title: Effects of Thermal Electronic Excitations on the Diffusion of Oxygen Adatoms on Graphene.
abstract: We conduct first-principles calculations to study oxygen diffusion on the graphene surface as a function of temperature up to 3000 K. The minimum energy migration path and the corresponding activation energy are determined by the nudged elastic band method with explicit inclusion of thermal electronic excitations. Below 1000 K the activation energy for epoxy oxygen to migrate remains close to its room temperature value (0.72 eV). Above 1000 K the activation energy decreases near linearly with temperature, from 0.70 eV at 1000 K to 0.47 eV at 3000 K. We show that this reduction originates from thermal electronic excitations. In particular, the effect is determined by the large contrasts in the electronic structures of the initial and transition states: the transition state exhibits much larger electronic density of states near the Fermi level and is more susceptible to thermal electronic excitations. The reduction in activation energy leads to appreciable enhancement in the diffusivity of oxygen adatoms. A moderate decrease in the vibrational prefactor, also caused by thermal electronic excitations, does not alter this trend. These findings may facilitate future works to accurately describe the dynamics of O adatoms on graphene at high T, which are critical for determining surface thermodynamic properties such as equilibrium coverage.
authors.affiliation: College of Earth Sciences, University of Chinese Academy of Sciences , Beijing 100049, China.|Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Sun
authors.affiliation: College of Earth Sciences, University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Yao
authors.affiliation: CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche , Via Bonomea 265, 34136 Trieste, Italy.|SISSA , Scuola Internazionale Superiore di Studi Avanzati, via Bonomea 265, I-34136 Trieste, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Fabris