Growth and Characterization of Al₂O₃ Atomic Layer Deposition Films on sp²-Graphitic Carbon Substrates Using NO₂/Trimethylaluminum Pretreatment

The growth of Al2O3 films by atomic layer deposition (ALD) on model sp(2)-graphitic carbon substrates was evaluated following a nitrogen dioxide (NO2) and trimethylaluminum (TMA) pretreatment to deposit an Al2O3 adhesion layer. Al2O3 ALD using TMA and water (H2O) as the reactants was used to grow Al2O3 films on exfoliated highly ordered pyrolitic graphite (HOPG) at 150 °C with and without the pretreatment procedure consisting of five NO2/TMA cycles. The Al2O3 films on HOPG substrates were evaluated using spectroscopic ellipsometry and electrochemical analysis to determine film thickness and quality. These experiments revealed that five NO2/TMA cycles at 150 °C deposited an Al2O3 adhesion layer with a thickness of 5.7 ± 3.6 Å on the HOPG substrate. A larger number of NO2/TMA cycles at 150 °C deposited thicker Al2O3 films until reaching a limiting thickness of ∼80 Å. Electrochemical impedance spectroscopy (EIS) measurements revealed that five cycles of NO2/TMA pretreatment enabled the growth of high quality insulating Al2O3 films with high charge-transfer resistance after only 20 TMA/H2O Al2O3 ALD cycles. In contrast, with no NO2/TMA pretreatment, EIS measurements indicated that 100 TMA/H2O Al2O3 ALD cycles were necessary to produce an insulating Al2O3 film with high charge-transfer resistance. Al2O3 films grown after the NO2/TMA pretreatment at 150 °C were also demonstrated to have better resistance to dissolution in an aqueous environment.