Basov, D. N.

Blanchard, Romain

Capasso, Federico

Genevet, Patrice

Kats, Mikhail A.

Qazilbash, Mumtaz M.

Ramanathan, Shriram

Yang, Zheng

English

We demonstrate that the resonances of infrared plasmonic antennas can be tuned or switched on/off by taking advantage of the thermally driven insulator-to-metal phase transition in vanadium dioxide (VO2). Y-shaped antennas were fabricated on a 180 nm film of VO2 deposited on a sapphire substrate, and their resonances were shown to depend on the temperature of the VO2 film in proximity of its phase transition, in good agreement with full-wave simulations. We achieved tunability of the resonance wavelength of approximately 10% (\u3e1 μm at λ ∼ 10 μm)

...,

Qazilbash, M. M.

al., et

College of William & Mary: W&M Publish

W&M ScholarWorks Arts & Sciences Articles Arts and Sciences 2013 Thermal tuning of mid-infrared plasmonic antenna arrays using a phase change material Mikhail A. Kats Romain Blanchard Patrice Genevet Zheng Yang Mumtaz M. Qazilbash William and Mary, mmqazilbash@wm.edu See next page for additional authors Follow this and additional works at: https://scholarworks.wm.edu/aspubs  Part of the Condensed Matter Physics Commons Recommended Citation Kats, Mikhail A.; Blanchard, Romain; Genevet, Patrice; Yang, Zheng; Qazilbash, Mumtaz M.; Basov, D. N.; Ramanathan, Shriram; and Capasso, Federico, Thermal tuning of mid-infrared plasmonic antenna arrays using a phase change material (2013). Optics Letters, 38(3), 368-370. https://doi.org/10.1364/OL.38.000368 This Article is brought to you for free and open access by the Arts and Sciences at W&M ScholarWorks. It has been accepted for inclusion in Arts & Sciences Articles by an authorized administrator of W&M ScholarWorks. For more information, please contact scholarworks@wm.edu. Authors Mikhail A. Kats, Romain Blanchard, Patrice Genevet, Zheng Yang, Mumtaz M. Qazilbash, D. N. Basov, Shriram Ramanathan, and Federico Capasso This article is available at W&M ScholarWorks: https://scholarworks.wm.edu/aspubs/1734 Thermal tuning of mid-infrared plasmonic antennaarrays using a phase change materialMikhail A. Kats,1 Romain Blanchard,1 Patrice Genevet,1 Zheng Yang,1 M. Mumtaz Qazilbash,2,3D. N. Basov,2 Shriram Ramanathan,1 and Federico Capasso1,*1School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA2Department of Physics, University of California—San Diego, La Jolla, California 92093, USA3Department of Physics, The College of William & Mary, Williamsburg, Virginia 23187, USA*Corresponding author: capasso@seas.harvard.eduReceived November 16, 2012; revised December 20, 2012; accepted December 30, 2012;posted January 2, 2013 (Doc. ID 179906); published January 29, 2013We demonstrate that the resonances of infrared plasmonic antennas can be tuned or switched on/off by takingadvantage of the thermally driven insulator-to-metal phase transition in vanadium dioxide (VO2). Y-shapedantennas were fabricated on a 180 nm film of VO2 deposited on a sapphire substrate, and their resonances wereshown to depend on the temperature of the VO2 film in proximity of its phase transition, in good agreement withfull-wave simulations. We achieved tunability of the resonance wavelength of approximately 10% (>1 μm atλ ∼ 10 μm). © 2013 Optical Society of AmericaOCIS codes: 250.5403, 240.6680, 130.3060, 130.4815.Optical antennas have in recent years become a back-bone of optics at subwavelength scales. Due to localizedsurface plasmon resonances arising from the collectivemotion of free electrons in metals, optical antennas havebecome useful for sensing, photodetection, heat transfer,and emission enhancement schemes [1–5]. More re-cently, optical antennas have also become relevant forthe manipulation of the amplitude, phase, and polariza-tion of light [6–10].To date, most of the applications that utilize optical an-tennas have involved static, nonreconfigurable designs.These applications all stand to benefit from dynamic tun-ability. To this end, a number of approaches have beeninvestigated, including antenna loading with liquid crys-tals [11] and photoconductive materials [12], tuning thegap of dimer antennas with scanning probes [13] or elas-tomeric substrates [14,15], and modification of the localenvironment with active polymer coatings [16].In this Letter, we demonstrate that resonances of mid-infrared (IR) plasmonic antennas can be tuned andswitched on/off by thermal control of phase coexistencein a vanadium dioxide (VO2) substrate. A similar ap-proach has been previously explored for tuning of the ef-fective refractive index of metamaterials in the terahertz(THz) [17–19] and near-IR [20], tuning nanoparticlescattering spectra in the visible [21–23], and control oftransmission through apertures in the THz [24]. Weutilized a normalization procedure that helps isolatethe antenna resonances from the optical response of theunpatterned underlying substrate in proximity to the VO2phase transition [25]. To validate our results, we incorpo-rated the literature complex refractive indices of VO2throughout its phase transition into full-wave numericalsimulations and observed qualitative agreement betweenthe simulated and experimental reflectivity spectra.VO2 undergoes a thermally driven insulator-to-metaltransition (IMT) above ∼67°C, which takes the materialfrom an insulating state to a metallic state. In recent yearsthis phase transition has been explored for the develop-ment of novel electronic switches and memories [26]. Inthe insulating phase, VO2 has a bandgap correspondingto λ  1.8–2.5 μm, depending on the growth conditions(e.g., [27]), and in the metallic phase it has Drude-like op-tical conductivity at IR frequencies [28]. This largechange in optical properties makes VO2 films useful foroptical switching applications [29,30]. As the IMT occurs,the bandgap collapses and nanoscale islands of the me-tallic phase begin to form in the surrounding insulatingVO2, which then grow and connect in a percolative pro-cess [27,31]. This nanoscale phase coexistence makes in-termediate-state VO2 an effective optical medium withtunable dispersion and losses [25].A plasmonic antenna can be made tunable by incorpor-ating a material such as VO2 into its design; here, wefocus on Y-shaped antennas that can be used as phaseelements and form birefringent metasurfaces [10]. Wefabricated a square array of gold (Au) Y-shaped antennaswith a period of 3 μm on a thick, single-side-polished c-plane sapphire substrate coated with ∼180 nm of single-crystalline VO2. The antenna spacing is large to minimizenear-field coupling between neighboring antennas. Theoxide film was deposited using magnetron sputteringfrom a V2O5 target at 550ºC under 10 mTorr pressure with100 sccm Ar gas flow at a power of 120 W to obtain phasepure VO2. The antennas were defined using electron-beam lithography and deposition of 5 nm of Ti and40 nm of Au, and lift-off. A scanning electron microscope(SEM) image of the structures is shown in Fig. 1(a); thevertical and horizontal arms are ∼1.05 μm long and thediagonal arm is ∼0.75 μm long, all with a width of∼160 nm. The roughness of the VO2 film is visible in theSEM image and was transferred to the metallic antennas.An antenna array situated on a dielectric substrate canbe viewed as a frequency selective surface and is ex-pected to have a peak in its reflectivity spectrum whenon resonance [32]. We collected temperature-dependentreflectivity spectra by using a Fourier transform infrared(FTIR) spectrometer (Bruker Vertex 70), connected to amid-IR microscope (Bruker Hyperion 2000) equippedwith a temperature-controlled stage (Bruker A599). Aschematic of the setup is shown in Fig. 1(b). A Cassegrainobjective (15×, NA  0.4) was used to focus a polarized368 OPTICS LETTERS / Vol. 38, No. 3 / February 1, 20130146-9592/13/030368-03$15.00/0 © 2013 Optical Society of Americabeam from a Globar source onto the sample, with the re-flected light collected by the same objective and sent to amercury–cadmium–telluride (MCT) detector. Nearly allof the light that is not reflected is absorbed within theantennas, the VO2 film, and the underlying sapphire asit is not transparent for λ > 5 μm. At each temperature,the reflectivity spectra were normalized to (i.e., dividedby) the reflectivity of the bare VO2∕sapphire substrate atthat same temperature. Such normalization helps isolatethe reflectivity feature due to the antennas at each tem-perature from the nontrivial reflectivity of the underlyingVO2 film on sapphire [25].The normalized reflectivity is shown in Fig. 2(a), withthe incident polarization along the symmetry axis of theantennas as indicated with the double-sided arrow inFig. 1(a); this ensures that no polarization conversiontakes place at the antenna array [10]. When the VO2 isin the dielectric state (e.g., T  28°C), the resonances ofthe antennas in the array lead to a peak in reflectivity ataround λ  9.3 μm. As the temperature increases toT  69°C, this peak is redshifted to λ  10.5 μm, corre-sponding to a greater than 10% shift in the resonance fre-quency. This shift coincides with a decrease in the peakreflectivity and increase in the linewidth. The wavelengthof the reflectivity peak and its value are plotted inFig. 2(b) as a function of temperature when heating (solidcurves) and then cooling back down (dashed curves).There is hysteresis in this plot that is inherent to theVO2 phase transition [26], though the full hysteresis loopis not visible in Fig. 2(b) because we truncated the tem-peratures at 69°C for heating and 63°C for cooling, re-spectively; beyond these temperatures the reflectivitypeak disappears.The key features of Fig. 2(a) are reproduced by three-dimensional finite-difference time-domain (FDTD)simulations (Lumerical Solutions) in Fig 3(a). Periodicboundary conditions were used to capture the effect ofthe array. The IR complex refractive index data for sap-phire, Ti, and Au was interpolated from literature data[33], while the VO2 refractive indices throughout its phasetransition were taken from ellipsometry measurements in[28]. The differences between the experimental results ofFig. 2(a) and the calculations of Fig. 3(a) are primarily dueto the differing growth conditions and thicknesses be-tween our VO2 sample and the one measured in [28],which lead to a different temperature-dependent complexrefractive index, as well as the surface roughness that isnot accounted for in the simulations.This shift in the resonance occurs because the refrac-tive index of the underlying VO2 changes as a function oftemperature. At the onset of the transition, the real partof the complex refractive index n increases at mid-IRwavelengths [curves for 9.3 and 10.5 μm are shown inblue (upper on the left, lower on the right) in Fig. 3(b)].This increase in the substrate index is strongly felt by theantenna, which acts as a dispersive Fabry–Perot resona-tor for surface plasmons with the effective index of themode dependent on the index of the substrate [34,35]. Inthe present demonstration, we are exciting one of thetwo plasmonic eigenmodes of the Y-shaped antenna [10];the other eigenmode feels the index change of the sub-strate in the same way. Through the course of the VO2phase transition the antenna resonance is also impactedby the increase of losses [the values of the imaginary partk of the complex refractive index of VO2 are shown inblack (lower on the left, upper on the right) in Fig. 3(b)],which increase as the fraction of the metallic-phase VO2increases, resulting in a lower-amplitude reflectivitymaximum. As the VO2 film transitions into its high-temperature metallic state (where k > n), the antennasbecome “shorted” and can no longer be viewed as iso-lated resonant elements, so the reflectivity maximum dis-appears [flat orange curves in Figs. 2(a) and 3(a)]. Thepeak in normalized reflectivity in Figs. 2(a) and 3(a) at11–12 μm that appears at temperatures close to theFig. 1. (Color online) (a) SEM image of the fabricated samplecomprising an array of gold antennas on a ∼180 μm VO2 filmdeposited on a sapphire wafer. Inset: zoomed-in image of asingle Y-shaped antenna with arrows indicating the flow of thecurrent. (b) Schematic of the reflectivity measurement. Lightfrom an FTIR is incident on the temperature-controlled sample,and the reflection is sent to a detector.Fig. 2. (Color online) (a) Reflectivity spectra of the antennaarray for increasing temperatures, showing the evolution ofthe antenna resonance through the VO2 phase transition. Ateach temperature, the spectrum was normalized to reflectivityof the substrate without the antennas. (b) Wavelength at whichthe reflectivity peaks [blue (lower left to upper right)] and thenormalized peak reflectivity value [green (upper left to lowerright)] as a function of temperature during heating (solidcurves) and cooling (dashed curves).Fig. 3. (Color online) (a) Calculated normalized reflectivityspectra corresponding to the experimental data in Fig. 2(a)using the FDTD method, incorporating literature values for thecomplex refractive indices of gold, VO2, and sapphire. (b) Real(n) and imaginary (k) parts of the refractive index of VO2 atwavelengths of 9.3 and 10.5 μm.February 1, 2013 / Vol. 38, No. 3 / OPTICS LETTERS 369critical IMT temperature is a result of a “division by zero”:at this wavelength and temperature the reflectivity of theunderlying VO2∕sapphire substrate is ∼0 as a result ofcritical coupling to an ultrathin cavity resonance [25],causing a divergence in the normalized curves. The dipat this same wavelength but at a slightly lower tempera-ture [Fig. 2(a)] is an indication that the critical couplingcondition is reached for a lower temperature in the pre-sence of antennas due to enhanced absorption inthe VO2.The manipulation of optical antenna resonances usingphase change materials such as VO2 is promising fordynamic optical devices. In this Letter, we showed thatthe resonances of plasmonic elements can be tuned orturned off by utilizing the large change of the opticalproperties of the underlying VO2 substrate in proximityto its phase transition. While we demonstrated thermaltuning of an entire antenna array, DC and AC fields canbe applied to individual antennas or even individual sec-tions of antennas on isolated patches of VO2, creating atunable inhomogeneous distribution of amplitude andphase responses within an array of antennas. Such ademonstration would be of interest to realizing anten-na-based spatial light modulators capable of addressingamplitude and phase of infrared and THz light, active andpassive thermal labels and emitters, displays, and relateddynamically reconfigurable devices.We thank J. Lin, N. Yu, D. Sharma, and Y. Zhao forhelpful discussions. The fabrication was performed atthe Harvard CNS. FC acknowledges support from theAFOSR under grant number FA9550-12-1-0289. ZY andSR acknowledge ONR for financial support. M. Kats issupported by the NSF Graduate Research Fellowship.References1. K. B. Crozier, A. Sundaramurthy, G. S. Kino, and C. F.Quate, J. Appl. Phys. 94, 4632 (2003).2. P. Muhlschlegel, H.-J. Eisler, O. J. F. Martin, B. Hecht, andD. W. Pohl, Science 308, 1607 (2005).3. R. Adato, A. A. Yanik, J. J. Amsden, D. L. Kaplan, F. G.Omenetto, M. K. Hong, S. Erramilli, and H. Altug, Proc. Natl.Acad. Sci. USA 106, 19227 (2009).4. L. Novotny and N. van Hulst, Nat. Photonics 5, 83 (2011).5. E. Cubukcu, N. Yu, E. J. Smythe, L. Diehl, K. B. Crozier, andF. Capasso, IEEE J. Sel. Top. Quantum Electron. 14, 1448(2008).6. N. Yu, P. Genevet, M. A. Kats, F. Aieta, J. P. Tetienne, F.Capasso, and Z. Gaburro, Science 334, 333 (2011).7. Y.-J. Tsai, S. Larouche, T. Tyler, G. Lipworth, N. M. Jokerst,and D. R. Smith, Opt. Express 19, 24411 (2011).8. M. A. Kats, N. Yu, P. Genevet, Z. Gaburro, and F. Capasso,Opt. Express 19, 21749 (2011).9. Y. Zhao and A. Alu, Phys. Rev. B 84, 205428 (2011).10. M. A. Kats, P. Genevet, G. Aoust, N. Yu, R. Blanchard, F.Aieta, Z. Gaburro, and F. Capasso, Proc. Natl. Acad. Sci.USA 109, 12364 (2012).11. J. Berthelot, A. Bouhelier, C. Huang, J. Margueritat, G.Colas-des-Francs, E. Finot, J.-C. Weeber, A. Dereux,S. Kostcheev, H. ibn El Ahrach, A.-L. Baudrion, J. Plain,R. Bachelot, P. Royer, and G. P. Wiederrecht, Nano Lett.9, 11 (2009).12. N. Large, M. Abb, J. Aizpurua, and O. L. Muskens, Nano Lett.10, 1741 (2010).13. P. Olk, J. Renger, M. T. Wenzel, and L. M. Eng, Nano Lett. 8,4 (2008).14. F. Huang and J. J. Baumberg, Nano Lett. 10, 5 (2010).15. I. M. Pryce, K. Aydin, Y. A. Kelaita, R. M. Briggs, and H. A.Atwater, Nano Lett. 10, 4222 (2010).16. H. Gehan, C. Mangeney, J. Aubard, G. Levi, A. Hohenau,J. R. Krenn, E. Lacaze, and N. Felidj, J. Phys. Chem. Lett.2, 926 (2011).17. T. Driscoll, S. Palit, M. M. Qazilbash, M. Brehm, F.Keilmann, B.-G. Chae, S.-J. Yun, H.-T. Kim, S. Y. Cho,N. M. Jokerst, D. R. Smith, and D. N. Basov, Appl. Phys. Lett.93, 024101 (2008).18. M. D. Goldflam, T. Driscoll, B. Chapler, O. Khatib, N. M.Jokerst, S. Palit, D. R. Smith, B.-J. Kim, G. Seo, H.-T.Kim, M. D. Ventra, and D. N. Basov, Appl. Phys. Lett. 99,044103 (2011).19. M. Liu, H. Y. Hwang, H. Tao, A. C. Strikwerda, K. Fan, G. R.Keiser, A. J. Sternbach, K. G. West, S. Kittiwatanakul, J. Lu,S. A. Wolf, F. G. Omenetto, X. Zhang, K. A. Nelson, and R. D.Averitt, Nature 487, 345 (2012).20. M. J. Dicken, K. Aydin, I. M. Pryce, L. A. Sweatlock, E. M.Boyd, S. Walavalker, J. Ma, and H. A. Atwater, Opt. Express17, 18330 (2009).21. J. Y. Suh, E. U. Donev, D. W. Ferrara, K. A. Ketz, and L. C.Feldman, J. Opt. A 10, 055202 (2008).22. D. Y. Lei, K. Appavoo, Y. Sonnefraud, R. F. Haglund, andS. A. Maier, Opt. Lett. 35, 23 (2010).23. D. W. Ferrara, E. R. MacQuarrie, J. Nag, A. B. Kaye, andR. F. Haglund, Appl. Phys. Lett. 98, 241112 (2011).24. M. Seo, J. Kyoung, H. Park, S. Koo, H. Kim, H. Bernien,B. J. Kim, J. H. Choe, Y. H. Ahn, H.-T. Kim, N. Park,Q-H. Park, K. Ahn, and D. Kim, Nano Lett. 10, 2064(2010).25. M. A. Kats, D. Sharma, J. Lin, P. Genevet, R. Blanchard,Z. Yang, M. M. Qazilbash, D. Basov, S. Ramanathan, andF. Capasso, Appl. Phys. Lett. 101, 221101 (2012).26. Z. Yang, C. Ko, and S. Ramanathan, Annu. Rev. Mater. Res.41, 337 (2011).27. W.-T. Liu, J. Cao, W. Fan, Z. Hao, M. C. Martin, Y. R. Shen,J. Wu, and F. Wang, Nano Lett. 11, 466 (2011).28. M. M. Qazilbash, M. Brehm, B.-G. Chae, P.-C. Ho, G. O.Andreev, B.-J. Kim, S. J. Yun, A. V. Balatsky, M. B. Maple,F. Keilmann, H.-T. Kim, and D. N. Basov, Science 318, 1750(2007).29. L. A. Gea and L. A. Boatner, Appl. Phys. Lett. 68, 3081(1996).30. D. Ruzmetov, K. T. Zawilski, S. D. Senanayake, V.Narayanamurti, and S. Ramanathan, J. Phys. 20, 465205(2008).31. H. S. Choi, J. S. Ahn, J. H. Jung, T. W. Noh, and D. H. Kim,Phys. Rev. B 54, 4621 (1996).32. B. A. Munk, Frequency Selective Surfaces: Theory andDesign (Wiley-Interscience, 2000).33. E. D. Palik, Handbook of Optical Constants of Solids II(Elsevier, 1998).34. I. Puscasu, D. Spencer, and G. D. Boreman, Appl. Opt. 39,1570 (2000).35. E. Cubukcu and F. Capasso, Appl. Phys. Lett 95, 201101(2009).370 OPTICS LETTERS / Vol. 38, No. 3 / February 1, 2013

Thermal tuning of mid-infrared plasmonic antenna arrays using a phase change material

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Thermal tuning of mid-infrared plasmonic antenna arrays using a phase change material

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