Omnidirectional Absorber by the Void Plasmon Effect in the Visible Region with Greatly Enhanced Localized Electric Field
- 104 Downloads
We propose and investigate a wide-angle and high-efficiency absorber by using the void plasmon (VP) effect in a Fabry–Perot (FP)-like system, which consists of a perforated metal film and a ground metal plane separated by a dielectric spacer. A hybrid FP/VP resonance mode contributes to the high absorption efficiency. Besides the increased absorption, greatly enhanced localized electric-field intensity at “hot spots” (~ 2284 times) can be achieved. In addition, by varying the thickness of the perforated metal layer and the environmental refractive index, the position of resonance peak can be easily controlled. The proposed absorber can also work as a sensor for detecting the surrounding dielectric constant with the maximum value of the figure of merit (FOM) achieving 3.16 in theory. This work creates an alternative design for high-efficiency absorption devices.
KeywordsAbsorbers Plasmonics Fabry–Perot resonance Void plasmons
Figure of merit
Localized surface plasmons
Perfectly matched layer
Propagating surface plasmons
Surface plasmon resonance
Surface plasmon resonance (SPR), which is the coherent oscillations of electrons at the interfaces of noble metals and dielectric materials, is able to enhance the light absorption efficiency of noble metals . Nowadays, the SPR-based absorbers have been widely researched with various plasmonic systems, including arrays of gratings [2, 3, 4, 5, 6, 7, 8, 9], metallic nanoparticles [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21], and nanoholes in metal films [22, 23, 24, 25]. By changing the geometrical and physical parameters such as the shape, size, and material of structures as well as the dielectric environment, the absorption properties in the visible region can be effectively controlled and improved. In general, propagating surface plasmons (PSPs) and localized surface plasmons (LSPs) are belonging to SPR. Metallic nanoparticles are usually in company with the LSPs effect, while the perforations on the metallic film can induce both the PSPs effect and the void plasmon (VP) effect. The VPs are one type of LSPs associated with nanohole structures, which can sustain an electromagnetic dipole resonance akin to that of metallic nanoparticles [26, 27]. The PSPs effect in nanohole array-based absorbers can not only eliminate the drawbacks of polarization sensitivity in one-dimensional metallic grating-based absorbers, but also realize nearly perfect absorption at the same wavelength in the visible region using a larger feature size of nanopatterns compared to nanoparticle-array-based devices. Considering the above advantages, the absorption mechanism of the PSPs effect in nanohole array structures has been widely investigated and reported [22, 23, 24, 25]. However, the PSP effect-induced absorption is very sensitive to the incident angle due to its inherent mechanism , which reduces the whole absorption efficiency in absorbers. In contrast, the VP effect-induced absorption is insensitive to the angle and the polarization of incident light. Meanwhile, as it is sensitive to the surrounding dielectric constant, the position of resonant absorption peak can be tuned via changing environmental materials, showing the potential for differentiating the refractive index of surrounding materials. Thus, a systematic study on the VP effect is very meaningful [25, 29, 30, 31, 32]. Nonetheless, the VP-induced absorption efficiency is usually lower than that achieved with other effects, e.g., the Fabry–Perot (FP) effect in a metal-insulator-metal (MIM) structure.
In this paper, a wide-angle and highly efficient absorber, consisting of a perforated metal film and a ground metal plane separated with a dielectric layer, has been systematically studied. The combination and interplay of FP resonance in the spacer and the VP effect in the nanoholes give rise to absorption efficiency as high as 99.8%. Furthermore, the VP effect-induced absorption peak is controllable by modifying structural or physical parameters such as the perforated metallic film thickness, the period of the nanohole arrays, and the environmental refractive index. In addition, the position of the resonance wavelength is insensitive to the edge length of the square nanohole and the incident angle of light. It is worthy of mentioning that the proposed device could also work as a sensor detecting the environmental refractive index, where a figure of merit (FOM) of 3.16 (which is compatible with that of conventional metal nanoparticles [33, 34]) can be obtained. The results presented in this work could enlarge the scope of the absorption mechanism and may provide a new way for designing absorbers that have potential applications in such as solar cells, photodetectors, and thermal emitters.
Results and Discussion
The geometric effect of the nanoholes on the VP properties is also calculated. In Fig. 5c, the period of hole lattice p is fixed at 200 nm and the hole width w is changed from 50 to 150 nm. For FP absorption peaks, when w increases, the first-order mode resonance at 1113 nm shows a redshift, while the position of the second-order mode at 546 nm and the third-order mode at 372 nm almost remain unchanged. In addition, a redshift of the VP effect is also witnessed with the increase of w, as the electrons will experience a longer time when oscillating between two sides of the void (when the hole width w is larger enough, near-field coupling between two voids will be present as well ). In Fig. 5d, the effect of the lattice period on absorption properties of the VP effect is plotted. Here, w is fixed at 60 nm and p changes from 100 to 500 nm. For FP resonance absorption peaks, when p increases, the first-order resonance mode at 1113 nm shows a redshift when p is smaller than 200 nm and remains unchanged when p is larger than 200 nm. The redshift for the smaller p (p < 200 nm) is due to variation of effective medium refractive index of the top layer with p (or aspect ratio w2/p2). But, when p is larger than 200 nm, the effective medium refractive index is rarely affected by the small pore size. The second-order resonance mode at 546 nm and the third-order resonance mode at 372 nm show no shift when p changes. For the second FP mode, when p is larger than 300 nm, multiple emerged narrow absorption peaks will be present, which can be attributed to the PSPs effect. When the VP absorption peak (~ 635 nm) is concerned, a redshift is observed and the absorption efficiency becomes smaller as p grows. A similar phenomenon was also observed for absorbers based on the nanoparticle array and the redshift originates from a long-range dipole interaction . Furthermore, we also find that the strong coupling of the VP resonance may inhibit the nearby FP effect. This phenomenon is observed in the situation where w is above 100 nm or p is smaller than 150 nm, as revealed in Fig. 5c and d. In general, a redshift of the VP absorption peak is in company with the increase of w or p.
In conclusion, we have systematically studied the VP effect in the nanohole-array-based tri-layer absorber using the FDTD method. By the VP effect, high absorption efficiency up to 99.8% and strongly boosted electric-field intensity (enhanced by 2284 times) can be achieved at the resonance wavelength. The high absorption efficiency is also benefited from the hybridization between the FP and VP mode. With the simulation, the intensity of the VP effect to light polarization and incident angle is proved, and the dependence of VP effect on the structural parameters is also investigated. Furthermore, the VP mode owns a maximal FOM value of 3.16, which may be useful for constructing the plasmonic sensors for detecting the environmental dielectric constant. The systematic study presented in this paper highlights the void of the absorption mechanism based on the VP effect and proposes a new design for high efficiency and multifunctional absorbers.
The authors thank Wenbin Ye and Wanlin Wang for fruitful discussion.
National Natural Science Foundation of China (Grant No. 61805160, 61704109), Natural Science Foundation of Guangdong Province (Grant No. 2017A030310325), the Key Project Department of Education of Guangdong Province (Grant No. 2016KQNCX146), Natural Science Foundation of SZU (Grant No. 2017009), Natural Science Foundation of SZU (Grant No. 2018047) and the Department of Education of Guangdong Province (Grant No. 2017KTSCX160).
Availability of Data and Materials
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
SS drafted the manuscript simulated results. MZ and YY discussed and analyzed the simulated results. CH revised the manuscript and discussed the simulated results. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
- 14.Watts CM, Liu X, Padilla WJ (2012) Metamaterial electromagnetic wave absorbers. Adv Mater 24:OP98–OP120Google Scholar
- 42.Liu Z, Shao H, Liu G, Liu X, Zhou H, Hu Y, Zhang X, Cai Z, Gu G (2014) λ 3/20000 plasmonic nanocavities with multispectral ultra-narrowband absorption for high-quality sensing. Appl Phys Lett 104:081116Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.