Optimizing the near‐field and far‐field properties of tips in tip‐enhanced Raman scattering. (2nd May 2021)

• Record Type: Journal Article
• Authors: Sifat, Abid Anjum; Potma, Eric O.
• Other Names: Kiefer Wolfgang guestEditor.; Colomban Philippe guestEditor.; Edwards Howell G. M. guestEditor.
• Is Part Of: Journal of Raman spectroscopy. Volume 52:Number 12(2021)
• Page Start: 2018
• Page End: 2028
• Publication Date: 2021-05-02
• Subjects: finite‐difference time‐domain simulations -- tip‐enhanced Raman scattering; Raman spectroscopy -- Periodicals; 535.846
• DOI: 10.1002/jrs.6113
• Languages: English
• ISSNs: 0377-0486

Abstract

Abstract: The process of tip‐enhanced Raman scattering (TERS) depends critically on the morphology near the apex of the tip used in the experiment. Many tip designs have focused on optimization of electromagnetic enhancement in the near‐field, which is controlled to a large extent by subtle details at the nanoscale that remain difficult to reproduce in the tip fabrication process. The use of focused ion beams (FIB) permit modification of larger features on the tip in a reproducible manner, yet this approach cannot produce sub‐20‐nm structures important for optimum near‐field enhancement. Nonetheless, FIB milling offers excellent opportunities for improving the far‐field radiation properties of the tip‐antenna, a feature that has received relatively little attention in the TERS research community. In this work, we use finite‐difference time‐domain (FDTD) simulations to study both the near‐field and far‐field radiation efficiency of several tip‐antenna systems that can be constructed with FIB techniques in a feasible manner. Starting from blunt etched tips, we find that excellent overall enhancement of the TERS signal can be obtained with pillar‐type tips. Furthermore, by applying vertical grooves on the tip's shaft, the overall efficiency can be improved even more, producing TERS signals that are up to 10‐fold stronger than signals obtained from an ideal (unmodified) sharp tip of 10‐nm radius. The proposed designs constitute a feasible route toward a tip fabrication process that not only yields more reproducible tips but also promises much stronger TERS signals. Abstract : Optimized tip geometries can greatly improve the signal yields in tip‐enhanced Raman scattering (TERS). In this work, various tip designs are simulated, and both their near‐field and far‐field enhancement properties are studied. A particular design is presented, which produces significantly higher TERS signals than what can be obtained with conventional tips.