Intercalation at the graphene/SiC interface provides a controlled route to stabilize atomically thin layers with properties distinct from their bulk counterparts. In this platform, the structure and stability of the intercalated phase depend sensitively on the defect landscape of the starting substrate. For intercalated two-dimensional silver at the graphene/SiC interface, two phases have been observed: a phase epitaxial to the SiC lattice, called ${\mathrm{Ag}}_{\left(1\right)}$, readily obtained following the conventional intercalation method under ultra-high-vacuum conditions and extensively characterized, and a more densely packed phase, called ${\mathrm{Ag}}_{\left(2\right)}$, which has remained largely unexplored. Here we report an in situ ultra-high-vacuum preparation method of the second phase intercalated at the graphene/SiC interface; this phase was previously prepared via high-pressure confinement heteroepitaxy. Low-energy electron diffraction shows that ${\mathrm{Ag}}_{\left(2\right)}$ is rotated by ${30}^{\circ }$ relative to the SiC lattice and forms supercells, in contrast to the $(1\times 1)$ epitaxial relation of ${\mathrm{Ag}}_{\left(1\right)}$ with SiC. High-resolution angle-resolved photoemission spectroscopy reveals a more complex ${\mathrm{Ag}}_{\left(2\right)}$ band dispersion compared to ${\mathrm{Ag}}_{\left(1\right)}$, as a consequence of the modified Ag-Si interaction in the denser phase. In density functional theory calculations, by defining the unfolding entropy, which, in a quantified way, finds that the band structure of ${\mathrm{Ag}}_{\left(2\right)}$ is more suitable to be unfolded to the SiC primitive cell, the resulting unfolded band dispersion is in great agreement with the experimental data. We further show that the different intercalated Ag phases tune the electronic properties of the overlying quasi-free-standing graphene layer differently: compared with ${\mathrm{Ag}}_{\left(1\right)}, {\mathrm{Ag}}_{\left(2\right)}$ yields an $\sim 1.75$ times higher charge carrier density and modifies the charge-plasmon interaction of the graphene layer, indicating a change in effective screening at the interface.

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• Density of states
• Electronic structure of atoms & molecules
• Fermi surface
• Intercalation
• Surface & interfacial phenomena
• Surface states
• Graphene
• Two-dimensional electron system
• Angle-resolved photoemission spectroscopy
• Density functional theory
• Low-energy electron diffraction
• Photoemission spectroscopy
• X-ray photoemission electron microscopy