Chemically engineered Au-Ag plasmonic nanostructures to realize

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Functional Nanostructured Materials (including low-D carbon)

Chemically engineered Au-Ag plasmonic nanostructures to realize large area and flexible metamaterials Soo-Jung Kim, Mingi Seong, Hye-Won Yun, Junhyuk Ahn, Heon Lee, Soong Ju Oh, and Sung-Hoon Hong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07454 • Publication Date (Web): 06 Jul 2018 Downloaded from http://pubs.acs.org on July 6, 2018

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ACS Applied Materials & Interfaces

Chemically engineered Au-Ag plasmonic nanostructures to realize large area and flexible metamaterials Soo-Jung Kim†,‡, Mingi Seong†,‡, Hye-Won Yun†,§, Junhyuk Ahn†, Heon Lee†, Soong Ju Oh†,*, Sung-Hoon Hong§,* †

Department of Materials Science and Engineering, Korea University, Anam-dong 5-1,

Sungbuk-Ku, Seoul 136-701, Republic of Korea §

ICT Materials & Components Research Laboratory, ETRI, Daejeon 305-700, Republic of Korea

KEYWORDS Plasmonics, metamaterials, nanoimprint lithography, galvanic replacement, silver nanocrystal, ligand exchange

ABSTRACT

We developed a simple and systematic method for fabricating optically tunable, thermally and chemically stable Au-Ag nanocrystal-based plasmonic metamaterials. An Ag nanocrystal-based metamaterial with desirable optical properties was fabricated via nanoimprinting and ligand

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exchange process. Its optical properties were controlled by selectively substituting Ag atoms with Au atoms through a spontaneous galvanic replacement reaction. The developed Au-Ag based metamaterials provide excellent tunable plasmonic properties required for various applications in the visible and NIR region by controlling the Au-Ag composition according to the conditions of the galvanic displacement. Furthermore, its thermal and chemical stabilities significantly improved due to the protective Au thin layer on the surface. Using this developed process, chemically and thermally stable, and flexible plasmonic metamaterials were successfully fabricated on a flexible polyester terephthalate substrate.


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Plasmon resonance is a unique optical phenomenon that produces highly confined optical fields in metal nanostructures. This has been utilized in chemical and biomedical sensors1-2 , plasmonic color generation3-9, plasmonic light absorber10-14, photovoltaic cells15-17, and surfaceenhanced Raman scattering (SERS)18-21. For such applications, plasmonic nanostructures must have optical properties that are tunable over a wide spectral range and can achieve desired functionality. Previous studies focused on plasmonic nanostructures based on a few conventional noble metals (Ag, Au, etc.), resulting in a limited spectral range. Recently, newly designed nanostructures composed of alloys have received a significant amount of attention owing to their advantageous tunable properties such as improved incident photon to charge carrier efficiency of the photoanodes22, excellent SERS sensitivity23 beyond those of pure metals, and other optical functionalities. Cu-Ag alloy24, Pt-Ag alloy25-27 and Pd-Rh alloy nanocrystal (NC) materials28 exhibit CO oxidation catalytic properties that are more effective than pure materials. Deposited metal (Au, Ag, and Cu) alloy nanostructure29, synthesized Ag-Au bimetallic NCs30-31 and metal-semiconductor core/shell NCs32 with tunable and enhanced plasmonic properties have been studied. However, most of these require complex synthesis procedures and are still in their nascent stages of development. Furthermore, NCs with equal spacing over a large area are difficult to achieve despite various NC assembly methods33-34. Therefore, simple and efficient nano-patterning methods such as a nanoimprint lithography, and direct patterning, are necessary, to produce plasmonic nanostructure arrays. Previous studies35-36 implemented nanoimprinting technology to create plasmonic nanostructure arrays of Ag NCs. This approach is advantageous in that it incorporates synthesized NCs in metamaterials and can fabricate them on various large-area substrates through the solution process. However, issues


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such as limited spectral range, tunability, and stability still exist. Hence, more intensive studies on NC structures are required. In this work, Au-Ag alloy NC-based metamaterials with adjustable plasmonic properties, and enhanced thermal and chemical stabilities, were designed through a spontaneous redox reaction with galvanic replacement. The synthesized Ag NC-based metamaterials were fabricated by the sequential process of nanoimprinting, ligand exchange, and galvanic replacement. Structural, elemental, optical, and chemical analyses were conducted to understand the change in the materials’ properties. This systematic process allowed the fabrication of patterned and coupled Ag NC-based metamaterials. Moreover, galvanic replacement facilitated tunability of the plasmonic properties and stabilities of the product by adjusting synthesis conditions like the degree of Au coating.

RESULTS AND DISCUSSIONS


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Figure 1. (a) Schematic diagram of engineering Au-Ag metamaterial thin films through ligand exchange and galvanic replacement. (b) EDX spectra of NC thin films before and after HAuCl4 treatment in 0.007, 0.014, and 0.035 mM HAuCl4 solutions for 30 min. (c) (Ag+Au) to Au atomic ratio at different HAuCl4 solution concentrations (0.007, 0.014, 0.035 mM) and reaction times (10, 30, 60 min) according to EDX measurement. The galvanic replacement in the Au-Ag thin film is shown in Fig. 1(a) to understand the change in its elemental composition. First, 100 nm-thick Ag NC thin films were deposited on a Si substrate by spin-coating. However, colloidal NCs typically have long chains, such as oleylamine (OLA) and oleic acids, when synthesized for shape control and dispersion37. Hence, electrical and optical interactions between NCs do not exist. Therefore, these long and dielectric ligands were replaced with short and conductive ligands38-41. Ligand exchange was performed by


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immersing the NC thin film samples in 1% ammonium thiocyanate (NH4SCN) solution, replacing the OLA ligand with SCN ligand. The Au-Ag thin film was fabricated by replacing the Ag atoms on the surface of Ag NCs with Au atoms through galvanic replacement. Upon immersing the Ag NC thin films in the aqueous solution (HAuCl4•3H2O) containing Au ions, the redox reaction occurred spontaneously owing to the higher reduction potential of Au compared with that of Ag42. The Ag ions were liberated from the NCs, and the Au ions bonded with the corresponding free electrons to form thin Au layers on the surface of the Ag NCs. Uniform and high reaction temperatures are necessary because the rate of galvanic displacement increases with temperature following the Arrhenius equation43-44. However, the HAuCl4•3H2O solution boiled, and bubbles were generated above 80 °C, effectively preventing uniform gold treatment. Consequently, the temperature was fixed at 80 °C to attain a stable reaction. To analyze the elemental contents at varying concentrations of HAuCl4 solution and treatment periods, Ag NC thin films were subjected to galvanic replacements in 0.007, 0.014, and 0.035 mM HAuCl4 aqueous solutions for 10, 30, and 60 min. The elemental composition of the Ag NC thin films before and after galvanic replacement was analyzed by energy-dispersive X-ray spectroscopy (EDX). After the treatment, a peak corresponding to the Au M line was observed at 2.13 keV as shown in Fig. 1(b). Au content (at %) surpassed the Ag content as the concentration of HAuCl4 solution increased. At 0.007 mM HAuCl4 solution, the lowest concentration, the Au/(Ag+Au) ratio slightly changed to 3.35% after 60 min, as shown in Fig. 1(c). For 0.035 mM HAuCl4 solution, the Au/(Ag+Au) atomic ratio increased to 84.39% after 60 min. Thus, the tunability of product properties depending on solution concentration and processing time confirmed.


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Figure 2. (a) Real and (b) imaginary components of the dielectric constants (ε = ε' + ε'') of HAuCl4-treated Ag NC thin films, (c) quality factor (Q-factor) of the localized surface plasmon resonance (LSPR) at varying HAuCl4 solution concentration and reaction time. (d) Dependence of Q-factor on the Au to Au-Ag ratio of the thin film at a wavelength of 1000 nm.

The optical properties of the Ag NC thin film treated with HAuCl4 solution were obtained by spectroscopic ellipsometry. In Fig. 2(a), the real component of the complex dielectric function was negative, with increasing slope towards the infrared range. The real dielectric function for the Ag NC thin film after HAuCl4 treatment was less negative and less steep than that before the


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treatment. Although ε' should be negative to realize the surface plasmon, HAuCl4 treated Ag NC thin film shows a positive values under certain condition. For the 0.007mM HAuCl4 treated Ag NC film for 10 min, this is fulfilled for λ > 342 nm. For the treatment with higher concentration or longer time, this is only valid for λ > 643 nm (0.035mM, 60min). As the Ag NC thin films are combined with a short and conductive ligands (-SCN), they are not consistent with pure metal thin films because of the dielectric spaces between the NCs. In addition, the galvanic replacement process increases the dielectric spacing. These lead to a positive value of ε'. As expected from effective medium approximation, our metamaterials with metal and dielectric materials exhibit a weaker metallic behavior than bulk in the optical regime with ε' nearly close to zero. Figure 2(b) shows that the imaginary part of the function decreased after the treatment, suggesting a low relative absorptive loss in the NC thin film. Furthermore, the permittivity in the 0.035 mM solution was relatively closer to zero than that in 0.007 mM. The quality factor (Qfactor) of the localized surface plasmonic resonance is important in advancing LSPR-based devices45. It is defined as the ratio of the real part (ε') of the permittivity to the imaginary part (ε'') or ε'/ε''. The wavelength band in which the Q factor is over zero can cause the plasmon effect. The onset of this band shifts from 342 nm to 643 nm as more Au replaced, as seen in Fig. 2(c). In addition, the Q-factor value is dependent on the ration of Ag and Au. At 1000 nm, the Q-factor decreases exponentially as Au content increases, as shown in Fig. 2(d). Despite moderate Qfactors, the large imaginary part of the dielectric function of Au-Ag NC-based materials indicates its potential as an optical absorber in the visible and NIR region.


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Figure 3. (a) Schematic diagram of Au-Ag NC-based metamaterial fabrication. SEM images of (b) Ag NC-based nanodisk arrays treated with NH4SCN for ligand exchange and (c) after HAuCl4 treatment. (d) Pattern-size distribution of Ag NC-based nanodisk arrays before and after HAuCl4 treatment. (e) TEM images of HAuCl4-treated Ag NC-based nanodisks prepared by FIB.

Since Ag NCs have sizes in the order of 10 nm, metamaterial structures 100 nm or more in size could be fabricated by nanoimprint lithography. To fabricate Ag NC-based nanopatterns, an Ag NC layer was coated on a polymer layer with nanoimprinted patterns. Consequently, an array of Ag NCs was formed by lifting off the polymer layer as shown in Fig. 3(a). The Si master stamp used in the nanoimprinting process was composed of square nanodisk arrays (diameter 220 nm, pitch: 550 nm, height: 220 nm). This was pressed onto the poly (benzyl methacrylate) (PBMA) resist layer and heated, forming a nanohole array complementary to the master stamp. (Supporting Information, Part 1) For the NCs to fill the nanohole patterns of the PBMA layer


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completely, a soft blade scanned the PBMA layer, effectively distributing the film uniformly. Consequently, an array of Ag NC-based nanodisks were obtained. Subsequently, ligand exchange was performed in the SCN solution to enhance the coupling between NCs. The scanning electron microscope (SEM) image of the nanodisk array, composed of coupled Ag NCs with short ligands, uniformly fabricated on the glass substrate, is shown in Fig. 3(b). To modify the properties of Ag NCs, Au was chemically embedded on the surface of the Ag NCs via galvanic displacement. After treatment in 0.007 mM HAuCl4 for 30 min, the nanostructures were well preserved but slightly shrunk, as shown in Fig. 3(c). The size distribution of the nanodisks was automatically generated using ImageJ program. An average diameter of 209.95 nm and 175.29 nm before and after HAuCl4 treatment, respectively, was obtained (Fig. 3(d)). The standard deviation values before and after treatment were 8.51% and 6.36%, respectively, indicating that the nanodisks were statistically uniform. Atomic force microscopy (AFM) analysis confirmed the reduction of nanodisk diameter and height to about 180 and 50 nm, respectively, as shown in Supporting Information, Part 2. As Ag atoms were continuously dissolved during Au treatment, the number of atoms forming the nanodisks decreased. The stoichiometric equation for the Ag-Au galvanic reaction is presented as follows46:

3Ag (s) + AuCl4- (aq.) → Au (s) + 3Ag+ (aq.) + 4Cl- (aq.)

(1)

Here, three Ag atoms on the surface are oxidized in exchange of one Au atom due to the difference in the number of their electrons. Consequently, a portion of the surface of the NCs is dissolved and coated with Au.


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To analyze the composition of the engineered nanodisks after galvanic exchange, scanning transmission electron microscopy (STEM) observation and energy-dispersive spectroscopy (EDS) mapping were conducted. The samples were treated in 0.007 mM HAuCl4 for 30 min. The cross-section samples of the NC-based nanodisk for TEM were prepared using a focused ion beam (FIB). The TEM image in Fig. 3(e) shows that the NCs are well-formed and are composed of Ag and Au that are distributed over the entire area of the structure. The Ag and Au contents were 91.3% and 8.7%, respectively. SEM-EDX data anlalysis confirmed that galvanic exchange yields uniform Au coating across the entire NC area (Supporting Information, Part 3). Based on the concentration of the HAuCl4 solutions and treatment time, the thickness of Au layers change. In order to check the penetration depth of Au in each NC and calculate the maximum thickness of Au layer to be formed in one NC, the atomic percent of Au and Ag was compared by EDX analysis. The content of Au according to the reaction time was measured and the penetration depth/ thickness of Au layer using the equation in Supporting information, Part 4. The thickness of Ag layer according to the content of Au show in Supporting information, Part 5. As the atomic percentage of Au increases and saturates to 92-95 % in 0.035mM HAuCl4 treatment, it can be assumed that the penetration depth or maximum thickness will be about 2.85-3.16 nm for NCs with a diameter of 10 nm.


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Figure 4. Transmittance spectra of Au-Ag NC-based nanodisk arrays with 200 nm diameter at different HAuCl4 solution concentrations and treatment periods. Curves have been normalized. (a) Treatment in 0.007 mM HAuCl4 for different periods, (b) treatment in 0.014 mM HAuCl4 for different periods, and (c) treatment in 0.035 mM HAuCl4 for different periods. and (d) Nanodisks with varying diameters of 200, 330, 400 and 450 nm were also treated in 0.014 mM HAuCl4 for 30 min.

The visible and near-IR (350-2000 nm) transmittance were measured using Varian's Cary 5000 UV-visible-NIR spectrometer to confirm the change in the resonance characteristics after the Au


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treatment. For NC-based metamaterials, double-resonance characteristics can be realized in a single nanostructure. The resonance peaks of the array of Ag NC nanodisks with a diameter of 200 nm could be observed at both wavelengths of 415 and 773 nm, unlike that of conventional Ag thin films (Fig. 4(a)). Ag thin films have only interband absorption peak in UV wavelength range as shown in Supporting Information, Part 6. The resonance at 415 nm was characteristic of LSPR in Ag NCs, while that at 773 nm was attributed to the nanostructure and coupling effect of Ag NCs. As the amount of Au increased with treatment period and/or solution concentration, both peaks were gradually shifted to the red spectral range, which is dominated by the Au plasmonic band47. As shown in Fig. 4(a), Au treatment in 0.007 mM HAuCl4 led to a slight shift in the peak from 773 to 778 nm, even after 60 min, because of the insufficient amount of Au. In 0.014 mM HAuCl4 for different treatment periods, Au formed on the surface of each Ag NC samples, and the first resonance characteristic peaks shifted from 415 nm to 492, 519, and 529 nm for treatment periods of 10, 30, and 60 min, respectively (Fig. 4(b)). The second plasmonic resonance peak redshifted from 773 nm to 875, 957, and 973 nm for treatment periods of 10, 30, and 60 min, respectively. These shifts result from the increasing thickness of substituted Au on the Ag NC surface of the nanodisks, despite their size reduction. As the treatment period increased, the chemical reaction, evidenced by the plasmonic band shift, gradually saturated. Upon complete replacement of Ag by Au on the surface of the NC, the reaction terminated. In the 0.035 mM solution, the degree of plasmonic shift was strongly affected by the duration of treatment. After 20 min, the second resonance peak remarkably shifted from 773 nm to 1040 nm as shown in Fig. 4(c). By galvanic replacement, the properties of the NCs in the metamaterial can be easily and precisely adjusted. Furthermore, their plasmonic resonances could be controlled even with similar metamaterial structure. Fig. 4(d) shows the transmittance spectra for


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the nanoimprinted array of nanodisks from treatment in 0.014 mM HAuCl4 with varying diameters and approximately 50 nm in height. Increasing the disk diameter from 180 to 450 nm, shifted the plasmon resonance peaks from 957 to 1170 nm. Therefore, we have succeeded in realizing metamaterials with adjustable resonance characteristics over a wide spectrum.

Figure 5. (a) Optical image (b) and transmittance spectra of Au- Ag NC-based large-area flexible plasmonic film from 0.014 mM HAuCl4 treatment for 30 min.

The nanoimprinting and galvanic solution processes, which allow large-scale processing at low temperature, can be utilized for the production of mechanically flexible metamaterials with new functions and applications. The Au-Ag NC-based nanostructures was successfully applied on a flexible polyester terephthalate (PET) film, 6 cm × 6 cm in area, as shown in Fig. 5(a). The resultant plasmonic metamaterial film displayed excellent tunable plasmonic properties after treatment in 0.014 mM HAuCl4 for 30 min (Fig. 5(b)). The resonance peak located at shorter wavelength around 400-450nm overlaps with the specific peak of the PET film as shown in


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Supporting Information, Part 7. Our method can be applied to produce devices, such as reflective plasmonic displays and plasmonic sensors.

Figure 6. Transmittance spectra showing the thermal stabilities of (a) untreated Ag NC-based metamaterial and (b) HAuCl4-treated Ag NC-based metamaterial at varying temperatures. (c) The percent shift in the resonance spectrum at different temperatures for treated and untreated samples. (d) Confirmation of the plasmonic stability after 180 days.


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Ag nanostructures, including NCs, are known to exhibit strong surface plasmonic resonance, but their applications are limited by their poor chemical and thermal stabilities48-49. When exposed to air, Ag reacts with sulfur and oxygen species to form Ag2S (silver sulfide)50 or Ag2O51 (silver oxide). These reactions are further promoted with temperature, and the plasmonic properties are degraded. The plasmonic property of the HAuCl4-treated Ag NC-based metamaterial developed in this study was expected to be protected from thermal and chemical external factors by the Au coating. To investigate this stability against temperature, heat treatment was performed between 130 °C and 330 °C for 1.5 min on a hotplate. As shown in Fig. 6(a), the plasmonic resonance of the untreated Ag NC-based metamaterial was blueshifted at over 150 °C, and the resonance characteristics degraded. The Ag NCs were coupled with SCN short ligands, which have a melting point of 149.6 °C. Hence over 150 °C, the Ag NCs immediately oxidize because the surrounding SCN ligand disappears. The resonance peaks were almost negligible over 200 °C. In contrast, the 0.007 mM HAuCl4-treated Ag NC-based metamaterial experienced only minor variation in the bandwidth at high temperature. The resonance peak was unchanged over 330 °C (Fig. 6(b)). The treated sample displayed a 1.33% change rate, while the untreated sample experienced 27.27% (Fig. 6(c)). Furthermore, the plasmonic properties were very stable even after exposure to air for more than 180 days, as shown in Fig. 6(d).


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Figure 7. Chemical stability of (a) Ag NC-based metamaterials and (b) Au-Ag NC-based metamaterials in an aqueous solution of H2O2 (1 vol%), as indicated by UV-vis spectral changes with time.

The Au-protected Ag NC metamaterials exhibited plasmonic properties with improved thermal stability and significantly enhanced chemical stability against corrosive environments. H2O2 solvent is an excellent etchant for metallic Ag, but not Au52-53. To test the chemical stability, we used 1 vol% H2O2 water solution as the standard Ag etchant at room temperature. Upon immersing in the solution, oxygen bubbles were generated on the surface of the sample. The chemical reaction accelerated over time. As shown in Fig. 7(a), after 3 min, the reduction in plasmonic band intensity of the untreated sample confirmed the corrosion of Ag. Moreover, the peak disappeared almost completely after 9 min. However, the plasmonic properties of the AuAg metamaterial were well-protected even after 2 h as shown in Fig. 7(b). Additionally, the shape of the nanostructure was retained. Therefore, the Au-Ag NC metamaterial exhibited


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tunable plasmonic properties and significantly enhanced thermal and chemical stabilities for more applications.

CONCLUSION In this study, we controlled the properties of the alloyed Au-Ag materials using a simple galvanic replacement process. The contents of Ag and Au for substitution were adjusted by manipulating the Au concentration of the precursor solution and treatment period. Consequently, the real and imaginary components of the permittivity of the material altered. Moreover, the plasmonic resonance peaks redshifted with an increase in the Au content. In addition, the Autreated Ag NC-based metamaterials were thermally and chemically stable. The Au-Ag based plasmonic metamaterial has potential in various applications, including sensors and energyharvesting devices.

METHODS NC-based plasmonic metamaterials by nanoimprinting method To fabricate tunable plasmonic metamaterials, Ag NC-based nanostructures were developed using nanoimprint lithography. Corning’s Eagle glass substrates were ultrasonicated, with a sequence of solvents as follows: acetone, ethanol, and deionized water. Poly(benzyl methacrylate) (PBMA) resist at 7 wt% was uniformly coated on the glass substrate by spin coating (2000 rpm, 30 s), and subsequently heat-treated at 140 °C. The nanodisk-patterned silicon master stamp was then pressed on the PBMA layer at a pressure of 20 bar for 20 min while maintaining heat treatment. Consequently, the PBMA resist adjusted to the shape of the


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master stamp, leaving a patterned PBMA layer of nanoholes with minimum residual on the glass. After the PBMA resist hardened by cooling, pressure was removed, and the stamp was separated from the substrate. The residual PBMA layer was removed through O2 dry etching. To improve the adhesion of Ag NCs onto the glass substrate during ligand exchange and galvanic replacement, the substrates were immersed in a mixture of 5 mM 3aminopropyltriethoxysilane (APTES) in hexane for 1 h. They were then rinsed with hexane to remove weakly attached APTES molecules on the surface before applying the Ag NCs on the PBMA nanohole structure. The nanoholes were filled with 5 wt% Ag NC-octane dispersion via drop casting. The excess NC dispersion was expelled using a soft blade. The NC layer was heattreated at 100 °C for 3 min for stabilization. To isolate the nanostructures, PBMA was dissolved in dimethyl-formamide (DMF) solution. Coupled NCs via ligand exchange process The Ag NCs were coupled via the ligand exchange process. The Ag NC-based metamaterial samples were immersed in 1% NH4SCN acetone solution for 1 min. The samples were then transferred to a bath of pure acetone for 1 min to wash the excess ligand. Subsequently, a heat treatment was performed at 90 °C for 1 min. Control of material properties by galvanic exchange Au was chemically deposited on the surface of Ag NC by galvanic displacement. The Ag NCbased metamaterial was immersed in a gold chloride hydrate aqueous solution (HAuCl4•3H2O) containing Au ions. The temperature of the solution was maintained at 80 °C using a hot plate for uniform reaction rate and was stirred with a magnetic stirrer. The process was carried out at different concentrations of 0.007 mM, 0.014 mM, and 0.035 mM for different treatment periods


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of 10, 30, and 60 min. The samples were then collected from the solution and were washed with deionized water multiple times to remove impurities. Optical Characterization The optical properties of the Au-Ag thin films were characterized by SE. The measurements were conducted at room temperature with an angle of incidence of 75°. The variable angle reflectance and ellipsometry spectra of the uniform NC films on polished silicon substrates were measured using an M-2000D ellipsometer (J.A. Woollam Co.). The complex reflectance ratio ρ (= tan( between the Fresnel reflection coefficients of light polarized parallel and perpendicular to the plane of incidence was measured from 192 to 1654 nm at 65, 70, and 75° to extract the Psi () and Delta (Δ). The dielectric functions were obtained from SE data following a model-based technique which minimized the difference between the measured spectrum and the calculated counterpart using the Complete EASE software package (J.A. Woollam Co.). For the Au-Ag NC films, the first layer was set as a mixed Au-Ag NC film above the silicon wafer, while the second layer was set as a rough layer of Au-Au NC film intermixed with air using Bsplines (Basis-splines). The transmittance spectra of the nanoimprinted NC-based nanodisk arrays were measured with a Cary 5000 UV-Vis-NIR spectrophotometer (Agilent Technologies) without polarization, at a 5nm spectral bandpass between 350 and 2000 nm. These were reported after subtracting the contribution of Corning’s Eagle glass substrate.

ASSOCIATED CONTENT


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Supporting Information. Additional SEM images of nanoimprinting process, AFM topography of Ag NC based nanodisks, additional SEM-EDX mapping data of HAuCl4 treated Ag NC film, the equations of Au coating layer thickness, additional atomic percent and thickness of Au layer, additional FDTD simulation results and extended transmittance results. This material is available free of charge via Internet at http://pubs.acs.org.

ACKNOWLEDGMENT This work was financially supported by the Pioneer Research Center Program through the National Research Foundation of Korea (NRF-2014M3A6B3063702), Electronics and Telecommunications Research Institute (ETRI) grant funded through the Korean government. (18ZB1100, Development of Basic Technologies for 3D Photo-Electronics) and by Global Ph. D. Fellowship (NRF-2016H1A2A1909313).

AUTHOR INFORMATION Corresponding Author *Email: [email protected], [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally. REFERENCES 1. Rodrigo, D.; Limaj, O.; Janner, D.; Etezadi, D.; Garcia de Abajo, F. J.; Pruneri, V.; Altug, H., Mid-infrared plasmonic biosensing with graphene. Science 2015, 349 (6244), 165168. 2. Paulo, P. M.; Zijlstra, P.; Orrit, M.; Garcia-Fernandez, E.; Pace, T. C.; Viana, A. S.; Costa, S. M., Tip-specific functionalization of gold nanorods for plasmonic biosensing: effect of linker chain length. Langmuir 2017, 33 (26), 6503-6510.


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TOC Graphic


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ACS Applied Materials & Interfaces 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

(a)

-3e-

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3Ag +

OLA SCN

Ligand exchange

(b)

Untreated

Ag NC film

+3eAu3+ Galvanic Replacement

(c)

0.007mM

0.014mM

0.035mM ACS Paragon Plus Environment

Au-Ag NC film

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(a)

(b)

(c)

(d)


(a)

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


1) Nanoimprinting Master stamp PBMA

Blade

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(c)

(b)

Ag NCs

Glass

200nm

180nm

2) Ligand exchange 1% NH4SCN

Ag NCs

(d) 3) Galvanic replacement Ag NC

Au-Ag NC

5𝟎𝟎𝐧𝐦

5𝟎𝟎𝐧𝐦

Mean: 175.29nm Std. dev.: 6.36%

(e)

Ag 91.3%

Mean: 209.95nm Std. dev.: 8.51%

HAuCl4 solution

Au 8.7%

1𝟎𝟎𝐧𝐦 Au Ag ACS Paragon Plus Environment

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(a)

(b)

(c)

(d)


ACS Applied Materials & Interfaces 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

(a)

(b)

PET film 6cm*6cm


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(a)

(b)

(c)

(d)

rate of change 1.96%

28.57%


ACS Applied Materials & Interfaces 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

(a)

(b)


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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


-3e-

Ag NC

3Ag+

Au-Ag NC +3eAu3+


Chemically engineered Au-Ag plasmonic nanostructures to realize

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