Carbon Chain Length Dependence of Graphene Formation via Thermal Decomposition of Alkenes on Pt(111)
Abstrakt
Graphene layers were prepared by isothermal decomposition of different unsaturated hydrocarbons on Pt(111) single crystal surface and characterized by SRPES and LEED. Four different alkenes (ethene, propene, 1pentene, 1-hexene) were used in order to elucidate the eventual role of the carbon chain length in the graphene growth kinetics.
The process of dehydrogenation was followed stepwise from sample temperatures of 160 K (molecular adsorption) to over 1000 K, at which the surface carbon remains almost exclusively in the form of graphene. Reaction intermediates were identified for each alkene and the corresponding reaction rates were determined.
The attachment of carbon during the thermally activated growth of graphene islands on Pt(111) and similar metals is predicted to proceed via prior formation of small clusters or chains in order to overcome a large energetic and spatial barrier which exists between a single adsorbed C atom (monomer) and the graphene layer. In accordance with this assumption the growth process is shown to depend on the size of the initial reactant molecule, with a distinct preference for Cs species.