Plasmonic Nanorod Antenna Array: Analysis in Reflection and

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Plasmonic Nanorod Antenna Array: Analysis in Reflection and Transmission Vera Fiehler, Fabian Patrovsky, Lisa Ortmann, Susan Derenko, Andreas Hille, and Lukas M. Eng J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b02419 • Publication Date (Web): 09 May 2016 Downloaded from http://pubs.acs.org on May 15, 2016

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The Journal of Physical Chemistry

Plasmonic Nanorod Antenna Array: Analysis in Reflection and Transmission Vera Fiehler*φ, Fabian Patrovskyφ, Lisa Ortmannφ,ε, Susan Derenkoφ, Andreas Hilleφ,ρ, and Lukas M. Engφ φ

Institute for Applied Physics, TU Dresden, 01062 Dresden, Germany,

ε

Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany

AFFILIATION: Dr. Andreas Hille also affiliated to:

ρ

Sim4tec, Arnoldstraße 18b, 01307

Dresden

ACS Paragon Plus Environment

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ABSTRACT: Gold nanorod antenna arrays provide ultra strong plasmonic field enhancement and a superb broadband spectral tunability, as needed e.g. for label-free bio-sensing, surfaceenhanced Raman spectroscopy, or optical filter design. The key issue when integrating such nanorod substrates is the question whether the plasmonic properties are superior to be applied in reflection or transmission geometry, which clearly needs a thorough analysis. Here we provide a complete and fundamental experimental and theoretical investigation of such gold nanorod antenna arrays embedded in an anodized aluminum oxide matrix. We show that the excitation of individual and coupled plasmonic eigenmodes in such nanorod arrays under an oblique angle of incidence provides an efficient tool for tuning the photonic response for both reflection and transmission applications. Moreover, simultaneous recording of the transmitted and reflected intensities under s- and p- polarization for angles ranging from 0° to 80° over the whole visible wavelength range, allows us, for the first time, to quantify also the absorptive losses in these embedded gold nanorod antenna arrays.


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INTRODUCTION Surface Plasmon Polaritons (SPPs), the collective excitation of electron oscillations at the interface between two materials, first appeared after experimental investigations carried out in the late 1960s by various researchers.1-3 Those experiments were triggered initially by the seminal work of Sommerfeld4, Zenneck5 and Rayleigh6-7 describing the phenomena of electromagnetic waves bound to surface interfaces, an effect that Wood8 had already mentioned in his reflection measurements when investigating optical gratings in the early 20th century. With their strong field enhancement, surface plasmons opened new strategies for surface enhanced detection methods like surface-enhanced Raman spectroscopy (SERS) and surface plasmon resonance (SPR) spectroscopy. To date, SPR sensors already constitute a standard method for the label-free analysis in biological and medical applications9,10. Especially SPR spectroscopy based on localized surface plasmons (LSPR) possesses great potential for lab-onchip bio-sensing in the low cost regime, due to the broad tunability of plasmon resonances on the nanometer length scale. For the last decades, we witnessed an immense progress in the investigation of optical properties of noble metal particles for sensing, display and imaging technologies11,12; nanostructures like dots, holes, disks, antennas and split ring resonators13-16 have emerged and are just a few prominent examples to be mentioned. In order to provide nanostructures with the appropriate precision, they are commonly fabricated by top-down methods such as electron beam lithography (EBL) or focused ion beam (FIB) milling. Despite their positive attributes, both EBL and FIB suffer great drawbacks due to their low speed and high costs, which makes large-scale industrial implementation rather unfavorable. A great approach towards faster array fabrication was presented in the 1940s17


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introducing a bottom-up, low-cost technique using anodized aluminum oxide (AAO) matrices. Anodization constitutes a fast and inexpensive method in order to fabricate large-area porous template arrays that may then be filled with the material of choice. Numerous work18-20 has been published based on this template-assisted fabrication of plasmonic nanostructures with a majority of works focusing on thick (> 50 µm) aluminum foils for fabrication21,22. Thin aluminum films, in contrast, as applied in this paper, bear a manifold of advantages: Firstly, thin back electrodes (of less than 10 nm thickness) may be used, while secondly the fabrication of free-standing, vertically aligned nanorod arrays with exceptionally high surface areas becomes possible. The optical properties of such plasmonic nanorod arrays can be widely tuned by adjusting diameter, length and distance between the nanorods (NRs)23, while less raw material is used for fabrication as compared to thick aluminum foils. The benefits are straightforward, not only in the view of production costs, but equally when inspecting the optical properties of such templates. However, it raises a set of important questions: Which optical properties stem from the plasmonic responses of such thin-film nanorod arrays and which ones can be attributed to the thin-film alumina matrix? Which of these optical features can be accessed in reflectance measurements, and which ones in transmittance? This work focuses on the complete description of these optical properties of thin-film nanorod arrays embedded in alumina templates as obtained from reflectance and transmittance measurements. To the best of our knowledge, no such description exists yet. Kabashin24 and coworkers used similar substrates, however, they employed a prism-based excitation in totalinternal reflection in Kretschmann-Raether configuration, which gave rise to a unique guided


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mode through the nanorod substrate. Lyvers and coworkers used thick alumina foils instead, having a thick back electrode in order to perform reflectance measurements at various nanorod lengths; nevertheless, they did not consider the exact thickness of the alumina templates hence, neglecting possible thin film interference effects25. To completely understand the transmittance (T) and reflectance (R) of such embedded thinfilm nanorod arrays, here we present both experimental results and theoretical simulations using finite element modeling (FEM method, COMSOL; see methods section) of gold NR samples with 220 nm rod length (L) at variable angles of incidence (AOI) in both transmission and reflection geometry for s- and p-polarized light. The complexity of the structure demands numerical simulations, although few attempts were conducted to derive analytical formulas as well26,27. All measurements were recorded in one and the same setup as presented in Fig. 1 a) (see methods section) and stem from the same sample and surface area. With our work, we provide a detailed description of the optical behavior of such thin-film plasmonic nanorod substrates, which otherwise is not accessible through analytical approximations28-30 due to their complexity. Our work thus allows to gain insight into the origin of the optical resonances in both transmission and reflection properties of nanorod arrays.


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Figure 1. a) Sketch of the experimental setup for transmittance and reflectance measurements, b) cross-section of a gold nanorod antenna array (Au-NRAA) (length L = 220 nm, interrod distance IR = 63 nm, diameter d = 28 nm) embedded in an anodized aluminum oxide matrix (FIB – SEM image) and c) top view SEM image of a Au-NRAA embedded in an anodized aluminum oxide matrix. Methods Fabrication A template-based approach as described by Evans31 was used here in order to produce gold nanorod arrays on microscope glass slides (Thermo Fisher Scientific). The layered system consists of 3 nm Ti for adhesion, 10 nm gold as a subsequent working electrode material, and 200 nm aluminum deposited via magnetron sputtering (base pressure < 10-7 mbar). The aluminum layer was completely transformed into a porous alumina template via anodization in an aqueous 0.3 M H2SO4 solution at 1 °C at a voltage of 26 V using a pure aluminum counter electrode. The remaining barrier layer at the bottom of the pores was completely removed via a 30 s exposure to an aqueous 0.03 M NaOH solution at room temperature, and the pores were widened simultaneously. The pores were then filled electrochemically with gold, with the gold bottom layer acting as the working electrode for electroplating. The used aqueous gold solution was composed of 0.05 M HAuCl4, 0.42 M Na2SO3, and 0.42 M Na2S2O3. DC electrodeposition was carried out in potentiostatic mode (to achieve similar deposition conditions for different sample areas) at room temperature using a platinum counter electrode and a potential of -0.45 V was maintained versus a standard calomel reference electrode.


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Optical measurements All optical measurements were performed with the same goniometer setup and an Ocean Optics Maya2000 Pro spectrometer. An Osram halogen lamp (Xenophot 64610 HLX) was used for illumination while s- or p-polarization was selected using a Glan-Thompson prism. The light was collected with a fiber and guided to the spectrometer. For transmittance measurements the AOI was increased continuously from 0 to 80° in steps of 0.5°. The lowest possible AOI for direct reflectance measurements was 9°, limited by the dimensions of the setup. For better comparability all spectra in this paper are plotted over the range from 10 to 80° in a false color plot. All measurements are normalized to the intensity of the halogen lamp which provides consistent data and allows a comparison of both geometries. Simulations All simulations where performed by FEM modeling using COMSOL Multiphysics 5.0 with wave optics module. To model the hexagonal array, a rectangular unit cell (see Fig. 2) was constructed with periodic boundary conditions at the planes normal to x, and PEC/PMC (Perfect Electric Conductor/ Perfect Magnetic Conductor) boundary conditions for s- /p-polarized light at the planes normal to y. The incident electric field was chosen to be a plane wave with variable angles of incidence entering the simulation domain from the top with the normal of the plane of incidence pointing along the y direction. The transmitted and reflected wave was obtained via the port boundary condition 200 nm above or below the NR array. These also acquired the scattering coefficients used for the calculation of the transmittance and reflectance. As dielectric function for gold the data of Johnson and Christy32 was used. The refractive indices of air, aluminum


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oxide and glass were assumed to be constant with values of n = 1, n = 1.6 and n = 1.5, respectively.

Figure 2. 3D – (a)) and top view (b)) of one unit cell used for FEM simulations. An infinite array is composed by translation in x-direction and reflection in y-direction. Results 1.

Substrate Characterization


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AAO templates were fabricated using thin film anodization as explained in the methods section. Starting with an aluminum layer of 200 nm in thickness, the resulting porous AAO layer has gained 10% in height due to incorporation of oxygen into the atomic lattice resulting in a 220 nm thick AAO (see Fig. 1 b)). The samples have a 10 nm thin Au conducting layer required for the subsequent electrochemical pore filling. The layer thickness of the AAO matrix limits the length (L) of the NRs, resulting in a maximum length of L = 220 (± 20) nm as evaluated from the SEM/FIB images (Fig. 1 b)). To determine both rod diameter and interrod distance, top view SEM images (see Fig. 1 c)) of 8-15 µm² were taken on four different sample spots. An automated image processing algorithm was used to identify and measure all rods of an image. The average diameter was determined to be D = 28 (± 3) nm. Averaging the distance between nearest neighbors leads to an interrod distance of IR = 63 (±7) nm. The nanorods are arranged in a quasi-hexagonal order. 2.

Optical measurements and simulation

Due to the very thin gold bottom electrode it is possible to perform measurements in both transmittance and refelectance configuration on one and the same sample (see Fig. 1 a)). The sample is illuminated either with p- or s- polarized white light under an AOI of 0-80° for transmittance and 10-80° for reflectance measurements. For a better comparability, we display all the data for the AOI range of 10-80°, and label their magnitude in extinction units [i.e. -ln(T) or -ln(R)]. To allow a convenient referencing between the measurements, all optical features are labeled using a letter T (transmission) or R (reflection) and a successive number throughout this paper. The spectral position of every feature was acquired fitting a combination of Lorentz functions to the specific spectra. The error is less than 2 nm for each value.


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A.

Transmittance

At first, the measured and the simulated transmittance spectra for s-polarized and p-polarized illumination of gold NRs embedded in the AAO matrix for increasing AOIs are shown in Fig. 3. Using s-polarized illumination in transmission geometry, two main optical features appear: A high absorbance is observed at λT1,exp = 524 nm for all AOIs and labeled T1-mode in the following. It is followed by a high transmission at λT2,exp = 625 nm, which is labeled as T2-mode in Fig. 3 a)). Both features, T1 and T2, are also well reproduced by FEM simulations for spolarization, with the T2 dip, however, being red shifted to λT2,sim = 694 nm and appearing more pronounced. When exciting the sample with p-polarized light, two absorbance maxima are observed centered at λT1,exp = 524 nm and λT3,exp = 700 nm, respectively (see T1 and T3 in Fig. 3 b)). For isolated, individual nanorods these two resonances usually are referred to as the short axis and long axis plasmonic resonances14. In order to verify their origin, the measured transmittance spectra are compared to the simulated data. Both maxima are well reproduced by simulations as seen from Fig. 3 d), with the T3-mode, however, appearing at λT3,sim = 591 nm. Additionally, this T3 maximum splits into two peaks and shows varying intensities in the simulations. The peak starts to appear at approximately 10° AOI at 623 nm, fades around 40° AOI, and then rises again


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above 50°, then being centered at 591 nm. The simulation reveals an additional third maximum in absorbance, the T4-mode, located at λT4,sim = 701 nm, appearing when the AOI exceeds 20°.

Figure 3. Measured (a,b) and simulated (c,d) transmittance spectra of gold NR (D = 28 nm, IR = 63 nm, L = 220 nm) embedded in AAO and excited with (a,c) s- and (b,d) p-polarized light. The dotted lines in the simulated data show the positions of the extracted field plots (see Fig. 5).


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B.

Reflectance

In direct reflectance measurements illuminated with s-polarized light two peaks can be distinguished (R1 and R2), which are highlighted in the corresponding plots (see Fig. 4 a)) at λR1,exp = 491 nm and λR2,exp = 586 nm for an AOI of 20°. Both peaks first appear above 10° AOI and slightly shift to smaller wavelengths with increasing AOI. The simulation for s-polarized excitation confirms the measured results. R1 is found at the same position, albeit less pronounced. The maximum R2, which is more distinct, is red shifted compared to the experimental data. When using p-polarized light (Fig. 4 b)) we observe the same maxima as with s-polarization, with the addition of two maxima, R3 and R4, emerging for higher AOIs. The measured spectra show a peak emerging at λR3,exp = 731 nm at 20° AOI, which strongly shifts to higher wavelengths when increasing the AOI, while finally a fourth peak is found above AOIs of 75° at λR4,exp = 616 nm. Also, in the p-pol measurement, R2 shows a stronger blue shift with increasing AOI compared to s-pol excitation. The simulated reflectance spectra for p-polarized excitation show a more complicated behavior. The R1-mode is reproduced quite well and is located at the same position as for spolarized excitation. Also, mode R3 and R4 are clearly distinguishable in the simulation appearing at roughly the same AOI as for our measurements, however, at lower center wavelengths. Moreover, R2 also appears in the p-polarized reflectance simulation, albeit not as pronounced as for s-polarization. Further local extrema around the R2, R3 and R4 feature are


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discernable from this reflectance simulation. However, those were not labeled, as will be explained in the following section.

Figure 4. Measured (a,b) and simulated (c,d) reflectance spectra of gold NR (D = 28 nm, IR = 63 nm, L = 220 nm) embedded in AAO excited with (a,c) s- and (b,d) p-polarized light. The dotted lines in the simulated data show the positions of the extracted field plots (Fig. 6).


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Discussion The first maximum T1, which is observed in the transmittance of s- and p-polarization, corresponds to the excitation of the conduction band electrons parallel to the short axis of the NR at λT1,exp = 524 nm. This mode is well known26 and called transversal LSPR mode. It is excited by the electric field component aligned parallel to the short axis of the NRs, which is present in s- as well as in p- polarization, and is not dependent on the AOI. Additionally, gold has an interband transition at this wavelength, which also contributes to this peak and is responsible for the reduced transmittance and reflectance below 500 nm. Fig. 5 shows the simulated, time-averaged electric field at λ = 530 nm in and around a NR for different AOIs (0°, 20°, 45°, 60°) excited with p-polarized light. This sequence shows that at this wavelength the plasmon dominates the response for all angles. A non-zero electric field distribution can be observed within the gold rods. However, the field does not penetrate the entire length of the NR due to the high absorption and backscattering at this wavelength. For 0° AOI the field is symmetric to the short axis of the rod and is maximal at the upper apex of the nanorod. With increasing AOI, the field becomes increasingly asymmetric but still does not penetrate the whole NR. The elevated electric field does not extend far beyond the confinements of a single NR, leading to the conclusion that there is no significant coupling between neighboring NRs at this wavelength.


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Figure 5. Field plots of the time-averaged electric fields in and around a gold NR embedded in AAO excited at 0°, 20°, 45° and 60° AOI at λT1 = 530 nm excited with p-polarized light.

The short axis resonance also shows up in the reflectance measurements and is labeled R1 in the corresponding s- and p-polarized investigations. However, the short axis resonance R1 appears to be blue shifted compared to T1. This can be explained by the dielectric function of gold31 and its difference in absolute values for the real and imaginary parts. While the high absorption cross section (σabs ~ Im[α(ω)]) of the short axis resonance mode shows up in the reflectance measurement as R1, the backscattering (σscatt ~ |α(ω)|2) is large at wavelengths


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> 500 nm. Therefore, the increased backscattering of the short axis resonance leads to a dip in reflectance in our measurements. However, since the transmittance measurement takes backscattering and absorption into account, the short axis resonance seems to appear at slightly different wavelengths, leading to a higher extinction where backscattering occurs. To understand the occurrence of the absorbance maxima T2 and T3 we must take a closer look at the electric field distribution around a NR at the involved wavelengths under p-polarized excitation, as shown in Fig. 5 for AOIs of 20°, 45° and 60° in the wavelength regime from 550 nm - 830 nm. The second optical feature in both transmittance and reflectance measurement, labeled T2 and R2, are closely interrelated. In s-polarized excitation, an enhanced transmittance can be observed around 700 nm (T2), which is accompanied by a symmetric electric field distribution between the NRs, with a node at the bottom electrode and an antinode at the top of the AAO. Both of these features cancel each other out, meaning a loss in reflectance is compensated by a higher transmittance. This in conjunction with a lack of electric field in the NR itself suggests that this behavior can be explained by simple thin film interference rather than plasmonic resonance33. For T3, which is believed to be closely connected to the long axis resonance of a single NR26, we see an asymmetric field distribution (see Fig. 6) with high electric fields inside the NR at 630 nm, leading to the conclusion that for these excitation conditions an LSPR is excited, which couples to the neighboring nanorods and explains the reduced transmittance. For lower AOIs, this excitation and coupling occurs over the whole length of the NR, whereas for higher AOIs only the upper part of the NR is excited, which is very pronounced at the wavelength of 630 nm (Fig.6 b)). Additionally, the resonance emerges at a shorter wavelength upon increasing AOI in the simulation. This behavior was also found by Evans34 for silver NR of different dimensions in


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both measurements and simulations, and was associated with different orders of the LSPR mode. The fact that in our measurement this particular feature T3 is shifted to a longer wavelength compared to the simulations and the lack of a shift in position with higher AOI can be explained by imperfections in the actual NR system. A lesser degree of order, resulting in a finite distribution of interrod distances (∆ IR = 7 nm) rather than one fixed distance, leads to both a broadening and a red shift of the plasmonic resonances. This in conjunction with a finite distribution in length (∆ L = 20 nm) and diameter (∆ D = 3 nm) also leads to a broader resonance peak and can explain why there is only a single peak observed in the measurement rather than two distinct peaks for different AOIs in the theoretical simulations.


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Figure 6. FEM simulated field plots of the time-averaged electric field in and around a gold NR embedded in AAO for different AOI. a) - c) excited with p- polarized illumination, d) with spolarized illumination. During data analysis the question arose, whether T3 or T4 of the simulated transmittance spectra represents the measured extinction at 690 nm. However, when inspecting the field plots


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in Fig. 6, it becomes obvious that the T4-mode is connected to a high electric field directly excited at the bottom electrode. This effect is not visible in s-polarized excitation. The increased electric field is also visible at the glass/gold interface at the bottom, from which we conclude that a transverse mode through the gold bottom electrode is excited here. To test this hypothesis, FEM simulations were carried out, varying the thickness of the bottom electrode from 0 to 15 nm. Those simulated transmittance spectra at 50° AOI are shown in Fig. 7. The simulation reveals a blue shift of this resonance with increasing thickness of the gold layer. Furthermore, this resonance vanishes completely for no gold layer being present. The reason why this resonance cannot be seen in our measurement is again owned to slight imperfections of the real NR system as compared to simulations. The imperfect arrangement of the real nanorod array (Fig. 1c)) hampers the appearance of coupling artifacts at the bottom electrode as can be seen in the simulation. Fig. 1 b) shows that the cross-section of the NRs are never as perfectly aligned perpendicular to the bottom electrode, nor that the edges of the NRs are as sharply defined as in our simulations. Hence, this plasmonic mode at the bottom electrode cannot emerge in our measurements.


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Figure 7. FEM simulation showing transmittance spectra for varying bottom electrode thicknesses ranging from 0 to 15 nm at 50° AOI excited with p-polarized light. Now that we have gained a deeper insight into the resonance properties in the transmittance spectra excited by p-polarized light, the reflection properties need to be further clarified. To facilitate the distinction between pure aluminum oxide and gold nanorod properties, we also investigated an empty AAO matrix (D = 28 nm, IR = 63 nm, L = 220 nm) in reflectance with both p- and s-polarized light. The corresponding plots and simulated spectra are shown in Fig. 8.


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While the s-polarized results show a clear thin-film interference effect, it appears blue shifted compared to the thin-film interference R2 in the nanorod-AAO substrate. This blue shift can be attributed to the reduced effective refractive index of the aluminum oxide when the pores are filled with air 29. Furthermore, using p-polarized light, two features are obtained, showing that the R2 resonance is accompanied by a second peak R4 at high angles (> 70°). The reason for this additional R4 peak can be assumed in a phase-change of the light upon penetration of the nanoporous AAO structure at such high angles. However, deducing this effect analytically is beyond the scope of this work. Our inspection of the bare AAO matrix thus considerably helps associating the R2 and R4 peaks to interference effects within the pure AAO matrix. In both measurements without gold NRs, peak R1 and R3 are absent, which is again a proof for their plasmonic origin.


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Figure 8. Measured (a,b) and simulated (c,d) reflectance spectra of an empty AAO matrix (D = 28 nm, IR = 63 nm, L = 220 nm) excited with (a,c) s- and (b,d) p-polarized light. The simulated reflectance spectra (Fig. 4 d)) show further features between 550 and 700 nm, which are not seen in our measurements. Considering the s-polarized reflectance simulation, the R2-mode can be expected at 700 nm in p-polarization as well. In the simulations this mode seems to be intersected by the T3- and T4-mode, which leads to the splitting of R2. However,


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due to the blue shift of R2 in the actual measurement and the absence of T4 in the real AuNRAA sample, such a splitting is not observed. Finally, a closer look is taken at the R3-mode of the reflectance measurement and the corresponding simulation. Obvious from our data, this resonance shifts to higher wavelengths when the AOI is increased, especially for angles > 60°. The corresponding field plots (Fig. 6 a)) – c)) show a similar field distribution at the resonance wavelength of 730 nm (20°), 790 nm (45°) and 830 nm (60°): The electric field reveals a node at the bottom electrode and an antinode at the top of the NR within the AAO, while the electric field inside the NR is hardly increased. Therefore, this resonance can be interpreted as a standing wave of an odd multiple of λ/2 at the NR-dielectric interface with plasmonic origin. To fulfill this condition of a standing wave, a phase shift upon reflection at the NR bottom/bottom electrode needs to be taken into account, which is known to be dependent on e.g. the wavelength, the interrod spacing, and the angle of incidence25,33. However, although this mode is obtained in the reflectance measurements (Fig. 3 b)) in the same wavelength regime compared to the simulation, its counterpart, the enhanced transmittance, is not as clearly visible from the measurement (Fig. 3 b)) compared to the simulation (Fig. 3 d)). The reason can be seen in the enhanced absorption due to the broad plasmonic resonance T3-mode on the one hand, and due to the inhomogeneous distribution of rod length and interrod spacing, which influence the standing wave formation, e.g. through an inhomogeneous phase behavior in such real Au-NRAAs. To verify the assumptions of the plasmonic and thin-film origin of the observed features we also calculated and plotted the absorption A = 1 - T - R from our simulations (see Fig. 9 a) and b)). The absorption plot of the s-polarized simulation shows that the sample absorbs energy only at wavelengths below 530 nm. This clarifies that in the s-polarized simulation features T2 and R2


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are the result of thin-film interference with no light being absorbed at this wavelength, whereas resonances T1 for both polarizations and T3 and T4 for p-polarization are causing absorption (see Fig. 9 b)) which is a clear evidence for their plasmonic behavior.

Figure 9. Simulated absorbance spectra for a) s-polarization and b) p-polarization of a AuNRAA in AAO matrix. The absorptive features with plasmonic origin are highlighted.


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Experimental

Simulated Fitting Angle

Results

Results

524 nm

516 nm

(s-/ p-pol)

(s-/ p-pol)

625 nm

694 nm

(s-/ p-pol)

(s-/ p-pol)

690 nm

591 nm

(p-pol)

(p-pol)

-

700 nm

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Origin

Transmission T1 (Max)

T2 (Min)

T3 (Max)

T4 (Max)

20°

Plasmonic, short axis resonance

20°

Thin-film interference

60°

Plasmonic, coupled mode

60°

Plasmonic, transverse mode at bottom electrode

20°

Plasmonic, short axis resonance

20°

Thin-film interference

20°

Plasmonic, coupled modes

75°

Thin-film effect

(p-pol) Reflectance R1 (Max)

R2 (Max)

R3 (Max)

R4 (Max)

490 nm

468 nm

(s-/ p-pol)

(s-/ p-pol)

586 nm

701 nm

(s-/ p-pol)

(s-/ p-pol)

731 nm

733 nm

(p-pol)

(p-pol)

616 nm

547 nm

(p-pol)

(p-pol)

Table 1. Summarized resonances in transmittance (T) and reflectance (R), their simulated and experimental positions and their physical origin.


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AUTHOR INFORMATION Corresponding Author [email protected] , phone: +49 351 46333740

Author Contributions The manuscript was written by contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT The authors kindly acknowledge experimental support by Stephan Barth from the FraunhoferInstitut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP and Alexander Than from the Dresden Center of Nanoanalysis (DCN), respectively. This work was supported by DFG grant RTG 1401 and the BMBF (German Ministry of Education and Research) grant number 03V0762.


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For Table of Contents Only


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Plasmonic Nanorod Antenna Array: Analysis in Reflection and

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