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0951-E09-35

Physically Self-assembled Au Nanorod Arrays for SERS Motofumi Suzuki1, Kaoru Nakajima1, Kenji Kimura1, Takao Fukuoka2, and Yasushige Mori3 1 Kyoto University, Kyoto, 606-8501, Japan 2 JST Kyoto Pref. CREATE, Seika, Kyoto, 619-0237, Japan 3 Doshisha University, Kyotanabe, Kyoto, 610-0394, Japan

ABSTRACT We have demonstrated surface-enhanced Raman spectroscopy on arrays of Au nanorods aligned in line by a dynamic oblique deposition technique. For the light polarized along the major axis of the nanorods, the plasma resonance of the Au nanorods has been tuned to a wavelength suitable for Raman spectroscopy. The Raman scattering on the discrete nanorods is enhanced significantly compared with that on semi continuous Au films. Since the preparation process is physically bottom-up, it is robust in its selection of the materials and is useful in providing the SERS sensors at low cost. INTRODUCTION For applications of the local field enhancement due to local plasmons in noble metal nanoparticles to biochemical sensors such as surface enhanced Raman scattering (SERS) sensors, controlling both the shape and the arrangement of the nanoparticles is important[1]. It is well known that the well-ordered 2D periodic arrays of triangular nanoparticles prepared by nanosphere lithography (NSL) show the plasma resonance within a rather narrow wavelength region, and the sharp corners of the triangle lead the strong SERS. Although the NSL enables the tuning of the size of the nanoparticles, the number density of the particles is fixed geometrically. Some applications such as a Raman imaging may require more SERS active spots to improve space resolution. In addition, it is not easy to tune the lowest order of the local plasma resonance to near infrared (NIR) region, which is appropriate for biological applications[2]. The drastic enhancement of the local field is also expected at the end of the elongated particles[3]. For the light from visible to NIR region, actually, the SERS has been observed on the aggregates or the arrays of the elongated metal particles so-called nanorods whose width and aspect ratio are a few 10 nm and 2-5, respectively[4-7]. Taking account of the gap enhancement of the local field[8], in-line alignment of the nanorods is more desirable than side-by-side alignment[5, 6] or random aggregation[7]. At the very early stage of the history of SERS studies, virtue of the in-line nanorod arrays has been already reported for the Ag nanorod arrays prepared on the lithographically produced templates[4]. Even today, however, it is not easy to produce sub-µm patterns over large area at low cost.

Recently, we have demonstrated the direct formation of Ag nanorods with a quasiparallel major axis on a template layer of SiO2 having a strongly anisotropic surface morphology[9]. Those Ag nanorods show excellent surface enhanced Raman scattering (SERS) properties[10, 11]. From the practical viewpoints, however, chemically stable Au is preferred to Ag. In this presentation, we report that the physically self-assembled Au