1. Oxidation barrier for Cu and Fe powder by Atomic Layer Deposition
Véronique Cremers1, Geert Rampelberg1, Ahmed Barhoum2, Perry Walters2, Nathalie Claes3, Thais Milagres de Oliveira3, Guy Van Assche2, Sara Bals3, Jolien Dendooven1, Christophe Detavernier1
1CoCooN Research Group, Department of Solid State Sciences, Ghent University
2FYSC Research Group, Department of Materials and Chemistry, Vrije Universiteit Brussel
3EMAT Research Group, Department of Physics, University of Antwerp
Atomic Layer Deposition (ALD)
ALD is an ultrathin film deposition method based on sequential
self-terminating gas-solid surface reactions. Key advantages of ALD are the capability to deposit uniform and conformal thin films with an excellent thickness control at the atomic scale.
Experiment
Using a thermal ALD process with sequential pulses of trimethylaluminum (TMA) and water (H2O), we deposited a Al2O3 coating on Cu and Fe micron powder. The depositions were performed at T=100°C in a rotary ALD reactor. The aim of the depositions was to protect the powder against oxidation.
Characterization of the coating
HAADF-STEM measurements show a conformal, uniform and pinhole free coating on the Cu and Fe micron sized powder.
(a) (b) .
(a)
HAADF-STEM images of the coated dendritic Cu micron sized powder.
HAADF-STEM images of the coated Fe micron sized powder.
Rotary ALD reactor
Testing the properties of the ALD coating as an oxidation barrier
The ability of the Al2O3 ALD coating to protect the powder against oxidation, was investigated using insitu X-Ray Diffraction (XRD) and thermogravimetric analysis (TGA) during annealing in ambient air up to 800°C. The thickness of the coating was varied in the range from 6-25 nm.
Out of the insitu XRD measurements we observe a clear shift of the Cu and CuO peaks
towards an increased temperature. The shifts increase with increasing thickness of the coating.
CuO
CuO Cu Cu
CuO
CuO
Cu2O
CuO
Cu2O
CuO
Blanco Cu powder
Cu powder coated with 15 nm of Al2O3
TGA of the coated Cu powder.
TGA of the coated Fe powder.
TGA of the coated Fe powder.
The TGA measurements show similar results as the insitu-XRD measurements: the oxidation temperature increases with increasing thickness of the coating. For the Cu powder, a coating of 6 nm causes already a large shift in oxidation temperature, however in case of the Fe powder, a coating of 25 nm is required.
Integrated intensity of the Cu and CuO peak.
Conclusion:
With ALD, we were able to deposit a pinhole free Al2O3 coating on Fe and Cu micron powder. This coating can act as a barrier and protect the powder against oxidation. The oxidation temperature increases with increasing thickness of the coating. For the Fe powder, an Al2O3 coating of 25 nm is required, however for the Cu powder, an Al2O3 coating of only 6 nm causes a shift in oxidation temperature of 200°C.
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