Making Use of Si Contaminants during Chemical Vapor Deposition of Graphene on Cu: Synthesis of a Stable Material with the Textbook-like Band Structure of Free-Standing Graphene.

We report on a gentle procedure for the complete electronic decoupling of graphene from Cu. The procedure can be added to the growth protocol of graphene synthesis by chemical vapor deposition making use of the widely unnoticed silicon release from hot wall quartz tube reactors. So far, Si release was observed if the effect was large, so that it deteriorates the grown graphene. However, the effect can also be used to turn the electronic band structure of CVD-grown graphene on Cu into that of free-standing graphene as shown in a combined spectroscopic photoelectron and low energy electron microscopy study. Adding a foil pretreatment to the synthesis protocol in the reactor turns the polycrystalline foil into (111)-textured Cu, and the electronic band structure of CVD-grown graphene on Cu(111) is achieved with n-doping by -0.4 eV and band gap formation of 0.3 eV. If, however, graphene is synthesized on a Si-loaded Cu foil, subsequent oxygen exposure in the reactor segregates the dissolved Si to the surface and converts it to intercalated silica without destroying the covering graphene. The graphene decouples electronically, and the textbook-like electronic band structure of free-standing graphene emerges. The alternating stacking of 30°-rotated layers in thicker graphene leads to electronically noninteracting layers. Moreover, in angle-resolved photoemission, replica bands due to Umklapp processes emerge without the opening of an energy gap.