Unexpected Structures for Intercalation of Sodium in Epitaxial Graphene-SiC Interfaces

TL;DR

This study reveals multiple sodium intercalation structures in epitaxial graphene on SiC, demonstrating room-temperature intercalation, electron doping, and decoupling effects, which differ from graphite and enable electronic property tuning.

Contribution

It uncovers new sodium intercalation configurations in epitaxial graphene and shows their effects on electronic decoupling and doping, expanding understanding of intercalation mechanisms.

Findings

Na intercalates at room temperature in multiple structures

Intercalation causes electron doping of graphene

Annealing accelerates decoupling of graphene layers

Abstract

We show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that several intercalation structures exist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature and Na electron-dopes the graphene. It intercalates in-between single-layer graphene and the carbon-rich interfacial layer. It also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. This decoupling is accelerated by annealing and is verified by direct Na deposition onto the interface layer. Our observations show that intercalation in graphene is fundamentally different than in graphite and is a versatile means of electronic control.