Rubidium intercalation in epitaxial monolayer graphene

TL;DR

This study systematically investigates rubidium intercalation in epitaxial monolayer graphene on SiC(0001), revealing phase formation, doping effects, and the reversibility of intercalation through a multi-technique approach.

Contribution

It provides the first detailed analysis of rubidium intercalation phases, structures, and thermal stability in epitaxial graphene, expanding understanding of alkali metal intercalation mechanisms.

Findings

Formation of $(2 imes 2)$ and $(rac{ ext{ extmu}}{ ext{ extmu}}3) imes (rac{ ext{ extmu}}{ ext{ extmu}}3)$R30° structures.

Strong n-type doping of graphene due to Rb intercalation.

Reversible intercalation process with Rb diffusion and desorption at high temperatures.

Abstract

Alkali metal intercalation of graphene layers has been of particular interest due to potential applications in electronics, energy storage, and catalysis. Rubidium (Rb) is one of the largest alkali metals and the one less investigated as intercalant. Here, we report a systematic investigation, with a multi-technique approach, of the phase formation of Rb under epitaxial monolayer graphene on SiC(0001). We explore a wide phase space with two control parameters: the Rb density (i.e., deposition time) and sample temperature (i.e., room- and low-temperature). We reveal the emergence of $(2 \times 2)$ and $(\sqrt{3} \times \sqrt{3})$R30{\deg} structures formed by a single alkali metal layer intercalated between monolayer graphene and the interfacial C-rich reconstructed surface, also known as buffer layer. Rb intercalation also results in a strong n-type doping of the graphene layer. Progressively annealing to high temperatures, we first reveal diffusion of Rb atoms which results in the enlargement of intercalated areas. As desorption sets in, intercalated regions progressively shrink and fragment. Eventually, at approximately 600{\deg}C the initial surface is retrieved, indicating the reversibility of the intercalation process.