Quasi-BIC in Split Ring Metasurfaces for Optical Trapping of Nanoparticles

Metasurfaces offer unique capabilities in manipulating electromagnetic waves, making them highly useful in various nanophotonic applications. This paper presents split ring metasurfaces made of amorphous silicon designed for optical trapping of smaller nanoparticles. The asymmetry in the structure is achieved by cutting a certain portion of the ring, leading to a quasi-bound state in the continuum (quasi-BIC) at 1064 nm, with a quality factor (Q-factor) of 227. A maximum field enhancement of around 54 is obtained in the gap between the split ring, which acts as a hotspot for the optical trapping of nanoparticles. The split ring metasurface provides two hotspots in a single unit cell, allowing an individual nanoparticle to be trapped at each hotspot. It is shown that a 50 nm polystyrene (PS) bead can be stably trapped using a moderate input intensity. Additionally, the study explores how varying the geometric parameters of the split ring influence the quasi-BIC characteristics. The proposed split ring metasurface can function as nanotweezers, enabling simultaneous trapping of multiple nanoparticles.