Coulomb Blockade in Graphene Nano-islands Formed by Direct CVD Growth on Si/SiO ₂ Substrate

Graphene nano-islands (GNIs) are promising building blocks for quantum devices owing to their unique potential. However, direct electrical measurements of GNIs have been challenging due to the requirement of metal catalysts in typical synthesis methods. In this study, we demonstrate electrical transport measurements of GNIs by using microwave plasma chemical vapor deposition, which is a catalyst-free method to deposit graphene directly on SiO ₂ substrates. This approach enables the fabrication of metal electrodes on GNIs, allowing us to measure their quantum transport properties. At low temperatures, one of our devices shows clear Coulomb diamonds with twofold degeneracy, indicating the formation of a quantum dot and the lifting of valley degeneracy. The charge state of the GNI is also modulated by a local side gate, showing behavior similar to that observed with a global back gate. These results provide fundamental insights into GNI-based quantum devices relevant to next-generation computing.