  Surface plasmons (SP) and their mediated effects have been widely used to
manipulate micro- and nanoscale objects of dielectric and metallic nature. In
this work, we show how SP excitation can be used to induce thermofluidic and
thermoelectric effects to manipulate colloidal dynamics on a large scale. In an
evanescent plasmonic trap, temperature gradients induce fluid flow that can
facilitate particle accumulation. However, large out-of-plane flows expel
particles from the trap, resulting in a shallow trap potential. Here, we
numerically demonstrate how adding thermoelectric fields can overpower the
optical and hydrodynamic forces to achieve a stable nanoparticle assembly at
low excitation powers. We calculate the corresponding optical, fluidic, and
thermoelectric trapping forces and potentials. These potentials can be enabled
without resonant SP excitation, which requires careful optical alignment. Thus,
we explain the mechanism of how, despite weak optical intensities and forces,
sufficient trapping force can be supplied via the evanescent optothermoelectric
trap to obtain large-scale reversible nanoparticle assemblies, irrespective of
their shape, size, or material.
