Phase Engineering of Confined Heteroepitaxial (CHet) 2D Silver and Its Use in Fano Resonance-Based Sensing

Two-dimensional (2D) metals, distinct from their three-dimensional counterparts, exhibit remarkable electronic, optical, and quantum characteristics due to their reduced dimensionality. However, their inherent instability and susceptibility to oxidation pose challenges. Leveraging the Confinement Heteroepitaxy technique, we achieve the growth of centimeter-scale, air-stable 2D metals with gradient bonding, non-centrosymmetric structures, and unique features, including superconductivity. These metal films intercalate at the graphene/silicon carbide interface, where graphene protects against oxidation. Specifically, 2D silver displays semiconducting behavior and manifests in two distinct phases—3:3 (Ag₁) and 4:3 (Ag₂)—relative to the silicon carbide lattice. Our research demonstrates that tailoring the defects in the starting epitaxial graphene layer allows preferential intercalation of phases. By starting with buffer-layer graphene rich in sp³ defects, we achieve Ag₂ phase localization in buffer regions and Ag₁ phase dominance in monolayer graphene regions, resulting in a large-area Ag₂ sample. Additionally, controlled He plasma treatment induces line defects, facilitating selective Ag₁ phase growth post-intercalation. Notably, 2D Ag exhibits a pronounced asymmetric Fano resonance, which can be modulated by molecules, making it promising for sensitive single-molecule detection sensors. Despite minimal structural differences, these phases exhibit distinct optical absorption and saturation, suggesting potential applications in chemical sensors and optoelectronic devices.