Near Field Properties of Coupled Metallic Nanostructures

Anran Li School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore Sivan Isaacs Department of Electro-Optic Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel Chihao Liow School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore Ibrahim Abdulhalim Department of Electro-Optic Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel Shuzhou Li School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore

Noble metallic nanostructures have great potential in optical sensing applications in the visible and the near-infrared frequencies, especially for water sensing. Hot spots with a large electric field enhancement usually come in small volumes, limiting their applications in surface-enhanced spectroscopy. Using a finite-difference time-domain method, we demonstrate that spiky nanoparticle dimers (SNPD) can provide hot spots with both large electric field enhancement and large volumes because of the pronounced lightning rod effect of spiky nanoparticles. We find that the strongest electric fields lie in the gap region when SNPD is in a tip-to-tip (T–T) configuration. The enhancement of electric fields intensity (|E|²/|E₀|²) in T–T SNPD with a 2 nm gap can be as large as 1.21 × 10⁶. The hot spot volume in T–T SNPD is almost 7 times and 5 times larger than those in the spike dimer and sphere dimer with the same gap size of 2 nm, respectively. Our results provide a strategy to obtain hot spots with both intense electric fields and large volume by adding a bulky core at one end of the spindly building block in dimers. Using the same methodology, recently we have also investigated electromagnetic field enhancement in the gap between a flat metal surface and gold nanoparticle in several geometries. Both simulation results and experimental results show high potential for enhanced spectroscopic sensing and other optoelectronic applications.

lian0092@e.ntu.edu.sg