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Orientation-Dependent Exciton−Plasmon Coupling in Embedded Organic/Metal Nanowire Heterostructures Yong Jun Li,†,∥ Yan Hong,‡ Qian Peng,§ Jiannian Yao,†,∥ and Yong Sheng Zhao*,†,∥ †
Key Laboratory of Photochemistry, Institute of Chemistry and §Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ State Key Laboratory of Electronic Thin-Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China ∥ University of Chinese Academy of Sciences, Beijing 100049, China S Supporting Information *
ABSTRACT: The excitation of surface plasmons by optical emitters based on exciton−plasmon coupling is important for plasmonic devices with active optical properties. It has been theoretically demonstrated that the orientation of exciton dipole can significantly influence the coupling strength, yet systematic study of the coupling process in nanostructures is still hindered by the lack of proper material systems. In this work, we have experimentally investigated the orientation-dependent exciton−plasmon coupling in a rationally designed organic/metal nanowire heterostructure system. The heterostructures were prepared by inserting silver nanowires into crystalline organic waveguides during the self-assembly of dye molecules. Structures with different exciton orientations exhibited varying coupling efficiencies. The near-field exciton−plasmon coupling facilitates the design of nanophotonic devices based on the directional surface plasmon polariton propagations. KEYWORDS: exciton−plasmon coupling, surface plasmons, nanowire heterostructures, organic nanowires, exciton orientation
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regime where the energy transfer from the excitons to SPPs is considered unidirectional. Frenkel-type excitons in organic molecules are ideal systems for investigating the relationship between the dipole orientations and exciton−plasmon coupling, because they have one-dimensional transition dipoles16 and high stability at room temperature with binding energy of as high as ∼1 eV.17 As for the plasmonic materials, chemically synthesized silver nanowires (AgNWs) have emerged as promising candidates due to their atomically smooth surfaces and low propagation loss.5,18 Figure 1A presents the numerical simulation results of the SPPs excitation in the AgNW by an electric dipole. The electric-field intensity |E|2 distributions of the SPPs clearly show that the exciton−plasmon coupling is much stronger when the dipole is parallel to the radial (x-axis) or longitudinal direction (y-axis) of the AgNW than that when the dipole orients perpendicularly to the radial direction (z-axis). The great difference of coupling efficiency results from the different wave-
urface plasmon polaritons (SPPs) bound at a metal/ dielectric interface exponentially decay into the metal with a skin depth of ∼10 nm, two orders smaller than the wavelength of the light in air.1 This feature endows SPPs with ability to localize and guide light in subwavelength metallic structures, which have shown attractive applications for miniaturized components in photonic and optoelectronic devices.2−4 Currently, the excitation of SPPs in these devices is mainly realized with photon−plasmon coupling, which usually requires special structures, such as prisms,5 gratings,6 antennas,7 etc., due to the momentum mismatch between the SPPs and photons. However, these coupling schemes do not lead to easy interconnection with conventional material components.4 An alternative strategy is to launch SPPs by direct coupling with exciton dipoles, which have a large range of wave-vectors in their near-field regime.8−12 Nevertheless, the distribution of wave-vectors at the dielectric/metal interface would be quite different if the dipole orientation is changed with respect to the metal surface, which may lead to significant difference of SPP excitation efficiency as well as the performances of the SPP based devices.13−15 It is worth noting that the exciton−plasmon coupling here is in the weak coupling © 2017 American Chemical Society
Received: June 30, 2017 Accepted: September 20, 2017 Published: September 20, 2017 10106
DOI: 10.1021/acsnano.7b04584 ACS Nano 2017, 11, 10106−10112
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Cite This: ACS Nano 2017, 11, 10106-10112
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RESULTS AND DISCUSSION We propose to construct a kind of hybrid nanostructure with AgNWs partially embedded into organic single crystals for the study of orientation-dependent exciton−plasmon coupling, because the dye molecules are orderly packed at the organic/ metal interfaces (Figure 1B). At the excitation of a locally focused laser beam, the ordered molecular aggregates would provide Frenkel-type excitons with regular orientations around the AgNW (Figure 1C). Each exciton can be regarded as an electric dipole, and the ordered exciton dipoles at the interface can efficiently launch the SPPs through near-field coupling, which will subsequently propagate along the AgNW and couple out from the distal ends in form of photons. More importantly, by altering the direction of AgNW in the hybrid structure, we can obtain structures with different cross angles (α) between the exciton dipoles and the AgNW, and the simulated |E|2 distributions of the SPPs show that α has great influence on the exciton-SPP coupling efficiency, as illustrated in Figure 1D. Tris[1-phenylisoquinolinato]iridium(III) (Ir(piq)3) (Figure S2) was chosen as the model compound for the fabrication of the embedded heterostructures and for the further study of the exciton−plasmon coupling therein, which is motivated by its good self-assembly characteristic,25 high exciton stability, and the photoluminescence (PL) wavelength range, where SPPs enjoy very low ohm losses.4 The three bidentate ligands that octahedrally coordinate with the iridium center of Ir(piq)3 make the molecules to be quite flexible,24 which require less specific coordination numbers in a lattice and benefit the growth of organic crystals around the AgNWs.26 As shown in Figure 2A, a strategy of wetting-effect-assisted self-assembly was developed to construct the organic/metal nanowire heterostructures. When the solution of the Ir(piq)3 molecules was dropped onto the substrate, the AgNWs preloaded on the substrates were lifted off due to the wetting of the solvent that can reduce the van der Waals’ interaction between the AgNWs and the substrate. Driven by the liquid surface tension, the lifted AgNWs were kept parallel to the substrate during the
Figure 1. Organic/metal nanowire heterostructures for the study of orientation-dependent exciton−plasmon coupling. (A) Numerically simulated |E|2 distribution of SPPs at the end of a 200 nm diameter and 6 μm-long AgNW, where SPPs are launched by a dipole oriented along three coordinate axes x, y, and z, respectively. The dipole is positioned at the middle of the wire with a distance of 20 nm. (B) Schematic illustration for the proposed heterostructure with orderly arranged molecules around a partially embedded AgNW. (C) Oriented Frenkel-type exciton dipoles created around the AgNW by irradiation of an incident light at the junction. SPPs can be efficiently launched by the exciton dipoles, which will subsequently propagate along the AgNW and scatter into free space at the distal ends. (D) SPPs coupling by multiple exciton dipoles. The cross angles between the AgNW and the polarization of dipoles are 0°, 45°, and 90°.
vector distributions of the dipoles on the AgNW surface (Figure S1). However, in most hybrid systems,19−23 especially nanostructures, the molecules are distributed randomly nearby the interfaces, which makes it difficult to study the effect of exciton orientation on SPPs excitation. Embedding metallic nanostructures into crystalline organic materials might be a viable solution,24 where the excitonic molecules should be orderly arranged around the metal surface. In addition, the embedding strategy would provide a large interfacial area that can ensure efficient energy transfer from the exciton dipoles to the SPP modes. In this work, we demonstrate the orientation-dependent exciton−plasmon coupling in embedded organic/metal nanowire heterostructures. With the assistance of the wetting effect of liquid solvent, the hybrid structures were prepared by inserting AgNWs into crystalline organic waveguides during the self-assembly of dye molecules. Different exciton orientations with respect to the AgNWs were obtained in the hybrid structures with various cross angles between the organic waveguide and the AgNW. The exciton−plasmon coupling efficiency varies with the exciton orientations, and the most efficient coupling was found when all exciton dipoles are parallel to the AgNW. In this case, the corresponding structure displayed excellent performance in light coupling at subwavelength scale, which ensured the design of optical signal routing with multiple input and output ports. In comparison to the photon−plasmon coupling, exciton−plasmon coupling exhibited much higher efficiency in these heterostructures and proved the perspective of improving the properties of nanophotonic devices.
Figure 2. Fabrication of embedded organic/metal nanowire heterostructures. (A) Schematic illustration for the wetting-effectassisted self-assembly of Ir(piq)3/Ag heterostructure. (B) SEM image of the fabricated heterostructure. Inset: SEM image of the Ir(piq)3 wire end. Scale bar is 0.5 μm. (C) TEM image of the heterostructure. Insets: SAED patterns of the Ir(piq)3 and AgNWs. Scale bar is 500 nm. 10107
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Figure 3. Efficient exciton−plasmon coupling in the nanowire heterostructures. (A) Bright-field microscopy of an embedded nanowire heterojunction. Scale bar is 5 μm. (B) FLIM image collected at the junction area marked with black box in (A). (C) Average lifetimes across the junction (marked with red line in (B)). (D,E) Optical micrographs under the irradiation of a CW laser beam with wavelengths of 633 nm (D) and 532 nm (E), respectively. (F) Intensity of the SPPs scattering from O1 and O2 in (D,E).
Figure 4. Orientation-dependent exciton−plasmon coupling. (A) Bright-field and PL images of the heterostructures with different cross angles between the exciton dipoles and the AgNWs under a 532 nm CW laser excitation. Scale bars are 5 μm. (B) Normalized SPPs intensities Iα versus α. Iα is the SPP intensity detected at AgNW distal ends with a same propagation distance. Error bars represent standard deviations of five measurements. (C) Schematic illustration for the superposition of hybrid systems with different distances (d1 and d2) between exciton dipoles and AgNW in cases of α = 0°, 45°, and 90°. (D) Numerically calculated results of the coupling efficiency with different distance versus α. Intensities are normalized to the values at d = 20 nm and α = 0°.
evaporation of the solvent. Meanwhile, the Ir(piq)3 molecules nucleated and self-assembled into crystals in the liquid phase. The crystals nearby the AgNWs grew around the wire to avoid the major disruption of lattice structure and reduce the overall interfacial energy,24 which result in the formation of the final embedded heterostructures. In these structures, both the organic crystal and the AgNW were parallel to the substrate plane, which makes it much more accurate to determine the cross angle between the crystal and the AgNW as well as the dipole orientations in the heterostructures. The microscopy images of the prepared heterostructures (Figure S3) show that the average length and diameter of the Ir(piq)3 waveguides are 55 and 1.2 μm, respectively; the length of the AgNW ranges from 6 to 12 μm, and their diameters are
about 190 nm. These AgNWs with such dimension can ensure the detection of SPPs at AgNW distal ends because of the relatively low ohm losses during propagation.27,28 These structures with cross angles of ∼20°−90° between the AgNW and the Ir(piq)3 waveguide would provide exciton dipoles with different orientations with respect to the AgNW. In addition, the solidly embedded structure, as shown in Figure 2B, can ensure a stable exciton−plasmon coupling insensitive to external mechanical vibrations. The high crystallinity of the organic waveguide at the junction reveals ordered arrangement of Ir(piq)3 molecules around the AgNW (Figure 2C). Taking into account the crystal structure of Ir(piq)3, we can learn that each organic waveguide lies on the substrate by one of its six equivalent side faces (Figure 2B, inset and Figure S4), thus the 10108
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Figure 5. Construction of optical signal routing based on the exciton−plasmon coupling. (A) Bright-field and PL microscopy images under the excitation of a 532 nm CW laser on the organic wire body. Scale bar is 5 μm. (B) Schematic illustration for the design of an optical signal routing device with three input ports on the organic wire (I1, I2, and I3) and four output ports corresponding to AgNW tips (O1, O2, O3, and O4). (C) Bright-field and PL images of the device under the excitation of an input laser beam (532 nm) at I1, I2, and I3. Scale bar is 5 μm. (D) Scattering spectra of SPPs collected at the four output ports when the heterostructure was excited at I1, I2, and I3, respectively. The dash lines indicate the on/off intensity of the signals.
realized due to the efficient generation of exciton dipoles at the junction. As shown in Figure 3E, the scattering of SPPs from the AgNW tips was fairly strong, and two bright red points can be clearly identified (see Figure S8 for spectra). Furthermore, the intensity of scattered SPPs showed a linear increase when the beam power was gradually increased (Figure 3F), which can be understood in terms of the linear growth of the exciton densities.4 In the crystalline heterostructure, the excited ordered molecular aggregates would provide regularly oriented exciton dipoles around the AgNW for experimentally investigating the relationship between the dipole orientations and exciton− plasmon coupling. The exciton dipole orientations were determined to be parallel to the cross-section of the organic wire, and the cross angles between the orientation components and the AgNWs (α) are the complements of the cross angles between the organic waveguide and the AgNWs (Figures S9 and S10). In heterostructures with different α, as shown in Figure 4A, it was observed that when α is 0° and 14°, the scattered SPPs (red points magnified in white circles) were much stronger than that when α is 45° and 65°, which indicates the decrease of exciton−plasmon coupling efficiency. It is worth noting that the scattered SPPs intensities (Iα) are proportional to the exciton−plasmon coupling efficiencies,29 and thus Iα versus α can be utilized to descript the change of the coupling efficiency. Exhilaratingly, Iα decreased gradually by around 45% in the heterostructures with α ranging from 0° to 70° (Figure 4B), which reveals that the orientation of exciton dipoles would significantly influence the exciton−plasmon coupling efficiency. When α is 0°, the exciton dipoles are parallel to the AgNW, and a high exciton−plasmon coupling efficiency can be obtained; with the increase of α, the excitons located on the top and bottom of the AgNW would gradually change their orientation from a wave-vector well-matched configuration to a poorer matched one (from y-oriented to z-oriented in Figure 1A), which leads to the decrease of coupling efficiency.
dipole orientations relative to the AgNW in these structures can be determined by the cross angle between the AgNW and the organic waveguide. These embedded heterostructures provide much larger dielectric/metal interfacial area as compared with the junction constructed by simple point contact, which would be beneficial for the energy transfer from exciton dipoles to SPPs in the AgNWs. This advantage was demonstrated by studying the decay of excitons in a typical heterostructure as shown in Figure 3A. Here, the decay kinetics was characterized by fluorescence lifetime imaging microscopy (FLIM), which can be used to record the fluorescence lifetimes of chromophores at each spatially resolvable element of a microscope image. In the FLIM image, the distribution of the lifetime manifests that the PL decay at the junction is obviously faster than that at the body of the organic wire (Figure 3B,C). In comparison, the faster decay at the junction was not observed when the AgNW was put on the top or at the bottom of the organic waveguide with point contact (Figure S5). The faster decay results from the formation of new exciton decay channels (Figure S6), which reveals that the larger contact area of the embedded structure would enable efficient SPP excitation in the AgNW.8 The efficient launching of SPPs by means of exciton− plasmon coupling was demonstrated by comparing with the photon−plasmon coupling (see Figure S7 for the setup). In a comparison experiment, a 633 nm continuous wave (CW) laser beam was utilized to generate a photon−plasmon coupling at the junction. From the absorption spectrum (Figure S2), we can see that the Ir(piq)3 wire cannot be excited by the 633 nm light, therefore, such laser beam should be passively coupled into the junction without formation of exciton dipoles. With this coupling mode, the scattered SPPs from the AgNW tips were too weak to be collected (Figure 3D, see Figure S8 for spectra), and the intensity remained at a very low level even when the beam power was gradually increased (Figure 3F). On the contrary, when the irradiation light was changed to a 532 nm CW laser beam, efficient exciton−plasmon coupling was 10109
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CONCLUSIONS In conclusion, orientation-dependent exciton−plasmon coupling was experimentally investigated by designing a type of embedded organic/metal nanowire heterojunctions. With a wetting-effect-assisted self-assembly, desired structures with AgNWs inserted in crystalline organic waveguides were successfully fabricated. Exciton dipoles with different orientations with respect to the AgNWs were obtained in the embedded structures with various cross angles between the AgNWs and organic waveguides. The exciton orientation was demonstrated to play a decisive role in the exciton−plasmon coupling, which was subsequently utilized to construct active devices with specific photonic performances, like optical signal routing. Investigation of exciton−plasmon coupling is of great importance for understanding the energy transfer between emitters and metal nanostructures, which would promote the design of device geometries in photonic integrated circuits.
The exciton−plasmon coupling normally occurs in the whole near-field range of exciton dipoles, and thus the SPPs launched in AgNWs should result from the linear superposition of SPPs excited by exciton dipoles with different distances from the AgNWs (Figure 4C). The numerically calculated results shown in Figure 4D elucidated that the coupling efficiencies decrease with α, and the longer the distance, the smaller the variation. When the distance reached up to 750 nm (the near-field range is ∼735 nm), both the coupling efficiency and the variation were dramatically decreased. In contrast, as d = 20 nm, the orientation-dependent exciton−plasmon coupling was prominent, and the highest coupling efficiency were also achieved. These results indicate that the orientation-dependent exciton− plasmon coupling was mainly affected by the proximal exciton dipoles. Therefore, the experimentally observed orientationdependent coupling occurred in the near-field regime of the exciton dipoles. The variation of the coupling efficiency is solid proof to directly demonstrate that the exciton orientations do have a great influence on exciton−plasmon coupling even in nanoscale hybrid material systems. In this kind of heterostructure, when the AgNW is perpendicular to the organic waveguide, the best performance was achieved as a hybrid waveguide, and thus the coupling efficiencies as well as the performances of nanophotonic devices could be improved by properly designing the structure of hybrid material system. By utilizing the heterostructure with the best performance as a hybrid waveguide, we found that even when the focused 532 nm CW laser beam was moved from the junction to the organic wire body, the out-coupled light from the AgNW tips can still be observed (Figure 5A and Figure S11), which indicates that the SPPs can be efficiently launched remotely. Such optical performance inspired us to design multi-input and multi-output optical components for simultaneous manipulation of multiple optical signals. Figure 5B schematically illustrates the design of a signal routing device with three input ports located on the organic wire (I1, I2, and I3) and four output ports corresponding to the tips of two perpendicularly embedded AgNWs (O1, O2, O3, and O4). The optical signals inputted from the end of the organic waveguide (I1 or I3) can be transferred to the nearby output ports (O1, O2 or O3, O4). Based on the same principle, if we alter the input position to the middle section (I2), the signals can be simultaneously transferred to all the four output channels (O1, O2, O3 and O4). The performance of the designed device was experimentally demonstrated in a heterostructure with one organic waveguide and two AgNWs. The PL images and the corresponding spectra in Figure 5C,D show that when the optical signals were inputted from the end ports (I1 and I3), the signals outputted via SPPs were clearly identified at the two adjacent ports, while no signals were observed from the other two. In contrast, the signals inputted from the middle port (I2) were simultaneously detected from all the four tips. More output channels and functions could be realized by further increasing the number of embedded AgNWs. As a comparison experiment, it is found that these functions cannot be realized with photon−plasmon coupling (Figure S12) due to the mismatch of wave vectors between the photons and the SPPs,28 which further confirms that the efficient output of optical signals via SPPs results from the exciton−plasmon coupling. These results exhibit that the exciton−plasmon coupling provides a strategy to design functional photonic devices for manipulation of optical signals at nanoscale regime.
MATERIALS AND METHODS Synthesis of Organic/Metal Nanowire Heterostructures. Ir(piq)3 was purchased from Sigma-Aldrich. Ethanol (HPLC grade) and dichloromethane (HPLC grade) were obtained from Beijing Chemical Agent, Inc. The AgNWs were synthesized by reducing AgNO3 (Beijing Chemical Agent) with ethylene glycol (Aldrich) in the presence of polyvinylpyrrolidone (K30, Aldrich).30 All of the chemical reagents were used without further treatment. The nanowire heterostructures were prepared through a strategy of wetting-effectassisted self-assembly. In a typical preparation, the AgNW solution in ethanol was drop-cast onto a glass substrate at room temperature. After the evaporation of ethanol, a stock solution of Ir(piq)3 in dichloromethane (∼150 μL, 0.25 mM) was immediately dropped onto the same substrate. The dichloromethane can reduce the van der Waals interaction between the AgNWs and the substrate and lift up the preloaded AgNWs off the substrate. Driven by the liquid surface tension, the lifted AgNWs were kept parallel to the substrate during the evaporation of the solvent. Meanwhile, the Ir(piq)3 molecules nucleated and self-assembled into crystals in the liquid phase. With the complete evaporation of dichloromethane (∼20 min), the heterostructures with AgNWs embedded in Ir(piq)3 waveguide were obtained on the substrate for the following characterizations. Characterization. The morphology of Ir(piq)3/Ag nanowire heterojunctions was characterized with SEM (Hitachi, S-4800) and TEM (Tecnai, F20), respectively. Bright-field and PL microscopy images were taken with an inverted microscope (Nikon, Ti−U). The fluorescence measurement of the nanowires was carried out on a fluorescence spectrometer (Hitachi F7000). Emissions from distal ends of AgNWs were dispersed with a grating (150 G/mm) and recorded with a thermal-electrically cooled CCD (Princeton Instruments, ProEM: 1600*200B). The schematic illustration of the experimental setup for optical characterization is shown in Figure S7. PL lifetime images were taken with FLIM by scanning the samples with a 485 nm picosecond pulse laser. The FLIM (PicoQuant) was composed of picosecond pulsed diode laser (PDL800-D), fiber coupling unit (FCU II), laser scanning microscope (Olympus FV1000), four channel detector router (PHR 800), and photomultiplier detector assembly (PMA Series). Calculation Methods. The numerical simulations are carried out with the finite-difference time-domain (FDTD) solution. Because many atomic or molecular transitions that produce light are electric dipoles in nature,13 the electric dipoles are utilized to model the Frenkel excitons. The geometry optimization of Ir(piq)3 molecule at ground state was performed by using the B3LYP funtional and the basis sets 6-31G* for light atoms (C, N, and H atoms) and Stuttgart/ Dresden ECP for heavy iridium atom in Gaussian 09 program. Based on the optimized geometry, the transition dipole moment vector (μ) of Ir(piq)3 from T1 to S0 was theoretically calculated by using the quadratic response function approach at the same level in Dalton 10110
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ACS Nano program.31 The detailed description of the calculation of transition dipole moment can be found in Figures S9 and S10.
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ASSOCIATED CONTENT S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.7b04584. Structure and morphology (SEM images); fluorescence properties (spectrum, lifetime); experimental setup for the optical characterization are given in Figures S1−S12 (PDF)
AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. ORCID
Qian Peng: 0000-0001-8975-8413 Yong Sheng Zhao: 0000-0002-4329-0103 Author Contributions
Y.S.Z. conceived the idea. Y.S.Z. and J.Y. supervised the project. Y.J.L. designed the experiments and prepared the materials. Y.J.L. performed the optical measurements. Y.J.L., Y.H., and Q.P. put forward the theoretical model and contributed to the theoretical calculations. Y.J.L., Y.H., Q.P., and Y.S.Z. analyzed the data. Y.J.L. and Y.S.Z. wrote the manuscript. All authors discussed the results and commented on the manuscript. Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS This work was supported by the Ministry of Science and Technology of China (grant no. 2017YFA0204502), National Natural Science Foundation of China (21533013, 21521062, 21603241), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB12020300). REFERENCES (1) Ozbay, E. Plasmonics: Merging Photonics and Electronics at Nanoscale Dimensions. Science 2006, 311, 189−193. (2) Pyayt, A. L.; Wiley, B.; Xia, Y.; Chen, A.; Dalton, L. Integration of Photonic and Silver Nanowire Plasmonic Waveguides. Nat. Nanotechnol. Nat. Nanotechnol. 2008, 3, 660−665. (3) Yan, R.; Pausauskie, P.; Huang, J.; Yang, P. Direct PhotonicPlasmonic Coupling and Routing in Single Nanowires. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 21045−21050. (4) Yan, Y.; Zhang, C.; Zheng, J. Y.; Yao, J.; Zhao, Y. S. Optical Modulation Based on Direct Photon-Plasmon Coupling in Organic/ Metal Nanowire Heterojunctions. Adv. Mater. 2012, 24, 5681−5686. (5) Ditlbacher, H.; Hohenau, A.; Wagner, D.; Kreibig, U.; Rogers, M.; Hofer, F.; Aussenegg, F. R.; Krenn, J. R. Silver Nanowires as Surface Plasmon Resonators. Phys. Rev. Lett. 2005, 95, 257403. (6) Hooper, I. R.; Sambles, J. R. Dispersion of Surface Plasmon Polaritons on Short-Pitch Metal Gratings. Phys. Rev. B: Condens. Matter Mater. Phys. 2002, 65, 165432. (7) Fang, Z.; Fan, L.; Lin, C.; Zhang, D.; Meixner, A. J.; Zhu, X. Plasmonic Coupling of Bow Tie Antennas with Ag Nanowire. Nano Lett. 2011, 11, 1676−1680. (8) Akimov, A. V.; Mukherjee, A.; Yu, C. L.; Chang, D. E.; Zibrov, A. S.; Hemmer, P. R.; Park, H.; Lukin, M. D. Generation of Single Optical Plasmons in Metallic Nanowires Coupled to Quantum Dots. Nature 2007, 450, 402−406. (9) Fedutik, Y.; Temnov, V.; Woggon, U.; Ustinovich, E.; Artemyev, M. Exciton-Plasmon Interaction in A Composite Metal-Insulator10111
DOI: 10.1021/acsnano.7b04584 ACS Nano 2017, 11, 10106−10112
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DOI: 10.1021/acsnano.7b04584 ACS Nano 2017, 11, 10106−10112
