Conductivity of Graphene-Like Thin Films Prepared from Chemically Exfoliated Carbon Nanotubes (CNTs), Highly Oriented Py
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Conductivity of Graphene-Like Thin Films Prepared from Chemically Exfoliated Carbon Nanotubes (CNTs), Highly Oriented Pyrolytic Graphite (HOPG), Natural Flake Graphite, and Carbon Powder Matthew M. Marchese1 and Rosario A. Gerhardt2,* 1 School of ME, Georgia Institute of Technology, Atlanta, GA, U.S.A. 2 School of MSE, Georgia Institute of Technology, Atlanta, GA, U.S.A. *contact e-mail: [email protected] ABSTRACT The use of super acids such as chlorosulfonic acid (CSA) has proven to be extremely effective at exfoliating different forms of graphite in high concentrations without covalently functionalizing the surface of the graphene. Once quenched, the acid solutions can then be vacuum filtered through acid resistant polypropylene filter paper with an average pore size of 0.2 m to collect the exfoliated carbon into a free standing retentate film. These films can then be easily washed, removed, and redispersed into solution by sonicating the films in a surfactant solution. Films were deposited onto various substrates using a range of spin coating parameters. This study has found that exfoliated CNTs provide the best conductivity out of the four types of chemically exfoliated carbon structures studied. CNTs have also proven to be the easiest type of exfoliated carbon to disperse and are able to stay in solution with less than 1%wt surfactant. The findings have shown that the electrical conductivity of the spin coated films actually increases with RPM and is inversely proportional to the film thickness. It is possible to achieve electrical conductivities as high as 10,507 ± 3728.64 [S/m] while still maintaining the transparency of the thin films. The initial spin coating step is more efficient at low ramp rates around 100 rpm/s and results in very smooth films. High spin speeds of 1800 rpm during the casting stage are found to play a large role in improving the conductivity of the films. Lastly, drying the samples on a hot plate for 5 min. on high has significantly improved the films electrical properties and virtually eliminated the need for tedious and expensive plasma cleaning treatments. INTRODUCTION Graphene has become one of the most popular subjects of research in the new decade due to its extraordinary properties in almost all aspects of science. It is particularly useful in the field of microelectronics due to its incredible carrier mobility of about 200 000 cm2/V·s [1] and its extremely small size. Recently, graphene thin films have been studied due to their transparent conductive properties [2,3], and have been able to undergo extreme deformation while maintaining high conductivities. This durability gives graphene thin films an advantage over more rigid transparent conductors such as indium tin oxide (ITO) [4,5]. The abundance of carbon graphite as a source also makes graphene thin films a more financially viable option than rare earth metals such as indium [4,6]. Applications for transparent graphene thin films range from flexible touch panels and LCD displays [7], to electroluminescent devic
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