Degeneracy in Intercalated Pb Phases under Buffer-Layer Graphene on SiC(0001) and Diffuse Moiré Spots in Surface...

Area of Science:

• Materials Science
• Surface Science
• Computational Materials Science

Background:

• Graphene on silicon carbide (SiC) is a promising platform for 2D material research.
• Understanding the behavior of intercalated species, like lead (Pb), is crucial for device applications.
• The atomic structure and stability of intercalated phases influence material properties.

Purpose of the Study:

• To investigate the thermodynamic stability of lead (Pb) intercalated phases beneath graphene on SiC(0001).
• To determine the influence of supercell size, Pb coverage, and ordering on phase stability.
• To correlate theoretical predictions with experimental observations of Pb subsurface structures.

Main Methods:

• First-principles density functional theory (DFT) calculations were employed to model Pb intercalated structures.
• Chemical potentials were compared to identify thermodynamically preferred Pb configurations.
• Spot Profile Analysis Low-Energy Electron Diffraction (SPA-LEED) was used for experimental validation.

Main Results:

• DFT identified a family of structurally distinct, thermodynamically favorable Pb subsurface configurations.
• Calculated stability differences between these phases are minimal, comparable to thermal energy at growth temperatures.
• SPA-LEED experiments showed broad, low-intensity moiré spots, indicating the coexistence of multiple degenerate Pb phases.

Conclusions:

• The growth of Pb intercalated phases on graphene/SiC results in a mixture of energetically similar, structurally distinct subsurface configurations.
• The observed degeneracy and coexistence of phases are consistent with theoretical predictions of minute stability differences.
• This finding has implications for controlling and understanding the properties of such 2D material heterostructures.