title: Template-Stripped Multifunctional Wedge and Pyramid Arrays for Magnetic Nanofocusing and Optical Sensing.
abstract: We present large-scale reproducible fabrication of multifunctional ultrasharp metallic structures on planar substrates with capabilities including magnetic field nanofocusing and plasmonic sensing. Objects with sharp tips such as wedges and pyramids made with noble metals have been extensively used for enhancing local electric fields via the lightning-rod effect or plasmonic nanofocusing. However, analogous nanofocusing of magnetic fields using sharp tips made with magnetic materials has not been widely realized. Reproducible fabrication of sharp tips with magnetic as well as noble metal layers on planar substrates can enable straightforward application of their material and shape-derived functionalities. We use a template-stripping method to produce plasmonic-shell-coated nickel wedge and pyramid arrays at the wafer-scale with tip radius of curvature close to 10 nm. We further explore the magnetic nanofocusing capabilities of these ultrasharp substrates, deriving analytical formulas and comparing the results with computer simulations. These structures exhibit nanoscale spatial control over the trapping of magnetic microbeads and nanoparticles in solution. Additionally, enhanced optical sensing of analytes by these plasmonic-shell-coated substrates is demonstrated using surface-enhanced Raman spectroscopy. These methods can guide the design and fabrication of novel devices with applications including nanoparticle manipulation, biosensing, and magnetoplasmonics.
authors.forename: Shailabh
authors.initials: S
authors.lastname: Kumar
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Johnson
authors.affiliation: Department of Chemistry, Imperial College London , South Kensington, SW7 2AZ London, United Kingdom.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Wood
authors.forename: Tao
authors.initials: T
authors.lastname: Qu
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Wittenberg
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Otto
authors.forename: Jonah
authors.initials: J
authors.lastname: Shaver
authors.affiliation: Department of Chemistry, Imperial College London , South Kensington, SW7 2AZ London, United Kingdom.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Long
authors.forename: Randall H
authors.initials: RH
authors.lastname: Victora
authors.affiliation: Department of Chemistry, Imperial College London , South Kensington, SW7 2AZ London, United Kingdom.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Edel
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Oh
keywords: SERS; magnetic nanofocusing; magnetic trapping; magnetoplasmonics; template stripping
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