity is defined as:
where Δλ represents the change of central wavelength corresponding to a certain resonance mode when the background material changes and Δn is the change in refractive index (n). Figure 7(a) shows the reflectance spectra for varying n with P = 900 nm, W = 500 nm, D = 70 nm and θ = 0°. There are two obvious reflection valleys in each reflectance spectrum, in addition, the reflection valley corresponding to the shorter wavelength shows a significant red shift with an increase of n, while the one corresponding to the longer wavelength hardly moves. According to the previous analysis, we aware that the reflection valley at the shorter (longer) wavelength is dominated by the diffraction coupled SPP at the top (bottom) surface of the Au layer. Because the top surface of the Au layer directly contacts with the background material, only the characteristic reflection valley from the SPR generated at the top surface of the Au layer leads to a high sensitivity. Therefore, we will focus on the reflection valley or absorption peak from the SPR at the top surface of the Au layer. Figure 7(b) shows the reflectance spectra for P = 900 nm, W = 700 nm, D = 70 nm and θ = 0°. It is observed that a perfect reflectance dip of <1% can be obtained when n = 1.33, and the overall reflectance dip of <10% can be sustained as the n increases from 1.33 to 1.50. In addition, the central wavelength of the sharp reflection valley shows a significant red shift with the increasing n.Fig. 7. (a) Reflectance spectra for various n with θ = 0°, P = 900 nm, W = 500 nm and D = 70 nm; (b) change of reflectance valley from the SPR at the top surface of the Au layer for various n with θ = 0°, P = 900 nm, W = 700 nm and D = 70 nm; (c) on-resonant wavelength versus refractive index of background materials; (d) electrical response curves when the background material is water (n = 1.33) or trichloromethane (n = 1.45) for θ = 0°, P = 900 nm, W = 500 nm and D = 70 nm.
Figure 7(c) shows the on-resonant wavelength versus n of background material. The central wavelength of the reflection valley has an ideal linear relationship with n, where S is fitted to be 1009 nm/RIU and 746 nm/RIU for the results in Fig. 7(a) and 7(b), respectively. Besides, the sensing sensitivity under oblique incidence is also considered, e.g., the central wavelength of the reflection valley also shows a good linear relationship with n for θ = 10°, P = 900 nm, W = 700 nm and D = 70 nm, where the S of 1020 nm/RIU is achieved [indicated by the blue line in Fig. 7(c)]. By comparing the results of the same device with a change of the incident angle (i.e., θ = 0° and θ = 10°), one can see that the sensitivity can be maintained at a very close level, suggesting that the optical response has a high tolerance for incident angle.
Finally, we calculate and analyze the electrical response. The hot electrons are first generated in the stratified Au films via SPR, then these hot electrons with enough energy (larger than the barrier of Schottky junction, assumed as 0.75 eV in our calculation) and suitable diffusion angle can be injected into the Si substrate, and finally collected by the rear electrode. The n-type Si with light doping level should be used as effective electron transport layer. Since the focus of this work is the design of the plasmonic sensor with optical and electrical responses, the details of the photocurrent calculation are not shown herein, but one can found it in our previous publications [27–29]. Figure 7(d) shows the electrical response curves for P = 900 nm, D = 70 nm and W = 500 nm when the background material is water or trichloromethane, respectively. It can be found that: (1) there is a significant peak for the electrical response curve, which is consistent with the light absorption spectrum of the device; (2) as n changes, the peak wavelength of the electrical response shifts significantly; (3) for the light source with a specific wavelength, the electrical response under different background materials obviously changes. For instance, when λ = 1230 nm, the electrical response is reduced by 1.74 mA/W after replacing water with trichloromethane. Assuming the light power irradiated on the device is 1 mW, the photocurrent will be reduced from 2.1 µA to 0.36 µA when the background material is changed from water to trichloromethane, and the estimated electrical response sensitivity is 14.5 mA/(W·RIU).
The proposed device can be fabricated by the following suggested processes. After coating a photoresist, the patterning process can be achieved by using photolithography. Considering the feature size in the proposed device, the stepper exposure technique is a good choice. Then, the patterns can be copied to the Si substrate by dry etching of Si and removing the residual photoresist. The stratified Au films can be deposited by the E-beam evaporator, which has good collimation. Finally, the rear and front conductive electrodes can be prepared by thermal evaporation of Au and Al. Note that the front electrode should be designed to be comb-like and arranged perpendicularly to the nanochannel orientation, so that most region of the front surface of the device would not be covered by the electrode layer and these stratified Au films can be connected. With the specialty of electrical readout, the proposed sensing system not only can be work in the conventional spectral mode, but also can work without employing a spectrometer, a rotary motor or a pre-filter. The latter work mode with electric signal can greatly improve the sensing efficiency, simplify the system, reduce the cost, and facilitate the compatibility with other test systems. As a result, a multi-functional and integrated test system including the sensor may become reality.
4. Conclusions
We propose a plasmonic sensor based on the Schottky junction of Au/Si nanochannel arrays. The device is demonstrated to have an adjustable SPR, which enables it to display characteristic and narrowband reflection valleys and absorption peaks. Since the SPR generated around the bottom surface of the Au layer is not sensitive to the background material, while the one generated around the top surface shows a strong linear relationship, the optical resonance should be intentionally focused on the top surface of the metallic film. The optical response of the optimized device can be over 1000 nm/RIU with a high tolerance for incident angle, and the electrical response is predicted to reach 14.5 mA/(W·RIU). This work provides a new way for the application of ultra-fast and convenient optoelectronic sensors compatible with the silicon technology in the fields of clinical detection, chemical substance detection and micro-spectrum at chip level.
Funding
National Natural Science Foundation of China (61504088, 61705151, 61905170); Natural Science Foundation of Jiangsu Province (BK20181169); China Postdoctoral Science Foundation (2017M611898, 2018T110549); Priority Academic Program Development of Jiangsu Higher Education Institutions.
References
1. P. Kannan, P. Jogdeo, A. F. Mohidin, P. Y. Yung, C. Santoro, T. Seviour, J. Hinks, F. M. Lauro, and E. Marsili, “A novel microbial-Bioelectrochemical sensor for the detection of n-cyclohexyl-2-pyrrolidone in wastewater,” Electrochim. Acta 317, 604–611 (2019). [CrossRef]
2. W. Li and J. G. Valentine, “Harvesting the loss: surface plasmon-based hot electron photodetection,” Nanophotonics 6(1), 177–191 (2017). [CrossRef]
3. L. Qi, Z. Yang, and T. Fu, “Defect modes in one-dimensional magnetized plasma photonic crystals with a dielectric defect layer,” Phys. Plasmas 19(1), 012509 (2012). [CrossRef]
4. A. M. Brown, R. Sundararaman, P. Narang, W. A. Goddard, and H. A. Atwater, “Nonradiative plasmon decay and hot carrier dynamics: effects of phonons, surfaces, and geometry,” ACS Nano 10(1), 957–966 (2016). [CrossRef]
5. A. Shalabney and I. Abdulhalim, “Figure of merit enhancement of surface plasmon resonance sensors in the spectral interrogation,” Opt. Lett. 37(7), 1175–1177 (2012). [CrossRef]
6. J. F. Li, Y. F. Huang, Y. Ding, Z. L. Yang, S. B. Li, X. S. Zhou, F. R. Fan, W. Zhang, Z. Y. Zhou, D. Y. Wu, B. Ren, Z. L. Wang, and Z. Q. Tian, “Shell-isolated nanoparticle-enhanced Raman spectroscopy,” Nature 464(7287), 392–395 (2010). [CrossRef]
7. S. A. Elfeky, F. D’Hooge, L. Poncel, W. B. Chen, S. P. Perera, J. M. H. van den Elsen, T. D. James, A. T. A. Jenkins, P. J. Cameron, and J. S. Fossey, “A surface Plasmon enhanced fluorescence sensor platform,” New J. Chem. 33(7), 1466–1469 (2009). [CrossRef]
8. N. P. Hylton, X. F. Li, V. Giannini, K.-H. Lee, N. J. Ekins-Daukes, J. Loo, D. Vercruysse, P. Van Dorpe, H. Sodabanlu, M. Sugiyama, and S. A. Maier, “Loss mitigation in plasmonic solar cells: aluminium nanoparticles for broadband photocurrent enhancements in GaAs photodiodes,” Sci. Rep. 3(1), 2874 (2013). [CrossRef]
9. G. Tagliabue, A. S. Jermyn, R. Sundararaman, A. J. Welch, J. S. DuChene, R. Pala, A. R. Davoyan, P. Narang, and H. A. Atwater, “Quantifying the role of surface plasmon excitation and hot carrier transport in plasmonic devices,” Nat. Commun. 9(1), 3394 (2018). [CrossRef]
10. X. P. Zhang, B. Q. Sun, J. M. Hodgkiss, and R. H. Friend, “Tunable ultrafast optical switching via waveguided gold nanowires,” Adv. Mater. 20(23), 4455–4459 (2008). [CrossRef]
11. L. Li, S. Wu, L. Li, Z. Zhou, H. Ding, C. Xiao, and X. Li, “Gap-mode excitation, manipulation, and refractive-index sensing application by gold nanocube arrays,” Nanoscale 11(12), 5467–5473 (2019). [CrossRef]
12. L. Wen, L. Li, X. Yang, Z. Liu, B. Li, and Q. Chen, “Multiband and ultrahigh figure-of-merit nanoplasmonic sensing with direct electrical readout in Au-Si Nano junctions,” ACS Nano 13(6), 6963–6972 (2019). [CrossRef]
13. X. X. Wang, J. K. Zhu, X. L. Wen, X. X. Wu, Y. Wu, Y. W. Su, H. Tong, Y. P. Qi, and H. Yang, “Wide range refractive index sensor based on a coupled structure of Au nanocubes and Au film,” Opt. Mater. Express 9(7), 3079–3088 (2019). [CrossRef]
14. X. X. Wang, X. X. Wu, J. K. Zhu, Z. Y. Pang, H. Yang, and Y. P. Qi, “Theoretical investigation of a highly sensitive refractive-index sensor based on TM0 waveguide mode resonance excited in an asymmetric metal-cladding dielectric waveguide structure,” Sensors 19(5), 1187 (2019). [CrossRef]
15. M. Abutoama and I. Abdulhalim, “Self-referenced biosensor based on thin dielectric grating combined with thin metal film,” Opt. Express 23(22), 28667–28682 (2015). [CrossRef]
16. M. Abutoama and I. Abdulhalim, “Angular and intensity modes self-referenced refractive index sensor based on thin dielectric grating combined with thin metal film,” IEEE J. Sel. Top. Quantum Electron. 23(2), 72–80 (2017). [CrossRef]
17. M. W. Knight, H. H. Sob, P. Nordlander, and N. J. Halas, “Photodetection with active optical antennas,” Science 332(6030), 702–704 (2011). [CrossRef]
18. A. Sobhani, M. W. Knight, Y. Wang, B. Zhang, N. S. King, L. V. Brown, Z. Fang, P. Nordlander, and N. J. Halas, “Narrowband photodetection detection in the near-infrared with a Plasmon-induced hot electron device,” Nat. Commun. 4, 163 (2018).
19. E. C. Nice and B. Catimel, “Instrumental biosensors: new perspectives for the analysis of biomolecular interactions,” BioEssays 21(4), 339–352 (1999). [CrossRef]
20. A. E. Miroshnichenko, S. Flach, and Y. S. Kivshar, “Fano resonances in nanoscale structures,” Rev. Mod. Phys. 82(3), 2257–2298 (2010). [CrossRef]
21. L. Qin, S. Wu, J. H. Deng, L. Li, and X. Li, “Tunable light absorbance by exciting the plasmonic gap mode for refractive index sensing,” Opt. Lett. 43(7), 1427–1430 (2018). [CrossRef]
22. V. G. Kravets, F. Schedin, and A. N. Grigorenko, “Extremely narrow plasmon resonances based on diffraction coupling of localized plasmons in arrays of metallic nanoparticles,” Phys. Rev. Lett. 101(8), 087403 (2008). [CrossRef]
23. L. Qin, C. Zhang, R. Li, and X. Li, “Silicon-gold core-shell nanowire array for an optically and electrically characterized refractive index sensor based on plasmonic resonance and Schottky junction,” Opt. Lett. 42(7), 1225–1228 (2017). [CrossRef]
24. H. J. Chen and L. Z. Wang, “Nanostructure sensitization of transition metal oxides for visible-light photocatalysis,” Beilstein J. Nanotechnol. 5(1), 696–710 (2014). [CrossRef]
25. E. D. Palik, “Handbook of optical constants of solids,” Academic Press, Orlando, 1985.
26. H. Chalabi, D. Schoen, and M. L. Brongersma, “Hot-electron photodetection with a plasmonic nanostripe antenna,” Nano Lett. 14(3), 1374–1380 (2014). [CrossRef]
27. K. Wu, Y. H. Zhan, S. Wu, J. Deng, and X. Li, “Surface-plasmon enhanced photodetection at communication band based on hot electrons,” J. Appl. Phys. 118(6), 063101 (2015). [CrossRef]
28. C. Zhang, G. Cao, S. Wu, W. Shao, V. Giannini, S. A. Maier, and X. Li, “Thermodynamic loss mechanisms and strategies for efficient hot-electron photoconversion,” Nano Energy 55, 164–172 (2019). [CrossRef]
29. C. Zhang, K. Wu, Y. Zhan, V. Giannini, and X. Li, “Planar microcavity-integrated hot-electron photodetector,” Nanoscale 8(19), 10323–10329 (2016). [CrossRef]
30. R. Ortuño, C. García-Meca, F. J. Rodríguez-Fortuño, J. Martí, and A. Martínez, “Role of surface plasmon polaritons on optical transmission through double layer metallic hole arrays,” Phys. Rev. B 79(7), 075425 (2009). [CrossRef]
