Figure 4. Hexagonal graphene grains grown on Pt foils and transferred to Si/SiO₂ substrates.

(a–c) Scanning electron microscope (SEM) images of hexagonal graphene grains grown on Pt foils with different growth times of 60 (a), 120 (b) and 180 min (c), showing that their sizes are roughly proportional to the growth time. The reaction temperature was 1,040 °C, and the flow rates of CH₄ and H₂ were 4 and 700 sccm, respectively. (d–f) Optical images of the graphene grains in (a–c) transferred to Si/SiO₂ substrates by the bubbling transfer process, showing that the transferred graphene grains perfectly retain their original shapes. The scale bars in (a–f) are 400 μm.