Mechanistic modeling study of atomic layer deposition process optimization in a fluidized bed reactor

Surface modification of nanoparticles has attracted much attention owing to its superior ability to design nanoparticles with unique physical, chemical, or biological properties. Atomic layer deposition (ALD) has shown great promise in the precise surface decoration of nanoparticles. However, the large surface area of nanoparticles requires a large quantity of precursors, and the nonuniform interstitials among the particles limit the precursor diffusion and lead to long process times. Fluidized bed reactors (FBRs) have been proven applicable for ALD on nanoparticles owing to its high gas-solid interactions and potential scalability for practical production. The ALD process in a fluidized bed is sophisticated and with many variables, resulting in long and tedious process optimization through substantial experimental trials. In this paper, the ALD process in a FBR-ALD is investigated through mechanistic modeling using computational fluid dynamics and theoretical calculations of molecular flow diffusion. The result shows that the minimum pulse time and the precursor waste are inversely proportional to the increase in precursor mass fraction. The optimal precursor utilization is obtained under the minimum fluidizing velocity. Because the fluid kinetics is independent of the specific structure, the mechanistic modeling study is instructive for the process optimization of FBR-ALD. (C) 2016 American Vacuum Society.