Optical trapping using T-shaped copper nanoantennas

Abstract

Nanophotonic devices are the very fundamental functions in a photonic integrated circuit, which have led to a revolutionary development in many fascinating applications. Toward this end, researches have demonstrated different kinds of nanostructures that are made from plasmonic and dielectric materials, including optical waveguides, ring resonators, photonic crystal resonators, nanoapertures, and nanoantennas. Plasmonics is considered to be the most promising candidate for the next generation of integrated chip-scale technology. In particular, using plasmonic nanoantennas, optical field enhancement and confinement can be achieved with deeply subwavelength range, leading to strong light–matter coupling and with enhanced optical forces. Another reason for the use of plasmonics is its ease of integration with other photonic waveguides for optical information processing at nanoscales. As predicted by Maxwell’s equations, light fields have linear momentum and thus can generate optical forces on tiny objects via momentum transfer. Nanoantennas utilize optical forces to trap and manipulate small particles at relatively low incident intensities. For the field of nanoscience, the on-chip ability to handle single nanoparticles at the integrated devices is quite advantageous. Various nanoparticles have been trapped, including polystyrene and gold nanoparticles. Traditionally, gold has been used as the material of choice in plasmonics because of their relatively good optical properties and chemical stability. Advances in plasmonic materials research have ushered in alternative materials. Among them, copper particularly has attracted significant attention because of its good plasmonic properties and abundant quantity. Copper is comparably cheap, which is compatible with industry-standard fabrication processes, such as the complementary metal-oxide-semiconductor (CMOS) technology, and has been widely used in microelectronics. In this work, we demonstrate a coupled T-shaped Cu plasmonic nanoantenna for the optical trapping of single dielectric nanoparticles and investigate its plasmonic and optical properties interacting with an infrared trapping laser. The electric field enhancement (and thus optical force), temperature rise, and induced fluid velocity it provides are quite similar in comparison to those provided by the Au nanoantenna design. Cu is cheap and compatible with standard microelectronic fabrication technologies. Large local field enhancements mean that low incident power can be utilized. In addition, we show that the oxidization effects on the Cu surface have a weak influence on trapping characteristics compared to pure Cu nanoantenna, and the Si heat sink substrate can reduce the temperature rise in water. Our results verify that T-shaped Cu nanoantennas are robust as nanophotonic devices for optical information manipulation at nanoscales. They could also be used to manipulate and investigate single quantum emitters and small molecules. Beyond this, we anticipate a multitude of topics of Cu nanostructures could be performed for future optical computer investigation and lab-on-a-chip application.