Coupling Enhancement and Giant Rabi-Splitting in Large Arrays of

Subscriber access provided by University of Colorado Anschutz Medical Campus Health Sciences Library

Article

Coupling Enhancement and Giant Rabi-Splitting in Large Arrays of Tunable Plexcitonic Substrates Panit Chantharasupawong, Laurene Tetard, and Jayan Thomas J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp506091k • Publication Date (Web): 21 Sep 2014 Downloaded from http://pubs.acs.org on October 1, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Coupling Enhancement and Giant Rabi-Splitting in Large Arrays of Tunable Plexcitonic Substrates Panit Chantharasupawong †, Laurene Tetard †, Jayan Thomas †,* † College of Optics and Photonics (CREOL) and NanoScience Technology Center, University of Central Florida, Orlando, FL, 32826, USA KEYWORDS : nanofabrication, Raman, plasmon, exciton, nanoimprint ABSTRACT

Advances in active manipulation of light at the nanoscale are rapidly emerging with the concept of plexcitonic coupling at the interface between plasmonics nanostructures and excitonic molecules. In this work, we devise a simple fabrication scheme to produce and optimize large area tunable plasmonic substrates for strong plasmon-exciton interactions. By tuning the diameter of the nanoholes using a simple plasma etching process, we demonstrate the potential of our approach to deliver tunable plasmonic substrates. Thus, large enhancements of fluorescence and Raman scattering could be measured. Moreover, hybridized states appeared in presence of excitonic molecules (RG6) give rise to anticrossing behaviors in extinction spectroscopy, a phenomenon also known as Rabi-

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 33

splitting. The results demonstrate the great potential of our large nanofabricated arrays as plexcitonic substrates for numerous applications including sensors, light harvesters and all-optical switches.

INTRODUCTION The art of combining metallic and organic materials to tune their properties has always been a fascinating subject in the quest for superior materials functionalities1. Exploiting interactions between localized surface plasmons (LSP) and molecular excitons is one of the many examples of such exciting mission. Hybridization phenomena, observed in presence of interacting metallic plasmonic structures and organic species2, offer a unique opportunity to control plasmon resonances to create active plasmonic systems such as switches or modulators. In fact, the rising interest in such hybrid structures resides in their ability to overcome the inherent limitation of purely plasmonic devices for active control due to their low nonlinearity2. In the weak interaction regime, the presence of molecular adsorbates modifies the resonance characteristics of the plasmonic states. Conversely, the properties of the adsorbates such as fluorescence3-4, Raman scattering5, and ultrafast nonlinearities6-7 can be significantly transformed by the presence of the plasmonic states. Hence, strong nonlinear interaction between the two materials makes it possible to synthesize hybridized energy states, called plexcitons, whose properties are distinct from either of its subsystems. Several recent studies have reported plexcitonic nanostructures composed of metallic nanostructures interacting with excitonic materials2, 8-11

. Such hybrid nanostructures provide a unique platform for active control of strong

coupling at optical frequencies in nano-optical devices, which encompass many


Page 3 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


applications such as sensors

12

, light harvesters

1, 13

, nanolasers

14-15

, and all-optical

switches16-17. In the field of sensing, the concepts of hybridized states manifesting in the forms of Fano resonance18-19 and Rabi-splitting20 have been shown to significantly improve the sensitivity of molecular detections. They are promising directions for achieving a few molecule-level detections21-22. However, scalability and practicability of these devices could become potential bottlenecks. To date, plasmonic nanostructures used as sensing platforms are typically fabricated using expensive equipment such as Electron Beam Lithography (EBL) 23 and Focused Ion Beam Lithography (FIBL) 24. In addition to being very time consuming and labor intensive, nanofabricated structures resulting from EBL and FIBL only offer small areas, which hinder their use in real-world applications. Template-based approaches such as anodized alumina oxide25 and nanospheres26-27 have been considered as a low cost alternative to this dilemma. However, the nanostructures obtained via such processes exhibit relatively poor quality and the templates used are sacrificial in nature. Therefore, uniformity, flexibility and high quality in making plasmonic nanostructures are still very relevant issues. Nanoimprinting, on the other hand, has been demonstrated to provide large areas (several cm) of well-ordered nanostructures with high spatial resolution and reproducibility without frequently resorting to expensive tools28. This constitutes a good compromise between the high-cost techniques, like EBL and FIBL, and the low-cost template based approaches for low-cost high quality production. Nevertheless, nanostructures fabricated using nanoimprinting methods usually offer limited flexibility in tuning the structures’ size or shape, as they are restricted by the initial pattern of the master mold.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 33

In this work, we devise a simple fabrication scheme for large area tunable plasmonic substrates. We show that our process can be used to easily fabricate an optimized substrate for strong plasmon-exciton interaction, resulting in large enhancements of fluorescence and Raman scattering as well as observations of anticrossing behaviors. EXPERIMENTAL METHODS Substrate fabrication: The square lattice nanohole arrays of polyacrylonitrile (PAN) were fabricated using a Si mold following the SNAP technique (a simple spin coating technique), as illustrated in Figure 1. First, 8 wt% of PAN was prepared in dimethylformamide and heated at 150 °C. The PAN solution was then spin-coated on the mold at 3000 rpm for 10 seconds. The film was cured at 150˚C for a minute and transferred to a glass substrate by simply peeling off the polymer film and cementing it on the substrate with the help of thin adhesion layer of the same polymer. To tune the hole diameters, O2 Plasma (PE50, PlasmaEtch) cleaner was used. The plasma power and RF-frequency were set at 20 Watt and 13.56 MHz, respectively. The vacuum setpoint was 201.1mtorr and the oxygen flow rate was 5 sccm. A silver metal thin film of 35 nm thickness was evaporated on the samples with a deposition rate of 0.06 Å/s. The thickness of the silver was monitored using quartz crystal microbalance. A fiber-coupled spectrophotometer (Ocean optics) was used for light absorption measurements. Raman scattering measurements: Raman scattering measurements from our R6G coated plexcitonic samples were acquired using a confocal Raman microscope (WITec alpha 300AR). All samples were prepared with the same deposited concentration of R6G of 1 mM. The excitation wavelength of the Raman system was 532 nm, with a power on the 4 ACS Paragon Plus Environment

Page 5 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


sample of 100 µW. The laser was focused on the surface of the sample and the scattered spectrum was collected with a 20X microscope objective lens. The spectrum data are acquired at 20 different points across the samples and the averages are presented. FDTD simulation: FDTD simulation was performed using commercially available software, Lumerical FDTD Solutions. The simulated unit cell is presented in the Supporting Information (SI), Figure S2(a). The depth profile was described by a fourth order Gaussian curve. Periodic boundary condition was used for simulating square lattice nanohole arrays. Phase matching layers were selected at the light input and output boundaries. The experimental dielectric dispersions of silver were chosen as input29. Built-in multi coefficient models (MCMs) were used to fit the material dispersions. The R6G layer was modeled as a dispersive medium with dielectric permittivity described by Lorentz model:

ε R6G (ω ) = ε∞ +

f ω 20 (ω 20 − ω 2 − iγ 0ω )

(1)

where the high frequency component ε∞=2.5, f is the oscillator strength, ω0 is the resonance frequency of 3.392×1015rad/s , and γ0 is the exciton line width of 2.14×1014 rad/s , derived from the resolved spectra of R6G on silver. Geometrical parameters of the samples and thicknesses of the coatings used in the simulation were measured using AFM. RESULTS and DISCUSSTION We prepared a set of nanohole-structured samples using our high throughput technique, coined spin on nano-printing (SNAP) 30, on a polyacrylonitrile (PAN) polymer 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 33

substrate. The first step consists of a printed polymer with square lattice of nanoholes of diameter of 80nm, prepared by spin coating a layer of polymer on top of the prefabricated mold (step 1 in Figure 1). The film is then peeled off after curing at 1500C for one minute, as shown in step (2) in Figure 1.

Figure 1. Schematic representation of large area plasmonic nanostructures fabrication process by SNAP method. PAN solution is spin coated on top of a Si mold (step 1). The polymer film is then cured at 150˚C for one minute and transferred to a glass substrate by simply peeling off the polymer film (step 2). The films are etched at variable etching time, allowing a range of the nanoholes sizes. A 35nm layer of silver (grey color) is then deposited on top of the structure (step 3). Unlike, typical Nanoimprinting Lithography (NIL), our process does not require high pressure, temperature or UV light during the printing of these nanostructures and can be fabricated in a few minutes. It is also possible to create nanostructures on large areas by printing the patterns side-by-side in a very short time. In addition, with this technique, nanostructures can be printed on a variety of materials such as polysilazanes and polyvinyl alcohol30. The resulting polymeric arrays of nanoholes with fixed diameters constitute an ideal platform for plasmonic structures but LSP only exist in metallic structures. Therefore we investigated the requirements to optimize the structures for this purpose. One of the key aspects of plasmonic nanostructures is the strong dependence of 6 ACS Paragon Plus Environment

Page 7 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


their LSP resonance wavelength on their geometries. For instance, in the case of metal nanospheres, the resonance peak is red-shifted as the size of the sphere increases

31

.

Anisotropic shapes like metal nano-ellipsoids exhibit plasmon resonance depending on the orientation of the structure relative to the incident light polarization 32. As previously stated, plasmonic structures fabricated by regular imprinting technique have limited flexibility in tuning the size and shape of the structures. Hence, the ability to tune the plasmon resonance is limited. Typical methods for tuning the resonance of patterned plasmonic structures include changing the polarization of the incident light33, rotation of the sample relative to the light propagation axis34, and increasing the thickness of the deposited metal35-36. Nevertheless, these approaches have their respective constraints. For instance, changing the polarization and sample rotation impose a physical and geometrical complexity to the design of the read-out instruments in sensing applications. Increasing the thickness of deposited metal can be detrimental to the application, in which variations in transmission of the sample and the spacing between the nanostructures are important. In addition, vacuum thermal or e-beam depositions are time consuming, especially with batches of samples requiring different selected thicknesses. As a result, we have established an easy-to-adopt fabrication scheme to overcome these problems. This fabrication scheme offers tunable plasmonic nanostructures by optimizing the size of fabricated nanohole structures using a simple and inexpensive plasma cleaner etching process (step 3 in Figure 1). Excellent wavelength tuning was achieved with less than 10 minutes added to the SNAP procedure. We chose a simple starting geometry of sub-100nm hole arrays (Figure 2(a)) to demonstrate this concept. By adjusting the plasma etching time up to 5 min, different



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 33

sizes of hole diameters from 80 to 180nm were realized. AFM images of the fabricated nanohole arrays with increasing plasma etching time up to 5min are shown in Figure 2(ae). The average hole sizes at the corresponding etching times were also measured and are presented in Figure 2(f), showing a linear dependence. Finally, in order to turn the polymeric arrays into plasmonic structures, we deposited silver films on top of the printed nanostructures using electron beam deposition (step 3 in Figure 1).

Figure 2. AFM images of fabricated PAN nanohole structures with varied etching time of (a) 0 minute, (b) 2 minutes, (c) 3 minutes, (d) 4 minutes, and (e) 5 minutes. (f) Diameters of the nanoholes as a function of the etching time. The red line corresponds to the linear fit of the data.


Page 9 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To characterize the plasmonic response of the structures, we acquired extinction spectra of the samples, shown in Figure 3. As can be seen in Figure 3, the resonance peak of the nanoholes arrays is red-shifted with increasing hole diameters. We observed a large redshift of 66nm (from 480nm with no etching to 546nm) after 5min etched plasmonic sample, while the other samples exhibited resonances between 491 and 505nm. From the FDTD simulations of our structures [see SI], the larger shift at 5min treatment is attributed to partial merging of adjacent holes, resulting in larger features. Our FDTD simulations of the plasmon resonance with varied nanohole diameter are in very close agreement with the experimental data. With this tuning scheme, direct applications such as tunable color filters37-38 could easily be derived from this facile SNAP-based fabrication technique for tunable plasmonic response.

Figure 3. (a) Normalized extinction of the plasmonic nanohole samples at different etching time as a function of illumination wavelength. (b) Extinction vs wavelength of plasmonic nanohole samples coated with 1mM of R6G By geometrically tuning the optical properties of the substrates, we intend to enhance the Raman signal of the analyte. Several studies have shown the importance of geometry



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 33

optimization for detection enhancement39-44. These studies substantiate the importance of optimizing the geometry of the nanostructure in Surface Enhanced Raman Scattering (SERS) applications as well as other optical enhancement processes that involve plasmons and molecular excitons. To further demonstrate the advanced optical properties of our easy-to-fabricate plasmonic substrates, we measured extinction and Raman scattering of the nanostructures with an overlayer of Rhodamine 6G (R6G) molecules. Only plasma-etched samples were used in this study to ensure that all samples under study have the same surface absorption properties. R6G was used as the analyte because of its excitonic absorption within our tuning range of the substrates. Solutions of 1 to 11mM R6G in ethanol were deposited on a planar silver film by spin coating at 3000 rpm for 10s. The corresponding extinction spectra are presented in Figure 4(a). The extinction spectra of the R6G coated nanohole samples are shown in Figure 4(c). When compared to their corresponding extinction spectra before R6G deposition, the extinction curves of the nanohole samples with the over layer of R6G dyes are not only spectrally shifted but also altered. These observations indicate a coupling between the plasmon mode in the nanosized cavities and molecular excitons of R6G. The coupling of the photon and exciton states can be classified into two distinct regimes, namely weak and strong couplings

45

. In the former

regime, the spectral and spatial distributions are modified but the exciton dynamics is only slightly altered. In the latter regime, however, mixing of the states results in strongly modified excitonic dynamics. From our measurements, we found that the samples with etching time from 2-4min showed a red-shift in their plasmon resonance. In fact, the interaction between plasmon resonance and molecular resonance has been previously


Page 11 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


studied with nanoparticle systems46-47. Three local maxima were observed when plotting the plasmon shift of R6G coated nanoparticles versus plasmon resonances without the dye (bare plasmon resonance) due to formation of dimers on the metal surface. Local maxima in plasmon shift were observed when bare plasmon resonances were close to the molecular resonance energy. To investigate the properties of R6G films on our plasmonic samples, evolution of absorption spectra of R6G coated on planar silver substrate was studied. Glass slides coated with 20nm thick silver layer were used as substrates in this study. R6G with different concentrations (1-11mM) were spun coated on the substrates at 3000 rpm for 10s. The absorption spectra acquired for each concentration are shown in Figure 4(a). All samples showed increasing absorption from blue to red region due to the presence of the silver layer. Absorption shoulders within the wavelength range of 500600nm were found. Two absorption peaks at around 518 and 555nm could clearly be distinguished for the 6mM and 11mM sample. The features can be attributed to dimer and monomer absorption20. By subtracting the silver baseline, the spectral profiles of R6G species could be better visualized for low concentration samples. From this concentration dependent study, it was found that all of our R6G samples show two absorption features [SI, Figure S1]. Furthermore, it is known that R6G can form both Jtype (head-to-tail dipole moment) and H-type (parallel dipole moment) dimers. Head-totail geometry in J-type dimers leads to a decrease in energy whereas parallel geometry in H-type dimer leads to an increase in energy. As a result, the absorption of H-type and Jtype dimers is expected to blue shift and red shift from the monomer peak respectively. However, in the case of (silver) surface adsorption, the H-type conformer is more likely to form due to the adsorption of R6G through one of its N atoms48. This supports our



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 33

observation that H-type dimers are predominantly present in our samples. Similar absorption profile of solid R6G film was previously reported 20, 49. When investigating the effect of R6G on extinction profile of the plasmonic substrates, with 2-4min etched samples, only small plasmon shifts were observed. Such small shifts are possibly due to the fact that only a few nm thin layer of R6G was coated onto the substrates. However, among these samples, the plasmon shift is the highest with the 3min etched sample (497nm bare plasmon resonance). The shift then decreases when the bare plasmon resonance is at a higher wavelength before observing a curve splitting for the 5min etched sample. This local maximum of plasmon shift might be due to interaction of plasmon with R6G dimers similar to previous study 46.

Figure 4. (a) Evolution of absorption of 1-11mM R6G deposited on a planar silver film (b) Hybridization diagram of plexcitonic modes (c) Extinction of 5 min etched sample 12 ACS Paragon Plus Environment

Page 13 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with increasing R6G coverage from 1mM to 11mM (d) The magnitudes of the observed Rabi splitting versus the square root of the integrated R6G extinction on glass (arbitrary unit). The dash line is a guide to the eyes. In addition, the 2-4min etched samples also show a shoulder at around 550nm, Figure 3(b). The observed shoulders are close to the monomer absorption peak of the R6G dyes (555nm)

20

. These absorption shoulders cannot be attributed to the dye absorption alone

since they are too intense for the amount of dye molecule used in this experiment. Moreover, their magnitudes vary and do not satisfy Beer’s law. However, it was previously found that in a weakly coupling regime where the resonance of the photon mode is far from the exciton mode, the spectra of the coupled modes appear similar to the sum of the individual spectrum45, 50. Therefore, we attribute this observed absorption shoulder to weak coupling between plasmon mode in our structures and exciton mode of molecular transition of the dye. On the contrary, the spectrum of the sample with 5min etching exhibits a strong anti-crossing behavior with the R6G dye overlayer; the composite spectrum no longer resembles the sum of plasmon resonance and dye absorption.

When the optical mode frequency is tuned to the exciton resonance

frequency, the two states interact. The splitting at resonance, in analogy with the case of atoms in a microwave cavity, is called the Rabi splitting. When the Rabi splitting is large in comparison to the natural line widths of the optical mode and of the exciton, the strong coupling regime holds and two separate modes are produced51. Anti-crossing of the coupled modes and the appearance of two equal intensity transition separated by the vacuum Rabi splitting are indications of a strong coupling. The resulting two new modes



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 33

in the strong coupling regime can be explained in term of mode hybridization, analogous to the molecular orbital theory, and hybridization diagrams as shown in Figure 4(b). According to the spectrum of the 5min etched sample without dye (Figure 3), the sample has a plasmon resonance at about 547nm, which is the closest to the R6G monomer peak at 555nm. It is also possible that the presence of the dye overlayer red shifts the plasmon resonance of the structure such that the energy of the pure plasmon state of the structure is closer to the excitonic state of the dye, resulting in the observed anti-crossing behavior. However, this curve splitting behavior was only observed when plasmon resonance overlaps with the monomer resonance. In the case of dimer resonance, local maximum in plasmon shift was observed. To prove that the observed splitting is truly caused by Rabi splitting, we measured optical extinction of the 5min etched film with increasing R6G coverage; in the case of the strong coupling, the coupling strength may depend on the square root of the molecular absorption45,

52

. We have also found that the magnitude of the splitting

increases with the concentration of R6G deposited, as shown in Figure 4(c).

The

magnitude of the observed splitting occurring in the 5min etched sample displays a linear dependence with respect to the square root of the integrated extinction of the R6G deposited on glass (Figure 4(d)). Thus the results confirm that the observed splitting is in fact due to a strong coupling and is in agreement with previous studies11, 53. In fact, coupling between R6G and nanostructured metal have been previously reported with subsequent Rabi splitting of up to 380meV54-57. D. Richard etl al. reported a Rabi splitting of 380meV in extinction profile of R6G coupled silver nanostructured film at square root integrated extinction of 2.5. P Torma et. al. performed reflectometry 14 ACS Paragon Plus Environment

Page 15 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


measurements in the Kretschmann configuration to study coupling between surface plasmon polaritons and R6G. Maximum Rabi splitting of 200meV was reported. In our measurement, with 11mM deposited R6G or a square root integrated extinction of 0.44, Rabi splitting of 600meV was achieved. We also performed FDTD simulations of our 5min sample (180nm diameter) with an overlayer of R6G molecules. In order to account for R6G exciton, its dielectric permittivity was described by a Lorentz oscillator model of Equation (1). Rabi splitting is also observed with simulations and in very well agreement with the experimental results [see SI, Figure S2(d)].

Figure 5. (a) Emission spectra of the samples excited with laser wavelength of 532nm. Both Raman and fluorescence signals are present. (b) Measured and calculated enhancement factor vs. hole diameter. To deepen our understanding of the effect of hybridization, we measured Raman scatterings from the plexcitonic samples. Raman signals of the samples deposited with



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 33

the same concentration of R6G (1mM) are shown in Figure 5(a). All samples exhibit signal enhancement when compared to sample on bare glass. The samples with 2-3min etching time presented similar intensities of Raman signals and fluorescence background originating from the fluorescence of R6G dye centered at 560nm 58. With 4min etching time, slight increases in Raman intensities as well as the fluorescence intensity were measured. These enhancements can be due to: (1) the bare plasmon resonance peak of this sample is closer to the laser excitation and Stoke shift wavelengths of the dye 40, and (2) the coupling is stronger than the other two samples since its plasmonic state is closer in energy to the molecular exciton. The sample with 5 minute etching time, however, showed the largest Raman intensities as well as fluorescence background, which is in agreement with the observed strong coupling between the excitonic mode of the dye and the plasmon resonance of the structure.

To calculate the enhancement factor, R6G

adsorbed on a planar silver substrate is used as a reference to take into account the effect of surface adsorption on the properties of R6G. The analytical enhancement factor (EF) was calculated for these samples from the following equation:

EF =

I S / cS I ref / cref

(1)

Where, at any given frequency, I S is the signal intensity from the plasmon substrate ,

I ref is the signal intensity from the reference, cS is the concentration of the dye deposited on the substrate, and cref is the concentration of the dye deposited on the reference. These experimental enhancement factors of Raman peak at 555.152 nm (775cm-1 Raman shift) are plotted against bare plasmon resonance of the structure in Figure 5(b). Finite difference time domain (FDTD) simulation was used to evaluate the expected 16 ACS Paragon Plus Environment

Page 17 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


enhancement factor from our R6G coated 5min etched sample.

Since the Raman

enhancement factor is the product of the enhancements in excitation intensity and scattering intensity due to the presence of metal nanostructures, the FDTD computed EF was obtained using: 2

EFFDTD = g(ω ex ) g(ω sca )

2

(2)

where g(ω ) = Eloc (ω ) / E0 (ω ) with Eloc and E0 being the local and incident field at frequency

ω

respectively, ω ex is the excitation frequency of 532nm, and ω sca is the

scattering frequency of 555nm. The oscillator strength of R6G of f=1 was used since, in simulation, it produces similar peak positions and Rabi splitting magnitude to the experimental values. An analytical approximation of the oscillator strength also gives a similar value [see SI]. Figure 6 illustrates FDTD calculated EF profiles of the structures at different cross-sections.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 33

Figure 6 (a) EF profiles at different Z cross-sections. Color scales are kept uniform for better comparison (b) Schematic illustrations of the index profile of the simulated structure. (c) EF profile at the middle of the groove where two adjacent holes connect; largest EF within the R6G layer is located here. (d) EF of profile cut along x at Z=32nm of the 2D profile in (c).

It has been found that the absolute maximum EF of the overall structure lies at the silver/polymer-substrate interface. Searching algorithm was used to find a local maximum EF with in R6G layer. In the case of 5min etched sample, the local maximum EF is determined to be of 38.87 and located in a groove where two adjacent holes merge. The cross-sectional plot of this hot spot is shown in Figure 6(d). The local maximum EFs of other samples were also calculated in the same fashion. These computationally derived maximum local EFs are plotted in Figure 5(b) against their bare plasmon resonance for comparison. Albeit smaller, these theoretically calculated EFs follow the same trend as the experimentally obtained value. The sample that exhibits strong coupling shows the largest EF. This is because strong intensity enhancements both in the incident and the scattering frequencies are present in the sample. Table S1 in the SI tabulates the calculated intensity enhancements of the incident and scattering frequencies for different etching time. The relatively high intensity enhancements at both the incident and scattered frequencies might be due to the splitting and the resulted two resonance peaks that resonate with both frequencies. Increase in Raman intensity with double resonance plasmonic structures have been previously reported 59-60. However, in our case, the origin of the two resonance peaks is the coupling between plasmon and exciton.


Page 19 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


One of the possible reasons for smaller calculated EFs might be due to the fact that only electromagnetic (EM) enhancement is considered in the simulation. In real samples, however, additional EFs from other mechanisms, such as chemical enhancement might be responsible for the increase in the total enhancement factor.

In general, three

mechanisms are involved in the chemical enchantment, namely (1) ground state chemical interaction (2) resonance Raman enhancement and (3) charge-transfer (CT) resonance Raman enhancement61. While, the first mechanism are not associated with any excitations of the nanometal–molecule system, (2) and (3), however, require the excitation wavelength being resonant with either molecular transition or nanoparticle– molecule CT transitions respectively. Molecules adsorbed at certain surface sites, for example atomic clusters, terraces, and steps, can couple electronically with the surface, leading to the chemical enhancement effect62. Experimentally observed chemical enhancements are within an order of magnitude

63-64

. However, it cannot be neglected

that the plasmon resonance and geometrical mismatches between the actual and modeled samples might as well result in the discrepancy. It is also possible that the plexitonic coupling alters Raman scattering cross-section of the molecule since in the coupling regime the system is no longer composed of independent plasmon and excitons but rather described by the plexcitonic states, similar to polaritons in semiconductor microcavities65. Optical cross-sections are altered since electromagnetic enhancement and energy transfer rate between the molecule and metal can no longer treated separately 66. Previous studies have shown enhanced Raman scattering with coupling systems 66-67. Nevertheless, these findings prove the feasibility of our fabrication technique for a tailored interaction between photonic and excitonic modes. Our technique can be used to



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 33

tune the plasmonic resonance to match the excitonic resonance of the molecules of interest, leading to large enhancement in optical phenomena. This holds great potential for specific targeting of single or a few molecules. For example, the substrate can be tuned to match only the molecular absorption of a specific species, enabling low-level trace detections in sensors.

CONCLUSION In summary, we have demonstrated the fabrication of resonance tunable plasmonic nanostructures in four simple steps: spin coating, peeling off, plasma etching and silver metal deposition. The reported approach allows high throughput, large area fabrication of plasmonic optical enhancement devices with great versatility. By tuning the plasmon resonance of the nanoholes arrays, strong plexcitonic coupling could be observed. The ability to tune the resonance wavelength with simple fabrication process can be beneficial for applications such as surface enhanced Raman scattering and surface plasmon enhanced fluorescence. Finally, the largest enhancement in the Raman signals are the result of a strong coupling of the plasmonic states and molecular excitons, unveiling anticrossing behavior when the resonance of the structure overlaps with the excitonic transition of the dye. Such behavior is believed to be an important step towards active control of all-optical devices and sensors at the nanoscale.

AUTHOR INFORMATION Corresponding Author * [email protected]


Page 21 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ACKNOWLEDGMENT The authors thank Materials Characterization Facility (MCF), University of Central Florida for the sample characterization. We also acknowledge University of California, Santa Barbara (UCSB) for mold fabrication. J.T acknowledges NSF EAGER award (ECCS-1247838) for the financial support. SUPORTTING INFORMATION Resolved absorption spectra of R6G on planar silver surface and detailed FDTD simulation are provided in the supporting information. This information is available free of charge via the Internet at http://pubs.acs.org.

REFERENCES 1. Govorov, A. O.; Carmeli, I., Hybrid Structures Composed of Photosynthetic System and Metal Nanoparticles: Plasmon Enhancement Effect. Nano Lett. 2007, 7, 620625. 2. Fofang, N. T.; Park, T.-H.; Neumann, O.; Mirin, N. A.; Nordlander, P.; Halas, N. J., Plexcitonic Nanoparticles: Plasmon− Exciton Coupling in Nanoshell− J-Aggregate Complexes. Nano Lett. 2008, 8, 3481-3487. 3. Ming, T.; Zhao, L.; Yang, Z.; Chen, H.; Sun, L.; Wang, J.; Yan, C., Strong Polarization Dependence of Plasmon-Enhanced Fluorescence on Single Gold Nanorods. Nano Lett. 2009, 9, 3896-3903. 4. Lakowicz, J. R.; Ray, K.; Chowdhury, M.; Szmacinski, H.; Fu, Y.; Zhang, J.; Nowaczyk, K., Plasmon-Controlled Fluorescence: A New Paradigm in Fluorescence Spectroscopy. Analyst 2008, 133, 1308-1346. 5. Campion, A.; Kambhampati, P., Surface-Enhanced Raman Scattering. Chem. Soc. Rev. 1998, 27, 241-250. 6. Vasa, P.; Pomraenke, R.; Cirmi, G.; De Re, E.; Wang, W.; Schwieger, S.; Leipold, D.; Runge, E.; Cerullo, G.; Lienau, C., Ultrafast Manipulation of Strong Coupling in Metal− Molecular Aggregate Hybrid Nanostructures. Acs Nano 2010, 4, 7559-7565. 7. Wiederrecht, G. P.; Wurtz, G. A.; Bouhelier, A., Ultrafast Hybrid Plasmonics. Chem. Phys. Lett. 2008, 461, 171-179. 21 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 33

8. Panahpour, A.; Silani, Y.; Farrokhian, M.; Lavrinenko, A. V.; Latifi, H., Coupled Plasmon-Exciton Induced Transparency and Slow Light in Plexcitonic Metamaterials. JOSA B 2012, 29, 2297-2308. 9. Bellessa, J.; Bonnand, C.; Plenet, J.; Mugnier, J., Strong Coupling between Surface Plasmons and Excitons in an Organic Semiconductor. Phys. Rev. Lett. 2004, 93, 036404. 10. Wiederrecht, G. P.; Wurtz, G. A.; Hranisavljevic, J., Coherent Coupling of Molecular Excitons to Electronic Polarizations of Noble Metal Nanoparticles. Nano Lett. 2004, 4, 2121-2125. 11. Dintinger, J.; Klein, S.; Bustos, F.; Barnes, W. L.; Ebbesen, T., Strong Coupling between Surface Plasmon-Polaritons and Organic Molecules in Subwavelength Hole Arrays. Phys. Rev. B 2005, 71, 035424. 12. Ni, W.; Chen, H.; Su, J.; Sun, Z.; Wang, J.; Wu, H., Effects of Dyes, Gold Nanocrystals, Ph, and Metal Ions on Plasmonic and Molecular Resonance Coupling. JACS 2010, 132, 4806-4814. 13. Carmeli, I.; Lieberman, I.; Kraversky, L.; Fan, Z.; Govorov, A. O.; Markovich, G.; Richter, S., Broad Band Enhancement of Light Absorption in Photosystem I by Metal Nanoparticle Antennas. Nano Lett. 2010, 10, 2069-2074. 14. Noginov, M.; Zhu, G.; Belgrave, A.; Bakker, R.; Shalaev, V.; Narimanov, E.; Stout, S.; Herz, E.; Suteewong, T.; Wiesner, U., Demonstration of a Spaser-Based Nanolaser. Nature 2009, 460, 1110-1112. 15. Wu, X.; Xiao, Y.; Meng, C.; Zhang, X.; Yu, S.; Wang, Y.; Yang, C.; Guo, X.; Ning, C. Z.; Tong, L., Hybrid Photon-Plasmon Nanowire Lasers. Nano Lett. 2013, 13, 5654-5659. 16. Pacifici, D.; Lezec, H. J.; Atwater, H. A., All-Optical Modulation by Plasmonic Excitation of Cdse Quantum Dots. Nature photonics 2007, 1, 402-406. 17. Li, J.-B.; Kim, N.-C.; Cheng, M.-T.; Zhou, L.; Hao, Z.-H.; Wang, Q.-Q., Optical Bistability and Nonlinearity of Coherently Coupled Exciton-Plasmon Systems. Opt. Express 2012, 20, 1856-1861. 18. Luk'yanchuk, B.; Zheludev, N. I.; Maier, S. A.; Halas, N. J.; Nordlander, P.; Giessen, H.; Chong, C. T., The Fano Resonance in Plasmonic Nanostructures and Metamaterials. Nature Mat. 2010, 9, 707-715. 19. Hao, F.; Sonnefraud, Y.; Dorpe, P. V.; Maier, S. A.; Halas, N. J.; Nordlander, P., Symmetry Breaking in Plasmonic Nanocavities: Subradiant Lspr Sensing and a Tunable Fano Resonance. Nano Lett. 2008, 8, 3983-3988. 20. Cade, N.; Ritman-Meer, T.; Richards, D., Strong Coupling of Localized Plasmons and Molecular Excitons in Nanostructured Silver Films. Phys. Rev. B 2009, 79, 241404. 21. Savasta, S.; Saija, R.; Ridolfo, A.; Di Stefano, O.; Denti, P.; Borghese, F., Nanopolaritons: Vacuum Rabi Splitting with a Single Quantum Dot in the Center of a Dimer Nanoantenna. ACS nano 2010, 4, 6369-6376. 22. Nie, S.; Emory, S. R., Probing Single Molecules and Single Nanoparticles by Surface-Enhanced Raman Scattering. science 1997, 275, 1102-1106. 23. Tseng, A. A.; Kuan, C.; Chen, C. D.; Ma, K. J., Electron Beam Lithography in Nanoscale Fabrication: Recent Development. Electronics Packaging Manufacturing, IEEE Transactions on 2003, 26, 141-149.


Page 23 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


24. Shinji, M.; Yukinori, O., Focused Ion Beam Applications to Solid State Devices. Nanotechnology 1996, 7, 247-258. 25. Dickey, M. D.; Weiss, E. A.; Smythe, E. J.; Chiechi, R. C.; Capasso, F.; Whitesides, G. M., Fabrication of Arrays of Metal and Metal Oxide Nanotubes by Shadow Evaporation. ACS Nano 2008, 2, 800-808. 26. Haynes, C. L.; Van Duyne, R. P., Nanosphere Lithography: A Versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics. J. of Phys. Chem. B 2001, 105, 5599-5611. 27. Jensen, T. R.; Schatz, G. C.; Van Duyne, R. P., Nanosphere Lithography: Surface Plasmon Resonance Spectrum of a Periodic Array of Silver Nanoparticles by Ultraviolet−Visible Extinction Spectroscopy and Electrodynamic Modeling. J. of Phys. Chem. B 1999, 103, 2394-2401. 28. Guo, L. J., Nanoimprint Lithography: Methods and Material Requirements. Adv. Mat. 2007, 19, 495-513. 29. Ghosh, G., Handbook of Optical Constants of Solids: Handbook of Thermo-Optic Coefficients of Optical Materials with Applications; Elsevier Science, 1998. 30. Duong, B.; Gangopadhyay, P.; Brent, J.; Seraphin, S.; Loutfy, R. O.; Peyghambarian, N.; Thomas, J., Printed Sub-100nm Polymer-Derived Ceramic Structures. ACS App. Mat. & Int. 2013, 5(9), 3894-3899. 31. Link, S.; El-Sayed, M. A., Size and Temperature Dependence of the Plasmon Absorption of Colloidal Gold Nanoparticles. J of Phys. Chem. B 1999, 103, 4212-4217. 32. Grand, J.; Adam, P.-M.; Grimault, A.-S.; Vial, A.; Lamy de la Chapelle, M.; Bijeon, J.-L.; Kostcheev, S.; Royer, P., Optical Extinction Spectroscopy of Oblate, Prolate and Ellipsoid Shaped Gold Nanoparticles: Experiments and Theory. Plasmonics 2006, 1, 135-140. 33. Mertens, H.; Biteen, J. S.; Atwater, H. A.; Polman, A., Polarization-Selective Plasmon-Enhanced Silicon Quantum-Dot Luminescence. Nano Lett. 2006, 6, 2622-2625. 34. Wurtz, G. A.; PollardR; HendrenW; Wiederrecht, G. P.; Gosztola, D. J.; Podolskiy, V. A.; Zayats, A. V., Designed Ultrafast Optical Nonlinearity in a Plasmonic Nanorod Metamaterial Enhanced by Nonlocality. Nat Nano 2011, 6, 107-111. 35. Lucas, B. D.; Kim, J.-S.; Chin, C.; Guo, L. J., Nanoimprint Lithography Based Approach for the Fabrication of Large-Area, Uniformly-Oriented Plasmonic Arrays. Adv. Mat. 2008, 20, 1129-1134. 36. Park, H. J.; Kang, M.-G.; Guo, L. J., Large Area High Density Sub-20 Nm Sio2 Nanostructures Fabricated by Block Copolymer Template for Nanoimprint Lithography. ACS Nano 2009, 3, 2601-2608. 37. Xu, T.; Wu, Y.-K.; Luo, X.; Guo, L. J., Plasmonic Nanoresonators for HighResolution Colour Filtering and Spectral Imaging. Nature Communications 2010, 1, 59. 38. Park, H. J.; Xu, T.; Lee, J. Y.; Ledbetter, A.; Guo, L. J., Photonic Color Filters Integrated with Organic Solar Cells for Energy Harvesting. ACS nano 2011, 5, 70557060. 39. Perney, N.; de Abajo, F. G.; Baumberg, J.; Tang, A.; Netti, M.; Charlton, M.; Zoorob, M., Tuning Localized Plasmon Cavities for Optimized Surface-Enhanced Raman Scattering. Phys. Rev. B 2007, 76, 035426.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 33

40. Felidj, N.; Aubard, J.; Levi, G.; Krenn, J.; Hohenau, A.; Schider, G.; Leitner, A.; Aussenegg, F., Optimized Surface-Enhanced Raman Scattering on Gold Nanoparticle Arrays. Appl. Phys. Lett. 2003, 82, 3095-3097. 41. Jackson, J. B.; Halas, N. J., Surface-Enhanced Raman Scattering on Tunable Plasmonic Nanoparticle Substrates. Proceedings of the National Academy of Sciences 2004, 101, 17930-17935. 42. Lu, Y.; Liu, G. L.; Lee, L. P., High-Density Silver Nanoparticle Film with Temperature-Controllable Interparticle Spacing for a Tunable Surface Enhanced Raman Scattering Substrate. Nano Lett. 2005, 5, 5-9. 43. Qian, L.; Yan, X.; Fujita, T.; Inoue, A.; Chen, M., Surface Enhanced Raman Scattering of Nanoporous Gold: Smaller Pore Sizes Stronger Enhancements. Appl. Phys. Lett. 2007, 90, 153120-153120-3. 44. Zhang, L.; Lang, X.; Hirata, A.; Chen, M., Wrinkled Nanoporous Gold Films with Ultrahigh Surface-Enhanced Raman Scattering Enhancement. Acs Nano 2011, 5, 44074413. 45. Lidzey, D. G.; Bradley, D.; Skolnick, M.; Virgili, T.; Walker, S.; Whittaker, D., Strong Exciton–Photon Coupling in an Organic Semiconductor Microcavity. Nature 1998, 395, 53-55. 46. Zhao, J.; Das, A.; Zhang, X.; Schatz, G. C.; Sligar, S. G.; Van Duyne, R. P., Resonance Surface Plasmon Spectroscopy: Low Molecular Weight Substrate Binding to Cytochrome P450. JACS 2006, 128, 11004-11005. 47. Haes, A. J.; Zou, S.; Zhao, J.; Schatz, G. C.; Van Duyne, R. P., Localized Surface Plasmon Resonance Spectroscopy near Molecular Resonances. JACS 2006, 128, 1090510914. 48. Zhao, J.; Chemistry, N. U., Resonant Localized Surface Plasmon Resonance Spectroscopy: Fundamentals and Applications; Northwestern University, 2008. 49. Lu, Y.; Penzkofer, A., Absorption Behaviour of Methanolic Rhodamine 6g Solutions at High Concentration. Chem. Phys. 1986, 107, 175-184. 50. Glass, A.; Liao, P. F.; Bergman, J.; Olson, D., Interaction of Metal Particles with Adsorbed Dye Molecules: Absorption and Luminescence. Optics Letters 1980, 5, 368370. 51. Bassani, G. F.; Agranovich, V. M., Electronic Excitations in Organic Based Nanostructures; Elsevier Science, 2003. 52. Fontcuberta i Morral, A.; Stellacci, F., Light-Matter Interactions: Ultrastrong Routes to New Chemistry. Nat Mater 2012, 11, 272-273. 53. Hobson, P. A.; Barnes, W. L.; Lidzey, D.; Gehring, G.; Whittaker, D.; Skolnick, M.; Walker, S., Strong Exciton–Photon Coupling in a Low-Q All-Metal Mirror Microcavity. Appl. Phys. Lett. 2002, 81, 3519-3521. 54. Väkeväinen, A.; Moerland, R. J.; Rekola, H. T.; Eskelinen, A.-P.; Martikainen, J.P.; Kim, D.-H.; Törmä, P., Plasmonic Surface Lattice Resonances at the Strong Coupling Regime. Nano Lett. 2013, 14, 1721-1727. 55. Hakala, T.; Toppari, J.; Kuzyk, A.; Pettersson, M.; Tikkanen, H.; Kunttu, H.; Törmä, P., Vacuum Rabi Splitting and Strong-Coupling Dynamics for Surface-Plasmon Polaritons and Rhodamine 6g Molecules. Phys. Rev. Lett. 2009, 103, 053602.


Page 25 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


56. Cade, N.; Ritman-Meer, T.; Richards, D. In Plasmonic Engineering of Silver Films for Enhanced Fluorescence and Raman Scattering, SPIE BiOS: Biomedical Optics, International Society for Optics and Photonics: 2009; pp 71920J-71920J-7. 57. Rodriguez, S.; Feist, J.; Verschuuren, M.; Vidal, F. G.; Rivas, J. G., Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation. Phys. Rev. Lett 2013, 111, 166802. 58. Reisfeld, R.; Zusman, R.; Cohen, Y.; Eyal, M., The Spectroscopic Behaviour of Rhodamine 6g in Polar and Non-Polar Solvents and in Thin Glass and Pmma Films. Chem. Phys. Lett. 1988, 147, 142-147. 59. Chu, Y.; Banaee, M. G.; Crozier, K. B., Double-Resonance Plasmon Substrates for Surface-Enhanced Raman Scattering with Enhancement at Excitation and Stokes Frequencies. Acs Nano 2010, 4, 2804-2810. 60. Banaee, M. G.; Crozier, K. B., Mixed Dimer Double-Resonance Substrates for Surface-Enhanced Raman Spectroscopy. Acs Nano 2010, 5, 307-314. 61. Jensen, L.; Aikens, C. M.; Schatz, G. C., Electronic Structure Methods for Studying Surface-Enhanced Raman Scattering. Chem. Soc. Rev. 2008, 37, 1061-1073. 62. Doering, W. E.; Nie, S., Single-Molecule and Single-Nanoparticle Sers: Examining the Roles of Surface Active Sites and Chemical Enhancement. J of Phy. Chem. B 2001, 106, 311-317. 63. Valley, N.; Greeneltch, N.; Van Duyne, R. P.; Schatz, G. C., A Look at the Origin and Magnitude of the Chemical Contribution to the Enhancement Mechanism of SurfaceEnhanced Raman Spectroscopy (Sers): Theory and Experiment. J of Phy. Chem. Lett. 2013, 4, 2599-2604. 64. Saikin, S. K.; Chu, Y.; Rappoport, D.; Crozier, K. B.; Aspuru-Guzik, A., Separation of Electromagnetic and Chemical Contributions to Surface-Enhanced Raman Spectra on Nanoengineered Plasmonic Substrates. J of Phy. Chem. Lett. 2010, 1, 27402746. 65. Fainstein, A.; Jusserand, B.; Thierry-Mieg, V., Cavity-Polariton Mediated Resonant Raman Scattering. Phys. Rev. Lett. 1997, 78, 1576. 66. Itoh, T.; Yamamoto, Y. S.; Tamaru, H.; Biju, V.; Wakida, S.-i.; Ozaki, Y., SingleMolecular Surface-Enhanced Resonance Raman Scattering as a Quantitative Probe of Local Electromagnetic Field: The Case of Strong Coupling between Plasmonic and Excitonic Resonance. Phys. Rev. B 2014, 89, 195436. 67. Nagasawa, F.; Takase, M.; Murakoshi, K., Raman Enhancement Via Polariton States Produced by Strong Coupling between a Localized Surface Plasmon and Dye Excitons at Metal Nanogaps. J of Phy. Chem. Lett. 2013, 5, 14-19.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 33


Page 27 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


241x61mm (150 x 150 DPI)

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

117x179mm (150 x 150 DPI)


Page 28 of 33

Page 29 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


233x94mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

192x157mm (150 x 150 DPI)


Page 30 of 33

Page 31 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


289x129mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

499x345mm (150 x 150 DPI)


Page 32 of 33

Page 33 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


98x84mm (150 x 150 DPI)


Coupling Enhancement and Giant Rabi-Splitting in Large Arrays of

Recommend Documents