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Comparing graphene growth on Cu(111) versus oxidized Cu(111)

Graphene, a single layer of carbon atoms, is supposed to transcend conventional silicon-based electronics, because of its overwhelming electronic properties. However, a scalable and versatile route to obtain high quality graphene on noninteracting substrates that also preserves graphene’s intrinsic properties, a prerequisite for graphene electronic devices, has not been developed yet. In comparison to the established chemical vapor deposition growth on metals, the epitaxial growth of graphene on both noninteracting and high-k dielectric substrates like oxides, is a significant challenge that is gaining increasing interest.
In general, graphene grown on nonmetallic surfaces like oxides exhibits reduced quality in comparison to graphene grown on metals and in some cases graphene was even found to be either p- or n-doped. Scientific collaboration of Surfaces and Thin Films group of Groningen University (S. Gottardi as principal investigator supervised by Meike Stöhr and Petra Rudolf), Elettra - Sincrotrone Trieste and Department of Physics, Chemistry, and Biology, IFM, Linköping University compared the growth of graphene on a high purity oxide-free Cu(111) single crystal with the growth on a Cu(111) single crystal after the creation of a thin oxide layer. The sample growth and analysis by traditional surface science techniques such as Scanning Tunneling Microscopy and Low Energy Electron Diffraction were performed at Groningen. Electronic structure was measured by Angle Resolved Photoemission Spectroscopy (ARPES) at Spectromicroscopy beamline of Elettra. At Linköping University density functional theory calculations were performed in order to get insight into the reaction processes and help explaining the catalytic activity of copper oxide.

For graphene growth on Cu(111), the Cu single crystal was pre-annealed in a hydrogen atmosphere to guarantee an oxide-free metallic surface. For graphene growth on oxidized Cu(111), the clean copper single crystal was exposed to air for approximately 12 h to obtain an oxidized surface onto which graphene was grown subsequently without any hydrogen treatment. The results demonstrate the feasibility of growing high-quality monolayer graphene by a one-step growth process on a pre-oxidized Cu(111) surface.
The oxide layer has a dramatic effect on the electronic coupling between graphene and the substrate as revealed by ARPES data (Fig. 1). Graphene grown on metallic copper is n-type doped with the Dirac energy residing at about 0.38 eV below EF (Fig. 1c). The π–π* and σ-bands are shifted accordingly. On the other hand, for graphene grown on oxidized Cu(111) the σ- and π-bands are located closer to EF than for graphene on metallic Cu(111) (Fig. 1b). This becomes more evident when inspecting the Dirac cone (Fig. 1d). Summarizing this result, in contrast to graphene on Cu(111), where a weak interaction and doping are found, graphene grown on the oxidized Cu surface is effectively decoupled from its substrate and thereby its intrinsic properties are preserved. Importantly, this implies that the band structure of freestanding graphene is retained, where doping is absent. Because copper oxide is a high-κ dielectric material, these findings constitute an important contribution toward the realization of graphene-based electronic devices.

 

Figure 1. Comparison of the electronic properties of graphene grown on Cu(111) and on oxidized Cu(111). Energy dispersion curves along the ΓK direction of the graphene Brillouin zone (inset) for graphene grown on Cu(111) (a) and oxidized Cu(111) (b), respectively. The Cu 3d as well as the σ- and π-bands of graphene are labeled in yellow. Detail of the Dirac cone at the K-point of the graphene Brillouin zone for graphene grown on Cu(111) (c) and on oxidized Cu(111) (d), respectively. The white dashed line indicates the linear dispersion of the Dirac cone. (e) Normal emission spectra measured at the Γ-point of the graphene Brillouin zone for graphene on Cu(111) (blue) and on oxidized Cu(111) (pink), respectively. The Cu(111) surface state (SS) is shifted toward the Fermi energy for graphene grown on Cu(111) while it is not present anymore for graphene grown on oxidized Cu(111).

 

This research was conducted by the following research team:

  • Stefano Gottardi, Kathrin Müller, Luca Bignardi, Juan Carlos Moreno-López, Tuan Anh Pham, Oleksii Ivashenko, Petra Rudolf, Meike Stöhr, Zernike Institute for Advanced Materials, University of Groningen,  Groningen, The Netherlands.

  • Mikhail Yablonskikh, Alexei Barinov, Elettra - Sincrotrone Trieste S.C.p.A.,  Basovizza, Trieste, Italy.

  • Jonas Björk, Department of Physics, Chemistry, and Biology, IFM, Linköping University, Linköping, Sweden.



Contact person:

Alexei Barinov : alexei.barinov@elettra.eu


Reference

Stefano Gottardi, Kathrin Müller, Luca Bignardi, Juan Carlos Moreno-López, Tuan Anh Pham, Oleksii Ivashenko,Mikhail Yablonskikh, Alexei Barinov,Jonas Björk,Petra Rudolf, Meike Stöhr, Comparing Graphene Growth on Cu(111) versus Oxidized Cu(111), Nano Letters 15, 917-922 (2015), DOI: 10.1021/nl5036463.

 

Last Updated on Friday, 12 June 2015 15:40