Au₃-Decorated graphene as a sensing platform for O₂ adsorption and desorption kinetics

The adsorption and desorption kinetics of molecules is of significant fundamental and applied interest. In this paper, we present a new method to quantify the energy barriers for the adsorption and desorption of gas molecules on few-atom clusters, by exploiting reaction induced changes of the doping level of a graphene substrate. The method is illustrated for oxygen adsorption on Au₃ clusters. The gold clusters were deposited on a graphene field effect transistor and exposed to O₂. From the change in graphene's electronic properties during adsorption, the energy barrier for the adsorption of O₂ on Au₃ is estimated to be 0.45 eV. Electric current pulses increase the temperature of the graphene strip in a controlled way and provide the required thermal energy for oxygen desorption. The oxygen binding energy on Au₃/graphene is found to be 1.03 eV and the activation entropy is 1.4 meV K^-1. The experimental values are compared and interpreted on the basis of density functional theory calculations of the adsorption barrier, the binding energy and the activation entropy. The large value of the activation entropy is explained by the hindering effect that the adsorbed O₂ has on the fluxional motion of the Au₃ cluster.