Collapse-Induced Multimer Formation of Self-Assembled Nanoparticles for Surface Enhanced Raman Scattering

Ju Young Kim,Young Chun Ko,Seung Hee Kim,Shin Park,Seung Won Seon,Min Kyu Jung,Young Taek Oh,Jun Pyo Hwang,Tae Sang Yu,Su Eon Lee,Bong Hoon Kim,Jun Hyun Park,Se Gi Lee

doi:10.3390/coatings11010076

Ju Young Kim, Young Chun Ko + Show 11 more

Open Access

https://doi.org/10.3390/coatings11010076

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Abstract

Metallic nanoparticle ensemble, with narrow inter-particle distance, is a useful element for diverse optical devices due to highly enhanced electric field intensity at the gap. Self-assembly of block copolymer (BCP) can provide the versatile solution to fabricate precise nanostructures, but this methodology has the intrinsic limitation to realize optically coupled metallic multimer geometry with narrow inter-particle distance. This is because BCP-based nanotemplate possesses a minimum size limit for interparticle distance imposed by its thermodynamic restriction. Herein, we investigate the facile formation of metallic multimer with scalability and area-selectivity through the collapse of self-assembled BCP nanopattern. The capillary-force-induced collapse phenomenon enables a spatial transformation of lateral regular ordering in metallic nanoparticle array and enhances electric field intensity. The fabrication of this metallic nanoparticle ensemble from BCP lithography is successfully utilized for surface enhanced Raman scattering (SERS). The enhancement factor of metal nanoparticle multimer is calculated as ~6.74 × 105 at 1000 cm−1, 2.04 × 106 at 1022 cm−1, and 6.11 × 106 at 1580 cm−1, respectively.

Highlights

Localized surface plasmon resonance (LSPR), the collective motion of conduction electrons in metallic nanoparticles excited by light, has been exploited mainly due to its novel electric near-field enhancement at the resonance frequency [1,2,3,4]
Metallic nanoparticles coupled with extremely small gaps can generate a much stronger near-field profile at the gap region compared to single metallic nanoparticle configurations
After the water immersion and subsequent drying process, Au nanoparticle conjugated PS pillars were completely collapsed by strong capillary force

Summary

Introduction

Localized surface plasmon resonance (LSPR), the collective motion of conduction electrons in metallic nanoparticles excited by light, has been exploited mainly due to its novel electric near-field enhancement at the resonance frequency [1,2,3,4]. Metallic nanoparticles coupled with extremely small gaps can generate a much stronger near-field profile at the gap region compared to single metallic nanoparticle configurations. This lets further performance improvement in optoelectronic applications [9]. Due to the intrinsic thermodynamic nature of self-assembly, BCP forms the nanostructures with relatively large inter-particle distance. The fabricated nanostructures with large inter-particle distance lead pattern transfer into the monomeric metallic nanoparticle array with weak optical coupling. For the active utilization of BCP self-assembly in LSPR, the pattern dimension of BCP should be manipulated to induce the strong optical coupling between metallic nanoparticles [13,14]

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Conclusion