Rotary reactor for atomic layer deposition on large quantities of nanoparticles

Abstract

Challenges are encountered during atomic layer deposition (ALD) on large quantities of nanoparticles. The particles must be agitated or fluidized to perform the ALD surface reactions in reasonable times and to prevent the particles from being agglomerated by the ALD film. The high surface area of nanoparticles also demands efficient reactant usage because large quantities of reactant are required for the surface reactions to reach completion. The residence time of the reactant in a fluidized particle bed reactor may be too short for high efficiency if the ALD surface reactions have low reactive sticking coefficients. To address these challenges, a novel rotary reactor was developed to achieve constant particle agitation during static ALD reactant exposures. In the design of this new reactor, a cylindrical drum with porous metal walls was positioned inside a vacuum chamber. The porous cylindrical drum was rotated by a magnetically coupled rotary feedthrough. By rotating the cylindrical drum to obtain a centrifugal force of less than one gravitational force, the particles were agitated by a continuous “avalanche” of particles. In addition, an inert N2 gas pulse helped to dislodge the particles from the porous walls and provided an efficient method to purge reactants and products from the particle bed. The effectiveness of this rotary reactor was demonstrated by Al2O3 ALD on ZrO2 particles. A number of techniques including transmission electron microscopy, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy confirmed that the Al2O3 ALD film conformally coats the ZrO2 particles. Combining static reactant exposures with a very high surface area sample in the rotary reactor also provides unique opportunities for studying the surface chemistry during ALD.

Surface modification of acetaminophen particles by atomic layer deposition

“…ALD on acetaminophen particles was carried out in a rotary ALD reactor as described by McCormick et al 2007, shown in Figure 1, using static exposures of reactants at temperature around 100 °C. The reactor assembly consisted of a stainless steel vacuum sealed main chamber with heater, vacuum pump and pump line separated from the vacuum chamber by a gate valve.…”

“…Layer-by-layer growth allows one to change the material composition abruptly after each step (George, 2010;Miikkulainen et al, 2013). ALD producing conformal nanometer scale films is a well demonstrated method on various particles with different size and composition (Ferguson et al, 2000;Ferguson et al, 2004a;Ferguson et al, 2004b;Hakim et al, 2005;McCormick et al, 2007;King et al, 2008;Nevalainen et al, 2009;King et al, 2012;Longrie et al, 2014). Furthermore, ALD on powder substrates is scalable for manufacturing.…”

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

“…The term "static" is used here to refer to the sample inside the reactor being exposed to non-flowing (i.e., static) precursors. The reactor itself can be rotating, or the particles inside the reactor can be agitated in various other ways [44,66,67], although simple static reactors without any moving parts have successfully been used to coat catalysts and SOFC electrodes [68][69][70][71][72][73][74][75]. In a static reactor, the sample is held in a sealed vessel that can be evacuated.…”

“…However, since only a few ALD cycles are required to reach substantial weight loadings (see Section 1.4), long exposure and purge times (on the order of 10's of minutes or perhaps even hours) may be acceptable, as demonstrated by the fixed bed static reactor design developed by researchers at BASF [56]. It should be noted that exposure times can be shortened by using agitated or rotating bed reactors [44,66,67], using thin pelletized samples (Figure 3) [70][71][72][73], and increasing precursor partial pressures [56,57].…”

Scalable Production of Nanostructured Particles using Atomic Layer Deposition

“…Despite the fact that the fluidized bed reactor provided a good scalability potential in terms of the batch handling capabilities, the high total surface area of the powdersand the subsequent need for large amounts of precursor dosing (due to the residence time of the gaseous precursor in the fluidized bed)-called for research focussed on more efficient utilization of the precursor. The use of a rotary reactor operated at very low pressures (less than 133 Pa) was suggested (McCormick et al, 2007), in an effort to obtain a static exposure scheme and proper mixing during deposition. In this reactor, fluidization and agitation of the particles is achieved by rotation, and therefore a constant gas flow is not required.…”