Transformation of starphenes into amorphous graphene nanoribbons with attached carbon chains under electron irradiation†

Transformation of starphene molecules with four acene arms on a graphene substrate under electron irradiation is studied by molecular dynamics (MD) simulations using the CompuTEM algorithm. A set of various pure carbon molecules ranging from carbon propeller-like molecules with four long carbon atomic chains connected to the central polycyclic aromatic region to amorphous graphene nanoribbons with short attached chains are observed after hydrogen removal by electron impacts. A two stage atomistic mechanism is revealed for the transformation. The first stage is spontaneous breaking of bonds between zigzag atomic rows in starphene arms during hydrogen removal with formation of atomic carbon chains. The second stage is formation of new carbon–carbon bonds between neighboring chains that leads to an increase in the size of the central polycyclic region that survived the first stage. The kinetic electron energy in the range from 45 to 80 keV has negligible influence on the distribution of the obtained molecules. The performed DFT calculations confirm the revealed atomistic mechanism and the adequacy of the REBO-1990EVC-EH potential used in the MD simulations.