Hydrophobicity of Rare Earth Oxides Grown by Atomic Layer Deposition

Rare earth oxide (REO) atomic layer deposition (ALD) processes are investigated for hydrophobic coatings. Thermal and plasma-enhanced ALD (PE-ALD) Er2O3 and Dy2O3 are developed using the newly synthesized Er and Dy precursors bis-methylcyclopentadienyl-diisopropyl-acetamidinate-erbium and bis-isopropylcyclopentadienyl-diisopropyl-acetamidinate-dysprosium, with H2O and O2 plasma counter oxidants. The Er and Dy precursors show typical ALD growth characteristics with no nucleation incubation, indicating that they are suitable ALD precursors. The hydrophobicities of ALD-grown Er2O3 and Dy2O3 are investigated, together with those of ALD-grown Y2O3, La2O3, and CeO2 that were previously developed for high-k applications. All the ALD-grown REOs show high hydrophobicity, with water contact angles as high as 90°. After annealing at 500 °C in air for 2 h, hydrophobicity is degraded depending on the kind of material; this degradation is related to the hygroscopy of REOs. In addition, we demonstrate the fabrication of a superhydrophobic surface by depositing highly conformal ALD REO films on 3D Si nanowire nanostructures. The Si NWs are conformally coated with ALD Y2O3, yielding a surface with a water contact angle of about 158°. The ALD REOs reported herein should find widespread applicability in the fabrication of robust hydrophobic coatings.