Plasmonic Properties of Vertically Aligned Nanowire Arrays

Hua Qi,S M Prokes,O J Glembocki

doi:10.1155/2012/843402

Hua Qi, S M Prokes + Show 1 more

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https://doi.org/10.1155/2012/843402

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Abstract

Nanowires (NWs)/Ag sheath composites were produced to investigate plasmonic coupling between vertically aligned NWs for surface-enhanced Raman scattering (SERS) applications. In this investigation, two types of vertical NW arrays were studied; those of ZnO NWs grown on nanosphere lithography patterned sapphire substrate via vapor-liquid-solid (VLS) mechanism and Si NW arrays produced by wet chemical etching. Both types of vertical NW arrays were coated with a thin layer of silver by electroless silver plating for SERS enhancement studies. The experimental results show extremely strong SERS signals due to plasmonic coupling between the NWs, which was verified by COMSOL electric field simulations. We also compared the SERS enhancement intensity of aligned and random ZnO NWs, indicating that the aligned NWs show much stronger and repeatable SERS signal than those grown in nonaligned geometries.

Highlights

Nanostructures, especially nanowires (NWs), have inspired much interest due to their potential applications in electronics, photonics, and life science [1,2,3,4,5]
It has been demonstrated that the geometry of the nanowires and the orientation of the molecules play an important role in the surface-enhanced Raman scattering (SERS) process [10,11,12,13,14]
Most of the reported NW structures were randomly distributed on a surface, where the largest SERS enhancements noted were in the NW crossing [10] and between the NW and the substrate [14]

Summary

Introduction

Nanostructures, especially nanowires (NWs), have inspired much interest due to their potential applications in electronics, photonics, and life science [1,2,3,4,5]. We used two types of vertical NWs, ZnO NWs, and Si NWs, respectively, to investigate SERS enhancement due to the plasmonic coupling between closely packed NWs. Many lithographic techniques have been used to fabricate ordered patterns on a surface, including photolithography, e-beam lithography [15, 16], ion beam lithography [17], X-ray lithography [18, 19], nanoimprint lithography [20, 21], and scanning probe lithography [22, 23]. We employed the nanosphere lithography (NSL) approach [24,25,26], which has the advantages of low cost and simplicity, to produce the hexagonal gold dot patterns on c-sapphire and to successfully grow vertically aligned ZnO nanowires by the well-known VLS process In this way, the ZnO NWs can be arranged in a repeatable hexagonal pattern creating ordered and aligned NW arrays for surface-enhanced Raman scattering (SERS) applications. The Si NWs and ZnO NWs arrays were coated with a thin layer of Ag, using an electroless plating technique, and their plasmonic properties were investigated

Experimental Details

Results and Discussion

Conclusion