Plasmonic field enhancement effect of tip sharpness on bowtie structure with curved side arm

Abstract Plasmonic bowtie nanostructures have been widely used to enhance electric fields by concentrating the electromagnetic field within nanoscale gaps. Various structural modifications of the bowtie geometry have been proposed to achieve stronger light confinement within the nanogaps. Among them, bowtie structures with curved arms have demonstrated a significantly higher enhancement factor (EF) compared to those with linear arms. However, although tip sharpness plays a critical role in electric field enhancement, the tip sharpness of the curved bowtie has not been systematically examined. In this study, we investigated the influence of tip sharpness on the EF of curved bowtie nanostructures using finite-difference time-domain (FDTD) simulations. We systematically optimized four structural parameters, including the tip sharpness and curvature of the side arms, and evaluated their impact on the resulting EF. The curved bowtie with sharp tips showed substantial increases in the EF (5.33 × 10 3 ), which is approximately 26% higher than that of the normal bowtie with sharp tips (4.23 × 10 3 ), whereas the bowtie with blunt tips exhibited an even lower EF than those with linear arms. These results highlight the critical role of the tip sharpness in achieving high-field enhancement. This study underscores the need for advanced nanofabrication techniques, such as domino lithography, to realize sharp tips, which are often limited by proximity effects in conventional photolithography and electron-beam lithography (EBL). Our findings provide valuable insight into the design of high-performance plasmonic nanostructures and pave the way for their practical applications in biosensing and nanophotonic technologies.