Evanescent Optothermoelectric\nTrapping: Deeper Potentials\nat a Largescale

Surface plasmons (SP) and their mediated effects have\nbeen widely\nused to manipulate micro- and nanoscale objects of dielectric and\nmetallic nature. In this work, we show how SP excitation can be used\nto induce thermofluidic and thermoelectric effects to manipulate colloidal\ndynamics on a large scale. In an evanescent plasmonic trap, temperature\ngradients induce a fluid flow that can facilitate particle accumulation.\nHowever, large out-of-plane flows expel particles from the trap, resulting\nin a shallow trap potential. Here, we numerically demonstrate how\nadding thermoelectric fields can overpower the optical and hydrodynamic\nforces to achieve a stable nanoparticle assembly at low excitation\npowers. We calculate the corresponding optical, fluidic, and thermoelectric\ntrapping forces and potentials. These potentials can be enabled with\nnonresonant SP excitation and do not require careful optical alignment.\nAn experimental validation of the evanescent OTE trap demonstrates\na compact assembly of colloids, implying deeper potentials. Thus,\nwe explain the mechanism of how, despite weak optical intensities\nand forces, a sufficient trapping force can be supplied via the evanescent\noptothermoelectric trap to obtain large-scale reversible nanoparticle\nassemblies, irrespective of their shape, size, or material.