Growth Structure and Work Function of Bilayer Graphene on Pd(111)

TL;DR

This study combines experimental microscopy and theoretical calculations to analyze the growth, structure, and work function variations of bilayer graphene on Pd(111), revealing orientation-dependent electronic properties.

Contribution

It provides new insights into the growth mechanisms and electronic behavior of bilayer graphene on Pd(111), highlighting the role of layer orientation and interface dipoles.

Findings

Bilayer graphene exhibits multiple rotational orientations on Pd(111).

Work functions are higher for bilayer than monolayer graphene and depend on layer orientation.

Electrostatic dipoles at interfaces explain work function variations.

Abstract

Using in situ low-energy electron microscopy and density functional theory, we studied the growth structure and work function of bilayer graphene on Pd(111). Low-energy electron diffraction analysis established that the two graphene layers have multiple rotational orientations relative to each other and the substrate plane. We observed heterogeneous nucleation and simultaneous growth of multiple, faceted layers prior to the completion of second layer. We propose that the facetted shapes are due to the zigzag-terminated edges bounding graphene layers growing under the larger overlying layers. We also found that the work functions of bilayer graphene domains are higher than those of monolayer graphene, and depend sensitively on the orientations of both layers with respect to the substrate. Based on first-principles simulations, we attribute this behavior to oppositely oriented electrostatic dipoles at the graphene/Pd and graphene/graphene interfaces, whose strengths depend on the orientations of the two graphene layers.