Impact of Interfacial Configurations on the Growth of Few-Layer NbSe₂ on Sapphire

Two-dimensional van der Waals (vdW) heterostructures enable versatile material integration for advanced electronic and quantum devices. This study employs coherent Bragg rod analysis (COBRA) to study subangstrom interfacial effects in three types of wafer-scale NbSe₂ heterostructures grown on sapphire substrates via a two-step growth method. The sapphire surface Se-O mixing and nonstoichiometry from direct NbSe₂ growth, the interface passivation with a graphene insert, and the complex growth mechanism with MoSe₂ stacking are identified and quantified. These distinctly different interface chemical activities and structural morphologies lead to different growth behaviors and crystalline quality of the NbSe₂ grown on top, which are correlated with the film superconductivity performance. Our findings highlight the importance of interfacial control in vdW heterostructure design, providing atom-level insights to optimize growth strategies for enhanced functionality.