DEVELOPMENT AND OPTIMIZATION OF NEW PLASMONIC STRUCTURES

MARÍA LAURA PEDANO, SHUZHOU LI2, GEORGE C. SCHATZ2 AND CHAD A. MIRKIN2

Córdoba

Taller; Plasmons 2011; 2011

FCEyN - UBA

Over the past six years, Professor?s Mirkin Group have been developing a novel electrochemistry-enabled nanofabrication technique known as on-wire lithography (OWL).[1] This technique allows control of the chemical composition and architecture of a one-dimensional wire from the nanometer to micrometer length scale.[1, 2] Periodic structures that consist of gaps as small as 2 nm and segment lengths that span the 20 nm to many micrometer length scale have been synthesized by OWL.[3] OWL is particularly useful for creating plasmonically active structures from noble metals such as Au and Ag.[2] In collaboration with Professor Schatzs, it has been demonstrated that by tailoring disk (120 nm thick, 360 nm diameter) and gap sizes (30 nm) in one-dimensional Au nanostructures, one could create Raman hotspots, which have been optimized for spectroscopic identification purposes.[3] Gapped rods provide a unique platform for elucidating structure/function relationships, both for single-molecule electrochemical  techniques and for surfaceenhanced Raman scattering (SERS). In this presentation we elucidate the dependence of SERS intensities on the rod segment length, gap topography and gap distance, for gold gapped rods with segment lengths varying over a wide range (40-2000 nm). Significantly, we have determined that the SERS enhancement and localized fields in the gap simply do not monotonically decrease with segment length but rather are a periodic function of the segment length. The periodic dependence is determined by the SPP wavelength. Both theory and experiment show periodic variation of SERS intensity with segment length as determined by odd-symmetry plasmon multipoles. Additionally, we have determined that rough gaps lead to a smaller SERS enhancement than smooth gaps for these structures, even though the rough gaps have a larger total surface area. Excitation of even-symmetry modes is dipole forbidden (for polarization along the rod axis), but this selection rule can be relaxed by roughness or, for smooth gaps, by near-field coupling between the rod segments. Therefore, there is a strong dependence on the gap size if the gap is smooth, but roughness significantly reduces this sensitivity and it also quenches any effect of the polarization direction. From these results we can conclude that one can indeed create idealized geometries that have both, macroscopically addressable long segments to be  attached to electrochemical devices, and nanogaps that lead to a high signal enhancement to be able to spectroscopically characterize the gap composition by surface-enhanced Raman scattering (SERS). References: [1] L. D. Qin, S. Park, L. Huang, C. A. Mirkin, Science 2005, 309,113. [2] X. Chen, Y. M. Jeon, J. W. Jang, L. Qin, F. Huo, W. Wei, C. A. Mirkin, J. Am. Chem. Soc. 2008, 130, 8166. [3] L. D. Qin, S. L. Zou, C. Xue, A. Atkinson, G. C. Schatz, C. A. Mirkin, Proc. Natl. Acad. Sci. USA 2006, 103, 13300.Science 2005, 309,113. [2] X. Chen, Y. M. Jeon, J. W. Jang, L. Qin, F. Huo, W. Wei, C. A. Mirkin, J. Am. Chem. Soc. 2008, 130, 8166. [3] L. D. Qin, S. L. Zou, C. Xue, A. Atkinson, G. C. Schatz, C. A. Mirkin, Proc. Natl. Acad. Sci. USA 2006, 103, 13300.J. Am. Chem. Soc. 2008, 130, 8166. [3] L. D. Qin, S. L. Zou, C. Xue, A. Atkinson, G. C. Schatz, C. A. Mirkin, Proc. Natl. Acad. Sci. USA 2006, 103, 13300.. 2008, 130, 8166. [3] L. D. Qin, S. L. Zou, C. Xue, A. Atkinson, G. C. Schatz, C. A. Mirkin, Proc. Natl. Acad. Sci. USA 2006, 103, 13300.Proc. Natl. Acad. Sci. USA 2006, 103, 13300.2006, 103, 13300.