Theoretical Study of Atomic Layer Deposition Reaction Mechanism and Kinetics for Aluminum Oxide Formation at Graphene Nanoribbon Open Edges

The atomic layer deposition (ALD) reaction of Al2O3 at graphene nanoribbon open edges has been studied theoretically by ab initio density functional theory and transition state rate theory. The structures of reactants, adsorption complexes, products, and transition states of the model reactions were optimized at the B3LYP/6-311G(d,p) level of theory. The potential energy profiles have revealed the mechanisms of the chemical adsorption and the dissociation reactions. The potential barriers of the adsorption reactions for the zigzag edge (eq 1z) and armchair edge (eq 1a) are predicted to be 1.5 and 6.5 kcal/mol, respectively, while in the following steps the adsorption process is a barrierless reaction and the dissociation process undertakes the release of CH4 via a tight transition state. The reaction rates for all five solid-gas interface reaction steps have been calculated in the temperature range 300-1000 K and the pressure range 0.1 Torr-10 atm. The result shows that the adsorption rate of the zigzag edge with H2O is much faster than that of the armchair edge with H2O. Theoretical prediction for reaction temperature and pressure is in good agreement with the experimental conditions. This work outlines a way by ALD to selectively decorate and passivate the zigzag and armchair edges of graphene nanoribbons, which have significantly different electrical and magnetic properties.