Pattern deposition on an ultrasonic actuator

Abstract

In recent years, one has observed an increasing interest in the pattern deposition of colloidal particles from an evaporating carrier liquid, a process associated with the coffee ring effect. In particular, various companies employ pattern deposition for the fabrication of medium resolution conducting circuits for various applications from touch screens to antennae. In this talk, I will discuss the pattern deposition of solute particles off an evaporating solution film atop an ultrasonic actuator. We use the actuator to generate a MHz vibration in the form of a Rayleigh surface acoustic wave (SAW), propagating in the solid substrate and under the solution film at a phase velocity of 4000 m/s. Transfer of momentum from the SAW to the neighboring solution translates to an acoustic stress, supporting various flow mechanisms, i.e., acoustic streaming, and altering the geometry of the evaporating film. The interplay between the capillary, acoustic, and evaporative stresses within the solution determines the transport dynamics of the solute particles in the solution and the state of pattern deposition on the solid substrate. Using different SAW power levels we alter the dynamic state of the deposition, changing the qualitative geometry of the deposited patterns from dots to stripes and from stripes to solid films.