Letter pubs.acs.org/NanoLett
Gigahertz Acoustic Vibrations of Elastically Anisotropic Indium−TinOxide Nanorod Arrays Peijun Guo,† Richard D. Schaller,*,‡,§ Leonidas E. Ocola,‡ John B. Ketterson,∥ and Robert P. H. Chang*,† †
Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, Illinois 60208, United States ‡ Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Building 440, Lemont, Illinois 60439, United States § Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States ∥ Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States S Supporting Information *
ABSTRACT: Active control of light is important for photonic integrated circuits, optical switches, and telecommunications. Coupling light with acoustic vibrations in nanoscale optical resonators offers optical modulation capabilities with high bandwidth and small footprint. Instead of using noble metals, here we introduce indium−tin-oxide nanorod arrays (ITO-NRAs) as the operating media and demonstrate optical modulation covering the visible spectral range (from 360 to 700 nm) with ∼20 GHz bandwidth through the excitation of coherent acoustic vibrations in ITO-NRAs. This broadband modulation results from the collective optical diffraction by the dielectric ITO-NRAs, and a high differential transmission modulation up to 10% is achieved through efficient near-infrared, on-plasmon-resonance pumping. By combining the frequency signatures of the vibrational modes with finite-element simulations, we further determine the anisotropic elastic constants for single-crystalline ITO, which are not known for the bulk phase. This technique to determine elastic constants using coherent acoustic vibrations of uniform nanostructures can be generalized to the study of other inorganic materials. KEYWORDS: Indium−tin-oxide, nanorod, acoustic phonon, ultrafast spectroscopy, elasticity, single crystalline
T
expansion of the lattice have a duration much shorter than the vibrational periods of nanostructures (nanorods in the present study) and hence can excite various high-frequency acoustic modes.18,19 In such experiments, the geometrical deformation as well as strain-dependent change of refractive index produce oscillations in the intensity of a transmitted (or reflected) signal beam. However, the usual single resonance and internal loss of plasmonic systems place limits on the achievable wavelength range and modulation strength of the signal beam, with differential transmission modulation on the order of 0.0001− 1%.20,21 On the other hand, controllably doped materials such as transparent conducting oxides that behave as dielectrics in the visible range offer attractive metallic properties (e.g., LSPRs) in the infrared.22,23 These materials have robust physical properties such as rigidity and high melting points.24 In particular, indium−tin-oxide (ITO), widely used for solar cells,25 displays,26 light-emitting diodes,27,28 touch sensors,29 and heat-reflecting glasses,30 has recently been exploited for emerging applications in infrared plasmonics,31,32 electro-
he coupling of light to high-frequency acoustic vibrations is of interest for applications such as acousto-optic modulators1,2 and also represents an integral part of the emerging field of optomechanics.3−8 The ability to control light with coherent acoustic vibrations in nanoscale optical resonators offers unique opportunities for all-optical modulation with tailored spectral and temporal responses.9 This arises from the strong, shape-dependent confinement that can be achieved for both photons and phonons, which offers enhanced light intensity modulation capabilities with high bandwidths in the gigahertz (GHz) to terahertz (THz) range.10−12 In turn, the vibrational frequencies of nanometersized objects can be analyzed to determine the elastic constants.13−15 Plasmonic noble metal nanostructures have been widely exploited to optically excite and probe acoustic phonon modes.16,17 The large absorption cross-section at the localized surface plasmon resonances (LSPRs) facilitates phonon generation by the following mechanism: on-resonance pumping yields a rapid electron temperature rise (in a couple hundred femtoseconds), which is followed by a lattice temperature rise through electron−phonon coupling (in subpicosecond to a few picoseconds); this impulsive heating and the associated thermal © XXXX American Chemical Society
Received: June 1, 2016 Revised: August 6, 2016
A
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 1. SEM and static optical characterizations of the ITO-NRA. (a) Top-down and 30° views of the ITO-NRA under scanning electron microscope. Scale bars in panel a are 2 μm. Zoom-in views illustrate the crystalline directions of the nanorod. (b) Transmission spectrum of the ITONRA in the visible range (referenced to air). (c) Schematic diagram of the optical diffraction, as well as the static and transient absorption measurements. (d) Photograph of the diffraction spots produced from a white-light probe transmitted through the sample at normal incidence.
optical modulators,33,34 and nonlinear optical switching devices.35−37 In this work we combine the unique optical and mechanical properties of ITO to achieve strong modulation and steering of light via coherent acoustic vibrations in periodic indium−tinoxide nanorod arrays (ITO-NRAs). Because of the low carrier concentration compared to noble metals, ITO-NRAs exhibit an LSPR in the near-infrared (NIR), as well as a number of transmission minima in the 360 to 700 nm (denoted as the visible range in the paper) range resulting from the collective light diffraction by the periodic array. By resonantly pumping the ITO-NRA in the NIR, we demonstrate coherent acoustic vibrations, which modulate and steer the probe signals in the visible range at ∼20 GHz frequency with a maximal differential transmission modulation amplitude up to ∼10%. In addition, two complementary transient absorption (TA) measurement techniques were employed to probe the delay time windows of 0−1 ns and 0−50 ns; together they permit a detailed investigation of both the breathing and extensional modes of the ITO-NRAs with a large aspect ratio. By comparing the experimental vibrational frequencies with the finite-element simulation yielded counterparts, we for the first time report the anisotropic elastic tensor for single-crystalline ITO, which can shed light on the design and integration of mechanically robust, ITO-based electronic and optical devices, especially when their critical dimensions approach the tens of nanometer scale.38−42 The ITO-NRA shown in Figure 1a was fabricated via a vapor−liquid−solid nanorod growth technique, starting from a periodic array of gold nanoparticle catalysts where the latter were produced by electron beam lithography.37 The array studied has a periodicity of 1 μm; the nanorods have an average edge length of 180 (±5) nm and height of 2561 (±68) nm, respectively (see Figures S1 and S2). As indicated in Figure 1a, the edges of each nanorod are along the [1 0 0] and [0 1 0] directions, whereas the growth axis is along the [0 0 1] direction. The ITO-NRA grown epitaxially on a lattice-matched
yttria-stabilized zirconia (YSZ) (100) substrate exhibits high size uniformity and alignment over a large area of 0.6 cm × 0.9 cm (see Figure S3). Figure 1b and Figure S4 depict the static transmission spectra in the visible and the NIR ranges, respectively. The strong dip in the transmission spectrum at 1500 nm shown in Figure S4 arises from the transverse-LSPR of the ITO-NRA with electrons oscillating perpendicular to the length of the nanorods.31 The five transmission minima observed in the visible range (where ITO is “transparent”) from 360 to 700 nm at normal incidence arise from destructive interferences of electromagnetic waves propagating in the nanorod and free space.43 The periodic ITO-NRA acts as a two-dimensional dielectric diffraction grating; that is illustrated by a schematic drawing of the optical diffraction (Figure 1c) and the photograph of a white-light probe diffracted by the ITO-NRA (Figure 1d). The transmission minima of the forward scattered (0, 0) order measured at normal incidence (Figure 1b) are not due to light absorption. Instead, the transmission minima arise because light propagates in the nanorod and the surrounding free space at different velocities and become out of phase (that is, a phase difference equal to an odd number times π) at certain wavelengths; the interference between these two portions of light produces intensity minima of the (0, 0) order and at the same time intensity maxima of the (1, 0) and (1, 1) orders. Having determined the static spectral response, we then studied the transient behaviors using pump−probe TA experiments. To efficiently excite the coherent acoustic vibrations, we tuned the center wavelength of the pump to the transverse-LSPR of the ITO-NRA at 1500 nm. A white light probe covering the visible range was used to study the vibration-induced intensity modulation. To ensure sampling the array instead of an individual nanorod, the pump beam was adjusted to have a diameter of 190 μm. Both the pump and the probe beams were normal to the substrate (as indicated in Figure 1c). B
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 2. Transient absorption measurements of the ITO-NRA. (a) ΔT/T spectral map of the (0, 0) order for the spectral range between 360 to 700 nm with delay time up to 1 ns. Pump fluence is 8.46 mJ·cm−2. (b, c, and d) ΔT/T spectral maps of the (0, 0), (1, 0), and (1, 1) orders, respectively, plotted for delay times up to 500 ps. The solid arrow indicates the spectral window from 465 to 480 nm, and the dotted arrow indicates the spectral window from 490 to 520 nm. Data for the (0, 0) order are same as in panel a, but truncated in panel b for the ease of comparison.
We first ran TA experiments with delay times ranging from 0 to 1 ns using probe pulses generated via a translational delay stage. Figure 2a shows the measured ΔT/T spectral map for the (0, 0) order under a pump fluence of 8.46 mJ·cm−2. Notably, we found the ΔT/T spectral map composed of two pronounced transient features. The first transient feature is associated with a ΔT/T signal exhibiting spectrally alternating line-shapes and persisting throughout the entire delay time window of 1 ns with negligible decay of intensity. The second transient feature is an oscillation of ΔT/T signal, which is superimposed on the first transient feature and is mostly pronounced during the first 600 ps. Close inspection of the first transient feature reveals that each ΔT/T zero-crossing-wavelength from a blue, positive ΔT/T region to its red, adjacent negative ΔT/T region matches a static transmission minimum (in Figure 1b), manifesting a pump-induced redshift of the entire visible transmission spectrum. From a Drude description of ITO’s permittivity, ε(ω) = ε∞(ω) − ωp2/(ω2 + iγpω), the probe lies in the dielectric range of ITO, which is spectrally isolated from the NIR range that is dominated by the freeelectron-like behavior. The pump-induced redshift is expected to originate from a positive change of the background permittivity, ε∞(ω), due to thermal and elastic effects of the lattice (as during the nanosecond delay time window the electron and lattice are in thermal equilibrium so the hot electron effect is suppressed37,44−46). A detailed study of the change of ε∞(ω) under intraband pumping is outside the scope of the paper. The second transient feature, the periodic oscillation of ΔT/T signal, is attributed to the excitation of coherent acoustic vibrations of the ITO-NRA, which introduces strain (and a concomitant refractive index change) and geometrical deformation, and thereby modifying the optical transmission; this will be the focus of the following discussion.
The coherent acoustic vibrations of the ITO-NRA are manifested by the temporal oscillations of the ΔT/T signals with a period of ∼50 ps shown in Figure 2a. Notably, the transmission modulation covers the 360−700 nm spectral range, with a maximal ΔT/T approaching 10% at 564 nm under the highest experimental pump fluence of 24.4 mJ·cm−2 (see Figure S5 and Supporting Information Note 1). We note that this broadband modulation is a unique spectral feature that arises from the uniform, large aspect-ratio, dielectric ITO-NRA structure that supports multiple visible transmission minima due to a sufficient phase difference accumulation and is an array effect. In addition, the high-temperature durable, epitaxially anchored ITO-NRA is stable under high pump fluences (beyond 20 mJ·cm−2), thereby allowing strong phonon excitation; this is in sharp contrast to the noble metal counterparts that may change shape, melt, or peel off from substrates under a few mJ·cm−2 fluence.47,48 Due to the dielectric nature of the ITO-NRA, the vibrationinduced intensity modulation of the (0, 0) order is expected to be associated with complementary modulation of the (1, 0) and (1, 1) orders. This was investigated in extra TA experiments by collecting the (1, 0) and (1, 1) diffracted spots of the probe beam using an optical fiber. Only narrow spectral windows were measured due to the large spatial dispersion of the higher grating modes (Figure 1d). The measured ΔT/T spectral maps for the (1, 0) and (1, 1) orders, shown in Figure 2c and d, reveal that, at a given wavelength, the vibration-induced ΔT/T for the (1, 0) and (1, 1) orders are opposite in sign to that of the (0, 0) order shown in Figure 2b, which indicates that instead of being absorptive, the ITO-NRA periodically redistributes intensity between the centered (0, 0) order and the oblique higher orders. This high-frequency beam-steering capability, which permits control of both the intensity and direction of light, is a unique feature of ITO-NRA that cannot C
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 3. Frequency signatures of the breathing modes. (a) Fourier transform of the ΔT/T spectral map for the (0, 0) order shown in Figure 2a. (b) ΔT/T kinetics at 475 and 507 nm for the (0, 0) order and their corresponding Fourier transform. (c) ΔT/T kinetics at 475 and 507 nm for the (1, 0) order and their corresponding Fourier transform. (d) ΔT/T kinetics at 475 and 507 nm for the (1, 1) order and their corresponding Fourier transform.
Hence the 22.1 GHz oscillation appearing in the (0, 0) order is only related to the (1, 0) order, whereas the 18.7 GHz oscillation in the (0, 0) order is correlated with both the (1, 0) and the (1, 1) orders. Nanorods exhibit three types of vibration modes, namely, breathing, extensional, and bending modes; the first two correspond to expansion and compression along the radial and longitudinal directions, respectively.49−52 The frequencies of the breathing and extensional modes are inversely proportional to the radial and longitudinal dimensions51 and are expected to differ by an order of magnitude in the present case (aspect ratio of ITO nanorod is ∼14). Since ∼100 nm radius nanorods exhibit breathing modes at a few to tens of GHz,50,53,54 we assign the 18.7 and 22.1 GHz frequencies to the first and second breathing modes, respectively. These two modes are consistent with observations in pentagonal gold nanowires,53 in which the displacement fields for the two modes were found to concentrate at the corners and edges of the cross-sectional plane, respectively, due to the break of the cylindrical symmetry. To determine the elastic properties of ITO based on the vibrational frequencies, we performed finite-element simulations using COMSOL Multiphysics. Since simulations of a large aspect-ratio nanorod with sharp corners are computationally expensive, we first reduced the problem to a two-dimensional (2D) cross-section; this accurately captures the vibrational behaviors of the breathing modes which are dominated by lattice displacements within the cross-sectional plane. Justifications regarding the use of the 2D model appears in the Supporting Information Note 2 and Figures S6−S8. Full threedimensional (3D) simulations for a unit cell of the periodic ITO-NRA were also performed and agree well with the 2D
be easily achieved by metallic nanostructures due to weaker diffraction efficiencies arising from their optical loss in similar spectral ranges. The frequency signatures of the ΔT/T spectral map for the (0, 0) mode (Figure 2a), which appear in the Fourier transform shown in Figure 3a, exhibit two prominent features centered at around 20 GHz. Figure 3a further shows that the negative ΔT/ T maxima centered at around 507 and 613 nm primarily oscillate at a single frequency, whereas all other positive and negative ΔT/T maxima, such as that at 475 nm, contain two frequencies. This is further supported by Figure 3b, which shows the time evolution of ΔT/T and their Fourier transform at 475 and 507 nm. We find the 475 nm response involves a peak at 18.5 GHz with a full-width-half-maximum (fwhm) of 1.23 GHz, and a second peak at 22.1 GHz with a fwhm of 1.21 GHz. As indicated in Figure 3b, the beating of the two vibrational modes at 475 nm leads to a cancellation of the vibration-induced ΔT/T signal. In contrast, the 507 nm response exhibits a single peak of 18.9 GHz with a fwhm of 1.49 GHz. Since the frequency difference of 0.4 GHz between 18.5 and 18.9 GHz is significantly smaller than the FWHMs of each peak, we assign these two frequencies to the same mode and take their average value of 18.7 GHz as the mode frequency; the 0.4 GHz difference likely arises from the slight tapering of the ITO nanorod and a different spatial coupling of the electric and displacement fields at these two wavelengths. The time dependence and associated Fourier transform for the (1, 0) and (1, 1) orders at 475 and 507 nm are shown in Figure 3c and d, respectively. We note that the (1, 0) order exhibits two frequencies at 475 nm with equal weights, but only one frequency of 18.9 GHz at 507 nm. For the (1, 1) order, however, a single frequency is observed at both wavelengths. D
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 4. Finite-element simulations of the breathing modes. (a, b, and c) 2D cross-section simulation predicted volumetric strain integrated over the nanorod cross-section plotted as a function of frequency (shown as the vertical axis) and C11, C12, and C44, respectively (shown as the horizontal axis). (d) Displacement amplitudes for the first and second breathing modes (linearly scaled into the range of 0−1). The edge length of the crosssection is 180 nm. The common elastic constants used in simulations are C11 = 277.5 GPa, C12 = 107 GPa, and C44 = 33.8 GPa.
experiment and modeling combine to indicate elastic constant values for C11 of 277.5 GPa and C44 of 33.8 GPa, C12 only adjusts the relative strength of the two modes (as indicated in Figure 4b) and hence cannot be uniquely determined. The measured ΔT/T oscillations result from a poorly understood strain dependent permittivity, hence correlating the relative strengths of the two modes from simulations with the optical signals measured from TA experiments was not attempted. In order to determine C12, we further examined the extensional mode of the ITO-NRA using a different TA technique, in which a maximal delay time of ∼50 ns was realized via electronically delayed white light probe pulses. The measured ΔT/T spectral map and associated Fourier transform are shown in Figure 5a and b, respectively, from which we find an oscillation frequency with a weighted average of 0.524 GHz and a standard deviation of 0.0325 GHz (see Supporting Information Note 6, Figure S13). To understand the extensional mode, we performed 3D simulations for a unit cell composed of a single ITO nanorod anchored on YSZ substrate. As there is no adhesion layer between ITO and YSZ (the growth is epitaxial), no thin elastic layer was used in our 3D simulation. This is in contrast to the gold/titanium/glass structures reported elsewhere, in which the titanium adhesion layer alters the vibrational frequencies of the gold nanoparticles.9,16 We treated the single-crystalline, cubic-symmetry YSZ substrate using the reported elastic constants of C11 = 403.5 GPa, C12 = 102.4 GPa and C44 = 59.9 GPa,55 and a density of 6.0 g·cm−3.56 Fixing C11 = 277.5 GPa and C44 = 33.8 GPa for ITO (determined from the breathing mode frequencies), we varied C12 from 40 to 130 GPa in the 3D simulations. Figure 5c shows the displacement of the center of the nanorod top plane along the long axis as a function of
simulation results. In all simulations the theoretical density of 7.16 g·cm−3 for ITO was assumed (see Supporting Information Note 3). We first attempted simulations by taking ITO as an isotropic material described by the Young’s modulus, E, and Poisson’s ratio, υ (see Supporting Information Note 4). As shown in Figures S9 and S10, for all possible E and υ values, the simulations cannot reproduce the two experimentally observed breathing mode frequencies of 18.7 and 22.1 GHz. This strongly suggests that the isotropic elastic model of ITO cannot capture the vibrational behaviors of our single-crystalline ITONRA, and hence ITO is expected to be elastically anisotropic. To clarify the effects of anisotropy, we performed 2D simulations using the three elastic constants, C11, C12, and C44; those are required to characterize the cubic ITO. We varied these constants over a wide range until the two simulated breathing mode frequencies agreed well with the experimental values. Figure 4a, b, and c shows the color-coded maps of the frequency dependent integration of the volumetric strain over the square cross-section for varying values of C11, C12, and C44. We find that C11 shifts the frequencies of both modes, C12 has little effect on the frequencies but tunes the relative strengths of the two modes, and C44 mainly affects the frequency of the second mode as well as the relative strengths of the two modes. Note that in each panel only one elastic constant was swept. The fixed values of C11, C12, and C44 in the sweeps are 277.5, 107, and 33.8 GPa, respectively, which, as shown below, are our best estimates of the elastic constants for ITO. Figure 4d shows the displacement fields for the two breathing modes, which are maximized at the corners and edge centers for the respective first and second breathing modes (also see Supporting Information Note 5, Figures S11 and S12). Whereas the E
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 5. Analysis of the extensional mode of the ITO-NRA. (a) ΔT/T spectral map of the (0, 0) order for the spectral range between 380 to 700 nm with delay times up to 28 ns. The pump fluence is 34.2 mJ·cm−2. (b) Fourier transform of the ΔT/T spectral map shown in (a). The dashed line shows the weighted average of the vibrational frequency. (c) Simulated displacement amplitude of the center of the nanorod top plane along the nanorod long axis for various C12 values plotted as a function of frequency. Nanorod height and edge length in the simulation are 2561 and 180 nm, respectively. C11 and C44 are 277.5 and 33.8 GPa. (d) Displacement amplitudes for the extensional mode and the two breathing modes. The displacement amplitude along the nanorod long axis is color-coded for the extensional mode, whereas total displacement amplitude is color-coded for the breathing modes. All displacement amplitudes are linearly scaled into the range of 0 to 1, and the deformation of the structure is linearly proportional to the corresponding displacement amplitudes.
vibration frequency for different C12 values. Note that the extensional mode is manifested as a peak in the curves of tip displacement versus frequency, so Figure 5c suggests that increasing C12 yields a lower extensional mode frequency. A C12 of 107 GPa provided the closest match between the experiments and simulations. Using the three determined elastic constants, we performed full 3D simulations for the extensional and breathing modes. Figure 5d shows the colorcoded displacement amplitude along the nanorod long axis for the extensional mode, which monotonically increases from the bottom to the top of the nanorod. Figure 5d also shows the color-coded amplitude of the total displacement for the two breathing modes, which match well with the 2D cross-section analogue shown in Figure 4d obtained from 2D simulations. With the three elastic constants in hand, we can determine the Young’s modulus of ITO along any crystalline direction (see Supporting Information Note 7). The Young’s modulus of ITO along its three primary directions are determined to be E[100] = 217.9 GPa, E[110] = 110.5 GPa, and E[111] = 94.9 GPa, which suggests that ITO is elastically anisotropic, as further presented graphically by the orientation dependent Young’s modulus diagram in Figure 6a. The Young’s modulus for crystal directions lying in the three low-index (100), (110), and (111) planes are plotted in Figure 6b, c, and d, respectively. Based on the single-crystalline elasticity, we further estimate the lower and upper bounds on the Young’s modulus for polycrystalline ITO, which are determined to be 122.6 and 146.9 GPa,
respectively. A comparison with literature reported values appears in Supporting Information Note 8. In conclusion, we have demonstrated robust GHz optical modulation and beam-steering capabilities covering the visible spectrum, enabled by coherent acoustic vibrations of periodic, uniform ITO-NRAs. Such high-frequency broadband modulation has not been previously demonstrated, and the peak amplitude change in transmission is particularly large, which opens the door to active, compact, and wide-bandwidth optical components. Second, by comparing the experimental vibration frequencies with simulation results, we determined the anisotropic elastic constants for single-crystalline ITO in the absence of information on the bulk values. The scheme demonstrated here can potentially facilitate the determination of the elastic constants of other crystalline materials where the bulk values are unknown owing to the lack of large single crystals needed for ultrasonic measurements57 or the difficulty of growing smooth single-crystalline films along multiple orientations as required for nanoindentation measurements (as minimization of surface energy favors film termination in the most stable surfaces58−60 regardless of the film growth direction), provided they can be formed into uniform nanostructured arrays. F
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
Figure 6. Directional-dependent Young’s modulus of ITO. (a) Crystal-orientation dependent Young’s modulus diagram for single-crystalline ITO. The distance from the origin to the surface is equal to the Young’s modulus along that particular direction, which is also color-coded. (b, c, and d) Crystal orientation dependent Young’s modulus for crystal directions in the (1 0 0), (1 1 0), and (1 1 1) planes, respectively. Certain low-index directions are shown by the dashed line.
■
ASSOCIATED CONTENT
University), which has received support from the MRSEC program (NSF DMR-1121262) at the Materials Research Center, the International Institute for Nanotechnology (IIN) and the State of Illinois through the IIN. We acknowledge support from the Ultrafast Initiative of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, through Argonne National Laboratory under Contract No. DEAC02-06CH11357. The work also utilized the Northwestern University Micro/Nano Fabrication Facility (NUFAB), which is supported by the State of Illinois and Northwestern University.
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.6b02217. Experimental section; Figures S1−S13; Notes 1−8 (PDF)
■
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail:
[email protected],
[email protected]. *E-mail:
[email protected]. Author Contributions
REFERENCES
(1) Kapfinger, S.; Reichert, T.; Lichtmannecker, S.; Muller, K.; Finley, J. J.; Wixforth, A.; Kaniber, M.; Krenner, H. J. Nat. Commun. 2015, 6, 8540. (2) Saleh, B. E. A.; Teich, M. C. Fundamentals of Photonics, 2nd ed.; Wiley-Interscience: Hoboken, 2007. (3) Gil Santos, E.; Baker, C.; Nguyen, D. T.; Hease, W.; Gomez, C.; Lemaître, A.; Ducci, S.; Leo, G.; Favero, I. Nat. Nanotechnol. 2015, 10, 810−816. (4) Ding, L.; Baker, C.; Senellart, P.; Lemaitre, A.; Ducci, S.; Leo, G.; Favero, I. Phys. Rev. Lett. 2010, 105, 263903. (5) Bahl, G.; Kim, K. H.; Lee, W.; Liu, J.; Fan, X.; Carmon, T. Nat. Commun. 2013, 4, 1994. (6) Safavi-Naeini, A. H.; Alegre, T. P. M.; Chan, J.; Eichenfield, M.; Winger, M.; Lin, Q.; Hill, J. T.; Chang, D. E.; Painter, O. Nature 2011, 472, 69−73. (7) Favero, I.; Karrai, K. Nat. Photonics 2009, 3, 201−205. (8) Zheludev, N. I.; Plum, E. Nat. Nanotechnol. 2016, 11, 16−22. (9) Chang, W.-S.; Wen, F.; Chakraborty, D.; Su, M.-N.; Zhang, Y.; Shuang, B.; Nordlander, P.; Sader, J. E.; Halas, N. J.; Link, S. Nat. Commun. 2015, 6, 7022. (10) Tadesse, S. A.; Li, M. Nat. Commun. 2014, 5, 5402.
P.G., R.D.S., and R.P.H.C. designed the research. P.G. fabricated the sample, performed static measurements and simulations, and analyzed data; R.D.S. performed TA experiments; L.E.O. assisted electron beam fabrication; J.B.K. contributed to the analysis of the vibrational modes. All authors discussed the results. P.G. prepared the manuscript with input and editing from all authors. R.P.H.C. and R.D.S. supervised the project. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The work was funded by the MRSEC program (NSF DMR1121262) at Northwestern University. Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The work made use of the EPIC facility (NUANCE Center-Northwestern G
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters (11) Van Laer, R.; Kuyken, B.; Van Thourhout, D.; Baets, R. Nat. Photonics 2015, 9, 199−203. (12) Juvé, V.; Crut, A.; Maioli, P.; Pellarin, M.; Broyer, M.; Del Fatti, N.; Vallée, F. Nano Lett. 2010, 10, 1853−1858. (13) Zijlstra, P.; Tchebotareva, A. L.; Chon, J. W. M.; Gu, M.; Orrit, M. Nano Lett. 2008, 8, 3493−3497. (14) Mahmoud, M. A.; O’Neil, D.; El-Sayed, M. A. Nano Lett. 2014, 14, 743−748. (15) Hu, M.; Hillyard, P.; Hartland, G. V. Nano Lett. 2004, 4, 2493− 2497. (16) O’Brien, K.; Lanzillotti-Kimura, N. D.; Rho, J.; Suchowski, H.; Yin, X.; Zhang, X. Nat. Commun. 2014, 5, 4042. (17) Pelton, M.; Sader, J. E.; Burgin, J.; Liu, M.; Guyot-Sionnest, P.; Gosztola, D. Nat. Nanotechnol. 2009, 4, 492−495. (18) Hartland, G. V. Chem. Rev. 2011, 111, 3858−3887. (19) Perner, M.; Gresillon, S.; März, J.; von Plessen, G.; Feldmann, J.; Porstendorfer, J.; Berg, K. J.; Berg, G. Phys. Rev. Lett. 2000, 85, 792− 795. (20) Schumacher, T.; Kratzer, K.; Molnar, D.; Hentschel, M.; Giessen, H.; Lippitz, M. Nat. Commun. 2011, 2, 333. (21) Kelf, T. A.; Tanaka, Y.; Matsuda, O.; Larsson, E. M.; Sutherland, D. S.; Wright, O. B. Nano Lett. 2011, 11 (9), 3893−3898. (22) Boltasseva, A.; Atwater, H. A. Science 2011, 331, 290−291. (23) Sachet, E.; Shelton, C. T.; Harris, J. S.; Gaddy, B. E.; Irving, D. L.; Curtarolo, S.; Donovan, B. F.; Hopkins, P. E.; Sharma, P. A.; Sharma, A. L.; Ihlefeld, J.; Franzen, S.; Maria, J.-P. Nat. Mater. 2015, 14, 414−420. (24) Guler, U.; Boltasseva, A.; Shalaev, V. M. Science 2014, 344, 263− 264. (25) Zhu, J.; Hsu, C.-M.; Yu, Z.; Fan, S.; Cui, Y. Nano Lett. 2010, 10, 1979−1984. (26) Betz, U.; Kharrazi Olsson, M.; Marthy, J.; Escolá, M. F.; Atamny, F. Surf. Coat. Technol. 2006, 200, 5751−5759. (27) Helander, M. G.; Wang, Z. B.; Qiu, J.; Greiner, M. T.; Puzzo, D. P.; Liu, Z. W.; Lu, Z. H. Science 2011, 332, 944−947. (28) Kim, H.; Piqué, A.; Horwitz, J. S.; Mattoussi, H.; Murata, H.; Kafafi, Z. H.; Chrisey, D. B. Appl. Phys. Lett. 1999, 74, 3444−3446. (29) Maheshwari, V.; Saraf, R. F. Science 2006, 312, 1501−1504. (30) Hjortsberg, A.; Hamberg, I.; Granqvist, C. G. Thin Solid Films 1982, 90, 323−326. (31) Li, S. Q.; Guo, P.; Zhang, L.; Zhou, W.; Odom, T. W.; Seideman, T.; Ketterson, J. B.; Chang, R. P. H. ACS Nano 2011, 5, 9161−9170. (32) Garcia, G.; Buonsanti, R.; Runnerstrom, E. L.; Mendelsberg, R. J.; Llordes, A.; Anders, A.; Richardson, T. J.; Milliron, D. J. Nano Lett. 2011, 11, 4415−4420. (33) Lee, H. W.; Papadakis, G.; Burgos, S. P.; Chander, K.; Kriesch, A.; Pala, R.; Peschel, U.; Atwater, H. A. Nano Lett. 2014, 14, 6463− 6468. (34) Krasavin, A. V.; Zayats, A. V. Phys. Rev. Lett. 2012, 109, 053901. (35) Abb, M.; Wang, Y.; de Groot, C. H.; Muskens, O. L. Nat. Commun. 2014, 5, 4869. (36) Tice, D. B.; Li, S.-Q.; Tagliazucchi, M.; Buchholz, D. B.; Weiss, E. A.; Chang, R. P. H. Nano Lett. 2014, 14, 1120−1126. (37) Guo, P.; Schaller, R. D.; Ketterson, J. B.; Chang, R. P. H. Nat. Photonics 2016, 10, 267−273. (38) Riha, S. C.; DeVries Vermeer, M. J.; Pellin, M. J.; Hupp, J. T.; Martinson, A. B. F. ACS Appl. Mater. Interfaces 2013, 5, 360−367. (39) Lee, B.; Guo, P.; Li, S.-Q.; Buchholz, D. B.; Chang, R. P. H. ACS Appl. Mater. Interfaces 2014, 6, 17713−17722. (40) Gregory, S. A.; Wang, Y.; de Groot, C. H.; Muskens, O. L. ACS Photonics 2015, 2, 606−614. (41) Abb, M.; Albella, P.; Aizpurua, J.; Muskens, O. L. Nano Lett. 2011, 11, 2457−2463. (42) Yoon, J.; Baca, A. J.; Park, S.-I.; Elvikis, P.; Geddes, J. B.; Li, L.; Kim, R. H.; Xiao, J.; Wang, S.; Kim, T.-H.; Motala, M. J.; Ahn, B. Y.; Duoss, E. B.; Lewis, J. A.; Nuzzo, R. G.; Ferreira, P. M.; Huang, Y.; Rockett, A.; Rogers, J. A. Nat. Mater. 2008, 7, 907−915.
(43) Li, S.-Q.; Sakoda, K.; Ketterson, J. B.; Chang, R. P. H. Appl. Phys. Lett. 2015, 107, 031104. (44) Del Fatti, N.; Vallée, F.; Flytzanis, C.; Hamanaka, Y.; Nakamura, A. Chem. Phys. 2000, 251, 215−226. (45) Voisin, C.; Christofilos, D.; Loukakos, P. A.; Del Fatti, N.; Vallée, F.; Lermé, J.; Gaudry, M.; Cottancin, E.; Pellarin, M.; Broyer, M. Phys. Rev. B: Condens. Matter Mater. Phys. 2004, 69, 195416. (46) Link, S.; El-Sayed, M. A. Annu. Rev. Phys. Chem. 2003, 54, 331− 366. (47) Gordel, M.; Olesiak-Banska, J.; Matczyszyn, K.; Nogues, C.; Buckle, M.; Samoc, M. Phys. Chem. Chem. Phys. 2014, 16, 71−78. (48) Li, W.; Guler, U.; Kinsey, N.; Naik, G. V.; Boltasseva, A.; Guan, J.; Shalaev, V. M.; Kildishev, A. V. Adv. Mater. 2014, 26, 7959−7965. (49) Ruijgrok, P. V.; Zijlstra, P.; Tchebotareva, A. L.; Orrit, M. Nano Lett. 2012, 12, 1063−1069. (50) Mariager, S. O.; Khakhulin, D.; Lemke, H. T.; Kjær, K. S.; Guerin, L.; Nuccio, L.; Sørensen, C. B.; Nielsen, M. M.; Feidenhans’l, R. Nano Lett. 2010, 10, 2461−2465. (51) Hu, M.; Wang, X.; Hartland, G. V.; Mulvaney, P.; Juste, J. P.; Sader, J. E. J. Am. Chem. Soc. 2003, 125, 14925−14933. (52) Mante, P.-A.; Ho, C.-Y.; Tu, L.-W.; Sun, C.-K. Opt. Express 2012, 20, 18717−18722. (53) Yu, K.; Major, T. A.; Chakraborty, D.; Devadas, M. S.; Sader, J. E.; Hartland, G. V. Nano Lett. 2015, 15, 3964−3970. (54) Li, Y.; Clady, R.; Park, J.; Thombare, S. V.; Schmidt, T. W.; Brongersma, M. L.; McIntyre, P. C. Nano Lett. 2014, 14, 3427−3431. (55) Kandil, H. M.; Greiner, J. D.; Smith, J. F. J. Am. Ceram. Soc. 1984, 67, 341−346. (56) Schlichting, K. W.; Padture, N. P.; Klemens, P. G. J. Mater. Sci. 2001, 36, 3003−3010. (57) Mason, W. P. J. Acoust. Soc. Am. 1956, 28, 1197−1206. (58) Zhang, K. H. L.; Walsh, A.; Catlow, C. R. A.; Lazarov, V. K.; Egdell, R. G. Nano Lett. 2010, 10, 3740−3746. (59) Chambers, S. A. Surf. Sci. Rep. 2000, 39, 105−180. (60) Taga, N.; Maekawa, M.; Kamei, M.; Yasui, I.; Shigesato, Y. Jpn. J. Appl. Phys. 1998, 37, 6585−6586.
H
DOI: 10.1021/acs.nanolett.6b02217 Nano Lett. XXXX, XXX, XXX−XXX
