Formation, Optical Properties and Applications of Edge Gold-Coated Silver Nanoprisms
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Formation, Optical Properties and Applications of Edge Gold-Coated Silver Nanoprisms Mohammad M. Shahjamali1,2 Michael Salvador3,4 Negin Zaraee1 1
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA. 2 School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. 3 Department of Chemistry, University of Washington, Seattle, Washington 98195, USA. 4 Instituto de Telecomunicações, Instituto Superior Técnico, Av. Rovisco Pais, P-1049-001 Lisboa, Portugal ABSTRACT A facile, high-yield synthesis of edge gold-coated silver nanoprisms (GSNPs) with a gold nanoframe as thin as 1.7 nm and their comprehensive characterizations by using various spectroscopic and microscopic techniques is introduced. The GSNPs exhibit remarkably higher stability than silver nanoprisms (SNPs) and are therefore explored as effective optical antennae for light-harvesting applications. When embedded into a bulk heterojunctions film of P3HT:PCBM, plasmonic GSNPs with a localized surface plasmon resonance (LSPR) around 500 nm can effectively act as optical antennae to enhance light harvesting in the active layer. As a result, we measured up to 7-fold enhancement in the polaron generation yield through photoinduced absorption spectroscopy. Owing to the high stability and strong field enhancement, the presented GSNPs feature great potential as plasmonic probes for photovoltaic applications and LSPR sensing. INTRODUCTION The extraordinary optical properties of noble metal nanoparticles (NPs) have led to significant interest into potential application as subwavelength optical elements in a diverse range of technologies across all scientific fields. These optical properties are governed by the localized surface plasmon resonance (LSPR), i.e., the coherent oscillation of the metal’s conduction band electrons induced by the electromagnetic field of incident light.1 The high sensitivity of metal NPs’ LSPR to the variation of shape, size, dielectric constant of the metal, and dielectric constant of the surrounding medium has resulted in extensive development of noble metal nanostructures for technologically relevant applications including molecular and cellular imaging,2 plasmon-enhanced photocatalysis,3-5 and chemical and biological sensing.6, 7 It has been demonstrated that anisotropic silver nanostructures, including nanoprisms,8, 9 nanocubes,10 etc, are capable of showing higher LSPR sensitivities and stronger field enhancement due to the intense surface charge polarizability arising from their anisotropic shapes. However, a major problem with many polyhedral noble metal NPs is their unstable vertices that are often related to high-energy facets. As a design criterion for developing a reliable LSPR-based sensing platform, the plasmonic nanostructures need to not only feature high dielectric sensitivity, but also be structurally robust and amenable to chemical functionalization without undergoing morphology changes before integrated into any dev
