Abstract
In this report, gold cauldrons are proposed and proved as efficient candidates for plasmonic tweezers. Gold cauldrons benefit from high field localization in the vicinity of their apertures, leading to particle trapping by a reasonably low power source. The plasmonic trapping capability of a single gold cauldron and a cauldrons cluster are studied by investigating the plasmon-induced variations of the optical trap stiffness in a conventional optical tweezers configuration. This study shows that the localized plasmonic fields and the consequent plasmonic forces lead to enhanced trap stiffness in the vicinity of the cauldrons. This observation is pronounced for the cauldrons cluster, due to the additive plasmonic fields of the neighboring cauldrons. Strong direct plasmonic tweezing by the gold cauldrons cluster is also investigated and confirmed by our simulations and experimental results. In addition to the presented plasmonic trapping behavior, gold cauldrons benefit from a low cost and simple fabrication process with acceptable controllability over the structural average dimensions and plasmonic behavior, making them attractive for emerging lab-on-a-chip optophoresis applications.
Highlights
In order to investigate the functionality of the realized gold cauldrons to enhance the optical tweezers force, first we study the trap stiffness modulation of an optically trapped particle at the vicinity of our plasmonic structures
We introduced a controllable fabrication of gold cauldrons, as 3D cavity-like plasmonic structures, using microsphere lithography method
We investigated the plasmonic behavior of the fabricated cauldrons clusters by simulation and near infrared spectroscopy, and proved high plasmonic field localization on the apertures, owing to the additive fields of the neighboring cauldrons
Summary
Mohammad Ali Khosravi[1,5], Abolfazl Aqhili[1,5], Shoaib Vasini[2], Mohammad Hossein Khosravi[3], Sara Darbari1* & Faegheh Hajizadeh[3,4]. Plasmonic tweezers take advantage of the strong plasmonic field gradient at the vicinity of the metal/dielectric interface, leading to a strong gradient force at a lower laser power and without the need for light focusing equipment. In this line of research, there are different plasmonic tweezers reports, using different metallic structures, such as nanodiscs[9,10], nano-holes[11,12,13,14], nano-pillars[15], nano-pyramids[16], nano-triangles[17,18,19], micro/nano-stripes[20], micro/nano-rings[21], as well as graphene-based s tructures[22,23,24]. We prove successful plasmonic trapping of polystyrene (PS) particles with radius of 500 nm, utilizing the presented gold cauldrons as the plasmonic structures
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