Optimization of MoCl₅ intercalation for low-resistance and low-damage exfoliated highly-oriented pyrolytic graphite

This study developed a damageless molybdenum pentachloride (MoCl₅) intercalation doping process of exfoliated highly-oriented pyrolytic graphite (e-HOPG). We optimized the chemical concentration and reaction temperature and time for doping crystalline multilayer graphene. We found that thick e-HOPG films are more susceptible to intercalation damage than previously reported few-layer graphene. Lowering the chemical concentration reduced the damage; however, there was a trade-off between doping efficiency and damage. Efficient doping with a 77% reduction of sheet resistance without significant damage was achieved by further optimizing the reaction temperature and time with reduced chemical concentration. The correlation plots of G and 2D peak positions in the Raman spectra were used to analyze the strain and carrier density induced during the intercalation process and investigate the cause of damage. The stability of the intercalated e-HOPG was confirmed for storage in a nitrogen box for 40 weeks.