Study of ultrasonic vibration-assisted particle atomic layer deposition process via the CFD-DDPM simulation

Abstract

Atomic layer deposition (ALD) is a unique surface modification technology by providing conformal ultrathin films on particulate materials. Fluidized bed ALD (FB-ALD) shows excellent scale-up potential for the mass production of particle coating, where different external fields have been developed to enhance the fluidization quality of cohesive micro-nanoparticles. Ultrasonic vibration is a promising assisting method for it can promote effective agglomeration breakage as well as enhance the heat and mass transfer rates in the reactor. In this paper, a multiscale computational fluid dynamics (CFD) simulation based on the dense discrete phase method (DDPM) is developed to study the ultrasonic vibration-assisted FB-ALD process. Dynamic mesh method and discrete element method are adopted to introduce the ultrasonic field and compute the particle movement with an accurate description of particle-particle and particle-vibrating wall interactions. Results show that ultrasonic vibration effectively promotes the contact efficiency between uncoated particles and precursor molecules in the precursor pulsing process, leading to higher deposition rates and coating uniformity. During the purge process, ultrasonic vibration also increases the removal rate of ALD byproducts, thus shortening the purge time by 25%. Through the CFD-DDPM model, the maximum precursor utilization rate for uniform coating can be predicted quantitatively under a given precursor mass fraction and a ratio of the pulse time to the theoretical saturation time. The multiscale numerical model developed in this work can be adapted to optimize the process conditions for the scale-up of FB-ALD reactors.