First-principles investigation on the bonding mechanisms of two-dimensional carbon materials on the transition metals surfaces

Understanding the bonding mechanisms between carbon and metal atoms are crucial for experimental preparations of low-dimensional carbon materials and metal/low-dimensional carbon composites. In this work, various bonding modes are summarized through a systematical study on the adsorptions of graphene and graphyne on surfaces of typical transition metals. If a carbon atom is adjacent to a transition metal atom, the C-p(z) electron may form a covalent bond with a s or a d electron of the transition metal atom. When a metal atom lies below two carbon atoms of graphene or graphyne, two new covalent bonds may be formed between the metal atom and the two carbon atoms by two C-p(z) electrons with two d or two sd-hybridized orbital electrons of the transition metal atom. Specially, the two covalent bonds are almost identical by two sd-hybridized orbital electrons, but the two bonds should show significant differences by two d-orbital electrons. Three covalent bonds formed between three carbon atoms and one sd(2)-hybridized Ti atom are observed on the graphyne/Ti (0001) interface. In addition to the existing sp and sp(2) hybridizations, the carbon atom may show the sp(3) hybridization after graphyne adsorbs on some metals. These research results are obtained through a comprehensive analysis of the adsorption configuration, the differential charge density, and the projected of states from the first-principles calculations in the present study.