Graphene and Boron Nitride Single Layers

TL;DR

This paper reviews the synthesis, structure, and properties of single-layer graphene and boron nitride on transition metal substrates, highlighting their anisotropic elastic properties, nanotechnology applications, and robustness outside ultra-high vacuum.

Contribution

It provides a comprehensive overview of the atomic and electronic structure, properties, and potential nanotechnological uses of sp2 honeycomb layers on metal supports.

Findings

Layers are stiff in-plane and soft out-of-plane.

Bond energies enable nanometer-scale molecular interactions.

Sp2 layers are robust in liquid environments.

Abstract

This Chapter deals with single layers of carbon (graphene) and hexagonal boron nitride on transition metal surfaces. The transition metal substrates take the role of the support and allow due to their catalytic activity the growth of perfect layers by means of chemical vapor deposition. The layers are sp2 hybridized honeycomb networks with strong in plane sigma and weaker pi bonds to the substrate and to the adsorbates. This hierarchy in bond strength causes anisotropic elastic properties, where the sp2 layers are stiff in plane and soft out of plane. A corrugation of these layers imposes a third hierarchy level in bond energies, with lateral bonding to molecular objects with sizes between 1 and 5 nanometer. This extra bond energies are in the range of thermal energies kT at room temperature and are particularly interesting for nanotechnology. The concomitant template function will be discussed. The peculiar bond hierarchy also imposes intercalation as another property of sp2 layer systems. Last but not least sp2 layer systems are particularly robust, i.e. survive immersion into liquids, which is a promise for sp2 layers being useful outside ultra high vacuum. The Chapter shortly recalls the synthesis, describes the atomic and electronic structure, is followed by a discussion of properties like intercalation and the use of sp2 layers on metals as tunneling junctions or as templates. The Chapter ends with an Appendix that summarizes the basics of atomic and electronic structure of honeycomb lattices. Of course the Chapter does not cover all aspects of sp2 single layers. Topics like free standing layers, edge structures of ribbons, topological defects, or mechanical and chemical properties were not covered.