Chemical vapor deposition of thin graphitefilms of nanometer thicknessA.N.Obraztsova,b,*,E.A.Obraztsova b ,A.V.Tyurnina b ,A.A.Zolotukhinba University of Joensuu,Joensuu 801101,Finland bMoscow State University,Moscow 119992,Russia Received 9March 2007;accepted 31May 2007Available online 24June 2007AbstractWell-ordered graphite films with a thickness of a few graphene layers have been grown on Ni substrates by chemical vapor deposition (CVD)from a mixture of hydrogen and methane activated by a DC discharge.According to Auger,Raman and scanning tunneling microscopy (STM)data the CVD graphite film thickness is about 1.5±0.5nm.The graphene layers were perfectly adhered to the sub-strate surface except for upthrusted ridges of a few tens of nanometers in height.STM has revealed an atomically smooth surface with the atomic arrangement typical of graphite between the ridges.A difference in the thermal expansion coefficients of nickel and graphite is considered as a reason for the ridge formation.Ó2007Elsevier Ltd.All rights reserved.1.IntroductionGraphite 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 cou-pled by van der Waals interaction.Each graphene sheet looks like a hexagonal network of carbon atoms connected by strong covalent ‘‘in-plane’’r Àr bonds.The delocalized electrons appear only due to an additional p Àp bonding of electronic orbitals oriented perpendicularly to the graphene plane.They are responsible for the graphite electrical con-ductivity which is highly anisotropic.Recently,the uncon-ventional 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 [4–7],because the unusual electron behav-ior is considered as a result of two-dimensional confine-ment of charge carriers.Graphene can be produced by mechanical exfoliation of individual layers from the surface of highly oriented pyro-lytic graphite (HOPG)crystal [2–5].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(111)surface in ultra-high vacuum [9].However,such ‘‘hand-made’’graph-ene 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 acti-vated 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 charac-terization of such films are also reported.2.ExperimentalThe 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 method0008-6223/$-see front matter Ó2007Elsevier Ltd.All rights reserved.doi:10.1016/j.carbon.2007.05.028*Corresponding author.Address:Moscow State University,Moscow 119992,Russia.Fax:+74959392988.E-mail address:obraz@polly.phys.msu.ru (A.N.Obraztsov).www.elsevier.com/locate/carbonCarbon 45(2007)2017–2021
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