Elsevier

Chemical Physics Letters

Volume 697, April 2018, Pages 7-11
Chemical Physics Letters

Research paper
Effectiveness of Co intercalation between Graphene and Ir(1 1 1)

https://doi.org/10.1016/j.cplett.2018.02.054Get rights and content

Highlights

  • The intercalation of Co films through defective Graphene is thickness dependent.

  • Non-intercalated Co forms a disordered CoO phase under ambient pressure exposure.

  • The oxide phase can be used to evaluate the amount of non-intercalated Co.

  • Further annealing induces the oxide reduction to metallic Co and its intercalation.

  • The intercalated Co is prevented from oxidation upon ambient pressure exposure.

Abstract

Graphene can be used to avoid the oxidation of metallic films. This work explores the effectiveness of such stabilizing effect on Cobalt (Co) films intercalated between Graphene and Ir(1 1 1). After intercalation at 300 °C, two Co films are exposed to ambient pressure and investigated using Co-K edge X-ray Absorption Near Edge Spectroscopy. The formation of a disordered oxide phase is observed, and associated to the presence of some non-intercalated Co. Further annealing at 500 °C causes the oxide reduction to metallic Co which further intercalates below the Graphene. Once the intercalation is completed, Graphene prevents the Co from oxidation under ambient pressure conditions.

Introduction

Among their unique and promising properties, graphene (Gr) has an exceptional chemical stability which can be used to passivate highly reactive surfaces [1], [2]. This is a valuable benefit for thin films presenting perpendicular magnetic anisotropy (PMA) that, once stabilized against oxidation, become suitable candidates to develop ultra-high density magnetic recording devices [3], [4].

Large-area high-quality epitaxial Gr can be grown via chemical vapor deposition (CVD) [5], [6] on transition metal substrates. On Ir(1 1 1), CVD growth of Gr has been successfully performed in a range of growth temperatures from 600 to 1000 °C [7]. Thin films intercalation below Gr on Ir(1 1 1) has already been proven effective against deterioration for several systems [8], [9], [10], [11], [12], [13]: among these, intercalated Co films (Gr/Co/Ir) have raised particular interest [14], [15], [16], [17], [18], [19], [20], [21] due to an unexpected PMA enhancement with respect to bare Co films grown on Ir(1 1 1) [22].

This work explores the thickness-dependent efficiency of the Co intercalation and the effects of air exposure at ambient pressure on Co films intercalated between Gr and Ir(1 1 1). By exploiting the chemical selectivity and the sensitivity to the coordination chemistry of X-ray Absorption Fine Structure (XAFS) spectroscopy, the stability of the film against oxidation is probed. The amount of oxidised Co is then used to evaluate the intercalation effectiveness. A thermal method for the Co oxide reduction is described. This method induces also the final intercalation of Co which becomes protected against further oxidation.

Section snippets

Experimental

The Gr/Co/Ir samples were prepared in the UHV chamber available at the ID03 preparation laboratory (ESRF – Grenoble, France), at a base pressure of 10-10 mbar, following a well established procedure [19], [21]. The Ir(1 1 1) substrate was cleaned through several cycles of Ar+ sputtering at 1 kV, and thermal annealing at 850 °C. The surface quality was inspected by X-ray Photoelectron Spectroscopy (XPS), and Low Energy Electron Diffraction (LEED). The substrate was considered clean when XPS showed

Results and discussion

The spectra collected after the first, μ,300C(E), and the second annealing treatment, μ,500C(E), are shown in Fig. 2a and b for the thick and thin film, respectively. At the bottom of every panel, the difference Δμ(E)=μ500C(E)-μ300C(E) is reported for each polarization to facilitate the identification of the thermally-induced modifications.

Upon annealing and further air exposure, the two samples undergo a similar evolution and two major changes (labels A and B in Fig. 2) emerge in the first

Conclusion

We have investigated the effectiveness of Co intercalation below Gr. Two films of 5 and 10 ML were intercalated between Gr and Ir(1 1 1) by annealing at 300 °C for 5 min. Upon 15 min of air exposure under ambient pressure, a disordered Co oxide phase was found on both the films, being more abundant in the thickest film. This has been interpreted as a sign of incomplete and thickness-dependent intercalation process. The disordered Co oxide was removed by annealing at 500 °C. A second exposure to

Acknowledgements

The authors wish to thank the staff of ID03 and BM23 beamlines, in particular, F. Carlà, T. Dufrane, H. Isern, S. Pascarelli, and O. Mathon for the scientific and technical support provided during the experiments.

References (36)

  • J. Coraux et al.

    Growth of graphene on ir (1 1 1)

    New J. Phys.

    (2009)
  • Y.S. Dedkov et al.

    Electronic and magnetic properties of the graphene–ferromagnet interface

    New J. Phys.

    (2010)
  • S. Schumacher et al.

    Europium underneath graphene on Ir(1 1 1): intercalation mechanism, magnetism, and band structure

    Phys. Rev. B

    (2014)
  • M. Petrović, I. Rakić, S. Runte, C. Busse, J. Sadowski, P. Lazić, I. Pletikosić, Z. Pan, M. Milun, P. Pervan, The...
  • D. Pacilé et al.

    Artificially lattice-mismatched graphene/metal interface: graphene/Ni/Ir(1 1 1)

    Phys. Rev. B

    (2013)
  • H. Vita et al.

    Understanding the origin of band gap formation in graphene on metals: graphene on Cu/Ir (1 1 1)

    Sci. Rep.

    (2014)
  • J. Coraux et al.

    Air-protected epitaxial graphene/ferromagnet hybrids prepared by chemical vapor deposition and intercalation

    J. Phys. Chem. Lett.

    (2012)
  • H. Vita et al.

    Electronic structure and magnetic properties of cobalt intercalated in graphene on Ir(1 1 1)

    Phys. Rev. B

    (2014)
  • Cited by (0)

    View full text