摘要：Acoustic manipulation technology has the advantages such as less heat damage to samples, no selectivity to sample material, and simple device structures. Conventional acoustic manipulation technology uses the acoustic radiation force to trap micro particles, and cannot be applied to the manipulations of individual nanowires (NWs) because the acoustic streaming usually flushes a trapped NW away. Here we propose a principle of acoustic nano-manipulation which utilizes controlled mobile acoustic streaming eddies, and demonstrate that the manipulators based on this principle, can effectively suck, align and trap an individual NW in a water suspension film on substrate surface. We also show that the trapped and aligned NW can be stably transferred to a desired location along an arbitrary path (2D or 3D) in the water film on substrate surface, by moving the manipulator system mounted on an XYZ stage.
Our experiments are conducted under an optical microscope (VHX-1000, Keyence). AgNWs used in the NW suspension are about 100 nm thick and several ten to more than one hundred microns long. Basic configuration of the ultrasonic manipulators is that a micro-rod, used for generating the mobile acoustic streaming eddies, is mechanically excited by an acoustic needle, and the acoustic needle by a Langevin transducer; vibration direction of the microrod is parallel to the substrate surface. To increase the manipulation stability, the manipulator systems operate in non-resonance. The operating frequency is between 100 kHz ~ 150 kHz, and driving voltage is not higher than 30 Vp-p. A trapped NW and the manipulator may be in contact or without contact, and the micro-rods for the contact and noncontact trapping have different shape.
The technology reported here has potential applications in the assembling of nano/micro structures, and measurement of nano/micro scale materials.