Templated Nanodimple Arrays with Tunable Nanostructures for

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Templated Nanodimple Arrays with Tunable Nanostructures for Sensitive Surface Plasmon Resonance Analysis Pei-Yu Chung, Po-Yuan Wang, Xuan Dou, and Peng Jiang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp4014477 • Publication Date (Web): 29 Mar 2013 Downloaded from http://pubs.acs.org on March 31, 2013

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The Journal of Physical Chemistry

Templated Nanodimple Arrays with Tunable Nanostructures for Sensitive Surface Plasmon Resonance Analysis Pei-Yu Chung,† Po-Yuan Wang,† Xuan Dou,‡ and Peng Jiang‡,* Department of Materials Science and Engineering, and Department of Chemical Engineering, University of Florida, Gainesville, FL 32611 Abstract This paper reports a simple and scalable colloidal templating technology for fabricating wafer-scale periodic plasmonic nanodimple arrays with tunable nanostructures. A double-layer, non-close-packed colloidal crystal-polymer nanocomposite created by a spin-coating technique is used as structural template in a simple oxygen plasma etching process to fabricate periodic arrays of nanodimples. The resulting plasmonic arrays can sense a small dielectric refractive index change of ~0.008 and they exhibit high SPR sensitivity of up to ~520 nm per refractive index unit. The experimental plasmonic performance of the nanodimple arrays matches with the numerical simulations using a finite-difference time-domain model. Keywords: SPR, plasmonics, self-assembly, template, colloidal crystals

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Department of Materials Science and Engineering.

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Department of Chemical Engineering.

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Corresponding author. E-mail: [email protected]. ACS Paragon Plus Environment

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Introduction Surface plasmons are light-excited coherent oscillations of electrons at metal/dielectric interfaces.1-4 Since these electromagnetic oscillations can only propagate submicrometer-scale distances in the dielectric media,5 they have been exploited extensively for label-free biosensing based on changes in local refractive index (RI) caused by binding of biomolecules.6-13 To efficiently couple the incident light with electrons at the metal/dielectric interface and excite surface plasmons, bulk prisms in the Kretschmann geometry,8,14 waveguides,15 grating couplers,16-24 and noble metal nanoparticles25-32 have been used in matching the momentum of light and surface plasmons. After exciting surface plasmons at the metal/dielectric interface where high-affinity capturing molecules are conjugated, binding events between the capturing molecules and the targets of interest result in local RI changes, and therefore shift surface plasmon resonance (SPR) peaks to different spectral positions or alter the light out-coupling angles. Therefore, the change in the resonant wavelength, optical intensity including transmission, reflection, or extinction, and the excitation angle can all be used to monitor bio-binding events.1,5,10 The prism-coupling-based SPR method has been developed for decades and has demonstrated its applications in kinetic characterization and highly sensitive quantitative analysis for studying various biomolecules, such as DNA, proteins, and cells, in a label-free manner.33-35 Compared with label-based analytical methods that require fluorescent, enzymatic, or radioactive labels, a label-free bio-analysis method enables rapid and real-time measurements, eliminates interferences such as background signals or label photobleaching, and preserves the structures of the targets of interest.36 However, the use of bulky prisms hampers the development of inexpensive, miniaturized, and high-throughput sensing apparatuses. Nanograting-based light coupling is an alternative approach to excite surface plasmons, generating opportunities in the development of high-throughput and image-based sensing systems.17,37-39 In recent decades, a large variety of wet-synthesis and advanced nanofabrication techniques have been developed to make a spectrum of plasmonic nanostructures for efficient SPR sensing.6,25-26 Electron-beam lithography and focused ion-beam (FIB) milling are commonly used for generating high-resolution ACS Paragon Plus Environment

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nanostructures with arbitrary geometries.16,28,40-43 Unfortunately, these top-down techniques encounter major obstacles of high manufacturing cost and low throughput. By contrast, bottom-up methodologies such as soft lithography and nanosphere lithography are simple, fast, simple-to-implement, and costeffective in creating a large variety of periodic plasmonic nanostructures. Soft lithography involves the preparation of elastomeric (e.g., poly(dimethylsiloxane), PDMS) stamps or molds against nanopatterns generated by high-resolution lithographic techniques, such as phase-shift photolithography and interference lithography, and the nanopattern transfer from the PDMS template to UV-curable polymers such as polyurethane (PU).44-45 One major advantage of this method is that the PDMS mold can be reused to generate hundreds of polymer replicates with a high density of nanopatterns, so the cost can be greatly reduced. Nanosphere lithography is another inexpensive and widely used method in fabricating periodic plasmonic nanostructures.23,46-53 In this methodology, self-assembled monolayer or multilayer colloidal crystals are utilized as either deposition or etching masks to pattern periodic nanostructures in a large variety of materials ranging from metals and polymers to ceramics and semiconductors. Unfortunately, traditional colloidal self-assembly techniques, such as spin-coating,46,54 gravity sedimentation,55-56 electrostatic repulsion,57-60 template-assisted assembly,61-63 and capillary force induced self-assembly,64-67 are only favorable for low volume, laboratory-scale production. Attaining high-throughput and large-area fabrication continues to be a major challenge with these bottom-up techniques. We have recently developed a novel spin-coating technological platform that enables wafer-scale assembly of high-quality colloidal crystals with unusual non-close-packed structure.68-69 The spincoated monolayer colloidal crystals can also be used as structural templates to fabricate a number of periodic plasmonic nanostructures with sharp features that can efficiently concentrate electromagnetic fields for surface-enhanced Raman scattering (SERS), including nanopyramids,70-71 metal Petri dishes,72, and metal half shells.73 The SPR performance of the templated gold nanopyramid arrays has also been evaluated and a SPR sensitivity of ~240 nm per refractive index unit (nm/RIU) is obtained.74 Unfortunately, all our previous spin-coating-based templating technologies require multiple ACS Paragon Plus Environment

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microfabrication steps to get the resulting nanostructures. This could significantly affect the quality and reproducibility of the final plasmonic gratings as defects introduced in each step will be accumulated to affect the final structures. In this paper, we will report a much simpler templating nanofabrication technique based on the spincoating platform for fabricating periodic plasmonic nanodimple arrays with high SPR sensitivity (up to ~520 nm/RIU) over wafer-sized areas. A simple oxygen plasma etching process is used to tune the resulting nanostructures of the templated nanodimples. The plasmonic properties of the nanodimple arrays are studied by both optical reflection measurements and numerical simulations based on a finitedifference time-domain (FDTD) model. Experimental Section Materials and Substrates. All solvents and chemicals are of reagent quality and are used without further purification. Ethanol (200-proof) is purchased from Decon Labs. Ethoxylated trimethylolpropane triacrylate monomer (ETPTA) is obtained from Sartomer. The photoinitiator, Darocur 1173 (2-hydroxy2-methyl-1-phenyl-1-propanone), is provided by BASF Corporation. Silicon wafers [test grade, n type, (100), Wafernet] are primed by swabbing 3-acryloxypropyl trichlorosilane (APTCS, Gelest) on the wafer surfaces using cleanroom Q-tips, followed by rinsing with 200-proof ethanol twice. Hydrofluoric acid (HF, 49% aqueous solution) is purchased from Fisher Scientific. Polydimethylsiloxane (Sylgard 184) is obtained from Dow Corning. Instrumentation. Scanning electron microscopy (SEM) is carried out on a JEOL 6335F FEG-SEM. A thin layer of gold is sputtered onto the samples prior to imaging. A standard spin coater (WS-400B6NPP-Lite Spin Processor, Laurell) is used to prepare silica colloidal crystal-polymer nanocomposites. A pulsed UV curing system RC 742 (Xenon) is utilized to cure ETPTA monomer. Oxygen plasma etching is performed on a Unaxis Shuttlelock RIE/ICP reactive-ion etcher. A CMS-18 Multi Target Sputter Deposition System (Kurt J. Lesker) is used to deposit thin layers of chromium (Cr) and gold (Au). Optical reflection spectra at normal incidence are obtained using an Ocean Optics HR4000 High Resolution Fiber Optic Vis-near-IR spectrometer with a reflection probe. ACS Paragon Plus Environment

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Fabrication of Plasmonic Nanodimple Arrays. Periodic plasmonic nanodimple arrays with tunable nanostructures are fabricated by using the scalable spin-coating technology,68 followed by simple oxygen plasma etching and metal deposition processes (Figure 1). The synthesis of monodispersed silica microspheres with 320 nm diameter and less than 5% diameter standard deviation are performed by following the well-established Stöber method.75 After purification by multiple (at least four times) centrifugation/redispersion cycles in 200-proof ethanol, the purified silica microspheres are redispersed in ETPTA monmer to prepare colloidal supsensions with a particle volume fraction of 0.20 and a 2 wt% of photoinitiator (Darocur 1173). The as-prepared silica-ETPTA suspension is dispensed on a APTCSprimed silicon wafer and the wafer is then spin-coated at 200 rpm for 2 min, 300 rpm for 2 min, 1000 rpm for 1 min, 3000 rpm for 20 s, and finally at 6000 rpm for 90 s. The ETPTA monomer is rapidly photopolymerized by exposing to UV radiation for 4 s. The solidified ETPTA matrix is partially removed by a brief oxygen plasma etching process operated at 40 mTorr oxygen pressure, 40 sccm flow rate, and 100 W for varied durations ranging from 30 to 120 s. The exposed silica microspheres are removed by dissolving in a 2 vol% HF aquesion solution, followed by rinsing with deionized water and blowing dry with nitrogen. This results in the formation of wafer-scale nanodimple arrays in ETPTA. Thin layers of Cr (5 nm) and Au (100 nm) are sequentially deposited on the templated ETPTA nanodimple arrays to complete the fabrication of plasmonic nanodimple arrays with tunable nanostructures. Optical Characterization. Specular optical reflection spectra from the templated plasmonic nanodimple arrays are obtained by using a tungsten halogen light source (LS-1), a reflection probe (R600-7), and a high-resolution portable spectrometer (HR4000), all from Ocean Optics. A sandwich cell consisting of a plasmonic nanodimple array sample, a 2-mm-thick PDMS spacer, and a glass microslide is used to hold solutions (water or sodium chloride aqueous solution) in between. The refractive indices of the sodium chloride solutions with different concentrations are measured by using a refractometer. Optical reflection measurements are performed at normal incidence using unpolarized light and the cone angle of collection is less than 5°. Absolute reflectivity is obtained as the ratio of the ACS Paragon Plus Environment

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sample spectrum and the reference spectrum, which is the optical density obtained from an aluminumsputtered (1000 nm thickness) silicon wafer. Finite-Difference Time-Domain Simulation. The Lumerical FDTD Solution software, which implements the finite-difference time-domain algorithm to simulate the propagation of electromagnetic radiation through complex media by numerically solving the Maxwell’s equations,76 is used to simulate the SPR properties of the plasmonic nanodimple arrays. The geometrical parameters of the nanodimple arrays used for modeling are determined by SEM images. A planar wave source is placed at 140 nm above the top of the nanodimple array. The simulation boundary conditions for the x-axis, y-axis, bottom, and top are anti-symmetry, symmetry, metal, and perfect matched layers (PML).76 The monitor that is used to calculate the far-field reflection spectra is placed at 20 nm above the source. Results and Discussion The schematic illustration of the templating processes for fabricating plasmonic nanodimple arrays with tunable nanostructures is shown in Figure 1. The scalable spin-coating technology is firstly utilized to assemble multilayer non-close-packed silica colloidal crystal-polymer nanocomposites on silicon substrates.68-69 The assembled silica microspheres are non-close-packed as they show a characteristic inter-particle distance (~1.4-fold of particle diameter), while they are exhibit long-range hexagonal ordering. Wafer-scale (up to 12-in.) samples with high crystalline quality can be assembled in minutes by this bottom-up technology. As shown in our previous work, the thickness of the self-assembled colloidal crystals can be easily tuned by controlling the spin-coating speed and time.68-69 In this work, spin-coated double-layer colloidal crystals are used, though thicker colloidal arrays generate almost identical results. The ETPTA polymer matrix can be selectively removed by a brief oxygen plasma etching process. The exposed silica microspheres can then be dissolved in a 2 vol% HF aqueous solution, leaving behind a polymer nanodimple array. After sputtering deposition of 5 nm Cr and 100 Au layers, plasmonic nanodimple arrays are resulted. By simply controlling the oxygen plasma etching conditions (e.g., etching power and time), the portions of the embedded silica microspheres protruding out of the ETPTA matrix and the structure of the resulting nanodimple arrays can be easily tuned. ACS Paragon Plus Environment

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Figure 2 shows a photograph of a 4-in.-sized, Au-coated nanodimple array templated from 320 nm silica microspheres illuminated with white light. It exhibits a characteristic six-arm Bragg diffraction pattern, indicating long-range hexagonal ordering of the templated nanodimples.68,77 Although some defects (such as comets caused by the dusts deposited on the sample surface during spin-coating) are present, the sample is quite uniform across the wafer-scale areas. Figures 3A and 3B show typical topand side-view SEM images of a metalized nanodimple array prepared by plasma-etching a double-layer nanocomposite sample consisting of 320 nm silica microspheres at 40 mTorr oxygen pressure, 40 sccm flow rate, and 100 W for 30 s. The long-range hexagonal ordering of the templated nanodimples is clearly evident from these images. The center-to-center distance between neighboring nanodimples is determined to be ~450 nm by using the pair correlation function (PCF) calculation,78 complying with the inter-particle distance (~1.4-fold of the microsphere diameter) of the original non-close-packed colloidal crystals created by spin-coating.68 The average diameter of the resulting nanodimples (266 ± 13 nm) is smaller than that of the templating silica microspheres (Figure 3A) and the depth of the nanodimples is shallower than the radius of the silica particles (Figure 3B). These indicate the ETPTA polymer matrix has been plasma-etched to a level that is a little bit below the equators of the top-layer silica microspheres under the above plasma etching conditions. When the same silica-ETPTA nanocomposite sample is plasma-etched using the above receipt for 60 s, the polymer matrix surrounding the top-layer silica microspheres is removed almost completely. However, the ETPTA polymer underneath the silica particles is only partially etched because of the protection provided by the top-layer silica microspheres which function as etching masks. After dissolving the templating silica microspheres by hydrofluoric acid, the resulting hexagonally ordered nanodimples have a ring-like structure shown by the top- and side-view SEM images in Figures 3C and 3D. The nanostructure of the templated nanodimple arrays can be further changed by extending the oxygen plasma etching time for an additional 30 s. In this case, the bottom-layer silica microspheres of the original double-layer nanocomposite start to be exposed. Both layers of the silica particles are then ACS Paragon Plus Environment

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removed by the subsequent hydrofluoric acid wash, resulting in the formation of small openings in the triangular interstitials of the hexagonally ordered nanodimples templated from the top-layer silica microspheres as shown by the SEM images of a 90 s-etched sample in Figures 3E and 3F. By comparing with Figures 3C and 3D, it is apparent that the average diameter of the 90 s-etched nanodimples is smaller than that of the 60 s-etched sample, while the depth of the former is larger than that of the latter. The horizontal etching of the polymer matrix underneath the top-layer silica microspheres, although its rate is smaller than the vertical etching rate at the unprotected regions, contributes to the observed diameter decrease and depth increase of the resulting nanodimples. When the oxygen plasma etching time is increased to 120 s, the exposed portion of the bottom-layer silica microspheres is significantly increased. After removing the templating silica particles of both layers, periodic nanodimple arrays with a unique binary nanodimple structure are resulted (Figures 3G and 3H). As shown by the top-view SEM image and the inset in Figure 3G, the average diameter of the top-layer ring-like nanodimples becomes even smaller compared with the samples in Figures 3C and 3E. The large voids in the triangular interstitials of the top-layer nanodimples are templated from the bottom-layer silica microspheres. The plasmonic properties and the refractive index sensing performance of the templated plasmonic nanodimple arrays with tunable nanostructures are evaluated using an Ocean Optics Vis-near-IR spectrometer with a reflection probe. The normal-incidence specular reflection spectra in Figure 4A-D obtained from the above 30, 60, 90, and 120 s-etched samples reveal the good spectral tunability enabled by the efficient electromagnetic coupling of the incident light with the adjustable SPR modes of the nanodimple arrays. As both the periodic nanostructure and the RI of the dielectric medium interfacing with the plasmonic grating are able to change the oscillation conditions for surface plasmon resonances, the templated gold nanodimple arrays with tunable configurations immersed in dielectric media with different RIs show varied SPR dips in their reflection spectra. These dips correspond to different SPR modes and are caused by light diffraction from the periodic nanodimple arrays. As a

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result, the electromagnetic fields available to excite the SPR modes are strongly adsorbed by the plasmonic substrates, resulting in the dips in the specular reflection spectra. Figure 4A shows that the 30 s-etched plasmonic nanodimple array exhibits two shallow SPR resonant dips around 475 nm and 525 nm in air (RI = 1.0). The dips shift to ~525 nm and ~675 nm when air is replaced by water (RI = 1.3325) and sodium chloride solutions with different concentrations. The redshift of the single SPR resonant dip for the 60 s-etched nanodimple sample from ~600 nm in air to around 750 nm in water and salt solutions is clear from Figure 4B. The 90 s-etched sample with both layers of the templating silica microspheres being removed does not show a distinct SPR dip in air (possibly two neighboring resonant dips overlap to form a broad shoulder near 500 nm), though two resonant dips around 525 nm and 625 nm become evident when the sample is immersed in water and salt solutions (Figure 4C). Meanwhile, the 120 s-etched array with a binary nanodimple structure exhibits a large SPR shift from ~600 nm in air to around 775 nm in solutions with higher RIs (Figure 4D). The SPR sensitivities of the templated plasmonic nanodimple arrays can be determined by calculating the slopes of the linearly fitted lines correlating the positions of the SPR resonant dips versus the RIs of the dielectric media (Figure 5). The calculated SPR sensitivities for the four types of nanodimple arrays prepared with different oxygen plasma etching durations are summarized in Table 1. The 60 s and 120 s-etched samples show highest SPR sensitivity (~500 nm/RIU) which is higher than many of the self-assembled and templated periodic plasmonic nanostructures, such as arrays of nanoparticles,12,31,79 nanoholes,42,80 nanopyramids,74 and nanorings.30,81-83 Above we have characterized the SPR sensitivities of the templated nanodimple arrays by monitoring the wavelength shifts of the SRP dips induced by the dielectric RI changes. In practical chemical and biological SPR sensing, the RI difference caused by the change in the local dielectric environment (e.g., specific adsorption of a monolayer of antigens by antibodies) is usually very small, leading to stringent demands of high-resolution spectrometers and/or sensitive SPR substrates. To amplify the spectral difference caused by trivial RI changes, we can subtract the reflection spectra of the nanodimple arrays immersed in pure water from the spectra of the same arrays immersed in sodium chloride solutions with ACS Paragon Plus Environment

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higher RIs. Figures 6A and 6B show the resulting differential spectra of the 60 and 120 s-etched gold nanodimple arrays responding to RI changes from 0.008 to 0.031. In the 60 s-etched sample, the differential reflection intensity of the peaks around 725 nm increases proportionally to the refractive index difference (∆RI). On the other hand, the differential spectra of the 120 s-etched nanodimple array show a peak around 750 nm and two valleys near 640 and 810 nm. The absolute reflection intensities of these differential peaks and valleys are all proportional to ∆RI. Figures 6A and 6B demonstrate that the templated gold nanodimple arrays are able to sense ∆RI as small as 0.008. The optical characterization of the templated gold nanodimple arrays is complemented by numerical FDTD simulations. The structural parameters of the nanodimple arrays used for modeling are determined by SEM images (see Figure 3). Figure 7A shows the simulated normal-incidence reflection spectra for a hexagonal array of gold nanodimples with a ring-like structure (see Figures 3C and 3D) immersed in dielectric media with different RIs. The inner radius, outer radius, height, lattice constant, and Au thickness are set as 100 nm, 180 nm, 80 nm, 450 nm, and 100 nm. The red-shift of the distinct SPR dips caused by the increase in dielectric RIs is clearly evident from the simulated spectra. The SPR sensitivity of the simulated nanodimple array with a perfect periodic structure is determined to be 622 nm/RIU using the linear relationship of the SPR dip wavelengths versus dielectric RIs as shown in Figure 7B. The difference in structural parameters between model and experimental gratings, as well as intrinsic defects of the self-assembled and templated arrays, could contribute to the observed discrepancy in the theoretical and experimental (~500 nm/RIU) SPR sensitivities. Conclusions In conclusion, we have developed a scalable bottom-up technology for fabricating periodic arrays of gold nanodimples with adjustable nanostructures. The templated plasmonic arrays exhibit tunable SPR properties and enable high SPR sensitivity (up to ~520 nm/RIU). The FDTD simulations have also been conducted to complement the experimental measurements and the simulated SPR performance matches reasonably well with the experimental results. We have also demonstrated that the nanodimple arrays


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can sense a small dielectric RI change (~0.008). The novel templating technology is scalable and compatible with standard microfabrication, enabling large-scale production of sensitive SPR substrates for rapid and label-free detection of various chemical and biological analytes. Acknowledgment. Acknowledgments are made to the National Science Foundation (Grant No. CBET-0744879 and CMMI-1000686) and the Donors of the American Chemical Society Petroleum Research Fund for support of this research.


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Tables Table 1. Summary of the measured SPR sensitivities for the four types of nanodimple arrays prepared with different plasma etching durations.

Oxygen Plasma Etching Time (s)

30

60

90

120

SPR Sensitivity (nm/RIU)

446

492

344

519


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Figure Captions Figure 1. Schematic illustration of the templating procedures for fabricating ETPTA nanodimple arrays with tunable nanostructures by using a spin-coated double-layer colloidal crystal as structural template. Figure 2. Photograph of a 4-in.-sized, 120 s-etched gold nanodimple array sample consisting of 300 nm silica microspheres illuminated with white light. Figure 3. (A, C, E, G) Top- and (B, D, F, H) side-view SEM images of 30, 60, 90, and 120 s-etched nanodimple array samples. Insets of (A, C, E, G) show higher magnification images. Figure 4. Normal-incidence optical reflection spectra obtained from four templated nanodimple arrays plasma-etched at (A) 30 s, (B) 60 s, (C) 90 s, (D) 120 s, exposed in air, water, and sodium chloride aqueous solutions with different RIs. Figure 5. Dependence of the positions of the SPR dips vs. dielectric RIs for the templated nanodimple arrays plasma-etched at (A) 30 s, (B) 60 s, (C) 90 s, and (D) 120 s. Figure 6. Differential reflection spectra corrected by the water baselines for (A) 60 s and (B) 120 setched nanodimple arrays. Figure 7. (A) FDTD-simulated normal-incidence optical reflection spectra of a nanodimple array, which has a structure similar to the 60 s-etched sample, exposed to dielectric media with different RIs. (B) Dependence of the positions of the SPR dips vs. dielectric RIs for the simulated spectra.


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Figures


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A

B

450

500

550

RI = 1.000 RI = 1.3325 RI = 1.3405 RI = 1.3490 RI = 1.3563 RI = 1.3635

Reflectivity (arb. units)


RI = 1.000 RI = 1.3325 RI = 1.3405 RI = 1.3490 RI = 1.3563 RI = 1.3635

600

650

700

750

800

500

550

Wavelength (nm)

C

450

500

550

600

650

700

750

800

850

800

850

Wavelength (nm)

D RI = 1.000 RI = 1.3325 RI = 1.3405 RI = 1.3490 RI = 1.3563 RI = 1.3635


RI = 1.000 RI = 1.3325 RI = 1.3405 RI = 1.3490 RI = 1.3563 RI = 1.3635


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


600

650

700

750

800

500

550

Wavelength (nm)

600

650

700

750

Wavelength (nm)

Figure 4


25

670

665

660

B

760

Wavelength (nm)

A

755

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750

745

655 740

1.33

1.34

1.35

1.36

1.33

1.37

Refractive Index 615

610

1.34

1.35

1.36

1.37

1.36

1.37

Refractive Index

D Wavelength (nm)

C Wavelength (nm)

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

Wavelength (nm)


605

790

785

780

775

600

770 1.33

1.34

1.35

1.36

1.37

1.33

Refractive Index

1.34

1.35

Refractive Index

Figure 5


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A 0.12

0.08

∆RI = 0.0080 ∆RI = 0.0165 ∆RI = 0.0238 ∆RI = 0.0310

∆R

0.04

0.00

-0.04

-0.08 500

550

600

650

700

750

800

850

800

850

Wavelength (nm)

B 0.08

0.04

∆R

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


∆RI = 0.0080 ∆RI = 0.0165 ∆RI = 0.0238 ∆RI = 0.0310

0.00

-0.04

-0.08

-0.12 500

550

600

650

700

750

Wavelength (nm)

Figure 6


27



A

RI = 1.000 RI = 1.333 RI = 1.341 RI = 1.349 RI = 1.364

700

800

900

1000

Wavelength (nm)

B

935 930

Wavelength (nm)

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

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925 920 915 910 905 1.33

1.34

1.35

1.36

1.37

Refractive Index

Figure 7


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Table of Contents (TOC) Image


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Templated Nanodimple Arrays with Tunable Nanostructures for

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