Conformality of ALD – ALD into nanoporous materials

A direct and macroscopic illustration of the excellent conformality of ALD is shown below. Tissue paper was coated with aluminum oxide using ALD. After combustion of the cellulose template with a lighter, a network of hollow alumina tubes is left behind. This experiment clearly demonstrates the potential of ALD for coating porous and fibrous materials. 

"Original" tissue paper

Al2O3 ALD coated tissue paper

Making a tissue hydrophobic...

"Original" tissue paper

Al2O3 ALD coated tissue paper

We have developed two approaches to investigate the conformality of ALD processes:

              setup for an ALD conformality experimentA ALD deposition
A schematic of a macroscopic test structure (left) and the ALD deposition (right). 
The color shift from light-blue to yellow inside the trench is due to the macroscopic trench.

 1- When performing ALD at low pressures (i.e. in a pump-type reactor), molecular flow persists up to millimeter sized structures, and therefore macroscopic test structures can be used for quantifying the conformality of ALD processes. This simple and efficient approach allowed us to investigate the conformality of plasma enhanced ALD (Dendooven et al., J. Electrochem. Soc. 157(4) G111 (2010), J. Musschoot et al., Surface and Coatings Technology 206 (2012) 4511) and to characterize and model the effect of the sticking probability of precursor molecules on the conformality (Dendooven et al., J. Electrochem. Soc. 156, P63 (2009))

 illustration of ALD in nanopores

2 - Nanoporous thin films were used as model systems to explore the conformality of ALD inside nanopores (see e.g. Dendooven et al., J. Phys. Chem. C 115(2011) 6605, Dendooven et al., Chem. Mater. 24, 1992 (2012)).  

 

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