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Abstract
Inspired by the growing family of Van der Waals materials, hBN supported phonon polaritons have attracted much attention due to their inherent hyperbolic dispersion properties in the mid-infrared. However, the lack of tunability imposes a severe restriction on the diversified, functional and integrated applications. Here, we propose a phase-gradient heterostructure metasurface to realize a dynamically tunable and polarization-sensitive perfect absorber in the mid-infrared through combining hBN and phase change VO2. Narrow-band perfect absorption at 7.2 µm can be switched to broadband around 11.2 µm through controlling the temperature of VO2. The governed physics of the bandwidth and absorption differences are demonstrated. Phonon polaritons in hBN phase-gradient configurations and plasmon polaritons in periodic VO2 blocks are respectively excited. We also investigate the absorption dependence on the polarization states of designed absorber. The method of engineering the absorption through controlling the temperature and polarization states opens up a new avenue for tunable applications such as data storage and integrated optical circuits.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Monocrystalline graphitic films which are a few atoms thick show stable metallic properties resulting from coherent oscillations of the free carriers by Novoselov and Geim in 2004 [1]. The hBN is chosen as an ‘ideal substrate’ for graphene, providing an amazing clean environment for graphene owing to its crystal structure, which closely matches that of graphene (∼1.8% lattice constant mismatch) [2,3]. Specifically, encapsulating graphene between two slabs of hBN increases the graphene plasmon lifetime by a factor of 5, up to 500 fs [4]. After 2014, the research on infrared nanophotonic hBN itself began in earnest. As one of the latest natural hyperbolic materials, bulk-hBN has two kinds of infrared active phonon modes, featuring spectrally distinct Reststrahlen bands and negative permittivity [5–8]. The iso-frequency surfaces obey a hyperbolic shape instead of a closed sphere for common isotropic materials. In lower Reststrahlen bands (760-825 cm-1), its in-plane permittivity is positive and the out-of-plane permittivity is negative, which is opposed to that in upper Reststrahlen bands (1360-1620 cm-1). Similar to plasmonic resonance which is usually excited in graphene [9,10], surface phonon polaritons are supported in hBN according to the previous researches with various shapes such as turriform [11], trapezoid [12], rectangle [13], and disk [14]. Zhou team found the nearly perfect absorption with high quality factor resulting from the impedance of the absorber matches to that of free space in the structure composed of hBN and the silver back reflector layer separated by insulative CaF2 [15]. In fact, the in-plane phonon absorption is easy to be enhanced with a Fabry–Pérot cavity. However, the traditional way to modulate the optical devices by changing the structural parameters imposes a restriction on the applications.
Active, tunable, or reconfigurable materials have been found as important building blocks in designing metamaterials with modifiable optical responses. These facts invoke a natural curiosity about the properties and possible applications of multilayer heterojunction structure. The gate tunability of graphene plasmons can be combined with the high confinement property of hBN supported phonon polaritons, contributing to the new metamaterials that marry the unique qualities of the two [16–18]. However, the requiring of external voltage and limited tuning range in graphene is pretty complicated compared with the temperature-controlled phase change system.
The phase change materials undergo Mott transition of the composite atom array between insulator-to-conductor states upon an appropriate stimulus, like thermal, optical, or electrical [19–21]. Vanadium dioxide (VO2) switches between its insulator to metallic phase at Tc = 340 K [22], thus rendering it highly attractive for applications requiring reversible switching physical properties. Generally, temperature-controlled absorption can be achieved in plasmonic resonance or magnetic resonance metamaterial based on VO2 [23,24]. The researches combining VO2 with graphene have achieved tunable polarization sensitive wideband absorption in THz [25,26]. VO2 conformal resonators are also realized with controllable dual-band absorption in infrared [27]. Besides, high contrast switching ability of VO2 based metamaterial absorbers with ITO ground plane can switch transmission light to a highly reflecting state for infrared light by heating the metamaterial [28]. VO2-hBN-graphene-based bi-functional metamaterial for mid-infrared have obtained bi-tunable asymmetric transmission and nearly perfect resonant absorption [29]. Heterostructure combined of hBN and VO2 has high tunability and easy modulation [30–35]. The combination of VO2 and hBN has many possibilities especially in constructing a simple and diverse dynamic tunable perfect absorber in mid-infrared.
Conventional metasurface-based absorbers are mainly in the form of periodic arrays with uniform meta-cells. There is no further light manipulation like phase change within a super period [36]. The absorption generally originates from the vertical or lateral plasmonic resonances. However, the advent of phase gradient metasurface provides an additional degree of freedom to enhance the light-matter interaction. The gradient metasurface introduces a unidirectional phase gradient dΦ/dx along the surface and has been used to demonstrate the generalized Snell’s laws [37]. This gives us an opportunity to couple the propagation wave in free space into surface wave supported by the structure and enhance the absorption.
Here, we propose a mid-infrared tunable perfect absorber based on phase gradient metasurface with hBN/VO2 heterostructure. Upper reststrahlen band phonon polaritons in hBN and plasmon polaritons in VO2 are respectively excited when changing the temperature. The polarization dependent property of the absorber is also investigated before and after the VO2 phase transition.
2. Results and discussions
Figure 1 illustrates the heterostructure of phase gradient metasurface, which consists of hBN patches and periodic VO2 blocks on a thin silicon film (ɛ = 11.7) [38]. The simulation is conducted with the wave optics module in Comsol. The optical properties of hBN and VO2 materials are derived from [39,40]. The permittivity of hBN is approximated with a Drude-Lorentz model:
Fig. 1. Schematics of the mid-infrared hBN/VO2 heterostructure and the phase of each unit cell. (a) Illustration of the metasurface which is composed of subwavelength hBN patches and VO2 blocks. (b) The unit cell structure with a hBN patch and VO2 block on top of the silicon layer and gold substrate. (c) The phase of each unit in electric field E//Ex and E//Ey.
To realize phase gradient, it’s necessary to realize 2π phase coverage with meta-cells. The phase change as function of meta-cell number is shown as Fig. 1(c). The additional wave vector provided by the metasurface can be determined by the number of meta-cells according to the expression ka = 2π/Lx, where Lx is the super period and can be adjusted by the meta-cells’ number. We want to mention that the phase change of each meta-cell should be evenly picked to increase the coupling efficiency. At the condition that the sum of ka and transverse component of wave vector in free space matches with the vector of surface wave, the incident light can be converted into surface waves. In this paper, the number is chosen as 12. For normal incidence along x polarization at 7.2 µm, the phase gradient is ξ = 2π/Lx = 1.167k0, where k0 is the wave vector in free space. Besides, at T < Tc the phonon polariton is also excited with matched phase condition.
With the designed structure, we calculate the absorption spectra at different normal incident polarization states with temperatures under and above the critical point of VO2 in mid-infrared. As shown in Fig. 2, perfect absorptions are achieved at 7.2 µm, 7.37 µm for x- and y-polarized incidence at T < Tc, respectively. The change of polarization state results in a 170 nm shift of the absorption peak. The full width at half maximums (FWHM) of absorption are 0.2 µm and 0.4 µm, respectively. However, at T > Tc the absorption peaks move to 10.8 µm and 12 µm for x- and y-polarized incidence, respectively. Besides, we want to emphasize that the FWHMs (∼4 µm) for both polarization states are much larger than those at T < Tc. The polarization states lead to a 1.2 µm absorption peak shift.
Fig. 2. The absorption spectra of the designed structure for normal incidence at different polarization states. The absorptions at T < Tc (a) and T > Tc (b).
In order to reveal the underlying physics behind the absorption behaviors shown in Fig. 3, we calculate and illustrate the phase change profiles and the electric field distributions at absorption peaks for the metasurface for x- and y-polarizations at T < Tc in Fig. 3. As shown in Fig. 3(a), 2π phase coverage and gradually changed phase profile is achieved at x-polarization state. Since the period of meta-cell is 6 µm which is subwavelength compared with the absorption wavelength, the normally incident light will be compensated with an additional wave vector provided by the metasurface and converted in the form of surface wave which propagates at the interface of air and heterostructure from the point view of transverse momentum conservation. The envelop of Ex distributions at x-z cross section shown in Fig. 3(b) confirms the surface wave generation (see Visualization 1). What’s more, a zigzag field pattern in the hBN layer is observed as the inset shown, which we believe it is the phonon polaritons profile. Phonon polaritons are excited and exist in the form of multiple reflections at the top and bottom corners of the hBN edge before it is absorbed. To clarify the role of phase gradient metasurface in the absorption enhancement, the electric filed distributions of periodic structures without phase gradient design is shown in Fig. 3(c). It can be seen that neither the surface wave envelops nor the zigzag phonon polaritons are observed. The absorption of this period structure is only 0.31, which is much less than that with phase gradient metasurface.
Fig. 3. The characterizations of the perfect absorptions at T < Tc. Phase distributions of the designed heterostructure with x-polarized (a) and y-polarized (d) incidence. Electric field Ex distributions at absorption peaks for x-polarized (b) and Ey distributions for y-polarized (e) incidence. The figures show two meta-cells for demonstration. (c) and (f) show the electric field profiles for periodic structures without phase gradient arrangement for comparison. The structural parameters of hBN used in the (c) and (f) calculations are 95 nm and 410 nm in length and width.
For y-polarized incidence, the phase change profile of the metasurface is shown in Fig. 3(d). Different from that in Fig. 3(a), the phase has a rapid change of π over one super period. However, this can be regarded as 1-bit coding metasurface, where we define the first six units as “0” and the last six units as “1”. A metasurface with “0101” in sequence is achieved. This coding metasurface can also convert the normal incidence into surface wave with the same mechanism demonstrated in Fig. 3(a). This is confirmed by the electric field Ey distribution in Fig. 3(e) (see Visualization 2). The envelope period is in well agreement with the absorption peak 7.37 µm for y-polarization. Here we want to mention that there is no phonon polaritons existence, which is different from that in Fig. 3(b). With the simulation results, the absorption originates from the intrinsic dielectric loss of hBN but not in the form of polaritons. One similarity for both cases is that the incident light is coupled into surface wave with the phase gradient metasurface and absorbed by the hBN. The absorption peaks are relatively narrow with FWHMs less than 0.5 µm. Corresponding to different incident polarization states, the type of phase gradient is different: one for gradually changing and the other abruptly. This leads to the difference at absorption peak position and offers a way for the polarization-controlled absorption at T < Tc.
Normally incident light is compensated with an additional wave vector and coupled in the form of surface wave that propagates along the metasurface. To some extent, the phase gradient metasurface provides another interaction channel for the light and structure compared with those periodic structures composed of uniformly meta-cells. As shown in Figs. 3(c) and 3(f), the absorption efficiency is only about 0.3. The phase gradient metasurface enhances the efficiency more than three times to perfect absorption.
At T > Tc, the VO2 has a phase transition from dielectric to metal and the imaginary part of the permittivity changes dramatically. This results in a totally distinct absorption mechanism compared with that at T < Tc. In order to demonstrate the physics behind the broadband absorption in Fig. 2(b), we calculate the electric field distributions of heterostructure metasurface for different polarization states in Fig. 4. It can be seen that the most energy is localized at the edge of VO2 for both polarizations at x-z and y-z cross sections. Similar to conventional plasmonic nanostructures, the field profiles are obvious dipole-like resonances. The dipole resonance is formed by a positive and negative charge at both ends of the meta-cell which is in consistence with the incident polarization state. From the distribution of electric field in Fig. 4, it is clearly shown that the electric field is alternately positive and negative in a meta-cell period. This is in coincidence with dipole resonance. The broad FWHMs of absorption peaks also confirm the plasmonic feature. Through changing of the incident polarization states, the absorption peak has a large shift from 10.8 µm for x-polarization to 12 µm for y-polarization. Due to the structural size difference along x and y directions, the polarization leads to a 1.2 µm shift of absorption peak.
Fig. 4. Electric field distribute at wavelength of 10.8 µm (a) and 12 µm (b) for different polarization states at T > Tc.
It’s straightforward to have further consideration on the experimental feasibility. As to the proposed structure, the bottom gold and silicon layers can be deposited with accurate thickness through electron beam evaporation [42] or sputtering methods [43]. The VO2 array with minimum feature size 95nm can be realized with magnetron sputtering [44] or atomic layer deposition [45] after the etching of silicon using dry etching method with inductively coupled plasma [46] or reactive ion [47]. Before the etching electron beam lithography with thin photoresist like ZEP 520 or ma_N2400 series should be used to generate the predefined metasurface pattern. At the same time the marks which is used to align with hBN particles should be prepared. Afterwards, hBN pattern can be defined with electron beam lithography and deposited with sputtering [48] or chemical vapor deposition [49]. Finally, the prepared marks help to align the hBN and VO2 particles.
The alignment will introduce the displacement between the two patterns. To evaluate the alignment influence on the absorption performance, we calculate the absorptions with different displacement along x and y directions as shown in Fig. 5. It can be seen that there is little change on the absorption peaks and efficiencies for misalignment within 50 nm. Thus, it is safe to conclude that the proposed structure can be flexibly fabricated and robustly performed.
Fig. 5. The absorption in misalignment condition at T < Tc. (a) The absorption with 30 nm, 60 nm, 90 nm misalignment in x axis for hBN layer in x polarization and y polarization. (b) The absorption with 30 nm, 60 nm, 90 nm misalignment in y axis for hBN layer.
Taking advantage of the phase gradient metasurface, polarization dependent perfect absorptions are achieved. For data storage or related integrated optical circuits which need to be written or read out in infrared for security consideration, VO2 is an excellent candidate since its phase transition is temperature dependent. The absorption peaks can be adjusted through the metasurface design. Besides, hBN also have phonon absorptions in mid-infrared. The structure also promises applications like infrared stealth or protection layer which is sensitive to the incident energy if the structure is preset around the phase transition point of VO2. The polarization dependence property provides an additional channel for reflection. However, there are some challenges that impose some limitations on the practical applications, such as the conformal and large area fabrication of metasurface and the preset temperature conditions.
3. Conclusion
In conclusion, a controllable polarization and temperature sensitive perfect absorber consisting of hBN/VO2 phase-gradient heterojunction has been proposed. demonstrated. based on plasmon polaritons and hyperbolic phonon polaritons. At T < Tc of VO2 for both polarization states, incident light is coupled and localized along the interface of air and metasurface. Two different phase gradients metasurface is realized. Phonon polaritons and intrinsic loss of hBN accounts for the two perfect absorptions at 7.2 µm and 7.37 µm, respectively. However, for metallic VO2 the absorption peaks have position shifts to 10.8 µm for x-polarization and 12 µm for y-polarization. Dipole-like plasmonic resonances are achieved. Our design realized perfect absorption at multiple wavelengths and can be controlled with different temperatures and polarizations. This tunable absorber in mid-infrared may find applications in infrared sensing, thermal imaging and thermal-protective coating.
Funding
Shanghai Municipal Science and Technology Major Project (2019SHZDZX01); Science and Technology Commission of Shanghai Municipality (18JC1420401, 20JC1416000); Shanghai Rising-Star Program (20QA1410400); Strategic Priority Research Program of Chinese Academy of Sciences (XDB43010200); Key Research Program of Frontier Science, Chinese Academy of Sciences (QYZDJSSWJSC007); Youth Innovation Promotion Association of the Chinese Academy of Sciences (2017285); National Natural Science Foundation of China (61521005, 61705249, 61874126, 61875218, 61991440, 91850208); National Key Research and Development Program of China (2017YFA0205800, 2018YFA0306200).
Acknowledgments
This work was partially carried out at the Center for Micro and Nanoscale Research and Fabrication in University of Science and Technology of China.
Disclosures
The authors declare that there are no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, “Electric Field Effect in Atomically Thin Carbon Films,” Science 306(5696), 666–669 (2004). [CrossRef]
2. A. Giacomo, M. Andreas, R. A. M. Mohammad, C. Yang, J. P. Timothy, M. Clemens, K. Christian, K. Jani, K. G. Andre, and J. C. Meyer, “Unraveling the 3D Atomic Structure of a Suspended Graphene/hBN van der Waals Heterostructure,” Nano Lett. 17(3), 1409–1416 (2017). [CrossRef]
3. C. R. Dean, A. F. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, K. Watanabe, T. Taniguchi, P. Kim, K. L. Shepard, and J. Hone, “Boron Nitride Substrates for High-Quality Graphene Electronics,” Nat. Nanotechnol. 5(10), 722–726 (2010). [CrossRef]
4. A. Woessner, M. Lundeberg, Y. Gao, A. Principi, P. Alonso-González, M. Carrega, K. Watanabe, T. Taniguchi, G. Vignale, M. Polini, J. Hone, R. Hillenbrand, and F. H. L. Koppens, “Highly confined low-loss plasmons in graphene–boron nitride heterostructures,” Nat. Mater. 14(4), 421–425 (2015). [CrossRef]
5. T. Low, A. Chaves, J. Caldwell, A. Kumar, N. X. Fang, P. Avouris, T. F. Heinz, F. Guinea, L. Martin-Moreno, and F. Koppens, “Polaritons in layered two-dimensional materials,” Nat. Mater. 16(2), 182–194 (2017). [CrossRef]
6. P. Li, P. Dolado, F. J. Alfaro-Mozaz, A. Y. Nikitin, F. Casanova, L. E. Hueso, S. Velez, and R. Hillenbrand, “Optical nanoimaging of hyperbolic surface polaritons at the edges of van der waals materials,” Nano Lett. 17(1), 228–235 (2017). [CrossRef]
7. S. Dai, Z. Fei, Q. Ma, A. S. Rodin, M. Wagner, A. S. McLeod, M. K. Liu, W. Gannett, W. Regan, K. Watanabe, T. Taniguchi, M. Thiemens, G. Dominguez, A. H. Castro-Neto, A. Zettl, F. Keilmann, P. Jarillo-Herrero, M. M. Fogler, and D. N. Basov, “Tunable Phonon Polaritons in Atomically Thin van der Waals Crystals of Boron Nitride,” Science 343(6175), 1125–1129 (2014). [CrossRef]
8. J. Caldwell, A. Kretinin, Y. Chen, V. Giannini, M. M. Fogler, Y. Francescato, C. T. Ellis, J. G. Tischler, C. R. Woods, A. J. Giles, M. Hong, K. Watanabe, T. Taniguchi, S. A. Maier, and K. S. Novoselov, “Sub-diffractional volume-confined polaritons in the natural hyperbolic material hexagonal boron nitride,” Nat. Commun. 5(1), 5221 (2014). [CrossRef]
9. A. Andryieuski and A. V. Lavrinenko, “Graphene metamaterials based tunable terahertz absorber: effective surface conductivity approach,” Opt. Express 21(7), 9144–9155 (2013). [CrossRef]
10. Z. Fei, G. O. Andreev, W. Bao, L. M. Zhang, A. S. McLeod, C. Wang, M. K. Stewart, Z. Zhao, G. Dominguez, M. Thiemens, M. M. Fogler, M. J. Tauber, A. H. Castro-Neto, C. N. Lau, F. Keilmann, and D. N. Basov, “Infrared nanoscopy of Dirac plasmons at the graphene-SiO2interface,” Nano Lett. 11(11), 4701–4705 (2011). [CrossRef]
11. J. C. G. Henriques, G. B. Ventura, C. D. M. Fernandes, and N. M. R. Peres, “Optical absorption of single-layer hexagonal boron nitride in the ultraviolet,” J. Phys.: Condens. Matter 32(2), 025304 (2020). [CrossRef]
12. L. Xu, B. Peng, X. Luo, X. Zhai, and L. Wang, “A broadband and polarization-insensitive perfect absorber based on a van der Waals material in the mid-infrared regime,” Results Phys. 15, 102687 (2019). [CrossRef]
13. M. Autore, P. Li, I. Dolado, F. Alfaro-Mozaz, R. Esteban, A. Atxabal, F. Casanova, L. Hueso, P. Alonso-González, and J. Aizpurua, “Boron nitride nanoresonators for phonon-enhanced molecular vibrational spectroscopy at the strong coupling limit,” Light: Sci. Appl. 7(4), 17172 (2018). [CrossRef]
14. M. Tamagnone, A. Ambrosio, K. Chaudhary, L. A. Jauregui, P. Kim, W. L. Wilson, and F. Capasso, “Ultra-confined mid-infrared resonant phonon polaritons in van der Waals nanostructures,” Sci. Adv. 4(6), eaat7189 (2018). [CrossRef]
15. Y. Zhou and J. J. Wang, “High-Q Localized Phonon Polaritons in Thin hBN Discs with Omnidirectional Strong Light Absorptions,” Plasmonics 14(6), 1855–1861 (2019). [CrossRef]
16. A. Sayem, M. Rahman, M. Mahdy, I. Jahangir, and M. Rahman, “Negative Refraction with Superior Transmission in Graphene-Hexagonal Boron Nitride (hBN) Multilayer Hyper Crystal,” Sci. Rep. 6(1), 25442 (2016). [CrossRef]
17. A. Kumar, T. Low, K. H. Fung, P. Avouris, and N. X. Fang, “Tunable Light–Matter Interaction and the Role of Hyperbolicity in Graphene–hBN System,” Nano Lett. 15(5), 3172–3180 (2015). [CrossRef]
18. H. Hodjat, G. Amir, B. Bayram, and O. Ekmel, “Tunable, omnidirectional, and nearly perfect resonant absorptions by a graphene-hBN-based hole array metamaterial,” Opt. Express 26(13), 16940–16954 (2018). [CrossRef]
19. J. Rensberg, S. Zhang, Y. Zhou, A. S. Mcleod, and M. A. Kats, “Active optical metasurfaces based on defect-engineered phase-transition materials,” Nano Lett. 16(2), 1050–1055 (2016). [CrossRef]
20. H. Zhang, L. Zhou, J. Xu, N. Wang, H. Hu, L. Lu, B. M. A. Rahman, and J. Chen, “Nonvolatile waveguide transmission tuning with electrically-driven ultra-small GST phase-change material,” Sci. Bull. 64(11), 782–789 (2019). [CrossRef]
21. H. Zheng and L. K. Wagner, “Computation of the Correlated Metal-Insulator Transition in Vanadium Dioxide from First Principles,” Phys. Rev. Lett. 114(17), 176401 (2015). [CrossRef]
22. F. J. Morin, “Oxides Which Show a Metal-to-Insulator Transition at the Neel Temperature,” Phys. Rev. Lett. 3(1), 34–36 (1959). [CrossRef]
23. Q. E. Wen, H. W. Zhang, Q. H. Yang, Z. Chen, Y. Long, Y. L. Jing, Y. Lin, and P. X. Zhang, “A tunable hybrid metamaterial absorber based on vanadium oxide films,” J. Phys. D: Appl. Phys. 45(23), 235106–235110 (2012). [CrossRef]
24. Y. Zhao, Q. Huang, H. Cai, X. Lin, and Y. Lu, “A broadband and switchable VO2 - based perfect absorber at the THz frequency,” Opt. Commun. 426, 443–449 (2018). [CrossRef]
25. H. Li and J. Yu, “Metal-VO2 hybrid grating structure for a terahertz active switchable linear polarizer,” Opt. Express 28(17), 25225–25337 (2020). [CrossRef]
26. H. Li, W. Xu, Q. Cui, Y. Wang, and J. Yu, “Theoretical design of a reconfigurable broadband integrated metamaterial terahertz device,” Opt. Express 28(26), 40060–40074 (2020). [CrossRef]
27. J. Yang, S. Qu, H. Ma, J. Wang, and Y. Pang, “Dual-band tunable infrared metamaterial absorber with VO2 conformal resonators,” Opt. Commun. 402, 518–522 (2017). [CrossRef]
28. J. K. Pradhan, S. A. Ramakrishna, B. Rajeswaran, A. M. Umarji, V. G. Achanta, A. K. Agarwal, and A. Ghosh, “High contrast switchability of VO2 based metamaterial absorbers with ITO ground plane,” Opt. Express 25(8), 9116–9121 (2017). [CrossRef]
29. H. Hajian, A. Ghobadi, A. E. Serebryanniko, B. Butun, G. A. E. Vandenbosch, and E. Ozbay, “VO2-hBN-graphene-based bi-functional metamaterial for mid-infrared bi-tunable asymmetric transmission and nearly perfect resonant absorption,” J. Opt. Soc. Am. B 36(6), 1607–1615 (2019). [CrossRef]
30. T. G. Folland, A. Fali, S. T. White, J. R. Matso, S. Liu, N. A. Aghamiri, J. H. Edga, R. F. Haglund, Y. Abate, and J. D. Caldwell, “Reconfigurable infrared hyperbolic metasurfaces using phase change materials,” Nat. Commun. 9(1), 4371 (2018). [CrossRef]
31. S. Dai, J. Zhang, Q. Ma, S. Kittiwatanakul, A. McLeod, X. Chen, S. G. Corder, K. Watanabe, T. Taniguchi, J. Lu, Q. Dai, P. Jarillo-Herrero, M. Liu, and D. N. Basov, “Phase-Change Hyperbolic Heterostructures for Nanopolaritonics: A Case Study of hBN/VO2,” Adv. Mater. 31(18), 1900251 (2019). [CrossRef]
32. S. Genchi, M. Yamamoto, K. Shigematsu, S. Aritomi, R. Nouchi, T. Kanki, K. Watanabe, T. Taniguchi, Y. Murakami, and H. Tanaka, “Growth of vanadium dioxide thin films on hexagonal boron nitride flakes as transferrable substrates,” Sci. Rep. 9(1), 2857 (2019). [CrossRef]
33. S. T. White, A. Fali, T. G. Folland, J. D. Caldwell, Y. Abate, and R. F. Haglund, “Interactions of Hexagonal Boron Nitride with the Insulator-Metal Phase Transition of Vanadium Dioxide,” Frontiers in Optics / Laser Science, OSA Technical Digest, paper FW5E.3 (2018).
34. X. Song, Z. Liu, J. Scheuer, Y. Xiang, and K. Aydin, “Tunable polaritonic metasurface absorbers in Mid-IR based on hexagonal boron nitride and vanadium dioxide layers,” J. Phys. D: Appl. Phys. 52(16), 164002 (2019). [CrossRef]
35. C. Peng, K. Ou, G. Li, X. Li, W. Wang, Z. Zhao, X. Li, X. Chen, and W. Lu, “Tunable phase change polaritonic perfect absorber in the mid-infrared region,” Opt. Express 28(8), 11721–11729 (2020). [CrossRef]
36. K. Arik, S. Abdollahramezani, S. Farajollahi, A. Khavasi, and B. Rejaei, “Design of mid-infrared ultra-wideband metallic absorber based on circuit theory,” Opt. Commun. 381, 309–313 (2016). [CrossRef]
37. S. Sun, Q. He, S. Xiao, Q. Xu, X. Li, and L. Zhou, “Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves,” Nat. Mater. 11(5), 426–431 (2012). [CrossRef]
38. M. Desouky, A. M. Mahmoud, and M. A. Swillam, “Silicon based mid-IR super absorber using hyperbolic metamaterial,” Sci. Rep. 8(1), 2036 (2018). [CrossRef]
39. F. J. Alfaro-Mozaz, P. Alonso-González, S. Vélez, I. Dolado, M. Autore, S. Mastel, F. Casanova, L. E. Hueso, P. Li, A. Y. Nikitin, and R. Hillenbrand, “Nanoimaging of resonating hyperbolic polaritons in linear boron nitride antennas,” Nat. Commun. 8(1), 15624 (2017). [CrossRef]
40. L. Yang, P. Zhou, T. Huang, G. Zhen, L. Zhang, L. Bi, X. Weng, J. Xie, and L. Deng, “Broadband thermal tunable infrared absorber based on the coupling between standing wave and magnetic resonance,” Opt. Mater. Express 7(8), 2767–2776 (2017). [CrossRef]
41. M. A. Ordal, R. J. Bell, R. W. A. Jr, L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V, and W,” Appl. Opt. 24(24), 4493–4499 (1985). [CrossRef]
42. C. Becker, T. Sontheimer, S. Steffens, S. Scherf, and B. Rech, “Polycrystalline silicon thin films by high-rate electronbeam evaporation for photovoltaic applications–influence of substrate texture and temperature,” Energy Procedia 10(39), 61–65 (2011). [CrossRef]
43. T. J. Colla, R. Aderjan, R. Kissel, and H. M. Urbassek, “Sputtering of Au (111) induced by 16-keV Au cluster bombardment: Spikes, craters, late emission, and fluctuations,” Phys. Rev. B 62(12), 8487–8493 (2000). [CrossRef]
44. C. Ba, S. T. Bah, M. D. Auteuil, P. V. Ashrit, and R. Vallée, “Fabrication of High-Quality VO2 Thin Films by Ion-Assisted Dual ac Magnetron Sputtering,” ACS Appl. Mater. Interfaces 5(23), 12520–12525 (2013). [CrossRef]
45. D. Lee, D. Yang, H. Kim, J. Kim, S. Song, K. S. Choi, J. S. Bae, J. Lee, J. Lee, Y. Lee, J. Yan, J. Kim, and S. Park, “Deposition-Temperature-Mediated Selective Phase Transition Mechanism of VO2 Films,” J. Phys. Chem. C 124(31), 17282–17289 (2020). [CrossRef]
46. M. R. Rakhshandehroo, J. W. Weigold, W. C. Tian, and S. W. Pang, “Dry etching of Si field emitters and high aspect ratio resonators using an inductively coupled plasma source,” J. Vac. Sci. Technol., B: Microelectron. Process. Phenom. 16(5), 2849 (1998). [CrossRef]
47. H. X. Qian, W. Zhou, J. Miao, L. Lim, and X. R. Zeng, “Fabrication of si microstructures using focused ion beam implantation and reactive ion etching,” J. Micromech. Microeng. 18(3), 035003 (2008). [CrossRef]
48. Q. Li, X. Qin, Q. Zhang, Y. Bai, H. Tang, C. Hu, S. Shen, Y. Li, and F. Yun, “Resistance switching behaviors of continuous-thick hBN films fabricated by radio-frequency-sputtering,” J. Mater. Res. 35(23-24), 3247–3256 (2020). [CrossRef]
49. S. Sinha, Y. Takabayashi, H. Shinohara, and R. Kitaura, “Simple fabrication of air-stable black phosphorus heterostructures with large-area hbn sheets grown by chemical vapor deposition method,” 2D Mater. 3(3), 035010 (2016). [CrossRef]
