Tunable Plasmonic Neutral Density Filters and Chromatic Polarizers

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Tunable Plasmonic Neutral Density Filters and Chromatic Polarizers: Highly Packed 2D Arrays of Plasmonic Nanoparticle on Elastomer Substrate Mahmoud A. Mahmoud J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b05041 • Publication Date (Web): 27 Jul 2016 Downloaded from http://pubs.acs.org on July 28, 2016

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 28

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

Tunable Plasmonic Neutral Density Filters and Chromatic Polarizers: Highly Packed 2D Arrays of Plasmonic Nanoparticle on Elastomer Substrate Mahmoud A. Mahmoud* Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 * E-mail: [email protected] Phone number: +1 404 894 4049

ABSTRACT

Highly packed gold nanocube (AuNC) 2D arrays sandwiched between two layers of polydimethylsiloxane (PDMS) substrates act as an optical neutral density filter (NDFs) and a chromatic polarizer. Upon mechanical stretching, the intensity of the absorption spectrum of the AuNC 2D arrays-PDMS is found to decrease evenly in the UV, visible, and NIR regions of the electromagnetic spectrum. The color of the polarized light transmitted through the filter is dependent on its angle of polarization. The localized surface plasmon resonance (LSPR) extinction spectrum of the AuNC arrays arises mainly from scattering rather than absorption, unlike standard NDFs where their function is based on light absorption. Absorption of light causes heat generation that has a negative impact on the function of the NDFs. The ordering of the AuNCs inside the array after stretching was examined by dark field imaging, polarization dependent optical measurements, and surface-enhanced Raman scattering spectroscopy.

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

INTRODUCTION The strong interaction of the plasmonic nanoparticles with light of resonant frequency generates a strong electromagnetic field and an intense localized surface plasmon resonance (LSPR) spectrum.1,2 The strong plasmon field can be used to enhance the rate of different electronic processes such as light absorption,3 Rayleigh4 and Raman scattering,5-9 vibrational spectroscopy,10 and surface enhanced fluorescence11,12. Many exciting optical applications of plasmonic nanoparticles, such as enhancing the efficiency of solar cells by concentrating the light on the solar materials,13,14 wave guide optics,2 photonic crystals,15 integrated plasmonic infrared quantum dot camera,16 and optical nanosensing17-19 are based on their strong LSPR spectrum. Among the important applications of the plasmonic nanoparticles is the optical switching induced by mechanical force,20 electrical potential,21 UV illumination of photochromic materials,22-25 and chemical modification, as in the case of acid doping of polyaniline shell coating the surface of the gold nanoparticles.26-28 The LSPR spectrum of individual, well-separated plasmonic nanoparticles is narrow.21,29 However, the LSPR peak position of the plasmonic nanoparticles can be tuned in the visible and NIR regions by changing their shape, size, composition, and the dielectric function of the surrounding medium.30-34 The Langmuir-Blodgett (LB) technique was used efficiently to assemble the colloidally prepared nanoparticles30-34 into a monolayer of different engineered structures on the surface of various substrates.35-39 Using LB technique plasmonic nanoparticle 2D arrays of different structures were fabricated such as highly ordered21 and highly packed40 arrays. Due to the plasmon field coupling of the field of nanoparticles in close proximity, the LSPR spectrum of a nanoparticle assembly on the surface of a substrate relays on their order.21,38,41-45 Well-separated


Page 2 of 28

Page 3 of 28

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


highly ordered nanocube arrays showed a sharp LSPR21, while the highly packed arrays have a broad LSPR spectrum extending in the visible and NIR regions.40 The 2D plasmon field coupling between the nanoparticles forming the arrays and the plasmon energy transportation along the array are responsible for the broad structure of the LSPR spectrum.40,46,47 Ancient Romans used metals such as gold to dye glass with colorful patterns as in case of Lycurgus Cup.48 The transmission and the reflection view are known to produce radiant red and green colors, respectively.48 Electron microscopy imaging of the cup showed that the bright color of the cup originated from the formation of gold nanoparticles, which has high absorption and scattering cross-sections.48 The color filtration by the plasmonic nanoparticles drives the efforts to use them in color filtering49, spectral imaging49, and as chromatic polarizers50. Reducing the intensity of the light either white or mono-chromatic by using light filters is useful in many optical applications.51,52 Neutral density filters (NDFs) are used to reduce the intensity of the white light without altering its color, while chromatic filters cut-off a range of wavelengths. This study focuses on the fabrication of tunable plasmonic neutral density filters (PNDFs) of highly packed gold nanocube (AuNC) 2D arrays sandwiched between two layers of stretchable polydimethylsiloxane (PDMS) substrates. The LB technique is used to fabricate the AuNC arrays on the surface of PDMS substrate, followed by casting a top film of PDMS on the top of the arrays. The absorption spectrum of such PNDFs is broad covering the UV, visible, and NIR regions and its intensity can be reduced upon stretching the PDMS support. The polarization dependent optical measurements and the surface-enhanced Raman spectroscopy (SERS) studies are used to examine the order of the AuNCs forming the arrays upon stretching the PDMS support. Stretching the connected arrays resulted in separate 2D arrays. The 2D plasmon field coupling in the highly packed nanocube arrays generates super- and sub- radiant plasmon 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

the effect of stretching on these two plasmon modes will be addressed. Stretched AuNC arrays showed different optical responses when excited by polarized light with different polarization angles. A dip is generated in the LSPR spectrum of the stretched arrays upon using parallel polarized light, while a small hump peak appeared in the center of the LSPR spectrum of the arrays when excited by orthogonally polarized light. The dip in the spectrum overlaps with the small hump peak; consequently, the shape of the LSPR spectrum obtained upon unpolarized light excitation does not have a dip or hump. Due to the change of the shape of the LSPR spectrum upon changing the angle of polarization the color of the transmitted through PNDFs is polarization dependent. EXPERIMENTAL The seed mediated technique introduced by Murphy’s group53 was used to prepare the gold nanocubes the with minor modification discussed in SI.37 The prepared AuNCs were centrifuged at 8,000 rpm for 10 minutes and the precipitate was dispersed in 100 mL deionized (DI) water. The nanocubes were again concentrated by centrifugation at 8,000 rpm for 10 minutes, and the precipitate was then dispersed in 20 mL DI water. 0.2 mL 5 mM aqueous solution thiolated polyethylene glycol (Sigma-Aldrich, PEG) of average molecular weight 2,000 (MW) was added to the AuNCs solution. After shaking the resulting solution for 10 hours, the AuNCs functionalized with PEG were cleaned from the free PEG and cetyltrimethylammonium bromide (CTAB, Sigma-Aldrich) by centrifugation for 20 minutes at 6,000 rpm and the precipitated nanocubes were dispersed in 50 mL DI water. The AuNCs in the resulting solution were re-precipitated again by centrifugation at 6,000 rpm for 20 minutes. The precipitated pelleted was then dispersed in 10 mL ethanol (Sigma-Aldrich) and centrifuged at 5,000 rpm for


Page 4 of 28

Page 5 of 28

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


10 minutes. Finally, the pelleted AuNCs were dispersed in 4 mL ethanol and diluted by 4 mL chloroform (Sigma-Aldrich). The polydimethylsiloxane (PDMS) substrate was prepared by stirring of a mixture of 100 mL base (Dow Corning) and 10 mL Sylgard 184 elastomer (Dow Corning) for 2 minutes. After 30 minutes, the PDMS mixture was drop casted on glass substrate (30 cm x 30 cm) and cured at 70°C in the oven for 12 hours. The resulting PDMS film was cut into small pieces of 3 cm x 7.5 cm dimension. A quartz substrate was coated with a thin film of PDM by spinning a drop of PDMS base-curing agent mixture for 40 seconds at speed of 600rpm using the spin coater. The PDMS sheets and PDMS on quartz substrate were dipped in an oxidizing solution mixture of 20 mL hydrogen peroxide (Sigma-Aldrich), 20 mL concentrated HCl (Sigma-Aldrich), and 100 mL DI water for 30 minutes to introduce hydrophilic groups on their surfaces.54 The oxidized PDMS sheets were washed with DI water and left to dry in air. The highly packed AuNC arrays were fabricated on the surface of PDMS substrate using Nima 611D Langmuir-Blodgett trough. 2 mL of AuNCs in chloroform was sprayed over water sub-layer of the LB trough using micro-syringe. The AuNC arrays were transferred to the surface of silicon, PDMS, and quartz coated with a thin film of PDMS substrates simultaneously at LB surface pressure of 8 mN/m by vertical dipping with a speed of 15 mm/min. The AuNC arrays on PDMS were coated with a top layer of PDMS by drop casting of 2 mL from the PDMS basecuring agent mixture of ratio 10 to 1. The resulting sample was left 12 hour to dry and then was cured in the oven at 50°C for 6 hours. A JEOL 100C transmission electron microscope (TEM) was used to characterize the prepared AuNCs. Figure S1A shows the TEM image of the AuNCs after cleaning. Statistical analysis using imageJ software for 350 particles collected from 3 different TEM images showed that the wall length of the AuNC is 41.9±1.8 nm (see Figure



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

S1B). Ocean Optics HR4000Cg-UV-NIR was used to collect the optical measurements.20 The LSPR spectrum of the aqueous AuNCs functionalized with is shown in Figure S2. A single sharp peak was observed at 540 nm. The Optical imaging carried out by photography of the transmitted light from the DH-2000-BAL balanced Deuterium, Halogen (UV-Vis-NIR, Ocean Optics) light source after passing through a light polarizer using colored camera. OLIS 245 absorbance spectrophotometer equipped with CLARiTY 620 integrating cavities was used to measure the absolute absorption spectrum of the AuNC 2D arrays on quartz substrate. The AuNC arrays were imaged using a Zeiss Ultra60 scanning electron microscopy (SEM) and A DI (Digital Instruments) Dimension-3000 atomic force microscope (AFM). The homemade device used for stretching the arrays is shown in Figure S3. DDSCAT 7.3 software was used for the discrete dipole approximation (DDA) simulations of the LSPR spectrum of the 49 AuNC arrays. The shape file used for the simulation contains 40 nm AuNCs of dipole density of 1 dipole per 1 nm3. The arrays placed 2 nm away from the surface of PDMS substrate to account for the PEG layer thickness. The calculation carried out for unstretched arrays of interparticle separation distance of 4 nm and 45 % expanded arrays. RESULTS AND DISCUSSION Tunable Plasmonic Neutral Density Filters The main function of the neutral density filters is to reduce or modify the intensity of all the wavelengths of light evenly.55 In the traditional NDFs, the density of the light filtration is controlled by changing the thickness of the absorbing materials.55 Recently, studies showed that, the LSPR spectrum of plasmonic nanoparticle organized into highly packed 2D arrays is broad and covering both the visible and NIR regions.40 The broad LSPR spectrum of the arrays is


Page 6 of 28

Page 7 of 28

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


attributed to the 2D plasmon field coupling of the nanoparticles and the plasmon energy transport along the arrays.40 PDMS is an elastic polymer having chemical, thermal, and photochemical stability. This makes it possible to use PDMS as an efficient support for plasmonic nanoparticles for different kind of applications. For optical applications of plasmonic nanoparticles on PDMS substrate, it is necessary to examine the optical properties of PDMS substrate itself. Figure1B shows the optical absorption spectrum of PDMS sheet. PDMS is highly transparent to visible light and has a low absorption cross-section in the NIR region. The exciting optical properties of the PDMS promote it to be used as a support for AuNC arrays. Figure 1A shows the optical absorption spectrum of 41.9±1.8 nm AuNC 2D arrays sandwiched between two PDMS layers, measured at different polymer stretching percent. AFM and SEM imaging techniques were used to investigate the change in morphology of the AuNCs 2D arrays before and after stretching and also to study the effect of changing the substrate on the order of the AuNCs inside the arrays. The effect of the substrate on the fabricated arrays was studied by comparing the structure of the AuNCs arrays that transferred to the surface of silicon, PDMS, and PDMS thin film on quartz substrates simultaneously via vertical dipping technique. Figure 1B shows the SEM image of the AuNC arrays fabricated on the surface of silicon substrate. The AuNCs forming the arrays is highly packed and the interparticle separation distance between the individual AuNC is 4.2±1.4 nm. Figure 1C shows an AFM image of AuNC arrays on quartz substrate coated with a thin film of PDMS. It is obvious from the AFM and SEM images that highly packed arrays were obtained in case of the silicon and PDMS coating silicon substrate. The quartz acts as a support that keeps the elastic PDMS fixed. The great matching of the low magnification SEM image of the AuNC arrays on silicon and AFM image of the AuNC arrays on silicon and PDMS-quartz substrate in Figure S4A and B confirms that changing the substrate has no effect on the structure of the



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

highly packed arrays. However, it was observed that highly packed connected arrays contains voids. As the AuNCs organized into 2D arrays are assembled together through the PEG chains, it is necessary to examine whether stretching the PDMS substrate affect the organization of the AuNC inside the arrays. Figure 1D shows the AFM image of AuNCs arrays on PDMS substrate collected after 30 times stretching. Interestingly, the highly packed connected arrays split into separate smaller 2D AuNC arrays after stretching the PDMS substrate (see the low magnification AFM in Figure S4B and C). The absorption spectrum of the AuNC arrays on PDMS is broad covering the UV, visible, and NIR regions. The broad optical absorption spectrum of arraysPDMS makes it possible to be used as neutral density light filter. The intensity of the absorption spectrum of the AuNC arrays-PDMS is found to decrease evenly through the whole range of the spectrum while retaining the extinction profile upon increasing the stretching percent of the PDMS support. In other words, the intensity of the transmitted light from the plasmonic neutral density filter (PNDF) is mechanically controlled.


Page 8 of 28

Page 9 of 28

1.6

0% 5% 10% 15% 20% 25%

A

1.4 1.2

Absorbance

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


30% 35% 40% 45% PDMS

B

1.0 0.8 0.6 0.4 0.2 0.0

C

300

400

500

600

700

800

Wavelength (nm)

900

1000

D

Figure 1 A) Optical absorption spectrum of AuNC 2D arrays sandwiched between PDMS elastic substrates collected at different stretching percent of the polymer support and absorption spectrum of PDMS polymer (green spectrum). The optical spectrum of the AuNCs-PDMS is broad and its intensity decreased upon stretching without altering the shape of the spectrum. B) SEM image of AuNC 2D arrays on silicon substrate. C) AFM image of AuNC arrays on the surface of quartz coated with a thin film of PDMS. D) AFM image of AuNC arrays on the surface of PDMS substrate that was stretched 30 times.

Optical measurements were conducted for the AuNC arrays after subtracting the absorption spectrum of the PDMS substrate to examine the effect of stretching of the PDMS substrate on the LSPR spectrum of the AuNC arrays. The baseline of the LSPR spectrum of the



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 28

arrays before and after stretching was corrected to a zero value at 480 nm. Figure 2A shows the LSPR spectrum of AuNC 2D arrays sandwiched between PDMS sheets measured at different stretching percent. Due to the elimination of the absorption of PDMS in the NIR region, the LSPR spectrum of the AuNC arrays became narrower than the optical extinction spectrum of the PNDF. While, stretching showed no effect on the shape of the LSPR spectrum of the arrays, the center of spectrum is slightly blue shifted upon stretching. As the LSPR extinction spectrum of the plasmonic nanoparticles is composed of absorption and scattering spectra,29 the intensity of the light reduction by PNDF depends on both the absorption and scattering of light, unlike the standard NDFs, which their reduction is based on light absorption only. The amount of absorbed light by the NDFs is usually converted into heat, which has a negative impact in their efficiency during operation. The efficiency of the tunable PNDF is improved by increasing the ratio between the scattering spectrum and the absorption spectrum. Discrete dipole approximation (DDA) technique is used to calculate the extinction, absorption, and scattering spectrum of the plasmonic nanoparticles.29 Figure 2B shows the LSPR spectrum of 49 AuNC organized into 2D arrays (7 rows and 7 columns), the interparticle separation distance is taken to be 4 nm (see inset of Figure 2B). The calculated extinction LSPR spectrum of the AuNC array matches well the experimentally measured LSPR spectrum of the AuNC arrays inside the unstretched PDMS. It is clear that, the majority of the extinction spectrum of array arose from the scattering spectrum rather than the absorption spectrum. The idea of the low absorption spectrum compared with the scattering spectrum of the highly packed 2D arrays was confirmed by measuring the absolute absorption spectrum of the arrays experimentally. Figure S5 shows the absolute absorption and extinction spectrum of the AuNCs 2D arrays fabricated on the surface of quartz substrate. The absolute absorption spectrum measured in the range of 250 to 820 nm showed a weak absorption


Page 11 of 28

spectrum compared to the extinction spectrum. Consequently, in addition to the ability of tuning the intensity of light by the fabricated PNDF mechanically, the function of the PNDF is mainly based on plasmonic light scattering rather than light absorption as in case of standard NDFs. 1.2

1.0

A

B Experimental Ext. Abs. Scat.

1.0

0.8 0.8

Extinction

0.6

Intensity

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


0.6

0.4

0.4 0% 5% 10% 15% 20% 25%

0.2

0.0

500

600

700

800

25% 30% 35% 40% 45%

900

Wavelength (nm)

0.2

0.0 1000

1100

500

600

700 800 900 Wavelength (nm)

1000

1100

Figure 2 A) LSPR extinction spectrum of 2D AuNC arrays sandwiched between two PDMS films measured at different stretching percent of the PDMS, the inset is a photography of unstretched arrays taken when the arrays placed between the camera and a light source (left grey color) and when the light source and the camera are in the same direction (right golden color). The grey color is for the transmission mode and the golden color is for the scattering mode. B) LSPR spectrum of 49 AuNC organized into 2D array (7 particles x 7 particles) and separated by 4 nm calculated by DDA technique, extinction spectrum (blue), absorption spectrum (red), and scattering spectrum (magenta). Inset of Figure B is the shape file used in the DDA calculation. The experimental extinction spectrum obtained for the AuNC arrays sandwiched between PDMS matches the calculated extinction spectrum of the arrays. It is clear that, most of the extinction spectrum of the arrays originated from the plasmonic light scattering rather than light absorption.



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 28

Chromatic plasmonic polarizer Reducing the intensity of the polarized light is useful in many optics setups and in photography. It is necessary to examine the effect of changing the angle of polarization on the color of the transmitted polarized light through the PNDFs. Figure 3 shows the LSPR extinction spectrum of the 2D AuNC arrays sandwiched between PDMS layers, measured at different polymer stretching percent, and at different polarization angles of the exciting light. It is important to confirm that the baseline of the LSPR spectrum was corrected as in case of spectrum shown in Figure 2A collected for the arrays when excited with unpolarized light. Polarizing the light passes through the AuNC 2D arrays parallel to the direction of the stretching force of the PDMS induced an observable change in the shape of their LSPR spectrum (see Figure 3A). In addition to the decrease of the intensity of the LSPR spectrum of the arrays upon stretching, a dip in the spectrum at 810 nm is formed. Stretching induces a shape change of the LSPR spectrum of the arrays, which increases by increasing the percent of stretching. When the polarization direction of the light was changed to be orthogonal to the stretching force, it was found that, the intensity and the width of the LSPR spectrum of the arrays are reduced upon stretching the PDMS support (Figure 3B). Opposite to the LSPR spectrum collected using parallel light polarization, a small hump is observed at 800 nm in the LSPR spectrum. The reason for the opposite responses of the PNDF upon changing the angle of light polarization and stretching is based on the 2D plasmon field coupling in the stretched arrays. The 2D plasmon field coupling in the highly packed arrays is sensitive to both the interparticles separation distance between the individual nanoparticle and the organization of the nanoparticles inside the array.40,56


Page 13 of 28

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


Further polarization dependent optical measurement was carried out on the stretched AuNC arrays. Figure 3C shows the LSPR spectrum of 45% expanded AuNC arrays measured using polarized light of angle of 0, 45, 90 degree to the direction of the stretching force. The peak centered at 800 nm was found to increase by increasing the angle of polarization of the exciting light. Conversely, the peak at 560 nm showed opposite response to the increase of the angle of polarization. As the ratio between the peak at 800 nm and 560 nm changes by changing the angle of polarization of the exciting light, the color of the transmitted light from the PNDFs can be controlled by changing the angle of polarization. The schematic depiction in Figure 3E shows the direction of polarization of the exciting light with respect to of the stretching force direction of 49 nanocube array on PDMS substrate before and after starching the substrate. Optical imaging for the light transmitted from the stretched PNDF is carried out when the light is unpolarized and after polarization at different angles. The inset of Figure 3 C shows the image of the transmitted light through the 45% stretched PNDF when the incident light is unpolarized and polarized at angle of 0, 45, and 90 degrees. The color of the transmitted unpolarized light is white, while reddish color is observed for the when the parallel polarized light passed through the PNDF. When the angle of polarized light was increased to be 45 degrees, the transmitted light turned to pinkish. Ultimately, bluish color is transmitted through the PNDF when the angle of polarization was increased to 90 degrees. In summary, the color of the transmitted light through the 45 % stretched PNDF can be changed by tuning the angle of polarization of the light. This encouraging different optical response of the PNDF makes it possible to use it as chromatic polarizer.



1.0

1.0

Parallel polarization

A

0.9

B

0.9 0.8

0.7

0.7

Extinction

Extinction

0.8

0.6

0.6

0.5

0.5 0.4

0% 5% 10% 15% 20% 25% 30% 35% 40% 45%

Orthogonal polarization

0.4

0.3

0.3

0.2 0.1 0.0 500

600

0% 5% 10% 15% 20% 700 800

25% 30% 35% 40% 45% 900

0.2 0.1 1000

0.0

1100

Wavelength (nm) 0.5

Unpolarized o Parallel polarization θ=0 o 45 degree polarization θ=45 o Orthogonal polarization θ=90

C

500

0.5

0.4

700

800

900

1000

1100

o

Parallel polarization θ=0 o 45 degree polarization θ=45 o Orthogonal polarization θ=90

D

0.4

Extinction

0.3

0.3

0.2

0.2

0.1

0.1

0.0

600

Wavelength (nm)

Extinction

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 28

0.0

500

600

700

800

900

Wavelength (nm)

1000

1100

500

600

700

800

900

1000

1100

Wavelength (nm)

E

Figure 3 LSPR spectrum of 2D AuNC arrays sandwiched between two PDMS layers measured at different stretching percent when: A) the excitation light is parallel to the stretching force, B) the light polarization is orthogonal to the stretching force. A dip in the LSPR spectrum of the stretched arrays is observed in case parallel polarized light, while a little hump peak appeared in the center of the LSPR spectrum in case of orthogonal light polarization. LSPR spectrum of 45 % stretched AuNC arrays C) measured, D) calculated by DDA technique when the exciting light is unpolarized black) polarized of angle of 0o (red), 45o (magenta) and 90o (blue). The


Page 15 of 28

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


experimental spectrum accorded-well with the calculated one. The inset of (C) is the optical image of the transmitted light from the 45 % expanded AuNC arrays collected when excited by unpolarized light (white), polarized light of angle of 0o (reddish), 45o (pink) and 90o (bluish). Changing the ratios between the intensity of the 800 and 560 nm peaks led to such color change of the transmitted through PNDFs. E) Schematic depiction showing 49 nanocube array on PDMS substrate before stretching (black cubes) and after 45% expansion (red cubes). The direction of polarization of the exciting light with respect to the direction of the stretching force is shown in the scheme.

AFM images showed that the connected AuNC arrays splits into separated 2D arrays after stretching. It is necessary to examine whether the interparticle separation distance between the nanocubes forming the arrays is changed upon stretching. Former studies showed that decreasing the number of nanocubes per array in the highly packed 2D arrays of 40 nm gold nanocube with interparticles separation distance in the range of 4-7 nm showed a great impact on the LSPR spectral peak position and spectral width.40 The shape of the LSPR spectrum of the AuNC 2D arrays is remarkably changed when the interparticle separation distance between the individual nanoparticles was increased from 4 nm to 6 nm, the spectral peak positions were also red shifted.40 No clear blue shift is observed in the LSPR spectrum of the AuNC arrays when measured using either parallel or orthogonal polarized light excitation. This could be due to the unequal change of the interparticles separation distance between the individual AuNC inside the array.



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 28

Due to the strong light scattering of the plasmonic nanoparticles they are used as a contrast for dark field (DF) imaging of flat and rough surfaces accurately. DF imaging measurements were conducted for unstretched and 45% stretched PNDF using unpolarized white light excitation and polarized light in both the same and the orthogonal stretching direction. Figure 4 A shows the DF image of unstretched PNDF collected using parallel polarized light. Yellow-reddish colored areas corresponding to the scattering from the AuNC arrays is observed. Figure 4B shows the DF images of the unstretched PNDF excited by unpolarized light. The unstretched PNDF scatter the polarized and unpolarized light similarly, which agreed-well with the idea that, changing the polarization of the exciting light has no effect on the optical properties of the unstretched PNDF. The DF images matches the AFM images, each group of AuNC organized into an array scatter the light together. The DF image of the 45% stretched PNDF excited by polarized light parallel to the stretching direction is shown Figure 4 C. Reddish colored strips is observed. The DF imaging was conducted also for the 45% stretched PNDF upon excitation using unpolarized light (Figure 4D) and orthogonally polarized light source (Figure S6). Stripes are observed too in the DF image of stretched PNDF when collect using polarized and unpolarized light excitation, but the color of the strips depends greatly on the polarization direction. The information obtained from the DF imaging of the PNDF before and after stretching, suggests that stretching induces a structural change of the separated 2D AuNC arrays, this was observed in the AFM image to be linearly elongated arrays. Stretching the PDMS support from one direction causes it’s shrinking from the orthogonal direction20, is responsible for the expansion of the arrays in in the same direction of the stretching force.


Page 17 of 28

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


In order to account for the effect of stretching of PDMS support on the order of the AuNC inside the arrays, the measured LSPR spectrum of 45% expanded arrays is compared with the DDA simulated LSPR spectrum of 49 AuNC array (7 cubes x 7 cubes) separated by 4 and 36 nm in the orthogonal and the same direction of the stretching force, respectively (see Figure S4B). Figure 3D shows the simulated LSPR spectrum of the 45% expanded arrays calculated at angle of polarization of 00, 45o, and 90o. The theoretically calculated LSPR spectrum agreed-well with the measured LSPR spectrum (Figure 3C). This confirms that stretching the PNDF splits the 2D arrays into organized columns and the separation distance between them increases by increasing the stretching percent.

A

C

Unstretched parallel polarized

45% Stretched parallel polarized

Unstretched unpolarized

B

D

45% Stretched unpolarized

Figure 4 Dark field image for 2D gold nanocube arrays sandwiched between two PDMS layers support collected when: A) Unstretched and excited with parallel polarized light, B) 45% stretching and excited with parallel polarized light. C) Excited with unpolarized light while unstretched and, D) stretched by 45% and excited with unpolarized light. Strips are observed in



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 28

the image of the stretched arrays excited with parallel polarized light suggesting the splitting of the 2D arrays into linear columns.

Studying the Plasmon Field Coupling in the Plasmonic Neutral Density Filter by SERS According to the electromagnetic mechanism of the surface-enhanced Raman spectroscopy (SERS),5 the electromagnetic field of the plasmonic nanoparticles is responsible for enhancing the Raman signal of analytes located in its domain. The amount of SERS enhancement factor (EF) is directly proportional to the intensity of the electromagnetic field of the plasmonic nanoparticles. Due to the plasmon field coupling, the strength of the plasmon field for a pair or a group of plasmonic nanoparticles and so the SERS EF depends on the interparticle separation distance between the nanoparticles.40 Due to the 2D plasmon field coupling in the highly packed arrays, two plasmon modes are formed, a broad direction dependent super-radiant mode and a narrow direction independent sub-radiant plasmon mode.46 The super-radiant plasmon mode is centered at low energy, while the sub-radiant plasmon mode appears at higher energy.46 As shown in the former section, upon stretching the PNDF, the order of the nanocubes inside the arrays changes in the same direction of the stretching force, but the separation distance between the nanocubes in the orthogonal direction remain constant. Consequently, the change of the optical properties of the arrays using parallel polarized light exciting resulted from the change in both the super-radiant and subradiant plasmon modes upon stretching. The small variation in the optical properties collected at parallel light polarization resulted from the change of the sub-radiant plasmon mode only. Following the SERS EF of a Raman reporter such as 4-nitrothiophenol (4NTP) adsorbed on the surface of AuNC 2D arrays-PDMS will make it possible to track the change of the plasmon field coupling between the individual nanocubes upon stretching. Figure 5 shows the 18 ACS Paragon Plus Environment

Page 19 of 28

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


SERS spectrum of 4NTP adsorbed on the surface of AuNC arrays measured at different stretching percent of the PDMS substrate. In Figure 5 A, a 532 nm Raman laser was used to generate the SERS signal. The SERS band intensity was found to slightly increase by increasing the stretching percent of the PDMS substrate. This high energy photon is able to excite the subradiant plasmon mode of the arrays, which is direction independent. Conversely, when the Raman measurement was conducted using 785 nm laser, the SERS band intensities of the 4NTP was found to decrease upon increasing the stretching percent (Figure 5B). The decrease of the SERS EF of the super-radiant plasmon mode excited by 785 nm upon increasing the stretching percent attributed to the increase of the separation distance between the nanocubes columns in the same direction of the stretching force. Further information about the plasmon field coupling in the stretched 2D arrays can be obtained by correlating the SERS band intensities with the corresponding LSPR spectral peak intensity. Figure 5C shows the LSPR spectrum of the stretched AuNCs arrays in wavenumber unit. The LSPR spectrum of the arrays between 4001700 cm-1 correlates to the SERS spectrum at 532 nm laser excitation. The band intensities can be divided into two parts. The band intensities of the first part of the SERS spectrum, which have energy close to energy of the laser, are slightly decreased upon stretching the arrays. The second half of the LSPR spectrum of relatively low energy showed an obvious decrease on its intensity upon stretching. The SERS generated at 532 nm laser excitation and the optical response of the arrays behave oppositely, which suggests that the contribution of the chemical enhancement in the SERS mechanism is larger than typically anticipated.6-9 Conversely, the shape of the LSPR spectrum in the range of 400-1700 cm-1 relative to the 785 nm Laser, did not change by stretching the arrays but its intensity is decreased. The retention of the shape of the optical spectrum of the arrays upon stretching in the range of 400-1700 cm-1 relative to the 785 nm laser



line agreed-well with the SERS measurement, which showed a constant ratio between the values of the intensity of SERS band at different stretching percent. The SERS spectrum collected at a 532 nm laser excitation showed a background spectrum below the Raman bands, which was not clearly shown in case of the SERS spectrum reported upon using the 785 nm laser excitation. This attributed to the strong SERS band intensities relative to the background spectrum in case of Raman signal generated by 785 nm photons. The SERS results provided information about the behavior of the sub-radiant and supperradiant plasmon modes of the AuNC 2D arrays upon stretching. However, stretching the arrays enhances the sub-radiant plasmon mode at the expense of the super-radiant plasmon mode, which is diminished. This also indicates that, the sub-radiant plasmon mode of the highly packed plasmonic nanoparticle organized linearly is more efficient than in case of 2D ordered. Conversely, the super-radiant plasmon mode of the 2D ordered plasmonic nanoparticles is more efficient than linearly organized nanoparticles. 0% 5% 10 % 15 % 20 %

A

B

25 % 30 % 35 % 40 %

400

Raman Unit

Raman Unit

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 28

600

800 1000 1200-1 1400 1600 Wavenumber (cm )

400

0% 5% 10 % 15 % 20 % 25 % 30 % 35 % 40 % 600

800 1000 1200 -11400 1600 Wavenumber (cm )


1 .0

0% 5% 10% 15% 20%

532 n m L aser 0 .9 18796cm -1 1700 cm

0 .8 400 cm

400 cm

25% 30% 35% 40% % (10 )

-1

-1

C

Extinction

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


1700 cm

Page 21 of 28

-1

-1

0 .7 0 .6 0 .5 0 .4 0 .3

12339 cm 18396cm

19000

785 n m L aser -1

-1

17096cm 18000 17000

-1

12739 cm

16000

15000

14000 -1

13000

-1

11039 cm 12000

-1

11000

W a ve n u m b e r (c m )

Figure 5 Surface-enhanced Raman spectrum of 4 nitrothiophenol adsorbed on the surface of AuNC 2D arrays-PDMS collected at different stretching percent when: A) 532 nm laser used which excites the sub-radiant plasmon mode of the arrays, B) 785 nm laser used that excite the super-radiant plasmon mode of the arrays. Expansion of the highly packed arrays of plasmonic nanoparticles enhances their sub-radiant plasmon mode and suppresses the super-radiant plasmon mode. C) LSPR spectrum of AuNC arrays on PDMS after coating with 4 nitrothiophenol measured at different stretching percent in wavenumber unit. The range of SERS measurement was highlighted for the 532 nm laser (magenta) and for 785 nm laser (blue).

CONCLUSIONS Highly packed gold nanocube 2D array sandwiched between two layers of PDMS support was used as a neutral density light filter. Such stretchable plasmonic neutral density filters (PNDFs) make it possible to tune the intensity of the transmitted light through it mechanically. Unlike the standard neutral density filters, which the light intensity reduction is based on light absorption, PNDFs reduce the light intensity in the visible and NIR via plasmonic light scattering. The light absorption led to heat generation, which has a negative impact on the



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 28

operation of the neutral density filters. The absolute absorption measurement for the AuNC 2D arrays on the surface of quartz substrate proved that the intensity of the absorption spectrum is small compared with their extinction spectrum. Theoretical calculation for the LSPR spectrum of the highly packed AuNC 2D arrays also showed that most of the extinction spectrum arose from light scattering, which limited the thermal heating by the PNDF. In order to investigate the effect of stretching of the PDMS support on the order of the nanocubes forming the arrays, optical measurements were conducted for stretched AuNC arrays at different light polarizations. Interestingly, the LSPR spectrum of the stretched AuNC arrays was sharply changed and a dip appeared in the center of the spectrum when measured upon excitation with light polarized parallel to the stretching force. Conversely, when the light polarized orthogonal to the direction of stretching force was used to excite the stretched arrays, the shape of the LSPR spectrum did not change except the a little hump was observed in the center of the spectrum. The dip in the LSPR spectrum obtained upon the parallel polarized light excitation of the stretched arrays was found to overlap with the small peak that appeared when orthogonally polarized light was used. For this reason, the shape of the LSPR spectrum of the stretched arrays excitation with unpolarized light was retained. Optical imaging of the transmitted white light through the stretched PNDFs, showed a color change when collected using polarized light of different angle of polarization. This nominates the PNDFs to be used as chromatic polarizers. Due to the 2D plasmon field coupling in the highly packed 2D arrays, a broad super-radiant plasmon mode and a narrow high energy sub-radiant plasmon mode are formed. Surface-enhanced Raman spectroscopy measurement showed that stretching the arrays enhanced the sub-radiant plasmon mode at the expense of the super-radiant plasmon mode which diminished. Square bright areas were observed in the dark field image of the unstretched PNDF,


Page 23 of 28

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


which changed to be bright strips when the PNDF was stretched. AFM imaging confirmed that, the square bright areas observed in the dark field were resulted from the split of the connected arrays into smaller arrays. The change of the shape of the LSPR spectrum of the stretched arrays upon parallel light polarization and the slight increase of the intensity of the center of the LSPR spectrum upon orthogonal light polarization suggests that the smaller nanocubes arrays was expanded in same direction of the stretching force. The DDA calculation confirmed the idea of stretching the smaller arrays parallel to the stretching force. SUPPORTING INFORMATION Figure S1 is the LSPR spectrum of colloidal AuNCs coated with PEG and dispersed. Figure S2 is TEM image of AuNCs and statistical analysis for the nanocube wall length. The homemade device used for stretching the arrays is shown in Figure S3. Low magnification SEM and AFM images of AuNC 2D arrays on silicon and PDMS substrates are shown in Figure S4. Figure S5 is the absolute absorption and extinction spectrum of the AuNCs 2D arrays fabricated on the surface of quartz substrate. Figure S6 is dark field image of PNDF after 45% stretching excited by orthogonally polarized light. This material is available free of charge via the Internet at http://pubs.acs.org/.

ACKNOWLEDGMENT This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award DE-FG02 09ER46604. I would like to thank Dr Kyril Solntsev for contacting the absolute absorption measurement and Mr Mena Aioub for proofreading the manuscript and for his useful discussion.



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 28

REFERENCES (1) Ritchie, R. H. Plasma Losses by Fast Electrons in Thin Films. Phys. Rev. 1957, 106, 874-881. (2) Barnes, W. L.; Dereux, A.; Ebbesen, T. W. Surface Plasmon Subwavelength Optics. Nature 2003, 424, 824-830. (3) Mühlschlegel, P.; Eisler, H.-J.; Martin, O. J. F.; Hecht, B.; Pohl, D. W. Resonant Optical Antennas. Science 2005, 308, 1607-1609. (4) Rogers, A. J.; Handerek, V. A. Frequency-Derived Distributed Optical-Fiber Sensing: Rayleigh Backscatter Analysis. Appl. Opt. 1992, 31, 4091-4095. (5) Jeanmaire, D. L.; Van duyne, R. P. Surface Raman Spectroelectrochemistry .1. Heterocyclic, Aromatic, and Aliphatic-Amines Adsorbed on Anodized Silver Electrode. J. Electroanal. Chem. 1977, 84, 1-20. (6) Nie, S.; Emory, S. R. Probing Single Molecules and Single Nanoparticles by SurfaceEnhanced Raman Scattering. Science 1997, 275, 1102-1106. (7) Gómez-Graña, S.; Fernández-López, C.; Polavarapu, L.; Salmon, J.-B.; Leng, J.; PastorizaSantos, I.; Pérez-Juste, J. Gold Nanooctahedra with Tunable Size and Microfluidic-Induced 3D Assembly for Highly Uniform SERS-Active Supercrystals. Chem. Mater. 2015, 27, 8310-8317. (8) Fernández-López, C.; Polavarapu, L.; Solís, D. M.; Taboada, J. M.; Obelleiro, F.; ContrerasCáceres, R.; Pastoriza-Santos, I.; Pérez-Juste, J. Gold Nanorod–pNIPAM Hybrids with Reversible Plasmon Coupling: Synthesis, Modeling, and SERS Properties. ACS Appl. Mater. Interfaces. 2015, 7, 12530-12538. (9) Gruenke, N. L.; Cardinal, M. F.; McAnally, M. O.; Frontiera, R. R.; Schatz, G. C.; Van Duyne, R. P. Ultrafast and nonlinear surface-enhanced Raman spectroscopy. Chem. Soc. Rev. 2016, 45, 2263-2290. (10) Baldelli, S.; Eppler, A. S.; Anderson, E.; Shen, Y.-R.; Somorjai, G. A. Surface Enhanced sum Frequency Generation of Carbon Monoxide Adsorbed on Platinum Nanoparticle Arrays. J. Chem. Phys. 2000, 113, 5432-5438. (11) Liebermann, T.; Knoll, W. Surface-Plasmon Field-Enhanced Fluorescence Spectroscopy. Colloids Surf., A 2000, 171, 115-130. (12) Hill, C. M.; Bennett, R.; Zhou, C.; Street, S.; Zheng, J.; Pan, S. Single Ag Nanoparticle Spectroelectrochemistry via Dark-Field Scattering and Fluorescence Microscopies. J. Phys. Chem. C 2015, 119, 6760-6768. (13) Atwater, H. A.; Polman, A. Plasmonics for Improved Photovoltaic Devices. Nat. Mater. 2010, 9, 205-213. (14) Wadams, R. C.; Yen, C.-w.; Butcher Jr, D. P.; Koerner, H.; Durstock, M. F.; Fabris, L.; Tabor, C. E. Gold Nanorod Enhanced Organic Photovoltaics: The Importance of Morphology Effects. Org. Electron. 2014, 15, 1448-1457. (15) Rosenberg, J.; Shenoi, R. V.; Krishna, S.; Painter, O. Design of Plasmonic Photonic Crystal Resonant Cavities for Polarization Sensitive Infrared Photodetectors. Opt. Express 2010, 18, 3672-3686. (16) Lee, S. J.; Ku, Z.; Barve, A.; Montoya, J.; Jang, W.-Y.; Brueck, S. R. J.; Sundaram, M.; Reisinger, A.; Krishna, S.; Noh, S. K. A Monolithically Integrated Plasmonic Infrared Quantum dot Camera. Nat. Commun. 2011, 2, 286-292. (17) Mahmoud, M. A.; El-Sayed, M. A. Gold Nanoframes: Very High Surface Plasmon Fields and Excellent Near-infrared Sensors. J. Am. Chem. Soc. 2010, 132, 12704-12710. 24 ACS Paragon Plus Environment

Page 25 of 28

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


(18) Chen, H.; Kou, X.; Yang, Z.; Ni, W.; Wang, J. Shape- and Size-Dependent Refractive Index Sensitivity of Gold Nanoparticles. Langmuir 2008, 24, 5233-5237. (19) Kadasala, N. R.; Wei, A. Trace Detection of Tetrabromobisphenol A by SERS with DMAPModified Magnetic Gold Nanoclusters. Nanoscale 2015, 7, 10931-10935. (20) Mahmoud, M. A. Polarized Optomechanical Response of Silver Nanodisc Monolayers on an Elastic Substrate Induced by Stretching. J. Phys. Chem. C 2015, 119, 19359-19366. (21) Mahmoud, M. A. Effective Optoelectrical Switching by Using Pseudo-Single Crystal of Monolayer Array of 2D Polymer–Plasmonic Nanoparticles System. J. Phys. Chem. C 2015, 119, 29095-29104. (22) Nishi, H.; Asahi, T.; Kobatake, S. Light-Controllable Surface Plasmon Resonance Absorption of Gold Nanoparticles Covered with Photochromic Diarylethene Polymers. J. Phys. Chem. C 2009, 113, 17359-17366. (23) Ming, T.; Zhao, L.; Xiao, M.; Wang, J. Resonance-Coupling-Based Plasmonic Switches. Small 2010, 6, 2514-2519. (24) Joshi, G. K.; Blodgett, K. N.; Muhoberac, B. B.; Johnson, M. A.; Smith, K. A.; Sardar, R. Ultrasensitive Photoreversible Molecular Sensors of Azobenzene-Functionalized Plasmonic Nanoantennas. Nano Lett. 2014, 14, 532-540. (25) Zheng, Y. B.; Kiraly, B.; Cheunkar, S.; Huang, T. J.; Weiss, P. S. Incident-AngleModulated Molecular Plasmonic Switches: A Case of Weak Exciton–Plasmon Coupling. Nano Lett. 2011, 11, 2061-2065. (26) Jiang, N.; Shao, L.; Wang, J. (Gold Nanorod Core)/(Polyaniline Shell) Plasmonic Switches with Large Plasmon Shifts and Modulation Depths. Adv. Mater. 2014, 26, 3282-3289. (27) Leroux, Y.; Lacroix, J. C.; Fave, C.; Trippe, G.; Félidj, N.; Aubard, J.; Hohenau, A.; Krenn, J. R. Tunable Electrochemical Switch of the Optical Properties of Metallic Nanoparticles. ACS Nano 2008, 2, 728-732. (28) Jeon, J.-W.; Ledin, P. A.; Geldmeier, J. A.; Ponder, J. F.; Mahmoud, M. A.; El-Sayed, M.; Reynolds, J. R.; Tsukruk, V. V. Electrically Controlled Plasmonic Behavior of Gold Nanocube@Polyaniline Nanostructures: Transparent Plasmonic Aggregates. Chem. Mater. 2016, 28, 2868-2881. (29) Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C.: The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment. J. Phys. Chem. B 2003, 107, 668-677. (30) Grzelczak, M.; Perez-Juste, J.; Mulvaney, P.; Liz-Marzan, L. M. Shape Control in Gold Nanoparticle Synthesis. Chem. Soc. Rev.2008, 37, 1783-1791. (31) Pastoriza-Santos, I.; Liz-Marzán, L. M. Formation of PVP-Protected Metal Nanoparticles in DMF. Langmuir 2002, 18, 2888-2894. (32) Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chemistry and Properties of Nanocrystals of Different Shapes. Chem. Rev. 2005, 105, 1025-1102. (33) Murphy, C. J.; Sau, T. K.; Gole, A. M.; Orendorff, C. J.; Gao, J.; Gou, L.; Hunyadi, S. E.; Li, T. Anisotropic Metal Nanoparticles: Synthesis, Assembly, and Optical Applications. J. Phys. Chem. B 2005, 109, 13857-13870. (34) Jones, M. R.; Osberg, K. D.; Macfarlane, R. J.; Langille, M. R.; Mirkin, C. A.: Templated Techniques for the Synthesis and Assembly of Plasmonic Nanostructures. Chem. Rev. 2011, 111, 3736-3827. (35) Tao, A.; Sinsermsuksakul, P.; Yang, P. Tunable Plasmonic Lattices of Silver Nanocrystals. Nat. Nanotechnol. 2007, 2, 435-440. 25 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 26 of 28

(36) Mahmoud, M. A.; O’Neil, D.; El-Sayed, M. A.: Hollow and Solid Metallic Nanoparticles in Sensing and in Nanocatalysis. Chem. Mater.2014, 26, 44-58. (37) Mahmoud, M. A.: Dynamic Template for Assembling Nanoparticles into Highly Ordered Two-Dimensional Arrays of Different Structures. J. Phys. Chem. C 2015, 119, 305-314. (38) Mahmoud, M. A. Controlling the Orientations of Gold Nanorods inside Highly Packed 2D Arrays. Phys. Chem. Chem. Phys. 2014, 16, 26153-26162. (39) Collier, C. P.; Saykally, R. J.; Shiang, J. J.; Henrichs, S. E.; Heath, J. R. Reversible Tuning of Silver Quantum dot Monolayers through the Metal-Insulator Transition. Science 1997, 277, 1978-1981. (40) Mahmoud, M. A. Super-Radiant Plasmon mode is more Efficient for SERS than the SubRadiant mode in Highly Packed 2D Gold Nanocube Arrays. J. Chem. Phys. 2015, 143, 074703074711. (41) Zhou, W.; Odom, T. W. Tunable Subradiant Lattice Plasmons by Out-of-Plane Dipolar Interactions. Nat. Nanotechnol. 2011, 6, 423-427. (42) Chen, H.-Y.; He, C.-L.; Wang, C.-Y.; Lin, M.-H.; Mitsui, D.; Eguchi, M.; Teranishi, T.; Gwo, S. Far-Field Optical Imaging of a Linear Array of Coupled Gold Nanocubes: Direct Visualization of Dark Plasmon Propagating Modes. ACS Nano 2011, 5, 8223-8229. (43) Hanske, C.; Tebbe, M.; Kuttner, C.; Bieber, V.; Tsukruk, V. V.; Chanana, M.; König, T. A. F.; Fery, A. Strongly Coupled Plasmonic Modes on Macroscopic Areas via Template-Assisted Colloidal Self-Assembly. Nano Lett. 2014, 14, 6863-6871. (44) Lee, O. S.; Prytkova, T. R.; Schatz, G. C. Using DNA to Link Gold Nanoparticles, Polymers, and Molecules: A Theoretical Perspective. J. Phys. Chem. Lett. 2010, 1, 1781-1788. (45) Solis, D.; Paul, A.; Olson, J.; Slaughter, L. S.; Swanglap, P.; Chang, W.-S.; Link, S. Turning the Corner: Efficient Energy Transfer in Bent Plasmonic Nanoparticle Chain Waveguides. Nano Lett. 2013, 13, 4779-4784. (46) Willingham, B.; Link, S. Energy Transport in Metal Nanoparticle Chains via Sub-radiant Plasmon Modes. Opt. Express 2011, 19, 6450-6461. (47) Halas, N. J.; Lal, S.; Chang, W. S.; Link, S.; Nordlander, P.: Plasmons in Strongly Coupled Metallic Nanostructures. Chem. Rev. 2011, 111, 3913-3961. (48) Freestone, I.; Meeks, N.; Sax, M.; Higgitt, C. The Lycurgus Cup-A Roman nanotechnology. Gold Bulletin 2007, 40, 270-277. (49) Xu, T.; Wu, Y.-K.; Luo, X.; Guo, L. J. Plasmonic Nanoresonators for High-Resolution Colour Filtering and Spectral Imaging. Nat. Commun. 2010, 1, 59-63. (50) Ellenbogen, T.; Seo, K.; Crozier, K. B. Chromatic Plasmonic Polarizers for Active Visible Color Filtering and Polarimetry. Nano Lett. 2012, 12, 1026-1031. (51) Zhao, Y.; Belkin, M. A.; Alù, A. Twisted Optical Metamaterials for Planarized Ultrathin Broadband Circular Polarizers. Nat. Commun. 2012, 3, 870-876. (52) Aydin, K.; Ferry, V. E.; Briggs, R. M.; Atwater, H. A. Broadband Polarization-Independent Resonant Light Absorption using Ultrathin Plasmonic Super Absorbers. Nat. Commun. 2011, 2, 517-523. (53) Sisco, P. N.; Murphy, C. J. Surface-Coverage Dependence of Surface-Enhanced Raman Scattering from Gold Nanocubes on Self-Assembled Monolayers of Analyte. J. Phys. Chem. A 2009, 113, 3973-3978. (54) Sui, G.; Wang, J.; Lee, C.-C.; Lu, W.; Lee, S. P.; Leyton, J. V.; Wu, A. M.; Tseng, H.-R. Solution-Phase Surface Modification in Intact Poly(dimethylsiloxane) Microfluidic Channels. Anal. Chem. 2006, 78, 5543-5551. 26 ACS Paragon Plus Environment

Page 27 of 28

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


(55) Banning, M. Neutral Density Filters of Chromel A1. J. Opt. Soc. Am. 1947, 37, 686-687. (56) Solis, D. M.; Taboada, J. M.; Obelleiro, F.; Liz-Marzan, L. M.; Garcia de Abajo, F. J. Toward Ultimate Nanoplasmonics Modeling. ACS Nano 2014, 8, 7559-7570.



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

TOC


Page 28 of 28

Tunable Plasmonic Neutral Density Filters and Chromatic Polarizers

Recommend Documents