H2 has etchant effect. The etchant ability of H2 help to remove of defected site and edges in graphene structure. If we increase H2 flow rate over it's optimum amount, what would be happen????
What material do you use as the precursor of carbon? I think you must thermodynamically calculate the required amounts (flow rate of your gaseous precursors considering the volume of your reaction chamber) of your reactants. As you know, based-on Le Chatelier's principle if the amounts of reactants being more than that of required amounts of equilibrium conditions, the reaction will be proceed in reverse order and this can damage the formed graphenes.
Dear Dr Samira, The extent of damage depends on the quality of the graphene produced. There are several factors which help you gain good quality graphene in the synthesis process. When you choose H2 as an etchant in small quantities you may get the defects removed successfully,(again here the gas flow velocity, residence time, nozzle area, Temperature and few other parameters should be also be considered and studied). But more of hydrogen also causes severe damage to the the graphene film. These papers may help you in understanding the effects: http://aip.scitation.org/doi/full/10.1063/1.4979023
http://pubs.acs.org/doi/abs/10.1021/ja107071g
Best Wishes
Vivek
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