This study investigates the growth mechanisms of graphene on copper (Cu) and nickel (Ni) substrates using carbon isotope labeling. The research clarifies that graphene grows on Cu via surface adsorption, while on Ni it occurs through segregation-precipitation. Understanding these mechanisms is crucial for producing uniform graphene films. Graphene, a single layer of sp²-bonded carbon atoms, has unique properties making it suitable for advanced electronic devices. The study uses carbon isotope labeling to track the growth process on Cu and Ni substrates. Cu foils and Ni films were used as substrates, with methane (either normal or isotopically labeled) introduced in specific sequences during growth. The Raman spectroscopy technique was used to analyze the spatial distribution of carbon isotopes in the graphene films. The Raman mode frequency depends on the isotope composition, allowing the researchers to distinguish between different growth mechanisms. For Cu, the isotope distribution reflects the dosing sequence, indicating surface adsorption. For Ni, the isotope distribution is random, suggesting segregation-precipitation. The study shows that graphene grown on Cu is a single layer with uniform thickness, while graphene on Ni consists of multiple layers. The growth on Cu is self-limiting, making it suitable for manufacturing. In contrast, the growth on Ni is not uniform and involves precipitation, leading to multiple layers. The results indicate that the low solubility of carbon in Cu makes it an excellent substrate for producing uniform graphene films. The study also highlights the importance of controlling growth conditions to achieve desired graphene structures. The findings provide insights into the growth mechanisms of graphene on different substrates, which is essential for the development of high-quality graphene films for various applications.This study investigates the growth mechanisms of graphene on copper (Cu) and nickel (Ni) substrates using carbon isotope labeling. The research clarifies that graphene grows on Cu via surface adsorption, while on Ni it occurs through segregation-precipitation. Understanding these mechanisms is crucial for producing uniform graphene films. Graphene, a single layer of sp²-bonded carbon atoms, has unique properties making it suitable for advanced electronic devices. The study uses carbon isotope labeling to track the growth process on Cu and Ni substrates. Cu foils and Ni films were used as substrates, with methane (either normal or isotopically labeled) introduced in specific sequences during growth. The Raman spectroscopy technique was used to analyze the spatial distribution of carbon isotopes in the graphene films. The Raman mode frequency depends on the isotope composition, allowing the researchers to distinguish between different growth mechanisms. For Cu, the isotope distribution reflects the dosing sequence, indicating surface adsorption. For Ni, the isotope distribution is random, suggesting segregation-precipitation. The study shows that graphene grown on Cu is a single layer with uniform thickness, while graphene on Ni consists of multiple layers. The growth on Cu is self-limiting, making it suitable for manufacturing. In contrast, the growth on Ni is not uniform and involves precipitation, leading to multiple layers. The results indicate that the low solubility of carbon in Cu makes it an excellent substrate for producing uniform graphene films. The study also highlights the importance of controlling growth conditions to achieve desired graphene structures. The findings provide insights into the growth mechanisms of graphene on different substrates, which is essential for the development of high-quality graphene films for various applications.