Particle manipulation based on the controllable light field of graphene nano-butterfly structures

In this Letter, we have proposed a nano-optical convey belt consisting of three sets of graphene nano-butterfly structures (GNBS) with different lengths arranged in a periodic pattern to trap, transport, and sort particles depending on controlling the Fermi level of graphene. The graphene nano-butterfly structure, based on a couple of trapezoids, can form a potential well to capture particles by localized surface plasmon resonance under the excitation of an incident laser. There are three adjustable geometric parameters containing width (W1, W2) and length (L) that make the GNBS have a high degree of design flexibility. Graphene can support surface plasmons in the mid-infrared region, and at the same time, it possesses a more flexible tuning mechanism compared to metals. When the incident light power is 1 mW/μm2 and the resonance wavelength is 10.6 μm, the depth of the potential well is greater than 10KbT for 50 nm particles. Moreover, the sorting of particles with different diameters has also been validated under appropriate power and switching time. Based on the capabilities of capture and sorting verified by numerical analysis, our design offers a new scheme for on-chip optofluidic applications. •An optical conveyor belt based on the periodically arranged graphene nano-butterfly structures is proposed.•The mechanism relies on the tunable surface plasmon resonance via manipulating Fermi energy of graphene.•The feasibility of the particle separation is demonstrated.