A Rotation Fluidization Coupled Atomic Layer Deposition Reactor for Nanoparticle Coating
Authors: Duan Chen-Long , Chen Rong 
Published: February 2020

Atomic layer deposition (ALD) is an attractive approach for atomically controllable and conformal coatings on nanoparticles (NPs) for the fields of catalysts, optical detections, biomedicines, etc.[1] There have been many kinds of ALD reactors for particles.[2] Some of these designs are static reactors which rely on long time precursor diffusion to coat particles. Fluidized bed reactors utilize gas flow to disperse nanoparticles for enhanced gas-solid interactions, though obtaining steady fluidization of nanoparticles and limited precursor residence time are challenges.[3] Rotary reactors disperse particles through rotary agitation and increase precursor usage by a static exposure stage.[4]

In this talk, a rotation fluidization coupled atomic layer deposition reactor will be introduced. Such design allows the fluidization to facilitate the precursor transport in the particle bed and intensify the dynamic breaking up of the particle agglomerates to expose particle surfaces to precursors.[5] In the deposition procedure, the coating process could be expedited due to the enlarged and homogenized void fraction in the particle bed, large gas distribution area and higher particle concentration in the rotating fluidized bed. The rotation not only enhances the gas-solid interactions to stabilize fluidization, but also provides large centrifugal force to break up soft agglomerates together with the fluid drag force derived from gas-solid interactions and the collision between particles. In situ mass spectrometry monitoring of the reaction was performed to optimize the coating process. Under high precursor feed rate, the precursor utilization was improved from below 80% to nearly 100% with thicker rotating bed. The microscale morphology of the coating layers, the macro statistical element mass concentrations and the changes of specific surface area as well as the size distribution after coating confirmed the uniformity and conformity of coatings on individual particles. As an example, magnetic Fe3O4 nanoparticles have been uniformly coated with ultrathin Al2O3 passivation layers using this reactor. With 5nm coating layer, the nanoparticle could be stable under oxidation resistance with minimum magnetization loss (less than 10%). This is quite attractive in practical magnetic based biomedical applications. Well controllable amorphous Al2O3 passivation layers were also deposited on crystalline AlH3 particles to postpone their decompose process, which could enhance the safety storage or transportation of these energetic materials.

References:

[1] C. Marichy, M. Bechelany, N. Pinna, Advanced Materials, 24 (2012) 1017-1032.

[2] D. Longrie, D. Deduytsche, C. Detavernier, Journal of Vacuum Science & Technology A, 32 (2014).

[3] D.M. King, X.H. Liang, A.W. Weimer, Powder Technology, 221 (2012) 13-25.

[4] D. Longrie, D. Deduytsche, J. Haemers, K. Driesen, C. Detavernier, Surface & Coatings Technology, 213 (2012) 183-191.

[5] C.-L. Duan, X. Liu, B. Shan, R. Chen, The Review of scientific instruments, 86 (2015) 075101-075101.