  Linear chains of about 10-13 carbon atoms were predicted to be the most
favorable phase on different metal surfaces prior to graphene nucleation.
However, unlike the graphene that widely studied both theoretically and
experimentally, carbon chains on metal surfaces were not directly studied by
STM yet. Here we fill in the gap and report on STM experiments of linear carbon
chains synthesized on Ni(111) through on-surface coupling of dehydrogenated
propene molecules. Identification of chains was supported with DFT calculations
and the proposed models consist of 12 carbon atoms, possibly covered by
hydrogen atoms. Heating to 580 K leads to dramatic decrease of carbon chains
and new phase appearance - graphene nucleus coexisted with nickel carbide.
After flash annealing to 773 K (temperature of graphene synthesis), a small
number of chains were presented on the Ni(111) surface, together with graphene
islands and nickel carbide. The carbon chains are stable at room temperature
and their mobility was directly observed by STM.
