Experimental Study of Transverse Trapping Forces of an Optothermal Trap Close to an Absorbing Reflective Film

Abstract

The optothermal manipulation of micro-objects is significant for understanding and exploring the unknown in the microscale word, which has found many applications in colloidal science and life science. In this work, we study the transverse forces of an optothermal trap in front of a gold film, which is an absorbing reflective surface for the incident laser beam. It is demonstrated that optothermal forces can be divided into two parts: optical force of a standing-wave trap, and thermal force of a thermal trap. The optical force of the standing-wave trap can be obtained by measuring the optical trapping force close to a non-absorbing film with same reflectance. The thermal force can be obtained by subtracting the optical force of the standing-wave trap from the total trapping force of the optothermal trap close to the gold film. The results show that both optical and thermal trapping forces increase with laser power increasing. The optical trapping force is larger than the thermal trapping force, which is composed of convective drag force and thermophoretic force. Further experiment is run to study the composition of thermal force. The result shows that the convective flow is generated later than the thermophoretic flow. The results proposed here are useful for enabling users to optimize optothermal manipulation method for future applications.

On-Chip Optical Trapping with High NA Metasurfaces

“…This geometrical configuration is substantially different from arrangements where thermal effects play a role, both in the near field of plasmonic resonators 50 and in the proximity of a metallic film. 51,52 This is further confirmed by the results of Figure S4, where we show that the particles can be trapped in offset locations with respect to the center of the incident beam. We can therefore exclude meaningful thermophoretic effects in the trapping dynamics presented here.…”

Autonomous nanorobots with powerful thrust under dry solid-contact conditions by photothermal shock

“…At nanoscale, the interaction between two objects in contact is governed by interfacial adsorption and friction, which are induced by van der Waals forces and much stronger than gravity and inertial forces. Conventional nanomotor technologies utilize thrusts from the momentum of particles in the ambient medium, such as photophoretic force 8 , thermophoretic force 9 , optothermal trapping force 10 and chemical fuel (catalysis) propulsion force 11 , and convection-induced force, and they usually produce small thrust (~10 −12 N). Overcoming nanofriction (~10 −6 N) on dry substrates or component contact is a critical challenge [12][13][14] , which cannot be directly realized by these technologies, and thus previous researches mainly investigate nanomotors or nanorobots in fluid environments [8][9][10][11] .…”

“…Conventional nanomotor technologies utilize thrusts from the momentum of particles in the ambient medium, such as photophoretic force 8 , thermophoretic force 9 , optothermal trapping force 10 and chemical fuel (catalysis) propulsion force 11 , and convection-induced force, and they usually produce small thrust (~10 −12 N). Overcoming nanofriction (~10 −6 N) on dry substrates or component contact is a critical challenge [12][13][14] , which cannot be directly realized by these technologies, and thus previous researches mainly investigate nanomotors or nanorobots in fluid environments [8][9][10][11] . Meanwhile, the thrust generated by widely used optical tweezers, originating from momentum transfer of photons, is also too small (~10 −12 N) to overcome the interface friction 15 (Supplementary Note 1), so their applications are also limited to the fluid environments.…”

Autonomous nanorobots with powerful thrust under dry solid-contact conditions by photothermal shock

“…At nanoscale, the interaction between two objects in contact is governed by interfacial adsorption and friction, which are induced by van der Waals forces and much stronger than gravity and inertial forces. Conventional nanomotor technologies utilize thrusts from the momentum of particles in the ambient medium, such as photophoretic force 8 , thermophoretic force 9 , optothermal trapping force 10 and chemical fuel (catalysis) propulsion force 11 , and convectioninduced force, and they usually produce small thrust (~10 −12 N). Overcoming nanofriction (~10 −6 N) on dry substrates or component contact is a critical challenge [12][13][14] , which cannot be directly realized by these technologies, and thus previous researches mainly investigate nanomotors or nanorobots in fluid environments [8][9][10][11] .…”

“…Conventional nanomotor technologies utilize thrusts from the momentum of particles in the ambient medium, such as photophoretic force 8 , thermophoretic force 9 , optothermal trapping force 10 and chemical fuel (catalysis) propulsion force 11 , and convectioninduced force, and they usually produce small thrust (~10 −12 N). Overcoming nanofriction (~10 −6 N) on dry substrates or component contact is a critical challenge [12][13][14] , which cannot be directly realized by these technologies, and thus previous researches mainly investigate nanomotors or nanorobots in fluid environments [8][9][10][11] . Meanwhile, the thrust generated by widely used optical tweezers, originating from momentum transfer of photons, is also too small (~10 −12 N) to overcome the interface friction 15 (Supplementary Note 1), so their applications are also limited to the fluid environments.…”