Chemical vapor deposition of thin graphite films of nanometer thickness
Introduction
Graphite is a widely used material with well-developed synthesis methods and properties investigated in detail [1]. A peculiarity of graphite is its layered structure formed by parallel two-dimensional graphene sheets weakly coupled by van der Waals interaction. Each graphene sheet looks like a hexagonal network of carbon atoms connected by strong covalent “in-plane” σ−σ bonds. The delocalized electrons appear only due to an additional π−π bonding of electronic orbitals oriented perpendicularly to the graphene plane. They are responsible for the graphite electrical conductivity which is highly anisotropic. Recently, the unconventional electric field and quantum Hall effects have been demonstrated experimentally for a single sheet of graphite–graphene [2], [3]. These experiments have triggered a great interest to the graphite films containing one or a very few graphene sheets [4], [5], [6], [7], because the unusual electron behavior is considered as a result of two-dimensional confinement of charge carriers.
Graphene can be produced by mechanical exfoliation of individual layers from the surface of highly oriented pyrolytic graphite (HOPG) crystal [2], [3], [4], [5]. Thin heteroepitaxial graphite films consisting of a few graphene layers can be produced by graphitization of silicon carbide surface [6], [8] or dissociation of ethylene gas on Ni(1 1 1) surface in ultra-high vacuum [9]. However, such “hand-made” graphene or heteroepitaxial thin films have relatively small lateral sizes and are suitable only for pure scientific studies. For deposition of extended films appropriate for practical applications a chemical vapor deposition (CVD) from activated gaseous phase could be efficient. But up to now only rather thick graphite films with a high number of structural defects were deposited by CVD technique [1].
In this paper, we describe a high yield technique of deposition of the large area graphitic films with thickness of a few graphene layers. The results of structural characterization of such films are also reported.
Section snippets
Experimental
The graphite films were grown by chemical vapor deposition technique from a hydrogen–methane gas mixture activated by DC discharge. A detailed description of the deposition facility and the growth method has been done elsewhere [10]. Our CVD system allows production of different types of carbon films ranging from polycrystalline diamond to carbon nanotubes. A type of the material deposited depends essentially on the methane concentration and on the substrate temperature. In this work, the
Results and discussion
Our previous studies have revealed no significant difference in the structure of graphite-like materials deposited on Ni and Si substrates in CVD-process lasted 45 min or longer [10]. For the shorter deposition times (5–10 min) substantially different carbon materials have been grown onto substrates made from these two materials. To provide the identical conditions of CVD process for both types of substrates the sets of Ni and Si wafers have been located side by side on a holder in the deposition
Conclusions
The well-ordered graphite films of nanometer thickness have been grown on Ni substrates by chemical vapor deposition from hydrogen–methane gas mixture activated by DC discharge. These films have the atomically smooth micron-size regions separated from each other by ridges. The ridges have been formed due to the difference in thermal expansion coefficients for graphite and nickel. The film thickness has been estimated as 1.5 ± 0.5 nm. The proposed mechanism of the film formation assumes a
Acknowledgements
The authors are grateful to Drs. K.N. Eltsov and B.V. Andryushechkin from General Physics Institute of Russian Academy of Sciences (Moscow, Russia) for collaboration in STM studies and registration of the STM images.
This work was supported by EU FP6 Project No. 12881 FERROCARBON: “Room Temperature Ferromagnetism in Graphite and Fullerenes” and by INTAS (Grant nos. #04-84-297 and #05-109-4966).
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