Understanding and controlling plasmon-induced convection

Abstract

The heat generation and fluid convection induced by plasmonic nanostructures is attractive for optofluidic applications. However, previously published theoretical studies predict only nanometre per second fluid velocities that are inadequate for microscale mass transport. Here we show both theoretically and experimentally that an array of plasmonic nanoantennas coupled to an optically absorptive indium-tin-oxide (ITO) substrate can generate 4micro-metre per second fluid convection. Crucially, the ITO distributes thermal energy created by the nanoantennas generating an order of magnitude increase in convection velocities compared with nanoantennas on a SiO 2 base layer. In addition, the plasmonic array alters absorption in the ITO, causing a deviation from Beer-Lambert absorption that results in an optimum ITO thickness for a given system. This work elucidates the role of convection in plasmonic optical trapping and particle assembly, and opens up new avenues for controlling fluid and mass transport on the micro-and nanoscale.

Characterization of the near-field and convectional transport behavior of micro and nanoparticles in nanoscale plasmonic optical lattices

“…24 Toussaint's group calculated the convection flow induced by an array of nanoantennas, and concluded that the optically absorptive, thermally conductive indium tin oxide (ITO) could efficiently distribute the thermal energy to generate an increase in convection velocity. 25 As a result, high fluidic velocities of the order of $lm/s could be achieved. They also demonstrated that the optically and thermally induced forces could be tuned to generate various distinct states of trapping, including lateral delocalization, and hexagonally closed-packed clusters.…”

“…25 These microspheres, rather than nanospheres with a diameter of 500 nm, were used because they yielded consistent results in the power range of interest, especially at low optical powers. Measurements performed using nanospheres with a diameter of 500 nm suffered from the excessive Brownian motion of the nanospheres.…”

“…These two features distinctly differed from Toussaint's work on the arrays of bowtie nanoantennas. 25 …”

Optofluidic vortex arrays generated by graphene oxide for tweezers, motors and self-assembly

“…Abundant experimental cases 14,15 have shown that individual trapping at the vortex center is stable, but to the best of our knowledge no clear theoretical analysis has been given. The other type is through buoyancy convection, generated by thermal gradient in the liquid from opto-electrical, 18 − 22 or plasmonic 23 heating. Buoyancy convection can flow in the vertical direction with a large and fixed scale, leading to extensive rotation in the vortices and high-throughput aggregation and migration outside the vortices.…”

Local field enhancement and thermoplasmonics in multimodal aluminum structures

“…This active research field, called thermoplasmonics, could potentially lead to breakthroughs in several fields like hyperthermia-induced apoptosis in oncology 24 , nanochemistry 25 or thermo-hydrodynamically assisted plasmonic trapping and manipulation 26,27 , where the onset of temperature gradients is critical. The power dissipated in a nanostructure is a complex interplay between the optical near-field intensity and the material properties 9,28 .…”