Elsevier

Surface Science

Volume 560, Issues 1–3, 1 July 2004, Pages 183-190
Surface Science

Highly oriented monolayer graphite formation on Pt(1 1 1) by a supersonic methane beam

https://doi.org/10.1016/j.susc.2004.04.039Get rights and content

Abstract

We have found that the surface reaction on Pt(1 1 1) induced by the collision of supersonic methane molecules with a sufficiently high kinetic energy (670 meV) results in huge domains of highly oriented monolayer graphite without any unidentified carbon-related materials, and that the monolayer graphite completely covers the Pt(1 1 1) surface. The mechanism is discussed in terms of the surface insensitivity of the collision-induced process and the thermal stability of the graphite with a specific superstructure. This implies the effectiveness of supersonic molecular beam to the practical surface modification.

Introduction

The monolayer graphite receives much attention because it is a well-defined two-dimensional material and also a fundamental component of graphite-related materials, such as carbon nanotubes and fullerenes having outstanding electrical and mechanical properties. The phonon dispersion relation and the atomic arrangement of monolayer graphite adsorbed on various substrates have been investigated by means of electron diffraction and electron energy loss spectroscopy for decades [1], [2], [3], [4], [5].

Recently the microscopic formation process and the real space atomic arrangement of monolayer graphite were observed by scanning tunneling microscopy (STM) [6], [7], [8], [9]. In particular, the monolayer graphite on Pt(1 1 1) with 13% of lattice mismatch apparently showed interesting features of moiré-like superstructures in the topograph of STM [8], [9], [10], [11], [12]. The period of the superstructure is determined by the angle between the graphite lattice and the substrate Pt lattice. Moreover, the local barrier height (LBH) imaging in STM has made clear that the origin of the moiré-like contrast is the spatial distribution of the interlayer interaction between monolayer graphite and Pt atoms [11]. The LBH imaging easily reveals the atomic arrangement of graphite with respect to the substrate lattice [12].

The monolayer graphite has usually been prepared by the exposure to effusive hydrocarbon materials such as ethane and ethylene, followed by annealing, so far. In this case, the formed monolayer graphite shows a wide variety of STM and/or LBH images [8], [9], [10], [11], [12]. Most of the obtained images contain several domains with moiré-like superstructures with different periods corresponding to different lattice orientations of graphite. This is consistent with the observed ring shape pattern of low energy electron diffraction (LEED). Furthermore, in addition to the monolayer graphite, there exist unidentified carbon materials, although graphite is the most stable carbon-related material. This prevents us from investigating real properties of monolayer graphite with a specific orientation.

The collision-induced chemical reaction of methane has been examined with a supersonic molecular beam technique, controlling the kinetic energy of incident methane molecules, which enables us to study the dynamical behavior of the surface reaction [13], [14], [15], [16], [17], [18]. While thermal methane molecules do not decompose on the Pt(1 1 1) surface easily, it has been found that methane molecules decompose efficiently at normal kinetic energies higher than the threshold of about 200 meV [19]. However, the decomposition of methane with kinetic energies a little higher than the threshold is suppressed after a specific amount of carbon deposition before fully covering the surface [19], [20], [21]. This is interpreted by the mechanism that the potential barrier to decomposition increases upon adsorption of reaction products, originated from the decrease in the work function. Thus, it is expected that the methane molecules with much higher kinetic energies reduce the decomposition suppression and that the surface is fully covered with the reaction products, which is possibly the most thermally stable material, graphite. However, the microscopic surface feature after a sufficient amount of methane supply with a sufficiently high kinetic energy has not been examined, so far.

In this paper, we examine the microscopic behavior of the carbon-related surface material formed by the supersonic methane beam using a newly developed molecular beam scattering apparatus connected with an STM system. The obtained results demonstrate that a highly oriented monolayer graphite is formed by the supersonic methane beam at higher normal kinetic energies.

Section snippets

Experiment

We performed the experiments by means of an apparatus consisting of a supersonic molecular beam scattering chamber and an STM chamber connected with an ultrahigh vacuum tunnel as shown in Fig. 1.

In the scattering chamber, the supersonic methane molecular beam, generated with a temperature-variable nozzle and a skimmer, is supplied to the sample surface mounted on a goniometer. The kinetic energy of the incident methane molecules is controlled by the nozzle temperature and the mixture with

Results and discussion

The methane with the highest energy gives the most specific feature of the surface reaction induced by supersonic beams, which is quite different from that formed by thermal process. Every LBH image taken from the surface irradiated with the methane beam with the normal kinetic energy of 670 meV (1% methane; the nozzle temperature, 800 K; normal incidence) is found to be filled over with similar periodic patterns, whose period is within the range of 0.6–1.0 nm. Fig. 2 shows a typical LBH image

Summary

The Pt(1 1 1) surfaces irradiated with supersonic methane beams are examined by means of the LBH imaging method. From the obtained images, we find that the process induced by the collision of methane molecules with a sufficiently high kinetic energy (E=670 meV) results in highly oriented monolayer graphite, that is, huge domains of monolayer graphite showing the moiré-like superstructure with a small range of period (0.6–1.0 nm), which corresponds to a small range of rotation angle of monolayer

Acknowledgements

The authors would like to thank Asawin Sinsarp for the fruitful discussions. This work is partly supported by a Grant-in-Aid for Scientific Research on Priority Areas (B) from the Ministry of Education, Culture, Sports, Science and Technology.

References (30)

  • B Lang

    Surf. Sci.

    (1975)
  • T Aizawa et al.

    Surf. Sci.

    (1992)
  • H Itoh et al.

    Surf. Sci.

    (1991)
  • T.A Land et al.

    Surf. Sci.

    (1992)
  • A.V Hamza et al.

    Surf. Sci.

    (1987)
  • G Binnig et al.

    Surf. Sci.

    (1983)
  • M Komai et al.

    Appl. Surf. Sci.

    (1999)
  • P.J Feibelman et al.

    Surf. Sci.

    (1985)
  • Y Gamo et al.

    Surf. Sci.

    (1997)
  • Z.-p Hu et al.

    Surf. Sci.

    (1987)
  • T Aizawa et al.

    Phys. Rev. Lett.

    (1990)
  • A Nagashima et al.

    Phys. Rev. B

    (1994)
  • X.-L Wu et al.

    Phys. Rev. Lett.

    (1988)
  • T.A Land et al.

    J. Chem. Phys.

    (1992)
  • M Enachescu et al.

    Phys. Rev. B

    (1999)
  • Cited by (136)

    • Band gap formation of 2D materialin graphene: Future prospect and challenges

      2022, Results in Engineering
      Citation Excerpt :

      Researchers have studied ultrathin graphitic coatings epitaxially grown on metal surfaces for a long time [92,96–105]. Recently, epitaxial single-layer graphene films have been made using the same metals [106–114]. At high temperatures, most of these metals exhibit reactant migration.

    • Substrate effect on the electronic properties of graphene on vicinal Pt(1 1 1)

      2021, Applied Surface Science
      Citation Excerpt :

      The inset shows the (1x1) spot of platinum and two graphene rotations at ± 5° (R5, R5′). When graphene grows on Pt(1 1 1), it forms different rotational domains (R0, R30, R19), whose signature in diffraction techniques are well-defined spots rotated with respect to those of the substrate [19,32,33]. On the other hand, diffraction arcs also form because of indistinguishably close rotational domains.

    • Scanning tunneling microscopy (STM) of graphene

      2021, Graphene: Properties, Preparation, Characterization and Applications, Second Edition
    View all citing articles on Scopus
    View full text