Influence of the Total Gas Flow at Different Reaction Times for CVD-Graphene Synthesis on Polycrystalline Nickel

Optimization of the total gas flow (CH4+H-2) during the reaction step for different reaction times for CVD-graphene synthesis on polycrystalline nickel foil using an atmospheric pressure set-up is reported. A thickness value related to number of graphene layers in each of the synthesized samples was determined using an Excel-VBA application. This method assigned a thickness value between 1 and 1000 and provided information on the percentage of each type of graphene (monolayer, bilayer, and multilayer) deposited onto the polycrystalline nickel sheet. The influence of the total gas flow during the reaction step and the reaction time was studied in detail. Optical microscopy showed that samples were covered with different types of graphene, such as multilayer, few-layer, bilayer, and monolayer graphene. The synthesis variables were optimized according to the thickness value and the results were verified by Raman spectroscopy. The best conditions were obtained with a reaction temperature of 980 degrees C, a CH4/H-2 flow rate ratio of 0.07 v/v, a reaction time of 1 minute, and a total gas flow of 80 NmL/min. In the sample obtained under the optimized conditions, 80% of the area was covered with monolayer graphene and less than 1% with multilayer graphene.