摘要
Small gas molecules acting as good capping agents play important roles in controlling the morphologies and surface structures of metal nanocrystals.In the present work,the thermodynamic and kinetic roles of H2 molecules in the morphology of Co nanocrystals were systematically studied by density functional theory(DFT).The Gibbs surface free energies of Co(100),Co(110),and Co(111)at different hydrogen surface coverages were determined by ab initio thermodynamics.The phase diagram of stable H coverage on each plane was obtained and morphology evolution of the Co nanocrystals with various surface hydrogen coverages was predicted by the Wulff construction.Addition of H2 changes the facet stability,generating diverse morphological Co nuclei.The kinetic role of H2 in adatom Co surface diffusion at different H coverages was investigated by DFT.The results suggest that surface H hinders Co surface diffusions,except for Co(100)at 0.56 monolayer coverage.The projected density of states gives deeper insight into the electronic structures of Co adatoms with addition of the surface H atoms,which affect its surface diffusion ability.
基金
We thank the National Natural Science Foundation of China(Major Program 91534201,Nos.21476012 and 21571012)for financial support.The computing time was provided by a scien-tific theme user proposal at the William R.Wiley Environmental Molecular Sciences Laboratory(EMSL),which is a United States Department of Energy national scientific user facility located at PNNL in Richland,Washington.Part of computing time was pro-vided by the National Energy Research Scientific Computing Center(NERSC).D.Mei is supported by the United States Department of Energy,Office of Sciences,Office of Basic Energy Sciences,Division of Chemical Sciences,Geosciences and Biosciences.
