Spot formation and alignment of silver nanowires using ultrasonic stage

In this work, we report the use of a low-frequency circular ultrasonic stage to form a circular spot of silver nanowires (AgNWs) at the stage center and to align AgNWs on the stage surface radially. The manipulations are implemented within aAgNW suspension droplet at the center of the ultrasonic stage. The operating frequency of the ultrasonic stage is 21.3 kHz and the AgNWs have diameter of 100 nm and length of 30 μm approximately. The spot diameter and thickness are several hundred microns to several microns, respectively. After the droplet dries out by natural evaporation without ultrasound, the spot and radial alignment have little change in the size and pattern. Principle analyses show that the spot formation and radial alignment of AgNWs are caused by the acoustic streaming in the radial direction in the droplet.