Confinement Epitaxy of Large-Area Two-Dimensional Sn at the Graphene/SiC Interface

Abstract

Confinement epitaxy beneath graphene stabilizes exotic material phases by restricting vertical growth and altering lateral diffusion, conditions unattainable on bare substrates. However, achieving long-range interfacial order while maintaining high-quality graphene remains a significant challenge. Here, we demonstrate the synthesis of large-area quasi-free-standing monolayer graphene (QFMLG) via the intercalation of a two-dimensional (2D) Sn. While the triangular Sn(1x1) interface exhibits a robust metallic band structure, the decoupled QFMLG maintains charge neutrality, confirmed by photoemission spectroscopy. Using high-resolution Raman spectroscopy and microscopy, we distinguish between direct intercalation and diffusion-driven expansion, identifying the latter as the critical pathway to superior QFMLG crystalline quality. Temperature-dependent analysis reveals dynamical structural coupling between the decoupled QFMLG and the Sn interface, providing a novel degree of freedom for strain engineering. Beyond uncovering the diffusion-driven mechanism, this work establishes metal intercalation as an effective strategy for tailoring durable graphene-metal heterostructures with tunable properties for next-generation quantum materials platforms.

Figures (7)

• Figure 1: In situ study of the Sn intercalation and structural properties. a) SPA-LEED image for ZLG on SiC(0001). b) The same surface after Sn intercalation. The $R_{1}$ and $R_{2}$ in (a) denote the (6/13,-1/13) and (6/13,1/13) orders of the 6$\sqrt{3}$ periodicity. c,d) High-resolution spot profiles along the SiC and Gr directions, respectively. The shaded areas mark the BSC. e) Close-up of the Gr(10) spot at different intercalation stages. The x-axis indicates the lattice constants ($a$) of ZLG (bottom, black) and QFMLG (top, blue), determined from the distance to the (00) diffraction spot (arrow). f,g) Reciprocal space maps of the (00) spot along the SiC direction for pristine ZLG and after Sn intercalation, respectively. h,i) Reciprocal space maps for the (5/13,0) and (6/13,1/13) orders of the 6$\sqrt{3}$ periodicity (black arrow in the inset). j) Intensity versus primary electron energy (E) plot extracted from (h,i).
• Figure 2: a,b) Spot profiles of the SiC(10) spot at different temperatures. c,d) Reciprocal-space maps of the SiC(10) spot at 300 K and 950 K, shown as second derivatives for clarity. e) Lattice separation as a function of temperature. f) Side view of the Sn(1$\times$1) layer on SiC(0001); arrows denote the thermal lattice expansion.
• Figure 3: Schematic view of the anticipated Sn intercalation process at elevated temperatures.
• Figure 4: Characterization of the samples via micro-Raman spectroscopy. a) Raman spectra of the intercalated QFMLG sample, recorded for direct Sn deposited (red, A1), diffusion-driven (green, A2), and nonintercalated (blue, ZLG) areas. The insets 1, 2, and 3 show zoom-ins of the graphene G band, low-frequency Sn band, and spatial mapping of the 2D band in the area A1 in (b). b-g) Mapping of the Raman bands of the QFMLG across the shadow mask over an 80$\times$12 $\mu{m^{2}}$ area. b) D band intensity, c) D band frequency, d) G band intensity, e) G band frequency, f) 2D band intensity, and g) 2D band frequency. h) I(2D)/I(G) ratio for the areas A1 and A2, relating lateral doping profiles. i) Strain and doping correlation in A1 and A2. The inset shows strain ($\epsilon$, blue) and doping ($\textit{n}$, orange) lines. j) Dispersions with excitation energy: frequencies (black) and width (blue) for the QFMLG/Sn (squares) and MLG (circles). The nonintercalated ZLG areas are masked in (b-h) for proper evaluation.
• Figure 5: a) Representative temperature-dependent Raman spectra of the 2D band for the QFMLG/Sn sample. b-e) TSRs of the G and 2D bands for the MLG and QFMLG/Sn samples; solid lines show linear fits. f) Correlation plot of the G and 2D band TSRs for both surfaces. Dashed (blue, green) and dotted (orange) lines indicate the strain and doping trends, respectively.