Two Distinct Phases of Bilayer Graphene Films on Ru(0001)

TL;DR

This study uses spectroscopy and microscopy to identify two distinct bilayer graphene phases on Ru(0001), revealing their structural differences, electronic properties, and potential for novel electronic behaviors.

Contribution

It demonstrates the synthesis of two different bilayer graphene phases with unique stacking orders and electronic characteristics on Ru(0001).

Findings

First phase has Bernal AB stacking with electron doping.

Second phase exhibits AA stacking with p-doping.

The second phase shows nearly-freestanding Dirac electrons.

Abstract

By combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy we reveal the structural and electronic properties of multilayer graphene on Ru(0001). We prove that large ethylene exposure allows to synthesize two distinct phases of bilayer graphene with different properties. The first phase has Bernal AB stacking with respect to the first graphene layer, displays weak vertical interaction and electron doping. The long-range ordered moir\'e pattern modulates the crystal potential and induces replicas of the Dirac cone and minigaps. The second phase has AA stacking sequence with respect to the first layer, displays weak structural and electronic modulation and p-doping. The linearly dispersing Dirac state reveals the nearly-freestanding character of this novel second layer phase.