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SERS in Ordered Array of Geometrically Controlled Nanodots Obtained Using Anodic Porous Alumina Toshiaki Kondo, Hideki Masuda, and Nishio Kazuyuki J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp306470r • Publication Date (Web): 26 Nov 2012 Downloaded from http://pubs.acs.org on December 2, 2012

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The Journal of Physical Chemistry

SERS in Ordered Array of Geometrically Controlled Nanodots Obtained Using Anodic Porous Alumina Toshiaki Kondo,† Hideki Masuda,*,†,‡ Kazuyuki Nishio†,‡

†Kanagawa Academy of Science and Technology, 5-4-30 Nishihashimoto Midori-ku, Sagamihara, Kanagawa 252-0131, Japan

‡Tokyo Metropolitan University, 1-1 Minamiosawa, Hachioji, Tokyo 192-0397, Japan

KEYWORDS. Localized surface plasmon, SERS, Anodic porous alumina

ABSTRACT.

The fabrication of geometrically controlled nanodot arrays based on anodic porous alumina and their application as substrates used for surface-enhanced Raman scattering (SERS) measurements were studied. Ordered arrays of circular, square and triangular Au nanodots were obtained using anodic porous alumina as an evaporation mask. The shape and arrangement of the nanodots were precisely controlled by adjusting the geometrical structure of the nanoholes in the anodic porous alumina. We also fabricated triangular nanodots that had sharp corners with a curvature radius of 15 nm. SERS spectra of pyridine molecules adsorbed on the Au nanodots were measured using the obtained nanodot arrays as substrates for measurements. The SERS intensity obtained from the triangular nanodot array was strongly enhanced compared with that obtained from the array of circular nanodots. The intensity of signals was dependent on the shape and arrangement of the nanodots. It is expected that

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nanodot arrays obtained by this fabrication method using anodic porous alumina can be used for the formation of functional optical devices requiring an ordered array of geometrically controlled nanostructures.


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Introduction The fabrication processes of noble metal nanostructures are attracting attention because these nanostructures can enhance the electric field of incident light due to localized surface plasmon resonance (LSPR) [1,2]. Many types of applications utilizing the enhanced electric field have been proposed, for example, sensing devices, nonlinear optical devices and so on [3-5]. It is thought that the performances of these functional devices are dependent on the LSPR properties, which are determined by the shape and arrangement of the nanostructures [6,7]. A number of approaches to fabricating shape-controlled nanostructures by bottomup and top-down processes have been reported. Nanoparticles with various shapes, such as circular, square, and rod-shaped nanoparticles, can be fabricated by processes involving chemical synthesis [8-12]. However, it is difficult to order these nanoparticles with an arbitrary arrangement over a large area on a substrate. It is possible to fabricate ordered arrays of shape-controlled nanoparticles by a top-down process using an electron beam lithography system and/or a focused ion beam etching system. An advantage of using these processes is the controllability of the shape and arrangement of the nanoparticles [13,14]. As a candidate structure with the ability to efficiently enhance an electric field, the bow-tie structure has been proposed [5,14]. This structure consists of two triangular nanodots or nanovoids close to each other. Nanogaps composed of such triangular nanostructures with sharp corners effectively enhance the electric field. However, it takes a long time to fabricate an ordered array of shape-controlled nanostructures as long as a top-down


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process with an electron beam lithography system and/or focused ion beam etching system is used. Furthermore, these apparatuses are expensive. A method of forming an ordered array of geometrically controlled nanodots over a large area is yet to be established. In previous works, we have reported the fabrication of two-/three-dimensional (2D/3D) ordered arrays of metal nanostructures using anodic porous alumina and their application to plasmonic devices [15-19]. Anodic porous alumina is formed on the surface of Al by anodizing Al plate in an acidic solution. Using anodic porous alumina as an evaporation mask, ordered arrays of uniformly sized nanoparticles can be obtained. Generally, nanoholes in porous alumina are circular. However, we had demonstrated the formation of the anodic porous alumina with the square and triangular nanoholes by the application of a pretexturing process before the anodization of Al [16]. In the present paper, we describe the precise control of the geometrical structure of arrays of ordered metal nanodots and their application to substrates used for surface-enhanced Raman scattering (SERS) measurements. The enhancement factors of the light intensity around the nanodot arrays originating from LSPR are investigated by numerical calculations based on the finite-difference time-domain (FDTD) method. Applying the fabrication method discussed in this paper makes it possible to fabricate an ordered array of geometrically controlled nanodots over a large area for the first time. It is expected that nanodot arrays obtained by this method can be applied to functional optical devices requiring highly geometrically controlled nanostructures.


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Experimental The fabrication process of nanodot arrays using anodic porous alumina as an evaporation mask has been reported [15-19], so is briefly described here. A pretexturing process was carried out before the anodization of Al. An ordered array of nanodents was formed on an Al surface by pressing a metal mold with an ordered array of nanoprojections onto the Al surface. Each nanodent acts as the starting point of a nanohole grown during the anodization process. After the anodization of Al with a textured pattern, geometrically controlled nanoholes were obtained. In this study, the shapes of nanoholes were circular, square, and triangular. The shapes of the nanoholes could be controlled by changing the arrangement of the pattern formed by pretexturing [16]. The porous alumina with circular nanoholes was obtained by anodizing Al in 1 M phosphoric acid at 1 ℃ at 80 V for 15 min. For the formation of square and triangular nanohole arrays, Al was anodized in 0.05 M oxalic acid at 16 ℃ at 80 V for 6 min and in 0.5 M phosphoric acid at 16 ℃ at 80 V for 20 min, respectively. The Al beneath the porous alumina and the bottom part of the nanoholes were dissolved by a wet-etching process to obtain the through-hole membrane of the anodic porous alumina. The diameter of the nanoholes was adjusted by a postetching treatment in 5 wt% phosphoric acid solution at 30 ℃. The anodic porous alumina membrane was set on a glass substrate, and Au was deposited onto the substrate thorough the nanoholes of the membrane using


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thermal evaporation apparatus. After removing the alumina mask, a Au nanodot array was obtained. The geometrical structures of the Au nanodot arrays were observed using a scanning electron microscope (SEM, JSM-6700F; JEOL). Extinction spectra of the nanodot arrays were measured using a spectrometer equipped with an integrated sphere. SERS spectra of pyridine molecules adsorbed on Au nanodot arrays were measured using a Raman microscope (NRS-3100; JASCO) equipped with a He-Ne laser as a light source (wavelength: 633 nm). Before the SERS measurements, pyridine solution (HPLC grade, >99.9 %) was added dropwise onto the nanodot array, and dried in air. The concentration and the amount of instillation of pyridine solution were 1.2 M and 20 µl, respectively. The light intensity of the electric field around the Au nanodot arrays was calculated by the 3D FDTD method. Commercial software (Crystalwave; PhotonDesign) was used for the FDTD calculations. The grid size was 2 nm, and the boundary condition was periodic. The enhancement factor was obtained by comparing the light intensity around the Au nanodots with that of the incident light.

Results and discussion Figure 1 shows SEM images of ordered arrays of Au nanodots with different shapes, namely (a) circular, (b) square, and (c) triangle. The shapes of the nanodots reflected the shapes of the nanoholes in he anodic porous alumina membranes. The nanogap size and the interval between nanodots in Figures 1a - 1c were 40 and 200


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nm, respectively. The height of the dots was 20 nm. The inhomogeneity of the contrasting density on Au surface shown in SEM images of Figures 1 and 5 originates in the influence of weak charge up during the SEM observation. Figure 2 shows the extinction spectra of the Au nanodot arrays. The extinction peak for the array of circular nanodots based on LSPR was observed at approximately 750 nm. For the arrays of square and triangular nanodots, no peaks were observed in the visible wavelength range. Measurements in the near-infrared wavelength region could not be implemented owing to the specifications of the spectrometer. However, it is expected that the extinction peaks of the arrays with square and triangular nanodots will appear at longer wavelengths than that obtained from the arrays with circular nanodots. This can be explained in terms of the strength of the coupling of LSPR between the nanodots. The arrangement and shape of nanodots are important parameters in controlling the LSPR properties of the nanodot arrays. It is thought that the regularly ordered square and triangular nanodots enabled the coupling of LSPR between neighboring nanodots more efficiently than the array of circular nanodots. Figure 3 shows the Raman spectra measured using the Au nanodot arrays. On the assumption that the Au nanodots were entirely covered by mono layer of pyridine molecules, it is estimated that the number of molecules adsorbed on one nanodot with circular, square and triangle shapes were 1.2×105, 1.5×105 and 2.0×105, respectively. The intensity of the SERS signals was normalized by the surface area of Au nanodots. Two peaks originating from pyridine molecules were observed at


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1014 and 1040 cm-1. The intensity of SERS signals obtained from the triangular nanodots was 2 and 4 times larger than those measured using the square and circular nanodot arrays, respectively. However, as shown in Figure 2, the extinction coefficient of the triangular nanodots at 633 nm, which is the excitation wavelength used for the Raman measurements, was smaller than those of the circular and square nanodots. Thus, the enhancement factor of Raman signals was not only dependent on the extinction coefficient but also dependent on the shape and arrangement of the nanodots. It is also important in evaluating Raman signal intensity to consider the scatter and absorption components in extinction coefficient [20,21]. In this present research, it is thought that the scatter component is dominant in the extinction coefficient due to the large volume of the metal nanodots. However, quantitative evaluation of the dependences of Raman intensity on the scatter and absorption components are still under discussion, and will be discussed in future publication. In addition, it was observed that the intensity of signals did not vary with the changes of the polarization of the excitation light. Relative standard deviations (RSD) of the intensity of SERS signals that were measured at different points of the arrays with shape-controlled nanodots were evaluated. For comparison, the mechanically scratched surface of Au film was prepared. When the ordered arrays of circular, square and triangular nanodots were used for the SERS measurements, the RSDs were 7.7 %, 18.5 % and 17.5 %, respectively. In the case of using the scratched sample, RSD was 45.6 %. It was shown that the reproducibility of the intensity of SERS signals measured using the


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nanodot arrays was higher than the case of using the scratched one. And RSD that was measured on the ordered arrays of circular nanodots was smaller than the case of using the ordered arrays with square or triangular nanodots. It is thought that this was due to the high homogeneity of the geometrical structures of the circular nanodots. The enhancement factor of the light intensity around the Au nanodots was calculated by the 3D FDTD method. The Au nanodot arrays were assumed to be set on a glass substrate (refractive index: 1.50), and a plane wave (wavelength: 633 nm) was irradiated in the direction perpendicular to the substrate. The light was polarized along the X-axis shown in Figure 4. The material constants of Au were taken from the literature [22]. Figure 4 shows front views of the enhancement factor obtained at a distance of 1 nm above the glass substrate. The light intensity was enhanced near the surface of the nanodots. As shown in Figures 4b and 4c, the light intensity was also enhanced efficiently at the sharp corners of the dots. In addition, the coupling of the near filed based on LSPR was observed between nanodots. Owing to the coupling, the light intensity was strongly enhanced between the triangular dots (Figure 4c). The light intensity at the (a) circular, (b) square, and (c) triangular nanodots was enhanced ca. 20, 30, and 40 times, respectively. The relative intensities of SERS signals that were measured using the (a) circular, (b) square, and (c) triangular nanodots were (a) 1, (b) 2, and (c) 4. The calculation results were in qualitative agreement with the results of Raman measurements.


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Figure 5 shows SEM images of ordered arrays of triangular nanodots. The curvature radii at the corners of the nanodots were precisely controlled by adjusting the shape of the nanoholes in the anodic porous alumina masks. The curvature radii were (a) 60 nm and (b) 15 nm, respectively. Figure 6 shows the SERS spectra measured on these nanodot arrays. The signal intensity was normalized by the surface area of Au dots. The signal intensity obtained from the nanodot array in Figure 5b was larger than that obtained from the array in Figure 5a. It is thought that the SERS signals were strongly enhanced at the nanodots with sharper corners.

Conclusions We investigated the fabrication of ordered arrays of geometrically controlled nanodots using anodic porous alumna and their application to substrates used for SERS measurements. Circular, square and triangular nanodots were obtained using anodic porous alumina masks. We also fabricated triangular nanodots that had sharp corners with curvature radius of 15 nm by controlling the shape of the nanoholes in anodic porous alumina. It was confirmed that these Au nanodot arrays could be applied to substrates for SERS measurements. The SERS intensity obtained from the triangular nanodot array was strongly enhanced compared with that obtained from the arrays of circular nanodots. These results were in qualitative agreement with FDTD simulation results. The intensity of SERS signals was dependent not only on the extinction coefficient but also on the


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geometrical structure of the nanodots. It is expected that nanodot arrays obtained by this fabrication method based on anodic porous alumina can be used for the formation of functional optical devices requiring an ordered array of geometrically controlled nanostructures.


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Cover graphics


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Figure 1. SEM images of (a) circular, (b) square, and (c) triangular Au nanodots. Interval between nanodots: 200 nm. Nanogap size: ca. 40 nm. Height of nanodots: 20 nm.


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Figure 2. Extinction spectra of Au nanodot arrays consisting of (a) circular, (b) square, and (c) triangular nanodots.


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Figure 3. Raman spectra of pyridine molecules adsorbed on Au nanodot arrays consisting of (a) circular, (b) square, and (c) triangular nanodots.


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Figure 4. Enhancement factor of the light intensity around (a) circular, (b) square, and (c) triangular nanodot arrays calculated by 3D-FDTD method. Nanogap size: 40 nm.

Interval between nanodots: 200 nm.

Height of

nanodots: 20 nm. Wavelength of incident light: 633 nm. The color bar scale of (b) and (c) is same of (a).


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Figure 5. SEM images of triangular nanodots with curvature radii of (a) 60 nm and (b) 15 nm.


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Figure 6. Raman spectra of pyridine molecules adsorbed on triangular Au nanodots with curvature radii at the corners of (a) 60 nm and (b) 15 nm.


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AUTHOR INFORMATION Corresponding Author *Phone: +81 42 677 2843. Fax: +81 42 677 2841 E-mail: [email protected]

ACKNOWLEDGMENT This work was partially supported by Grant-in-Aid for Scientific Research No.19049013 on Priority Area "Strong Photons-Molecules Coupling Fields (470)" from the Ministry of Education, Culture, Sports, Science and Technology of Japan.


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REFERENCES (1) Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C. J. Phys. Chem. B 2003, 2003 107, 668-677. (2) Mulvaney, P. Langmuir 1996, 1996 12, 788-800. (3) Jain, P. K.; El-Sayed, M. A. Chem. Phys. Lett. 2010, 2010 487, 153-164. (4) Mayer, K. M.; Hafner, J. H. Chem. Rev. 2011, 2011 111, 3828-3857. (5) Kim, S.; Jin, J.; Kim, Y.-J.; Park, I.-Y.; Kim, Y.; Kim, S.-W. Nature 2008, 2008 453, 757-760. (6) Camden, J. P.; Dieringer, J. A.; Zhao, J.; Van Duyne, R. P. Acc. Chem. Res., 2008, 2008 41, 1653-1661. (7) Grand, J.; Lamy de la Chapelle, M.; Bijeon, J.-L.; Adam, P.-M.; Vial, A.; Royer, P.

Phys. Rev. B, 2005, 2005 72, 033407. (8) Jin, R.; Cao, C.; Hao, E.; Métraux, G. S.; Schatz, G. C.; Mirkin, C. A. Nature 2003, 2003 425, 487-490. (9) Grzelaczak, M.; Pérez-Juste, J.; Mulvaney, P.; Liz-Marzán, L. M. Chem. Soc. Rev. 2008, 2008 37, 1783-1791. (10)

Teranishi, T.; Kiyokawa, I.; Miyake, M. Adv. Mater. 1998, 1998 10, 596-599.

(11)

Nehl, C. L.; Liao, H.; Hafner, J. H. Nano Lett. 2006, 2006 6, 683-688.


20

Page 21 of 23

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


(12)

Kameyama, T.; Ohno, Y.; Kurimoto, T.; Okazaki, K.; Uematsu, T.; Kuwabara,

S.; Torimoto, T. Phys. Chem. Chem. Phys. 2010, 2010 12, 1804-1811. (13)

Ueno, K.; Juodkazis, S.; Mizeikis, V.; Sasaki, K.; Misawa, H. Adv. Mater. 2008, 2008

20, 26-30. (14)

Schuck, P. J.; Fromm, D. P.; Sundaramurthy, A.; Kino, G. S.; Moerner, W. E.

Phys. Rev. Lett. 2005, 2005 94, 017402. (15)

Masuda, H.; Satoh, M. Jpn. J. Appl. Phys. 1996, 1996 35, L126-L129.

(16)

Masuda, H.; Asoh, H.; Watanabe, M.; Nishio, K.; Nakao, M.; Tamamura, T.

Adv. Mater. 2001, 2001 13, 189-192. (17)

Matsumoto, F.; Ishikawa, M.; Nishio, K.; Masuda, H. Chem. Lett. 2005, 2005 34,

508-509. (18)

Kondo, T.; Matsumoto, F.; Nishio, K.; Masuda, H.; Chem. Lett. 2008, 2008 37, 466-

467. (19)

Kondo, T.; Miyazaki, H.; Nishio, K.; Masuda, H. J. Photochem. Photobiol. A

2011, 2011 221, 199-203. (20)

Jain, P. K.; Huang, X.; El-Sayed, I. H.; El-Sayed, M. A. Acc. Chem. Res., 2008, 2008

41 1578-1586.

(21)

Jain, P. K.; Lee, K. S.; El-Sayed, I. H.; El-Sayed, M. A. J. Phys. Chem. B, 2006,

110 7238-7248.


21


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(22)

Page 22 of 23

Johnson, P. B.; Christy, R. W. Phys. Rev. B 1972, 1972 6, 4370-4379.


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