Vacuum Ultraviolet Light-Generating Metasurface - Nano Letters (ACS

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Vacuum Ultraviolet Light-Generating Metasurface Michael Semmlinger, Ming Lun Tseng, Jian Yang, Ming Zhang, Chao Zhang, Wei-Yi Tsai, Din Ping Tsai, Peter Nordlander, and Naomi J. Halas Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b02346 • Publication Date (Web): 01 Aug 2018 Downloaded from http://pubs.acs.org on August 4, 2018

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Vacuum Ultraviolet Light-Generating Metasurface Michael Semmlinger,1,2 Ming Lun Tseng,3,4 Jian Yang,2,5 Ming Zhang,2,5 Chao Zhang,1,2 Wei-Yi Tsai,3,4 Din Ping Tsai,3,4 Peter Nordlander,1,2,5 and Naomi J. Halas1,2,5,6* 1

Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, United States. 2

Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, United States. 3

Research Center for Applied Sciences, Academia Sinica, Taipei 115, Taiwan. 4

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Department of Physics, National Taiwan University, Taipei 10617, Taiwan.

Department of Physics and Astronomy, Rice University, Houston, Texas 77005, United States. 6

Department of Chemistry, Rice University, Houston, Texas 77005, United States. *Corresponding Author: Naomi J. Halas, E-mail: [email protected]

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ABSTRACT Vacuum ultraviolet (VUV) light has important applications in many fields, ranging from device fabrication to photochemistry, from environmental remediation to microscopy and spectroscopy. Methods to produce coherent VUV light frequently utilize high harmonic generation in media such as rare gases or atomic vapors; nonlinear optical crystals that support second harmonic generation into the VUV are quite rare. Here, we demonstrate an all-dielectric metasurface designed for the nonlinear optical generation of VUV light. Consisting of an array of zinc oxide nanoresonators, the device exhibits a magnetic dipole resonance at a wavelength of 394 nm. When excited with ultrafast laser pulses at this wavelength, the second harmonic at 197 nm is readily generated. Manipulation of the metasurface design enables control over the radiation pattern. This work has the potential to open the door towards simple and compact VUV sources for new applications.

KEYWORDS: Second harmonic generation, vacuum ultraviolet, VUV, magnetic dipole, all-dielectric metasurface, nonlinear metasurface, zinc oxide, ZnO


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Vacuum ultraviolet (VUV) light -in the wavelength regime between 100 nm and 200 nm- has many current and potential research and technological applications. For example, it can be used to study the electronic structure of crystals1 or to analyze chemical reaction mechanisms2. Coherent VUV light has been produced using high harmonic generation in gases3-5 and also in solids.6, 7 Other methods include excimer lasers,8 free electron lasers,9 and supercontinuum generation in photonic crystal fibers.10 While these methods all have their specific advantages and uses, there is a need for a simple and robust way to generate and manipulate coherent VUV light. Conventional nonlinear crystals such as β-BaB2O4 (BBO) have been shown to efficiently generate visible and near UV light, but suffer from limited transparency in the VUV. Even though some novel nonlinear crystals with improved transparency have been developed;11-14 growing and utilizing such crystals remains challenging. Often special experimental configurations such as prism coupling are required to achieve phase matching.12 Developing manufacturable materials that enable straightforward coherent VUV light generation is clearly an important challenge. All-dielectric metasurfaces provide an alternative to nonlinear crystals and have recently gained much interest in the field of nonlinear optics. They are composed of low loss optical resonators (called metaatoms) and have been used for second (SHG) and third (THG) harmonic generation from the near IR to the visible.15-20 Unlike their plasmonic counterparts,21-28 all-dielectric metasurfaces do not suffer from inherent absorption, and therefore have much higher laser damage thresholds.27 Moreover, the resonance modes of all-dielectric metasurfaces are generally strongly confined inside the low-loss resonators 29, 30, allowing efficient access to the bulk nonlinearity of the constituent dielectric material. Here, we demonstrate an all-dielectric metasurface designed to generate VUV light using SHG. Consisting of a square array of meta-atoms fabricated from zinc oxide on a silica substrate, the metasurface is designed to support a magnetic dipole resonance mode at a fundamental wavelength of 394 nm. ZnO was selected due to its nonlinear properties31, 32, which have already been exploited for visible and near UV (300nm to 400nm) light generation33, 34, as well as its near-zero extinction coefficient at the fundamental wavelength. Under near-normal incident illumination, the substantial enhancements ACS Paragon Plus Environment

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introduced by the resonant metasurface allow generation of second harmonic (SH) radiation at 197 nm. We show that through variation of the metasurface design, this diffraction pattern can be controlled and manipulated. Our nonlinear metasurface consists of a two-dimensional periodic array of ZnO [(002)-orientation] nanoresonators fabricated on a glass substrate (Figure 1). The geometric design parameters of the metasurface unit cell are shown in Figure 2a. To fabricate the device, a 150-nm sputtered ZnO film was nano-patterned using a focused ion beam (FIB) system (see Methods). A scanning electron microscope (SEM) image of the array is shown in Figure 2b. The metasurface shows an optical resonance close to the pump wavelength of 394 nm (the top panel of Figure 2c). To understand the resonance properties, a detailed electromagnetic mode analysis was performed using finite element method simulations (see Methods). The simulated transmission spectrum is shown in the bottom panel of Figure 2c. Its profile is similar to the experimental spectrum. The discrepancies could originate from sample imperfections or gallium ion implantation introduced during the fabrication process. By calculating the relative strength of the multipoles in a metasurface,35-37 we can gain the insight of the resonance qualities of our metasurface sample. The relative strength of the leading multipoles around the excitation wavelength is shown in Figure 2d. Near the fundamental frequency, the magnetic dipole resonance is strongest. The electric (Figure 2e) and magnetic (Figure 2f) field distributions inside the meta-atom further confirm the nature of this resonance mode. They show a clear magnetic hotspot and a closed-loop electric field pattern, both characteristics of a magnetic resonance.29


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Figure 1. Schematic of the nonlinear ZnO metasurface.


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Figure 2. ZnO metasurface for coherent VUV generation. (a) Geometrical parameters of the meta-atom: D=175 nm, Px=222 nm, Py=236 nm. (b) Titled scanning electron microscope (SEM) image of the metasurface. Scale bar: 300 nm. (c) Experimental (top panel) and simulated (bottom panel) relative transmission spectrum of the metasurface sample. The excitation laser spectrum is indicated by the blue area in the top panel. The relative transmission is defined as the ratio of the transmission intensity of the metasurface to the unstructured ZnO film. (d) Theoretical calculation of the resonance strength of several multipoles present. E-Dipole: Electric dipole; M-Dipole: Magnetic dipole; T-Dipole: Toroidal dipole. (e) Electric and (f) magnetic field enhancements in and around the cross section of the unit cell at 400 nm.

The SHG properties of the metasurface were measured by nonlinear spectroscopy, using a frequencydoubled Ti:Sapphire femtosecond laser as the excitation source (see Methods for details). The 394 nm beam was focused onto the metasurface through the substrate side with a fused silica lens. The metasurface was mounted on a rotational stage to precisely control the incident angle. Additional CaF2 lenses were used to collect the second harmonic, VUV signal. The VUV signal was guided to a UV monochromator, and detected with a photomultiplier tube (PMT). The SHG spectrum generated by the


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metasurface is shown in Figure 3a. A sharp peak centered at nominally 197 nm was observed when using a p-polarized pump beam with a 7° incident angle from normal. This slightly abnormal incident angle was used since it shows an increase of about a factor of two compared to normal incidence (Figure 3b). Since the efficiency of SHG is highly sensitive to the field enhancement in the nanostructure at the basic frequency,38 this increase could be associated with the slight mismatch between the resonance position and the pump wavelength under normal incidence (Figure 2c). Increasing the incident angle red shifts the magnetic dipole resonance closer to the pump wavelength. In addition, induced symmetry breaking with increasing incident angle may also contribute to this enhancement. In comparison, a bare ZnO film has a much weaker response, close to the noise level. More information about the incident angle dependence of both the metasurface and the bare thin film can be found in the Supporting Information. Notably, the wavelength of the SHG signal is slightly larger than half of the excitation wavelength. This discrepancy is most likely caused by a slight center wavelength difference between the excitation laser and the metasurface resonance, and has been observed and discussed in previous work at longer wavelengths.23, 39 To confirm that the signal is indeed associated with SHG in the metasurface, we measured the power dependence of the signal intensity. A log-log plot of the SHG intensity vs the pump power is shown in Figure 3c. For powers below 0.2 mW incident fundamental power, the data points follow the inserted line with a slope of two (indicating a quadratic power dependence). For values above 0.2 mW, the slope of the emission power law is slightly reduced. This may be associated with heating from defects inside the metasurface.16 When the laser power was gradually decreased, hysteresis was not observed in this power regime (Figure 3c), indicating a good reversibility of our metasurface as a durable component for coherent VUV light generation. The device also shows very good stability with extended exposure time (see Supporting Information). To further analyze the SHG efficiency, the effective nonlinear coefficient was calculated40, 41 as:

𝑑𝑑𝑒𝑒𝑒𝑒𝑒𝑒 =

𝑛𝑛𝜔𝜔 𝑐𝑐𝑤𝑤0 1 � 𝜋𝜋𝑛𝑛 𝑐𝑐𝜖𝜖 𝑃𝑃(2𝜔𝜔, 𝑙𝑙) 𝑃𝑃(𝜔𝜔)𝜔𝜔𝜔𝜔 2 2𝜔𝜔 0


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where deff is the effective nonlinear coefficient, nω and n2ω are the refractive indices at the fundamental and second harmonic wavelength, respectively, c is the speed of light, w0 is the beam waist radius, P is the peak power, ω is the angular frequency of the fundamental harmonic, l is the interaction length, and ε0 is the vacuum permittivity. At 7° incident angle, the sample has an average effective coefficient of 0.96 pm/V for pump powers below 0.2 mW, which is larger than the value of an unstructured ZnO thin film (nominally 0.20 pm/V). Moreover, the effective coefficient of the metasurface slightly declines to 0.66 pm/V for powers above this 0.2 mW (see Supporting Information for more detailed discussion). Due to the small interaction length, perfect phase matching was assumed. The quantum efficiency of the detector, as well as the transmission of all optical components in the detection path were considered in the calculation as well. For comparison, Potassium Fluoroboratoberyllate (KBBF),11 one of the few existing crystals that has been used for coherent VUV generation, has been reported to have a bulk nonlinear coefficient of 0.49 pm/V. However, KBBF is commonly used in a prism-coupled configuration to achieve phase matching.12 At an incident angle 𝜃𝜃 =54° for example, the effective coefficient of KBBF reduces to

0.29 pm/V.11 The metasurface presented here has an effective coefficient nominally three times larger

than a prism-coupled KBBF crystal. Furthermore, due to the absorptive nature of the glass substrate in the VUV regime, only the transmissive nonlinear signal can be detected. In the nonlinear simulations, the backward zero order signal is found to be nominally 79% of the forward zero order one. Therefore, the effective nonlinear coefficient could be even larger if a different substrate was used and the nonlinear signals in both directions were collected.


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Figure 3. Nonlinear Measurements. (a) Second harmonic spectrum. (b) Angle dependence of the nonlinear signal versus incident angle of the excitation. (c) Power dependence of the nonlinear signal with respect to the pump power in a log-log plot. The gray line represents ideal quadratic power dependence. The inset shows the respective conversion efficiencies. By manipulating the lattice constants of the metasurface, we can additionally control the diffraction pattern of the generated VUV signal similar to what has been demonstrated in the visible regime using ACS Paragon Plus Environment

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plasmonic metasurfaces.23, 42 This ability to generate VUV light in complex radiation patterns controlled by metasurface geometry may lead to novel components for VUV wavefront manipulation, and may yield new and useful applications in nanopatterning and nanofabrication. To demonstrate control of the VUV radiation pattern, the metasurface array period is adjusted to 640 nm and 450 nm in the x and y directions, respectively (Figure 4a). The theoretical and experimental first order diffraction modes are shown in Figure 4b and 4c, respectively. By modifying the periods along the x- and y-axis of the metasurfaces, the VUV spot separation can be seen to be different along the two axes. More details regarding measurement and image analysis for the nonlinear diffraction pattern experiment can be found in Supporting Information. With more sophisticated design and meta-atom arrangement, the energy distribution and radiation direction of the nonlinear signal could be manipulated even further.42


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Figure 4. Radiation Pattern. (a) SEM image of the metasurface. Geometrical parameters of the unit cell of the metasurface used for radiation pattern imaging: Diameter=375 nm, Px = 640 nm, Py = 450 nm. Thickness=100 nm. Scale bar: 1 μm. (b) Simulated radiation pattern of the nonlinear signal. The solid lines correspond to elevating angles of 10° and 20°, while the dashed lines correspond to different azimuthal angles. (c) Experimental radiation pattern of the nonlinear signal. Standard image enhancement techniques were used in post processing. The center is covered for clarity (gray, circular region).


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In conclusion, SHG at 197 nm was realized in an all-dielectric ZnO metasurfaces designed to have magnetic dipole resonances at the excitation wavelength. The magnetic resonance confines the incident energy to inside the material enabling efficient bulk SHG generation. Due to its compact size, the device can be readily integrated into ultrafast laser systems for tabletop VUV light sources without the need for complex experimental configurations or phase matching. Although the efficiency of the reported metasurface is already higher than for a KBBF prism-coupled device, we believe that it can be further improved by introducing a more complex or high-order multipole resonance, such as a Fano-type,

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anapole resonance,16 and/or a supercavity mode.43 We also demonstrated that our metasurface device can spatially manipulate the VUV light. The structure presented here can be efficiently fabricated using CMOS fabrication processes,44,

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laser nanofabrication,46 nanoimprinting,47 as well as nanostencil

lithography techniques.48 Our studies pave the way for many promising VUV applications which are difficult to realize using conventional components, such as multiple spot scanning systems for imaging and material analysis, and high-end multifunctional VUV sources for spectroscopy, lithography, and microscopy. Methods. Design and Simulations. The metasurface geometry was chosen to exhibit a resonance at the fundamental in order to generate field enhancement. The linear simulations were performed using the Finite Element Method (COMSOL Multiphysics 5.3a). We used plane wave incidence from the glass slide and calculated the transmission by integrating the Poynting vectors on a plane parallel to the substrate at the air side. Perfect matched layers were applied in the vertical direction to prevent reflection. In the horizontal direction a periodic boundary condition was used. For the simulations, we adopted the refractive index data of ZnO from Ref. [49]. However, after several trials, we found that multiplying the reported values by a factor of 1.2 yields better agreement between the simulated and experimental transmission spectra. We attribute this slight difference to known variations of the refractive index of ZnO, depending on the preparation method and the adopted substrate.49-53 In light of this, the modified refractive index of ZnO was used in all simulations reported in this work.


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We also performed nonlinear simulations of the SHG process. These were obtained in a two-step method. First, a linear simulation at the basic frequency was performed to obtain the electric field distributions within the nanoparticles. The near field distributions were then used to determine the �⃗𝑗𝑗 𝐸𝐸�⃗𝑘𝑘 . In a second nonlinear polarizations using the basic nonlinear tensor formulation:𝑃𝑃�⃗(2𝜔𝜔) = 𝜖𝜖0 ⃖��⃗(𝑖𝑖𝑖𝑖𝑖𝑖)𝐸𝐸 𝜒𝜒2 step, a linear simulation at the SH frequency was performed. The nonlinear polarizations were used as radiation sources, and the far field propagation was simulated to obtain the detected SHG. Fabrication. To fabricate the ZnO metasurface, a 150 nm sputtered ZnO film with (002)-orientation (MTI Corporation) on a soda lime glass substrate was used. A 5 nm Cr layer, as a conductive layer for nanofabrication, was evaporated on the top of the ZnO film with a base pressure less than 5×10-6 Torr. The metasurface was then patterned with a focused ion beam system (FEI Helios 660 NanoLab). To define the ZnO nanostructures, a commercial software NPGS (JC Nabity Lithography Systems) was used to precisely control the scan path of the ion beam. The beam current was 51 pA with an acceleration voltage of 30 kV. The gallium ion beam dose applied on the sample was 23 μC/cm2. Linear Measurements. Linear measurement: To characterize the optical response of the ZnO metamaterial in the vicinity of its fundamental frequency, a transmission measurement was performed. A schematic can be found in Figure S1. In short, a continuum laser-driven light source combined with a 1200 grooves/mm scanning monochromator was utilized to produce the excitation beam. It was then focused on the sample with a fused silica lens. The transmitted rays were collected by an objective and guided to a charge-coupled device. The relative transmission spectrum of the metasurface can be retrieved by comparing the signals from the metasurface and the adjacent bare film at different wavelengths. Nonlinear Measurements. The nonlinear measurements were performed using a mode locked, ultrafast Ti:sapphire laser (Figure S2). It consists of a seed laser (Coherent Mira 900) and an amplifier (Coherent RegA 9000) that together produce ultrafast pulses with a temporal width of about 205 fs. The repetition rate was 250 kHz, and the center wavelength around 788 nm. Both were pumped by Coherent Verdi 5 W, pump lasers. To generate the SH an optical parametric amplifier (OPA) was used (Coherent OPA 9400). The produced 394 nm beam was focused onto the sample with a UV fused silica lens (40 mm focal length). ACS Paragon Plus Environment

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Similar to the linear measurements, the light passed through the substrate first. The incident peak power density on the sample ranged between 0.3 and 15 GW/cm2 with a spot size of around 227 µm2 (8.5 µm beam waist radius). The peak power density was estimated based on the spot size, the pulse width and repetition rate of the laser. The transmitted linear and nonlinear signals were then collected with two CaF2 lenses (40 mm focal length each). For the spectral scan the light was then guided to the deep UV Monochromator (Thermo Jarrell Ash, 2400 groves/mm grating). Several UV filters were used to eliminate the pump signal. Two narrowband (25200FNB) and one broadband (25200FBB) filter from e-source optics, both centered at 200nm, were used throughout the experiments. The narrowband/broadband filters have a minimum peak transmission of 15%/35%, and an out-of-band rejection of (10-3-10-4)/10-3. For the radiation pattern experiment, we added a fourth filter (Newport 10LF20-193) with center wavelength of 193nm and a minimum peak transmission of 10%. The wavelength step for the spectral scans was 0.2nm. Two bandpass filters were used to reduce the linear signal. After the monochromator, the VUV light was detected with a PMT (ADIT Electron Tubes, 9781B6019). It was chilled to around -14°C to minimize dark current. To further increase the signal to noise ratio, the current signal from the PMT was fed into a lock-in amplifier (Stanford Research Systems SR850 DSP). Its reference frequency was provided by an optical chopper, which was placed in the laser path. The modulation frequency was 2.2 kHz. For all nonspectral scans a simplified setup (Figure S3) was used. More details about regarding this setup and the radiation pattern measurements can be found in the Supporting Information.

ASSOCIATED CONTENT Supporting Information. Sections discussing the choice of the nonlinear material, experimental measurements and data analysis, incident angle dependence, device stability, possible polarization of the SHG signal, absorption in the chromium layer, and radiation pattern; including Figures S1-S9. This material is available free of charge via the Internet at http://pubs.acs.org.


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AUTHOR INFORMATION Corresponding Author *(N.J.H.) E-mail [email protected]. ORCID: Michael Semmlinger: 0000-0001-5430-733X Ming Lun Tseng: 0000-0003-0418-8162 Jian Yang: 0000-0001-6186-6439 Ming Zhang: 0000-0003-1676-389X Chao Zhang: 0000-0001-5619-341X Wei-Yi Tsai: 0000-0002-3459-0120 Din Ping Tsai: 0000-0002-0883-9906 Peter Nordlander: 0000-0002-1633-2937 Naomi J. Halas: 0000-0002-8461-8494 Author Contributions M.S., M.L.T and J.Y. contributed equally to this work. N.J.H. conceived the project; M.L.T., J.Y. and M.S. performed the material investigation. J.Y., M.Z., and M.L.T. designed the samples and performed the theoretical simulations; M.L.T., M.S. fabricated the samples; M.S. and M.L.T. performed the optical measurements; C.Z. and W.-Y.T. assisted in the sample design and nanofabrication. All authors analyzed the results and contributed to the preparation of the manuscript and discussions. D.P.T., P.J.N., and N.J.H. supervised the research. ACKNOWLEDGMENTS We gratefully acknowledge support from the Robert A. Welch Foundation, C-1220 (N.J.H.) and C-1222 (P.N.), the National Science Foundation (NSF) MRI Award, NSF Grant ECCS-1610229, and the Air Force Office of Scientific Research Multidisciplinary Research Program of the University Research Initiative (AFOSR MURI FA9550-15-1-0022). M.L.T. and D.P.T. acknowledge financial support from the Ministry of Science and Technology, Taiwan (grant no. MOST-106-2745-MACS Paragon Plus Environment

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002-003-ASP). We thank Kyle Chapkin, Adam Lauchner, Ben Cerjan, Hossein Robatjazi, Linan Zhou, Shiung-Yu Lin, Pin Chieh Wu, Kuan-Wei Lee, Kun-Ching Shen, and Jia-Wern Chen for their useful discussions and support. M.L.T and D.P.T acknowledge the Research Center for Applied Sciences, Academia Sinica for their support in using the FIB system (FEI Helios 660 Nanolab). Notes The authors declare no competing financial interest.


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REFERENCES AND NOTES 1. Lipson, R. H.; Dimov, S. S.; Wang, P.; Shi, Y. J.; Mao, D. M.; Hu, X. K.; Vanstone, J. Instrum. Sci. Technol. 2000, 28, (2), 85-118. 2. Mu, R.; Fu, Q.; Jin, L.; Yu, L.; Fang, G.; Tan, D.; Bao, X. Angewandte Chemie International Edition 2012, 51, (20), 4856-4859. 3. McPherson, A.; Gibson, G.; Jara, H.; Johann, U.; Luk, T. S.; McIntyre, I. A.; Boyer, K.; Rhodes, C. K. J. Opt. Soc. Am. B 1987, 4, (4), 595-601. 4. Eden, J. G. Progress in Quantum Electronics 2004, 28, (3), 197-246. 5. Chang, Z.; Rundquist, A.; Wang, H.; Murnane, M. M.; Kapteyn, H. C. Physical Review Letters 1997, 79, (16), 2967-2970. 6. Ghimire, S.; DiChiara, A. D.; Sistrunk, E.; Agostini, P.; DiMauro, L. F.; Reis, D. A. Nat. Phys. 2010, 7, (2), 138-141. 7. Liu, H.; Li, Y.; You, Y. S.; Ghimire, S.; Heinz, T. F.; Reis, D. A. Nature Physics 2016, 13, (3), 262-265. 8. Hutchinson, M. H. R. Appl. Opt. 1980, 19, (23), 3883-3888. 9. Hemsing, E.; Dunning, M.; Hast, C.; Raubenheimer, T. O.; Weathersby, S.; Xiang, D. Physical Review Special Topics - Accelerators and Beams 2014, 17, (7). 10. Jiang, X.; Joly, N. Y.; Finger, M. A.; Babic, F.; Wong, G. K. L.; Travers, J. C.; Russell, P. S. J. Nat. Photonics 2015, 9, (2), 133-139. 11. Chen, C. T.; Wang, G. L.; Wang, X. Y.; Xu, Z. Y. Applied Physics B 2009, 97, (1), 9-25. 12. Kanai, T.; Wang, X.; Adachi, S.; Watanabe, S.; Chen, C. Opt. Express 2009, 17, (10), 8696-8703. 13. Wu, C.; Yang, G.; Humphrey, M. G.; Zhang, C. Coord. Chem. Rev. 2018. 14. Halasyamani, P. S.; Zhang, W. Inorg. Chem. 2017, 56, (20), 12077-12085. 15. Shcherbakov, M. R.; Neshev, D. N.; Hopkins, B.; Shorokhov, A. S.; Staude, I.; Melik-Gaykazyan, E. V.; Decker, M.; Ezhov, A. A.; Miroshnichenko, A. E.; Brener, I.; Fedyanin, A. A.; Kivshar, Y. S. Nano Lett. 2014, 14, (11), 6488-6492. 16. Grinblat, G.; Li, Y.; Nielsen, M. P.; Oulton, R. F.; Maier, S. A. Nano Lett. 2016, 16, (7), 4635-40. 17. Liu, S.; Sinclair, M. B.; Saravi, S.; Keeler, G. A.; Yang, Y.; Reno, J.; Peake, G. M.; Setzpfandt, F.; Staude, I.; Pertsch, T.; Brener, I. Nano Lett. 2016, 16, (9), 5426-32. 18. Li, G.; Zhang, S.; Zentgraf, T. Nature Reviews Materials 2017, 2, (5), 17010. 19. Yang, Y.; Wang, W.; Boulesbaa, A.; Kravchenko, II; Briggs, D. P.; Puretzky, A.; Geohegan, D.; Valentine, J. Nano Lett. 2015, 15, (11), 7388-93. 20. Timbrell, D.; You, J. W.; Kivshar, Y. S.; Panoiu, N. C. Sci Rep 2018, 8, (1), 3586. 21. Kauranen, M.; Zayats, A. V. Nat Photon 2012, 6, (11), 737-748. 22. Zhang, Y.; Grady, N. K.; Ayala-Orozco, C.; Halas, N. J. Nano Lett. 2011, 11, (12), 5519-23. 23. Wang, L.; Shorokhov, A. S.; Melentiev, P. N.; Kruk, S.; Decker, M.; Helgert, C.; Setzpfandt, F.; Fedyanin, A. A.; Kivshar, Y. S.; Neshev, D. N. ACS Photonics 2016. 24. Lee, J.; Tymchenko, M.; Argyropoulos, C.; Chen, P. Y.; Lu, F.; Demmerle, F.; Boehm, G.; Amann, M. C.; Alu, A.; Belkin, M. A. Nature 2014, 511, (7507), 65-9. 25. Zheludev, N. I.; Emel yanov, V. I. Journal of Optics A: Pure and Applied Optics 2004, 6, (1), 2628. 26. Thyagarajan, K.; Butet, J.; Martin, O. J. Nano Lett. 2013, 13, (4), 1847-51. 27. Krasnok, A.; Tymchenko, M.; Alù, A. Materials Today 2018, 8, (1), 21. 28. Bachelier, G.; Butet, J.; Russier-Antoine, I.; Jonin, C.; Benichou, E.; Brevet, P. F. Physical Review B 2010, 82, (23). 29. Jahani, S.; Jacob, Z. Nat Nano 2016, 11, (1), 23-36. 30. Kuznetsov, A. I.; Miroshnichenko, A. E.; Brongersma, M. L.; Kivshar, Y. S.; Luk'yanchuk, B. Science 2016, 354, (6314). 31. Cao, H.; Wu, J. Y.; Ong, H. C.; Dai, J. Y.; Chang, R. P. H. Appl. Phys. Lett. 1998, 73, (5), 572574. ACS Paragon Plus Environment

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32. Weber, N.; Protte, M.; Walter, F.; Georgi, P.; Zentgraf, T.; Meier, C. Physical Review B 2017, 95, (20), 205307. 33. Hyun, J. K.; Kang, T.; Baek, H.; Oh, H.; Kim, D.-s.; Yi, G.-c. ACS Photonics 2015, 2, (9), 13141319. 34. Boyd, R. W., Nonlinear Optics. Academic Press: 2003. 35. Wu, P. C.; Liao, C. Y.; Savinov, V.; Chung, T. L.; Chen, W. T.; Huang, Y. W.; Wu, P. R.; Chen, Y. H.; Liu, A. Q.; Zheludev, N. I.; Tsai, D. P. ACS Nano 2018. 36. Kaelberer, T.; Fedotov, V. A.; Papasimakis, N.; Tsai, D. P.; Zheludev, N. I. Science 2010, 330, (6010), 1510-1512. 37. Tseng, M. L.; Fang, X.; Savinov, V.; Wu, P. C.; Ou, J.-Y.; Zheludev, N. I.; Tsai, D. P. Scientific Reports 2017, 7, 44488. 38. Butet, J.; Brevet, P.-F.; Martin, O. J. F. ACS Nano 2015, 9, (11), 10545-10562. 39. Kruk, S.; Weismann, M.; Bykov, A. Y.; Mamonov, E. A.; Kolmychek, I. A.; Murzina, T.; Panoiu, N. C.; Neshev, D. N.; Kivshar, Y. S. ACS Photonics 2015, 2, (8), 1007-1012. 40. Bordui, P. F.; Engineers, S. o. P.-o. I., Inorganic crystals for optics, electro-optics, and frequency conversion: 25 July 1991, San Diego, California. SPIE: 1991. 41. Webb, C. E.; Jones, J. D. C., Handbook of laser technology and applications. Institute of Physics: 2004. 42. Segal, N.; Keren-Zur, S.; Hendler, N.; Ellenbogen, T. Nat Photon 2015, 9, (3), 180-184. 43. Rybin, M. V.; Koshelev, K. L.; Sadrieva, Z. F.; Samusev, K. B.; Bogdanov, A. A.; Limonov, M. F.; Kivshar, Y. S. Phys. Rev. Lett. 2017, 119, (24), 243901. 44. Seo, Y.; Song, M. Y.; An, H. M.; Kim, T. G. IEEE Electron Device Letters 2013, 34, (2), 238240. 45. Chen, C.; Pan, F.; Wang, Z. S.; Yang, J.; Zeng, F. Journal of Applied Physics 2012, 111, (1). 46. Tseng, M. L.; Chen, B. H.; Chu, C. H.; Chang, C. M.; Lin, W. C.; Chu, N.-N.; Mansuripur, M.; Liu, A. Q.; Tsai, D. P. Opt. Express 2011, 19, (18), 16975-16984. 47. Gao, L.; Zhang, Y.; Zhang, H.; Doshay, S.; Xie, X.; Luo, H.; Shah, D.; Shi, Y.; Xu, S.; Fang, H.; Fan, J. A.; Nordlander, P.; Huang, Y.; Rogers, J. A. ACS Nano 2015, 9, (6), 5968-5975. 48. Aksu, S.; Huang, M.; Artar, A.; Yanik, A. A.; Selvarasah, S.; Dokmeci, M. R.; Altug, H. Adv. Mater. 2011, 23, (38), 4422-4430. 49. HORIBA https://www.horiba.com/en_en/applications/materials/photovoltaics/characterizationof-photovoltaic-devices-by-spectroscopic-ellipsometry/ (accessed July 13, 2018), 50. Dejneka, A.; Aulika, I.; Makarova, M. V.; Hubicka, Z.; Churpita, A.; Chvostova, D.; Jastrabik, L.; Trepakov, V. A. Journal of The Electrochemical Society 2010, 157, (2). 51. Washington, P. L.; Ong, H. C.; Dai, J. Y.; Chang, R. P. H. Applied Physics Letters 1998, 72, (25), 3261-3263. 52. Zuo, J.; Erbe, A. Phys Chem Chem Phys 2010, 12, (37), 11467-76. 53. Gao, W.; Li, Z. Ceramics International 2004, 30, (7), 1155-1159.


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Vacuum Ultraviolet Light-Generating Metasurface - Nano Letters (ACS

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