Two-step CVD strategy for high-coverage twisted bilayer graphene

• Developed a two-step CVD strategy to overcome Cu-based self-limiting growth. • Optimized methane flow enables high bilayer nucleation and ∼ 99 % coverage. • Raman mapping reveals 85% twisted bilayers with broad angle range. Bilayer graphene (BLG) with controlled stacking orientation is crucial for exploring novel quantum phenomena and developing next-generation electronic and optoelectronic devices. However, conventional chemical vapor deposition (CVD) on Cu is inherently self-limiting, yielding only sparse bilayer islands. Here, we demonstrate a two-step CVD strategy that decouples nucleation and lateral propagation, enabling the synthesis of twisted bilayer graphene (t-BLG) with nearly full coverage. Time-dependent growth reveals that BLG coverage increases from ∼ 5 % after 10 min to ∼ 85 % at 30 min and ultimately reaching ∼ 99 % within 60 min. Raman mapping shows ∼ 85 % of the BLG adopt twisted configuration. This strategy provides a practical route to achieve large-area t-BLG for both fundamental studies and device integration.