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An Investigation Of Chemical Vapour Deposition Of Graphene On A Copper Substrate

1471 words - 6 pages

Graphene exhibits numerous unique properties, which have caused large-scale research of the material. For example, its charge carriers have zero effective mass (called Dirac fermions) and exhibit ultra-relativistic effects , therefore possess mobility’s of up to 200,000 cm2V-1s-1; the material shows the half-integer quantum Hall effect and shows absorption of 2.3% of the visible spectrum of light .
Graphene of the highest quality and best structural integrity is acquired by mechanical exfoliation of highly oriented graphite . As graphene produced in this method is structurally superior, it is used as a reference and new methods are compared relative to it. However, although mechanically exfoliated graphene exhibits low amounts of defects in its structure, the size, location and scalability are extremely difficult to control. Therefore a number of methods have been explored to create and reproduce high quality graphene in a large scale. Of the possible methods, three were explored in detail. One method explored used exfoliation of graphite in liquids . However, it is possible for this method to introduce structural defects into the resulting thin layer . Another possible method is the reduction of graphene oxide via HI and Woolins reagent.
The most effective method for producing graphene of high structural integrity is chemical vapour deposition (CVD) using transition metal surfaces. Common transition metals include Cu , Ni and Ru . The conditions of growth, and solubility of carbon in the metal determine how the deposition occurs, resulting in varied morphology and thinness of the produced graphene . The most promising metals for the growth of graphene have occurred using Ni11 or Cu10 as the substrate. Graphene that has been produced by CVD with deposition on to Ni show good quality, as defined by the electron mobility values of (3650 cm2V-1s-1), as well as exhibiting the half-integer quantum Hall effect11. Growth on Ni is however limited due to the resulting presence of single and multi-layer graphene islands of up to tens of microns in area, which are not deposited homogeneously over the surface of the catalyst . This phenomenon is a result of the separation of carbon from the metal carbide, which occurs at a high rate upon cooling, in Ni grains and occurs heterogeneously at the various grain boundaries. Thus, carbon can precipitate out of the grain boundaries, resulting in greater thickness of graphene at the edges of a layer. However, extremely high quality uniform monolayers of graphene have been deposited using polycrystalline copper foils, on diameters of up to 76 cm2,10. Raman analysis shows that copper foils treated at atmospheric pressure, show up to 95% monolayer coverage, with 5% bi-layer or tri-layer graphene10. These values are not related to the growth time or the rate of heating and cooling. In addition, copper foils are relatively cost-efficient and are etched simply with solvents that are readily available. Chemically...

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